Sulphonic acids, aromatic

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. 

B) Sulphonic Acids. Simple aromatic sulphonic acids. 

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). 

Aromatic sulphonic acids are usually soluble in water, forming a strongly acidic solution. 

C) AMINO AROMATIC SULPHONIC ACIDS. Sulphanilic or p-amino-benzene sulphonic acid, NH2CJH4SO3H. 

These salts are by far the most readily prepared derivatives (having sharp m.ps.) of the amino-aromatic sulphonic acids. 

Amino Aromatic Sulphonic Acids. Benzylthiouronium salts (p. 384). 

Amino aromatic sulphonic acid (sulphanilic acid)... 

COMPOUNDS DERIVED FROM AROMATIC SULPHONIC ACIDS... 

Sulphonic acids. The aromatic sulphonic acids and their alkali metal salts are soluble in water, but insoluble in ether (Solubility Group II). They are best characterised by conversion into crystalline S-benzyl-iso-thiuronium salts (see Section IV,33,2 and 111,85,5), which possess characteristic melting points. A more time-consuming procedure is to treat the well-dried acid or... 

Exposure of the ethylidene diacetate to an aromatic sulphonic acid in the presence of five times its weight of acetic anhydride as diluent at 136°C will yield the following mixture 40% vinyl acetate 28% acetic acid 20% acetic anhydride 4% ethylidene diacetate 8% acetaldehyde. 

The majority of aromatic sulphonic acids aie very soluble in water, and are difficult to obtain in the crystalline form On the other hand, the sodium or potassium salts generally ciystal-lise well, and it is customary to prepare them by pouiing the sulphonic acid directly after sulphonation into a strong solution of sodium or potassium chloride (Gattermann). 

Generally, the results of the measurements indicated that, where dissociation constants were determined by conductometry and also potentiometric titration, they were in agreement with each other further, KHX is low, e.g., about 10 4-10 6moll 1 for aromatic sulphonic acids and 10 13-10 16 moll-1 for carboxylic acids, Xhx2 is high, e.g., 102-104, and KBis low again, e.g., 10 5-10 6 for aliphatic amines and 10 10 for aromatic amines. 

An aromatic sulphonic acid amide-------NaCI° ----> A Monochloramine... 

Fig. 3.107. Comparison of micro-HPLC separations of aromatic sulphonic acids in different mobile phases (a) 0.005 M tetrabutylammonium hydrogensulphate (TBAS) in 15 per cent (v/v) methanol in water (1) Laurent acid, (2) amino-F-acid, (3) Cleve-1,6- and Peri acids, (4) unidentified impurity, (5) Cleve-1,7-acid and (6) unidentified impurity, (b) 0.005 M tetrabutylammonium hydrogensulphate (TBAS) in 15 per cent (v/v) methanol in water with 0.01 M /Lcyclodextrin (CD) (1) Laurent acid, (2) amino-F-acid, (3) Cleve-1,6-acid, (4) Peri acids, (5) unidentified impurity, (6) Cleve-1,7-acid and (7) unidentified impurity. Column, Biosphere Si C18, 162 X 0.32 mm i.d. flow rate 5 pl/min, column temperature ambient, detection, UV, 220-230 nm. Reprinted with permission from P. Jandera et al. [164].

Aliphatic and aromatic sulphonic acids have been reduced to symmetrical disulphides in almost quantitative yields using potassium iodide and ethyl polyphosphate... 

Aromatic sulphonic acids, 554 compounds derived from, 820 reactions and characterisation of, 552, 1077 ... 

Sulphones, 500, 1078 Sulphonephthaleins, 989, 990 Sulphonic acids, 548, 557, 1077 see also under Aromatic sulphonic acids alkyl esters of, 1079 ... 

This would have both a solvent effect and a mass law effect on the rate of ester formation. The error is systematic, since it is most serious for the slower ester formation reactions, and consequently the p value calculated by Jaffe144 from the data of Hartman and Borders142 is not accurate. Later workers allowed for this side-reaction 46 or used aromatic sulphonic acids rather than HC1 as the catalyst145147. However, whatever the exact p values, it is quite clear that the polar effects of substituents on acid-catalyzed ester hydrolysis and formation are small. 

A somewhat similar method of cyanide preparation is applicable in the aromatic series aromatic sulphonic acid potassium salts, on fusion with potassium cyanide or potassium ferrocyanide, yield aromatic nitriles. The reaction can be extended to derivatives of pyridine. 

Reaction LXXV. Fusion of Aromatic Sulphonic Acids with Caustic Alkalis. (Z. Ch (1876), 3, 299 J. pr., [2], 17, 394 20, 300.)—This method is of technical importance as it is employed to prepare phenols and naphthols from the parent hydrocarbons. These phenols and naphthols are much used as intermediates in the dye industry. The method cannot easily be applied to determine structure, owing to rearrangement liable to occur at the elevated temperatures. Caustic potash is more convenient than soda, since it generally yields a more easily fusible mixture. 

The compounds formed are termed sulphones they are also formed by the action of cone, and fuming sulphuric acid on hydrocarbons (see p. 313), and by heating aromatic sulphonic acids with an aromatic hydrocarbon in presence of a dehydrating agent, such as P205. 

Soluble polyaniline has been reported as being prepared in the presence of aromatic sulphonic acids 272). 

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