Oxydation Du Cyclohexane: Activation Par Les Aldéhydes

Abstract

AbstractThe oxidation of cyclohexane in liquid phase at 150°C by a mixture of oxygen and nitrogen in the ratio of 1:1 under an initial partial pressure of 11 kg. cm−2 by oxygen, and catalyzed by cobalt naphtenate ([Co] = 50 ppm by weight), gives principally cyclohexanol, cyclohexanone and adipic acid. The transformation of cyclohexane carried out in a stainless steel autoclave, is powerfully accelerated when concentrations of about 0 to 0.5 mol.l−1 of aldehydes are added to the cyclohexane at the start. Thus the rate of oxidation of cyclohexane in the presence of 0.150 mol.l−1 of benzaldehyde, is ten times greater in the mixture than the rate at which pure cyclohexane is oxidized under the same conditions. The activities of aldehydes, in the oxidation of cyclohexane, are in the order of: m‐methoxybenzaldehyde, 2, 3‐dimethoxybenzaldehyde > benzaldehyde, acrolein > p‐methoxybenzaldehyde > acetaldehyde > 3, 4‐dimethoxybenzaldehyde > phtalaldehyde. The dragging effect varies following the power one of the concentration of additive. Nevertheless, whenever this concentration exceeds a certain value, the acceleration diminishes. Therefore the optimum conditions for the use of these additives are situated in feeble concentrations of aldehyde. In addition, the induction time of reaction is reduced in their presence (t> 4 min, when [benzaldehyde] = 0.150 mol.l−1). The dragging effect is attributed to the increase in the concentration of radicals, produced by the oxydation of the additives. A comparison of the rate of oxidation of pure cyclohexane and of the same in the mixture form, permits an approximate evaluation of the rate constants specific to the oxidation of cyclohexane and relative to the different stages of the reaction mechanism:k3 = 1.8.102 (mol.l−1−1 (RO2.+RH → ROOH+R);k5 = 2.2. 10−3 sec−1 (ROOH → RO.+.OH); k8 = 3.6. 10−2 (mol.l−1)−1. sec−1 (ROOH+RH → 2 ROH); k9 = 2.2. 10−1 sec−1 (ROOH → R1 CO R2+H2O).