Isotopic studies on the dehydroalkylation of toluene with ethane

The complex network of alkylation, dealkylation, transalkylation, and isomerization reactions during the dehydroalkylation of toluene with ethane to ethyltoluenes on Pt/H-ZSM-5 has been investigated by studying separately the secondary hydroconversion reactions of several aromatics and by using deuterated toluene (Ph-CD3) as reactant for the dehydroalkylation reaction. Product analysis by GC–MS revealed that all aromatic products contained considerably fewer deuterium atoms than expected. This fact together with the appearance of large amounts of unlabeled toluene molecules at low toluene conversions and the presence of deuterium atoms within ethane molecules indicates that H/D exchange (via associative or dissociative adsorption of the reactants) is significantly faster than other reactions. The formation of 89% methane-d0 and only 10% methane-d1 can also be explained by H/D exchange and the interplay of total hydrogenolysis of aromatics and demethylation of toluene and/or ethyltoluene after H/D exchange.

The mechanism of dehydroalkylation of toluene with ethane was studied using CD3-labeled toluene. Extensive H/D exchange without formation of CD3H and interplay of several reactions were observed.Figure optionsDownload as PowerPoint slide