Sulphanilic acid

Sulphanilic acid crystallizes from water in plates, which contain 2 molecules of water of crystallization it is converted into tribromoaniline by an excess of bromine water. The yield in this preparation is about 25 grams. 

Place a mixture of 25 g. of a-naphthylamine (Section IV,3 7) and 125 g. (69 5 ml.) of concentrated sulphuric acid in a 250 ml. conical or round-bottomed flask, and heat in an oil bath for 4-5 hours or until a test sample, when made alkaline with sodium hydroxide solution and extracted witli ether, yields no naphthylamiue upon evaporation of the ether. Pour the warm reaction mixture cautiously and with stirring into 300 ml. of cold 

---

C HgNjOjS. Colourless needles, with iH20. Prepared by reducing diazotized sulphanilic acid with an excess of sodium sulphite. It is a typical hydrazine in its reactions with ketones, and with acetoacetic ester. The latter reaction gives rise to the tartrazine dyestuffs, and is much used commercially. 

This localization phenomenon has also been shown to be important in a case of catalysis by premicellar aggregates. In such a case [ ] premicellar aggregates of cetylpyridinium chloride (CPC) were shown to enhance tire rate of tire Fe(III) catalysed oxidation of sulphanilic acid by potassium periodate in tire presence of 1,10-phenantliroline as activator. This chemistry provides a lowering of tire detection limit for Fe(III) by seven orders of magnitude. It must also be appreciated, however, tliat such premicellar aggregates of CPC actually constitute mixed micelles of CPC and 1,10-phenantliroline tliat are smaller tlian conventional CPC micelles. 

A second preparation to illustrate sulphonation is that of sulphanilic acid, NH2C4H4SO3H, a highly crystalline substance which, having a low solubility in cold water, can be readily isolated. If aniline is treated with an excess of concentrated sulphuric acid, aniline hydrogen sulphate is first formed, and... 

One of the chief uses of sulphanilic acid is in the preparation of coloured derivatives of the methyhorange type (p. 214). 

When hydrochloric acid is cautiously added to an aqueous solution containing both sodium nitrite and the sodium salt of sulphanilic acid, NaOsSCgH NH, the amino group of the latter undergoes normal diazotisation, giving the diazonium chloride (A). The latter, however, ionises in solution, giving sodium and chloride ions and the internal salt (B), which possesses two opposite charges and is therefore neutral this internal salt is stable under... 

Required Anhydrous sodium carbonate, 2 g. sulphanilic acid, 7 g. sodium nitrite, 2-2 g. hydrochloric acid, 12 ml. dimethylaniline, 4 ml. 

Dissolve 2 g. of anhydrous sodium carbonate in 50 ml. of water contained in a 400 ml. beaker and add 7 g. of finely powdered crystalline sulphanilic acid (2H2O), warming the mixture gently in order to obtain a clear solution. Add a solution of 2 2 g. of sodium nitrite in 10 ml. of water and then cool the mixture in ice-water until the temperature has fallen to 5°. Now add very slowly (drop by drop) with continual stirring a solution of 8 ml. of concentrated hydrochloric acid in 15 ml. of water do not allow the temperature to rise above 10°. When all the acid has been added, allow the solution to stand in ice-water for 15 minutes to ensure complete diazotisation during this period fine crystals of the internal salt separate from the pink solution. Dissolve 4 ml. of dimethylaniline in a mixture of 4 ml. of concentrated hydrochloric acid and 10 ml. of water, cool the solution in ice-water, and add it slowly to the cold well-stirred diazo solution a pale red coloration is developed. Allow the mixture to stand for 5 minutes and then add slowly with stirring aqueous... 

C) Amino-aromatic sulphonic acids. Sulphanilic acid. 

B) SULPHONIC ACIDS. Aliphatic sulphonic acids are rarely encountered, for they are very soluble in water, and many are deliquescent. The aromatic sulphonic acids, although less uncommon, are encountered most frequently as their derivatives e.g.t the sulphonamides, pp. 247, 251), or as nuclear-substituted acids (e.g., sulphanilic acid, p. 384). 

