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

Abstract

We present a computational study on the concerted hydrolysis of several classes of N-sulfinylamines of generic formula R-N═S═O, such as the -amines themselves (R-NSO), -hydrazines (R-NH-NSO), -hydrazides (R-CO-NH-NSO) and -amides (R-CO-NSO), as these species are known to possess a wide range of hydrolytic reactivity. Two possible mechanisms of hydrolysis, with a water dimer across the S═O and N═S bonds, in the gas phase are investigated. The reactivity is discussed with respect to the electronic structures, established with the use of the quantum theory of Atoms in Molecules, Natural Bond Orbital and Natural Resonance Theory approaches. For the inert N-sulfinylhydrazines and the keto tautomers of N-sulfinylhydrazides, extended π-conjugation adds a sulfide-like resonance structure that is responsible for their insensitivity toward moisture. Activation barriers for hydrolysis, where water acts as a nucleophilic reagent, decrease with increasing positive charge on the NSO sulfur atom, a finding that might prove useful as a predictive tool in the determination of the general reactivity of an N-sulfinyl compound by experimentalists.

Computational Insight into the Carbenic Character of Nitrilimines from a Reactivity Perspective

“…An analysis of the charges determined from the electron density distribution gives C + N – N (Table ), which is not in accord with any of the possible valence bond structures for nitrilimines (Scheme ). This situation, different charge distributions from NBO and QTAIM approaches, is somewhat unexpected, as we found a good correspondence previously, albeit for a different, and less complex, electronic system (RNSO) . Both NBO and QTAIM agree, though, that the positive charge on the CNN carbon of 1 is much reduced from its value in the two species with large carbenic character, CF 2 and FCNNF (Table ).…”

“…This situation, different charge distributions from NBO and QTAIM approaches, is somewhat unexpected, as we found a good correspondence previously, albeit for a different, and less complex, electronic system (R-NSO). 50 Both NBO and QTAIM agree, though, that the positive charge on the CNN carbon of 1 is much reduced from its value in the two species with large carbenic character, CF 2 and F-CNN-F (Table 2).…”

Synthesis and experimental and theoretical characterization of m-fluorosulfinylaniline

“…Although about 600 N-sulfinyl compounds are known today [8], only a few Nsulfinyl-aromatic-imines have been characterized and their reactivity has not yet been completely understood. While it is assumed that steric hindrance could lead to kinetic stabilization, the electronic effects, which substituents may cause in the aromatic N-sufinyl compounds, have not been determined [9]. The inclusion of a substituent group/atom in Nsulfinylaniline leads to a variation of charge distribution in the molecule, with consequent effects on the structural, electronic and vibrational parameters.…”

“…While it is assumed that steric hindrance could lead to kinetic stabilization, the electronic effects, which substituents may cause in the aromatic N-sufinyl compounds, have not been determined. 9 The inclusion of a substituent group/atom in N-sulfinylaniline leads to a variation of charge distribution in the molecule, with consequent effects on the structural, electronic and vibrational parameters. Being an electron withdrawing group, 10 the presence of the NQSQO group could lead to the different mesomeric structures depicted in Scheme 1.…”

Assessing the Accuracy of Density Functional Approximations for Predicting Hydrolysis Reaction Kinetics

“…A particularly popular choice of DFA in such studies is B3LYP. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Beyond DFT, common methods employed in computational studies of hydrolysis reactions include Hartree-Fock (HF) 23,25,31,35,45 and second order Møller-Plesset perturbation theory (MP2), [23][24][25]30,32,47,48 with less frequent use of higher-order Møller-Plesset perturbation theory, 24,30,49 coupledcluster, 25,47 and configuration-interaction methods. 30,31,48 While numerous benchmark studies have been conducted to evaluate the performance of various exchange-correlation density functional approximations (DFAs) for the prediction of reaction thermochemistry, [50][51][52][53][54][55][56][57]…”