Premium
Geometries, Acidities, and Dissociation Reactions of the Gaseous Superacids H 2 S 2 O 3 , H 2 SO 5 , HSO 3 F, and HSO 3 Cl
Author(s) -
Steudel Ralf,
Otto André H.
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200011)2000:11<2379::aid-ejic2379>3.0.co;2-l
Subject(s) - chemistry , deprotonation , dissociation (chemistry) , endothermic process , standard enthalpy of formation , sulfuric acid , molecule , proton affinity , computational chemistry , gas phase , ab initio , thermochemistry , inorganic chemistry , protonation , ion , organic chemistry , adsorption
The gas‐phase geometries, dipole moments, enthalpies, and Gibbs free energies of thiosulfuric acid H 2 S 2 O 3 , peroxosulfuric acid H 2 SO 5 , fluorosulfuric acid HSO 3 F, and chlorosulfuric acid HSO 3 Cl as well as of their monoanions have been determined by ab initio MO calculations at various levels of theory. The most stable conformations of the four acid molecules are all of C 1 symmetry. The acidities, defined as Δ G° 298 of the deprotonation reaction, obtained by the G2 method are as follows [kJ mol −1 ]: H O−SO 2 −SH 1251 and HO−SO 2 −S H 1276, H O−SO(=S)−OH 1241, H O−SO 2 −OOH 1239, H O−SO 2 −F 1229, H O−SO 2 −Cl 1219. Good agreement of the calculated acidities of HSO 3 F and HSO 3 Cl is observed with the experimental gas‐phase acidities, which are the only experimental values available. The OH acidities of all five species are higher than that of sulfuric acid (1268 kJ mol −1 ). Therefore, these compounds may be termed as superacids. In contrast to the liquid state, chlorosulfuric acid is a stronger proton donor than fluorosulfuric acid in the gas phase. The dissociation of the acid molecules HSO 3 X (X = SH, OOH, F, Cl) into SO 3 and HX is endothermic and endergonic in all cases. The same holds for the dissociation of the anions SO 3 X − into SO 3 and X − . From these dissociation enthalpies and literature data the enthalpies of formation of the mentioned sulfonic acids and their anions are calculated.