The reactions of recoil tritium atoms with toluene in the C6F6-moderated systems.

The T-for-H substitution reaction was studied in the recoil tritium reactions with toluene in C6F6-moderated systems. The moderator-free control experiment showed an approximately uniform labeling in the aromatic ring, with a slightly enhanced reactivity in the ortho- and para-positions (o: 41%, m: 38%, p: 21%) and showed a preference for ring tritiation over methyl group tritiation (23 relative to the corresponding ring assumed as a standard (= 100)). The addition of hexafluorobenzene progressively changed the uniform distribution to a marked ortho- and para-orientation and decreased the relative tritium activity of the methyl group. If the C6F6/PhCH3 mole ratio is 204, the tritium distribution in the ring is o: 53%, m: 22%, p: 25% and the methyl group activity is reduced to 2. The data show the existence of the threshold energy of side chain tritiation and that the selective aromatic ring tritiation is given by increasing contribution of the reactions of tritium atoms having lower energy than the threshold energy.