The substitution raeaction of benzoyl chloride (PhCOCl) and sodium acetate (CH3COONa) using pyridine 1-oxide (PNO) as the inverse phase-transfer catalyst (IPTC) in a two-phase system of organic solvent and water was studied. The effects of the polarity of the organic slovent and water was studied. The effects of the polarity of the organic solvent on the conversion of benzoyl chloride, the yield of the main product acetic benzoic anhydride (PhCOOCOCH(3)), and the reaction rate was investigated. A larger reaction rate was observed for a more polar organic solvent. In order to confirm this deduction, mixtures of inert organic substances of varied polarity were used as organic solvents in a two-phase reaction. The effects of such solvents, pyridine 1-oxide (PNO), and temperature on the conversion of benzoyl chloride, the reaction rate, and the yield of the main product acetic benzoic anhydride (PhCOOCOCH(3)) were also investigated in detail.