Sulfides reaction with singlet oxygen

Photochemical oxidations of various substrates such as amines [763], alkenes [769,770,772,775,778-780], fiiran [764,765], sulfide [766,773], phytol [767], bi-adamantylidene [768], thiophenolate [771], catechol [774], allylsilane [776], and imines [777], etc., through reactions with singlet oxygen sensitized by porphyrins have been extensively studied. Photochemical atrop isomerization of picket-fence-type porphyrin should be noted here as another interesting type of photoreaction [793]. 

Fig. 25 Mechanism of the reaction of singlet oxygen with sulfides in solution.

Toutchkine, A. and Clennan, E.L. (2000). A new mechanism for oxidative C-S bond cleavage during reactions of singlet oxygen with organic sulfides electronically dictated reaction selectivity in the persulfoxide intermediate. J. Am. Chem. Soc. 122, 1834-1835... 

Formation of thiadioxiranes in reactions of singlet oxygen with sulfides (persulfoxides as intermediates) 01ACR875. 

Singlet oxygen reactions. Dialkyl sulfides are oxidized to sulfoxides by singlet oxygen. Diphenyl sulfide is practically inert under the same conditions. However, if it is added to the photooxidation of a dialkyl sulfide, it is converted into diphenyl sulfoxide. The interpretation advanced by Foote and Peters is that diphenyl sulfide reacts readily with persulfoxides, formed in the reaction of alkyl sulfides with singlet oxygen ... 

Wasserman and Saito have used diphenyl sulfide to intercept dioxetanes formed in the sensitized photooxidations of certain unsaturated systems. Thus reaction of cw-dimethoxystilbene (1) with singlet oxygen yields only the diox-etane (2) and the product of cleavage, methyl benzoate. However, addition of diphenyl sulfide to the reaction results in formation of benzil dimethyl ketal... 

The reaction of singlet oxygen with 2,3-disubstituted indoles yields labile dioxetanes but these are partially stabilized if the indole has an iV-acyl substituent (93JOC47) and the products (e.g. 41, R = Me, = Bu ) may then be isolated. Reduction of the dioxetane (41) with dimethyl sulfide gives the epoxide (42). The dioxetane (43) is photochemically decomposed with intense luminescence (93TL5247). 

The reaction of singlet oxygen with sulfides in aprotic solvents to form sulfones and sulfoxides proceeds by reactions (30)-(32). The reaction of O2... 

Nahm K, Li Y, Evanseck JD, Honk K, Foote CS (1993) Structures and energies of intermediates in the reactions of singlet oxygen with organic phosphines and sulfides. J Am Chem Soc 115(11) 4879 884... 

Since di-te/7-butylsulfide delivers the sulfoxide in the photosensitized reaction and no a-hydroxysulfides were observed from the other sulfides of Table XIV, the photosensitized oxidation of sulfides (and probably also that of sulfoxides) takes another course than in the thermal reaction. It was suggested that singlet oxygen (formulated as the sensitizer-oxygen adduct -Sens-CV278,280) reacts with a sulfide to give a highly reactive sulfo-peroxide intermediate, 431, which immediately reacts with another sulfide molecule to yield two stable sulfoxide molecules. 

Steric effects also can be important in some singlet oxygen reactions. Monroe (1979) reported that, for the series of dialkyl sulfides, R2S, where R varies from Me to t-Bu and Ph, values of kox (for reaction) decreased by a factor of 300. Analysis of his data using only the Taft (steric) Es values for R gave a fair correlation of five sulfides with 8 = 0.46 and r2 = 0.78 (Equation (25)). 

An earlier procedure reported from this laboratory for the isolation of sulfides was based on the selective oxidation of the sulfides to the sulfoxides with photoexcited singlet oxygen followed by silica gel chromatographic separation of the sulfoxides (9). Reduction of the isolated sulfoxides back to the sulfides and a subsequent chromatographic purification resulted in the isolation of the sulfides as a pale yellow oil. However, when the sulfur is in a five-membered ring, the photooxidation may lead to side reactions (22). Therefore, other oxidation methods had to be explored. 

Alcohols (as well as amines, sulfides and many hydrocarbons) may act as overall hydride donors towards excited nonbonding-rr " states of carbonyl compounds and heterocycles. The synthetic as well as the photophysical aspects of these processes have been discussed extensively. These reactions will not be dealt with further here. Singlet oxygen also accepts hydride from alkoxides in the gas phase the mechanisms of such reactions have received considerable study. ... 

The examples of reaction rates of O2 in Figure 12.7 show that O2 reacts only with deprotonated species (e.g., phenolate anions) that is, the apparent rate constants decrease in the pH region below the pKa of the chemical. Singlet oxygen is selective it is an electrophile that reacts only with particular functional chemical structures such as are present in 1,3 dienes (see chemical structure of fiirfuiyl alcohol) or polycondensed aromatic hydrocarbons (with delocalized 7T electron bonds) or in sulfides or mercaptans (Hoigne, 1990). 

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