The S_N3–S_N2 spectrum. Rate constants and product selectivities for solvolyses of benzenesulfonyl chlorides in aqueous alcohols

Abstract

Rate constants for a wide range of binary aqueous mixtures and product selectivities (S) in ethanol–water (EW) and methanol–water (MW) mixtures, are reported at 25 °C for solvolyses of benzenesulfonyl chloride and the 4‐chloro‐derivative. S is defined as follows using molar concentrations: S = ([ester product]/[acid product]) × ([water solvent]/[alcohol solvent]). Additional selectivity data are reported for solvolyses of 4‐Z‐substituted sulfonyl chlorides (Z = OMe, Me, H, Cl and NO2) in 2,2,2‐trifluoroethanol–water. To explain these results and previously published data on kinetic solvent isotope effects (KSIEs) and on other solvolyses of 4‐nitro and 4‐methoxybenzenesulfonyl chloride, a mechanistic spectrum involving a change from third order to second order is proposed. The molecularity of these reactions is discussed, along with new term ‘SN3–SN2 spectrum’ and its connection with the better established term ‘SN2–SN1 spectrum’. Copyright © 2009 John Wiley & Sons, Ltd.

SN1‐SN2 and SN2‐SN3 mechanistic changes revealed by transition states of the hydrolyses of benzyl chlorides and benzenesulfonyl chlorides

“…The kinetic isotope effect was examined and k(H 2 O)/k(D 2 O) values are calculated to be 1.64 (Z = MeO) and 1.97 (Z = O 2 N), respectively. They are somewhat larger than experimental values, 1.37 (Z = MeO) and 1.76 (Z = O 2 N) . The large difference indicates the different mechanism.…”

“…The distinction of these two phenomena is difficult . To clarify this issue, Bentley et al investigated the rate constants and product selectivities of the solvolyses of para‐Z‐benzenesulfonyl chlorides in aqueous alcohols; see Scheme b . They found that the reaction has a third‐order character when the EWG Z = O 2 N was used, indicating that the reaction proceeds with a termolecular process.…”

“…The two mechanisms of the hydrolysis of para‐Z‐benzenesulfonyl chloride (Z = MeO and O 2 N) suggested by Bentley et al in the “S N 3‐S N 2 spectrum.”. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.…”

Mechanistic Study of the Solvolysis of Piperidine‐1‐sulfonyl chloride in Binary Solvent Mixtures

“…12 In recent years, mechanistic studies of nucleophilic displacement reactions at the tetra-coordinate sulfur center have included intensive experimental 8,9,13,14 and theoretical 15 efforts due to the wide range of applications of such reactions in the synthesis of sulfur drugs. 19 S N 2-S N 1 and S N 3-S N 2 spectrum mechanisms were reported by Bentley et al 6,18 Recent theoretical calculations of a range of acetone-water mixtures have provided independent evidence of the S N 2-S N 1 spectrum of the mechanism involved in the solvolyses of substituted benzyl chlorides 17 as well as reports of S N 3-S N 2 spectrum mechanisms of the solvolysis of substituted benzenesulfonyl chlorides. Rogne and Lee favor S N 2, 7,9,17 whereas Ciuffarin favors an S A N (addition-elimination) mechanism.…”

“…16 There is, however, a considerable amount of debate regarding the mechanism of action, i.e., whether it is an S N 2, 7,9,17 an S N 1-S N 2 and S N 2-S N 3 (Scheme 2), 6,18 or an S A N 19 process. 6,18 From mechanistic studies of the solvolysis of substituted benzyl chlorides, 8,18 carbamoyl chlorides, 22b,27 and substituted benzenesulfonyl chlorides, 6,7,9 Bentley et al 18 reported that the positioning within the mechanistic spectrum depends on the GW l value (Scheme 3). 19 S N 2-S N 1 and S N 3-S N 2 spectrum mechanisms were reported by Bentley et al 6,18 Recent theoretical calculations of a range of acetone-water mixtures have provided independent evidence of the S N 2-S N 1 spectrum of the mechanism involved in the solvolyses of substituted benzyl chlorides 17 as well as reports of S N 3-S N 2 spectrum mechanisms of the solvolysis of substituted benzenesulfonyl chlorides.…”