Finkelstein reaction solvent effects

These substances accelerate the reaction, and their effectiveness increases in the order given. This suggestion was questioned by Pocker, who found that the effects of such added substances were not directly proportional to their concentrations and could easily be explained by macro effects on the solvent character. He also found that common-ion effects were small in the reaction, the effect of added 1-methylpyridinium bromide was negligible, and that there was no evidence for surface catalysis on the walls of the vessel. There is an exact parallel between the relative rates of the Finkelstein reactions... 

Ingold s (1957) calculations are for differences in an intrinsic entropy and enthalpy difference between a series of alkyl halides and their transition states. Two important requirements of his calculations are that differences in activation energy and in entropy of activation, for any one set of Finkelstein reactions, be independent of solvent and of salt effects as the alkyl group is changed. These requirements are tested in Table 25 and in Figs. 5, 6, and 7, for one Finkelstein reaction, of alkyl bromides with chloride ion, and for a closely related reaction, that of azide ion with alkyl bromides. 

The inadequacies of the present electrostatic models for solvent effects on reaction rates has been emphasised in the last ten years by the availability of a range of strongly dipolar aprotic solvents, typified by di-methylsulphoxide (DMSO), A,A-dimethylacetamide (DMA), N,N-dimethylformamide (DMF) and sulpholane (TMSOa). The magnitude of the effect that remains unaccounted for by the present electrostatic models can be demonstrated from measurements of the rate of the Finkelstein reaction ... 

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