Biobased Methacrylic Acid via Selective Catalytic Decarboxylation of Itaconic Acid

We report a biobased route to methacrylic acid via selective decarboxylation of itaconic acid utilizing catalytic ruthenium carbonyl propionate in an aqueous solvent system. High selectivity (>90%) was achieved at low catalyst loading (0.1 mol %) with high substrate concentration (5.5 M) at low temperature (200–225 °C) and pressure (≤425 psig) relative to previous contributions in this area. Direct decarboxylation of itaconic acid was achieved as opposed to the conjugate base reported previously, thereby avoiding basification and acidification steps. Also investigated was catalytic manganese(II) oxalate (5 mol %), but low yield (4.8%) and evolution of carbon monoxide via oxalate decomposition was problematic. Attempts at stabilization of the catalyst with triphenylphosphine were unsuccessful, but it exhibited greater catalytic efficacy (14.0% yield) than the manganese catalyst (4.8% yield) at 5 mol %. Neither carbon monoxide nor propylene (excessive decarboxylation) were detected during ruthenium-catalyzed decarboxylation. In addition, cosolvents such as tetraglyme lowered vapor pressures within the reaction vessel by >100 psig while minimizing decomposition of starting acids. In combination, these findings represent improvements over existing methodologies that may facilitate sustainable production of methacrylic acid, an important petrochemically based monomer for the plastics industry.