Selectivity engineered friedel–crafts acylation of guaiacol with vinyl acetate to acetovanillone over cesium-modified heteropolyacid supported on K-10 clay

Abstract

Acetovanillone or apocynin (4-hydroxy-3-methoxyacetophenone) is an effective natural drug. It is typically synthesized by using unsafe and expensive methods. The current paper deals with Friedel–Crafts acylation of guaiacol using several solid acids including modified heteropolyacids (HPA) and modified forms of sulfated zirconia, such as 20% w/w Cs_2.5H_0.5PW₁₂O₄₀/K-10, 20% w/w H₃PW₁₂O₄₀/hexagonal mesoporous silica (HMS), K-10 clay, UDCaT-5, UDCaT-6, and UDCaT-4. Among these, 20% w/w cesium modified dodecatungstophosphoric acid supported on K-10 clay (Cs_2.5H_0.5PW₁₂O₄₀/K-10) was found to be the best. Vinyl acetate was the best acylating agent. The effects of various factors affecting rate of reaction were studied to establish kinetics and mechanism of reaction. A mathematical model is built to interpret the kinetic data and develop a mechanism. The reaction is intrinsic kinetically controlled and the apparent energy of activation was found to be 15.46 kcal/mol.