The chemical structure of ketones is characterized by the presence of a carbonyl group (-C=O) that is linked to two carbon atoms. Ketones are represented by the general formula R-CO-R', where R and R' are usually alkyl or aryl groups. Considerable similarity exists between different ketones in the methods used for their production and also their properties—biological as well as chemical.
Ketones are produced by catalytic dehydrogenation or oxidation of secondary alcohols. In the petrochemical industry they are usually obtained by hydration of olefins. They are widely used as industrial solvents for dyes, resins, gums, tars, lacquers, waxes and fats. They also act as intermediates in chemical syntheses and as solvents in the extraction of lubricating oils. Ketones are used as solvents in the production of plastics, artificial silk, explosives, cosmetics, perfumes and pharmaceuticals.
The solvent acetone is used in the paint, lacquer and varnish, rubber, plastics, dye-stuff, explosives and photography industries. It is also used in the production of lubricating oils and the manufacture of artificial silk and synthetic leather. In the chemical industry, acetone is an intermediate in the production of many chemicals, such as ketene, acetic anhydride, methyl methacrylate, isophorone, chloroform, iodoform and vitamin C.
The major use of methyl ethyl ketone (MEK) is for the application of protective coatings and adhesives, which reflects its excellent characteristics as a solvent. It is also used as a solvent in magnetic tape production, dewaxing of lubricating oil, and food processing. It is a common ingredient in varnishes and glues, and a component of many organic solvent mixtures.
Mesityl oxide, methyl butyl ketone (MBK) and methyl isobutyl ketone (MIBK) are used as solvents in the paint, varnish and lacquer industries. 4-Methyl-3-pentene-2-one is a component of paint and varnish removers and a solvent for lacquers, inks and enamels. It is also used as an insect repellent, a solvent for nitrocellulose-vinyl resins and gums, an intermediate in the preparation of methyl isobutyl ketone, and a flavouring agent. Methyl butyl ketone is a medium evaporating solvent for nitrocellulose acrylates and alkyd coatings. Methyl isobutyl ketone is a denaturant for rubbing alcohol and a solvent for nitrocellulose, lacquers and varnishes, and protective coatings. It is used in the manufacture of methyl amyl alcohol, in the extraction of uranium from fission products, and in dewaxing of mineral oils.
The halogenated ketones are used in tear-gas. Chloroacetone, produced by the chlorination of acetone, is also used as a pesticide and in couplers for colour photography. Bromoacetone, produced by treating aqueous acetone with bromine and sodium chlorate at 30 to 40 °C, is used in organic synthesis. The alicyclic ketones cyclohexanone and isophorone are used as solvents for a variety of compounds including resins and nitrocellulose. In addition, cyclohexanone is an intermediate in the manufacture of adipic acid for nylon. The aromatic ketones acetophenone and benzoquinone are solvents and chemical intermediates. Acetophenone is a fragrance in perfumes, soaps and creams as well as a flavouring agent in food, non-alcoholic beverages and tobacco. Benzoquinone is a rubber accelerator, a tanning agent in the leather industry, and an oxidizing agent in the photography industry.
Ketones are flammable substances, and the more volatile members of the series are capable of evolving vapours in sufficient quantity at normal room temperatures to form explosive mixtures with air. Although in typical industrial exposures, the airways are the main route of absorption, a number of ketones are readily absorbed through the intact skin. Usually the ketones are rapidly excreted, for the most part in the expired air. Their metabolism generally involves an oxidative hydroxylation, followed by reduction to the secondary alcohol. Ketones possess narcotic properties when inhaled in high concentrations. At lower concentrations they can provoke nausea and vomiting, and are irritating to the eyes and respiratory system. Sensory thresholds correspond to even lower concentrations. These physiological properties tend to be enhanced in the unsaturated ketones and in the higher members of the series.
In addition to central nervous system (CNS) depression, effects on the peripheral nervous system, both sensory and motor, can result from excessive exposure to ketones. They are also moderately irritant to the skin, the most irritant being probably methyl-n-amyl ketone.
Acetone is highly volatile and may be inhaled in large quantities when it is present in high concentrations. It may be absorbed into the blood through the lungs and diffused throughout the body. Small quantities may be absorbed through the skin.
Typical symptoms following high levels of acetone exposure include narcosis, slight skin irritation and more pronounced mucous membrane irritation. Exposure to high concentrations produces a feeling of unrest, followed by progressive collapse accompanied by stupor and periodic breathing, and, finally, coma. Nausea and vomiting may also occur and are sometimes followed by bloody vomiting. In some cases, albumin and red and white blood cells in the urine indicate the possibility of kidney damage, and in others, liver damage can be presumed from the high levels of urobilin and the early appearance of bilirubin reported. The longer the exposure, the lower the respiratory rate and pulse; these changes are roughly proportionate to the acetone concentration. Cases of chronic poisoning resulting from prolonged exposure to low concentrations of acetone are rare; however, in cases of repeated exposure to low concentrations, complaints were received of headache, drowsiness, vertigo, irritation of the throat, and coughing.
