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Synthesis of novel 4,4'-bis(2,4-pyrimidinyl)-diaminostilbene-2,2'-disulfonic acid derivatives and their whitening effect on cotton fiber as fluorescent whitening agents

Some novel 4,4'-bis(2,4-pyrimidinyl)-diamino stilbene-2,2'-disulfonic acid derivatives 4a-d were designed and synthesized. Their structures were confirmed by proton nuclear magnetic resonance, elemental analysis and ultraviolet absorption spectra. All newly synthesized compounds were interrogated on their whitening effect on cotton fiber as fluorescent whitening agents. Their optical properties were evaluated by the degree of whiteness, color index, light fastness, wet rubbing fastness and dry rubbing fastness. The results indicated that compounds 4a-d showed an obvious whitening effect on cotton fiber and higher fastness than that of C186. The reflectivity of cotton fiber treated with compounds 4a-d at the critical concentration was up to 120.76%. In contrast, the reflectivity of untreated cotton fiber was only 87.23%. The ultraviolet absorption properties of compound 4d were tested under diverse pH values. The results showed that the ultraviolet absorption intensity of compound 4d decreased significantly and the absorption curve had blue shift under acidic conditions. Compound 4d was found to be the most effective molecule as a fluorescent whitening agent with a higher degree of whiteness (CIE Whiteness 135.04) compared to untreated cotton fiber (CIE Whiteness 73.02) at the critical concentration (0.1%).