Classification by acid and alkaline hydrolysis

The different classes of surfactant respond in various ways when exposed to hydrolytic conditions. This provides a basis for a broad classification. 

Amides in general can be hydrolysed, but with difficulty. N-acyltau-rates and methyltaurates, sulphosuccinamates and sarcosinates are hyd-rolised by boiling under pressure for 6 h at 150-160 C in 6 M hydrochloric acid [5]. Alkanolamides require rather less extreme conditions boiling for 8 h with 6 M hydrochloric acid is adequate. 

The sulphonate group itself is generally very resistant to hydrolysis, but in the case of fatty ester a-sulphonates the sulphonate group is removed by several hours boiling with 1 M alkali. Acid hydrolysis, however, has no effect. 

ISO 2869 [6] and ISO 2870 [7] deal with the determination of alkali-and acid-hydrolysable detergents respectively. ISO 2869 prescribes boiling 25 ml of a 0.003-0.005 M solution for 30 min with 5 ml of aqueous 10 M sodium hydroxide. ISO 2870 prescribes boiling a similar sample for 3h with 5 ml of aqueous 5M (490 g/1) sulphuric acid. In both cases the hydrolysed solution is neutralised and titrated with benzethonium chloride (see section 3.5). In the acid treatment, [H ] is only 1.67 M, and this may be insufficient for complete hydrolysis of the more resistant titratable species. Both methods should be used where appropriate, but ISO 2870 may not be universally valid, and if it is used for products containing 

The main classes respond as outlined below. It is necessary to identify and quantify the hydrolysis products, and methods are given in chapter 5. 

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