Hydrogen bond donor solvents enabled metal and halogen-free Friedel-Crafts acylations with virtually no waste stream

摘要

We have developed a metal and halogen-free Friedel-Crafts acylation protocol with virtually no waste stream generation. We propose a hydrogen bonding donor solvent will form a hydrogen bonding network and may provide significant rate enhancement for Friedel-Crafts reactions. Trifluoroacetic acid is one of the strongest H-bond donor solvents, which is also volatile and can be easily recovered by distillation without need for reaction workup. Our protocol is a 'green' Friedel-Crafts acylation process: 1) the catalyst can be recovered and reused; 2) using halogen free starting material (carboxylic acids anhydride or carboxylic acids); 3) no need for aqueous reaction work-up; 4) minimum or no waste steam generation. (C) 2018 Elsevier Ltd. All rights reserved.