Nitrobenzene sulphonation

Further nitration gives w-dinilrobenzene sulphonation gives w-nitrobenzene sulphonic acid. Reduction gives first azoxybenzene, then azobenzene and aniline depending upon the conditions. Used in the dyestufTs industry as such or as aniline. 

An X-ray crystal structure analysis of fraws-4-trimethylsilylcyclohexyl p-nitrobenzene sulphonate 67 reveals an elongated C(alkyl)-0(ester) bond, compared to the non-silicon substituted derivative61. 

Variations in the nature of "leaving groups" have not been studied systematically in the steroid field. Both tosylates and mesylates have been widely used for preparative purposes and in mechanistic studies, although work in other fields suggests that the more reactive -bromo and -nitrobenzene sulphonates may be valuable in special cases. Recent work [18] has demonstrated the use of the acetylsulphate (AcO-SOg-O-)... 

The following substances have also been mercuratedj but analysis indicates that the products are mixtures benzene sulphonic acid and its sodium salt, sodium p-bromobenzene sulphonate, p-iodobenzeiie sub phonic acid, 2 5-dichlorobenzene sulphonic acid, m-nitrobenzene sulphonic acid, o-toluene sulphonic acid and its sodium salt, sodium p-toluene sulphonate, 2-chlorotoluene 5-sulphonic acid. The mercuration of the sodium salts is a much slower process than in the case of the free acids. 

The ultraviolet spectrum of methyl nitrobenzene sulphonate in various solvents... 

An explosion followed by a tire occurred in a sulphonator during a 3-nitrobenzene sulphonic acid process. No-one was injured and plant damage was mainly confined to the sulphonator. adjacent pipework and electrical wiring. Damage was estimated at 120,000 (1993). 

In a 500 ml. bolt-head flask, provided with a mechanical stirrer, place 70 ml. of oleum (20 per cent. SO3) and heat it in an oil bath to 70°. By means of a separatory funnel, supported so that the stem is just above the surface of the acid, introduce 41 g. (34 ml.) of nitrobenzene slowly and at such a rate that the temperature of the well-stirred mixture does not rise above 100-105°. When all the nitrobenzene has been introduced, continue the heating at 110-115° for 30 minutes. Remove a test portion and add it to the excess of water. If the odour of nitrobenzene is still apparent, add a further 10 ml. of fuming sulphuric acid, and heat at 110-115° for 15 minutes the reaction mixture should then be free from nitrobenzene. Allow the mixture to cool and pour it with good mechanical stirring on to 200 g. of finely-crushed ice contained in a beaker. AU the nitrobenzenesulphonic acid passes into solution if a little sulphone is present, remove this by filtration. Stir the solution mechanically and add 70 g. of sodium chloride in small portions the sodium salt of m-nitro-benzenesulphonic acid separates as a pasty mass. Continue the stirring for about 30 minutes, allow to stand overnight, filter and press the cake well. The latter will retain sufficient acid to render unnecessary the addition of acid in the subsequent reduction with iron. Spread upon filter paper to dry partially. 

Gattefoss6 and Morel La Parfumerie Moderne, 1919, 114) describe a method for the production of vanillin by reducing nitrobenzene-sul-phonic acid with iron filings and hydrochloric acid in the presence of guaiacol and formic aldehyde. The first-named body is reduced to phenyl-hydroxylamine-sulphonic acid, which reacts with the guaiacol as follows —... 

Most research workers have employed an aqueous sulphuric acid solution of the aromatic, but a few have used other solvent systems and sulphonating agents. Principal among these are Hinshelwood et a/.139, who measured the rates of sulphonation of aromatics by sulphur trioxide in nitrobenzene at temperatures between 0 and 100 °C, a minimum of about 40 °C being employed for each compound. The initial reaction rate was given by... 

Hinshelwood et a/.145 measured the rates of sulphonation of a wide range of aromatics by sulphuric acid in nitrobenzene, at temperatures between 5 and 100 °C (Table 32), and in particular the effect of adding up to 0.012 M water was determined. The reaction followed the complex rate law... 

Parker37 defined class 4 as solvents "which cannot donate suitable labile hydrogen atoms to form strong hydrogen bonds with an appropriate species and proposed the designation dipolar aprotic solvents he extended their range down to s > 15 and quoted as examples acetone, acetonitrile, benzonitrile, dimethylformamide, dimethyl sulphoxide, nitrobenzene, nitromethane (41.8) and sulfolane (tetramethylene sulphone) (44), where e varies from 21 to 46.5, and the dipole moment p from 2.7 to 4.7 debye. 

There is a parallel for oxygen abstraction by a sulphonyl radical either from nitrobenzene or by disproportionation thermolysis of benzenesulphonyldiazomethane (54) in benzene gives, among other products, some sulphonate ester (55) 67>, which has been formulated as follows ... 

There are certain formal analogies here to m- attack on nitrobenzene (cf. p. 152), but pyridine is very much more difficult to substitute than the former. Thus nitration, chlorination, bromination and Friedel-Crafts reactions cannot really be made to take place usefully, and sulphonation only occurs on heating with oleum for 24 hours at 230°, with an Hg2 catalyst. This difficulty of attack is due partly to the fact that pyridine has an available electron pair on nitrogen, and can thus protonate (66), or interact with an electrophile (67) ... 

The ease with which the sulphonic group enters into aromatic compounds depends on the nature of the substituents present, just as it does in nitration. Benzene is rather difficult to sulphonate, toluene and naphthalene are somewhat more easy, phenols and amines very easy. The sulphonation of nitrobenzene or the further sulphonation of the benzene sulphonic acids proceeds with more difficulty, and the action of the sulphuric acid must here be intensified by increasing its S03-content. 

In the sulphonation of aniline small amounts of the o-compound are produced along with sulphanilic acid. Aniline o-sulphonic acid, however, is of no further interest. Metanilic acid, on the other hand, is also manufactured as an intermediate in the azo-dye industry. It is obtained from nitrobenzene-m-sulphonic acid by reduction. The amino-(iand hydroxy-) sulphonic adds of the naphthalene series are of the greatest technical importance. They are either diazotised themselves or serve for coupling with other diazo-compounds. In this way the most important azo-dyes are produced. 

Fig. 3.127. Representative coupling reaction between PNBD and the sodium salt of 2-naphtol-6-sul-phonic acid to yield the 6-sulphonate-2-naphtol-l-azo-p-nitrobenzene azo dye. Reprinted with permission from C. Bravo-Diaz et al. [177],...

---