Studies on the dissociation constants of some substituted coumarin azo dyes in mixed solvents

ABSTRACT

In order to shed light on the effect of different mixed solvents and temperatures on the dissociation of hydroxy coumarins, the pka values of a number of substituted 8-[arylazo]-7-hydroxy-4-methylcoumarins were determined pH-metrically in the presence of some water miscible organic solvents. The effect of solvent polarity on pka values was discussed. Increase in the concentration of organic solvent from 50 to 80% by volume results in the increase of pka for all azo coumarins was detected. The thermodynamic parameters, delta Go, delta Ho and delta So were also evaluated