Extraction of monosulphonic acids

Many monosulphonates can be extracted from 3 M hydrochloric acid with diethyl ether. Disulphonates and hydrotropes which are low-molecular-weight sulphonates are not extracted. In the case of a-olefin sulphonates the hydroxyalkane sulphonates are converted to sultones and extracted with the monosulphonic acid. The method is applicable to alkylbenzene sulphonates, mono- and dialkylsulphosuccinates and a-olefin sulphonates, but apparently not to alkane sulphonates. 

Dissolve in the minimum quantity of water. Transfer to a separating funnel, using sufficient water to bring the total volume to 75 ml. 

Extract with three 50 ml portions of diethyl ether. Keep the aqueous layer for extraction of disulphonic acids if necessary. 

Combine the ether extracts and wash with two 25 ml portions of 3M hydrochloric acid. Add the acid washes to the main aqueous extract. 

Evaporate almost to dryness in a tared beaker (caution flammable vapour) (see Note 2). 

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