The enzymatic reaction of benzoic acid and glycerol in the absence of organic solvents to obtain the 1- or 3-monobenzoate glycerol (alpha-MBG) is studied. Esterification runs were batch wise performed with a concentration of enzyme of 30 g/L, changing the initial concentration of the acid in glycerol from 20 to 60 g/L, and temperature from 50 to 70 degrees C. In these conditions, the most active lipase among those tested for this synthesis was lipase B isozyme from Candida antarctica (CALB), obtaining conversion values higher than 80% and a significant selectivity to alpha-MBG. Unlike the synthesis in organic media, water did not have an inhibitory behaviour; hence control of water activity was unnecessary. Temperature and benzoic acid act synergically as deactivating factors. Considering the aforementioned, a kinetic model according to a Michaelis-Menten mechanism is proposed. This model considers a partial enzymatic deactivation mechanism with two terms, one of them accounting for the deactivating action of the acid. (C) 2011 Elsevier Ltd. All rights reserved.