Kinetics of hydrogen isotope exchange reactions

Tritium uptake by benzene, dissolved in acidified tritiated water containing chloride ions at 50°, is catalysed by tetrachloroplatinate(II) ions. The first-order exchange rate constant λ is approximately proportional to the concentrations of catalyst and hydrogen ion and inversely proportional to the concentration of chloride ions. The reaction mechanism required by these reaction orders involves at least one (and probably two) low-concentration intermediates of the composition (C6H6–PtCl3)– and (at low acid concentrations) the rate-limiting protonation of such an intermediate. Possible structures of the various reaction intermediates are indicated.