Table of Contents

An inorganic acid is a compound of hydrogen and one or more other element (with the exception of carbon) that dissociates or breaks down to produce hydrogen ions when dissolved in water or other solvents. The resultant solution has certain characteristics such as the ability to neutralize bases, turn litmus paper red and produce specific colour changes with certain other indicators. Inorganic acids are often termed mineral acids. The anhydrous form may be gaseous or solid.

An inorganic anhydride is an oxide of metalloid which can combine with water to form an inorganic acid. It can be produced by synthesis such as: S + O₂ → SO₂, which can be transformed into an acid by the addition of a water molecule (hydration); or by eliminating water from an acid, such as:

2HMnO₄ → Mn₂O₇ + H₂O

Inorganic anhydrides share in general the biological properties of their acids, since hydration can readily occur in watery biological media.

Uses

Inorganic acids are used as chemical intermediates and catalysts in chemical reactions. They are found in a variety of industries, including metal- and woodworking, textile, dye-stuff, petroleum and photography. In metalworking they are often used as cleaning agents before welding, plating or painting. Sulphamic acid, sulphuric acid and hydrochloric acid are used in electroplating, and perchloric acid is used in metal plating.

Hydrochloric acid, sulphuric acid, perchloric acid and sulphamic acid are widely used in industry. Hydrochloric acid, or hydrogen chloride in aqueous solution, is used for industrial acidizing, for refining ores of tin and tantalum, for converting cornstarch to syrup, and removing scale from boilers and heat-exchange equipment. It is also a tanning agent in the leather industry. Sulphuric acid is used in parchment paper and in various processes including purification of petroleum, refining vegetable oil, carbonization of wool fabrics, extraction of uranium from pitchblende, and iron and steel pickling. Sulphuric acid and perchloric acid are used in the explosives industry. Sulphamic acid is a flame retardant in the wood and textile industries and a bleaching agent and bactericide in the pulp and paper industry. It is also used for chlorine stabilization in swimming pools.

Nitric acid is used in the manufacture of ammonium nitrate for fertilizer and explosives. In addition, it is used in organic synthesis, metallurgy, ore flotation, and for reprocessing spent nuclear fuel.

Hazards

The specific hazards of the industrially important inorganic acids will be found below; however, it should be noted that all these acids have certain dangerous properties in common. Solutions of inorganic acids are not flammable in themselves; however, when they come into contact with certain other chemical substances or combustible materials, a fire or explosion may result. These acids react with certain metals with the liberation of hydrogen, which is a highly flammable and explosive substance when mixed with air or oxygen. They may also act as oxidizing agents and, when in contact with organic or other oxidizable materials, may react destructively and violently.

Health effects. The inorganic acids are corrosive, especially in high concentrations; they will destroy body tissue and cause chemical burns when in contact with the skin and mucous membranes. In particular, the danger of eye accidents is pronounced. Inorganic acid vapours or mists are respiratory tract and mucous membrane irritants, although the degree of irritation depends to a large degree on the concentration; discolouration or erosion of the teeth may also occur in exposed workers. Repeated skin contact may lead to dermatitis. Accidental ingestion of concentrated inorganic acids will result in severe irritation of the throat and stomach, and destruction of the tissue of internal organs, perhaps with fatal outcome, when immediate remedial action is not taken. Certain inorganic acids may also act as systemic poisons.

Safety and Health Measures

Wherever possible, highly corrosive acids should be replaced by acids which present less hazard; it is essential to use only the minimum concentration necessary for the process. Wherever inorganic acids are used, appropriate measures should be instituted concerning storage, handling, waste disposal, ventilation, personal protection and first aid.

Storage. Avoid contact with other acids and combustible or oxidizable materials. Electrical installations should also be of the acid-resistant type.

Storage areas should be separated from other premises, well ventilated, sheltered from sunlight and sources of heat; they should have a cement floor and contain no substances with which an acid might react. Large stocks should be surrounded by kerbs or sills to retain the acid in the event of leakage, and provisions for neutralization should be made. A fire hydrant and a supply of self-contained respiratory protective equipment for emergency or rescue purposes should be provided outside the storage premises. Spillages should be dealt with immediately by hosing down; in the event of a large leakage, personnel should vacate the premises and then, having donned emergency equipment, return to neutralize the acid with water or calcined sand. Electrical equipment should be of the waterproof type and resistant to acid attack. Safety lighting is desirable.

Containers should be kept tightly closed and should be clearly labelled to indicate the contents. Decompression measures should be taken where necessary. Piping, couplings, gaskets and valves should all be made of material resistant to nitric acid. Glass or plastic containers should be adequately protected against impact; they should be kept off the floor to facilitate flushing in the event of leakage. Drums should be stored on cradles or racks and chocked in position. Gas cylinders of gaseous anhydrous acid should be stored upright with the cap in place. Empty and full containers should preferably be stored apart. Maintenance and good housekeeping are essential.

Handling. Wherever possible acids should be pumped through sealed systems to prevent all danger of contact. Wherever individual containers have to be transported or decanted, the appropriate equipment should be employed and only experienced persons allowed to undertake the work. Decanting should be done by means of special syphons, transfer pumps, or drum or carboy tilting cradles and so on. Cylinders of anhydrous acid gas require special discharge valves and connections.

Where acids are mixed with other chemicals or water, workers must be fully aware of any violent or dangerous reaction that may take place. For example, a concentrated acid should be slowly added to water, rather than vice versa, in order to avoid the generation of excessive heat and violent reactions which can cause splashes and skin or eye contact.

Ventilation. Where processes produce acid mists or vapours, such as in electroplating, exhaust ventilation should be installed.

Personal protection. Persons exposed to dangerous splashes of inorganic acids should be required to wear acid-resistant personal protective equipment including hand and arm protection, eye and face protection and aprons, overalls or coats. Provided safe working procedures are adopted, the use of respiratory protective equipment should not be necessary; however, it should be available for emergency use in the event of leakage or spillage.

When workers are required to enter a tank that has contained inorganic acids in order to carry out maintenance or repairs, the tanks should first be purged and all precautions for entry into enclosed spaces, as described elsewhere in the Encyclopaedia, should be taken.

Training. All workers required to handle acids should be instructed about their hazardous properties. Certain work activities, such as those involving enclosed spaces or handling of large quantities of acids, should always be done by two persons, one being ready to come to the other’s aid in case of need.

Sanitation. Personal hygiene is of utmost importance where there is contact with inorganic acids. Adequate washing and sanitary facilities should be provided and workers encouraged to wash thoroughly before meals and at the ends of shifts.

First aid. Essential treatment for inorganic acid contamination of skin or eyes is immediate and copious flushing with running water. Emergency showers and eyewash fountains, baths or bottles should be strategically located. Splashes in the eye should be treated with copious irrigation with water. Contaminated clothing should be removed and other appropriate emergency skin treatment procedures should be in place and personnel trained in their administration. Neutralization of the acid in the affected area with an alkaline solution such as 2 to 3% sodium bicarbonate, or 5% sodium carbonate and 5% sodium hyposulphite, or 10% triethanolamine is a standard procedure.

Persons who have inhaled acid mists should be removed immediately from the contaminated zone and prevented from making any effort. They should be put in the care of a physician immediately. In the event of accidental ingestion, the victim should be given a neutralizing substance, and gastric lavage should be carried out. In general, vomiting should not be induced since this may make the injury more widespread.

Medical supervision. Workers should receive pre-employment and periodic medical examinations. The pre-employment examination should be particularly directed at the detection of chronic respiratory, gastro-intestinal or nervous diseases and any eye and skin diseases. Periodic examinations should take place at frequent intervals and should include a check on the condition of the teeth.

Water pollution. This should be prevented by ensuring that wastewater containing spent acid is not emptied into watercourses or sewage systems until the pH (acidity) has been brought to a level that is between 5.5 and 8.5.

Hydrochloric acid

Anhydrous hydrogen chloride is not corrosive; however, aqueous solutions attack nearly all metals (mercury, silver, gold, platinum, tantalum and certain alloys are exceptions) with release of hydrogen. Hydrochloric acid reacts with sulphides to form chlorides and hydrogen sulphide. It is a very stable compound, but at high temperatures it decomposes into hydrogen and chlorine.

Hazards. The special hazards of hydrochloric acid are its corrosive action on skin and mucous membranes, the formation of hydrogen when it contacts certain metals and metallic hydrides, and its toxicity. Hydrochloric acid will produce burns of the skin and mucous membranes, the severity being determined by the concentration of the solution; this may lead to ulcerations followed by keloid and retactile scarring. Contact with the eyes may produce reduced vision or blindness. Burns on the face may produce serious and disfiguring scars. Frequent contact with aqueous solutions may lead to dermatitis.

