Wednesday, 03 August 2011 06:27

Phenols and Phenolic Compounds

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Phenols are derivatives of benzene and have a hydroxyl group (-OH) attached to the benzene ring.


Phenols find use in industry as antioxidants, chemical intermediates, disinfectants, tanning agents, photographic developers, and additives to lubricants and gasoline. They are widely used in the photography, petroleum, paint, explosive, rubber, plastics, pharmaceutical and agricultural industries. The three major uses for phenols are found in the manufacture of phenolic resins, bisphenol A and caprolactam.

Phenol is used in the manufacture of a variety of compounds, including drugs, dyes and colourless or light-coloured artificial resins. It is a general disinfectant for toilets, stables, cesspools, floors and drains, as well as an extractive solvent for petroleum refining. Phenol is found in germicidal paints, slimicides and glue. Catechol is used particularly as an antioxidant in the rubber, chemical, photography, dye, fat and oil industries. It is also employed in cosmetics and in some pharmaceuticals.

Resorcinol is used in the tanning, cosmetics, rubber, pharmaceutical and photography industries, and in the manufacture of explosives, dyes, organic chemicals and antiseptics. It is found in adhesives for tyres, rubber and wood. Resorcinol is also an indirect food additive polymer for use as a basic component of single and repeated use food contact surfaces. Hydroquinone is a reducing agent and is used extensively as a photographic developer, an antioxidant, and a stabilizer in paints, varnishes, motor fuels and oils. Many derivatives of hydroquinone have been used as bacteriostatic agents. Pyrogallic acid also serves as a developer in photography as well as a mordant for wool, a dyeing agent for furs and hair, an antioxidant in lubricating oils, and a reducing agent for gold, silver and mercury salts. It is used for staining leather, preparing synthetic drugs, and for maintaining anaerobic conditions for bacterial growth. Its use is based primarily on its property of being easily oxidized in alkaline solutions (even by atmospheric oxygen).

2,4-Dimethyl phenol is used to manufacture pharmaceuticals, plastics, insecticides, fungicides, rubber chemicals, wetting agents and dye-stuffs. It acts as a solvent, disinfectant, germicide and sanitizer in commercial mixtures used in all hospital areas, instruments and equipment. o-Phenyl phenol has numerous functions as a fungicide, germicide and household disinfectant. It is used in the rubber and food-storage industries and serves as a dye-stuff carrier for polyester fibres and a disinfectant for cutting oils, timber and paper.

The cresols have wide applications in the phenolic resin, explosive, petroleum, photographic, paint and agricultural industries. They are ingredients of many household disinfecting solutions. Cresol is also an additive to lubricating oils and a component of degreasing compounds and paintbrush cleaners. m-Cresol is a textile scouring agent; o-cresol is used in tanning, fibre treatment and metal degreasing; p-cresol is a solvent for wire enamels and an agent used in metal cleaning, ore flotation, synthetic flavouring and perfumes.

The chlorophenols are intermediates in the synthesis of dyes, pigments and phenolic resins. Certain chlorophenols are used directly as mould inhibitors, antiseptics, disinfectants and anti-gumming agents for gasoline. 

Pentachlorophenol and its sodium salt are used to protect various industrial products from microbiological attack. These include wood and other cellulosic products, starches, adhesives, proteins, leather, finished yarn and cloth, photographic solutions, oils, paints, latex and rubber. Pentachlorophenol is used in the construction of boats and buildings, for mould control in petroleum drilling and production, and as an antibacterial agent in disinfectants and cleaners. It is also useful in the treatment of cable coverings, canvas belting, nets, poles and cooling-tower water. Pentachlorophenol is equally important in controlling termites in wood and insulating board, powder post beetles and other wood-boring insects, and slime and algae. It is also used in manufacturing herbicides, and as an agent to inhibit fermentation in various materials.

Some chlorophenols are used as intermediates and preservatives in the paint, textile, cosmetics and leather industries. 2-Chlorophenol and 2,4-dichlorophenol are used in organic synthesis. 2-Chlorophenol is utilized in the manufacture of dye-stuffs and in the process for extracting sulphur and nitrogen compounds from coal. 2,4,5-Trichlorophenol is a preservative for adhesives, synthetic textiles, rubber, wood, paints and paper; and 2,4,6-trichlorophenol is a wood and glue preservative. The tetrachlorophenols (and their sodium salts) have been used as fungicides and wood preservatives.



