Two-Step Synthesis of Dialkyl Carbonates through Transcarbonation and Disproportionation Reactions Catalyzed by Calcined Hydrotalcites

A two-step methodology was implemented to prepare dialkyl carbonates from both primary and secondary alcohols, including glycerol acetals, tetrahydrofurfuryl alcohol, and cyclohexanol. Accordingly, alcohols were initially subjected to a batch transcarbonation (carbonate interchange) reaction with the nontoxic dimethyl carbonate, providing the corresponding asymmetrical methyl alkyl carbonates (ROCO2Me). These compounds were then used as reactants for a continuous-flow (CF) disproportionation reaction, producing the corresponding symmetrical dialkyl carbonates (ROCO2R). Although transcarbonation and dismutation took place at different operating temperatures (90 and 180–275 °C, respectively), both reactions were catalyzed by the same heterogeneous Mg/Al mixed oxides catalyst, obtained upon calcination of commercially available hydrotalcites (HTs). Yields and selectivities for methyl alkyl carbonates were excellent, in the range of 93–96% and 95–98%, respectively. CF-disproportionation reactions were strongl...