The chemo-enzymatic Baeyer–Villiger oxidation of cyclic ketones with an efficient silica-supported lipase as a biocatalyst

Abstract

The synthesis and characterisation of new, silica-supported lipase biocatalysts and studies of their performance in Baeyer–Villiger oxidation (BVO) of cyclic ketones to lactones were described. Biocatalysts were obtained by immobilisation of Candida Antarctica lipase B onto siliceous materials with multimodal pore structure (MH) and also on typical SBA-15, chemically modified with organosilanes terminated with methyl, octyl and hexadecyl group. Biocatalysts structure was characterised by nitrogen adsorption and TEM/SEM imaging. The lipase presence was confirmed by FTIR spectroscopy, whereas protein loads were obtained from thermogravimetric data. They appeared to be notably larger for MH catalysts than SBA-15s and correlated with surface hydrophobicity of supports which decreased in the order Hd>Oc>Me, from 198 to 80mg/g, for MH-Hd-L and MH-Me-L biocatalysts, respectively.Investigation of the biocatalysts performance (activity, stability, reusability) in BVO of cyclic ketones, using urea hydrogen peroxide as oxidant and ethyl acetate as both the peracid precursor and solvent, clearly demonstrated very large activity of MH biocatalysts. For the same lipase load activity decreased in the order MH-Me-L>MH-Oc-L>MH-Hd-L, with that of least active (MH-Hd-L) catalysts being even trice larger than of Novozyme-435 under equal mass basis. The biocatalysts showed good stability, even in the presence of 60% aq. hydrogen peroxide, and facile reuse. On this basis we proposed a general chemo-enzymatic BVO method for oxidation of cyclohexanones and cyclobutanone to obtain adequate lactones with high yields (80–98%).