The catalytic properties and mechanism of cyclohexane/DBSA/water microemulsion system for esterification

A model esterification reaction of hexanol and hexanoic acid in the cyclohexane/dodecylbenzenesulfonic acid (DBSA)/water microemulsion system has been investigated. Compared with cyclohexane/AOT/water microemulsion system and organic medium system, esterification reaction in the cyclohexane/DBSA/water system can perform relatively rapidly whether catalyzed by Candida cylindracea lipase (Ccl) or not, this demonstrated that DBSA itself can act as a kind of acid catalyst. Comparison of conversion in several acid-catalyzed reaction systems were also performed and the results showed that the conversion in DBSA system was the most highest, which proved the key factor affecting the conversion was not the acid strength, but the attribute of DBSA as a kind of surfactant. Furthermore, we also perform transesterification reaction of butanol and ethyl butyrate (and methyl butyrate) in the DBSA reverse microemulsion system; however, it cannot get remarkably high conversion like esterification, this reason may be alcohol produced during the transesterification cannot easily enter water droplet like water produced by the esterification. Comparison of conversion in the DBSA system with conversion in the O/W emulsion system DBSA as an emulsion agent also indicated that the conversion in the DBSA reverse microemulsion was much higher. Finally, the mechanism of reaction was also explored. After realizing that DBSA is both acid catalyst and surfactant, we concluded that it was concurrent function of acid catalyst and surfactant that played an important role in improving reaction rate and conversion of esterification.