Xanthates and amine oxides

Few kinetic investigations of xanthate pyrolyses have been reported. The mechanism was in doubt for some time, some workers favouring proton abstraction by the thion sulphur (161) and others by the thiol sulphur which gave the isolated products in a single step (162) . 

As dithiocarbonates are more stable than the corresponding xanthates , a route involving initial isomerisation of the xanthate to its dithiocarbonate can be discounted A careful investigation of the carbon and sulphur isotope effects showed the thion sulphur mechanism to be correct (IbS) . 

Calculated isotope efFects (mechanism 1611 Unity 1.007- 1.010 Unity 

Normally, menthyl xanthate decomposes to menthenes on distillation, but, after washing with ferrous salts which removes peroxide traces, a higher reaction temperature for elimination is required, although a similar product distribution is observed. The actual function of the peroxide impurities remains unsolved .  

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There is a class of intramolecular thermal elimination reactions that provides a new route to alkenes. Esters, xanthates, and amine oxides are commonly used in this reaction. The reactions are concerted (one-step), and steiic requirements dictate that a syn elimination must occur in the reaction, as the carbonyl group cannot reach a hydrogen in an anti position (Rg. 18.61). 

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