Cation sequences arabinate

The survey shows that by introduction of OH groups into oleate, the cation sequences change in the direction of those characteristic of arabinate, hexaoxystearate showing at pH 6 already almost wholly the sequences of arabinate. 

Fig. 47. Cation sequences for the reversal of charge of Na arabinate in water (a) or in 25, 40, and 50% acetone (b) and for the flocculation maxima of gum arabic in 30, 40 and 50% alcohol (c). The concentrations in c were taken from Fig. 46 (intersections of the curves with horiziontal lines at 30, 40 or 50% alcohol).

In order to check this supposition, Teunissen, Rosenthal and Zaayer compared the reversal of charge concentrations of oleate, trioxystearate, hexaoxystearate and arabinate for the alkali and alkaline earth cations. In this investigation also another factor — the influence of pH — showed it self very markedly. In the following survey the reversal of charge sequences at different pH values follow one another in such a way, that the inverse sequence for oleate (at pH 10 but also at pH 7) and arabinate (at pH 10 but also at pH 6) are interlinked as successively as possible. The intermediate sequences have in part the character of transition series ( 2g) ... 

Actually one would also expect the sequences mentioned under (d) and (e) to be reversed. That this however did not occur is an indication that the polarisability of the COO group of the arabinate is only but little stronger than that of water. One is concerned here in fact with large and relatively large ions, the polarising action of which is the smallest. Sequences occur here which on neglecting polarisation effects are precisely the ones which may be expected as a consequence of the decrease of the hydration of the cations with increasing ion volume. 

---

See also in sourсe #XX -- [ ]

---