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A deep insight into the mechanism of the acid‐catalyzed rearrangement of the Z ‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole in a non‐polar solvent
Author(s) -
D'Anna Francesca,
Fontana Gianfranco,
Frenna Vincenzo,
Macaluso Gabriella,
Marullo Salvatore,
Spinelli Domenico
Publication year - 2011
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1675
Subject(s) - chemistry , toluene , trichloroacetic acid , catalysis , acetic acid , medicinal chemistry , reaction rate constant , solvent , oxadiazole , organic chemistry , stereochemistry , kinetics , physics , quantum mechanics
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 ( HAA s, 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 ( k III / k II ) 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 HAA s ( 3a – h) with 4‐nitroaniline ( 4 ) in toluene. Also in this case, the formation of two complexes requiring one ( K 2 ) or two ( K 3 ) moles of acid has been evidenced, but now the K 3 / K 2 ratios are significantly affected by the strength of the acid examined. The variation of the K 3 / K 2 ratios larger than those concerning the k III / k II 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.