Hf[N(SO2C8F17)2]4 as a highly active and recyclable Lewis acid catalyst for direct esterification of methacrylic acid with methanol in a fluorous biphase system

Abstract

The activity of Hf[N(SO₂C₈F₁₇)₂]₄ catalyst for the direct esterification of methacrylic acid with methanol was studied and compared with representative acid catalysts including the present industrially employed H₂SO₄ and Nafion^® SAC-13. It was found that Hf[N(SO₂C₈F₁₇)₂]₄ in a fluorous biphase system (FBS) is most effective based on initial rate analysis and yield. In the simulated industrial solution (the reaction mixture was preliminarily doped with H₂O, H₂O/MAA = 1.6 mmol), the initial rate with Hf[N(SO₂C₈F₁₇)₂]₄ was shown to be about 9 times that with H₂SO₄. Meanwhile, an excellent yield (86%) and selectivity (97%) were obtained with Hf[N(SO₂C₈F₁₇)₂]₄, which are superior to the other evaluated catalysts. Furthermore, the immobilized fluorous phase was completely recovered and reused without loss of its catalytic activity either in the simulated industrial solution (both with and without preliminarily doping with H₂O) or in the practical industrial solution.