Catalytic benzoylation of 4-chloro-3-methylphenol sodium salt in third-liquid phase under conditions of phase-transfer catalysis

Abstract

In the present study, the benzoylation of 4-chloro-3-methylphenol sodium salt to synthesize 4-chloro-3-methylphenyl benzoate by triliquid phase-transfer catalysis (TL-PTC) was investigated. The third-liquid phase (catalyst phase) can be formed from benzyl tri-n-butylammonium bromide (QBr) reacted with sodium 4-chloro-3-methylphenoxide in the aqueous phase by extra addition of NaCl or NaBr using heptane as the solvent. Before the reaction, about 89% of the catalyst can be concentrated within 1.5 cm(3) of third-liquid phase to make a high catalyst concentration of 1.13 mol/L, which embraces 99.5% of benzyl tri-n-butylammonium 4-chloro-3-methylphenoxide (catalytic intermediate QOR) in the third-liquid phase. The product yield based on benzoyl chloride (limiting reactant) is 98.7% in 30 min of reaction at 20 C. The reaction rate is strongly dependent on the stirring speed, showing that the interfacial reaction is important. The variations of compositions in the third-liquid phase during the reaction are analyzed. The molar ratio of QOR to Q(+) in the third-liquid phase remains almost constant after 2 min of reaction, and QOR is not found in the organic phase. The main reaction region locates in the third-liquid phase. The experimental results can be well correlated by pseudo-first-order kinetics. A comparison of product yield under triliquid and liquid-liquid PTC systems shows that TL-PTC offers an effective method for ester synthesis.