The vapours have an irritant effect on the respiratory tract, causing laryngitis, glottal oedema, bronchitis, pulmonary oedema and death. Digestive diseases are frequent and are characterized by dental molecular necrosis in which the teeth lose their shine, turn yellow, become soft and pointed, and then break off.

Safety and health measures. In addition to the general measures described above, the acid should not be stored in the vicinity of flammable or oxidizing substances, such as nitric acid or chlorates, or near metals and metal hydrides which may be attacked by the acid with the formation of hydrogen. (The explosive limits of hydrogen are 4 to 75% by volume in air.) Electrical equipment should be flameproof and protected against the corrosive action of the vapours.

Nitric acid

Nitric acid is highly corrosive and attacks a large number of metals. Reactions between nitric acid and various organic materials are often highly exothermic and explosive, and reactions with metals may produce toxic gases. Nitric acid will cause skin burns, and the vapours are highly irritant to the skin and mucous membranes; inhalation of significant quantities will produce acute poisoning.

Fire and explosion. Nitric acid attacks most substances and all metals except the noble metals (gold, platinum, iridium, thorium, tantalum) and certain alloys. The rate of reaction varies depending on the metal and the concentration of the acid; the gases produced during the reaction include the nitrogen oxides, nitrogen and ammonia, which may have a toxic or asphyxiating effect. When in contact with sodium or potassium, the reaction is violent and dangerous, and nitrogen is released. However, in the case of certain metals, a protective oxide film is formed which prevents further attack. Nitric acid may react explosively with hydrogen sulphide. Nitrates obtained by the action of the acid on various bases are powerful oxidizing agents.

Even in dilute concentrations, nitric acid is a powerful oxidizing material. Solutions of a concentration higher than 45% may cause the spontaneous ignition of organic materials such as turpentine, wood, straw and so on.

Health hazards. Solutions of nitric acid are highly corrosive and will produce lesions of the skin, eyes and mucous membranes, the severity of which will depend on the duration of contact and the acid concentration; the lesions range from irritation to burns and localized necrosis following prolonged contact. Nitric acid mists are also corrosive to the skin, mucous membranes and dental enamel.

Nitric acid vapours will always contain a certain proportion of other gaseous nitrogen compounds (e.g., nitrogen oxides), depending on the concentration of the acid and the type of operation. Inhalation may produce acute poisoning and peracute poisoning. Peracute poisoning is rare and can be fatal. Acute poisoning generally comprises three phases: the first consists of irritation of the upper respiratory tract (burning in the throat, cough, feeling of suffocation) and of the eyes with tearing (lacrimation); the second phase is misleading, since pathological signs are absent for a period of up to several hours; in the third phase, the respiratory disorders reappear and may develop rapidly into acute pulmonary oedema, often with serious outcome.

Accidental ingestion will produce severe damage in the mouth, pharynx, oesophagus and stomach, and may have serious sequelae.

Safety and health measures. Depending on the quantities and concentrations involved, nitric acid should be stored in stainless steel, aluminium or glass containers. Glass carboys or winchesters should be protected by a metal envelope to provide resistance to impacts. However, nitric acid containing any fluorinated compounds should not be stored in glass. Organic materials such as wood, straw, sawdust and so on, should be kept away from operations involving nitric acid. When nitric acid is to be diluted with water, the acid should be poured into the water, and localized heating should be avoided.

Sulphuric acid

Sulphuric acid is a strong acid which, when heated to above 30 °C, gives off vapour and, above 200 °C, emits sulphur trioxide. When cold, it reacts with all metals including platinum; when hot, reactivity is intensified. Dilute sulphuric acid dissolves aluminium, chromium, cobalt, copper, iron, manganese, nickel and zinc, but not lead or mercury. It has a great affinity for water, absorbs atmospheric moisture, and abstracts water from organic materials, causing charring. It decomposes salts of all other acids except silicic acid.

Sulphuric acid is found in the native state in the vicinity of volcanoes, in particular in the volcanic gases.

Hazards. The action of sulphuric acid on the body is that of a powerful caustic and general toxic agent. Introduced into the body in liquid or vapour form, it causes intense irritation and chemical burns of the mucous membranes of the respiratory and digestive tract, the teeth, eyes and skin. On contact with the skin, sulphuric acid causes violent dehydration. It releases heat in sufficient quantities to produce burns that are similar to thermal burns and may be classified accordingly as first, second or third degree. The depth of the lesions depends on the concentration of the acid and the length of contact. Inhalation of vapours produces the following symptoms: nasal secretion, sneezing, a burning feeling in the throat and retrosternal region; these are followed by cough, respiratory distress, sometimes accompanied by spasm of the vocal cords, and a burning sensation in the eyes with lacrimation and conjunctival congestion. High concentrations may cause bloody nasal secretion and sputum, haematemesis, gastritis and so on. Dental lesions are common; they affect mainly the incisors and present as brown staining, enamel striation, caries and rapid and painless destruction of the tooth crown.

Occupational exposures to strong inorganic acid mists, such as sulphuric acid mists, have been classified by the International Agency for Research on Cancer (IARC) as being carcinogenic to humans.

Chemical burns are the injury most commonly encountered in sulphuric acid production workers. Concentrated solutions cause deep burns of mucous membranes and skin; initially the zone of contact with the acid is bleached and turns brown prior to the formation of a clearly defined ulcer on a light red background. These wounds are long in healing and may frequently cause extensive scarring that results in functional inhibition. If burning is sufficiently extensive, the outcome may prove fatal. Repeated skin contact with low concentrations of acid causes skin desiccation and ulceration of the hands, and panaris or chronic purulent inflammation around the nails. Splashes of acid in the eyes may have particularly serious consequences: deep corneal ulceration, kerato-conjunctivitis and palpebral lesions with severe sequelae.

The general toxic action of sulphuric acid causes alkaline depletion of the body (i.e., an acidosis which affects the nervous system and produces agitation, hesitant gait and generalized weakness).

Safety and health measures. The most effective measures are the total enclosure of processes and the mechanization of handling procedures to prevent all personal contact with sulphuric acid. Particular attention should be devoted to acid storage, handling and application procedures, the ventilation and lighting of workplaces, maintenance and good housekeeping, and personal protective equipment. In addition to the general precautions given above, sulphuric acid should not be stored in the vicinity of chromates, chlorates or similar substances in view of the fire and explosion hazard involved.

Fire and explosion. Sulphuric acid and oleum are not flammable per se. However, they react vigorously with numerous substances, especially organic materials, with the release of sufficient heat to produce a fire or explosion; in addition, the hydrogen released during reaction with metals may form an explosive mixture in air.

Catalysts. Where a vanadium catalyst is used in the contact process, workers should be protected against exposure to emissions of ammonium vanadate or vanadium pentoxide, which are employed on a diatomite or silica gel support.

Inorganic acids, tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3 - Physical and chemical hazards.

Table 4 - Physical and chemical properties.

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Organic acids and their derivatives cover a wide range of substances. They are used in nearly every type of chemical manufacture. Because of the variety in the chemical structure of the members of the organic acid group, several types of toxic effects may occur. These compounds have a primary irritant effect, the degree determined in part by acid dissociation and water solubility. Some may cause severe tissue damage similar to that seen with strong mineral acids. Sensitization may also occur, but is more common with the anhydrides than the acids.

For the purpose of this article, organic acids may be divided into saturated monocarboxylic and unsaturated monocarboxylic acids, aliphatic dicarboxylic acids, halogenated acetic acids, miscellaneous aliphatic monocarboxylic acids and aromatic carboxylic acids. Many carboxylic acids are of importance because of their use in food, beverages, drugs and a range of manufacturing processes. The following are among the most common: adipic acid, azelaic acid, fumaric acid, itaconic acid, maleic acid, malic acid, malonic acid, oxalic acid, pimelic acid, sebacic acid, succinic acid, tartaric acid and thiomalic acid.

The long-chain saturated monocarboxylic acids are the fatty acids and are in the main derived from natural sources. Synthetic fatty acids may also be manufactured by air oxidation of paraffins (aliphatic hydrocarbons) using metal catalysts. They are also produced by the oxidation of alcohols with caustic soda.

Uses

Organic acids are employed in the plastics, tanning, textile, paper, metal, pharmaceutical, food, beverage and cosmetics industries. Organic acids are also found in perfumes, herbicides, dyes, lubricants and cleaners.

Formic acid and acetic acid are the major industrial chemicals in the group of saturated monocarboxylic acids. Formic acid is primarily used in the textile and leather industries. It acts as a dye-exhausting agent for a number of natural and synthetic fibres and as a reducing agent in chrome dyeing. Formic acid is used as a deliming agent and a neutralizer in the leather industry, and as a coagulant for rubber latex. It also finds use in the manufacture of fumigants and insecticides. Acetic acid serves as a chemical intermediate, a deliming agent during leather tanning, a solvent, and an oil-well acidizer. In addition, it is an additive for various foods and glazes as well as a catalyst and a finishing agent in the dye-stuff and textile industries.

