The oxydation of cumene in liquid phase, at a temperature of about 100°C, by oxygen under a pressure of 730 mm Hg, gives principally the corresponding hydroperoxyde. The oxydation was carried out in the presence of various cobaltic compounds which are completely soluble in cumene at the used concentrations. The chelate of cobalt (11)-bis (2,2' hydroxybenzylidene) ethylene diamine, C. Co, catalyses vigorously this oxydation. The rate of reaction is initially high (16 mo1.x of cumene transformed an hour for [C.Co] = 10-4 ion g I F , and falls to 20% of the original value after an hour's reaction, showing thus the intervention of inhibition. The maximum rate of reaction varied following 0.5 power of the concentration in C.Co. The yield in hydroperoxyde as compared to the transformed cumene is above 90% for [C.Co] 1 1W4 ion g IF1. The same yield falls to 20% for a metal concentration 50 times greater. For [C.Co] = 1,05.1Op4 ion gl-l, the apparent energy of activation in this oxydation is about 12 kcal mo1-l between 80 and 120°C. The optimum conditions-the best compromise between the rate of reaction and the yield of hydroperoxyde-is using C. Co as compared to the cobalt naphtenate, N . Co, corresponds at 100°C, to a concentration of 2,l. lop4 ion g 1-4 of cobalt, for which the yields in hydroperoxyde are the same (85%), and the rate of oxydation of cumene 1,6 times faster in presence of C. Co. The different catalysts used fall under the following sequence in activity: C. Co.)N.Co)Acetate (11) 4 aq.)Sulfate (11) 7 aq. The differences in activity are interpreted by electronic effects and by the solvatation of the catalysts. L'oxydation du cumtne en phase liquide par l'oxygkne molkulaire engendre l'hydroperoxyde correspondant. La temperature ne peut toutefois dkpasser certaines limites (environ 130"C), faute de quoi la dkcomposition de l'hydroperoxyde intervient de faCon prkponderante. Certains sels de mktaux lourds ont une double influence. Tout en acck1Crant la rkaction, ils abaissent le pourcentage d'hydroperoxyde obtenu en fin de rkaction par rapport au cumtne transformk. Le problkme consiste dts lors a trouver le catalyseur et les conditions d'utilisation qui donnent le meilleur compromis entre la vitesse et le rendement.