Synthesis And Hydrolysis Of Substituted Imidazolinium Salts - Behavior Of The Degradation Products On Varying Ph

Reaction of l‐alkyl‐2,3‐diarylimidazolinium iodides 1a‐i with alkaline solutions afforded N' ‐alkyl‐ N ‐aroyl‐ N ‐arylethylenediamines 2a‐i. Compounds 2 are stable under acid conditions but in neutral or alkaline media rearrange giving N ‐alkyl‐ N ‐aroyl‐ N ‐arylethylenediamines 3a‐i. Treating compounds 3 with concentrated acids reverse reaction 3 → 2 takes place. Kinetic studies were performed on this intramolecular N → N' aroyl transfer over the H o ‐ p H range −0.9 to 2.30. Compounds 3 undergo acyl transfer to give 2 by a mechanism which involves a change in the rate determining step from formation to catalysed decomposition of a heterocyclic intermediate I 2+ on going from H o to p H values. The existence of maxima in the p H rate profile allowed to determine apparent p K a values of the imidazolidine intermediates which gave good correlation with Hammett sigma values. Stability of these heterocycles was also predicted by determination of thermodynamic parameters.