Nitrophenyl sulphides—

The deoxygenation of aryl 2-nitrophenyl sulphides with tervalent phosphorus compounds is analogous to that of the corresponding ethers except that in many cases the anticipated phosphoranes, e.g. (87), are thermally unstable.58 The extra stability of spirophosphoranes allows them to be isolated, e.g. (13), if cyclic phos-phonites are used in deoxygenation.8... 

The additional double bond in the corresponding allenyl 2-nitrophenyl sulphides causes a significant preference of the oxygen transfer to carbon88. The dominant ions correspond to the radical cations of 2[3//]-benzothiazolone and protonated benzothiazole, respectively88. Both ions require the transfer of two oxygens to carbon in the side-chain as well as extensive rearrangements of the molecules see Scheme 22. The transfer of... 

With the preformed ammonium persulphate, oxidation of sulphides to both sulphoxides and sulphones has been observed [e.g. 6, 7] whereas, when Oxone is used in conjunction with a quaternary ammonium salt, oxidation can be selectively stopped at the sulphoxide stage [6-8]. It has been recorded that electron-deficient aryl sulphides, e.g. di(4-nitrophenyl)sulphide, are not readily oxidized. 

Full details have appeared of the behaviour, inter alia of 2,6-disubstituted aryl 2-nitrophenyl sulphides with triethyl phosphite and of 2,6-disubstituted aryl 2-azidophenyl sulphides on thermolysis, following preliminary reports (see Volume 1, p. 470). In both cases the reaction involves a novel heteroaromatic rearrangement that is interpreted in terms of the intervention of nitrene intermediates. The process is exemplified by the behaviour of 2-nitrophenyl 2,6-dimethylphenyl sulphide (40) and 2-azidophenyl 2,6-dimethylphenyl sulphide (41) (Scheme 6). The sigmatropic rearrangement of the postulated intermediate (42), which is necessary to produce the [Z>,e]azepine (44), is not allowed in the suprafacial sense hence the intervention of a biradical species (43) is considered to be more likely. 

Olah and coworkers56 found that treatment of dialkyl, arylalkyl and diaryl sulphides with nitronium hexafluorophosphate (or tetrafluoroborate) 32 at —78° in methylene chloride resulted in the formation of sulphoxides in moderate to high yields (Table 3). In the oxidation of diphenyl sulphide which affords diphenyl sulphoxide in 95% yield, small amounts of the ring nitration products (o- and p-nitrophenyl phenyl sulphides) were formed. However, diphenyl sulphone and nitrophenyl phenyl sulphoxide were not detected among the reaction products. 

There has been a series of papers on the deoxygenation of 2-nitrophenyl phenyl ethers and sulphides. Of particular interest has been the role of pentacovalent intermediates (47) in these reactions. These are certainly not the primary intermediates in the reactions but are of great importance in determining the course of the reaction. Their genesis is thought to be that shown in Scheme 3.57... 

Di-m-aminophenyi diselenide, (NH2.C6H4)2Se2, may be obtained in three ways (1) The foregoing compound is reduced by an alkaline solution of sodium sulphide. (2) m-Nitrophenyl selenocyanate is reduced by tin and hydrochloric acid. (3) Diazotised m-nitroaniline is treated with potassium selenocyanate.5 The dihydrochloride crystallises from dilute hydrochloric acid in yellow grains formed of small needles melting with decomposition at 291° to 292° C. (corr.).6 It readily... 

Reduction of Nitro- to Amino-groups. - Sulphide catalysts continue to find application in selective hydrogenation of nitro-groups. Aromatic nitro-groups in the presence of acetylenes were selectively hydrogenated (373 K, 25-70 atm, in isopropanol) to amino-groups over cobalt polysulphide and RUS2 catalysts, for example (3-nitrophenyl)acetylene to (3-aminophenyl)acetylene in 75-85% yield. ... 

The double oxygen transfer to sulphur is also a characteristic feature of 2-nitrophenyl styryl sulphides. The rearranged molecular ion undergoes fragmentation in two parallel pathways. Elimination of SO2 affords the radical cation of 2-phenylbenzopyrole and is followed by a loss of H see Scheme 21. In addition, this ion is formed by a direct loss of HSO2 from the rearranged molecular ion. ... 

It seems interesting to compare the mass spectrometric features of 2-nitrophenyl-phenylethynyl sulphides with the fragmentation of the nitrodiphenylacetylenes discussed above. Apparently, oxygen transfers to both the acetylenic carbons and sulphur take place . The transfer of a single oxygen to the -carbon leads, via a mechanism closely resembling the fragmentation of nitrodiphenylacetylenes, to the benzoyl cation . The latter ion apparently is the base peak in the MS of the major part of the compounds studied see Scheme 23. 

Aralkyl trimethylsilyl sulphides RSSiMej give disulphides with sulphenyl chlorides, and symmetrical diselenides are formed from the selenium analogues with Ij (PhSeSiMcj - PhSeSePh + MejSil). The formation of unsymmetrical disulphides from steroidal A -diene-S-thiones and 2-nitrobenzenesulphenyl chloride is in accordance with the concept of hard and soft acids and bases, the soft thione nucleophile reacting with the soft sulphenyl halide, but not with the hard sulphonyl chloride. The resulting A -trienyl 2-nitrophenyl disulphides participate in thiol-disulphide exchange (see next section). 

The use of phenyl esters as terminal groups in polypeptide synthesis has been reconunended. They are stable to many of the usual conditions encountered in peptide coupling reactions and can be removed selectively by treatment with one equivalent of hydrogen peroxide at pH 10.5 in various solvents containing dimethyl sulphide. m-Nitrophenyl esters could also find use in this context being quite acid stable (they survive conditions which are sufficiently acidic to hydrolyse JV -Z groups) but rather base labile (removed by 0.1M-NaOH). p-Nitro-phenyl esters can be hydrolysed specifically in some cases by N-lauroylhistidine in the presence of cationic micelles. ... 

Conformational information derived from n.m.r. and i.r. studies of 2,4-di-nitrophenyl 2-chloroalkyl sulphides ArSCHR CHClR reveals a weak repulsive interaction between Cl and SAr, while an intramolecular attractive... 

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