O-hydroxyazo dye

This is an alternative method of introducing copper into an o-hydroxyazo dye structure. The azo compound is treated with a copper(II) salt and an oxidant in an aqueous medium at 40-70 °C and pH 4.5-7.0. Sodium peroxide, sodium perborate, hydrogen peroxide or other salts of peroxy acids may be used as oxidants, the function of which is to introduce a second hydroxy group in the o -position [25]. This process is reminiscent of earlier work on Cl Acid Red 14 (5.51 X = H), an o-hydroxyazo dye that will not react with a chromium (III) salt to form a 1 1 complex but will do so by oxidation with an acidified dichromate solution. This oxidation product was later found to be identical with that obtained by conventional reaction of Cl Mordant Black 3 (5.51 X = OH) with a chromium(III) salt [7]. 

In 1941 two different isomers of the 1 2 chromium complex of an o-carboxy-o -hydroxyazo dye were isolated. It was concluded that the three donor ligand atoms of each... 

Some researcher reported that photofading behaviour of a series of disperse azo dyes in polyester and nylon films may involve the initial oxidation of dye to the azoxy form, followed by a Wallach photorearrangement (Leaver I.H., 1980) to give an o-hydroxyazo dye (see scheme II) ... 

The reduction potential of Al(III) is similar to those of the alkali and alkali earth metals making its determination difficult. However, A1 may be determined indirectly by measuring an anodically shifted reduction current of an adsorbed di-o-hydroxyazo dye complexed with aluminum. The complexed dye would have a different reduction potential compared to the uncomplexed dye. 

For compounds or papers dealing with tautomeric equilibria not mentioned above, see the following o-hydroxyazo dyes [74], 3-acyltetronic acids [75], a-heterocyclic ketones [76], P-diketones [77], Schiff bases [78-80], P-ketothioamides [81, 82], perylene quinones [83], meldrum acid derivatives [84], nitromalonamide [85], and piroxicam [36], For other, possibly older, data, see also reviews [2, 4-13]. 

The influence of substituents on the rates of degradation of arylazo reactive dyes based on H acid, caused by the action of hydrogen peroxide in aqueous solution and on cellulose, has been investigated [43]. The results suggested that the oxidative mechanism involves attack of the dissociated form of the o-hydroxyazo grouping by the perhydroxyl radical ion [ OOH]. The mechanism of oxidation of sulphonated amino- and hydroxyarylazo dyes in sodium percarbonate solution at pH 10.6 and various temperatures has also been examined. The initial rate and apparent activation energy of these reactions were determined. The ketohydrazone form of such dyes is more susceptible to attack than the hydroxyazo tautomer [44]. 

Almost all of these depend on the availability of two o,o -dihydroxyazo ligands in the unmetallised direct dye molecule, although these may be present as the o-methoxy-o -hydroxyazo precursor system. In the manufacture of these dyes it is often easier to synthesise... 

METAL COMPLEXES OF AZO DYES Metal complexes of certain 0,0 -dihydroxyazo, 0-carboxy-0 -hydroxyazo, o -amino-o hydroxyazo, arylazosalicyclic acid, and formazan compounds are used as dyes for wool, nylon, and cotton with generally much improved washfastness and lightfastness properties when compared to their respective unmetallized precursors. Dyes that are chelated with the metal on the substrate during the dyeing process are termed metallizable or mordant dyes. Conversely, those dyes that have been metallized by the dye manufacturer prior to use by the dyer, are classified as premetallized dyes. The two important types of premetallized dyes are the 1 1 and 2 1 complexes, eg, complexes with 1 1 and 2 1 ligand-to-metal ratios, respectively. 

---