Selective esterification of phthalic acids in two ionic liquids at high temperatures using a thermostable lipase of Bacillus thermocatenulatus: A comparative study

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 BF4) and 1-butyl-3-methyl imidazolium hexafluorophosphate (Bmim PF6), 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 BF4 at 120 °C when isophthalic acid was employed. Nevertheless, in Bmim PF6 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 BF4 was performed at 90 °C (88% at 0.5 h).