Dibenzothiophene nitration

An unsuccessful attempt to repeat this reaction was made by Bird however, he was able to show that dibenzothiophene 5-oxide did, in fact, react with either thionyl chloride or phosphorus oxychloride to yield 2-chlorodibenzothiophene in good yield. Since all methods of nitration of dibenzothiophene yield a mixture of 2-nitrodibenzothio-phene and dibenzothiophene 5-oxide, which have identical melting points, it was concluded that the earlier workers had in fact been working with the sulfoxide and not the nitro compound. The reaction was rationalized as being a deoxygenative halogenation of a heterocyclic 5-oxide akin to the Meisenheimer reaction of A-oxides, which already had precedents in the sulfoxide field. Unfortunately the 2-chlorodibenzothiophene prepared by this route is contaminated with 2,8-dichlorodibenzothiophene which cannot be removed by crystallization. The best method of preparation of this compound is therefore via a Sandmeyer reaction on 2-aminodibenzothiophene. ... 

Direct nitration of dibenzothiophene occurs in the 2-position, while prior oxidation of the sulfur atom to either the sulfoxide or sulfone causes nitration to be directed to the 3-position. These two reactions form the starting point for the synthesis of most of the known derivatives of dibenzothiophene, which normally proceed via the derived amines. This has now been further illustrated by the synthesis of both 1-nitro- and 4-nitrodibenzothiophene from iV -derivatives of 2- and 3-aminodibenzo-thiophene, respectively, as described below. The synthesis of these two compounds thus completes the series of mononitrodibenzothiophenes. Unfortunately hopes of s3mthesizing nitrodibenzothiophenes via the chlorocyclohexanone route have been almost certainly ruled out by the failure to produce 2-nitrodibenzothiophene by this route (Section IV, A). 

Acetamidobenzothiophene is nitrated in the 1-position yielding 102 (73%), which upon hydrolysis with either sodium hydroxide or ethanolic hydriodic acid gives the nitroamine (103). The same nitroamine was also formed by the nitration and hydrolysis of 2-carbethoxyamino-dibenzothiophene. ... 

Three derivatives of 3-aminodibenzothiophene, 110a, 110b, and 110c, have been nitrated, and in each case substitution occurred in the 4-position. Hydrolysis of the products yielded 3-amino-4-nitro-dibenzothiophene, which was different from the previous two nitro-amines and which formed an imidazole different from both 104 and 109. Deamination of this nitroamine via diazotization gave a small amount of 4-nitrodibenzothiophene. An alternative synthesis of the 4-nitro compound is described later. The spectroscopic techniques used above by Sawicki were later extended to determine the positions of substitution in dibenzoselenophene, in this case by comparison with the above-established derivatives of dibenzothiophene. - ... 

As mentioned earlier, oxidation of dibenzothiophene to either the sulfoxide or sulfone causes electrophilic attack to occur at the 3-position rather than at the normal 2-position. This trend is further exemplified by the behavior of 4-methyldibenzothiophene which is nitrated in the 2-position (26%), while nitration of 4-methyldibenzothiophene 5,5-dioxide occurs in the 3-position yielding 112. The structures of both of these products were deduced from their NMR spectra. 

Phenylcalcium iodide metallates dibenzothiophene in the 3-position however, it has no effect on the corresponding sulfone. Mercuration of dibenzothiophene has been accomplished by adding mercuric acetate to a melt of dibenzothiophene, but the position of mercuration was not established. Mercuric nitrate or bisulfite give no identifiable products. An unsuccessful attempt to metallate dibenzothiophene with cross-linked poly(p-lithiost5Tene) in ether has been recorded. ... 

Nitration, 4-acetaminobiphenyl, 211 4-acetamino-l,3-dimethylbenzene, 211 2-acetaminonaphthalene, 212 benzonitrile, 215 cumene, 220 dibenzothiophene, 220 o-dichlorobenzene, 112 2,4-dimethylaniline, 131 ethyl acetoacetate, 159 ethylbenzene, 223 fluorobenzene, 223 p-hydroxyphenylarsonic acid, 224 isatin, 225 isoquinoline, 225 lepidine, 226... 

Several standard electrophilic reactions have been carried out on dibenzothiophene <85JHC215>. Nitration with cone. HNO3 and glacial acetic acid leads to a mixture (40% each) of 2-nitro-dibenzothiophene and dibenzothiophene-5-oxide. Nitration of the latter (fuming nitric acid and cone, sulfuric acid) gives 3-nitrodibenzothiophene-5-oxide, which could be deoxygenated to 3-nitrodibenzothiophene by 48% hydrobromic acid and glacial acetic acid. 

---