Mechanistic Insights Into the 2,2′‐Biphenol‐Derived Phosphoric Acid–Catalyzed Dehydrative Esterification of Carboxylic Acids and Alcohols

ABSTRACT 2,2′‐Biphenol‐derived phosphoric acid is an effective catalyst for the dehydrative esterification of an equimolar mixture of carboxylic acids and alcohols in toluene at 100°C without the need to remove water from the reaction. The acidic P–OH and basic P ═ O moieties can work together effectively as a cooperative acid–base catalyst system. In this study, mechanistic insights into this catalytic reaction are obtained through experimental kinetics studies, density functional theory (DFT) calculations, and microkinetic simulations of 2,2′‐biphenol‐derived phosphoric acid and related catalysts. The kinetics and DFT analysis support a reaction mechanism that involves the formation of a phosphate–carboxylate complex and activation of the alcohol by the catalyst. The catalyst structure affects the reaction barrier of the dehydration step, thereby determining the overall activity. This step is further modulated by noncovalent interactions, including steric and π–π effects, which depend on the steric demand and flexibility of the catalyst backbone. Microkinetic simulations based on DFT‐derived energy profiles successfully reproduce the experimentally observed conversion trends. Overall, the 2,2′‐biphenol‐derived phosphoric acid is found to have ideal properties for the catalysis of the present dehydrative esterification.