Sulphonation of aniline

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. 

As in the case of halogenation and nitration the sulphonation of aniline takes place more easily than that of benzene itself. When aniline is heated with concentrated or fuming sulphuric acid the sulphonic acid group enters the ring in the para position. The first reaction of the sulphuric acid on the aniline is of course the formation of the salt, aniline acid sulphate, but this loses water on heating and yields the sulphonic acid.. ... 

Under the sulphonation of aniline it was mentioned that the aromatic compounds differ from the aliphatic compounds in that they can be sulphonated by the action of sulphuric acid i.e. the benzene-hydrogen atoms are replaced by the sulphonic add group, SOaH. Thus the above reaction takes place in accordance with the following equation. -... 

Vrba and Allan investigated the sulphonation of aniline and also the rearrangement of phenylsulphamic acid. In H2S04 phenylsulphamic acid rearranges to 2- and 4-aminobenzenesulphonic acids (equation 2), and gives an identical distribution of the 2-... 

At the end of the last century, Bamberger put forward a theory of indirect sulphonation of aniline whereby the baking of aniline sulphate gave rise to a series of rearrangements that can be dissected as reaction (113). In support he claimed to demonstrate steps II... 

Sulphonamides.— Oxidative amidation of sulphinic acids gives primary sulphon-amides, though the severe reaction conditions (18% oleum with NaNj) restrict the potential of this route. Selective amino sulphonation of anilines, using CISOjNCO and AlClj, depends on the formation of cyclic A-carbamoyl-sulphonamides. More conventional preparative methods are covered in the conversion of naphthalene-1-thiol into 4-(2-hydroxyethylsulphonyl)naphthalene-1-sulphonamide (an assessment of standard routes has been made), and in the preparation of alkanesulphonyl- and trifluoromethanesulphonyl-hydroxyl-amines from hydroxylamines and the sulphonyl chlorides. In the latter study,conditions favouring N- rather than 0-sulphonylation were established. 

SULPHONATION OF AROMATIC AMINES If aniline is treated with excess of concentrated sulphuric acid and the resulting mixture, which contains aniline sulphate, is heated at 180° until a test portion when mixed with sodium hydroxide solution no longer liberates aniline, p-aminobenzenesulphonic acid or sulphanilic acid is formed this separates as the dihydrate upon pouring the cooled mixture into water. The reaction prohahly proceeds as follows ... 

In this method the order of addition of the reactants is changed. The most general application is to the diazotisation of aniline- and naphthylamine-sulphonic acids, many of which are sparingly soluble in acidic media and form sparingly soluble diazonium salts. Typically, the arylaminesulphonic acid is dissolved as its sodium salt in dilute alkali and sodium nitrite is then added to the solution. The resulting solution is run slowly into a mixture of hydrochloric acid and ice, the diazonium salt being formed almost instantaneously. 

Aniline is very easily sulphonated, for example, by heating its sulphate ( baking process). This change recalls that of aniline acetate into acetanilide. Actually, it is very probable that an analogous product acylated at the amino-group, a sulphaminic acid, is first formed, since examples of this type of change are known, e.g. the conversion of phenylhydroxylamine to p-aminophenol and of phenylnitramine to... 

Method I.—20 gms. of aniline are gradually added to 65 gms. of cone, sulphuric acid placed in a round-bottomed flask. Much heat is developed, and the contents of the flask should be cooled when the aniline is being added. The flask which contains aniline sulphate and excess cone, sulphuric acid is now heated on an oil or paraffin bath to 185° for about 5 hours. When a test portion, treated with dilute caustic soda solution, liberates no free aniline, the sulphonation is complete. The contents of the flask, after cooling, are poured into cold water, when the sulphanilic acid separates, usually as discoloured crystals. These are filtered off and recrystallised from water, adding a little animal charcoal, if necessary. A further crop can be obtained from the mother liquor. 

It is necessary to dilute the sulphuric acid slightly or to keep the temperature low, otherwise sulphonation occurs and a p-aminophenol sulphonic acid results.1 Elbs2 was the first to prove that a considerable quantity of aniline is formed at the same time, and that a lead cathode increases the amount of this substance. 

Induline 6 B, CseHjjNj. This is the best characterised of the induline series. Its hydrochloride forms well-defined crystals which are insoluble in alcohol. Its sulphonic acid dyes wool a pure blue shade. This induline is probably a phenazine produced by action of aniline on azophenine according to the equation [37] ... 

REACTION THE SULPHONATION OF AN AMINE Example Sulphanilic Add from Aniline and Sulphuric Acid1... 

The amidoazobenzene hydrochloride came into the market formerly, as a yellow dye, under tire name of Aniline Yellow. At present, it is scarcely used, but there is prepared from it, by heating with sulphuric acid, a mono- or di-sulphonic acid, which in the form of its alkali salts finds application as a dye under the name of Acid Yellow, or Fast Yellow. As already mentioned under the dis-azo dyes, from the diazo-compound of this dye, Biebrich Scarlet may be made-by combination with /3-naphthol. Finally, the amidoazobenzene is still used for the preparation of the Induline dyes. 

The first acid dye was made by Nicholson in 1862, when he sulphonated aniline blue it was known at that time as Bleu de Lyons (Chapter 1). Other basic dyes were subsequently sulphonated to convert them into acid dyes, making them more easily applicable to wool than the parent basic dyes. Acid Magenta (C.I. acid violet 19), formula (1), is obtained by the sulphonation of magenta ... 

Through researches in aromatic chemistry it was not tong before synthetic phenol became available. Prior to work by Griess on aromatic diazo compounds published in 1860, Hunt (ref.1) had in 1849 obtained phenol from a diazonium salt produced by the reaction of aniline hydrochloride and siver nitrite. F.A. Kekule, (1829-1896), Fig.3, in 1867 (ref.2) described the recently completed sulphonation of benzene and fusion of the sulphonic acid with alkali as a new... 

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