Determination of empirical parameters of solvent polarity E T in binary mixtures by solvatochromic pyridinium-N-phenol betaine dyes

Empirical parameters of solvent polarity E T of some pure solvents and their binary mixtures (especially with CCl4 and CHCl3) were determined spectrophotometrically using solvatochromic pyridinium-N-phendl betaine dyes. Calibration curves are given for 16 binary solvent mixtures. The obtained E T values show that a synergetic polarity effect appears with the organic solvents containing C=O, P=O, and S=O groups in the mixture with chloroform. With these binary mixtures the increase of E T values results from the formation of 1∶1 complexes X=O... H-CCl3 by means of hydrogen bonding. Increasing number of methylene groups in the chain increases the synergism with these type of complexes.