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    STUDIA CHEMIA - Issue no. 2 / 2003  
         
  Article:   AZOCOUPLING PRODUCTS. PART IV. THE STRUCTURE OF DYES OBTAINED BY AZO-COUPLING REACTION OF 1-(4-HYDROXY-6-METHYLPYRIMIDIN-2-YL)-3-METHYLPYRAZOLIN-5-ONE WITH AROMATIC DIAZONIUM SALTS.

Authors:  IOAN PANEA, ADINA GHIRIȘAN, I. BALDEA, IOAN SILAGHI-DUMITRESCU, LILIANA CRĂCIUN, IOAN ALEXANDRU SILBERG. 		 
       
         
  Abstract:  The number and positions of the absorption bands have been studied for the title dyes, in the range of 350-600 nm, as a function of solvent nature, acidity or basicity of the solutions as well as of the nature of the substituent X in para position on the benzene ring. The obtained results, including Hammett correlations, quantum calculation by using AM1- SM2 method and the mechanism of formation of the dyes 5 prove the existence of some tautomeric azo-hydrazono- and pyrazolin-5-one-5-hydroxy-pyrazole (5a  5b  5c  5d) equilibria, coupled with acid-base equilibria. The visible and (1H-, 13C-) NMR spectra support the hydrazonic structure 5d of the only species detectable in the used aprotic solvents.  
         
     
         
         
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