Sulphones potentiometric titrations

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. 

Titration to two successive end-points, usually inflections in potentiometric titration but sometimes with two indicator colour changes1,3,5,11,12,18,26-29. The first-end-point corresponds to reaction of the sulphonic acid(s) and the first proton of the sulphuric acid, the second to titration of the whole. The titration of the sulphonic acid(s) can then be obtained from the difference. 

Titration with benzethonium chloride in acid solution measures the sulphonated ester plus the sulphonated carboxylic acid, only the sulphon-ate group of the latter being titrated. In alkaline solution the titration measures the sulphonated ester plus twice the sulphonated carboxylate, both the sulphonate and the carboxylate group being titrated. Alpha-sulphonated esters give poor potentiometric titration curves, and two-phase titration is strongly preferred. 

The ester cannot be determined by saponification because this slowly removes the sulphonate group as well as hydrolysing the ester group. It can be determined by acid hydrolysis followed by measurement of the a-sulphonated carboxylate salt produced, either by potentiometric titration of the weak acid or by two-phase titration with benzethonium chloride. Both procedures measure the a-sulphonated ester plus the unsulphonated ester. If the latter is present at a significant level, it can be determined (section 5.11.2) and corrected for. 

All may be determined by two-phase or potentiometric titration with benzethonium chloride. Titration of sulphosuccinamates in acid solution measures the sulphonate group alone (but see section 5.13.3), and titration in alkaline medium measures the carboxylate group as well (cf. section 5.11.3). Sulphosuccinamates, possessing a carboxylate group, can also be determined by potentiometric acid-base titration. 

EEC titration in alkaline solution measures both species. EEC titration in acid solution measures only the sulphate or sulphonate. Potentiometric acid-base titration in alcoholic solution measures only the carboxylate. 

Obtemperanskaya and Kareva25 determined a, /J-unsaturated ketones and sulphones by adding sodium sulphite to the sample in p-dioxan. After 5-10 min they titrated with standard sulphuric acid potentiometrically or to thymolphthalein ... 

The products of hydrolysis of sulphonyl halides, i.e. sulphonic and hydrohalic acids, can be easily titrated with bases, which accelerate the hydrolysis as well. Thus Cundiff and Markunas titrated potentiometrically benzenesulphonyl chloride (and sulphuric acid) in pyridine with tetrabutylammonium hydroxide in benzene/methanol251. Jansseune and Janssen252 titrated sulphonyl fluorides in butylamine with potassium methoxide. Krivoruchko253 estimated 2-chloroethanesulphonyl chloride in air by hydrolysing it with alcoholic potassium hydroxide and determining the chloride ion colorimetrically or nephelometrically. Jansseune and Janssen252 also hydrolysed sulphonyl fluorides with alkali, acidified the mixture, distilled the HF and titrated it with alkali. 

Several neutralization-type reactions have been followed by potentiometric and conductometric techniques, and diethylamine, morphine, urea and triphenyl-carbinol have been titrated with toluene sulphonic acid. 

The combined sulphonated carboxylic acid and fatty acid or their salts are determined by potentiometric acid-base titration, after oxidation of sulphite/sulphur dioxide. 

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