Towards the mechanism of the oxidation of cyclohexylamine by molecular oxygen over alumina-based catalysts

Abstract

The oxidation of cyclohexylamine with molecular oxygen over a heterogeneous catalyst is an attractive one-step route to prepare a commercially important cyclohexanone oxime. The effect of the reaction conditions on the conversion of cyclohexylamine during its oxidation by molecular oxygen and on the selectivity of cyclohexanone and cyclohexanone oxime formation was investigated over heterogeneous catalysts (alumina and alumina supported silicotungstic acid). The present work is aimed at the enhancement of the cyclohexanone oxime yield, for which the optimized conditions were found as: reaction temperature of 180°C, LHSV of cyclohexylamine 1 ml g -1 h -1 , oxidant 33 % O 2 in nitrogen with a total GHSV of 24 ml min -1 . Cyclohexanone, formed from cyclohexylamine, reacts with cyclohexylamine to N-cyclohexylidenecyclohexylamine, their Schiff base. The most intense formation of cyclohexanone was observed in the initial period of the catalytic tests. Carbonaceous deposits, responsible for the catalyst deactivation, are formed mainly from the Schiff base; their amount increases by time on stream, and the rate of their formation correlates with the concentration of oxygen in the reaction mixture, as well as with the formation rate of cyclohexanone and the Schiff base. Injection of water to the reactant stream prolongs the catalyst lifetime and reduces the tar formation. However, it deteriorates the catalysts activity and selectivity. The supposed mechanism of cyclohexylamine oxidation is discussed.Electronic supplementary material The online version of this article (

SupportedTiO2/silica gel as an efficient and inexpensive catalyst for nonsolvent liquid‐phase oxidation of cyclohexylamine to cyclohexanone oxime

“…The oxidants mainly consist of dioxygen, hydrogen peroxide, and a series of alkyl hydroperoxides. [7][8][9][10][11] Compared with other oxidants, dioxygen has obvious advantages regarding cost and safety. Therefore, dioxygen was used in most studies as the oxidant for the green oxidation of CHA.…”

Highly Selective Preparation of Cyclohexanone Oxime from Liquid-Phase Catalytic Oxidation of Cyclohexylamine with Molecular Oxygen over Glucose-Modified TiO2 under Solvent-Free Conditions

“…10,11 research of the activity of heterogeneous acid catalysts, and the selectivity to CHO was about 60.4% with 33.4% of CHA conversion employing alumina-supported silicotungstic acid. 12 Maldotti et al reported that the heteropoly acid ((nBu 4 N) 4 W 10 O 32 ) catalyst was effective in the acetonitrile solvent, but the conversion and selectivity have not been enhanced significantly. 13 Rakottyay et al proposed to use an organic amine-modified WO 3 /γ-Al 2 O 3 catalyst, and the selectivity to CHO reached 64%.…”

“…In the past few decades, some notable research progress on the aerobic oxidation of CHA to CHO had been achieved. Early researchers were devoted to transition metal elements as active components for the synthesis of supported catalysts and had achieved good results. , Horváth et al focused on the research of the activity of heterogeneous acid catalysts, and the selectivity to CHO was about 60.4% with 33.4% of CHA conversion employing alumina-supported silicotungstic acid . Maldotti et al reported that the heteropoly acid ((nBu 4 N) 4 W 10 O 32 ) catalyst was effective in the acetonitrile solvent, but the conversion and selectivity have not been enhanced significantly .…”