IJD!llmr flD rlllllmlllm!!flllfmWW EJ52-1985-99 STRUCTURE OF 5-AMINO-4-ARYLAZOPYRAZOLES IN ETHANOLIC AQUEOUS MEDIA H. M. FAHMY*, M. H. ELNAGDI, A. ELSAID MAHGOUB AND A. KASEM Chemistry Department, Faculty of Seience , Cairo Unlversity, Giza, A.R.E. E.A. GHALl Faculty of Electronic Engineering, Ei-Monoufta University, A.R.E. Key Word Index-s-Aao-hydraeono conflict. The structure and tautomerism of (2a-£) ate investigated in aqueous media. In solutions of pH<5 these compounds exist as ring N-l protonated species. At pH>lO they afford anions which are stabilized by deloealization of the negative charge in the ring as well as on the arylazc moiety. Controlled potential electrolysis and polarographic analysis indicate that 2a-f ate reduced via Ii four electron reduction process to triaminopyrazole and the corresponding substituted aniline derivative. A mechanism is suggested and discussed. Whereas much research has been directed to the study of tautomerism of 4-arylazo-5-hydroxy-pyrazoles (l Y-3), only very little attention has been paid to the structurally related 5-amino-4-arylazo- pyrazoles (2) which are potentially tautomeric (d. forms 2-5) and each tautomer is mesomeric (cf. forms 6-9). In pervious Investigationsv"> compounds 2 were considered to exist as hydrazones", in ethanolic solution, based on their UV spectra which exhibited maximum at 1".3 360 nm reported characteistic for the hydrazone linkage':"? and the absence of maximum absorpton at ..1"'06 280nm for the arlylazo linkage. However, inspetion of literature revealed that assigning structures for azo-hydrazo tautomeric com- pounds based only on UV analysis might be an oversimplification of the problem for the fact that many azo compounds are reported to exhibit absorption bands in the hydrazone range and also several * To whom all correspondence should be addressed. hydrazones shaw maximum absorptions in the range claimed characteristic for azo compounds'-·'''>. Moreover, the structures suggested in previous work"'''), if even were correct, would only exist in neutral solutions. In this work we report the results of our attempts to define the structure of compounds 2a-f in a trial to provide a better understanding of the chemistry of such a class of compounds'<v'"?". ArN=N 011 ...... / R 1 2a, R==NH,; Ar=C,H, b. R==C,H,; Ar""C,H, c, R==C.H,; Ar=C.H,Br-p d, R ==C.H.; Ar= C.H,CH.-p e. R=C.H.; Ar=C.H.OCH,-p E, R";'C.H.; Ar=C.H.NO.-m J. Chin. Chem. Soc •• 32, 99-104 (1985)