Weak concentrations of acetic acid (vinegar contains about 4 to 6%) are produced by aerobic fermentation (Acetobacter) of alcohol solutions. Acetic acid is one of the most widely used organic acids. It is employed in the production of cellulose acetate, vinyl acetate, inorganic acetates, organic acetates and acetic anhydride. Acetic acid itself is used in the dyeing industry, pharmaceutical industry, the canning and food preserving industry and pigment production.

Chloroacetic acid is used in the pharmaceutical, dye-stuffs and chemical industries as a chemical intermediate. Salicylic acid acts as another chemical intermediate used in the synthesis of aspirin and in the rubber and dye-stuffs industries. Benzoic acid, nonanoic acid, ascorbic acid and oleic acid (9-octadecenoic acid) are other useful compounds found in the food, beverage and pharmaceutical industries.

Palmitic acid and stearic acid have a wide application in soaps, cosmetics, detergents, lubricants, protective coatings and intermediate chemicals. Propionic acid is used in organic synthesis. It is also a mould inhibitor and a food preservative. Acrylic acid, methacrylic acid and crotonic acid are employed in the manufacture of resins and plasticizers in the paper, plastics and paint industries. In addition, acrylic acid is an ingredient in floor-polish formulations. Crotonic acid finds use in the manufacture of softening agents for synthetic rubber. Lactic acid, butyric acid and gallic acid are employed in the leather-tanning industry. Lactic acid is also used in adhesives, plastics and textiles. It serves as a food acidulant and as an agent in oil-well acidizing. Glycolic acid is used in the leather, textile, electroplating, adhesives and metal-cleaning industries.

The dicarboxylic acids (succinic acid, maleic acid, fumaric acid, adipic acid) and the tricarboxylic acid (citric acid) are useful in the food, beverage and pharmaceutical industries. Succinic acid is also used in the manufacture of lacquers and dyes. Maleic acid is used in the manufacture of synthetic resins and in organic syntheses. Maleic acid acts as a preservative for oils and fats; its salts are used in the dyeing of cotton, wool and silk. Fumaric acid is used in polyesters and alkyd resins, plastics surface coatings, food acidulants, inks and organic syntheses. The majority of adipic acid is utilized for nylon production, while smaller quantities are used in plasticizers, synthetic lubricants, polyurethanes and food acidulants.

Oxalic acid is a scouring agent in textile finishing, stripping and cleaning, and a component of household formulations for metal cleaning. It also finds use in the paper, photography and rubber industries. Oxalic acid is used in calico printing and dyeing, bleaching straw hats and leather, and cleaning wood. Aminoacetic acid is used as a buffering agent and in syntheses. Peracetic acid is used as a bleach, catalyst and oxidant.

Commercial naphthenic acid is usually a dark-coloured malodourous mixture of naphthenic acids. Naphthenic acids are derived from cycloparaffins in petroleum, probably by oxidation. Commercial acids are usually viscous liquid mixtures and may be separated as low- and high-boiling fractions. The molecular weights vary from 180 to 350. They are used principally in the preparation of paint dryers, where the metallic salts, such as lead, cobalt and manganese, act as oxidizing agents. Metallic naphthenic acids are used as catalysts in chemical processes. An industrial advantage is their solubility in oil.

Organic acid anhydrides

An anhydride is defined as an oxide which, when combined with water, gives an acid or a base. Acid anhydrides are derived from the removal of water from two molecules of the corresponding acid, such as:

2HMnO₄ → Mn₂O₇ + H₂O

Industrially, the most important anhydrides are acetic and phthalic. Acetic anhydride is used in the plastics, explosives, perfume, food, textile and pharmaceutical industries, and as a chemical intermediate. Phthalic anhydride serves as a plasticizer in vinyl chloride polymerization. It is also used for the production of saturated and unsaturated polyester resins, benzoic acid, pesticides, and certain essences and perfumes. Phthalic anhydride is employed in the production of phthalocyanine dyes and alkyd resins used in paints and lacquers. Maleic anhydride has a significant number of applications as well.

Propionic anhydride is used in the manufacture of perfumes, alkyd resins, drugs and dyes, while maleic anhydride, trimellitic anhydride and acetic anhydride find use in the plastics industry. Trimellitic anhyide (TMA) is also utilized in the dye-stuff, printing and automotove upholstery industries. It is used as a curing agent for epoxy and other resins, in vinyl plasticizers, paints, coatings, dyes, pigments and a wide variety of other manufactured products. Some of these products find applications in high-temperature plastics, wire insulation and gaskets.

Hazards

Monocarboxylic acids

The low-molecular-weight monocarboxylic acids are primary irritants and produce severe damage to tissues. Strict precautions are necessary in handling; suitable protective equipment should be available and any skin or eye splashes irrigated with copious amounts of water. The most important acids of this group are acetic acid and formic acid.

The long-chain saturated monocarboxylic acids (the fatty acids) are non-irritant and of a very low order of toxicity. They appear to pose few problems in industrial use.

Unsaturated monocarboxylic acids are highly reactive substances and are recognized as severe irritants of the skin, eye and respiratory tract in concentrated solution. Hazards appear to be related to acute rather than cumulative exposures.

The majority of these acids appear to present minimal hazard from low-level chronic exposure, and many are normally present in human metabolic processes. Primary irritant effects are present with a number of these acids, however, particularly in concentrated solutions or as dusts. Sensitization is rare. As the materials are all solids at room temperature, contact is usually in the form of dust or crystals.

Acetic acid. Acetic acid vapour may form explosive mixtures with air and constitute a fire hazard either directly or by the release of hydrogen. Glacial acetic acid or acetic acid in concentrated form are primary skin irritants and will produce erythema (reddening), chemical burns and blisters. In cases of accidental ingestion, severe ulceronecrotic lesions of the upper digestive tract have been observed with bloody vomiting, diarrhoea, shock and haemoglobinuria followed by urinary disorders (anuria and uraemia).

The vapours have an irritant action on exposed mucous membranes, particularly the conjunctivae, rhinopharynx and upper respiratory tract. Acute bronchopneumonia developed in a woman who was made to inhale acetic acid vapours following a fainting attack.

Workers exposed for a number of years to concentrations of up to 200 ppm have been found to suffer from palpebral oedema with hypertrophy of the lymph nodes, conjunctival hyperaemia, chronic pharyngitis, chronic catarrhal bronchitis and, in some cases, asthmatic bronchitis and traces of erosion on the vestibular surface of the teeth (incisors and canines).

The extent of acclimatization is remarkable; however, such acclimatization does not mean that toxic effects will not also occur. Following repeated exposure, for example, workers may complain of digestive disorders with pyrosis and constipation. The skin on the palms of the hands is subject to the greatest exposure and becomes dry, cracked and hyperkeratotic, and any small cuts and abrasions are slow to heal.

Formic acid. The principal hazard is that of severe primary damage to the skin, eye or mucosal surface. Sensitization is rare, but may occur in a person previously sensitized to formaldehyde. Accidental injury in humans is the same as for other relatively strong acids. No delayed or chronic effects have been noted. Formic acid is a flammable liquid, and its vapour forms flammable and explosive mixtures with air.

Propionic acid in solution has corrosive properties towards several metals. It is irritant to eye, respiratory system and skin. The same precautions recommended for exposure to formic acid are applicable, taking into account the lower flashpoint of propionic acid.

Maleic acid is a strong acid and produces marked irritation of the skin and mucous membranes. Severe effects, particularly in the eye, can result from concentrations as low as 5%. There are no reports of cumulative toxic effects in humans. The hazard in industry is of primary irritation of exposed surfaces, and this should be averted where necessary by the provision of appropriate personal protective equipment, generally in the form of impermeable gloves or gauntlets.

Fumaric acid is a relatively weak acid and has a low solubility in water. It is a normal metabolite and is less toxic orally than tartaric acid. It is a mild irritant of skin and mucous membranes, and no problems of industrial handling are known.

Adipic acid is non-irritant and of very low toxicity when ingested.

Halogenated acetic acids

The halogenated acetic acids are highly reactive. They include chloroacetic acid, dichloroacetic acid (DCA), trichloroacetic acid (TCA), bromoacetic acid, iodoacetic acid, fluoroacetic acid and trifluoroacetic acid (TFA).

The halogenated acetic acids cause severe damage to the skin and mucous membranes and, when ingested, may interfere with essential enzyme systems in the body. Strict precautions are necessary for their handling. They should be prepared and used in enclosed plant, the openings in which should be limited to the necessities of manipulation. Exhaust ventilation should be applied to the enclosure to ensure that fumes or dust do not escape through the limited openings. Personal protective equipment should be worn by persons engaged in the operations, and eye protective equipment and respiratory protective equipment should be available for use when necessary.

