Biocatalytical synthesis of ethyl hexanoate

Ethyl hexanoate is a typical fragrance compound of Chinese liquor and Japanese sake with an annual demand of more than 2000 tons [1, 2]. Presently, the synthesis of ethyl hexanoate is mainly based on chemical methods, but its application is somewhat hampered by the environmental concern of the process as well as the increasing demand for natural flavor compounds [2–4]. On the contrary, enzymatic synthesis seems to be a promising alternative due to the mild reaction conditions and being environmentally friendly because esters from enzyme-mediated reactions can be considered natural [2, 5]. Synthesis of ethyl hexanoate catalyzed by Candida antartica lipase (Novozyme 435) in n-hexane was studied in this work. For that purpose three reactions were examined. The first one is the esterification of hexanoic acid and ethanol, and the other two were the reaction of transesterification of hexanoic acid using ethyl caprate ant ethyl acetate as the co-substrate. As in the first reaction (esterification of hexanoic acid and ethanol) the highest equilibrium conversion (64.15 %) was achieved this one was chosen for the further investigation. Optimal reaction rate of the reaction was remarked at water concentration of 0.3 %. The reaction kinetics was determined by the initial reaction rate method. The influence of substrates and products was examined in the reaction of esterification, as well in the reversible hydrolysis reaction. The experiments were carried out at 40 °C and at n = 200 min-1. The mathematical model was developed and validated by the experiments in the batch reactor. Hexanoic acid conversion of 85 % was achieved in the excess of ethanol (10:1). [1] Xu Y., Wang D., Mu X.Q., . Zhao G.A., Zhang K.C., J Mol Catal B: Enzyme, 2002, 18: 29–37 [2] Larios A., Garcia H.S., Oliart R.M, Valerio-Alfaro G., Appl Microbiol Biotechnol, 2004, 65: 373–376 [3] Pires-Cabral P., da Fonseca M.M.R., Ferreira-Dias S., Biochem Eng J, 2007, 33: 148–158 [4] Karra-Châabouni M., Ghamgui H., Bezzine S., Rekik A., Gargouri Y., Process Biochem, 2006, 41: 1692–1698 [5] Abbas H., Comeau L., Enzyme Microb Technol, 2003, 32: 589–595