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a lactam of €-aminocaproic acid; a white crystalline substance. Melting point, 68°-69°C; boiling point, 262.5°C; index of refraction n20D, 1.4768.
Caprolactam is highly soluble in water and organic solvents, such as alcohol, ether, and benzene, and is hydrolyzed in aqueous acid and alkaline solutions to €-aminocaproic acid, H2NN-(CH2)5CCOOH. An important property of caprolactam is its ability to polymerize, forming the vaulable polymer polycaproa-mide.
All of the commercial methods of preparing caprolactam include preparation of an intermediate—cyclohexanon oxime— and its conversion (Beckmann rearrangement) into caprolactam under the action of fuming sulfuric acid or concentrated H2 SO 4 at 60°-120°C. One of the main methods of preparing caprolactam from cyclohexane (I) involves the catalytic oxidation of cyclohexane (by atmospheric oxygen) into cyclohexanone (II). Upon interaction with hydroxylamine, the latter is converted into cyclohexanon oxime (III):
The most efficient and economical method is direct photochemical nitrosation of (I) into cyclohexanon oxime chlorhydrate. The procedure is simple: upon continuous saturation with gaseous HC1, a solution of nitrosylchloride, NOC1, in (I) is irradiated using a 10-kilowatt mercury lamp. The oxime (III) can also be obtained from other available raw material, such as benzoic acid, C6H5COOH; it is hydrogenated to cyclohexanocarboxylic acid, C6H11COOH, which is subsequently treated with nitrosylsulfu-ric acid. The original commercial method of preparation of caprolactam from phenol is still widely used.
In all methods, the caprolactam produced is isolated rectification (redistillation) or extraction (for example, by benzene), with subsequent rectification.
Caprolactam is used primarily in the preparation of polyamide plastics, films, and fibers. In 1970 the world production of caprolactam reached 1.6 million tons.