Kinetics of the reactions of aromatic amines and acid chlorides in hexamethylphosphoric triamide

The kinetics of the reaction between aromatic amines and aromatic acid chlorides in hexamethylphosphoric triamide (HMPT) have been studied by stopped‐flow spectrophotometry using an acid‐base indicator to follow the change in H⊕ during the reaction. Measurements on bifunctional amines and acid chlorides, e.g. p‐phenylenediamine (PPD) and terephthaloyl dichloride (TDC) have shown that the NH2 groups in PPD react approximately 12 times as fast as the NH2 group in the intermediate product, while the acid chloride groups in TDC and intermediate product have equal reactivities. It has been found for all reactions studied that protonation of the NH2 groups by the H⊕ produced is very important. The influence of substituents could be analysed by two Hammett relations. The reaction of substituted anilines with benzoyl chloride could be described by the relation log kR = −1.4σ+R + 2.10 and the reaction of substituted benzoyl chlorides with aniline by the relation log kR = 3.4σR + 2.10.