Tl(III) acetate oxidation of cyclohexanol, cyclopentanol, cycloheptanol,trans-2-chlorocyclohexanol,cis-4-t-butylcyclohexanol,trans-4-t-butylcyclohexanol, borneol, isoborneol, exo (β) norborneol and endo (α) norborneol has been studied in the presence of 0·90 M H2SO4. The observed reactivity pattern among the cyclanols is cyclopentanol < cyclohexanol > cycloheptanol < cyclooctanol which is the same as the one noted in V(V) oxidation of the substrates under similar conditions—an order contrary to the I-strain concept. In both cases Mn(II) catalysis and acrylonitrile polymerisation have been observed in cyclohexanol oxidation alone. The kinetic isotope effect in the Tl(III) oxidation of cyclohexanol is 2.82 as against a value of 6·4 obtained for Tl (III) oxidation of benzhydrol. The kinetic observations are explained on the basis of a radical mechanism operating in the case of cyclohexanol, as it is a strainless ring system, with the intermediacy of Tl (II).Trans-2-chloro andtrans-2-phenyl groups, due-I effect, retard the rate of the reaction.Cis-4-t-butylcyclohexanol reacts faster than the trans compound due to relief of strain in the transition state. The reactivity pattern among the bicyclo (2,2,1) heptan-2-ols is, isoborneol > borneol > exo (β)-norborneol > cyclopentanol >endo-(α)-norborneol. This is consistent with the relief of strain in the transition state due to the hybridisation change from sp3 to sp2 and lessening of torsional interaction. This can also be due to the formation of less-strained products.
Volume 134, 2022
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