Reaction intensification and selectivity control for palmitoyl transesterification of sucrose

Abstract

Long-chain fatty acid esters of sucrose are nonionic surfactants with important applications in food, cosmetics and pharmacy. Their synthesis by chemical and biocatalytic methods involves the difficult task of coordinating efficiency and selectivity of the reaction used. Here, we show transesterification of sucrose (200 mM; ∼70 g/L) from vinyl palmitate (≥ 1 mole equivalent) in dry 2-methyl-2-butanol (2M2B) containing variable amount of 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) ionic liquid (5–60 % by volume), in the absence or presence of immobilized lipase (Candida antarctica; Thermomyces lanuginosus). Due to its combined effect on sucrose solubility and catalytic rate acceleration, the [Bmim][OAc] (≥ 20 % by volume) was sufficient to promote the transesterification efficiently, with no additional benefit provided by the enzyme, not even on the product selectivity and the initial rate. Using ≥ 2 mole equivalents of vinyl palmitate, sucrose was converted nearly fully (93 %) at low hydrolysis of the palmitoyl donor (∼7 %) in 72 h at 60°C, giving sucrose ester product comprised of ∼75 % monoester. Other general strategies of reaction intensification for carbohydrate (trans)esterification, such as substrate microdispersion in organic solvent (here: 2M2B with 20 vol.% DMSO) or usage of low-solvent conditions, proved by far less efficient with sucrose, failing in conversion and monoester selectivity. Overall, this study shows reaction intensification (product ≥ 110 g/L; productivity ≥ 1.5 g/L h) for [Bmim][OAc]-driven synthesis of palmitoyl sucrose (mono)esters of desired hydrophilic-lipophilic balance.