r978 Ir has been proved that hydrogen atom abstraction from the hydroxy-group oI phenols in media containing polar molecules [e.9. vinyl acetate (VA)] proceeds along two simultaneous pathways starting from free and hydrogen bonded species.l For 2,6-dialkylphenols at 50 'C, the hydrogen bonded species is more reactive than the free form, thus indicating the role of the solvent (VA) molecule attached to the phenol in increasing reactivity. At the same time the primary kinetic deuterium effect (p.k.i.e.) for these phenols is >10 (i.e. greater than the largest p.k.i.e. value which could be accounted for by the total loss of zero-point energ'y difierences of all three vibrational modes of the phenolic OH and OD bonds), thus indicating tunnelling.2 In order to rationalise these facts we have supposed that hydrogen atom abstraction proceeds within the hydrogen bond.e This paper reports evidence for the mechanism. t (a) M. Simonyi, J. Kardos, I. Fitos, I. KovAcs, and J. Pos- pi5il, /.C.S. Chem. Comm., 1976, l5; (D) M. Simonyi, J. Kardos, I. Fitos, I. Kov6cs, and J. Pospi5il, /.C.S. Pe*in II, 1976, 1913. t (a) M.Simonyi, I. Fitos, J. Kardos, I. Lukovits, and J. PospGil, J.C.S. Chem. Comm., 1975, 262; (D) M. Simonyi, I. Fitos, J. Kardos, I. Kovdcs, I. Lukovits, and J. PospGil , J.C.S. Farcd,ay.f, 1977, 1286. I F. C. Whitmore and D. E. Badertscher, J. Amet. Chem. Soc., 1033,65, 1659. 406 The Mechanism of Hydrogen Atom Abstraction from Phenols involved in Hydrogen Bondingwith EsterCarbonylGroups By Julianna Kardos, llona Fitos, llona Kov5cs, J5nos Szammer, and Mikl6c Simonyi,' Central Resoarch Institutefor Chemistry of the Hungarian Academyof Sciences, H-1525 Budapest Pf. 17, Hungary Rate constants have been determined in different solventsfor hydrogen atom abstraction from alkyl-substituted phenols and deuteriated analogues by polyvinyl acetate radical(R'). The following solvents were used: ethyl acetate, ethyl [2Hr]acetate, ethyl pivalate, ethyl trifluoroacetate, acetone, [2H.]acetone, dimethyl sulphoxide. The reactivity of the phenols and the primary kinetic deuterium isotope effect(p.k.i.e.) demonstrate a strong solvent dependence exhibiting the highest valuesin ethyl trifluoroacetate (p.k.i.e. 57 t 23 for 2.4.6-trimethylphenol at 50'C). Incorporation of CHTTaCOOCHTCHT and (CHs)rCr'COOCHTCHs into polyvinyl acetate increases in the presence of phenols. These facts conclusively provethat hydrogen atom abstraction proceeds within the hydrogen bond to the radical formedby addition of B'to the ester carbonyl hydrogen bonded to phenol. EXPERIMENTAL Matetials and Techniques.-Commercially avaiLable (Merck, Uvasol) solvents, ethyl acetate (EA), acetone (A), [2H.]acetone ([,Hu]A), and dimethyl sulphoxide (DMSO) were used. Synthetic grade (Merck) ethyl pivalate (EP) was used after distillation according to ref. 3. Synthetic grade (Fluka) ethyl trifluoroacetate (EFA) was purif,ed according to ref. 4. Ethyl fHrlacetate ([rHlEA) was prepared by direct esterifi.cation of CDTCOOD formed by heating deuteriated malonic acid. The isotopic purity was found to be 960/o by mass spectrometry. CHsT.COOCHTCH, (3.5 ptCi g-r) was prepared from CHTTTCOOK with triethyl phosphate; the labelled potassium acetate 6 was formed by carbonyl exchange with uCOr. (CHs)sCr.COOCHrCHr (20 ptCi g-r) was prepared from the acid.. uia (CHr)rCr.COCl, treating the latter with ethanol. The techniques for purification of purum grade (Fluka) VA and azobisisobutyronitrile (AIBN) have been described elsewhere.T Oleic and trifluoroacetic acid (Fluka, synthetic . H. Gilman and R. G. Jones, ./. Amet. Chem. Soc.,1043, 05, 1458. 5 A. Szabolcs, J. Szammer,and L. Noszk6, Tetraheihon,1974, 80, 3647. 3 A. Murray, III and D. L. Williams in 'Organic Syntheses with Isotopes,'Interscience, New York, 1958, Part l, p. 96. ? T. Fcildes-Berezhnykh and F. Ttldds, Vysohomol. Soed,itettii, r904,0, r523.