1-Bromo-2-propanone (bromoacetone) is toxic and intensely irritating to the skin and mucous membranes. It should be stored in a ventilated area and wherever possible used in enclosed systems. Containers should be kept closed and plainly labelled. Personnel potentially exposed to its vapours should wear gastight chemical safety goggles and respiratory protective equipment. It is classified in some countries as a hazardous waste, thereby invoking special handling requirements.
2-Chloroacetophenone is a strong irritant of the eyes, inducing lacrimation. Acute exposure may lead to permanent damage to the cornea. The effects of this chemical appear primarily to be such irritating effects. On heating it decomposes in toxic fumes.
Cyclohexanone. High doses in experimental animals produced degenerative changes in liver, kidney and heart muscle; repeated administration on the skin produced cataracts; cyclohexanone also proved to be embryotoxic to chick eggs; however, in people exposed to much lower doses, the effects appear to be primarily those of a moderate irritant.
1-Chloro-2-propanone (chloroacetone ) is a liquid whose vapour is a strong lacrimator and is irritating to the skin and respiratory tract. Its effects as an eye irritant and lacrimator are so great that it has been used as a war gas. A concentration of 0.018 mg/l is sufficient to produce lacrimation, and a concentration of 0.11 mg/l will normally not be supported for more than 1 min. The same precautions should be respected in handling and storing as those applicable to chlorine.
Diacetone has irritant properties to eyes and upper airways; at higher concentrations it causes excitement and sleepiness. Prolonged exposure may result in liver and kidney damage and in blood changes.
Hexafluoroacetone [CAS 684-16-2] is a very irritating gas, particularly to the eyes. Exposure to relatively high concentrations causes respiratory impairment and conjunctival haemorrhages. A number of experimental studies have demonstrated adverse effects on the male reproductive system, including impairment of spermatogenesis. Changes in liver, kidneys and lymphopoietic system have also been observed. The irritating properties of this substance require that it be afforded special handling precautions.
Isophorone. In addition to strong irritation of the eyes, nose and mucous membranes, this chemical may affect the central nervous system and cause an exposed person to suffer from a feeling of being suffocated. The other signs of CNS effects can be dizziness, fatigue and inebriation. Repeated exposure in experimental animals caused toxic effects on lungs and kidneys; single exposure to high doses can produce narcosis and paralysis of the respiratory centre.
Mesityl oxide is a strong irritant both on contact with the liquid and in the vapour phase, and can cause necrosis of the cornea. Short exposure has narcotic effects; prolonged or repeated exposures can damage liver, kidneys and lungs. It is readily absorbed through the intact skin.
Methyl amyl ketone is an irritant to the skin and produces narcosis at high concentrations, but does not appear to be neurotoxic.
Methyl butyl ketone (MBK). Cases of peripheral neuropathy have been attributed to the exposure to this solvent in a coated-fabric plant where methyl-n-butyl ketone had been substituted for methyl isobutyl ketone at printing machines before any neurological cases were detected. This ketone has two metabolites (5-hydroxy-2-hexanone and 2,5-hexanedione) in common with n-hexane, which has also been regarded as a causative agent of peripheral neuropathies and is discusssed elsewhere in this Encyclopaedia. The symptoms of peripheral neuropathy included muscular weakness and abnormal electromyographic findings. Early signs of intoxication can include tingling, numbness and weakness in the feet.
2-Methylcyclohexanone. On contact it is a strong irritant to eyes and skin; by inhalation it is irritant to the upper airways. Repeated exposure can damage kidneys, liver and lungs. Methylcyclohexanone reacts violently with nitric acid.
Methyl ethyl ketone (MEK). Short exposure of workers to 500 ppm of MEK in air has provoked nausea and vomiting; throat irritation and headaches were experienced at somewhat lower concentrations. At high concentrations there have been some reports of neurological involvement, with the reported neuropathy symmetrical and painless with sensory lesions predominating; it may involve upper or lower limbs; in some cases the fingers have been affected following immersion of bare hands in the liquid. Dermatitis has been reported both after immersion in the liquid and after exposure to concentrated vapours.
Methyl isobutyl ketone (MIBK) shares both the irritating CNS effects of many other ketones. At high concentrations workers can feel giddy, develop headaches and be fatigued.
Safety and Health Measures
Measures recommended for flammable substances should be applied. Work practices and industrial hygiene techniques should minimize the volatilization of ketones in the workroom air in order to ensure that the exposure limits are not exceeded.
In addition, as far as possible, ketones with neurotoxic properties (such as methyl ethyl ketone and methyl-n-butyl ketone) should be replaced by products which lower toxicities. Preplacement and periodic medical examinations are recommended, with particular attention to the CNS and peripheral nervous system, respiratory system, the eyes, kidney and liver function. An electrodiagnostic examination with electromyography and nerve conduction velocity is appropriate particularly for workers exposed to methyl-n-butyl ketone.
Table 1 - Chemical information.
Table 2 - Health hazards.
Table 3 - Physical and chemical hazards.
Table 4 - Physical and chemical properties.