Thianthrene 5,5,10,10-tetroxide

Dipole moment measurements of solutions of cis- (64BSF2119 65JCS571) and tru/ii-thianthrene 5,10-dioxide (65JCS571) and of thianthrene 5,5,10,10-tetroxide (65JCS57I) gave values of 1.86 and 1.70, 4.88, and 5.11 D, from which fold angles of 139°, 130°, and 140° respectively, were calculated. 

Thianthrene 5,5,10,10-tetroxide can be ring cleaved, even with potassium hydroxide, in hot ethanol (Scheme 7) (11LA312). 

Sulfur, at 345°C for thianthrene tetroxide, or at 250°C for thianthrene 5-oxide, produced thianthrene in good yields. S-Labeling experiments showed that the former took place with 80% replacement of ring sulfur and the latter took place with 91% replacement (73BCJ650), so these processes, whatever their detailed mechanism, do not involve simple reductive cleavage of the S—O bond. In accordance with this, thianthrene 5,5,10,10-tetroxide is converted into selenanthrene by reaction with elementary selenium (1896CB443). 

Early attempts to nitrate thianthrene showed 5-oxidation to proceed more rapidly than C-nitration, both 5-mono- and 5,10-dioxides being available in this way. Production of these, and tri- and tetroxide formation, were already well-studied processes by 1960 (66HC1155). 

Attempted simple oxidation of alkyl groups on thianthrenes would also effect 5-oxidation. However, sulfones can be side-chain-oxidized 2,3,6,7-tetramethyl-, 1,2,7,8-tetramethyl-, 1,4,6,9-tetramethyl-, and 1,3,7,9-tetra-methylthianthrene tetroxides gave the tetra-acids with 25% HNO3 at 220°C. These tetra-acids were converted to esters and anhydrides in the usual ways (69USP3410868). 

The reaction of tellurium and thianthrene S,5,S,S-tetroxide under similar conditions also yielded dibenzotellurophene5. 

Thianthren and its a-dioxide, and tetroxide Equivalent conformations, folded about the S—S line by 140+10° in thianthren and about 138° in its a-dioxide or ca. 130° in the tetraoxide, are deduced for these flexible ( flapping ) solutes in B Aroney et al., 1965a... 

---