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ester and N-[4-(2-amino-3-hydroxy-pyridin-6-ylazo)phenyl]-acetamide compounds were studied. The dissociation constants were determined potentiometrically. The thermodynamic parameters of dissociation were evaluated. Regression analysis is applied for correlating the different parameters. The results help to assign the solute-solvent interactions and the solvatochromic potential of the investigated compounds. The electronic character of the substituent and the chemical nature of the solvent are major factors for the observed solvatochromism. Nitroso Pyridin-6-ylazo Triazene Effect of solvents Potentiometry Spectrophotometry

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Electronic spectra I Computers I Azobarbiturates I SolventsThe solvent effects on the spectra of 5-(p-substituted phenylazo) barbituric acid have been analyzed by the multiple linear regression technique using a Fortran IV program on a PC computer. The correlations based on one parameter equation gave that the solute permanent dipole-solvent induced dipole interaction (parameter M) plays the important role in determining the spectral shifts. The data based on two parameter equation gave that the solvent-solute hydrogen bonding combined with the solvent permanent dipolesolute permanent dipole interactions (E,N) are the important factors to explain the spectral shifts. For the three parameter correlations, the compounds with nitro, sulphonic, acetyl and iodo substituents gave that the combination ( , , ) gives a good fit to the observed spectral shifts. The HMO theory and the PPP method explain the phenomena of tautomerism of barbituric acid. The data predict that the diketo tautomer is the most stable one.Using the calculated PPP binding energy and singlets transition for the dienol tautomer which are nearly the same as those of the diketo tautomer to assign that a mixture of the diketo and dienol tautomers coexist. The agreement between the calculated and the experimental values of transition energies is reasonably good. The phenomena of tautomerism of barbituric acid is studied based on the Complete Neglect of Differential Overlap (CNDO) method.Calculations have shown that the dioxo form is the most stable tautomer. The singlets electronic transitions for 5-(p-substituted phenylazo) barbituric acid have been calculated by the CNDO method. The oscillator strength values of 5-(/>-substituted phenylazo) barbituric acid are calculated and found to be affected by other factors e.g., the dielectric constant of the solvent, the electronic property of the substituent and the solvation energy. on the central nervous system [1]. The barbiturates possess effects on the motor and sensory functions [2].

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The thermal behaviour of the entitled nickel(II) and copper(II) complexes of 4-acetylamino-2-hydroxy-5-methyl azobenzene has been studied by means of differential thermal analysis (DTA), thermogravimetry (TG), X-ray powder diffraction, IR and electrical conductivity. A light has been thrown on the nature of interaction of the solvents of crystallization with the host complex. Some of the kinetic parameters are calculated and discussed.Thermal analysis plays an important role in studying the structure and the properties of metal complexes. Nowadays a number of solid state reactions (e. g., thermal isomerization, conformational changes, polymorphic transformations, thermal phase transitions, thermochromism, etc...) of some metal chelates have been studied by means of thermal analysis [1-10]. In our laboratory, the structural chemistry of some transition metal chelates of simple substituted-azobenzenes was characterized [11][12][13][14][15] based on spectral and magnetic susceptibility techniques, but no work has been done on their thermal properties. The major goal of the present manuscript is conducted to study the thermal behaviour of some of these complexes to throw more light on the solid state reactions present.