Submitted to: European Journal of Lipid Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 2, 2010
Publication Date: February 1, 2011
Citation: Haas, M.J., Fox, P.S., Foglia, T. 2011. Lipase-catalyzed synthesis of partial acylglycerols of acetoacetate. European Journal of Lipid Science and Technology. 113(2):168-179. Interpretive Summary: Rising fossil fuel prices and concerns about the negative environmental impact of their combustion have triggered the development of biobased technologies and products to replace petroleum-based materials. Among the results of this effort is biodiesel, a diesel fuel produced from edible fats and oils. Glycerol is a byproduct of biodiesel production, and as biodiesel production has increased the supply of glycerol has become substantial. To find new uses for glycerol we have undertaken an investigation of its ability to be modified by the addition of a reactive chemical molecule known as acetoacetic acid. We have employed an enzyme as catalyst in these studies, because the harsher traditional methods that might be used could cause chemical degradation of the acetoacetate molecule. Upon the successful linkage of acetoacetate to glycerol achieved here, the chemical reactivity of the acetoacetate component could confer on the resulting molecules the ability to very readily undergo further reactions. In this way new oligomers and polymers could be formed which may find uses as new specialty chemicals or as replacements for various petroleum based materials presently functioning as lubricants, emulsifiers or polymers.
Technical Abstract: A commercially available immobilized preparation of Rhizomucor miehei lipase (Lipozyme RMIM) has been employed in the synthesis of partial glycerides of acetoacetate. Due to the chemical reactivitity of the acetoacetyl group, these glycerides could have novel uses in e.g. polymer formation. Both 1(3)-sn-monoacetoacetyl glycerol (MAcG) and 1,3-sn-diacetoacetyl glycerol (DAcG) were synthesized by enzyme-catalyzed esterification of glycerol with ethylacetoacetate. For analytical purposes, these were separated from one another by high performance liquid chromatography, and identified by proton and carbon NMR. The effects on product yield of coordinate variations in the amounts of enzyme, water, ethyl acetoacetate, and in the ratio of immobilizing silica to glycerol were explored in batch reactions containing 3 mmol of glycerol and conducted at 55°C for 18 hr. These data allowed the creation of predictive equations relating the value of these variables to product yield. Reaction conditions were thereby identified under which maximum amounts of MAcG and/or DAcG or total esters were predicted for one-pot reactions. The production of both MAcG and DAcG was markedly sensitive to the water content of the reaction, with optimal yields obtained within a narrow range of added water contents. Substantial excesses of ethylacetoacetate ameliorated the inhibitory effect of excessive water addition. MAcG was effectively produced with the lowest amount of RMIM investigated. However, it was necessary to use larger amounts of lipase to achieve high level production of DAcG, and even then yields were no greater than about 50% of theoretical maximum. In the absence of silica only MAcG, and no DAcG, was produced. When silica was added to the reactions as a glycerol carrier DAcG synthesis occurred. Variations in the ratio of silica to glycerol had little effect on yield.