Hydrolysis benzhydryl bromide

Numerous solvolytic studies on diarylmethyl derivatives have been carried out under a variety of conditions. The analysis of substituent effects in the solvolysis of the monosubstituted chlorides [22] was reported earlier (Yukawa and Tsuno, 1959 Yukawa etal., 1966). The purpose of this analysis is to clarify the effect of a fixed substituent Y in one ring on the substituent effect of the variable substituents X on the second ring. Three extensive sets of kinetic data for the solvolysis of X, Y-disubstituted benzhydryl systems under fixed conditions have been reported one for the ethanolysis (Nishida, 1967), one for the chloride hydrolysis in 85% aqueous acetone at 0°C (Fox and Kohnstam, 1964) and one for the bromide hydrolysis (Mindl et al., 1972 Mindl and... 

Neutral salts facilitate RX ionization affecting it through the ionic strength of the solution. For example, 0.1 mol/1 LiCl increases the hydrolysis rate of/er/-butyl bromide in 90% acetone (10% water) by 40% (323 K), 0.1 mol/1 LiBr accelerates the hydrolysis of benzhydryl chloride in 80% acetone (20% water) by 17% (298 K), and 0.1 mol/1 LiCl accelerates the hydrolysis of benzhydryl bromide, under the same conditions, by 27%. 

As a result of the inductive and hyperconjugative effects it is to be expected that tertiary carbonium ions will be more stable than secondary carbonium ions, which in turn will be more stable than primary ions. The stabilization of the corresponding transition states for ionization should be in the same order, since the transition state will somewhat resemble the ion. Thus the first order rate constant for the solvolysis of tert-buty bromide in alkaline 80% aqueous ethanol at 55° is about 4000 times that of isopropyl bromide, while for ethyl and methyl bromides the first order contribution to the hydrolysis rate is imperceptible against the contribution from the bimolecular hydrolysis.217 Formic acid is such a good ionizing solvent that even primary alkyl bromides hydrolyze at a rate nearly independent of water concentration. The relative rates at 100° are tertiary butyl, 108 isopropyl, 44.7 ethyl, 1.71 and methyl, 1.00.218>212 One a-phenyl substituent is about as effective in accelerating the ionization as two a-alkyl groups.212 Thus the reactions of benzyl compounds, like those of secondary alkyl compounds, are of borderline mechanism, while benzhydryl compounds react by the unimolecular ionization mechanism. 

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