Isomerization of allylic thionbenzoates

Another thermal isomerization which results in structural inversion of both the allylic system and the functional group is the apparently irreversible rearrangement of allylic thionbenzoates to allylic thiolbenzoates. 

The rate of this isomerization is increased by a- or y-alkyl substituents on the allylic system. The relative rates of isomerization of allyl, y-methylallyl and a-methylallyl thionbenzoates at 100°C are 1, 3,1, and 35 in cyclohexane and 1, 5.5, and 52 in acetonitrile These effects are some two powers of ten smaller than substituent effects on ionization of allylic chlorides (ref. 98, p. 786), 

For the same allylic thionbenzoates, isomerization rates increase with ionizing power of the solvent. Again, the effects are small the isomerization reactions are only 5-7 times faster in acetic acid and acetonitrile than in cyclohexane . The dependence of rate on solvent ionizing power corresponds to an m value of about 0.13, which is about the same as the m value for allylic azide isomerization and is much smaller than the values for reactions which involve ion pair formation .  

The entropy of activation for isomerization of allyl thionbenzoate, — 10 eu, is similar to entropies of activation for other cyclic, concerted allylic iso-merizations. Additional support for a concerted mechanism is provided by secondary deuterium isotope effects on the rate of isomerization of allyl thionbenzoate. Each a-deuterium atom lowers the isomerization rate by about 6%, while each y-deuterium atom increases the rate by about 3%. Since allylic reactions which proceed by carbonium ion, carbanion, and radical pathways are known to be retarded by about twice as much for each a-deuteron, while an allylic chloride solvolysis exhibited a y deuterium isotope effect of zero, the observed secondary isotope effects provide support for a concerted process whose transition state has little carbonium ion, carbanion, or radical character. 

Braverman and Stabinsky reported that allylic arenesulfinates isomerize to allylic sulfones 

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