Kinetics of hydrogen isotope exchange reactions. Part XVI. Aromatic exchange under the influence of β-radiation on aqueous solutions of mesitylene

Abstract

An uncatalysed exchange reaction between water and mesitylene has been observed in homogeneous solutions containing ca. 4 curies of tritiated water per litre. The predominant reaction product is mesitylene labelled in the aromatic ring. The exchange rate depends on the second power of the tritium concentration, and the exchange is therefore attributed to the influence of the β-radiation emitted by the tritium in solution. On the basis of the dependence of the exchange rate on the concentration of mesitylene and of added cupric and nickel ions, the exchange is considered to be initiated by attack of tritium atoms on mesitylene, leading to a methyl-substituted cyclohexadienyl radical as an intermediate. The results are incompatible with attack on mesitylene by solvated electrons as the initiating step.