Sustainable Routes to Alkenes: Applications of Homogeneous Catalysis to the Dehydration of Alcohols to Alkenes

With the growing scientific and social awareness of environmental issues, there is an increasing demand for renewablealkene feedstocks used to make the products we rely on. Alkenes are typically synthesised through high temperature‘cracking’ processes, but a more sustainable option is available through the dehydration of alcohols. This minireviewcompares the dehydration of alcohols to alkenes using homogeneous catalysts with well-established Brønsted acid andheterogeneous catalysts. Metal triflates M(OTf)₄ (M = Ti, Hf) are catalysts for the dehydration of primary, secondary andtertiary alcohols at decreasing temperatures with increasing substitution of the alcohol. The rhenium catalystsmethylrhenium trioxide (MTO) and Re₂O₇ are efficient catalysts at 100°C for dehydrating benzylic, allylic and tertiaryalcohols. A rhodium catalyst has been developed that utilises a catalytic quantity of HI to generate reactive alkyl halidesthat can undergo oxidative addition and β-H elimination. These expensive precious metal catalysts are contrasted by recentresults with iron triflate catalysts that promise more cost-effective processes in the near future.