Enzymatic synthesis of 1,3-dicaproyglycerol by esterification of glycerol with capric acid in an organic solvent system

• Synthesis of dicaprin by glycerol esterification with glycerol adsorbed on silica.
• Silica gel adsorbs capric acid and monocaprin, careful desorption needed.
• Acyl migration sn-1(3) to sn-2 through a proposed enzymatic mechanism.

In this work, the esterification of glycerol with capric acid catalyzed by an immobilized form of a 1,3-positionally selective lipase (Rhizomucor miehei) showed to be effective for the synthesis of 1,3-dicaprin in n-heptane as the reaction medium.The effects of the reaction parameters were studied using an experimental factorial design of three factors and three levels with two central points. The selected experimental variables were amount of glycerol adsorbed on silica gel (G), biocatalyst load (E) and reaction temperature (T), and the response variables were total conversion of capric acid, acylglycerol fractions, selectivity and yield of dicaprin, and acyl migration reaction. The range of each parameter was selected as follows: G = 50–250 mg, E = 20–40 mg and T = 40–60 °C. At optimum conditions 73% capric acid conversion was achieved, with 76% dicaprin selectivity, and selectivity to the specific 1,3-dicaprin of 70% of total products. An adequate selection of the reaction conditions is necessary not only to maximize the conversion of capric acid, but also to minimize the acyl migration reaction and the generation of undesired products. Evidence of kinetically controlled enzymatic acyl migration from sn-3/sn-1 to sn-2 is presented.

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