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Does the interconversion of polysulfur compounds proceed via hypervalent intermediates? An ab initio MO study
R Steudel1, Y Steudel, K Miaskiewicz
1Institut für Chemie, Sekr. C2, Technische Universität Berlin, Germany. steudel@schwefel.chem.tu-berlin.de
Chemistry (Weinheim an Der Bergstrasse, Germany)
|September 4, 2001
Summary
Computational studies reveal that sulfurane intermediates are unlikely in polysulfane interconversion reactions. Homolytic dissociation and radical chain mechanisms are favored over sulfurane formation pathways for sulfur chain and ring rearrangements.
Area of Science:
- Computational Chemistry
- Inorganic Chemistry
- Physical Chemistry
Background:
- Polysulfur compounds exhibit complex interconversion reactions.
- Sulfurane intermediates have been hypothesized to play a role in these transformations.
- Understanding reaction mechanisms is crucial for controlling sulfur chemistry.
Purpose of the Study:
- To computationally investigate the feasibility of sulfurane intermediates in polysulfane reactions.
- To determine the energetics of sulfurane formation and compare them to S-S bond dissociation energies.
- To elucidate the mechanism of sulfur atom exchange in polysulfanes.
Main Methods:
- Ab initio molecular orbital (MO) calculations were performed.
- Coupled-cluster with single, double, and triple excitations (CCSD(T)) and Møller-Plesset perturbation theory (MP2) methods were employed.
- Reaction energies and Gibbs energies were calculated at various theoretical levels.
Main Results:
- Sulfurane formation from hydrogen sulfide and sulfanes requires significant energy input, exceeding homolytic dissociation energies.
- Calculated energies for methyl-substituted sulfurane formation are substantially higher than S-S bond dissociation energies in related polysulfanes.
- The results indicate that sulfurane intermediates are energetically unfavorable.
Conclusions:
- Sulfurane-type intermediates are not likely involved in the interconversion of polysulfur compounds.
- Polysulfane interconversions are better explained by radical chain mechanisms at high temperatures.
- Low-temperature reactions are likely initiated by nucleophilic impurities or surface effects.