A New Sustainable Multistep Catalytic Process from Benzene to Caprolactam: Amination, Hydroximation and Beckmann Rearrangement Promoted and Catalyzed by Trifluoroacetic Acid

Abstract

Here we report some results on a 3 steps benzene caprolactam process via amination, aniline Hydroxymation and Beckmann rearrangement. The amination proceeds with hydroxylamine trifluoroacetate, with 97% of conversion and selectivity of 90%, catalyzed by V compounds. We achieve 98% of conversion and 95% of selectivity in the hydroxymation of aniline in the presence of hydroxylamine trifluoroacetate, sulfonic resin and Pd/C. While in the absence of the resin, hydrogenation of hydroxylamine trifluoroacetate occurs readily to the ammonium salt. The reaction occurs likely by the exchanged hydroxylamine and the aniline reduction intermediate. The use of hydroxylamine trifluoroacetate, instead of the chloride, favors the sustainability of the process by avoiding the ammonium chloride formation. The absence of salt except those derived from the trifluoroacetic acid allows a complete reuse of the trifluoroacetic acid and the only byproduct is ammonium nitrate obtained by resin regeneration. Beckmann rearrangement of the so produced cyclohexanone oxime occurs easily after diethyl ether evaporation and additions of a solution trifluoroacetic acid acetonitrile in high yield and selectivity.

Silica Gel Supported Chlorosulfonic Acid Catalyzed Beckmann Rearrangement of Cyclohexanone Oxime in Liquid Phase

“…It has a brilliant application in industry, which is cyclohexanone oxime Beckmann rearrangement to prepare caprolactam. Caprolactam is almost always used to synthesize nylon 6 fibers [1,2], and nylon 6 fibers are commonly used to produce civilian silk, carpets, and industrial silk, in transportation [3] and computers. In addition, caprolactam is widely used as a pharmaceutical raw material in the production of antiplatelet drugs such as 6-aminohexanoic acid [4], antimalarial drugs, and the production of laurylazone.…”

Synthesis of Caprolactam through Dehydration and Cyclization of 6-Hydroxycaproamide

“…Besides contributing to serious pollution during production, the traditional process technology exhibits a low atom utilization rate. The growing demand for CPL has prompted investigations into improvements to the conventional synthetic route and the exploration of alternative production routes [10][11][12][13] .…”