Methyl tosylate, solvolysis

Our next concern is the solvent nucleophilicity. Schadt et al. " chose the solvolysis of methyl tosylate, which should be an Sn2 process, as the defining process. For this standard reaction the parameter / in Eq. (8-69) was set at 1.00. An empirical estimate of m, describing the sensitivity of methyl tosylate to solvent ionizing power, was obtained as the slope of the two-point line for methyl tosylate solvolysis in... 

Y that utilizes the assumption that methyl tosylate solvolysis rates obey the equation NOTs = log (fc/fc0) — 0.3YOTs to determine the proportions of N and... 

For lack of a better system, the ratio of rate in an ethanol-water mixture of the same Y value as acetic acid to rate in the much less nucleophilic acetic acid, ( Etoii/ acoh) yj has served as a measure of sensitivity to solvent nucleophilicity. More recently, the problem has received renewed attention, and two groups have proposed possible approaches.114 Of the two proposals, that of Bentley, Schadt, and Schleyer is easier to apply. Their scheme defines the solvent nucleophilicity, N, by Equation 5.21, where k is the solvolysis rate constant of methyl tosylate in... 

Winstein et al. (1957). In (9), k, k0 and Y have the same meaning as for eqn (5), m is the sensitivity of the solvolysis of RX to solvent ionizing power, Y, and l is the sensitivity of the solvolysis of RX to solvent nucleophilicity, N. However, this equation was not evaluated until recently, when Bentley et al. (1972) made the following substitutions in the rearranged form (10). Methyl tosylate was... 

The Y-T correlations of ]3-aryl-assisted solvolyses are summarized in Table 5. -Aryl-assisted solvolyses characteristically show r values of 0.5 to 0.6. The solvolysis of (l-arylcyclopropyl)methyl tosylates [26(w = 2)] (Roberts, 1968 Roberts and Watson, 1970 Fujio et al., 1996), an analogue of the neophyl system, gave a linear Y-T correlation with an extremely low r value of 0.13 and... 

With tosylate solvolysis rates available for the first time in trifluoroacetic acid, Peterson and Waller (4) noted that plots of log k versus the ionizing power, Y, for the solvolysis of methyl, ethyl and secondary tosylates showed deviations from linearity that could be attributed to solvent nucleophilicity. 

The disrotatory mode, in which the methyl groups move away from each other, would be more favorable for steric reasons. If the ring opening occurs through a discrete cyclopropyl cation, the W-shaped allylic cation should be formed in preference to the sterically less favorable U-shaped cation. This point was investigated by comparing the rates of solvolysis of the cyclopropyl tosylates 6-8 ... 

V. 10(5 -> 6pH)Abeostero ds (A-Homo-B-Norsteroids) / 389 Solvolysis of 5a,6a-epoxy-6-methyl steroids / 389 Pinacol rearrangement of 5a-hydroxy-6a-tosylates / 392 Summary / 394... 

Aroyl esters of anthracene-9-methanol are photolysed in methanol to give products consistent with the anthracene-9-methyl cation as an intermediate.41 Rate constants for the solvolyses of secondary alkyl tosylates in fluorinated solvents were analysed in terms of the possible involvement of very short-lived carbocation-tosylate ion pair intermediates.42 The effect of added electrolytes on the rate of solvolysis of cumyl chloride and its -methyl derivative was studied in 90% aqueous acetone and 80% aqueous DMSO, with the results revealing a combination of a special salt effect and a mass law effect.43 Kinetic parameters obtained for the solvolysis of (8) (R1 = R2 = Me and R1 = Ar, R2 = H) show that there is substantial n, n participation in the transition state [e.g. (9). 44... 

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