Fluoroacetic acid. Di- and trifluoroacetic acids have a lower level of toxicity than monofluoroacetic acid (fluoroacetic acid). Monofluoroacetic acid and its compounds are stable, highly toxic and insidious. At least four biological plants in South Africa and Australia owe their toxicity to this acid (Dichapetalum cymosum, Acacia georginae, Palicourea marcgravii), and recently more than 30 species of Gastrolobium and Oxylobrium in Western Australia have been found to contain various amounts of fluoroacetate.

The biological mechanism responsible for the symptoms of fluoroacetate poisoning involves the “lethal synthesis” of fluorocitric acid, which in turn blocks the tricarboxylic acid cycle by inhibiting the enzyme aconitase. The resultant deprivation of energy by stopping of the Krebs cycle is followed by cellular dysfunction and death. It is impossible to be specific about the toxic dose of fluoroacetic acid for humans; a likely range lies between 2 and 10 mg/kg; but several related fluoroacetates are even more toxic than this. A drop or two of the poison by inhalation, ingestion and absorption through skin cuts and abrasion or undamaged skin can be fatal.

From a study of hospital case histories, it is apparent that the major toxic effects of fluoroacetates in humans involve the central nervous system and cardiovascular system. Severe epileptiform convulsions alternate with coma and depression; death may result from asphyxia during a convulsion or from respiratory failure. The most prominent features, however, are cardiac irregularities, notably ventricular fibrillation and sudden cardiac arrest. These symptoms (which are indistinguishable from those frequently encountered clinically) are usually preceded by an initial latent period of up to 6 h characterized by nausea, vomiting, excessive salivation, numbness, tingling sensations, epigastric pain and mental apprehension; other signs and symptoms which may develop subsequently include muscular twitching, low blood pressure and blurred vision.

Chloroacetic acid. This material is a highly reactive chemical and should be handled with care. Gloves, goggles, rubber boots and impervious overalls are mandatory when workers are in contact with concentrated solutions.

Other acids

Glycolic acid is stronger than acetic acid and produces very severe chemical burns of the skin and eyes. No cumulative effects are known, and it is believed to be metabolized to glycine. Strict precautions are necessary for its handling. These are similar to those required for acetic acid. Concentrated solutions can cause burns of the skin and eye. No cumulative effects are known. Personal protective equipment should be worn by persons handling concentrated solutions of this acid.

Sorbic acid is used as a fungicide in foods. It is a primary irritant of the skin, and individuals may develop sensitivities to it. For these reasons contact with the skin should be avoided.

Salicylic acid is a strong irritant when in contact with skin or mucous membranes. Strict precautions are necessary for plant operatives.

Anhydrides

Acid anhydrides have higher boiling points than the corresponding acids. Their physiological effects generally resemble those of the corresponding acids, but they are more potent eye irritants in the vapour phase, and may produce chronic conjunctivitis. They are slowly hydrolyzed on contact with body tissues and may occasionally cause sensitization. Adequate ventilation should be provided and suitable personal protective equipment should be worn. In certain circumstances, particularly those associated with maintenance work, suitable eye protection equipment and respiratory protective equipment are necessary.

There have been reports of conjunctivitis, bloody nasal excreta, atrophy of the nasal mucosa, hoarseness, cough and bronchitis in workers employed in the production of phthalic acid and anhydride. It has been recognized that phthalic anhydride causes bronchial asthma, and skin sensitization has been reported following prolonged exposure to phthalic anhydride; the lesion is usually an allergic dermatitis. A specific IgE to phthalic anhydride has also been identified.

Phthalic anhydride is flammable and constitutes a moderate fire hazard. Its toxicity is comparatively low in relation to other industrial acid anhydrides, but it acts as a skin, eye and upper respiratory tract irritant. Since phthalic anhydride has no effect on dry skin, but burns wet skin, it is probable that the actual irritant is phthalic acid, which is formed on contact with water.

Phthalic anhydride must be stored in a cool, well-ventilated place away from open flames and oxidizing substances. Good local and general ventilation are required where it is handled. In many processes phthalic anhydride is used not as flakes but as a liquid. When so used, it is brought to the plant in tanks and directly pumped into the pipe system, preventing contact as well as contamination of the air with dust. This has led to the complete disappearance of manifestations of irritations among the workers in such plants. However, vapours liberated from liquid phthalic anhydride are as irritating as the flakes; care must, therefore, be taken to avoid any leakage from the pipe system. In case of spillage or contact with the skin, the latter should be washed immediately and repeatedly with water.

Workers who are handling phthalic derivatives must be under medical supervision. Special attention should be paid to asthma-like symptoms and skin sensitization. If any such symptoms are noticed, the worker should be moved to another job. Skin contact is to be avoided under all circumstances. Suitable clothing, such as rubber hand protection, is recommended. Pre-employment examinations are necessary to ensure that persons with bronchial asthma, eczema or other allergic diseases are not exposed to phthalic anhydride.

Acetic anhydride. When exposed to heat, acetic anhydride can emit toxic fumes, and its vapours can explode in the presence of flame. It can react violently with strong acids and oxidizers such as sulphuric acid, nitric acid, hydrochloric acid, permanganates, chromium trioxide and hydrogen peroxide, as well as with soda.

Acetic anhydride is a strong irritant and has corrosive properties on contact with eyes, usually with delayed action; contact is followed by lacrimation, photophobia, conjunctivitis and corneal oedema. Inhalation can cause nasopharyngeal and upper respiratory tract irritation, with burning sensations, cough and dyspnoea; prolonged exposure may lead to pulmonary oedema. Ingestion causes pain, nausea and vomiting. Dermatitis can result from prolonged skin exposure.

When contacts are possible, protective clothing and goggles are recommended and eyewash and shower facilities should be available. Chemical cartridge respirators are appropriate for protection against concentrations up to 250 ppm; supplied air respirators with a full eyepiece are recommended for concentrations of 1,000 ppm; self-contained breathing apparatus is necessary in case of fire.

Butyric anhydride is manufactured by catalytic hydrogenation of crotonic acid. Butyric anhydride and propionic anhydride present hazards similar to those of the acetic anhydride.

Maleic anhydride can produce severe eye and skin burns. These may be produced either by solution of maleic anhydride or by flakes of the material in the manufacturing process coming into contact with moist skin. Skin sensitization has occurred. Strict precautions should be taken to prevent contact of the solution with skin or eyes. Suitable goggles and other protective clothing must be worn by plant operatives; ready access to eye irrigation solution bottles is essential. When suspended in air in a finely divided condition, maleic anhydride is capable of forming explosive mixtures with the air. Condensers in which the sublimed material settles in the form of fine crystals should be situated in a safe position outside an occupied room.

Trimellitic anhydride has been reported to have caused pulmonary oedema in workers after severe acute exposure, and airways sensitization after exposure periods of weeks to years, with rhinitis and/or asthma. Several incidents involving the occupational effects of exposure to TMA have been reported. Multiple inhalation exposures to an epoxy resin containing TMA being sprayed on heated pipes was reported to have caused pulmonary oedema in two workers. Exposure levels were not reported but there was no report of upper respiratory tract irritation while the exposures were being experienced, indicating that a hypersensitive reaction might have been involved.

In another report, 14 workers involved in the synthesis of TMA were observed to have respiratory symptoms resulting from sensitization to TMA. In this study three separate responses were noted. The first, rhinitis and/or asthma, developed over an exposure duration of weeks to years. Once sensitized, exposed workers exhibited symptoms immediately after exposure to TMA, which ceased when the exposure was stopped. A second response, also involving sensitization, produced delayed symptoms (cough, wheezing and laboured breathing) 4 to 8 hours after exposure had ceased. The third syndrome was an irritant effect following initial high exposures.

One study of adverse health effects, which also involved measurements of air concentrations of TMA, was conducted by the US National Institute for Occupational Safety and Health (NIOSH). Thirteen workers involved in the manufacture of an epoxy paint had complaints of eye, skin, nose and throat irritation, shortness of breath, wheezing, coughing, heartburn, nausea and headache. Occupational airborne exposure levels averaged 1.5 mg/m³ TMA (range from “none detected” to 4.0 mg/m³) during processing operations and 2.8 mg/m³ TMA (range from “none detected” to 7.5 mg/m³) during decontamination procedures.

Experimental studies with rats have demonstrated intra-alveolar haemorrhage with subacute exposures to TMA at 0.08 mg/m³. The vapour pressure at 20 °C (4 × 10^-6 mm Hg) corresponds to a concentration slightly more than 0.04 mg/m³.

