Catalytic Oxidation of Toluene to Bibenzyl and Stilbene

A new type of benzylic oxidation of toluene in vapor-phase was described in which toluene was dehydrodimerized to bibenzyl and stilbene over Bi2O3-SnO2, catalyst in the temperature range 400∼600°C. Effects of temperature, contact time, and oxygen-to-toluene ratio were investigated in detail, and a proposal of reaction scheme was made.The results obtained show that reactions with longer contact time and higher oxygen-to-toluene ratio are favorable to the formation of stilbene, while shorter contact time and lower oxygen-to-toluene ratio favor the formation of bibenzyl. A reaction route for the formation of stilbene consistent with these data involves the following consecutive steps; toluene→benzylic intermediates→bibenzyl→stilbene. This type of benzylic oxidation is considered to be analogous to the oxidative dehydroaromatization of C3-C4 olefins.