Sulfur Dioxide and Water: Structures and Energies of the Hydrated Species SO₂·nH₂O, [HSO₃]^–·nH₂O, [SO₃H]^–·nH₂O, and H₂SO₃·nH₂O (n = 0–8)

Abstract

The structures of a large number of hydrates of sulfur dioxide (SO2·nH2O), of the sulfonate ion ([HSO3]–·nH2O), of the tautomeric hydrogensulfite anion ([SO3H]–·nH2O), and of sulfurous acid (H2SO3·nH2O) with up to eight water molecules attached to these species have been optimized at the B3LYP/6‐31G(2df,p) level of theory (DFT). The calculated vibrational frequencies allow the definite assignment of certain characteristic modes, and in this way a convincing interpretation of published spectra of aqueous SO2 as well as of SO2 adsorbed on very cold ice crystals has been achieved for the first time. Single‐point calculations at the G3X(MP2) level of theory were used to calculate the binding energies of the water molecules in SO2·nH2O as well as the relative stabilities of the isomeric anionic species [HSO3]–·nH2O and [SO3H]–·nH2O. Generally, the water molecules tend to stick together forming clusters, whereas the particular sulfur‐containing molecule remains at the surface of the water cluster, but it is always strongly hydrogen‐bonded. Only when there are more than six water molecules are the anions more or less completely surrounded by water molecules. DFT calculations erroneously predict that the gaseous hydrated sulfonate ions are more stable than the isomeric hydrogensulfite ions, even when hydrated with six water molecules. However, if these hydrated species are calculated as being embedded in a polar continuum simulating the aqueous phase, the hydrogensulfite ions are more stable than the sulfonate ions, in agreement with various spectroscopic observations on aqueous sulfite solutions. On the other hand, at the higher G3X(MP2) level, the gaseous hydrated hydrogensulfite anions are more stable than the corresponding sulfonate ions only if the number of water molecules is larger than four, whereas for the weakly hydrated anions the order of relative energies is reversed. The possible implications of these results for the enzymatic oxidation of “sulfite ions” ([HSO3]– and [SO3H]–) by sulfite oxidase are discussed. The conversion of SO2·6H2O into its isomer H2SO3·5H2O is predicted to be exothermic (ΔH°298 = –56.1 kJ mol–1) and exergonic (ΔG°298 = –22.5 kJ mol–1). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Theoretical study of the auto-catalyzed hydrolysis reaction of sulfur dioxide

“…The solution of SO2 is comprised of hydrated SO2, sulfurous acid (H2SO3), and sulfonate ion (HSO3 -) [6,11,14]. As a hydrolysis product, sulfurous acid is also expected to be contained in the acidic aerosols [14].…”

“…However, H2SO3 has been successfully generated in a neutralization−reionization mass spectrometric experiment [21]. In addition, the solvated sulfurous acid H2SO3-5H2O is predicted to be more stable than hydrated sulfur dioxide SO2-6H2O [6]. In addition, the half-life of H2SO3 is estimated to be 24 hours at room temperature, and Voegele et al…”

“…In addition, in an aqueous or surface environment, the produced sulfurous acid with oxygen atoms and hydrogen atoms serving as either proton donor or acceptor of hydrogen bonds are capable of forming hydrogen bonds with other aerosol contributors such as water, sulfuric acid or VOC(s), to provide a precursor capable of oligomers, which will provide a potential implication for the particle growth. k 1 3.41×10 -10 3.57 ×10 -10 3.73×10 -10 3.89×10 -10 4.03×10 -10 4.16×10 -10 4.17×10 -10 4.31×10 -10 k -1 3.50×10 1 1.00×10 3 1.64×10 4 1.72×10 5 1.29×10 6 6.24×10 6 7.35×10 6 3.34×10 7 k uni 5.33×10 5 1.56×10 6 3.75×10 6 7.79×10 6 1.44×10 7 2.32×10 7 2.44×10 7 3.84×10 7 k tot 3.41×10 -10 3.57×10 -10 3.72×10 -10 3.8×10 -10 3.7×10 -10 3.28×10 -10 3. 4.3×10 -10 4.49×10 -10 4.68×10 -10 4.85×10 -10 5.01×10 -10 5.02×10 -10 5.19×10 -10 k -1 1.55×10 11 9.27×10 11 4.08×10 12 1.42×10 13 4.09×10 13 9.33×10 13 1.02×10 14 2.24×10 14 k uni 5.33×10 5 1.56×10 6 3.75×10 6 7.79×10 6 1.44×10 7 2.32×10 7 2.44×10 7 3.84×10 7 k tot 1.41×10 -15 7.22×10 -16 4.13×10 -16 2.57×10 -16 1.71×10 -16 1.25×10 - 16 1.21×10 - 16 8.89×10 -17…”

“…The reactions of SO2 in the atmosphere contribute to various environmental issues, including acid rain, formation of sulfate aerosols, and production of secondary organic aerosols [2]. As a result, substantial efforts have been dedicated to the understanding of the chemical processes of SO2 in the atmosphere [3][4][5][6][7][8][9]. A critical step in many atmospheric processes is the adsorption of SO2 on the gas-liquid surface [10][11][12][13].…”

Platinum-mediated monohydration of SO2

“…clusters have also been studied by quantum chemical calculations. 11,12 The reaction shown in scheme 1, eq 1 has been theoretically studied and the results reported show that the participation of several water molecules reduces the reaction barrier of the hydrolysis of SO 2 , although the resulting H 2 SO 3 •(OH 2 ) n-1 (n=1-5) adducts are thermodynamically unstable with regard to SO 2 •(OH 2 ) n ones. Compound 1 reacts with SO 2 at low temperature affording complex 2 (scheme 3), which forms as the result of SO 2 insertion into the Pt-OH 2 bond keeping a strictly one-to-one ratio between the SO 2 and the OH 2 molecules, in a reaction mediated by the platinum bis-benzamidate moiety.…”