Benzenesulphonic acid

CH3CH(0H)C(0)0Et. A colourless liquid with a pleasant odour, b.p. 154 C. Manufactured by distilling a mixture of ( )-lactic acid, ethanol and benzene in the presence of a little sulphuric or benzenesulphonic acid. It is a solvent for cellulose nitrate and acetate and also for various resins. Used as a lacquer solvent. 

A further difference between aliphatic and aromatic hydrocarbons is that only the latter are capable of direct sulphonation. Thus benzene when heated with concentrated sulphuric acid gives benzenesulphonic acid, a reaction which proceeds more readily, however, if chlorosulphonic acid is used instead of sulphuric acid an excess of chlorosulphonic acid however may convert the sul phonic acid into the sulphonyl chloride (c/. p. 181). 

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. 

Supplement (combined with Volume XII) XI, 2nd 1933 1605-1739 2. Sulphonic acids Benzenesulphonic acid, 26. p-Toluenesulphonic acid, 97. Naphthalene - sulphonic acid, 155. Hydroxy-Sulphonic acids Phenol-sulphonic acid, 234. Naphthol-sulphonic... 

Many aromatic compounds are sufficiently basic to be appreciably protonated in concentrated sulphuric acid. If nitration occurs substantially through the free base, then the reactivity of the conjugate acid will be negligible. Therefore, increasii the acidity of the medium will, by depleting the concentration of the free base, reduce the rateof reaction. This probably accounts for the particularly marked fall in rate which occurs in the nitration of anthraquinone, benzoic acid, benzenesulphonic acid, and some nitroanilines (see table 2.4). 

Some interesting results have been obtained by Akand and Wyatt56 for the effect of added non-electrolytes upon the rates of nitration of benzenesulphonic acid and benzoic acid (as benzoic acidium ion in this medium) by nitric acid in sulphuric acid. Division of the rate coefficients obtained in the presence of nonelectrolyte by the concentration of benzenesulphonic acid gave rate coefficients which were, however, dependent upon the sulphonic acid concentration e.g. k2 was 0.183 at 0.075 molal, 0.078 at 0.25 molal and 0.166 at 0.75 molal (at 25 °C). With a constant concentration of non-electrolyte (sulphonic acid +, for example, 2, 4, 6-trinitrotoluene) the rate coefficients were then independent of the initial concentration of sulphonic acid and only dependent upon the total concentration of non-electrolyte. For nitration of benzoic acid a very much smaller effect was observed nitromethane and sulphuryl chloride had a similar effect upon the rate of nitration of benzenesulphonic acid. No explanation was offered for the phenomenon. 

Cross-alkylations have been reported on a number of occasions. Thus, ethylbenzene when treated with aluminium bromide and hydrogen bromide at 0 °C forms some benzene and diethylbenzene168, and in the sulphonation of durene some trimethyl- and pentamethyl-benzenesulphonic acids are formed as well as the tetra-methyl compound. It has been suggested169 that these transfer reactions involve an SN2 type process... 

The application of / -(diphenylphosphinyl)benzenesulphonic acid (58) to the synthesis of esters of amino-acids has made the work-up much simpler, since the resultant oxide is water-soluble. Diphenylphosphinyl isocyanate (59) can be prepared from diphenylphosphinic amide. 

Because of the tendency to revert to the stable aromatic ring system, the intermediate product (shown in brackets) will lose water and change into benzenesulphonic acid. 

In the preparation of benzenesulphonic acid, diphenylsulphone is produced as a by-product. The benzene sulphonic acid which is first formed itself acts on benzene, just as sulphuric acid does, and water... 

On Sulphonyl Chlorides and Sulphonamides.—The conversion of benzenesulphonic acid into its chloride and amide shows that derivatives of sulphonic acids, analogous to those of carboxylic acids, can be obtained. The sulpho-chlorides are much less reactive than are the chlorides of the carboxylic acids benzene sulphochloride, for example, can be dis-stilled in steam almost without decomposition. 

The monoprotonation of p-[(/>-dimethylamino)phenyI]-azo-benzenesulphonic acid (methyl orange) also gives a mixture of the azonium ion and the ammonium ion, in which the former predominates according to Reeves (1966). Bolton et al. (1973). however, using linear free energy relationships, conclude that the ammonium form is dominant, and question the general acceptance of the tautomeric model for the protonation of p-aminoazobenzene and its derivatives. 

Some benzenesulphonic acids with an electron withdrawing carboxyl group in the ring will also undergo carbon-sulphur bond cleavage [83]. 

The addition of phosphine to olefins is accelerated by acidic and basic catalysts. Under the influence of non-oxidising acids or Lewis acid such as, for example, methanesulphonic acid, benzenesulphonic acid, trifluoro-acetic acid or boron trifluoride phosphine is quickly added to olefins at pressures of 20-40 at, and temperatures of 30-60 °C. It is assumed that the reaction proceeds via a carbonium ion which is first formed thus ... 

HCl, then crystd from dilute HCl (charcoal) to remove benzenesulphonic acid. It has been crystd from... 

HC1, then crystd from dilute HC1 (charcoal) to remove benzenesulphonic acid. It has been crystd from EtOH/water. Dried in a vacuum desiccator over solid KOH and CaCl2. p-Toluenesulphonic acid can be dehydrated by azeotropic distn with benzene or by heating at 100° for 4h under water-pump vacuum. The anhydrous acid can be crystd from benzene, CHCI3, ethyl acetate, anhydrous MeOH, or from acetone by adding a large excess of benzene. It can be dried under vacuum at 50°. 

---