Kinetics of α-hydrogen exchange of sodium α-[4-(4-bromophenyl)-thiazol-2-yl]propionate in D2O solutions
Abstract
Data are reported for the rate of incorporation of deuterium into sodium α-[4-(4-bromophenyl)thiazol-2-yl]propionate in D2O solutions studied as a function of pD by use of a quantitative n.m.r. technique. The first-order rate coefficients measured over the pD range 6–14 pass through a minimum at pD = 10. The data, measured at 30°, fit the kinetic expression kobs=kD3O+[D3O+]+kOD–[OD–] where kD3O+ and kOD– have the values 4·1 × 102 and 7·3 × 10–3 l. mole–1 sec.–1 respectively. No catalysis could be detected by other acidic or basic species. A mechanism involving a change in the position of the tautomeric equilibrium of the acid and its anion is advanced to explain the observed pD profile. Quantitative support for this interpretation is given by data for the tautomeric ratios of related model compounds.