Caprolactam is an organic compound with the formula5CNH. This colourless solid is a lactam of caproic acid. Global demand for this compound is approximately five million tons per year, and the vast majority is used to make Nylon 6 filament, fiber, and plastics.
Synthesis and production
Caprolactam was first described in the late 1800s when it was prepared by the cyclization of ε-aminocaproic acid, the product of the hydrolysis of caprolactam. World demand for caprolactam was estimated to reach five million tons per year for 2015. 90% of caprolactam produced is used to make filament and fiber, 10% for plastics, and a small amount is used as a chemical intermediate. Due to its commercial significance, many methods have been developed for the production of caprolactam. It was estimated that 90% of all caprolactam is synthesised from cyclohexanone, which is first converted to its oxime. Treatment of this oxime with acid induces the Beckmann rearrangement to give caprolactam : The immediate product of the acid-induced rearrangement is the bisulfate salt of caprolactam. This salt is neutralized with ammonia to release the free lactam and cogenerate ammonium sulfate. In optimizing the industrial practices, much attention is directed toward minimizing the production of ammonium salts. The other major industrial route involves formation of the oxime from cyclohexane using nitrosyl chloride, and this method accounts for 10% of world production. The advantage of this method is that cyclohexane is less expensive than cyclohexanone. Other paths to caprolactam include the depolymerization of waste Nylon6, and the reaction of caprolactone with ammonia. At bench scale, the reaction between cyclohexanone with hydrazoic acid to give caprolactam in the Schmidt reaction has been reported.
Uses
Almost all caprolactam produced goes into the manufacture of Nylon 6. The conversion entails a ring-opening polymerization: Nylon 6 is widely used in fibers and plastics. In situanionic polymerization is employed for cast nylon production where conversion from ε-caprolactam to Nylon 6 takes place inside a mold. In conjunction with endless fiber processing the term thermoplastic resin transfer molding is often used. Caprolactam is also used in the synthesis of several pharmaceutical drugs including pentylenetetrazol, meptazinol, and laurocapram.
