Sulphoxides photolysis

The photolysis of dimethyl sulphoxide (at 253.7 nm) in a wide range of solvents has been studied in detail176. Three primary reactions occur, namely (i) fragmentation into methyl radicals and methanesulphinyl radicals, equation (60), (ii) disproportionation into dimethyl sulphone and dimethyl sulphide, equation (61) and (iii) deactivation of the excited state to ground state dimethyl sulphoxide. All chemical processes occur through the singlet state. Further chemical reactions of the initial photochemical products produce species that have been oxidized relative to dimethyl sulphoxide. 

Gollnick and Stracke176 investigated the very complex mechanism involved in the photolysis of dimethyl sulphoxide and concluded that disproportionation is probably the route for the major sulphone-producing reaction. Other oxidized species such as methanesulphonic acid are also produced and are also probably formed by a series of disproportionation reactions, for example equation (62). Thus photolysis of dimethyl sulphoxide is not a synthetically useful reaction due to the large number of compounds produced. 

Aryl vinyl sulphones, reactions of 646 Aryl vinyl sulphoxides 620 optical resolution of 287 reactions of 354, 355, 360, 361, 621 Asscher-Vofsi reaction 189 Asymmetric induction 625 Asymmetric oxidation 72-78 Asymmetric reduction 78, 79 Asymmetric synthesis 824-846 Atomic orbitals 2, 3 Azetidinones 790, 791 ot-Azidoaldehydes, synthesis of 811 Azidosulphones, photolysis of 883, 884 Azosulphones, photolysis of 879 Azoxysulphones, photolysis of 879 1-Azulyl sulphoxides, synthesis of 265... 

Dihydrodithiin sulphoxides, synthesis of 243 Dihydrothiophene dioxides, reactions of 653 /(,/( -Dihydroxyketones 619 Dimerization, photochemical 877, 884 Dimethyl sulphoxide anion of - see Dimsyl anion hydrogen bonding with alcohols and phenols 546-552 oxidation of 981, 988 photolysis of 873, 874, 988 radiolysis of 890-909, 1054, 1055 self-association of 544-546 Dimsyl anion... 

Photolysis and flash vacuum pyrolysis of diaryl sulphoxides both lead to the formation of thiosulphonates as shown in equation (73). This reaction presumably occurs by initial S—C bond scission followed by combination of two arylsulphinyl radicals as depicted in equation (74). 

Photolysis of sulphonyl azides in dimethyl sulphoxide with 2537 A light gives IV-sulphonylsulphoximines 12 in 15—50% yield 5>. The reaction was formulated as going via a nitrene intermediate which was trapped by the nucleophilic solvent... 

In contrast to the problems encountered on photolysis of alkyl- and aryl-sulphonyl azides, we have found that ferrocenylsulphonyl azide 74 is smoothly decomposed by 3500 A light in cyclohexane or in benzene to give ferrocene 15, ferrocenylsulphonamide 16 and the novel bridged [2]ferrocenophanethiazine 1,1-dioxide 17 24>. The yield of 17 varied with the nature of the solvent, being 13.3% in cyclohexane, 67% in benzene, and zero in dimethyl sulphoxide or DMSO/benzene 25>. 

Photochemical decomposition can also be carried out in the presence of a suspension of photoactive material such as Ti02 where substrate absorption onto the uv activated surface can initiate chemical reactions e. g. the oxidation of sulphides to sul-phones and sulphoxides [37]. This technology has been adapted to the destruction of polychlorobiphenyls (PCB s) in wastewater and is of considerable interest in environmental protection. Using pentachlorophenol as a model substrate in the presence of 0.2 % TiOj uv irradiation is relatively efficient in dechlorination (Tab. 4.5) [38]. When ultrasound is used in conjunction with photolysis, dechlorination is dramatically improved. This improvement is the result of three mechanical effects of sonochemistry namely surface cleaning, particle size reduction and increased mass transport to the powder surface. 

The same products are also formed in the photolysis of 21a in dioxane in the presence of dimethyl sulphoxide (equation 57)113,114, and the fact that silatriene 21a is quenched rapidly by dimethyl sulphoxide in the same solvent [k = (3.0 0.2) x 109 M-1 s 1] indicates that the reaction involves the intermediacy of the silene47. Reaction of the sulphoxide with 21a presumably involves an intermediate, such as (singlet) 77 (equation 57), that... 

Photolysis of sulphonyl azides in the presence of nucleophilic trapping agents such as dimethyl sulphoxide or dimethyl sulphide gave imine derivatives. For example, irradiation of -toluenesulphonyl azide in dimethyl sulphide gave a 54% yield of iV-( -toluenesulphonyl) dimethylsulphimine (375) The use of dimethyl sulphoxide resulted in lower yields of the trapped nitrene (377) (13-32%), and... 

Iminosulphurans and iminooxysulphurans were obtained by photolysis of azides in sulphides or sulphoxydes. Benzoyl azide in dimethyl sulphoxide yielded compound 117 . 

A new type of sulphoxide rearrangement in the thermolysis of 1,4-dithiin sulphoxides at 70 C has produced the 1,3-dithiole (265) and the thiophen. Photolysis in methanol gave similar results ... 

The photolyses of H2Se,118 dimethyl sulphide, dibutyl sulphide, and methyl vinyl sulphide,119 and dimethyl sulphoxide,120 the role of concerted and hot biradical reactions in the photolysis of thietan and thietan-cyclopentadiene mixtures,121 and the photolysis of aromatic sulphur compounds122 have been reported. 

Tin.—Allyltin compounds, especially under rhodium-complex catalysis, react with acyl chlorides to give allyl ketones or with aryl halides to give allylarenes. Bridgehead alkyl bromides are reduced on photolysis with Bu"3SnH, whilst the system (Bu"3Sn)20-Br2 oxidizes sulphides to sulphoxides. )V-(Alkoxycar-bonyl)amino-acids are obtained upon treatment of cyclic anhydrides with Bu3SnN3 and heating in an alcohol. ... 

The nitrene (171), generated in a similar manner from the corresponding iV-amino-lactam, formed sulphoximide (e.g. 172) by addition to sulphoxides. The sulphoximide product on photolysis was found to regenerate the original sulphoxide and nitrene (171), which could be trapped with cyclohexene. Thermolysis of (172) again generated the nitrene (171), which under these... 

A condensation of vinyl sulphides of synthetic value involves the reaction of a-ethylthio-styrenes with an aldehyde in the presence of a Lewis acid catalyst to give 3-ethylthio-indenes. Regiospecific and stereospecific pentannelation i.e, fusion of a cyclopentane ring) of an alicyclic ketone involves arylthiomethylen-ation followed by base-catalysed addition to an aj8-unsaturated ester. a-Phenyl-thiobutenolides are less reactive Michael acceptors than their sulphoxide counterparts, and /SjS-dichlorovinyl sulphides are less reactive in electrophilic reactions than their oxygen counterparts. Dimerization of aryl a-cyanovinyl sulphides occurs more readily than that of alkyl analogues, since the intermediate 1,4-diradical ArSC(CN)CH2CH2d(CN)SAr, which cyclizes to the cyclobutane, is more stable. Products obtained by photolysis of methyl vinyl sulphide are accounted for by homolysis of both vinyl—S and methyl—S bonds. The kinetics of catalysed cis-trans isomerization of aryl vinyl sulphides have been studied. ... 

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