Sulphonic acids

Reaction CXLVI. Action of Concentrated Sulphuric Acid on Hydrocarbons or Substituted Hydrocarbons.—When cone, sulphuric acid acts on an aromatic hydrocarbon or substituted hydrocarbon, one or more of the H atoms in the nucleus is replaced by the sulphonic group (S02.0H). 

Some sulphonic acids, e.g., benzene and toluene sulphonic acids, may be formed at ordinary temperatures, while others require a considerably higher temperature. In some cases 100% H2S04 (monohydrate—-S03.H20) is necessary. The influence of temperature (see table below), concentration of acid, time of reaction, and the presence of other substituents is very marked, and different isomers are formed under different conditions. 

The reaction may be assisted mechanically by mixing with kieselgiihr, or other finely divided material, and catalytically by the addition of iodine, or alkali metavanadate (U.S.P., 1915925) in the case of benzene, and of boric acid, mercury and mercury salts in the case of anthraquinone. 

The sulphonic group is strongly acidic, and will decompose carbonates with the formation of stable salts, a property which is used in their separation. The presence of a basic group in the nucleus is not sufficient to neutralise its acidity, thus sulphanilic acid is distinctly acid. 

Isolation of Sulphonic Acids.—Sulphonic acids are usually isolated in the form of their salts in order to get rid of the excess of sulphuric acid used in the reaction. The calcium or barium salts are formed where these are soluble by adding lime or barium carbonate, and the excess sulphuric acid precipitated as CaS04 or BaS04, and removed by filtra- 

Preparatimi.— While most papers relevant to this section deal with aromatic sulphonation, there are interesting developments too in reagents for introduction of the sulphonic acid grouping, and in the chemistry of aliphatic sulphonic acids. 

SO3 Insertion studies of polarized bonds include indium trialkyls and 

Alkane sulphonation by SOz + Oz and a-sulphonation of N-alkyl-j3-alanines illustrate conventional studies in sulphonic acid synthesis sulphonation at C-1 in cyclopentanesulphonic acid proceeds via a relatively stable mixed anhydride when SO3 is used as sulphonation reagent.  

Bisulphite addition to cytosine and cytidine 5 -phosphate - accounts for the accelerated deamination rates of these 4-amino-pyrimidines, optimum pH being 5 at high bisulphite concentration for maximum rates. 5-Carboxypyrimidine decarboxylation is catalysed by bisulphite through 

Bourgeois, G. Merault, N. Duffaut, and R. Galas, J. Organometcdlic Chem., 1973,59,145. 

Sulphuric Acid Derivatives.—In the aliphatic series we considered the hydroxyl derivatives immediately following the halogen derivatives because in that series the hydroxyl compounds are directly and eeisily prepared from the halogen substitution products by the action of silver hydroxide, AgOH, or sodium hydroxide, NaOH. In the benzene series the halogen derivatives are followed by the sulphuric acid derivatives because, in the first place, the halogen derivatives are not converted into hydroxyl compounds by treatment with silver hydroxide, and in the second place, because the sulphuric acid derivatives of the benzene hydrocarbons are easily formed directly from the hydrocarbons by action of sulphuric acid, which was not the case in the aliphatic series and because they are exceedingly important as they are readily transformed into other classes of compounds, e.g, hydroxyl compounds, phenols. 

Esters.—It will be recalled that in the aliphatic series there are two classes of derivatives of sulphuric acid. When sulphuric acid reacts with an alcohol neutralization takes place between the alcohol, as a base, and the sulphuric acid water, H—OH, is eliminated and a compound known as an ethereal salt or ester is obtained. 

Sulphonic Acids.—When, however, an aliphatic mercaptan or thio- lcohol is oxidized we obtain a compound, containing a sulphuric acid residue, known as a sulphonic acid. 

The sulphonic acids are also formed in the aliphatic series by the action of a salt of sulphurous acid upon an alkyl halide. 

Though these sulphonic acids are isomeric with the esters of sulphurous acid they do not react like esters, i.e. they are not hydrolyzed by water or alkalies yielding the alcohol and sulphurous acid. We, therefore, represent the difference between esters and sulphonic acids by the following formulas  

Preparation.—Few examples of insertion of SO3 into organometallic compounds have been reported, in contrast with corresponding reactions of sulphur dioxide recent examples are the formation of RS03Re(C0)s (R = Me, Ph, or p-tolyl) and MeHgS03Me from HgMe2 and SO3 at — 70 °C, further reaction giving methylmercuric methanedisulphonate, MeHgSaOgMe.  

