Kinetics of the Reaction of 2-Chloro-quinoxaline with Hydroxide Ion in ACN-H2O and DMSO-H2O Binary Solvent Mixtures

The kinetics of alkaline hydrolysis of 2-chloroquinoxaline (QCl) with hydroxide ion was investigated spectrophotometrically at different percentages of aqueous-organic solvent mixtures with acetonitrile (10-60% v/v) and with dimethylesulphoxide (10-80%) over the temperature range from 25 to 45 A degrees C. The reaction was performed under pseudo first order conditions with respect to 2-chloroquinoxaline (QCl). An increase in the percentage of organic solvent (v/v) has different effects on the reaction rate constants, presumably due to hydrogen bond donor and acceptor differences of the media and other solvatochromic parameters. The data were discussed in terms of the Kamelt-Taft parameter and E (T)(30). A nonlinear relation between the logarithm of the rate constant and reciprocal of the dielectric constant suggests the presence of selective solvation by the polar water molecules. Activation parameters Delta H (#), Delta S (#) and Delta G (#) were determined and discussed.