2,2′-Biphenol-Derived Phosphoric Acid Catalyst for the Dehydra- tive Esterification of Carboxylic Acids with Alcohols

A dehydrative esterification from an equimolar mixture of carboxylic acids and primary or secondary alcohols in toluene at 100 degrees C was promoted without the necessity to remove water by using a simple 2,2'-biphenol-derived phosphoric acid catalyst (2.5-10 mol%). This reaction was also successfully conducted at the gram scale. To demonstrate the synthetic utility of this catalytic system, pharmaceutically useful substrates and acid-sensitive substrates were examined using these acid-base cooperative phosphoric acid catalysts, which exhibit relatively weak Bronsted acidity.

Automated summary

This article describes a new type of catalyst that promotes a dehydrative esterification reaction between carboxylic acids and primary or secondary alcohols without the need to remove water. The reaction is conducted in toluene at 100 degrees C using a 2,2'-biphenol-derived phosphoric acid catalyst (2.5-10 mol%). The catalytic system is demonstrated to be useful for synthesizing pharmaceutically useful and acid-sensitive substrates.