Studies in aromatic sulphonation include full details of the rearrangement of sodium 1-naphthylsulphamate into the 4-sulphonate in dioxan-sulphuric acid, where S-studies show that the reaction is partly intramolecular. There are few syntheses of natural products offering an opportunity for employing aromatic sulphonation as an essential step, though a recent synthesis of the demethyl derivative establishes the structure of aeruginosin B as 2-amino-6-carboxy-10-methylphenazinium-8-sul-phonate. Ionization of aromatic sulphonic acids in aqueous sulphuric acid has been studied by u.v. spectroscopy, showing that the benzo-phenone H% and the acidity functions are followed substituent effects are small (Hammett p-value 0.7 0.2). 

Grignon-Dubois, J. Dunogues, and R. Galas, Tetrahedron Letters, 1976, 1197. 

Aminolysis of 1,3-propanesultones gives 3-aminoalkylalkanesulphonic acids. Useful procedures have been worked out for the oxidation of alkanethiols and aromatic disulphides to sulphonic acids. Optimum conditions for oxidation of alkanethiols by HNO3 involves cooling to 1—2 °C above the freezing point of the thiol in a Nj atmosphere.  

Sulphonation of [(cyclobutadiene)Fe(CO)3] and of [(cyclohexa-l,3-diene)-Fe(CO)3l has been described, leading to the Fe(CO 3 complex of the 5-sulphonic acid in the latter case.  

---

Dissolves in alkaline solutions to give purple-red solutions which are precipitated as lakes by heavy metal salts. Occurs naturally as a glucoside in madder but produced synthetically by fusing anthraquinone-2-sulphonic acid with NaOH and some KCIO3. Applied to the mordanted fibre. Al(OH)3 gives a bright red lake, Cr(OH)3 a red lake, FefOH) ... 

C. A typical aromatic amine. Best prepared by the prolonged action of concentrated ammonia solution at a high temperature upon anthraquinone-l-sulphonic acid in the presence of BaClj and by reduction of the corresponding nitro compound or by amination of the chloroanthraquinone. 

Anthraquinone can be brominated, chlorinated directly to the tetrachloro (I, 4, 5, 8-) stage, nitrated easily in the 1-position, but gives the 1,5-and 1,8-dinitro-derivalives on prolonged nitration the nitro groups in these compounds are easily displaced by neutral solutions of alkali sulphites yielding the corresponding sulphonic acids. Sulphonation with 20-30 % oleum gives the 2- 2,6- and 2,7-derivatives in the presence of Hg the 1- 1,5- and 1,8- derivatives are formed. 

Anthraquinone-J -sulphonic acid. Colourless leaflets, m.p. 214 C. It is used in the preparation of l-aminoanthraquinone. 

Ordinary commercial camphor is (-i-)-cam phor, from the wood of the camphor tree. Cinnamonum camphora. Camphor is of great technical importance, being used in the manufacture of celluloid and explosives, and for medical purposes, /t is manufactured from pinene through bornyl chloride to camphene, which is either directly oxidized to camphor or is hydrated to isoborneol, which is then oxidized to camphor. A large number of camphor derivatives have been prepared, including halogen, nitro and hydroxy derivatives and sulphonic acids. 

Usually prepared from the corresponding sulphonic acids by alkali fusion, methylation of phenol or from the aminotoluene by treatment with nitrous acid followed by boiling. Both o- and p-cresol are used as end components in azo dyes. 

Naphthalene-1-sulphonic acid crystallizes with 2HiO, m.p. 90 C. Used for the preparation of 1,8- and 1,5-nitronaphlhalene sulphonic acids. 

Naphihalene-2-sulphonic acid crystallizes with 3H2O, m.p. 83 C. It is also used for the preparation of nitro-derivatives. 

