Studies in chrome mordanting. V. Kinetics and mechanism of the interaction of chromium (III) salts with wool

Abstract

The rate of uptake of chromium(111) by wool depends on the nature of the chromium(111) salt used and decreases in the order: chromium(111) fluoride > chromium(111) formate chromium(111) sulphate ≈ chromium(111) chloride. This order arises from a combination of differences in the rates of diffusion of chromium(111) salts into the fibre and differences in the rates of reaction of the chromium(111) species present with the carboxyl groups in wool. It is shown that the different rates of reaction of chromium(111) species with the carboxyl groups in wool are consistent with the slow step of this reaction involving the loss of a water ligand from the inner coordination sphere of the chromium(111) species. This slow step is preceded by a rapid equilibrium involving the formation of ionized carboxylate groups in wool. Comparisons of the chromium contents of the wool samples with the decrease in the number of carboxyl groups capable of being protonated in acid solution indicate that of the salts examined only ohromium(111) chloride definitely introduces cross-links between carboxyl groups in wool.