Oxalic acid and its derivatives. Oxalic acid is a strong acid which, in solid form or in concentrated solutions, can cause burns of the skin, eyes or mucous membranes; oxalic acid concentrations as low as 5 to 10% are irritating if exposure is prolonged. Human fatalities have been recorded following ingestion of as little as 5 g of oxalic acid. The symptoms appear rapidly and are marked by a shock-like state, collapse and convulsive seizures. Such cases may show marked renal damage with precipitation of calcium oxalate in the renal tubules. The convulsive seizures are thought to be the result of hypocalcaemia. Chronic skin exposure to solutions of oxalic acid or potassium oxalate have been reported to have caused a localized pain and cyanosis in the fingers or even gangrenous changes. This is apparently due to a localized absorption of the oxalic acid and a resultant arteritis. Chronic systemic injury from inhalation of oxalic acid dust appears to be very rare, although the literature describes the case of a man who had been exposed to hot oxalic acid vapours (probably containing an aerosol of oxalic acid) with generalized symptoms of weight loss and chronic inflammation of the upper respiratory tract. Because of the strongly acid nature of the dust of oxalic acid, exposure must be carefully controlled and work area concentrations held within acceptable health limits.

Diethyl oxalate is slightly soluble in water; miscible in all proportions in many organic solvents; a colourless, unstable, oily liquid. It is produced by esterification of ethyl alcohol and oxalic acid. It is used, as are other liquid oxalate esters, as a solvent for many natural and synthetic resins.

The symptoms in rats following ingestion of large quantities of diethyl oxalate are those of respiratory disturbances and muscle twitchings. Large quantities of oxalate deposits were found in the renal tubules of a rat after an oral dose of 400 mg/kg. It has been reported that workers exposed to 0.76 mg/l of diethyl oxalate over a period of several months developed complaints of weakness, headache and nausea together with some slight alterations in the blood count. Because of the very low vapour pressure of this substance at room temperature, the reported air concentrations may have been in error. There was also some use of diamyl acetate and diethyl carbonate in this operation.

Safety and Health Measures

All acids should be stored away from all sources of ignition and oxidizing substances. Storage areas should be well ventilated to prevent the accumulation of dangerous concentrations. Containers should be of stainless steel or glass. In the event of leakage or spillage, acetic acid should be neutralized by application of alkaline solutions. Eyewash fountains and emergency showers should be installed for dealing with cases of skin or eye contact. Marking and labelling of containers is essential; for all forms of transport, acetic acid is classified as a dangerous substance.

To prevent damage to the respiratory system and mucous membranes, the atmospheric concentration of organic acids and anhydrides with high vapour pressure should be kept below maximum permissible levels using standard industrial hygiene practices such as local exhaust ventilation and general ventilation, backed up by periodic determination of atmospheric acetic acid concentrations. Detection and analysis, in the absence of other acid vapours, is by means of bubbling in an alkaline solution and determination of residual alkali; in the presence of other acids, fractional distillation used to be necessary; however, a gas chromatographic method is now available for determination in air or water. Dust exposures should be minimized as well.

Persons working with the pure acid or concentrated solutions should wear protective clothing, eye and face protection, hand and arm protection and respiratory protective equipment. Adequate sanitary facilities should be provided and good personal hygiene encouraged.

Organic acids and anhydrides tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3 - Physical and chemical hazards.

Table 4 - Physical and chemical properties.

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Alcohols are a class of organic compounds formed from hydrocarbons by the substitution of one or more hydroxyl groups for an equal number of hydrogen atoms; the term is extended to various substitution products which are neutral in reaction and which contain one or more of the alcohol groups.

Uses

Alcohols are used as chemical intermediates and solvents in the textile, dye-stuff, chemical, detergent, perfume, food, beverage, cosmetics, and paint and varnish industries. Some compounds are also used in denaturing alcohol, cleaning products, quick-drying oils and inks, antifreeze, and as frothing agents in ore flotation.

n-Propanol is a solvent found in lacquers, cosmetics, dental lotions, printing inks, contact lenses and brake fluids. It is also an antiseptic, a synthetic flavouring agent for non-alcoholic beverages and food, a chemical intermediate and a disinfectant. Isopropanol is another important industrial solvent, which is used in antifreeze, quick-drying oils and inks, denaturing alcohol and perfumes. It is used as an antiseptic and a substitute for ethyl alcohol in cosmetics (i.e., skin lotions, hair tonics and rubbing alcohol), but cannot be used for pharmaceuticals taken internally. Isopropanol is an ingredient in liquid soaps, window cleaners, a synthetic flavouring additive for non-alcoholic beverages and food, and a chemical intermediate.

n-Butanol is employed as a solvent for paints, lacquers and varnishes, natural and synthetic resins, gums, vegetable oils, dyes and alkaloids. It is used as an intermediate in the manufacture of pharmaceuticals and chemicals, and employed in industries producing artificial leather, textiles, safety glass, rubber cement, shellac, raincoats, photographic films and perfumes. sec-Butanol is also used as a solvent and chemical intermediate, and is found in hydraulic brake fluids, industrial cleaning compounds, polishes, paint removers, ore-flotation agents, fruit essences, perfumes, dye-stuffs, and as a chemical intermediate.

Isobutanol, a solvent for surface coatings and adhesives, is employed in lacquers, paint strippers, perfumes, cleaners and hydraulic fluid. tert-Butanol is used for the removal of water from products, as a solvent in the manufacture of drugs, perfumes and flavours, and as a chemical intermediate. It is also a component of industrial cleaning compounds, a denaturant for ethanol, and an octane booster in gasoline. The amyl alcohols are frothing agents in ore flotation. Numerous alcohols, including methylamyl alcohol, 2-ethylbutanol, 2-ethylhexanol, cyclohexanol, 2-octanol and methylcyclohexanol, are used in the manufacture of lacquers. In addition to their numerous uses as solvents, cyclohexanol and methylcyclohexanol are useful in the textile industry. Cyclohexanol is employed in finishing textiles, leather processing, and as a homogenizer for soaps and synthetic detergent emulsions. Methylcyclohexanol is a component in soap-based spot removers and a blending agent for special textile soaps and detergents. Benzyl alcohol is used in the preparation of perfumes, pharmaceuticals, cosmetics, dye-stuffs, inks and benzyl esters. It also serves as a lacquer solvent, a plasticizer, and as a degreasing agent in rug cleaners. 2-Chloroethanol finds use as a cleaning agent and as a solvent for cellulose ethers.

Ethanol is the raw material for numerous products, including acetaldehyde, ethyl ether and chloroethane. It is an antifreeze agent, food additive and yeast growth medium, and it is used in the manufacture of surface coatings and gasohol. The production of butadiene from ethyl alcohol has been of great importance to the plastics and synthetic rubber industries. Ethyl alcohol is capable of dissolving a wide range of substances, and for this reason it is used as a solvent in the manufacture of drugs, plastics, lacquers, polishes, plasticizers, perfumes, cosmetics, rubber accelerators and so on.

Methanol is a solvent for inks, dyes, resins and adhesives, and is used in the manufacture of photographic film, plastics, textile soaps, wood stains, coated fabrics, unshatterable glass and waterproofing formulations. It is a starting material in the manufacture of many chemical products as well as an ingredient of paint and varnish removers, dewaxing preparations, embalming fluids and antifreeze mixtures.

Pentanol is used in the manufacture of lacquers, paints, varnishes, paint removers, rubber, plastics, explosives, hydraulic fluids, shoe cement, perfumes, chemicals, pharmaceuticals, and in the extraction of fats. Mixtures of the alcohols perform well for many of the solvent uses, but for chemical syntheses or more selective extractions, a pure product is often required.

Next to allyl chloride, allyl alcohol is the most important of the allyl compounds in industry. It is useful in the manufacture of pharmaceuticals and in general chemical syntheses, but the largest single use of allyl alcohol is in the production of various allyl esters, of which the most important are diallyl phthalate and diallyl isophthalate, which serve as monomers and repolymers.

Health Hazards

Methanol

Among the synthetic processes by which methyl alcohol is produced is the Fischer-Tropsch reaction between carbon monoxide and hydrogen, from which it is obtained as one of the by-products. It can also be produced by the direct oxidation of hydrocarbons and by a two-step hydrogenation process in which carbon monoxide is hydrogenated to methyl formate, which in turn is hydrogenated to methyl alcohol. The most important synthesis, however, is the modern, medium-pressure, catalytic hydrogenation of carbon monoxide or carbon dioxide at pressures of 100 to 600 kgf/cm² and temperatures of 250 to 400 °C.

Methyl alcohol has toxic properties under acute and chronic exposure. Injury has occurred amongst alcoholics from ingestion of the liquid, and to process workers from inhalation of the vapour. Animal experiments have established that methyl alcohol can penetrate the skin in sufficient quantity to cause fatal intoxication.

