Acyl Transfer Isomerization of Glycerol 1,2-Dibutyrate and Propane-1,2-diol 1-Butyrate

Abstract

The speciation of mixed butyrylglycerols (glycerol butyrates) and propanediol butyrate esters in the product mix from lamb pregastric lipase-catalysed hydrolysis of tributyrylglycerol and propane-1,2-diol dibutyrate has been examined by ¹³C n.m.r. spectroscopy. Samples from the quenched reaction mixture were extracted and allowed to stand in emulsion systems made up in bis tris propane buffer or water, pH 7·0, and in the absence of enzyme. There is clear evidence of uncatalysed conversion of rac-1,2-dibutyrylglycerol into the 1,3-isomer to form an equilibrium mixture containing c. 60–67% 1,3-isomer, and of conversion of propane-1,2-diol 1-butyrate into propane-1,2-diol 2-butyrate to form an equilibrium mixture containing c. 67% 2-monoester. Conversion kinetics to reach equilibrium are first order. Rate constants for acyl transfer of the diacylglycerol are 0·48 h^-1 (in water) and 0·68 h^-1 (in buffer) at 50°C, while those for acyl transfer of the 1-monoester are 0·72 h^-1 (50°C) and 0·35 h^-1 (35°C).