Thallium activation parameters

Thallium.—The decomposition of pyridinomethylthallium(iii) in aqueous solution in the presence of chloride is a redox reaction since the inorganic products are thallium(i) species, but the important step is 5 n2 attack of chloride at the methylene-carbon, with synchronous displacement of the thallium. The determined activation parameters, Aif = 28 kcal mol and - + 14 cal deg mol- for reaction of TlCl(CH2pyH) + with elimination of TlCl, are consistent with an 5n2 mechanism. The decomposition of RTIX2 into TlX + RX, in pyridine solution, also proceeds by nucleophilic attack, by pyridine or halide, at carbon. ... 

Rate constants and activation parameters have been determined for thal-lium(m)-catalysed aquation of a series of cations cw-[Co(en)2(RNHa)Cl] +, where R = H, Me, Et, Pr", or Pr The second-order rate law followed by these reactions is consistent with either of two likely mechanisms. The first is one-step attack of the thallium(m) at the co-ordinated chloride - 5 b2 attack at the thallium(m), Sud at the cobalt. The other mechanism is rapid preequilibrium formation of a chloride-bridged cobalt(m)-thallium(ni) species whose decomposition is rate-determining ... 

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