With the developments of ammoximation

The sulfuric KN-62 acts not only as the catalyst in the hydrolysis reaction of CHO, but also as a important component in the salt formation of HAS. To investigate the effect of the molar ratio of sulfuric acid to CHO on the hydrolysis reaction of CHO, the amount of CHO added was fixed at 0.1 mol, the molar ratio of H+ to CHO was varied in the range of 1:1–5:1. The results are shown in Fig. 1. It can be clearly observed that the conversion of CHO increased with the increasing acid-oxime molar ratio, whereas the selectivity to HAS and cyclohexanone decreases only slightly when the molar ratio of sulfuric acid to CHO was 3:1. However, the selectivity to HAS and cyclohexanone were obviously decreased when the acid-oxime molar ratio exceeded 3:1. The conversion of CHO was 22.8% with 99.1% of selectivity to cyclohexanone and 91.3% of selectivity to HAS when the molar ratio of sulfuric acid to CHO was 2:1. In this process, the hydrolysis of CHO is reversible, the increasing H+ can accelerate the reaction and promote the reaction performing toward the salt formation of HAS, which removes the product hydroxylamine from hydrolysis reaction timely. This may result in the growth of the CHO conversion with the increasing acid-oxime molar ratio. Unfortunately, with the increased concentration of sulfuric acid, some new subsidiary reactions, such as the Beckmann rearrangement reaction of CHO [31], the self-condensation reaction of cyclohexanone [32] and the decomposition of free hydroxylamine [33] simultaneously occurred. Thus the selectivity of HAS and cyclohexanone decreased obviously. Therefore, the suitable molar ratio of sulfuric acid to CHO adequately and efficiently catalyzed the hydrolysis reaction of cyclohexanone oxime for preparation of HAS. These results illuminate that the acid-oxime molar ratio has important influence on the hydrolysis reaction of cyclohexanone oxime.