Imidazoline derivatives titration

The ring opens at an appreciable rate at pH 10 and very rapidly at pH 13, and such compounds can be titrated only at pH 3. Imidazoline-derived quats having an amide structure with no ring, which may be the majority, would be expected to be titratable at all pHs, unless some other part of the structure is alkali-labile. 

Provided the solution is at least 0.1 M in hydrogen ion, betaines can be titrated potentiometrically with NaTPB. Vytfas et al. [18] successfully titrated cocodimethylbetaine, cocoamidopropylbetaine and an imidazoline derivative with NaTPB using the coated aluminium wire described in section 3.6.3. The potential changes at the end-point were not very large, and the method would probably be useful mainly for fairly pure samples such as raw materials rather than for products. 

Two-phase and potentiometric NaTPB titration at different pHs (section 7.1) will deal with some mixtures. Imidazolinium quats containing a ring structure are alkali-labile and titrate quantitatively only at pH 3 (but may give a variable and partial response at pH 10), alkylpyridinium and other aromatic nitrogen quats titrate at pH 3 and 10 and all others at pH 3, 10 and 13. The response of imidazoline-derived quats not containing a ring structure is uncertain they probably titrate at all pHs, but this would need to be confirmed for individual cases. 

In a few cases the formulae given above are oversimplified, in the sense that commercial materials contain other related compounds which may complicate their analysis. The complexity of a-olefin sulphonates has already been mentioned. With such mixtures, conversion of a titration volume to an active percentage is not straightforward, because it is debatable which constituents should be considered as actives, and the effective molecular weight is uncertain. A more complicated case is that of imidazoline and imidazolinium derivatives. The chemistry involved in the synthesis of these materials is very complex, and it seems likely that all the commercial materials contain a mixture of several different active structures [1,2]. 

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