Neighboring Group Participation in Organic Redox Reactions. 8. Kinetics and Products of the Aqueous Iodine Oxidation of 3-Hydroxy- and 3-Methoxy-1,5-dithiacyclooctanes

Article abstract of DOI:10.1021/jo00169a019

The aqueous iodine oxidation of 3-hydroxy- and 3-methoxy-1,5-dithiacyclooctanes (B and C) occurs about 10⁴ times faster than the similar reaction of thiacyclooctane but about 10² times slower than the oxidation of the parent compound 1,5-dithiacyclooctane (A).These observations are consistent with the formation of a dicationic intermediate.The cis- and trans-sulfoxides are formed in roughly equal amounts.Single-crystal X-ray diffraction of trans-3-methoxy-1,5-dithiacyclooctane 1-oxide (trans-K) and of cis-3-hydroxy-1,5-dithiacyclooctane 1-oxide (cis-E) reveals a transannular sulfur-sulfur close contact of 3.175 (2) and 3.135 (2) Angstroem, respectively, and S...S-O angles of 176.9(1) and 1.75.4 (1) deg.As predicted by the S...S-O alignment, the reverse reaction, the HI reduction of trans-3-methoxy-1,5-dithiacyclooctane 1-oxide (trans-K), is accelerated over that of a simple sulfoxide but is ca. 10 times slower than the reduction of 1,5-dithiacyclooctane 1-oxide.The equilibrium constant is ca. 150 for the reaction K + 2H(1+) + 3I(1-) <---> H2O + I3(1-) + C.Cyclic voltammetric measurements show that both B and C have low oxidation potentials but that, although the oxidation of B is reversible, that of C is quasi-reversible.