Radical oxidizing agent. Prepn: E. Fremy, Ann. Chim. Phys. 15, 408 (1845). Structural studies: W. Moser, R. A. Howie, J. Chem. Soc. A 1968, 3039; R. A. Howie et al., ibid. 3043. Mechanism of oxidation: B. Giethlen, J. M. Schaus, Tetrahedron Lett. 38, 8483 (1997). Synthetic applications: H. J. Teuber, G. Jellinek, Naturwissenschaften 38, 259 (1951); H. Schlude, Tetrahedron 29, 4007 (1973); P. M. Deya et al., ibid. 43, 3523 (1987); G. A. Kraus, N. Selvakumar, Tetrahedron Lett. 40, 2039 (1999). EPR studies: B. L. Bales, Chem. Phys. Lett. 10, 361 (1971); M. T. Jones et al., J. Phys. Chem. 83, 1327 (1979); B. L. Bales et al., J. Magn. Reson. 118, 227 (1996). Photochemistry study: H. Kunkely et al., J. Photochem. Photobiol. A 112, 9 (1998). Review of oxidation chemistry: H. Zimmer et al., Chem. Rev. 71, 229-246 (1971).