The conversion of the Z‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole (1a) into the relevant 1,2,3‐triazole (2a) has been quantitatively studied in toluene in the presence of several halogenoacetic acids (HAAs, 3a–h). Again, the occurrence of two reaction pathways has been pointed out: they require one or two moles of acid, respectively, thus repeating the situation previously observed in the presence of trichloroacetic acid. The observed rate constant ratios (kIII/kII) are only slightly affected by the nature of the acid used. To gain a deeper insight into the action of the acids used we have measured the association constants of the HAAs (3a–h) with 4‐nitroaniline (4) in toluene. Also in this case, the formation of two complexes requiring one (K2) or two (K3) moles of acid has been evidenced, but now the K3/K2 ratios are significantly affected by the strength of the acid examined. The variation of the K3/K2 ratios larger than those concerning the kIII/kII ratios appears useful to enlighten the very nature of the acid‐catalyzed pathways in toluene, which has been elucidated also carrying out the rearrangement in the presence of mixtures of tribromo‐ and trichloro‐acetic acids at different concentrations. Copyright © 2010 John Wiley & Sons, Ltd.