Conversion of Carboxylic Acids to Acid Chlorides Acid chlorides can be prepared by reacting a carboxylic acid with thionyl chloride. Thionyl chloride (shown below) is a very reactive When a carboxylic acid reacts with thionyl chloride, it reacts as a The mechanism for this reaction (shown below) is essentially TWO nucleophilic substitutions. Cl HCl(g)SO2(g) tetrahedral intermediate 2 - Draw the two tetrahedral intermediates in this mechanism in the sketchers below