Singlet Oxygen

[7782-44-7] O2 (MW 32.00) InChI = 1S/O2/c1-2 InChIKey = MYMOFIZGZYHOMD-UHFFFAOYSA-N (electrophilic oxidizing agent for oxygenation of cisoid 1,3-dienes, many types of heterocyclic systems, enamines, alkenes containing allylic hydrogen atoms, sulfides, carbon–phosphorus double bonds, and other electron-rich unsaturated organic compounds) Physical Data: singlet oxygen (1O2) is the first excited electronic state of molecular oxygen (1Δg), lying 22.4 kcal mol−1 above the ground state triplet. The second singlet state (1Σg+), 37 kcal mol−1 above the ground state, is relatively short-lived in solution (10−12 s) due to a rapid spin-allowed transition to the longer-lived (10−3–10−6 s) first excited state. Because of the short lifetime of the 1Σg+ state, the more stable singlet oxygen species (1Δg) is considered to be the reactive intermediate in the oxygenation of organic compounds in solution.1 Solubility: sol aqueous and organic solvents. Form Supplied in: singlet oxygen is an unstable, short-lived species and must be prepared in situ or immediately prior to use. Preparative Methods: among the methods for generating singlet oxygen in solution are: (a) the dye-sensitized photooxidation of triplet oxygen;2 (b) the decomposition of phosphite ozonides;3 (c) the decomposition of transannular peroxides such as 9,10-diphenylanthracene peroxide;4 (d) the reaction of Hydrogen Peroxide with Sodium Hypochlorite;5, 6 and (e) subjecting gaseous oxygen to electrodeless discharge.7 In the following section, the procedures for generating singlet oxygen by the methods (a)–(d) above are discussed, and some typical reactions of singlet oxygen with organic compounds are reviewed. Handling, Storage, and Precautions: the initial peroxidic products formed in 1O2 reactions usually undergo decomposition or rearrangement under the conditions of workup, but in some cases (certain transannular peroxides or dioxetanes) they may remain in the reaction mixture as potentially explosive materials. Unless the peroxides are sought as reaction products, they may be deoxygenated by the action of Dimethyl Sulfide, diphenyl sulfide, or Triphenylphosphine.