Reaction intermediates, studies using carbon-14 tracers

Solvent effects on, and products from, reaction of styrene with ethylene in the presence of di-)ti-chloro-dichlorobis(styrene)dipalladium(n), [Pd-(Ph CH—CH2)Cl2]2, indicate a mechanism similar to (i)->(iv) above, with the addition of a preliminary equilibrium between the dimer and solvated monomers. The mechanism of reaction of styrene with vinyl compounds, catalysed by the same chloride-bridged dipalladium complex, has been studied using isotopic tracer (H, D) experiments. Palladium-acetate-catalysed reaction of styrene with benzene, also investigated using deuterium tracer experiments, involves no hydride shift, in contrast to the rather closely related Wacker process. The importance of intermediates with palladium-carbon n-bonds in palladium(ii)-catalysed alkylation and arylation of alkenes has been demonstrated. 

Hall, Kokes, and Emmett (24), who used radioactive tracers to study the Fischer-Tropsch reaction, suggested that besides stepwise growth with single-carbon intermediates, multiple build-in could and probably did occur in the synthesis. They also showed that multiple build-in could not be distinguished from single-carbon stepwise growth below C12-C16 hydrocarbons, and thus the effect of multiple build-in could only be seen if detailed product distributions up to large carbon numbers were obtained. 

A more detailed study of the dehydration of 2-phenyl-1-propanol was reported and a radio tracer technique using C was used to delineate the mechanism. Of the reaction products, the allyl benzene formed was labelled only on the benzylic carbon and was thus produced by y hydrogen abstraction and concerted phenyl migration. In the a-methylstyrene, the label was equally distributed between the I and 3 carbon atoms and this product arose either through a symmetrical cyclopropane intermediate or a tertiary carbonium ion. viz-... 

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