Process systems for the carbonate interchange reactions of DMC and alcohols: efficient synthesis of catechol carbonate†
A range of organic carbonates was synthesised from dimethylcarbonate (DMC) and different alcohols by base-catalysed carbonate interchange reactions (CIRs). Dimethyl carbonate – used as a green and efficient reagent as well as the reaction solvent – was coupled to methanol-removing systems to break the reaction equilibrium and thus obtain near quantitative yields of the desired carbonates. Two different methanol-removing systems are described, one based on azeotropic distillation (reactive azeotropic distillation, RAD) and one based on methanol absorption (reactive vapour absorption, RVA). A comparison between the two systems is described and some conclusions based on reaction metrics are discussed. The methods were applied to the synthesis of aliphatic asymmetric alkyl-methyl carbonates and to the synthesis of catechol carbonate, using both homogeneous (NaOMe and trioctylmethylphosphonium methylcarbonate, P8881-MC) as well as heterogeneous (MgO) catalysts.