Preparation of Benzaldehyde by Aerobic Liquid-Phase Oxidation of Toluene with Co(acac)_2

The preparation of benzaldehyde by aerobic liquid-phase oxidation of toluene using Co(acac)2 as the catalyst was investigated. The effects of operation parameters, such as reaction time, reaction temperature, concentrations of Co, Co/Mn ratio were studied. The results show that the oxidation of toluene is a multiple reaction process with parallel and series reaction steps. The concentration of benzaldehyde increases fastly in the initial reaction stage(low toluene conversion), and then reaches a steady value. However, the yield of benzaldehyde decreases significantly with further toluene conversion because benzaldehyde is easier to be further oxidized to benzoic acid. Reaction temperature change has little effect on the concentration and the yield of benzaldehyde. Compared with cobalt acetate and cobalt naphthenate catalysts, cobalt acetylacetonate Co(acac)2 has a better catalytic effect with less amount needed. The addition of Mn(acac)2 as a co-catalyst is favorable for enhancing the reaction yield.