Influence of the number of water molecules on the mechanism of N-sulfinylaniline hydrolysis

Abstract

The mechanism of the uncatalyzed hydrolysis of N-sulfinylaniline (Ph-N=S=O) has been studied with B3LYP/6-31+G(2d,2p) in the gas phase, with explicit treatment of water molecules. Hydrolysis involves water attack on sulfur, with a close to perpendicular alignment of a water molecule and the NSO plane in both prereaction complexes and transition states for the rate-determining step. Consequently, the distance of the weak S···O interaction, together with the efficiency of protonation of either nitrogen (attack across the N=S bond) or oxygen (attack across the S=O bond) atoms of the NSO group, determines the height of the activation barrier for hydrolysis. While the reaction with one water molecule is characterized by an unreasonably high enthalpy of activation, a cooperative effect from the weak interactions appears with the inclusion of a second water molecule, where both participate in the reaction, and the activation enthalpy drops significantly. The preference for attack across the S=O bond that is found in the reaction with one water molecule switches to a dominance of attack across the N=S bond in the reaction with three water molecules.Résumé : Faisant appel à des calculs théoriques au niveau B3LYP/6-31+G(2d,2p), on a étudié le mécanisme de l'hydrolyse non catalysée du N-sulfinylaniline (Ph-N=S=O) en phase gazeuse, en faisant un traitement explicite des molécules d'eau. Dans l'étape cinétiquement déterminante, l'hydrolyse implique une attaque de l'eau sur le soufre, avec un alignement pratiquement perpendiculaire d'une molécule d'eau et du plan NSO tant dans les complexes préréaction-nels que dans les états de transition. En conséquence, la distance de la faible interaction S···O ainsi que l'efficacité de la protonation de l'atome d'azote (attaque à travers la liaison N=S) ou de l'atome d'oxygène (attaque à travers la liaison S=O) du groupe NSO détermine la hauteur de la barrière d'activation de l'hydrolyse. Alors que la réaction avec une molécule d'eau est caractérisée par une enthalpie d'activation anormalement élevée, il semble se développer un effet de synergie avec les interactions faibles lors de l'inclusion d'une deuxième molécule d'eau alors que les deux participent à la réaction et que l'enthalpie d'activation diminue d'une façon significative. La préférence pour l'attaque à travers la liaison S=O qui caractérise la réaction avec une molécule d'eau se déplace vers une dominance pour une attaque à travers la liaison N=S dans la réaction avec trois molécules d'eau.

From Inert to Explosive, The Hydrolytic Reactivity of R−NSO Compounds Understood: A Computational Study

“…Earlier experimental works conclude that hydroxylation of sulfur is the rate-determining step of hydrolysis. , Modeling of the reaction confirms this conclusion and suggests a concerted mechanism with simultaneous proton transfer to either oxygen or nitrogen of the NSO group. , …”

“…The enthalpy term (Δ H 298 and Δ H ‡ 298, kcal mol −1 ) is used throughout for consistency with our previous papers. , The electronic, unscaled zero-point vibrationally corrected energies, enthalpies and Gibbs free energies of the modeled molecules, complexes and transition states are summarized in Table S1 of the Supporting Information. The averaged entropy contribution − T Δ S is determined to be about 5 kcal mol −1 for reactions across both NS and SO bonds for various N-sulfinyl species, as can be seen from the correlation in Figure S1 of the Supporting Information.…”

“…Because only two kinetic studies of the hydrolysis of N-sulfinylanilines have been reported to date, , we have evaluated the mechanism of hydrolysis of several substituted N-sulfinylamines computationally. , Reaction can occur across the SO or the NS bond, according to the resonance structure representation (Scheme ), and the concerted hydroxylation of sulfur and protonation of either oxygen or nitrogen of the NSO group is indeed the rate-determining step of the reaction. , The two-water-molecule model was found to be sufficient for the description of the hydrolysis, and the reaction barrier decreases with an increased electron-withdrawing ability of the substituent …”

Cooperative Effect of Solvent in the Neutral Hydration of Ketenimine: An ab Initio Study Using the Hybrid Cluster/Continuum Model

“…In the hydration of heterocumulene, the surrounding water molecules can play the catalytic role by being located mainly in the reactive region and acting as a hydrogen bridge through donating or accepting protons to promote the proton transfer in numerous studies. − ,− Furthermore, water molecules can, in addition to taking part in the proton transfer, also interact with each other in the nonreactive region . This explains the catalytic effect of the solvent on the hydration of heterocumulene, such as NHCNH, − CO 2 , , COS, CS 2 and Ph-NSO . It was reported that the interaction among the water molecules and the reactant can influence the structures of the stationary points as well as the activation barriers of these reactions.…”

“…26 This explains the catalytic effect of the solvent on the hydration of heterocumulene, such as NHdCdNH, 27-29 CO 2 , 30,31 COS, 32 CS 2 33 and Ph-NSO. 34 It was reported that the interaction among the water molecules and the reactant can influence the structures of the stationary points as well as the activation barriers of these reactions. For example, in the hydration of COS, due to two other water molecules near the nonreactive oxygen atom, the activation barrier of the rate-determining step can be considerably reduced, from 137.4 kJ/mol in the three-water hydration to 107.9 kJ/mol for the five-water hydration.…”