Biradicals as reaction intermediates

In some well-known transformations involving inorganic ring systems, biradicals act as reaction intermediates that are sufficiently persistent to be detected by EPR spectroscopy (see Section 3.6). For example, the polymerisation of cyclo-Sg to form the helical sulfur polymer Soo (plastic sulfur) occurs via the 

The oxidation of phosphorus by elemental sulfur to give binary phosphorus sulfides, which is initiated by mild heating ( 100 °C) or upon photolysis at 0 °C, may involve the formation of the catenaS biradical in the rate-determining first step.  

Rawson, A. J. Banister and I. Favender, Adv. Heterocycl. Chem., 1995, 62, 137 (b) J. M. Rawson and A. Alberola, in Handbook of Chalco-gen Chemistry New Perspectives in Sulfur, Selenium and Tellurium, ed. F. A. Devillanova, Royal Society of Chemistry, Cambridge, 2007, pp. 737-742. 

Williams, Y. Kabe and S. Masamune, Angew. Chem. Int. 

Steudel, S. Passlack-Stephan and G. Holdt, Z. Anorg. Allg. Chem., 1984, 517, 7. 

---