Solvolyses of Benzoyl Chlorides in Weakly Nucleophilic Media

Abstract

Rate constants and activations parameters are reported for solvolyses of p-Z-substituted benzoyl chlorides (1, Z = OMe, Me, H, and Cl) in 97% w/w hexafluoroisopropanol-water (97H). Additional kinetic data are reported for solvolyses in acetic and formic acids. Plots of log k vs. σp in 97H are consistent with previous research showing that a cationic reaction channel is dominant, even for solvolyses of 1, Z = NO2. A benzoyl cation intermediate was trapped by Friedel-Crafts reaction with 1,3,5-trimethoxybenzene in hexafluoroisopropanol. The results are explained by an SN2-SN1 spectrum of mechanisms with variations in nucleophilic solvent assistance. Ab initio calculations of heterolytic bond dissociation energies of various chloro- and fluoro-substituted and other benzoyl chlorides are correlated with log k for solvolyses.

Concurrent pathways to explain solvent and substituent effects for solvolyses of benzoyl chlorides in ethanol-trifluoroethanol mixtures

“…The σ plot for 100% TFE is linear (Figure 4), and this may be due to a switch to the dissociative pathway, even for 1, Z = O 2 N for which ΔS ≠ = -10.7 cal mol -1 K -1 (Table 1, that solvolyses of 1, Z = O 2 N in 97% TFE-water were dissociative, but a highly negative ΔS ≠ was unexplained, and σ-plots are now preferred. 8 The products of reaction with TFE-water are a carboxylic acid (3), and a TFE ester (4). Product selectivities (S, equation 3, Table 3) vary significantly with solvent composition for solvolyses of 1, Z = O 2 N, but not for the other substrates.…”

“…There is a measurable resonance effect in some σ constants, 19,20 and there is also a large effect of electron-donating substituents on the C-Cl bond length and on the negative charge at the chlorine atom in benzoyl chlorides (1). 21 The stabilisation energies, calculated from equation (2), 21 were recently shown to correlate with σ, 8 so the resonance demand incorporated into…”

“…7 It has recently been found that substituent effects for dissociative solvolyses of benzoyl chlorides correlate unexpectedly well with the original Hammett σ function. 8 The two types of correlation (for substituents and solvents) will provide the first independent estimates of the locations where each of the two pathways contributes 50% to the observed rate constant.…”

Effect of Pyridine and Tribenzylamine on the Hydrolysis Kinetics of Benzoyl Chloride in Water-Dioxane System

“…and Harris [6] and fluoro alcohols or 1,1,1,3,3,3-hexafluoro-2-propanol by Kevill and D'souza [7]. The hydrolysis kinetic studies of acyl chlorides involving benzoyl chloride are necessary owing to the highly reactive acyl chloride, as unique monomers, in approaches of synthesizing polymers [8].…”

The Grunwald-Winstein Relationship in the Solvolysis of β-Substituted Chloroformate Ester Derivatives: The Solvolysis of 2-Phenylethyl and 2,2-Diphenylethyl Chloroformates

“…(1) and (2), we previously reported that the results of primary, secondary and tertiary alkyl chloroformates (ROCOCl) in a wide range of solvent mixtures can follow bimolecular and/or unimolecular pathways. [10][11][12][13][14][15][16][17] Kevill and D'Souza 10 showed that, particularly in ethyl chloroformate (4,EtOCOCl) solvolysis, an addition-elimination mechanism dominates [l = 1.56, m = 0.55] in all except the highly ionizing solvents, and the major reaction channel in the least nucleophilic solvents involves ionization mechanism [l = 0.69, m = 0.82]. Bentley et al also carried out a series studies of the solvolyses of acyl chloride and their derivatives using the G-W equation.…”