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Aggregation in Aqueous Solutions: Solochrome Black WDFA
Author(s) -
Coates E.,
Rigg B.,
Murton R.,
Smith D. H.
Publication year - 1963
Publication title -
journal of the society of dyers and colourists
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 0037-9859
DOI - 10.1111/j.1478-4408.1963.tb02511.x
Subject(s) - chemistry , dimer , dissociation constant , aqueous solution , molar absorptivity , dissociation (chemistry) , ion , electrolyte , equilibrium constant , titration , stability constants of complexes , analytical chemistry (journal) , inorganic chemistry , ion association , chromatography , organic chemistry , biochemistry , physics , receptor , electrode , optics
The second and third ionisation constants for pure Solochrome Black WDFA (C.I. Mordant Black 11; C.I. 14645; sodium 1‐(1‐hydroxy‐2‐naphthylazo)‐6‐nitro‐2‐naphthol‐4‐sulphonate =DH 2 Na + )† have been determined spectrophotometrically at 25·C in aqueous solutions (p K TD = 6·0: p K = 12·0). The variation with dye concentration of the apparent molar extinction coefficient for the dye ion (DH 2‐ ) at pH approx. 9 has been interpreted as being due to the formation of a dimer, the dissociation constant for which is given by p K TD = 3·0. A theoretical interpretation of pH‐titration data for the dye over the pH range 5·5–8 has permitted the calculation of the dissociation constants for several equilibria that exist in this complex system. The singly charged ion DH can exist in equilibrium with a dimer (p T K TD = 5·3), which has acidic ionisation constants represented by p T K TD = 6·7 and p T K TD = 7·7. The dissociation constant for the complex formed between DH and DH is given by p K TD = 4·7. There is no evidence for association of D 3‐ ions, the visible absorption spectrum for which is essentially unaffected by a change in the dye concentration or by the presence of electrolytes. Only slight changes occur in the spectrum for DH 2‐ , obtained at a constant dye concentration (ca. 10 ‐4 m ) by the addition of electrolytes such as soluble salts of Na + , K + , Ba 2+ , and Cr 3+ . However, at very low concentrations (ca. 10 ‐5 m ) of some salts (Cr 3+ ), marked differences from the spectrum for the pure dye in the form DH have been noted. The magnitude of the effect is dependent essentially on the concentration, nature, and charge of the positive ions. It is suggested that, under these conditions, micellisation of the dye DH occurs, with positively charged gegenions.