Immobilized Rhizomucor miehei lipase (Lipozyme RMIM) was employed in the synthesis of partial acylglycerols of acetoacetate (C4H6O3, 3-oxobutanoic acid). Both 1(3)-sn-monoacetoacetyl glycerol (MAcG) and 1,3-sn-diacetoacetyl glycerol (DAcG) resulting from esterification of glycerol with ethylacetoacetate were isolated and identified by 1H and 13C NMR. An HPLC method for the separation and quantitation of these species was developed. The effects on product yield of coordinate variations in the amounts of enzyme, water, ethyl acetoacetate, and the ratio of immobilizing silica to glycerol were explored. This allowed creation of predictive equations relating these variables to product yield. Reaction conditions were thereby identified and validated under which maximum yields of MAcG and/or DAcG or total ester were predicted. The production of both MAcG and DAcG was markedly sensitive to water, with optimal yields obtained within a narrow range of added water contents. Substantial excesses of ethylacetoacetate ameliorated the inhibitory effect of water. MAcG was effectively produced with the lowest amount of RMIM investigated. It was necessary to use larger amounts of lipase to achieve high yields of DAcG, and even then actual yields were only 30% of theoretical maximum. In the absence of silica only MAcG was produced.
Practical applications: Aceotacetyl esters of glycerol are potential prochiral building blocks for further chemical synthesis and exhibit the chemical reactivity of both the acetoacetyl moiety and of glycerol. They are thus of potential use in, for example, the production of biopolymers exhibiting any of a variety of features and functionalities. The use of enzymatic catalysis rather than chemical synthesis for their production offers advantages of reduced degradation and contamination due to the gentler reaction conditions characteristic of enzymatic catalysis, as well as a potential reduction in the costs to procure and dispose of catalyst.