Catalyzed Beckmann rearrangement of cyclohexanone oxime in heterogeneous liquid/solid system part 2: influence of acid catalysts and organic promoters

The influence of some transition metal oxide promoters in the catalyzed Beckmann rearrangement of cyclohexanone oxime was studied by preparing several heterogeneous H2SO4/M/SiO2 catalysts using SiO2 as support and H2SO4 as acid source. A definite effect of each metal has been observed and the best results have been obtained with Cr-, Zr- and Zn-oxides based promoter, which have shown an improved selectivity towards ɛ-caprolactam formation if compared to the H2SO4/SiO2 catalytic system. Moreover, the influence of some organic promoters on the reaction pathway was investigated. Acetic and trifluoroacetic anhydrides gave the best results, even if only the latter allowed the rearrangement even without solid acid catalysts. The transacetylation of the cyclohexanone oxime by using the acetyl caprolactam, which is the product of rearrangement of the acetyl cyclohexanone oxime, was studied for developing a step wise catalytic cycle. Finally, some preliminary results on a homogeneous organic catalyzed process are reported.