ISOTOPE EFFECT ON WEAK ACID DISSOCIATION

Weak acid dissociation of the deuterium-substituted 1-naphthol-2-sulfonate potassium salt (1-ROD-2-S) was examined as a function of pD and temperature. The kinetics of kdis and of the recombination rate krec, in agreement with our findings for 1-ROH-2-S, is dictated by the orientational motions of surrounding water molecules, specifically the Debye relaxation time τD. The dissociation rate kdis declines by approximately 1/3 upon deuteration, while the activation barrier ΔE‡ associated with kdis remains essentially constant. As in our other studies, this isotope effect is attributed to a larger hydration entropy difference ΔS for the hydration of D+ compared with H+. © 1990 American Chemical Society.