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The orientation of plantium-metal catalysed exchanged between tritiated water and pyridine, the picolines, 2,6-lutidine, and the quinolines has been carefully studied 3H n.m.r. Exchange at 130 °C occurs preferentially at a position adjacent to the nitrogen atom unless a methyl substituent on C-2 hinders exchange, when a position remote from the methyl substituent is preferred as in alkylaromatic exchange. The results are interpreted in terms of previously proposed π-complex exchange mechanisms.

Deuterium exchange between D2O–CH3CO2D solvent and a variety of aromatic compounds is catalysed by tetrachloroplatinate(II) ions. Rhodium and iridium salts are also shown to be homogeneous catalysts for these reactions. Multiple exchange is a consistent phenomenon of all systems. Conditions influencing the stability of platinum(II) in solution are discussed in detail and the basis for the very careful distinction between homogeneous catalysed exchange and the possibility of accompanying heterogeneous exchange by colloidal Pt0 is delineated. The exchange kinetics with benzene show inverse first-order dependence on Cl–. A complicated acid dependence on the reaction is found and interpreted in terms of the effect of acid on the stability of the platinum(II) in solution. These kinetic results are shown to be consistent with the predominant participation of a dissociative π-complex mechanism for the exchange process. The possible relevance of reaction intermediates proposed by other workers is also discussed.

The use of ethylaluminium chloride and a range of other halides, such as NbCl5, WCl6, SbCl5, and BBr3, as catalysts for the rapid deuteriation and tritiation of a variety of organic compounds is described in detail. In the deuterium exchange method [2H6]benzene is the isotope source and traces of water usually serve as co-catalyst. But for maximum reproducibility very dry conditions with HCl as co-catalyst are recommended. The tritiation procedure involves the use of traces of high specific activity tritiated water to hydrolyse a complex of the catalyst with the organic substrate, tritium labelling accompanying the hydrolysis. These simple and rapid labelling methods are particularly suitable for aromatic compounds and their derivatives and to a lesser extent alkenes and some oxygen-containing organic compounds. The possible role of π-complex intermediates in these reactions is discussed.