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    STUDIA CHEMIA - Issue no. 2 / 2003  
         
  Article:   AZOCOUPLING PRODUCTS. III. SPECTROSCOPIC INVESTIGATION AND SYNTHESIS OF SOME AZOCOUPLING PRODUCTS BETWEEN 1-(4-HYDROXY-6-METHYL-PYRIMIDIN-2-YL)-3-METHYL-PYRAZOLIN-5-ONE AND AROMATIC DIAZONIUM SALTS.

Authors:  IOAN PANEA, ADINA GHIRIŞAN, FLORIN IURA, RADU GROPEANU, IOAN ALEXANDRU SILBERG.
 
       
         
  Abstract:  By azocoupling of 1-(4-hydroxy-6-methyl-pyrimidin-2-yl)-3-methyl-pyrazolin-5-one (11) with disubstituted benzene diazonium salts (3) three new dyes (12-14) were synthesized. The comparative electronic absorption and 1H-NMR studies of these compounds (12-14) and of other azocoupling products (4-10, 15) of 11 with ortho-, respectively para- monosubstituted benzenediazonium salts support the manifestation of the azo-hydrazono tautomerism for the examined dyes. However, in aprotic solvents and in acidic medium only one species has been detected for the studied dyes. The 1H-NMR spectra of these dyes recorded in deutero-chloroform prove the hydrazonic structure (4a-10a, 12a-15a) of the detected species. In methanolic solution the hydrazonic tautomer is favored with respect to the azohydroxy tautomer by the ortho-substituent in benzenic ring of the examined azocoupling products (8, e.g.), as a manifestation of the ortho effect of the substituent. It is described also the ortho effect of the substituent situated in the ortho-position of the benzenic ring of azocoupling products 8-10, 15 concerning the acidity and the chemical shift of their mobile hydrogen having the 1H-NMR signal at about 14 ppm. The ortho effect of nitro group is unusually strong (o-p =1.5 ppm).  
         
     
         
         
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