The protonated ester so formed finally loses a proton to give the ester 3 Reactions with PCl5, PCl3 and SOCl2
The hydroxyl group of carboxylic acids, behaves like that of alcohols
and is easily replaced by chlorine atom on treating with PCl5, PCl3 or
SOCl2 Thionyl chloride (SOCl2) is preferred because the other two
products are gaseous and escape the reaction mixture making the
purification of the products easier