DEUTERIUM-ISOTOPE FRACTIONATION BETWEEN ORTHO-ALKYL SUBSTITUTED PHENOLS AND T-BUTYLTHIOL IN OXYGEN BASES

Equilibrium isotope effect in the exchange reaction of deuterium betwe en phenol (P), 2-isopropylphenol (IPP), 2,6-diisopropylphenol (DIPP), 2,6-ditertbutyl phenol (DTBP) and tertbutylthiol (TBT) has been studie d at 298 K. The fractionation factors (alpha) have been measured in cy clohexane and carbon tetrachloride solutions and in a few oxygen bases : acetone, 1,4-dioxane, ethyl formate, ethyl ether, tetrahydrofurane, N,N-dimethylformamide, dimethylsulphoxide and hexamethplphosphoramide. Using chemical shifts of phenol OH protons, the thermodynamic paramet ers of complex formation with the oxygen bases have been determined. T he experimental data show that 1n alpha correlates with the formation enthalpy of the phenol-oxygen base complex in DIPP-TBT-base system bur there is no simple correlation in IPP-TBT-base system. Furthermore it was found that in DTBT-TBT-base system 1n alpha depends linearly on t he basicity of the solvent (DN parameters). On the other hand, 1n alph a correlates with acidic parameters of the solvents (AN) in IPP-TET-ba se and P-TBT-base systems. All above correlations are explained by tak ing into account two competition processes: selfassociation of phenol molecules and their solvation by oxygen bases.