Syntheses of Phenylpyrazolone Derivatives. XIV

Solvent Effect on the Absorption Spectra of Pyrazolone-azomethine Derivatives. (2)

Abstract

Effect of a solvent on the ultraviolet and visible absorption spectra was examined in 12 kinds of pyrazolone-azomethine compounds, using solvents with widely varying dielectric constants. The maximum absorption of the x-band generally made a bathochromic shift with increasing dielectric constants, while that of compounds with a substituent containing -SO₂NH- bond in 3-position of the pyrazolone ring made a hypsochromic shift when the amount of water in the solvent exceeded a certain limit. Therefore, a transition curve with extinction ε at a specific wave length (550mμ) clearly agrees with the dissociation curve. Measurement of degree and constant of dissociation of these compounds indicated that compounds assumed to have a steric hindrance had larger dissociation constant and was less likely to be affected. Compounds with a substituent containing -SO₂NH₂ bond in 1-position of the pyrazolone ring had smaller dissociation constants than those not possessing such a substituent, while this state of dissociation was not observed in compounds other than those with -SO₂NH- bond in the substituent in 3-position.