
%0 Journal Article
%A Florence, TM 
%A Farrar, YJ 
%A Zittel, HE 
%T Dihydroxyanthraquinone complexes of zirconium
%J Australian Journal of Chemistry
%D 1969/11/01
%V 22
%N 11
%P 2321-2332
%K 
%R https://doi.org/10.1071/CH9692321
%U https://www.publish.csiro.au/paper/CH9692321 
%X The nature of the zirconium complexes of alizarin red S (1,2-dihydroxy- anthraquinone-3-sulphonate), alizarin (1,2-dihydroxyanthraquinone), and hystazarin (2,3-dihydroxyanthraquinone) were studied using spectrophotometric, kinetic, and voltammetric techniques. In HClO4- NaClO4, 75% methanol media, these compounds form 1 : 1 complexes with zirconium. The equilibrium constants, KC, for the reaction of zirconium with alizarin red S, alizarin, and hystazarin were found to be 2.8 x 105, 3.0 x 103, and 6.9 x 102, respectively, at 25° and &#956; = 1.0M. The concentration acid dissociation constants, pKca, for the dihydroxyanthraquinones in 75% methanol were determined as: alizarin red S 6.71 and 11.35; alizarin 7.31 and 11.84; hystazarin 7.57 and 11.40; at 25° and &#956; 1.0M. Zirconium reacts slowly with alizarin red S and alizarin, and mainly via the hydrolysed Zr(OH)22+ species, whereas the reaction with hystazarin is rapid. Rate constants were determined for the first two reactions. The zirconium-alizarin red S complex includes two coordinated hydroxyl groups, the alizarin complex one, and the hystazarin complex contains none. It is suggested that these coordinated hydroxyl groups hydrogen-bond to the sulphonate and/or quinone groups and enhance both the stability and colour of the zirconium complexes. 
