Addition of hydrogen sulfide to methyl acrylate over solid basic catalysts

Abstract

H 2S was added to methyl acrylate in a batch reactor at 313 K, 450 rpm, 0.2 M (in decane) in methyl acrylate, 5.5 bar of hydrogen sulfide pressure in the presence of solid bases. The bases differed in their chemical composition, structural properties, and acid–base properties. The bases were cation-exchanged X-faujasites, magnesium oxide, alkaline- and alkaline-earth-doped magnesium oxides, and commercially available and synthesized mixed magnesium/aluminum oxides. All of these catalysts were shown to achieve, in terms of both activity and selectivity, the addition of H 2S to methyl acrylate as compared with the patent literature. Catalytic runs have also been conducted on a fixed-bed continuous-flow reactor with performances, in terms of selectivity, better than those observed in batch mode, particularly with a Cs-exchanged X zeolite, which featured a selectivity level similar to that of modified ion-exchange resins. As previously assumed from kinetics and IR studies on H 2S and methyl acrylate adsorption and co-adsorption, the prerequisite for the title reaction to occur is the dissociation of H 2S into HS − and H + species over weak acid/strong basic Lewis pair sites. This assumption is confirmed in this work and is in agreement with the HSAB principle; H 2S is dissociated into a soft HS − nucleophilic species associated with a soft M x+ acid, and the hard H + species is associated with the hard O 2− basic species.