Hydrogen-deuterium exchange in thiazoles via phase-transfer catalysis

Hydrogen-deuterium exchange has been examined under phase-transfer conditions for 15 thiazoles and a number of other heteroaromatic compounds (pyridines, thiophens, and imidazoles). The effects of 11 quaternary (ammonium, phosphonium, and arsonium) salts and 17 solvents have been studied. The effect of chain-length of the salt [Me(CH₂)_n]₄N ⁺Br^- (n=1-5) has been examined. First-order kinetics (in thiazole) are reported for seven thiazoles. The present method offers a practical route to specifically and higher deuteriated (D ≥ 90%) thiazoles and other aromatics. Some of the results (such as the effects of various catalysts and solvent polarity) are at variance with existing data in the field of phase-transfer catalysis and it is suggested that interfacial and micellar effects may arise.