Benzylthiouronium salts. Add 0 5 g. of sulphanilic acid to 10 ml. of water and 5 ml. of 10% NaOH solution, zndgently warm the shaken mixture until a clear solution is obtained. Cool, add 1 drop of phenol-phthalein solution, and then add dilute HCl dropwise with shaking until the pink colour is just discharged. Now add very dilute NaOH solution until the pink colour yt/rZ returns. Cool and add with shaking a solution of 0-5 g. of benzylthiouronium chloride in 5 ml. of water. The thiouronium salt rapidly separates filter at the pump, wash with water, drain and recrystallise from ethanol. Colourless crystals, m.p. 185°. (M.ps., p. 548.)... 

Amino aromatic sulphonic acid (sulphanilic acid)... 

Aromatic amine produced,. mine salts anilides aromatic amino-carboxylic acids sulphanilic acid, sulphanilamide. 

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 ... 

The azo dyes are not of any great practical value owing to their slight solubility in water. Th4 introduction of a sulphonic acid group into the molecide has no effect upon the colour, but renders the dye water-soluble—a fact of great commercial value. The simplest way of achieving this is to employ an amine, e.g., sulphanilic acid, in which the — OjH group is already present. 

By condensation of diazotised sulphanilic acid with p-naphthol in the presence of sodium hydroxide, the useful dyestuff Orange II (p-sulphobenzene-azo-3-naphthol) is obtained ... 

It is interesting to note that azo dyestuffs may be conveniently reduced either by a solution of stannous chloride in hydrochloric acid or by sodium hyposulphite. Thus phenyl-azo-p-naphthol 3delds both aniline and a-amino-p-naphthol (see formula above), and methyl orange gives p-aminodimethylaniline and sulphanilic acid ... 

In a 250 ml. conical flask place 10 -5 g. of sulphanilic acid dihydrate,... 

Reduction of methyl orange to />-aminodimethylaniline. Method 1. Dissolve 2 0 g. of methyl orange in the minimum volume of hot water and to the hot solution add a solution of 8 g. of stannous chloride in 20 ml. of concentrated hydrochloric acid until decolourisation takes place gentle boiling may be necessary. Cool the resulting solution in ice a crystalline precipitate consisting of sulphanilic acid and some p-aminodimethylaniline hydrochloride separates out. In order to separate the free base, add 10 per cent, sodium hydroxide solution until the precipitate of tin hydroxide redisaolves. Extract the cold solution with three or four 20 ml. portions of ether, dry the extract... 

Method 2. Suspend 2-0 g. of methyl orange in 4 ml. of water, and add a small quantity of sodium hyposulphite (Na2S204). Heat the mixture and add more sodium hyposulphite until the colour is discharged. The sulphanilic acid remains in the solution as sodium sulphanilate and the p-aminodimethyl-aniline may be extracted with ether as in Method 1. 

In a 500 ml. three-necked flask, fitted with a reflux condenser and mechanical stirrer, place 121 g. (126-5 ml.) of dimethylaniline, 45 g. of 40 per cent, formaldehyde solution and 0 -5 g. of sulphanilic acid. Heat the mixture under reflux with vigorous stirring for 8 hours. No visible change in the reaction mixture occurs. After 8 hours, remove a test portion of the pale yellow emulsion with a pipette or dropper and allow it to cool. The oil should solidify completely and upon boiling it should not smell appreciably of dimethylaniline if this is not the case, heat for a longer period. When the reaction is complete, steam distil (Fig. II, 41, i) the mixture until no more formaldehyde and dimethylaniline passes over only a few drops of dimethylaniline should distil. As soon as the distillate is free from dimethylaniline, pour the residue into excess of cold water when the base immediately solidifies. Decant the water and wash the crystalline solid thoroughly with water to remove the residual formaldehyde. Finally melt the solid under water and allow it to solidify. A hard yellowish-white crystalline cake of crude base, m,p. 80-90°, is obtained in almost quantitative yield. RecrystaUise from 250 ml. of alcohol the recovery of pure pp -tetramethyldiaminodiphenylmethane, m.p. 89-90°, is about 90 per cent. 

The presence of certain substituents e.g., the amino group) may markedly affect the solubibty and other properties of the sulphonic acid or carboxylic acid. Thus such sulphonic acids as the aminobenzenesul-phonic acids, pyridine- and quinoline-sulphonic acids exist in the form of inner salts or zwitter-ions that result from the interaction of the basic amino group and the acidic sulphonic acid. Sulphanilic acid, for example, is more accurately represented by formula (I) than by formula (II) ... 

Sulphanilic acid (IV,55, scale heat reaction mixture in oil bath at 180-190° for 30 minutes). 

---