Kinetic features of catalytic decomposition of cyclohexyl hydroperoxide and 1-methylcyclohexyl hydroperoxide

Abstract

Catalytic decomposition of cyclohexyl and 1-methylcyclohexyl peroxides in the presence of 3d-metal acetylacetonates was studied.A cyclohexanol3cyclohexanone mixture is commercially produced on a large scale by oxidation of cyclohexane with atmospheric oxygen on a cobalt catalyst [1]. Cyclohexyl hydroperoxide (CHP, ROOH) is formed in the first step of this process. Kinetic features of the oxidation and the composition of the oxidation products are mainly determined by the course of catalytic decomposition of this intermediate. Previously, we have shown that the selectivity of cyclohexanone formation in the presence of chromiumcontaining catalysts is higher than that in the presence of industrial cobalt-containing catalysts [2].The oxidation of methylcyclohexane depends on the catalyst present in the system. The reaction yields either a tertiary alcohol (1-methylcyclohexanol) or a mixture of methylcyclohexanols and methylcyclohexanones, formed by reaction of the secondary C3H bonds with oxygen and peroxy radicals [3]. In the latter case, the reaction kinetics and composition of the oxidation products are determined by the course of transformation of tertiary 1-methylcyclohexyl hydroperoxide (MCHP, ROOH) into secondary methylcyclohexyl hydroperoxides.In this study, we examined the catalytic decomposition of CHP and MCHP in the presence of 3d-metal compounds.As shown previously [4, 5], s-and 3d-metal carboxylates form with MCHP complexes ML n 0 mROOH (n, m = 1, 2). This is due to the fact that intermolecular hydrogen bonds in the complexes of s elements and the coordination bond between 3d metals and the a-O atom of hydroperoxide are stronger than the hydrogen bonds in peroxide self-associates. These complexes catalyze decomposition of the hydroperoxide into radicals and molecular products. The catalytic activity of s-metal carboxylates [e.g., stearates (St)] in MCHP decomposition decreases with a decrease in the cation radius in the following order: CsSt > BaSt 2 > NaSt~Na 1 pel > CaSt 2 > LiSt [6]. EXPERIMENTALCyclohexyl hydroperoxide was prepared via intermediate trialkyl borates [7] at 378oC, which were oxidized with H 2 O 2 . MCHP was prepared by the procedure described in [8]. The content of the available oxygen in the hydroperoxides was 100%.3d-Metal acetylacetonates were prepared by the procedure described in [9].Decomposition of CHP and MCHP at 853105oC in the presence of catalysts listed in Table 1 was studied in decane and methylcyclohexane solutions, respectively. The catalyst concentration ranged from 3 0 10 !5 to 3 0 10 !4 and from 6 0 10 !4 to 8.8 0 10 !3 M; and the concentration of hydroperoxides, from 0.01 to 0.1 M. The first concentration range of the catalysts was chosen so as to minimize their association at 853105oC.The representative kinetic curves of overall CHP decomposition are shown in Fig. 1. The fast decomposition in the first steps decelerates with time owing to catalyst deactivation. The limiting degrees of CHP decomposition are determined by the nature and con-ÄÄÄÄÄÄÄÄÄÄÄ 1 Na pelargona...

Density Functional Theory Calculations of the Energetics and Kinetics of Jet Fuel Autoxidation Reactions

“…Thus, a direct reaction of the hydroperoxide with the metal ion, producing radicals and regenerating the metal ion via cannot result in a lower activation energy than the uncatalyzed pathway as there is no barrier to be lowered. Interestingly, the formation of a complex between metal ions and hydroperoxides has been proposed and studied. − Hiatt et al have even postulated that the OH - and H + ions of reactions 5 and 6 “may not be formed as free ions, but as part of the metal−ligand complex.” Formation of a metal ion and hydroperoxide complex may provide additional reaction pathways which offer lower energy routes to free radical formation than unimolecular hydroperoxide decomposition.…”

Use of Measured Species Class Concentrations with Chemical Kinetic Modeling for the Prediction of Autoxidation and Deposition of Jet Fuels

“…To assess the relative importance of dissolved metals in influencing oxidation behavior in the present work, a single metal-catalyzed reaction is appended to the kinetic mechanism (reaction 18 of Table ): This reaction increases the rate of hydroperoxide decomposition via a catalytic pathway but is a simplification of the complex chemistry associated with dissolved metal catalysis in a number of respects. For example, the varied reactivity of individual dissolved metals such as Cu and Mn which are known to catalyze hydroperoxide decomposition is not included here. In addition, the reaction is a simplification of the steps that may be involved in the catalysis of hydroperoxide decomposition.…”