Naphthalene (risulphonic acids can be obtained by more drastic sulphonation of naphthalene or its mono- and disulphonic acids. Only the 1,3,5-, 1,3,6- and 1,3,7-acids are obtained. The most important of the iri-sulphonic acids is the 1,3,6-acid which is used for the preparation of H-acid, a dyestufT intermediate. 

Neville-Wintber acid The trivial name given to 4-hydroxy-1-naphthalene sulphonic acid. 

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. 

Perfluoroalkyl derivatives have important technical uses, e.g. sulphonic acids as surfactants introduction of perfluoroalkyl groups confers useful properties on many drugs. 

Phenylhydrazine condenses with acetoacetic ester to give a pyrazolone derivative which on methylation gives phenazone. The sulphonic acid similarly gives rise to the tartrazine dyestuffs. It is used to make indole derivatives by the Fischer process. 

Schaffer s acid, CioHg04S. 2-hydroxy-7-naphthalene sulphonic acid. Obtained by sulphonating 2-naphthol with a small amount of sulphuric acid at a higher temperature than is used for the preparation of crocein acid. A valuable dyestuff intermediate. 

The sulphonic acids are usually prepared by the action of sulphuric acid upon a compound. The concentration of the acid and the temperature of reaction are varied according to the reactivity of the compound. Often oleum is used or even chiorosulphonic acid. Alternatively sulphur trioxide complexed to pyridine or dioxan can be used with reactive substrates. Aminosulphonic acids such as sulphanilic and naphthionic acids are most conveniently prepared by heating the sulphate of the amine at ISO C. 

The sulphonic acids are strongly acidic compounds, very soluble in water and readily give water-soluble metallic salts. 

The most important reaction of the sulphonic acids is their conversion into phenols by fusion with caustic alkalis. When they are fused with potassium cyanide, nitriles are obtained, e.g. benzonitriie from ben-zenesulphonic acid. 

CaH803. Fine white needles, m.p. 82°C, b.p. 285°C, strong vanilla odour, characteristic taste. It occurs extensively in nature, and is the odoriferous principle of the vanilla pod it can be obtained from the glucoside coniferin. Vanillin is made commercially from the ligno-sulphonic acid obtained as a by-product in the manufacture of wood pulp. It is one of the most important flavouring and perfuming... 

Aromatic nitriles (or aryl cyanides) can be obtained by methods (1) and (3). but not by method (2). In addition, aromatic nitriles can be prepared by two other methods, (a) from the corresponding diazo compound by Sandmeyer s Reaction (p. 189), (b) by fusing the corresponding sulphonic acid (or its salts)... 

If phenol is heated with more concentrated nitric add (in the presence of sulphuric acid), nitration occurs ultimately at the para and at both the ortho positions, giving picric acid or 2,4,6-trinitrophenol. To prepare picric acid, however, it is more convenient first to heat the phenol with sulphuric acid, whereby a mixture of 0- and p-phenol sulphonic acids is readily obtained. If this mixture is now heated with concentrated nitric acid, nitration occurs at the... 

Aromatic sulphonic acids are frequently difficult to obtain pure, since they almost invariably decompose on attempted distillation, and many are very soluble in water such aqueous solutions on being concentrated often give syrupy solutions from which the sulphonic acid crystallises with difficulty. 

Toluene however sulphonates readily, and the following preparation illustrates the rapid formation of toluene-p ulphonic acid mixed with a small proportion of the deliquescent o-sulphonic acid, and the isolation of the pure crystalline /lara-isomer. 

This direct sulphonation should be compared with the indirect methods for the preparation of aliphatic sulphonic acids, e.g., oxidation of a thiol (RSH -> RSOjH), and interaction of an alkyl halide with sodium sulphite to give the sodium sulphonate (RBr + Na,SO, -> RSO,Na + NaBr). 

A further crystallisation from 15 ml. of hydrochloric acid gives the sulphonic acid, 5 5 g., m.p. 105°, almost devoid of deliquescent properties. 

The Schotten-Baumann reaction may also be carried out, using, for example, benzene sulphonyl chloride, CeH,SO,Cl (. e., the acid chloride of benzene sulphonic acid, C H5SOjOH) in place of benzoyl chloride, and similar deri a-tives are obtained. Thus when phenol is dissolved in an excess of 10% sodium hydroxide solution, and then shaken with a small excess of benzene sulphonyl... 

---