Deoxydehydration of glycerol to allyl alcohol catalyzed by rhenium derivatives

Abstract

The deoxydehydration (DODH) of glycerol is effectively catalyzed by rhenium derivatives, either in neat glycerol or in the presence of solvents (in particular alcohols), in air or under hydrogen bubbling. Methyltrioxorhenium (MTO) and ReO₃ were the only rhenium catalysts tested that can selectively catalyze the DODH reaction at very low temperatures (140 °C). The presence of oxygen is not necessary, although under nitrogen the reaction requires higher temperatures to occur. On the other hand, the presence of hydrogen often noticeably increased the selectivity versus allyl alcohol formation, reaching the considerable value of 90% in the case of reaction conducted in 2,4-dimethyl-3-pentanol with ReO₃. The DODH reaction always exhibits a definite induction time that, in the case of MTO, corresponds more or less to the time required for its demethylation. Metal catalysts in both high – likely rhenium(VI) – and low oxidation states are involved. Re-addition of fresh glycerol at the end of the reaction indicates the feasibility of the reuse of the catalysts.