Metal Demethylative Coppering

As a rule many of these dyes only have moderate lightfastness on paper. To improve this metal complexes are used, particularly with the blue azo dyes. Because planarity of the dye molecule is advantageous for a good dyeing, virtually only Cu2+ complexes such as C.I. DirectBlue 218,24401 28407-37-6] (18) are of interest for paper. 3.3 -Dimcthoxy-4,4 -biphcnyldiaminc (o-dianisidine) has proved particularly suitable, because after coupling with a 1-naphthol derivative demethylative copperization can take place. 

Metal complex dyestuffs derived from tetradentate azo compounds (147) have very limited commercial significance but merit brief discussion on chemical grounds. The first dyestuffs of this type to be used commercially contained the o-hydroxy-o -carboxymethyleneoxydiarylazo system, e.g. (148). These were dyed on cotton and aftertreated with a copper salt to produce the copper complex dyestuff which was reported71 to be a triannelated species (149). Formation of complexes of this type has been confirmed105 in the case of 2-hydroxy-5-methyl-2 -carboxymethyleneoxy-azobenzene, which yields the complex (150) on treatment with copper acetate under mild conditions. Under more severe conditions, however, the complex (151) is produced. Loss of the carboxymethyl group from dyes of this type has also been shown105 to occur under dyebath conditions. This may be compared with the demethylation of o-methoxy-o -hydroxydiarylazo compounds (Section 58,2.3. l(iii)(a)) under similar conditions. 

Naphthol, l-(2-methoxyphenylazo)-copper complexes demethylation, 54 2-Naphthol, l-(4-nitrophenylazo)-copper complexes, 42 2-Naphthol, 1-phenylazo-metal complexes structure, 42 2-Naphthol, pyridylazo-metal complexes dyes, 74... 

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