Phenol is readily absorbed through the skin and from the gastroenteric tract, while phenol vapours are readily absorbed into the pulmonary circulation. After absorption of a sublethal dose, most of the phenol is oxidized or conjugated with sulphuric, glucuronic and other acids, and excreted with the urine as “conjugated” phenol. A small portion is excreted as “free” phenol. The toxic effects of phenol are related directly to the concentration of free phenol in the blood.

In humans, acute phenol poisoning results in vasodilation, cardiac depression, hypothermia, coma and respiratiory arrest. Ingested phenol causes intense abdominal pain, and mouth burning occurs. Acute renal failure may also result. In animals, the signs of an acute intoxication are very similar, regardless of the site or the mode of administration of this compound. The predominant effects are exerted upon the motor centres in the spinal cord, resulting in tremors and severe convulsions. Chronic phenol poisoning is reported comparatively infrequently today. Severe cases are characterized by systemic disorders such as digestive disturbances, including vomiting, difficulty in swallowing, ptyalism, diarrhoea and anorexia; by nervous disorders, with headache, fainting, vertigo and mental disturbances; and possibly by ochronosis and an eruption on the skin. The prognosis is grave when there is extensive damage to the liver and kidneys. Ingestion of a dose of 1 g of phenol has been lethal to humans. Approximately every second reported case of acute phenol poisoning has resulted in death.

Generally speaking, the signs and symptoms of intoxication by di- and trihydroxy phenols (resorcinol, hydroquinone, pyrogallol) resemble that of phenol toxicity. The antipyretic action of resorcinol is more marked than that of phenol. The cutaneous application of solutions or salves containing 3 to 5% of resorcinol has resulted in local hyperaemia, itching dermatitis, oedema and loss of the superficial layers of the skin. The approximate lethal dose of resorcinol, in aqueous solution, for rabbits is 0.75 g/kg, and for rats and guinea-pigs, 0.37 g/kg. Hydroquinone is more toxic than phenol. Lethal doses have been reported as 0.2 g/kg (rabbit) and 0.08 g/kg (cat). Skin breakdown and irritation has been reported with dermal application of pyrogallol. Eventually with repeated contact, skin sensitization can occur. The symptoms observed in acute intoxications in humans resemble closely the signs displayed by experimental animals. These may include vomiting, hypothermia, fine tremors, weakness, muscular incoordination, diarrhoea, loss of reflexes, coma, asphyxia, and death by respiratory failure. Estimated lethal doses of aqueous pyrogallol are 1.1 g/kg (orally) for the rabbit, 0.35 g/kg (subcutaneously) for a cat or dog , and 0.09 g/kg (intravenously) in dogs.

Pentachlorophenol and its sodium salt are capable of inducing discomfort and local or systemic effects. Skin irritation is likely to result from a relatively brief, single exposure to a solution containing approximately 10% of the material. A 1% solution may cause irritation if contact is repeated. A solution containing 0.1% or less may result in adverse effects after prolonged contact. The symptoms of severe systemic intoxication include loss of appetite, respiratory difficulties, anaesthesia, hyperpyrexia, sweating, dyspnoea and a rapidly progressive coma.

Fine dusts and sprays of pentachlorophenol or sodium pentachlorophenate will cause painful irritation to the eyes and upper respiratory tract, respiratory tract and the nose. Atmospheric concentrations appreciably greater than 1 mg/m3 of air will cause this pain in the uninitiated person. Pentachlorophenol is classified by IARC as a Group 2B possible human carcinogen.

Other chlorophenols. Dermatoses in humans caused by tetrachlorophenol and its sodium salt have been reported; these included papulofollicular lesions, sebaceous cysts and marked hyperkeratosis. Occupational exposure to chlorophenols increases the risk of soft-tissue sarcomas. Chlorophenoxy derivatives including 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, 2,4,5-trichlorophenoxypropionic acid, and 2,4-D salts and esters are discussed elsewhere in this chapter and Encyclopaedia.

