Solvent system ethanol-2,2,2-trifluoroethanol as a medium for solvolytic displacement

Roza, Daniel A. Da; Andrews, L. J.; Keefer, R. M.

doi:10.1021/ja00802a022

Cited by 29 publications

(12 citation statements)

References 5 publications

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“…52 (Table 111). 54 Harris and co-workers have reached a similar conclusion from a comparison of the solvolysis rates of benzyl chlorides in ethanol-water and in trifluoroethanolwater mixtures. This, and the smaller decrease in m , corresponds to movement of the transition state toward the lower left corner in Figure 4.…”

Section: Resultsmentioning

confidence: 63%

“…The observed increase in selectivity for ethanol-trifluoroethanol in the series p-methyl-, unsubstituted, and w-fluorobenzyl chlorides, as measured by product analysis, provides further evidence for such a shift in the transition state. 54 Harris and co-workers have reached a similar conclusion from a comparison of the solvolysis rates of benzyl chlorides in ethanol-water and in trifluoroethanolwater mixtures.56…”

Section: Resultsmentioning

confidence: 74%

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Separation of polar and resonance substituent effects in the reactions of acetophenones with bisulfite and of benzyl halides with nucleophiles

Young¹,

Jencks²

1979

J. Am. Chem. Soc.

106

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Application of the modified Yukawa-Tsuno equation log ( k / k o ) = p a n + p r ( u +a n ) to the reversible reaction of bisulfite with substituted acetophenones gives p = 0.6 and p r = -0.45 for the hydroxide ion catalyzed cleavage reaction, p = 1.8 and p r = 0.45 for attack of sulfite dianion, and p = 1.2 and p r = 0.95 for K,, for bisulfite addition. Rate constants for the cleavage reaction exhibit a U-shaped Hammett plot and require a negative value of the r+ parameter, although the reaction is facilitated by electron donation by resonance. Furthermore, the values of p and p r for the equilibrium and rate constants in the two directions are additive, but the r+ values are not. The same treatment accounts for most of the curvature in Hammett plots for the S N~ reactions of nucleophiles with benzyl halides without invoking changes in mechanism or transition-state structure. The changes in transition-state structure that do occur in some of these reactions are discussed and it is suggested that the "reactivity-selectivity principle" represents an oversimplification that should be abandoned for all but the simplest reactions.

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Section: Resultsmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 74%

Separation of polar and resonance substituent effects in the reactions of acetophenones with bisulfite and of benzyl halides with nucleophiles

Young¹,

Jencks²

1979

J. Am. Chem. Soc.

106

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“…The log ( k/k o ) values required for application of the equation are the Y values (based on t -butyl chloride solvolysis) listed, with original source indicated, within a review of solvent ionizing power scales [5]. Two additional values for 2,2,2-trifluoroethanol (TFE)-ethanol mixtures [34, 35] and three additional values [36] for highly aqueous acetonitrile-water and dioxane-water mixtures have been added. The 47 solvents used are the 46 used in previous analyses [37] plus a value in 60% TFE-40% EtOH [35].…”

Section: Application Of Equation 1 To Solvolyses Of Tertiary Alkylmentioning

confidence: 99%

Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

Kevill¹,

D’Souza²

2010

COC

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The original Grunwald-Winstein equation (1948) involved the development of a scale of solvent ionizing power (Y). Subsequent work has refined this scale and involved the development of scales of solvent nucleophilicity (N) and a term to correct for deviations when aromatic rings are present, governed by the aromatic ring parameter (I). These three scales, and the sensitivities towards each, can be related to specific rates of solvolysis through linear free energy relationships (LFERs). One important area of application of LFERs has been to the solvolyses of tert-alkyl halides. It has been proposed that the solvolysis of tert-butyl chloride involves a nucleophilic component, although other workers have suggested that the effects observed are related to electrophilic not nucleophilic influences. Takeuchi (1997) studied a compound with two of the methyl groups of tert-butyl chloride replaced by neopentyl groups. For this highly-hindered substrate there was no evidence for nucleophilic participation. Liu (1998) and Takeuchi (2001) have reported concerning the solvolyses of additional significantly-hindered tertiary alkyl chlorides. Liu (2009) has presented a parallel study of bromides. Martins (2008) has considered hindered tertiary alkyl halides, mainly with carbon-carbon multiple bonds as substituents. It was proposed that the hI term was of importance, with the sensitivities (h) sometimes positive and sometimes negative. To explain negative values, it was suggested that the I scale might contain a nucleophilicity component. In this review, we bring together, with analysis and commentary, the work of Takeuchi, Liu, Martins and others concerning the solvolyses of tertiary alkyl halides, with emphasis on the relevance of the three scales that have been developed for use in Grunwald-Winstein correlations.

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“…33, 34 In trifluoroethanol (100T) at 85 ЊC the ratio k Br /k Cl was 2.86 for 4-methylbenzyl halides and was 4.91 for unsubstituted benzyl halides. 33 From the data in Table 1 the rate ratio for 3/1 in 100T can be found as 2.97 at 25 ЊC. Table 5 shows that the k Br /k Cl ratio increases with diminishing trifluoroethanol or water content in the medium, up to about 20 as the limit.…”

Section: Resultsmentioning

confidence: 87%

“…The solvolytic reactivity ratios of substituted benzyl bromides and chlorides in ethanol-trifluoroethanol mixtures have been studied. 33 The insensitivity of k Br / k Cl in ethanol to a change in ring substituent and the increasing sensitivity in a medium containing more trifluoroethanol was ascribed to differences in the disposition of bromine and chlorine to form hydrogen bonds. 33, 34 In trifluoroethanol (100T) at 85 ЊC the ratio k Br /k Cl was 2.86 for 4-methylbenzyl halides and was 4.91 for unsubstituted benzyl halides.…”

Section: Resultsmentioning

confidence: 99%

Nucleophilic solvent participation in the solvolysis of 4-methoxybenzyl bromide and chloride

Liu¹,

Duann²,

Hou³

1998

J. Chem. Soc., Perkin Trans. 2

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The solvolysis of 4-methoxybenzyl chloride (1) and bromide (3), and 1-(4-methoxyphenyl)ethyl chloride (4) in a variety of solvents were carried out. The observation of linear correlation using the dualparameter Grunwald-Winstein equation, and the positive azide salt effect indicate significant nucleophilic solvent participation for 1 and 3. A smaller deviation of log k (in 100% 2,2,2-trifluoroethanol) for the bromide 3 than chloride 1 in the log k ؊ Y BnX plots reveals a lesser extent of nucleophilic participation and is also in harmony with the greater nucleofugality of the bromide ion. The use of a low k Br /k Cl ratio as evidence for the presence of solvent participation is discussed. The observed -deuterium kinetic isotope effect of 1.08 to 1.21 measured for 1 and 3 is inconsistent with the magnitude generally considered for a concerted mechanism.

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Solvent system ethanol-2,2,2-trifluoroethanol as a medium for solvolytic displacement

Cited by 29 publications

References 5 publications

Separation of polar and resonance substituent effects in the reactions of acetophenones with bisulfite and of benzyl halides with nucleophiles

Separation of polar and resonance substituent effects in the reactions of acetophenones with bisulfite and of benzyl halides with nucleophiles

Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

Nucleophilic solvent participation in the solvolysis of 4-methoxybenzyl bromide and chloride

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