In cases of severe poisoning, most commonly following ingestion, methyl alcohol has a specific effect on the optic nerve, causing blindness as a result of optic nerve degeneration accompanied by degenerative changes of the ganglion cells of the retina and circulatory disturbances in the choroid. Amblyopia is commonly bilateral and may occur within a few hours of ingestion, whilst total blindness usually requires a week. The pupils are dilated, the sclera is congested, there is pallor of the optic disc with central scotoma; breathing and cardiovascular function are depressed; in fatal cases the patient is unconscious but coma may be preceded by delirium.

The consequences of industrial exposure to methyl alcohol vapour may vary considerably among individual workers. Under varying conditions of severity and duration of exposure, indications of intoxication include irritation of the mucous membranes, headache, ringing in the ears, vertigo, insomnia, nystagmus, dilated pupils, clouded vision, nausea, vomiting, colic and constipation. There may be skin injuries arising from the irritant and solvent action of methyl alcohol and from the harmful effects of stains and resins dissolved in it, and these are most likely to be located on the hands, wrists and forearms. In general, however, these harmful effects have been caused by prolonged exposures to concentrations very much in excess of limits recommended by authorities on methyl alcohol vapour poisoning.

Chronic combined exposure to methanol and carbon monoxide has been reported as a causative factor of cerebral atherosclerosis.

The poisonous action of methyl alcohol is attributed to its metabolic oxidation into formic acid or formaldehyde (which have a specific dangerous effect on the nervous system), and possibly to a severe acidosis. This oxidation process may be inhibited by ethyl alcohol.

Ethanol

The conventional industrial hazard is exposure to the vapour in the vicinity of a process in which ethyl alcohol is used. Prolonged exposure to concentrations above 5,000 ppm causes irritation of the eye and nose, headache, drowsiness, fatigue and narcosis. Ethyl alcohol is quite rapidly oxidized in the body to carbon dioxide and water. Unoxidized alcohol is excreted in the urine and expired in air, with the result that the cumulative effect is virtually negligible. Its effect on the skin is similar to that of all fat solvents and, in the absence of precautions, dermatitis may result from contact.

Recently another potential hazard in human exposure to synthetic ethanol was suspected because the product was found to be carcinogenic in mice treated at high doses. Subsequently, epidemiological analyses have revealed an excess incidence of laryngeal cancer (on average five times greater than expected) associated with a strong acid ethanol unit. Diethyl sulphate would appear to be the causative agent, although alkyl sultones and other potential carcinogens were also involved.

Ethyl alcohol is a flammable liquid, and its vapour forms flammable and explosive mixtures with air at normal temperature. An aqueous mixture containing 30% alcohol can produce a flammable mixture of vapour and air at 29 °C. One containing only 5% alcohol can produce a flammable mixture at 62 °C.

While ingestion is not a likely consequence of the use of industrial alcohol, it is a possibility in the case of an addict. The danger of such illicit consumption depends upon the concentration of ethanol, which above 70% is likely to produce oesophageal and gastric injuries, and upon the presence of denaturants. These are added to make the spirit unpalatable when it is obtained free of tax for non-potable purposes. Many of these denaturants (e.g., methyl alcohol, benzene, pyridine bases, methylisobutylketone and kerosene, acetone, gasoline, diethylphthalate and so on) are more harmful to a drinker than the ethyl alcohol itself. It is important therefore to ensure that there is no illicit drinking of the industrial spirit.

n-Propanol

Ill effects from the industrial usage of n-propanol have not been reported. In animals it is moderately toxic via inhalation, oral and dermal routes. It is an irritant of the mucous membranes and a depressant of the central nervous system. After inhalation, slight irritation of the respiratory tract and ataxia may occur. It is slightly more toxic than isopropyl alcohol, but it appears to produce the same biological effects. There is evidence of one fatal case after ingestion of 400 ml of n-propanol. The pathomorphological changes were mainly brain oedema and lung oedema, which have also been often observed in ethyl alcohol poisoning. n-Propanol is flammable and a moderate fire hazard.

Other compounds

Isopropanol in animals is slightly toxic via dermal and moderately toxic via oral and intraperitoneal routes. No case of industrial poisoning has been reported. An excess of sinus cancers and laryngeal cancers has been found among workers producing isopropyl alcohol. This could be due to the by-product, isopropyl oil. Clinical experience shows that isopropyl alcohol is more toxic than ethanol but less toxic than methanol. Isopropanol is metabolized to acetone, which can reach high concentrations in the body and is in turn metabolized and excreted by the kidneys and lungs. In humans, concentrations of 400 ppm produce mild irritation of the eyes, nose and throat.

The clinical course of isopropanol poisoning is similar to that of ethanol intoxication. The ingestion of up to 20 ml diluted with water has caused only a sensation of heat and slight lowering of the blood pressure. However, in two fatal cases of acute exposure, within a few hours after ingestion respiratory arrest and deep coma were observed and also hypotension, which is regarded as a bad prognostic sign, was also observed. Isopropanol is a flammable liquid and a dangerous fire hazard.

n-Butanol is potentially more toxic than any of its lower homologues, but the practical hazards associated with its industrial production and use at ordinary temperature are substantially reduced by its lower volatility. High vapour concentrations produce narcosis and death in animals. Exposure of human beings to the vapour may induce irritation of the mucous membranes. The reported levels at which irritation occurs are conflicting and vary between 50 and 200 ppm. Transient mild oedema of the conjunctiva of the eye and a slightly reduced erythrocyte count may occur above 200 ppm. Contact of the liquid with skin may result in irritation, dermatitis and absorption. It is slightly toxic when ingested. It is also a dangerous fire hazard.

The response of animals to sec-butanol vapours is similar to that to n-butanol, but it is more narcotic and lethal. It is a flammable liquid and a dangerous fire hazard.

At high concentrations the action of isobutanol vapour, like the other alcohols, is primarily narcotic. It is irritating to the human eye above 100 ppm. Contact of the liquid with the skin may result in erythema. It is slightly toxic when ingested. This liquid is flammable and a dangerous fire hazard.

Although tert-butanol vapour is more narcotic to mice than that of n- or isobutanol, few industrial ill effects have as yet been reported, other than occasional slight irritation of the skin. It is slightly toxic when ingested. In addition, it is flammable and a dangerous fire hazard.

Although headache and conjunctival irritation may result from prolonged exposure to cyclohexanol vapour, no serious industrial hazard exists. Irritation to the eyes, nose and throat of human subjects results at 100 ppm. Prolonged contact of the liquid with the skin results in irritation, and the liquid is slowly absorbed through the skin. It is slightly toxic when ingested. Cyclohexanol is excreted in the urine, conjugated with glucuronic acid. The liquid is flammable and a moderate fire hazard.

Headaches and irritation of the eye and upper respiratory tract may result from prolonged exposure to the vapour of methylcyclohexanol. Prolonged contact of the liquid with the skin results in irritation, and the liquid is slowly absorbed through the skin. It is slightly toxic when ingested. Methylcyclohexanol, conjugated with glucuronic acid, is excreted in urine. It is a moderate fire hazard.

Other than temporary headache, vertigo, nausea, diarrhoea and loss of weight during exposure to a high vapour concentration resulting from a mixture containing benzyl alcohol, benzene and ester solvents, no industrial illness is known from benzyl alcohol. It is slightly irritating to the skin and produces a mild lacrimating effect. The liquid is flammable and a moderate fire hazard.

Allyl alcohol is a flammable and irritant liquid. It causes irritation in contact with the skin, and absorption through the skin gives rise to deep pain in the region where absorption has occurred in addition to systemic injury. Severe burns may be caused by the liquid if it enters the eye. The vapour does not possess serious narcotic properties, but it has an irritant effect on the mucous membranes and the respiratory system when it is inhaled as an atmospheric contaminant. Its presence in a factory atmosphere has given rise to lacrimation, pain in the eye and blurred vision (necrosis of the cornea, haematuria and nephritis).

Amyl alcohols

Pentyl alcohols exist in several isomeric forms, and of the eight possible structural isomers, three also have optical active forms. Of the structural forms, four are primary alcohols—1-pentanol (amyl alcohol), 2-methyl-1-butanol, isopentyl alcohol (3-methyl-1-butanol, isoamyl alcohol) and neopentyl alcohol (2,2-dimethyl-1-propanol); three are secondary alcohols—2-pentanol, 3-pentanol and 3-methyl-2-butanol; and the final one is a tertiary alcohol—tert-pentyl alcohol (2-methyl-2-butanol).

