Contribution of Nitro Gtoup on the Anomalous Photofading of Some Azo Disperse Dyes

Abstract

The behavior of photofading, of some azodisperse dyes containing nitr, group has been examined on polyester and o n polyamide films, The contributionof nitro group on the an, 4-nitro-4-hydroxy, malous photofading, of thesedyeswas discussed, 4rNitro-2 -hydroxy-4-, 4-nitro-2, , 4-dihydroxy-and 4-nitro-4-N-biscyan, ethyl in, az, benzenes, n p, lyamide fade It is observe thst there by light easier th he corresponding P ed deri is a correlation between the basicity of a dye and its sensitivity to the anomaleus photofading. Anomolous fading of a dye proceeds easily when it is less basic, and 4-nitro-4 -N, N-diethylaminoazobenzene dp. es not show the c, . haracter. The spec3. fioc anomqlous fading of 4-nitroazobenzenes on polyamide may be explained by the assumption that the nitro group can be photoreduced to amino group prior to photooxidation of azo group to azoxy group.2-Nitroazobenzenes on polyester and on polyamide fade by light much more easily than the corresponding 4-nitro derivatives. In anaerobic coRdition, 4-nitroazobenzenes are more resitant to fading than that in normal condition, however, the fading of 2-nitro-azobenzenes does not change practically in both conditions. The anomalous fading of 2-nitroazobenzenes is position specific and may be explained by the assumption that intramolecular photo-oxidation of azo group to azoxy group Proceeds exc usively by 2-nitro group. The behavior of fading of 2, 4-dinitroazobenZeneS has also been examined and discussed.