Tetracovalent Sulfur Compounds

Suter, C. M. 1944. The Organic Chemistry of Sulfur. Tetracovalent Sulfur Compounds. John Wiley Sons, New York, see pp. 126-136, 136-141. 

Potts and co-workers have used phosphorus pentasulfide and pyridine as a standard reagent for constructing annelated diphenylthiophene rings from o-dibenzoyl compounds. Many of these annelated thiophenes can be written only in the tetracovalent sulfur or ylid dipolar form (96) and are thus termed nonclassical 123 other examples, particularly of the synthesis of non-classical thienoisothiazoles, have been reported by Gotthardt.124... 

Mercaptophenylacetic acid, acetic anhydride, and sodium nitrite yielded the first example (169, R = Ph) of a meso-ionic 1,3,2-oxathiazol-5-one this compound has a dipole moment of 4.5 D. An X-ray crystallographic investigation of the 4-phenyl-l,3,2-oxathiazol-5-one (169, R = Ph) has been reported. This compound is incorrectly described as a thiosydnone. The bond distances support the structure with tetracovalent sulfur, and on this evidence alone the compound 169, R = Ph, could be judged not to be meso-ionic because it can, on the basis of the X-ray evidence, be more satisfactorily represented by a covalent formulation. 

Structures involving tetracovalent sulfur (279) have been used to represent this class of compound but the role of d-orbitals in their bonding is not clear (see Section IV,A). 

Selenium is more easily oxidized to Se(IV),but the oxidation stage Se(VT) is obtained with more difficulty than with the corresponding sulfur compounds. For example, selenuranes (tetracovalent selenium compounds) are more easily obtained than the sulfur analogs. The synthesis as well as the chemistry with selenium at higher oxidation stages is reviewed in Chap. 6 by M. Mikolajczyk and J. Drabowicz. 

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