Sulphonamides sulphonic acids

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). 

B) Sulphonamides. Mix 0 5 g. of the sulphonic acid or its alkali salt with 15 g. of phosphorus pentachloride, and heat under reflux in a silicone- or oil-bath at 150° for 30 minutes then allow it to cool. 

Sulphonic Acids. Benzylthiouronium salts (p. 359), Sulphonamides and sulphonanilides (p. 354). 

Dissolve 1 0 g. of the compound in 5 ml. of dry chloroform in a dry test-tuhe, cool to 0°, and add dropwise 5g. (2-8 ml.) of redistilled chloro-sulphonic acid. When the evolution of hydrogen chloride subsides, allow the reaction mixture to stand at room temperature for 20 minutes. Pour the contents of the test-tube cautiously on to 25 g. of crushed ice contained in a small beaker. Separate the chloroform layer and wash it with a httle cold water. Add the chloroform layer, with stirring, to 10 ml. of concentrated ammonia solution. After 10 minutes, evaporate the chloroform on a water bath, cool the residue and treat it with 5 ml. of 10 per cent, sodium hydroxide solution the sulphonamide dissolves as the sodium derivative, RO.CgH4.SO,NHNa. Filter the solution to remove any insoluble matter (sulphone, etc.), acidify the filtrate with dilute hydrochloric acid, and cool in ice water. Collect the sulphonamide and recrystallise it from dilute alcohol. 

Dilute sodium hydroxide solution. Carboxylic acids (RCOOH), sulphonic acids (RSO3H), phenols (ArOH), thiophenols (ArSH), mer-captans (RSH), imides (RCONHCOR), aryl sulphonamides (AxSOjNHj), arylsulphonyl derivatives of primary amines (AxSOjNHR), oximes (RCH=NOH), primary and secondary nitro compounds (RCH=NOOH and RjC=NOOH-oci forms), and some enols (e.g., of 1 3-diketones... 

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. 

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 amides derived from sulphonic acids are called sulphonamides. They are obtained from amines by the reaction with sulphonyl chloride (R SOCl2) in pyridine. 

The following structures indicate the range of aromatic sulphonic acids (1), sulphinic acids (2), sulphonyl chlorides (3), sulphonamides (4) and sulphonate esters (5) to be discussed below. 

Polyhydroxy- phenols. amino acids, di- and polyamino compounds, amino alcohols. Sulphonic acids. Sulphinic acids. Salts. sulphinic acids, aminosulphonic acids and sulphonamides. Some diketones and /3-keto esters. Ethers and acetals. Lactones. Acyl halides. Diaryl ethers. intermediate reduction products of nitro compounds. Sulphones, sulphonamides of secondary amines, sulphides, sulphates and other sulphur compounds. 

Sulphonacetamides are derivatives of sulphonamides (Section 9.6.27, p. 1286), but since the latter are readily prepared from the sulphonic acids or their salts, sulphonacetamides may be employed for the characterisation of sulphonic adds for this reason they are included in this Section. 

Sulphonic acid B.P. °C Sulphonyl chloride, B.P. °C Sulphonamide, M.P. °C 5-Benzyl-isothio-uronium salt M.P. °C Sulphon- aniltde M.P. °C... 

This section is devoted mainly to the derivatization and GC of thiols, sulphonic acids and related compounds. The GC of other sulphur compounds (sulphones, sulphonamides, etc.) is also mentioned in other sections, e.g., Pharmaceuticals, Insecticides. 

The NMR and ESR spectra of sulphonic acids TABLE 32. 15N NMR chemical shifts for some sulphonamides... 

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