Dehydrative Cyclocondensation Mechanisms of Hydrogen Thioperoxide and of Alkanesulfenic Acids

Abstract

Structural features of hydrogen thioperoxide (oxadisulfane, H–S–O–H) and of alkanesulfenic acids (R–S–O–H; R = CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, C(CH3)3, CF3, CCl3) and the mechanisms of their dehydrative cyclocondensation to the respective sulfinothioic acid (H–(SO)–S–H) and alkyl alkanethiosulfinates (R–(SO)–S–R) have been studied using coupled cluster theory with single and double and perturbative triple excitations [CCSD(T)] and quadratic configuration interaction with single and double and perturbative triple excitations [QCISD(T)] with the cc-pVDZ basis set and also using second-order Møller-Plesset perturbation theory (MP2) and the hybrid density functionals B3LYP, B3PW91, and PBE1PBE with the 6-311+G(d,p) basis set. The concerted cyclodehydration mechanisms include cyclic five-center transition states with relatively long distance sulfur–sulfur bonding interactions. Attractive and repulsive nonbonding interactions are predicted in the sulfenic acids, transition states, and thiosulfinates. In the alkyl alkanethiosulfinates attractive cyclic C–H----OS nonbonding interactions are predicted. CCSD(T) and QCISD(T) predict similar values for the relative energies and CCSD(T) predicts the barrier to the cyclocondensation of H–S–O–H to sulfinothioic acid (H–(SO)–S–H) to be 41.8 kcal/mol, and barriers in the range of 37.5 to 39.6 kcal/mol are predicted for the condensation of alkanesulfenic acids to alkyl alkanethiosulfinates.

Trapping Reactions of the Sulfenyl and Sulfinyl Tautomers of Sulfenic Acids

“…Sulfenic acids react as nucleophiles or electrophiles, which may be attributable to interconversion between sulfenyl and sulfinyl tautomers, Scheme . , Recent DFT studies have examined the equilibration between hydrogen thioperoxide tautomers, HSOH and H 2 SO, confirming the sulfenyl as the lowest energy state, but inclusion of water molecules dramatically lowers the energy of the sulfinyl tautomer . In this work, we report trapped products derived from glutathione (GSH) oxidation that most reasonably derive from distinct tautomers, and thus may provide a method to characterize the tautomeric equilibration in situ .…”

“…(3) Sulfenic acids react as nucleophiles or electrophiles, which may be attributable to interconversion between sulfenyl and sulfinyl tautomers, Scheme 1 19,20. Recent DFT studies have examined the equilibration between hydrogen thioperoxide tautomers, HSOH and H 2 SO, confirming the sulfenyl as the lowest energy state, but inclusion of water molecules dramatically lowers the energy of the sulfinyl tautomer 21.…”

Chemical trapping and characterization of small oxoacids of sulfur (SOS) generated in aqueous oxidations of H2S

“…5 . The simples polysulfide oxide, H 2 S 2 O, has nine possible tautomers [49] , [50] , but only products of the disulfanol, 26 and sulfinothioic acid, 27 are observed under our conditions, Scheme 8 . Trapping of 26 with dimedone followed by addition of iodoacetamide yielded disulfide 28 and the product 29 from the Knovenegal intermediate.…”

Mechanisms of Reactions of Sulfur Hydride Hydroxide: Tautomerism, Condensations, and C-Sulfenylation and O-Sulfenylation of 2,4-Pentanedione

“…Sulfur hydride hydroxide 1 is predicted to undergo condensation with selenium hydride hydroxide (10) to afford the isomeric products selenothiosulfinate (11) and thioseleninate (11a) (Figure 9). BD(T), CCSD(T), and QCISD(T) predict 11 to be 5.3, 5.3, and 5.1 kcal/mol, respectively, lower in energy than 11a.…”

“…Hydrogen thioperoxide ( 1 ) and sulfenic acids (R–SOH) exist as sulfenyl (H–SOH, 1 ) and sulfinyl (H 2 SO, C s , 1a ) tautomers (eq ). − Although there are a few exceptions, generally the sulfenyl tautomer is more stable than the corresponding sulfinyl tautomer. Analogous to sulfenic acids, hydrogen thioperoxide is expected to have electrophilic and nucleophilic character, to undergo condensation reactions (cyclodehydration, dehydrative cyclocondensation, self-condensation), and to react with 1,3-dicarbonyl compounds. − In this study, the mechanisms of the tautomerization of 1 (eq ), its condensation to form the parent thiosulfinic acid (sulfinothioic acid, 2 ) (eq ), , its condensation with other sulfenic acids to form organosulfur compounds (eq ), its condensation with selenenic acids 4 to form products 5 containing sulfur–selenium bonds (eq ), − and its C-sulfenylation and O-sulfenylation of 2,4-pentanedione (acetylacetone, Figure , eq ) have been investigated in order to enable a fuller understanding of and deeper insight into the chemistry of the sulfenyl and sulfinyl functional groups in 1 and in sulfenic acids. There are only a few procedures for preparing a diverse range of products with S–Se bonds, and compounds containing S–Se bonds have been implicated in biological processes. − The mechanisms of C-sulfenylation and O-sulfenylation of 1,3-dicarbonyl compounds are also of importance in the detection of protein sulfenic acids (protein–SOH). − …”