Enantioselective permeation of racemic alcohol through polymeric membrane

Copolymer of 1,2-bis(2-methyl-1-triethylsiloxy-1-propenyloxy)ethane and dialdehyde have been synthesized by Mukaiyama Aldol polymerization using lipase as the catalyst. The chirality of the polymer was tested by optical rotation and circular dichroism study. The membrane forming ability of this chiral polymer was examined by casting the membrane in three different solvents viz., N-methyl-2-pyrilidone (NMP), dimethyl formamide (DMF) and dimethyl acetamide (DMAc) using the phase inversion method and it was found that chiral polymer–NMP membranes formed more uniform and regular surface morphology as was evident from SEM analysis. The enantioselective membranes prepared in the solvents was tested for resolution of racemic alcohol and it was found that NMP is the best solvent for obtaining highest enantioselectivity value. It was also found that the enantioselectivity for adsorption favoured the (S)-isomer whereas permeation favoured the (R)-isomer which is confirmed from interpretation of the adsorption isotherm by Langmuir model. Accordingly, the enantioselective permeation was caused by suppression of the (S)-isomer permeation. Optical resolution of (±)trans-sobrerol was achieved by pressure driven permeation through the membrane. The highest enantioselectivity, enantiomeric excess and permeation co-efficient was obtained as 98.59%, 20.42 and 13.627 m² h⁻¹, respectively. With an increase in polymer content in the membrane, the permeation rate increases.