Biodiesel is a highly attractive fuel for well-known reasons. Its growing global production is expected to lead to a big prospective increase in the production of glycerol, which accounts for up to 10 wt% of the total products after transesterification of vegetable oils. This offers promising opportunities for upgrading the surplus glycerol. Some homogeneous but mostly heterogeneous catalysts have been employed to convert glycerol into added-value products such as propanediols, acrolein, dihydroxiacetone or glyceric acid. Only recently has lactic acid been targeted as a promising derivative with numerous applications in the food industry and as a feedstock for the biodegradable polyester, polylactic acid.We report here a family of N-heterocyclic carbene (NHC) iridium catalysts highly active in the conversion of glycerol to lactic acid, being the first homogeneous examples for this transformation. Our best catalyst exhibits conversions of up to 95% and turnover numbers up to 20,000, at least one order of magnitude above the current best in heterogeneous systems. Additional advantages over the current methods are having: (i) the highest selectivity to lactic acid reported to date; (ii) a considerably lower reaction temperature (<120 �C);  (iii) no requirement for high pressures of H2 or O2; (iv) no requirement for solvent; and (v) a >95% mass balance. Moreover, clean hydrogen gas is formed as a valuable co-product. Mechanistic studies confirm homogeneity and evidence an unprecedented rearrangement of the NHC moieties.

Selective iridium-catalyzed conversion of neat glycerol into lactic acid under mild conditions

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.