Signs of intoxication due to o-, m- and p-chlorophenol in rats include restlessness, increased rate of respiration, rapidly developing motor weakness, tremors, clonic convulsions, dyspnoea and coma. The 2,4- and 2,6-dichlorophenols and 2,4,6- and 2,4,5-trichlorophenols also produce these signs, but decreased activity and motor weakness do not appear quite so promptly. The tremors are much less severe, but, in this case also, they continue until a few minutes before death. Tetrachlorophenols take an intermediate place between the lower homologues and pentachlorophenol. These compounds also produce signs similar to those caused by the mono-, di- and trichlorophenols; however, they do not as a rule cause hyperpyrexia.

Dermatoses, including photoallergic contact dermatitis, have been reported in humans after exposure to 2,4,5-trichlorophenol, chloro-2-phenylphenol and tetrachlorophenols; these included papulofollicular lesions, comedones, sebaceous cysts and marked hyperkeratosis (chloracne).

Bromo- and iodophenols. The bromo- and iodophenols are rapidly absorbed from the gastroenteric tract. The approximate lethal oral dose of pentabromophenol is 200 mg/kg rat; of 2,4,6-tribromophenol, 2.0 g/kg rat; and of 2,4,6-triiodophenol, from 2.0 to 2.5 g/kg rat. In rats and guinea-pigs the subcutaneous LD50 of o-bromophenol are 1.5 and 1.8 g/kg, respectively. Generally, the symptoms are similar to those of pentachlorophenol. Pentabromophenol also caused tremors and convulsions.

On the basis of the results of animal experiments, the halogenated phenols, pentabromophenol and sodium and copper pentachlorophenate are considered safe for use as molluscicides in the field, if reasonable precautions are taken in their application.

Catechol (pyrocatechol). Contact with the skin has been known to cause an eczematous dermatitis, while in a few instances absorption through the skin has resulted in symptoms of illness closely resembling those induced by phenol, with the exception of certain marked central effects (convulsions). Toxic or lethal doses induced phenol-like signs of illness in experimental animals. However, unlike phenol, large doses of pyrocatechol cause a predominant depression of the central nervous system and a prolonged rise of blood pressure. The rise of blood pressure appears to be due to peripheral vasoconstriction.

The repeated absorption of sublethal doses by animals has induced methaemoglobinaemia, leucopenia and anaemia. Death is apparently initiated by respiratory failure.

Pyrocatechol is more acutely toxic than phenol. The approximate lethal oral dose is 0.3 g/kg for the dog, and 0.16 g/kg for the guinea-pig. Pyrocatechol is readily absorbed from the gastroenteric tract and through the intact skin. After absorption, part of the catechol is oxidized with polyphenol oxidase to o-benzoquinone. Another fraction conjugates in the body with hexuronic, sulphuric and other acids, while a small amount is excreted in the urine as free pyrocatechol. The conjugated fraction hydrolyzes in the urine with the liberation of the free compound; this is oxidized with the formation of dark-coloured substances which are responsible for the smoky appearance of the urine. Apparently, pyrocatechol acts by mechanisms similar to those reported for phenol.

Quinone. Large doses of quinone which have been absorbed from the subcutaneous tissues or from the gastroenteric tract of animals, induce local changes, crying, clonic convulsions, respiratory difficulties, drop in blood pressure and death by paralysis of the medullary centres. Asphyxia appears to play a major role in causing death because of pulmonary damage resulting from excretion of quinone into the alveoli and because of certain not too well defined effects of quinone upon haemoglobin. The urine of severely poisoned animals may contain protein, blood, casts, and free and conjugated hydroquinone.

In humans, severe local damage to the skin and mucous membranes may follow contact with the crystalline material, solutions of quinone and quinone vapour condensing upon exposed parts of the body (particularly moist surfaces). Local changes may include discolouration, severe irritation with erythema, swelling, and the formation of papules and vesicles. Prolonged skin contact may lead to necrosis. Vapours condensing upon the eyes are capable of inducing serious disturbances of vision. It was reported that the injury usually extends through the entire layer of the conjunctiva and is characterized by a deposit of pigment. The staining, varying from diffuse brown to globules of brownish-black, is located primarily in the zones extending from the canthi medially to the edges of the cornea. All layers of the cornea are involved in the injury, with a resultant discolouration that may be white and opaque or brownish-green and translucent. Alteration of the cornea can occur after the pigment has disappeared. Ulceration of the cornea has resulted from one brief exposure to a high concentration of the vapour of quinone, as well as from repeated exposures to moderately high concentrations.

