Study On The Effect Of Ammonium Salts On Ammoximation Of Ketones Catalyzed By Titanosilicates/H₂O₂

Oxime is an important chemical product,and the technique for high selectivity and activity formation of oxime by liquid phase ammoximation of ketones based on the titanosilicates/H₂O₂ catalytic system has always been the main route in its environment-friendly chemical developments.The reaction activity,selectivity and stability in this catalytic system have also attracted the attentions of many academic and industrial researchers.In this paper,it was mainly concentrated on the effect of ammonium salts on the formation and stability of intermediate hydroxylamine in the process of liquid phase ammoximation of cyclohexanone over TS-1/H₂O₂ system.Eventually,the effect of ammonium salts on the reaction activity,selectivity and stability in the continuous slurry reaction were evaluated systemically and the results could been concluded as follows:1.A two-step method in the batch-type reaction was adopted to study the effects of the introduction of ammonium salts to the ammoximation reactions of various ketones on the formation of the intermediate hydroxylamine.The results showed that the addition of appropriate amounts of ammonium salt were beneficial to the formation of hydroxylamine.Moreover,it had the universality for different topological structures of titanosilicates.Among them,the effects of different types of ammonium salts on the intermittent cyclohexanone oxime system showed the following trends:NH₄F>NH₄Cl>NH₄Br;NH₄NO₃>（NH₄）₂SO₄>NH₄Ac.Further analysis revealed that the hydrogen bond mainly due to the interaction between the anion and NH₃ enhanced the attack of reactive intermediate Ti-OOH,thus promoting the formation of hydroxylamine.2.The study of the effect of ammonium salts on the stability of hydroxylamine in two-step batch reaction showed that the anions in the ammonium salts may be combined with hydroxylamine to form hydroxylamine salts,which were beneficial to the stability of hydroxylamine.3.The study of the effect of ammonium salts on the decomposition of cyclohexanone oxime showed that the ammonium salts inhibited the decomposition of cyclohexanone oxime so as to reduce the side reactions and promote the conversion of cyclohexanone to cyclohexanone oxime.4.The ammonium salts played a positive role in boosting the conversion of cyclohexanone in the batch reaction based on the TS-1/H₂O₂ system.Under the optimized conditions,the conversion of cyclohexanone increased from 49.4%to 65.9%,the rate of which was up to 33.4%.5.The effect of ammonium salts on the stability in continuous ammoximation of cyclohexanone was also investigated.Tthe results showed that the introduction of ammonium salts greatly improved the stability of the reaction system,and the life time was extended from 28h to 91.5h when the dosage of NH₄Cl was l‰.