Synthesis, characterization and thermal behaviour of some metal indigodisulphonates

Abstract

Some indigodisulphonates of Cr(lll), Cu(ll), Ag(I ), An (11) and Cd (11) have been prepared in aqueous medium and characterized on the basis of elemental analyses, diffuse reflectance infrared spectra and magnetic measurements.The thermal behaviours of these salts were studied by TG, DTG and DSC techniques. Cr(lll), Cu(ll), Zn(ll) amd Cd(ll) indigodisulphonates contain 12, 2, 2 and 2 molecules of crystallization water, respectively. The end-products of thermal decomposition have been verified by infrared spectroScopy and X-ray diffraction. Values of dehydration enthalpies have been calculated from the DSC curves.The synthetic food dye indigocarmine, is the disodium salt of l-indigotin-5,5'-disulphonic acid (Structure 1). This dye has been used as an indicator in the titration ", 0 of antimony(V) with titanium(Ill) [1] and of iron(Ill)with chromium(ll) [2,3] in an atmosphere of carbon dioxide. Studies carried out in solution on the colour-fading of this dye have indicated that the fading is due to oxidation-reduction processes as well as to a dependency on the light intensity [4].Although the photodecomposition of indigocarmine appears to be the main cause of colour instability, the thermal decomposition of this dye in solution has been reported [4][5][6][7]. From the Arrhenius plot of the dye at pH 7.0, a half-life of 234 days at 25 ~ was reported [6].No studies have been performed in the solid phase on the thermal stability of indigodisu Iphonates.The aim of the present paper was to investigate the thermal behaviours of several indigodisulphonates in the solid phase, using thermogravimetric and differential scanning calorimetry methods.

Metal Complexes of Indigo and of Some Related Ligands

“…The magnetic moments and the antimicrobial activity of the metal compounds were studied . Furthermore, metal compounds with the dianion of indigocarmine and with Cr III , Cu II , Ag I , Zn II , and Cd II were reported …”