Solvent Effects on the Reactivity of a Phenolate Betaine: Kinetics and Theoretical Calculations of Transition‐State Solvation

ABSTRACT The kinetics of the reaction of solvatochromic 4‐(2,4,6‐triphenylpyridinio)phenolate with methyl iodide was followed at 25.0°C in various solvents (chloroform, dichloromethane, acetone, acetonitrile, dimethyl sulfoxide, 2‐octanol) and in six binary mixtures of variable composition. Rates in poorly acidic solvents correlated with the medium polarizability and dipolarity. Solvent effects in binary mixtures were rationalized by a non‐ideality approach based on the preferential solvation of the transition state in these media. Correlations of reactivities with solvent properties found support with theoretical calculations of the transition state of the reaction in different solvents, simulated by a continuum model and by the explicit solvation of the TS by molecules of a hydroxylic solvent.