Sulphonic acids isolation

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. 

Because of the great solubility of sulphonic acids in water and the consequent difficulty in crystallisation, the free sulphonic adds are not usually isolated but are converted directly into the sodium salts. The simplest procedure is partly to neutralise the reaction mixture (say, with solid sodium bicarbonate) and then to pour it into water and add excess of sodium chloride. An equilibrium is set up, for example ... 

Sulphonic acids are frequently crystalline solids, readily soluble in water and often hygroscopic. Because of the difficulty of isolation of the free acids, they are usually encountered as the alkah metal salts. 

Hydrolysis of a sulphonamide. Mix 2 g. of the sulphonamide with 3-5 ml. of 80 per cent, sulphuric acid in a test-tube and place a thermometer in the mixture. Heat the test-tube, with frequent stirring by means of the thermometer, at 155-165° until the solid passes into solution (2-5 minutes). Allow the acid solution to cool and pour it into 25-30 ml. of water. Render the resulting solution alkaline with 20 per cent, sodium hydroxide solution in order to liberate the free amine. Two methods may be used for isolating the base. If the amine is volatile in steam, distil the alkaline solution and collect about 20 ml. of distillate extract the amine with ether, dry the ethereal solution with anhydrous potassium carbonate and distil off the solvent. If the amine is not appreciably steam-volatile, extract it from the alkaline solution with ether. The sulphonic acid (as sodium salt) in the residual solution may be identified as detailed under 13. 

Dehydrocorydaline eontains four methoxyl groups. On reduetion it furnishes two stereoisomerides of eorydaline, m.p. 135°, and m.p. 158-9° (163-4° vac.), Spath) the latter ( 2f.9oeorydaline) by erj stallisation of the d-eamphorsulphonate can be partially separated into d- and Z-forms, the d-form of which is not identical with natural corydaline.The second isomeridc, m.p. 135°, has not been resolved into optically active components, but from the sulphonic acid the Z-compoiient has been isolated by crystallisation of the brucine salt, and this is taken to indicate that the inactive corydaline, m.p. 135°, is dZ-corydaliiie. °... 

The first report of the use of bromine for the oxidation of sulphoxides appeared in 1966116. Diphenyl sulphone was isolated in 0.5-1% yield when the sulphoxide was treated with bromine in aqueous acetic acid for several hours. The yield was increased to about 5% by quenching the reaction with sodium carbonate. A kinetic study117 of a similar reaction involving dimethyl sulphoxide showed no significant yield improvement but postulated that the mechanism proceeds via an equilibrium step forming a bromosulph-onium type intermediate which reacted slowly with water giving dimethyl sulphone as indicated in equation (35). 

Upon heating anthraquinone with fuming sulphuric acid at 160° for about 1 hour, the main product Is anthraquinone-p-sulphonic acid, which is isolated as the sparingly soluble sodium salt. The latter when heated imder pressure with sodium hydroxide solution and an oxidising agent (sodium or potassium chlorate) yields first the corresponding hydroxy compound further hydroxy-lation occurs in the a-position through oxidation by the chlorate and 1 2-di-hydroxyanthraquinone (alizarin) is formed. 

H acid (4.2) is possibly the most important single naphthalene-based intermediate. The preparation of this intermediate starts with a high-temperature sulphonation of naphthalene using 65% oleum (anhydrous sulphuric acid in which 65% by mass of sulphur trioxide has been dissolved) to give mainly naphthalene-1,3,6-trisulphonic acid, the nitration product from which is purified by selective isolation. Reduction of the nitro group followed by hydrolysis of the 1-sulphonic acid substituent by heating with sodium hydroxide solution at 180 °C completes the process (Scheme 4.27). 

In all the above sequences, single isomers are produced by careful control of the reaction conditions combined with purification by selective isolation at various points in the synthesis. Occasionally two isomers are produced which give dyestuffs that have very similar properties in these cases it is often quite acceptable and economically beneficial not to separate the individual components but to use the total mixture in dye preparation. An example is the mixture of l-naphthylamine-6- and 7-sulphonic acids (4.46 mixed Cleve s acids), which arises by nitration and reduction of naphthalene-2 Sulphonic acid (Scheme 4.30). 

That this is the course of the reaction is proved by the possibility of isolating the sulphaminic acid corresponding to a-naphthylamine if mild experimental conditions are chosen. At a higher temperature the naphthylsulphaminic acid is converted into l-naphtbylamine-4-sulphonic acid (naphthionic add). 

Each of the compounds mentioned, therefore, should exist in a racemic form and two optically active forms. After Werner had succeeded in isolating optically active forms of the corresponding cobalt compound, he attempted to isolate, by the same means, isomers of the chromic series. Optically active tartaric acid, chloro- or bromo-tartarie acid, eamphor-sulphonic acid, and brom-eamphor-sulphonic acid proved unsatisfactory, since the aqueous solutions change on evapora-... 

In the sulphite pulping process wood cut into pieces is subjected to kiering in a calcium bisulphite solution under a pressure of 3-8 kg/cm2, at 120-145°C for 7-30 hr. The higher the temperature, the shorter the time of boiling. Substances accompanying cellulose dissolve in the liquor. Lignin is converted into a soluble lignin sulphonic acid. Cellulose is isolated from the solution, known as sulphite cellulose lye, and washed with water. 

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-... 

When the sulphonic acid produced by the interaction of chlorosulphonic acid has to be nitrated afterwards, it must be isolated previous to nitration, otherwise the chlorine liberated may form chloro-derivatives. 

The preparation and isolation of S-benzylisothiouronium chloride by the interaction of benzyl chloride and thiourea is described in Expt 5.203. On recrystallisation the compound separates in either, or sometimes as both, of two dimorphic forms, m.p. 150 and 175 °C respectively. The former may be converted into the higher m.p. form by dissolving it in ethanol and seeding with crystals of the form, m.p. 175 °C the low m.p. form when warmed to 175 °C gives, after solidification, a m.p. of 175 °C. The compound is of particular interest as a reagent for the characterisation of carboxylic acids or sulphonic acids with which it forms the S-benzylisothiouronium carboxylate (or sulphonate) salts (Sections 9.6.15, p. 1264, and 9.6.26, p. 1285). Both dimorphic forms give identical derivatives. 

The sulphonation of toluene (Expt 6.37) with concentrated sulphuric acid at 100-120°C results in the formation of toluene-p-sulphonic acid as the chief product, accompanied by small amounts of the ortho and meta isomers these are easily removed by crystallisation of the sodium salt of the para isomer in the presence of sodium chloride. Sulphonation of naphthalene at about 160°C yields largely the 2-sulphonic acid (the product of thermodynamic control) (Expt 6.38) at lower temperatures (0-60 °C) the 1-sulphonic acid (the product of kinetic control) is produced almost exclusively. In both cases the product is isolated as its sodium salt. In anthraquinone the carbonyl groups deactivate the aromatic nucleus towards electrophilic attack and vigorous conditions of sulphonation are required, i.e. oleum at about 160 °C. The product is largely sodium anthraquinone-2-sulphonate (Expt 6.39). 

The free sulphonic acids [e.g. toluene-p-sulphonic acid, for preparation see, Expt 6.37, Note (1)], as opposed to their sodium salts, may sometimes be obtained directly if the sulphonation reaction is carried out with continuous removal of the water formed in the reaction, conveniently by using a Dean and Stark water separator. p-Xylene-2-sulphonic acid (Expt 6.40) is an example of a sulphonic acid whose solubility in water is such that it crystallises directly from the reaction medium and hence it may readily be isolated. 

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