Replacing HF or AlCl3 in the Acylation of Isobutylbenzene with Chloroaluminate Ionic Liquids

Abstract

The two most common commercial catalysts for the acylation of isobutylbenzene to produce the major ibuprofen intermediate 4-isobutylacetophenone are HF and AlCl3; however, both of these catalysts suffer from significant drawbacks including the stringent safety issues associated with using volatile/toxic HF and the requirement for additional processing for deacidification of AlCl3. Here, two chloroaluminate-based catalysts, the ionic liquid (IL) [HN222][Al2Cl7] ([HN222] = triethylammonium) and the liquid coordination complex (LCC, here an IL analog) AlCl3/O-NMPχAlCl30.6 (O-NMP = N-methyl-2-pyrrolidone), were investigated and found to be efficient in the acylation of isobutylbenzene. Of the tested catalysts, the LCC, which along with neutral species has both a Lewis acidic cation ([AlCl2(O-NMP)2]+) and anion ([Al2Cl7]−), had the best catalytic performance (99% conversion with 96% selectivity).