Asymmetric lactic acid esterification with biocatalysts in ionic liquid

Abstract

Biodegradability and environmentally friendly technologies recently came into prominence; this is the reason why we assayed to develop a new “green” technology for L-lactic-acid (LLA) production. Racemic lactic acid (rLA) mixture produced by chemical industry is difficult to handle. The product of esterification with low carbon chain alcohols has higher volatility than lactic acid (LA) itself, therefore it can be more effectively separated. Our reactions were carried out with biocatalysts (enzymes) — some of them prefer reactionswith L-enantiomer — result in enantioselective esterification. After LLA ester production the hydrolysis leads to separated LLA, which is the starting material of a biodegradable plastic. Our aim was to achieve enantioselectivity in phosphonium-type ionic liquid solvents by the optimization of several parameters, such as temperature, substrate molar ratio, amount of IL, water content. Reasonable results were achieved with three types (Candida antarctica, Candida rugosa, AMANO PS-IM) of lipases. The use of enzymes and ionic liquids can make the technology “greener”, where an ingredient of a biodegradable plastic can be produced. The toxic heavy metals or hazardous acids can be replaced by biocatalyst (enzymes). These intermediates are re-usable, and they work at lower temperature, than conventional catalysts, thus the operational costs can be reduced. Ionic liquids — compared with conventional organic solvents — have insignificant vapour pressure, they are non-flammable and re-usable after a purification process, furthermore they can betailor made for a certain application. It is not negligible that the structure affects the environmental features like biodegradability or toxicity. The high lactic acid dissolving capacity is the reason why phosphonium-type ionic liquids were used. There are research teams, apply them for lactic acid extraction from fermentation broth.