Solvent effect in a two phenoxyl radical equilibrium

The equilibrium of the reaction: 2,4,6-tri-tert-butylphenoxyl radical (1)+2,6-di-tert-butyl-4-methyl phenol (2)→2,4,6-tri-tert-butylphenol (3)+2,6-di-tert-butyl-4-methylphenoxyl radical (4) was studied from 243 to 298 K, for solutions 0.25 mol l−1 in phenols, in two groups of experiments. In the first group the equilibria were obtained in benzene–toluene (1:1) what yielded a second degree correlation in T−1: ln Keq=−23.31+1.3281×104 T−1−1.69038×106 T−2. In the second group the equilibria were performed in 0.25 mol l−1 1,4-dioxane solution in benzene–toluene (1:1) which gave a linear correlation: ln Keq=0.949+5.278×102 T−1, from which ΔH1=2.14±0.1 and Dsln (O–H)=338.0±0.5 kJ mol−1 in 2 were derived. The hydrogen bond of phenols to dioxane could explain the differences between the results found for the two sets of experiments.