Cresols and derivatives. Pure cresol is a mixture of ortho- (o-), meta- (m-) and para (p-) isomers, while cresylic acid, sometimes used synonymously for a mixture of cresols, is defined as a mixture of cresols, xylenols and phenol in which 50% of the material boils above 204 °C. The relative concentration of the isomers in pure cresol is determined by the source. The toxic effects of cresol are similar to those of phenol. It can be absorbed through the skin, from the respiratory system, and from the digestive system. The rate of penetration through the skin is more dependent upon the surface area than on the concentration.

Like phenol, it is a general protoplasmic poison and is toxic to all cells. Concentrated solutions are locally corrosive to the skin and mucous membranes, while dilute solutions cause redness, vesiculation and ulceration of the skin. Skin contact has also resulted in facial peripheral neuritis, impairment of renal function, and even necrosis of liver and kidneys. A sensitivity dermatitis may occur in susceptible people from solutions of less than 0.1%. Systemically, it is a severe depressant of the cardiovascular and central nervous systems, particularly the spinal cord and medulla. Oral administration causes a burning sensation in the mouth and oesophagus, and vomiting may result. Concentrations of vapour that can be produced at relatively high temperatures may cause irritation of the upper airways and nasal mucosa. Systemic absorption is followed by vascular collapse, shock, low body temperature, unconsciousness, respiratory failure and death. Pancreatic complications have been described. The oral toxic dose for small animals averages about 1 mg/kg, and specifically 0.6 mg/kg for
p-cresol, 0.9 mg/kg for o-, and 1.0 mg/kg for m-cresol. On the basis of its similarity to phenol, the human fatal dose can be estimated to be about 10 g. In the body, some of it is oxidized to hydroquinone and pyrocatechin, and the remainder and largest proportion is excreted unchanged, or conjugated with glycuronic and sulphuric acids. If urine is passed, it contains blood cells, casts and albumin. Cresol is also a moderate fire hazard.

Safety and Health Measures

These substances must be handled with caution. Inhalation of the vapours, and dust and skin contact with solutions of these materials, must be avoided to prevent local effects and absorption. The ingestion even of traces should be prevented. If exposure to the dust cannot be completely avoided, the nose and mouth should be protected with a respirator or folded gauze, and the eyes with tight-fitting goggles. Protective clothing, including rubber (not cotton) gloves, should be worn. Clothing should be removed immediately if contaminated by spillage. All clothing worn during one spraying operation should be laundered before re-use. Routine precautions include washing hands, arms, and face with soap and water before eating, drinking or smoking. At the end of each day, a worker should shower and change into clean clothing.

Measures that apply to phenol and its derivatives include:

  • careful instruction of persons engaged in the manufacture, handling, storage and transport of phenol
  • effective ventilation
  • proper disposal of phenolic wastes with precautions against the possible pollution of air, streams and underground waters, since aquatic species are particularly susceptible to the effects of chemicals in this family
  • special precautions in tank cleaning, which should not be attempted without proper gear, forced-air supply, a rescue harness and lifeline, hose mask, boots, rubber apron and gloves, and a “watcher” stationed at the entrance of the tank
  • continuous vigilance on the part of the hygienist or physician for signs and symptoms of acute or chronic (local or systemic) intoxication
  • fire prevention precautions.


First aid. In the event of an acute exposure, speed in treatment is essential. The offending agent must be removed from the skin, which is done most efficiently by flooding the affected area with water. After several minutes under the shower, continue decontamination with repeated swabbings or sprayings with polyethyleneglycol-300 until the danger of collapse has passed. If the exposed area is covered by clothing, remove it under the shower. Cover phenol burns lightly with a clean, white cloth. Do not use greases, powders or ointments in the first-aid treatment of such burns. Hospital treatment may include sedation, removal of dead tissue, fluid therapy, and the administration of antibiotics and vitamins. If phenol is splashed into eyes, copious irrigation with water for at least 15 minutes is necessary. All but the most trivial eye injuries should be referred to an ophthalmologist.

Speed is equally essential if a phenol has been ingested. Appropriate first aid must be available, and local medical facilities must be completely informed of the possibility of accidents and be prepared for emergency medical treatment. The treatment of chronic phenol poisoning is symptomatic after the individual has been removed from the site of exposure.

Phenols and phenolic compounds 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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