Efficient enzymatic acrylation through transesterification at controlled water activity

Enzymatic acrylation is a process of potentially strong interest to the chemical industry. Direct esterification involving acrylic acid is unfortunately rather slow, with inhibition phenomena appearing at high acid concentrations. In the present study the acrylation of 1-octanol catalyzed by immobilized Candida antarctica lipase B (Novozym 435) was shown to be as much as an order of magnitude faster when ethyl acrylate served as the donor of the acrylic group. Water activity is a key parameter for optimizing the rate of ester synthesis. The optimum water activity for the esterification of octanol by acrylic acid was found to be 0.75, that for its esterification by propionic acid to be 0.45 and the transesterification involving ethyl acrylate to be fastest at a water activity of 0.3. The reasons for these differences in optimum water activity are discussed in terms of enzyme specificity, substrate solvation, and mass transfer effects.