Novel SO3H-functionalized polyoxometalate-based ionic liquids as highly efficient catalysts for esterification reaction

Three novel heteropolyanion-based Bronsted acidic ionic liquids (BAILs), butane mono sulfoacid-functionalized 1,10-phenanthrolinum, butane mono and bis sulfoacid-functionalized 1,4-dimethylpiperazinium salts of phosphortungstate catalyst (PhBs(1)-PW, [PipBs(1)](3)-PW and [PipBs(2)](3)-(PW)(2)) were synthesized and well characterized with FTIR, H-1 and C-13 NMR, Electro-Spray Ionization Mass Spectrometry (ESI-MS), Elemental analysis (CHNS), EDX and TG analysis techniques. The esterification reactions of monocarboxylic acids with monohydric alcohols were carried out using these catalysts. The introduced catalysts present a self-separation performance after reaction, which can be easily recovered and quite steadily reused as confirmed by six-run recycling test. Moreover, bis sulfoacidfunctionalized 1,4-dimethylpiperazinium salt of phosphortungstate showed the best catalytic performance among the prepared catalysts for the esterification reaction. (C) 2019 Elsevier B.V. All rights reserved.