Dehydrative cyclocondensation mechanisms of hydrogen thioperoxide and of alkanesulfenic acids.
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.
Department of Chemistry, University of California , Irvine, Irvine, California 92697, United States.
Fillmore
F
Freeman
An
A
Bui
Lauren
L
Dinh
Warren J
WJ
Hehre
D000473:Alkanes / Q000737:chemistry*; D003500:Cyclization; D003681:Dehydration; D010545:Peroxides / Q000737:chemistry*; D011789:Quantum Theory; D013434:Sulfenic Acids / Q000737:chemistry*
D000473:Alkanes; D010545:Peroxides; D013434:Sulfenic Acids; C552843:hydrogen thioperoxide