Pentyl alcohol is irritating to the mucous membranes of the eyes, nose and throat at or somewhat above 100 ppm. Although it is absorbed by the gastrointestinal tract and the lungs, and through the skin, the incidence of industrial illness is quite low. Mucous membrane irritation occurs readily from the crude product because of the volatile extraneous materials present. The complaints from systemic illness include headache, dizziness, nausea, vomiting, diarrhoea, delirium and narcosis. Since pentyl alcohol is frequently used as the impure technical material and in conjunction with other solvents, distinctive symptoms and findings cannot be ascribed to the alcohol with any certainty. The ease with which the alcohols are metabolized is in the decreasing order of primary, secondary and tertiary; more tertiary is excreted unchanged than the others. Although toxicity varies with the chemical configuration, as a general estimation it can be said that a mixture of pentyl alcohols is about ten times as toxic as ethyl alcohol. This is reflected in the recommended exposure limits of the two alcohols—100 ppm and 1,000 ppm, respectively. The fire hazard from the amyl alcohols is not particularly great.

Alcohols tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3 - Physical and chemical hazards.

Table 4 - Physical and chemical properties.

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Aldehydes are members of a class of organic chemical compounds represented by the general structural formula R–CHO. R may be hydrogen or a hydrocarbon radical—substituted or unsubstituted. The important reactions of aldehydes include oxidation (whereby carboxylic acids are formed), reduction (with the formation of alcohol), aldol condensation (when two molecules of an aldehyde react in the presence of a catalyst to produce a hydroxy aldehyde), and the Cannizzaro reaction (with the formation of an alcohol and the sodium salt of an acid). Ketals, or acetals, as they are also called, are diesters of aldehyde or ketone hydrates. They are produced by reactions of aldehydes with alcohols.

Uses

Because of their high chemical reactivity, aldehydes are important intermediates for the manufacture of resins, plasticizers, solvents and dyes. They are used in the textile, food, rubber, plastics, leather, chemical and health care industries. The aromatic aldehydes and the higher aliphatic aldehydes are used in the manufacture of perfumes and essences.

Acetaldehyde is primarily used to manufacture acetic acid, but it is also used in the manufacture of ethyl acetate, peracetic acid, pyridine derivatives, perfumes, dyes, plastics and synthetic rubber. Acetaldehyde is utilized for silvering mirrors, hardening gelatin fibers, and as an alcohol denaturant and a synthetic flavoring agent. Paraldehyde, a trimer of acetaldehyde, is used in the dyestuff and leather industries and as a hypnotic agent in medicine. Industrially it has been used as a solvent, rubber activator and antioxidant. Metaldehyde is used as a fuel in portable cooking stoves and for slug control in gardening. Glycidaldehyde has been used as a cross-linking agent for wool finishing, for oil tanning, and for fat liquoring of leather and surgical sutures. Propionaldehyde is utilized in the manufacture of polyvinyl and other plastics and in the synthesis of rubber chemicals. It also functions as a disinfectant and as a preservative. Acrolein is used as a starting material for the manufacture of many organic compounds, including plastics, perfumes, acrylates, textile finishes, synthetic fibres and pharmaceuticals. It has been used in military poison gas mixtures and as a liquid fuel, an aquatic herbicide and biocide, and a tissue-fixative in histology.

Formaldehyde has an extremely wide range of uses related to both its solvent and germicidal properties. It is used in plastics production (e.g., urea-formaldehyde, phenol-form-aldehyde, melamine-formaldehyde resins). It is also used in the photography industry, in dyeing, in the rubber, artificial silk and explosives industries, tanning, precious metal recovery and in sewage treatment. Formaldehyde is a powerful antiseptic, germicide, fungicide and preservative used to disinfect inanimate objects, improve fastness of dyes on fabrics, and preserve and coat rubber latex. It is also a chemical intermediate, an embalming agent and a fixative of histological specimens. Paraformaldehyde is the most common commercial polymer obtained from formaldehyde and consists of a mixture of products with different degrees of polymerization. It is used in fungicides, disinfectants, bactericides and in the manufacture of adhesives.

Butyraldehyde is used in organic synthesis, mainly in the manufacture of rubber accelerators, and as a synthetic flavoring agent in foods. Isobutyraldehyde is an intermediate for rubber antioxidants and accelerators. It is used in the synthesis of amino acids and in the manufacture of perfumes, flavorings, plasticizers and gasoline additives. Crotonaldehyde is used in the manufacture of n-butyl alcohol and crotonic acid and in the preparation of surface active agents, pesticides and chemotherapeutic agents. It is a solvent for polyvinyl chloride and acts as a shortstopper in vinyl chloride polymerization. Crotonaldehyde is used in the preparation of rubber accelerators, the purification of lubricating oils, leather tanning, and as a warning agent for fuel gases and for locating breaks and leaks in pipes.

Glutaraldehhyde is an important sterilizing agent effective against all microorganisms, including viruses and spores. It is used as a chemical disinfectant for cold sterilization of equipment and instruments in the health care industry and as a tanning agent in the leather industry. It is also a component of embalming fluid and a tissue fixative. p-Dioxane is a solvent in pulping of wood and as a wetting and dispersing agent in textile processing, dye-baths, stain and printing compositions. It is used in cleaning and detergent preparations, adhesives, cosmetics, fumigants, lacquers, paints, varnishes, and paint and varnish removers.

Ketals are used in industry as solvents, plasticizers, and intermediates. They are capable of hardening natural adhesives like glue or casein. Methylal is used in ointments, perfumes, special purpose fuel, and as a solvent for adhesives and coatings. Dichloroethyl formal is used as a solvent and as an intermediate for polysulphide synthetic rubber.

Safety Precautions

Many aldehydes are volatile, flammable liquids which, at normal room temperatures, form vapours in explosive concentrations. Fire and explosion precautions, as described elsewhere in this chapter, must be most rigorous in the case of the lower members of the aldehyde family, and safeguards with respect to irritant properties must also be most extensive for the lower members and for those with an unsaturated or substituted chain.

Contact with aldehydes should be minimized by attention to plant design and handling procedure. Spillages should be avoided where possible and, where they occur, adequate water and drainage facilities should be available. For those chemicals labelled as known or suspected carcinogens, routine precautions for carcinogens, described elsewhere in this chapter, must be applied. Many of these chemicals are potent eye irritants and approved chemical eye and face protection should be mandatory in the plant area. For maintenance work, plastic face shields should also be worn. Where conditions require, suitable protective clothing, aprons, hand protection and impervious foot protection should be provided. Water showers and eye irrigation systems should be available in the plant area and, as with all protective equipment, operators must be fully trained in their use and maintenance.

Health Hazards

Most of the aldehydes and ketals are capable of causing primary irritation of the skin, eyes and respiratory system—a tendency which is most pronounced in the lower members of a series, in members that are unsaturated in the aliphatic chain, and in the halogen-substituted members. The aldehydes can have an anaesthetic effect, but the irritant properties of some of them may force a worker to limit exposure prior to having sufficient exposure to suffer anaesthetic effects. The irritating effect on the mucous membranes may be related to the ciliostatic effect where the hairlike cilia that line the respiratory tract and provide essential clearance functions are disabled. The degree of toxicity varies greatly in this family. Some of the members of the aromatic aldehydes and certain aliphatic aldehydes are rapidly metabolized and are not associated with adverse effects and thus have been found to be safe for use in foods and as flavourings. However, other members of the family are known or suspected carcinogens and due caution must be exercised in all situations in which contact may be possible. Some are chemical mutagens and several are allergens. Other toxic effects include the ability to produce an hypnotic effect. More detailed data on specific family members are included in the text which follows and in the accompanying tables.

Acetaldehyde is a mucous membrane irritant and also has general narcotic action of the central nervous system. Low concentrations cause irritation of the eyes, nose and upper respiratory passages, as well as bronchial catarrh. Extended contact can damage the corneal epithelium. High concentrations cause headache, stupor, bronchitis and pulmonary oedema. Ingestion causes nausea, vomiting, diarrhoea, narcosis and respiratory failure; death may result from damage to kidneys and fatty degeneration of the liver and heart muscle. Acetaldehyde is produced in the blood as a metabolite of ethyl alcohol, and will give rise to facial flushing, palpitations and other disagreeable symptoms. This effect is enhanced by the drug disulphiram (Antabuse), and by exposure to the industrial chemicals cyanamide and dimethylformamide.

In addition to its acute effects, acetaldehyde is a Group 2B carcinogen, that is, it has been classified as possibly carcinogenic to humans and a carcinogen in animals by the International Agency for Research on Cancer (IARC). Acetaldehyde induces chromosomal aberrations and sister-chromatid exchange in a variety of test systems.

Repeated exposure to the vapours of acetaldehyde causes dermatitis and conjunctivitis. In chronic intoxication, the symptoms resemble those of chronic alcoholism, such as loss of weight, anaemia, delirium, hallucinations of sight and hearing, loss of intelligence and psychic disturbances.

