Modeling the Gas‐Phase Thermochemistry of Organosulfur Compounds

Abstract

Key to understanding the involvement of organosulfur compounds in a variety of radical chemistries, such as atmospheric chemistry, polymerization, pyrolysis, and so forth, is knowledge of their thermochemical properties. For organosulfur compounds and radicals, thermochemical data are, however, much less well documented than for hydrocarbons. The traditional recourse to the Benson group additivity method offers no solace since only a very limited number of group additivity values (GAVs) is available. In this work, CBS-QB3 calculations augmented with 1D hindered rotor corrections for 122 organosulfur compounds and 45 organosulfur radicals were used to derive 93 Benson group additivity values, 18 ring-strain corrections, 2 non-nearest-neighbor interactions, and 3 resonance corrections for standard enthalpies of formation, standard molar entropies, and heat capacities for organosulfur compounds and organosulfur radicals. The reported GAVs are consistent with previously reported GAVs for hydrocarbons and hydrocarbon radicals and include 77 contributions, among which 26 radical contributions, which, to the best of our knowledge, have not been reported before. The GAVs allow one to estimate the standard enthalpies of formation at 298 K, the standard entropies at 298 K, and standard heat capacities in the temperature range 300-1500 K for a large set of organosulfur compounds, that is, thiols, thioketons, polysulfides, alkylsulfides, thials, dithioates, and cyclic sulfur compounds. For a validation set of 26 organosulfur compounds, the mean absolute deviation between experimental and group additively modeled enthalpies of formation amounts to 1.9 kJ mol(-1). For an additional set of 14 organosulfur compounds, it was shown that the mean absolute deviations between calculated and group additively modeled standard entropies and heat capacities are restricted to 4 and 2 J mol(-1) K(-1), respectively. As an alternative to Benson GAVs, 26 new hydrogen-bond increments are reported, which can also be useful for the prediction of radical thermochemistry.

First‐principles based group additivity values for thermochemical properties of substituted aromatic compounds

“…[22][23][24][25] This accuracy is comparable to that of high level ab initio methods, which require substantially more time and effort. Benson's method has been successfully applied to standard enthalpies of formation of gas phase molecules, 4,15,17,22,24,25 and also to entropies and heat capacities. [13][14][15][16][23][24][25] To ensure that the values obtained via GA are reliable, the GAV and NNI definitions have to be internally consistent.…”

“…The CBS-QB3 composite method is widely used and has been shown to produce accurate enthalpies of formation 22,24,25 and rate coefficients. [32][33][34][35] It was the method of choice for deriving GAV and NNI parameters in the previous studies by Sabbe et al, 22 Vandeputte et al, 24 and Paraskevas et al 25 and it would be the preferred method to extend the GAV database for aromatic species. However, CBS-QB3 calculated bond dissociation energies for the CAH bond in benzene (483.0 kJ mol 21 36 and 415.5 6 3.8 kJ mol 21 , 37 respectively).…”

“…The above described methodology is in line with the previous studies of Reyniers and coworkers. 22,24,25 Standard enthalpy of formation…”

“…Benson's method has been successfully applied to standard enthalpies of formation of gas phase molecules, 4,15,17,22,24,25 and also to entropies and heat capacities. [13][14][15][16][23][24][25] To ensure that the values obtained via GA are reliable, the GAV and NNI definitions have to be internally consistent. This means that (1) the GAV parameters are assigned in a systematic way resolving all linear dependencies, 14 (2) the set of NNIs are comprehensive and well defined, and (3) all parameters are determined from reference data of equal quality.…”

“…Currently this database contains GAV and NNI definitions that allow calculation of thermodynamic properties for aliphatic hydrocarbons like alkanes, alkenes, alkynes, and few cyclic hydrocarbons and their corresponding radicals, 22,23 oxygenates such as alcohols, esters, ethers, ketones, carboxylic acids, ketenes and their corresponding radicals, 25 and organic sulfur compounds. 24 The purpose of this study is to extend the GAV and NNI database to substituted monocyclic aromatic hydrocarbons (MAHs). As this extension is motivated by the interest in modeling pyrolysis products of lignin, the following substituent groups are considered: hydroxy (AOH), methoxy (AOCH 3 ), formyl (ACHO), vinyl (AC@CH 2 ), and methyl (ACH 3 ) and ethyl (ACH 2 CH 3 ).…”