Abstract
The aims of the present paper were to obtain the best conditions for improving the selectivity of the esterification and amidation reactions catalysed by Bacillus thermocatenulatus lipase (BTL) at 90 and 120 °C in two ionic liquids (IL), 1-butyl-3-methyl imidazolium tetrafluoroborate (Bmim BF 4) and 1-butyl-3-methyl imidazolium hexafluorophosphate (Bmim PF 6), changing: (i) substrates (isomeric phthalic acids and 4-aminobenzoic acid), (ii) nucleophiles (alcohols) and (iii) water activity. When the substrate was changed, best selectivity towards the formation of the monoester (74% at 1 h) over the diester (0% at 1 h) was obtained in Bmim BF 4 at 120 °C when isophthalic acid was employed. Nevertheless, in Bmim PF 6 though a higher yielding was reached, no selectivity was obtained with any substrate. Ethanol was selected as the best nucleophile, while the increase of length, steric hindrance and rigidity of the alcohol diminished the selectivity of the process. Reaction yield increased when setting a 0.4 water activity of the reaction media value at 30 °C, when the esterification of isophthalic acid with ethanol catalysed by BTL in Bmim BF 4 was performed at 90 °C (88% at 0.5 h).
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