Acrolein is a common atmospheric pollutant which is produced in the exhaust fumes of internal combustion engines, which contain many and varied aldehydes. Acrolein concentration is increased when diesel oil or fuel oil is used. In addition acrolein is found in tobacco smoke in considerable quantities, not only in the particulate phase of the smoke, but also, and even more, in the gaseous phase. Accompanied by other aldehydes (acetaldehyde, propionaldehyde, formaldehyde, etc.) it reaches such a concentration (50 to 150 ppm) that it seems to be among the most dangerous aldehydes in tobacco smoke. Thus acrolein represents a possible occupational and environmental hazard.

Acrolein is toxic and very irritating, and its high vapour pressure may result in the rapid formation of hazardous atmospheric concentrations. Vapours are capable of causing injury to the respiratory tract, and the eyes can be injured by both liquid and vapours. Skin contact may produce severe burns. Acrolein has excellent warning properties and severe irritation occurs at concentrations less than those expected to be acutely hazardous (its powerful lacrimatory effect in very low concentrations in the atmosphere (1 mg/m³) compels people to run away from the polluted place in search of protective devices). Consequently, exposure is most likely to result from leakage or spillage from pipes or vessels. Serious chronic effects, such as cancer, however, may not be completely avoided.

Inhalation presents the most serious hazard. It causes irritation of nose and throat, tightness of the chest and shortness of breath, nausea and vomiting. The bronchopulmonary effect is very severe; even if the victim recovers from acute exposure, there will be permanent radiological and functional damage. Animal experiments indicate that acrolein has a vesicant action, destroying respiratory tract mucous membranes to such an extent that respiratory function is fully inhibited within 2 to 8 days. Repeated skin contact may cause dermatitis, and skin sensitization has been observed.

The discovery of the mutagenic properties of acrolein is not recent. Rapaport pointed it out as long ago as 1948 in Drosophila. Research has been carried out to establish whether cancer of the lung, whose connection with the abuse of tobacco is unquestionable, can be traced to the presence of acrolein in the smoke, and whether certain forms of cancer of the digestive system that are found to have a link with the absorption of burnt cooking oil are due to the acrolein contained in the burnt oil. Recent studies have shown that acrolein is mutagenic for certain cells (Drosophila, Salmonella, algae such as Dunaliella bioculata) but not for others (yeasts such as Saccharomices cerevisiae). Where acrolein is mutagenic for a cell, ultrastructural changes can be identified in the nucleus which are reminiscent of those caused by x rays in algae. It also produces various effects on the synthesis of DNA by acting on certain enzymes.

Acrolein is very effective in inhibiting the activity of the cilia of the bronchial cells that help to keep the bronchial tree clear. This, added to its action favouring inflammation, implies a good probability that acrolein can cause chronic bronchial lesions.

Chloroacetaldehyde has very irritant properties not only with regard to mucous membranes (it is dangerous to the eyes even in the vapour phase and can cause irreversible damage), but also to the skin. It can cause burnlike injuries on contact at 40% solution, and an appreciable irritation at 0.1% solution on prolonged or repeated contact. Prevention should be based on the avoidance of any contact and the control of atmospheric concentration.

Chloral hydrate is mainly excreted in humans first as trichloroethanol and then, as time progresses, as trichloroacetic acid, which may reach up to half the dose in repeated exposure. On severe acute exposure chloral hydrate acts like a narcotic and impairs the respiratory centre.

Crotonaldehyde is a strongly irritant substance and a definite corneal burn hazard, resembling acrolein in toxicity. Some instances of sensitization in workers have been reported and some assays for mutagenicity have produced positive results.

In addition to the fact that p-dioxane is a dangerous fire hazard, it has also been classified by IARC as a Group 2B carcinogen, that is, an established animal carcinogen and possible human carcinogen. Inhalation studies in animals have demonstrated that p-dioxane vapour can cause narcosis, lung, liver and kidney damage, irritation of the mucous membrane, congestion and oedema of the lungs, behavioural changes and elevated blood counts. Large doses of p-dioxane administered in drinking water have led to the development of tumours in rats and guinea pigs. Animal experiments have also demonstrated that dioxane is rapidly absorbed through the skin producing signs of incoordination, narcosis, erythema as well as liver and kidney injury.

Experimental studies with humans have also shown eye, nose, and throat irritation at concentrations of 200 to 300 ppm. An odour threshold as low as 3 ppm has been reported, although another study resulted in an odour threshold of 170 ppm. Both animal and human studies have demonstrated that dioxane is metabolized to β-hydroxyethoxyacetic acid. An investigation in 1934 of the deaths of five men working in an artificial silk plant suggested that the signs and symptoms of dioxane poisoning included nausea and vomiting followed by diminished and finally absence of urine output. Necropsy findings included enlarged pale livers, swollen haemorrhagic kidneys and oedematous lungs and brains.

It should be noted that unlike many of the other aldehydes, the irritant warning properties of p-dioxane are considered poor.

Formaldehyde and its polymeric derivative paraformaldehyde. Formaldehyde polymerizes readily in both liquid and solid state to form the mixture of chemicals known as paraformaldehyde. This polymerization process is delayed by the presence of water and, consequently, commercial formaldehyde preparations (known as formalin or formol) are aqueous solutions containing 37 to 50% formaldehyde by weight; 10 to 15% methyl alcohol is also added to these aqueous solutions as a polymerization inhibitor. Formaldehyde is toxic by ingestion and inhalation and it may also cause skin lesions. It is metabolized into formic acid. The toxicity of polymerized formaldehyde is potentially similar to that of the monomer since heating produces depolymerization.

Exposure to formaldehyde is associated with both acute and chronic effects. Formaldehyde is a proven animal carcinogen and has been classed as a 1B probable human carcinogen by IARC. Consequently, when working with formaldehyde, appropriate precautions for carcinogens must be taken.

Exposure to low atmospheric concentrations of formaldehyde causes irritation, especially of the eyes and respiratory tract. Due to the solubility of formaldehyde in water, the irritant effect is limited to the initial section of the respiratory tract. A concentration of 2 to 3 ppm causes slight formication of the eyes, nose and pharynx; at 4 to 5 ppm, discomfort rapidly increases; 10 ppm is tolerated with difficulty even briefly; between 10 and 20 ppm, there is severe difficulty in breathing, burning of the eyes, nose and trachea, intense lacrimation and severe cough. Exposure to 50 to 100 ppm produces a feeling of restricted chest, headache, palpitations and, in extreme cases, death due to oedema or spasm of the glottis. Eye burns can also be produced.

Formaldehyde reacts readily with tissue proteins and promotes allergic reactions, including contact dermatitis, which has also arisen from contact with formaldehyde-treated clothing. Asthmatic symptoms may occur due to allergic sensitivity to formaldehyde, even at very low concentrations. Kidney injury may occur in excessive and repeated exposure. There have been reports of both inflammatory and allergic dermatitis, including nail dystrophy due to direct contact with solutions, solids or resins containing free formaldehyde. Inflammation follows even after short-term contact with large quantities of formaldehyde. Once sensitized, the allergic response may follow contact with only very small quantities.

Formaldehyde reacts with hydrogen chloride, and it was reported that such reaction in humid air could yield a non-negligible amount of bis(chloromethyl) ether, BCME, a dangerous carcinogen. Further investigations have shown that at ambient temperature and humidity, even at very high concentrations, formaldehyde and hydrogen chloride do not form bis-(chloromethyl) ether at the detection limit of 0.1 ppb. However, the US National Institute for Occupational Safety and Health (NIOSH) has recommended that formaldehyde be treated as a potential occupational carcinogen because it has shown mutagenic activity in several test systems and has induced nasal cancer in rats and mice, particularly in the presence of hydrochloric acid vapours.

Glutaraldehyde is a relatively weak allergen which can cause allergic contact dermatitis and the combination of irritant and allergen properties are suggestive of the possibility of respiratory system allergies as well. It is a relatively strong irritant to the skin and the eyes.

Glycidaldehyde is a highly reactive chemical which has been classified by IARC as a group 2B possible human carcinogen and established animal carcinogen. Thus precautions appropriate for the handling of carcinogens must be exercised with this chemical.

Metaldehyde, if ingested, may cause nausea, severe vomiting, abdominal pain, muscular rigidity, convulsions, coma and death from respiratory failure. Ingestion of paraldehyde ordinarily induces sleep without depression of respiration, although deaths occasionally occur from respiratory and circulatory failure after high doses or more. Methylal can produce liver and kidney impairment and acts as a lung irritant on acute exposure.

Aldehydes and ketals tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3 - Physical and chemical hazards.

Table 4 - Physical and chemical properties.

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