Characterization of yellow pyrazolyl azo pigments with or without Na integrated as the central metal

We were so far involved in the X-ray structure analysis of the title compounds in order to improve their solvent fastness from the structural point of view. Unexpectedly, we have isolated, from the same reaction pot, three kinds of single crystals: two Na-containing bisazo compounds of the cis form and one Na-free monoazo one. In addition, a Na-free bisazo compound of the trans form has also been isolated by eliminating the Na atom of the former by means of HCl. In the present investigation, we have carried out the electronic characterization of the Na-free bisazo compound together with its light-, heat-, and solvent fastness. As a result, the Na-free bisazo compound is found to exhibit a vivid yellow and possess a high fastness against light, heat and organic solvents.