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Chemical Engineering Science 54 (1999) 3967}3976

Uncatalysed oxidation of cyclohexene
S.M. Mahajani, M.M. Sharma, T. Sridhar*
Department of Chemical Engineering, Monash University, Clayton, Victoria 3168, Australia Received 13 October 1998; received in revised form 22 December 1998; accepted 23 December 1998

Abstract The oxidation products of cyclohexene "nd several applications as intermediates for the manufacture of useful chemicals like cyclohexanol, cyclohexenol/cyclohexenone, cyclohexadiene, etc. The uncatalysed oxidation of cyclohexene with molecular oxygen was studied in a batch reactor. The products, cyclohexene hydroperoxide, cyclohexenol, cyclohexenone and cyclohexene oxide were realised in the temperature range of 343}393 K. The e!ect of various kinetic parameters such as temperature, speed of agitation and wall material was studied. The kinetic data were generated at di!erent temperatures and "tted successfully with a rate equation based on autocatalysis by total products. The values of rate constants and activation energy were determined. Recognising the fact that the industrial route to cyclohexene from benzene hydrogenation yields a mixture of cyclohexene and cyclohexane which are di$cult to separate, some experiments on oxidation of the mixture of cyclohexene and cyclohexane were also conducted. The values of rate constants remain unchanged in the presence of cyclohexane. The reaction was also studied in an aluminium lined reactor to examine the wall catalytic e!ect, if any, of the stainless steel wall. The reaction was found to be signi"cantly slower in the aluminium reactor while the selectivity towards the hydroperoxide remained unchanged. The oxidation of cyclohexene represents a unique example of an 1999 Elsevier Science Ltd. uncatalysed liquid-phase organic oxidation which can be conducted up to relatively high conversions. Allrights reserved. Keywords: Cyclohexene; Cyclohexenyl hydroperoxide; Autoxidation; Cyclohexenone; Cyclohexenol; Cyclohexene oxide

1. Introduction Oxidation of cyclohexene by air or molecular oxygen gives various products such as cyclohexenyl hydroperoxide, cyclohexenol, cyclohexeneone, and cyclohexene oxide, etc. The reaction conditions and the catalyst (if any) in#uence the product distribution and rate of the reaction. The catalytic oxidation of cyclohexene has been investigated in the past, in view of obtaining high yields of industrially important products such as cyclohexene oxide and cyclohexanol (e.g. Takehira et al., 1980; Neuburg et al., 1976). While the uncatalysed autooxidation of cyclohexene in comparison, appears to have received less attention. Though the work on the basic mechanism and product distribution has been dealt with way back in 1939, the reaction engineering aspects and kinetic data have not been reported in the literature to the best of our knowledge.

*Corresponding author. Tel.: 00-61-3-9905-3427; fax: 00-61-3-99055686.

Cyclohexene hydroperoxide is unstable and can be obtained in maximum yields only through the uncatalysed oxidation. Fig. 1 shows the potentially important routes involving cyclohexene hydroperoxide as a vital intermediate. Hydrogenolysis of cyclohexene hydroperoxide selectively gives cyclohexenol; catalytic decomposition of the hydroperoxide can also lead to cyclohexenol. Epoxidation of ole"nic substances with cyclohexene peroxide would lead to the corresponding epoxide and cyclohexenol. Cyclohexenol is an important raw material for the manufacture of cyclohexanol and cyclohexadiene which "nd application in nylon and perfumery industries, respectively. A new route for the preparation of high purity cyclohexadiene through epoxidation of cyclohexene has been proposed by Asahi Chemicals (Ishida and Ono, 1995) and provides another motivation for the systematic study of this reaction. The present work is aimed at studying the oxidation of cyclohexene by molecular oxygen in a stirred tank batch reactor. The products obtained...
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