Solvent ionizing power - comparisons of solvolyses of 1-adamantyl chlorides, bromides, iodides, and tosylates in protic solvents

Abstract

Solvolytic rate constants for 1-adamantyl iodide (1-AdI) in binary aqueous mixtures of ethanol, methanol, acetone, trifluoroethanol, and hexafluoroisopropyl alcohol and in acetic and formic acids are reported. Additional kinetic data for solvolyses of 1-adamantyl halides in 97% w/w hexafluoroisopropyl alcohol/water were obtained by using a microconductivity cell (volume, ca. 0.4 mL). Kinetic data for iodine-catalyzed solvolyses of 1-AdI in methanol/water mixtures are also reported. A scale of solvent ionizing power for iodides (Yj) is defined by log (A/fc0)i-Adi = Yj, where k is the rate constant for solvolysis of 1-AdI in any solvent at 25 °C relative to 80%

Additional Solvent Ionizing Power Values for Binary Water- 1,1,1,3,3,3-Hexafluoro-2-propanol Solvents

“…The values (Table 1) for 97% HFIP are in very good agreement with earlier determinations [14,15]. The specific rates are the averages from at least four independent kinetic runs.…”

“…Variations in Y x values for different leaving groups will have components both from differences in interactions in the solvent under consideration and from differences in interactions in the 80% ethanol. However, the observation that the 1-AdI/1-AdBr specific rate ratio varies only from 2.3 in 90% EtOH to 1.9 in 60% EtOH [14] suggests that interactions in ethanol-rich ethanol-water mixtures are similar for different halides. In contrast, appreciably larger variation (0.46 to 1.14) is observed over the similar concentration range of 97% HFIP to 70% HFIP, consistent with the dominant influence of differences in the interactions of the various 1-adamantyl halides with a more electrophilic fluoroalcohol-rich solvent.…”

“…The specific rates are the averages from at least four independent kinetic runs. The specific rates are reported within Differences in Y X values for a given solvent are believed to be primarily due to differences in electrophilic solvent assistance [6] and the halide series, showing a reduction in electrophilicity as one moves down the periodic table, is a useful one for assessing the significance of the specific anion solvation [14].…”

“…It was found [14] that, while 1-adamantyl iodide reacts in most solvents faster than 1-adamantyl bromide, the rates become essentially identical in 97% TFE and the order was reversed in the most acidic solvents studied: 97% HFIP, acetic acid, and formic acid. In the present study (Table 1), we find the bromide to be the more reactive in both 97% HFIP and 90% HFIP.…”

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XLI. Solvent Effect on the Rate of 3-Methyl-3-chloro-1-butene Solvolysis. Correlation Analysis of Solvation Effects and Role of Solvent Nucleophilicity

“…The reaction rate decreases, and with adamantyl substrates this effect is stronger than with tert-butyl substrates. Since only the relative effect of the solvent nucleophilicity was determined, it was erroneously concluded that a solvent renders nucleophilic assistance in the heterolysis of tert-butyl substrates [4,7,8].The negative effect of the nucleophilic solvation is observed only in the heterolysis of tertiary substrates; it is indicative of the nonequilibrium solvation of the transition state when the solvation shells of the ground and excited states have different structures. This effect is usually pronounced in protic solvents, which is apparently associated with hydrogen bonding between molecules solvating nucleophilically and electrophilically pair A.…”