Colour of a xanthylium pigment in aqueous solutions at different pH values

A xanthylium salt pigment was synthesized from the reaction involving glyoxylic acid and (+)-catechin. After isolation, its spectral characteristics and colour intensity, influenced by pH, were studied. When varying pH from acidic to alkaline values, a steady bathochromic displacement of the visible wavelength was observed while no noticeable change was observed in the UV absorbance wavelengths. A concomitant increase in the intensity of the visible absorption wavelength was also observed. The pink reddish taint obtained in the alkaline pH values may allow the studied xanthylium compound to be regarded as a possible colorant for some slightly pink coloured alkaline products.