Sulphur from photolysis

The formation of 1,3,5-triphenylpyrazole by peroxy-acid oxidation of the pyrazoline (683) can be considered as a dehydration of the intermediate oxaziridine (684). The elusive thiaziridine moiety (686) has been proposed to account for the formation of benzonitrile and sulphur from photolysis of the mesoionic oxathiazolones (685). Diaziridine intermediates (688) and (690) have been suggested to account for the products in photolysis... 

The stable silathiirane 21 results from the silene and elemental sulphur on photolysis. It has an Si—S bond of 212.9 pm, slightly longer than that found in the silathiirane formed from Mes2Sil addition to tetramethyl-2-indanethione62. In addition, the cyclodisilthiane results and can also be made from the disilabicyclo[l.l.l] pentane (20) on hydrolysis. It possesses Si-S bonds of length 217-219 pm (Scheme 4)59. 

Perfluoralkanesulphonyl chlorides may be obtained from the corresponding iodides [219] (Figure 8.74), and they will act as a source of perfluoroalkyl radicals under pyrolysis or photolysis, by losing sulphur dioxide [220] (Figure 8.75). 

Thermal reactions of iodo compounds provide some useful direct S3mtheses of various sulphur and selenium compounds [240, 241], presumably involving radicals, and radicals are also produced from iodo derivatives by photolysis [242] (Figure 9.97). 

Organic arsenic species can be rendered reactive either by UV photolysis or by oxidation with potassium permanganate or a mixture of nitric and sulphuric acids. Arsenic(V) can be determined separately from total inorganic arsenic after extracting As " as its pyrrolidine dithiocarbamate into chloroform. 

The photochemical generation of arylmethyl cations from arylmethanols has been the topic of several papers this year. For mono-aryImethanols in which the aromatic group is phenyl, naphthyl, pyrenyl or phenanthryl, Wan has reported that ultra-violet light irradiation in aqueous alcoholic sulphuric acid solution yields the corresponding ether,presumably by way of an intermediate arylmethyl carbocation. Photolysis of (414) in aqueous alcohol to give (415) is found to proceed even in the absence of acid, while the non-cyclic analogue (416) reacts much less efficiently, even at low values of pH. This reactivity difference has been observed previously for fluorenol and benzhydrol and is attributed to extra stabilisation of the intermediate carbocation in the fluorenyl system. 

Carbon-sulphur bond homolysis has been shown to be, in addition to sulphur-sulphur bond homolysis, a primary process in the photolysis of disulphides in solution. Sulphur-sulphur bond homolysis is, however, responsible for the establishment of an equilibrium between various alkyl disulphides on irradiation." Other liquid-phase studies of the photodecomposition of acyclic alkyl disulphides have been reported," -and the quantum yield for the formation of methyl ethyl disulphide from methyl disulphide and ethyl disulphide has been determined. ... 

From Other Sulphur Heterocycles. The reaction of (46) with 2 eq. of bromine in CHjC gave (47), except for, (46d), which directly gave (48a). Further bromination of (47a) gave (48b). The formation of (47) from (46) has been assumed to proceed via (49) to (53).15 The reaction of (54) with chloroacetone under basic conditions unexpectedly yielded (55) in 44% yield.16 Photolysis of (56) gave tetraphenylthiophen, tetraphenyl-1,4-dithiine, diphenyl-acetylene and sulphur. The products are assumed to be formed via the dimer (57) and (58), which were isolable under appropriate conditions. Photolysis of (56) in the presence of dimethyl acetylenedicarboxylate gave a 17% yield of dimethyl 2,5-dif)henyl-thiophen-3,4-dicarboxylate.17 The reaction of (59) with diphenyl-acetylene at 300°C gave tetraphenylthiophen.1 ... 

Excited sulphur atoms S( D2), from the u.v. photolysis of COS in situ, react with ethene to yield thiiran and vinylthiol in 100% yield.The vinylthiol is formed via direct insertion into a C—H bond and by unimolecular isomerization of the chemically activated ground-state thiiran. This novel thiiran vinylthiol rearrangement is analogous to the cyclopropane propene rearrangement in the sense that both proceed concertedly via a bicyclic activated complex. 

The thiazetine (49) is in thermal equilibrium with the ring-opened heterodiene (50), and on exposure to Sb2Te3 at elevated temperature gives the novel A -l,2,4-thiatellurazoline system (51). A number of 1,2-thiazetine 5-oxides (52) have been prepared by thermolysis of diazo-ketones in the presence of A-suIphinyl-amines and from the reaction of 2-acyl-acetamides and thionyl chloride in the presence of base/ l,2-Thiazet-2-yls (53), a new class of stable radicals, are obtained by photolysis and thermolysis of (54) and sulphur amides, for example (55). They are useful as catalysts, regulators, or inhibitors in radical-initiated reactions. ... 

The sulphur-bridged naphthalene (93) has been prepared by photolysis and thermolysis of naphtho[l,8-< ]l,2,3-thiadiazine (94). The presumed intermediate (95) can be intercepted by CS2 to give (96), which is also formed in low yield when (93) is heated or irradiated in CS2. Oxidation of thiadiazine (94) with peracid gives the mono-5-oxide of (93) by spontaneous extrusion of nitrogen from the thiadiazine S-oxide. ... 

Other work on four-membered heterocycles containing one sulphur atom includes a study of the vacuum-u.v. photodecomposition of thietan 1,1-dioxide and the formation of a thietanone from a xanthate and diphenylketen, and reports of several thiets. There is evidence that photolysis of (107) in a matrix at 77 K leads to the o-thiobenzoquinone (108), which is interconvertible with the... 

Apart from hydrodesulphurization, reactions causing transformation or destruction of the thiophen ring are rather rare. Three interesting examples have been reported. In the first, photolysis of 3-cyanothiophen (22) in furan affords the adduct (23) as the major product. 2-Cyanothiophen behaves in a similar way, and an analysis of permutation patterns has indicated that there is a mechanism involving first the 2,5-bridged compound (24) followed by a walk of the sulphur atom. Anils (25) are converted into pyrroles (26) by triethyl phosphite a similar ring-opening by intramolecular insertion of nitrene has also been shown to occur with o-nitrophenyl-di-(2-thienyl)methanes. ... 

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