Chementator: Another ‘green’ process to make caprolactam

Professor Yasutaka Ishii, and colleagues from the Dept. of Applied Chemistry, Kansai University (Osaka, Japan; edlinks.chemengonline.com/5830-535), has developed a three-step production process to make epsilon-caprolactam (CPL) from cyclohexane. Compared to alternative methods, the process has a higher CPL yield, generates less waste, and avoids the use of corrosive reagents, says Ishii. The convectional route to CPL involves the Beckmann rearrangement of cyclohexanone oxime, a reaction that generates large quantities of ammonium sulfate waste. The cyclohexanone oxime precursor to CPL is made by either reacting cyclohexanone with hydroxyl amine, or by a photonitrosation (referred to as PNC) of cyclohexane with nitrosyl chloride. The former method suffers from a low (3–6%) single-pass conversion of cyclohexane to cyclohexanone, and the later PNC process requires NOCl, which is both toxic and very corrosive. Although another process, recently commercialized (CE, March 2002, p. 17) by Sumitomo Chemical Co. (Osaka), eliminates the (NH4)2SO4 byproduct, this process also suffers from a low cyclohexane-to-cyclohexanone conversion, says Ishii. In the new process, cyclohexane reacts with tert-butyl nitrite over a proprietary N-hydroxyphthalimide…