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Tuesday, 02 August 2011 23:53

Alcohols

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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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Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides
Guide to Occupations
Guide to Chemicals
Resources
Guide to Units and Abbreviations