Yellowing dyestuff

Uric acid couples with 2,6-dichloroquinone-4-chloroimide in position N-7 to yield a yellow dyestuff. 

Hofenk de Graff, J. H. and W. G. T. Roelofs (1978), The analysis of flavonoids in natural yellow dyestuffs occurring in ancient textiles, Proc. bit. Council of Museums Committee for Conservation, 5th Trienial Mtg., Zagreb. 

The color test results indicate that probably two dyes are present in the historic dress fabric. There seems to be a pink dyestuff and a yellow dyestuff that together yield the light orange color of the yardage. In the washing test, for example, the historic fabric became pink, while the... 

Yellow Dyestuff. The yellow-producing dyestuff is suspected to be an acid dye, primarily because its behavior responses to the A.A.T.C.C. tests parallel those typical of this class of dyes, as outlined by Corbman (17). The poor washfastness, tendency to bleed easily, and fair perspiration fastness exhibited by this yellow component are distinctly like those of the acid dyes. The historic textile, moreover, demonstrates the acid dye s typically excellent resistance to crocking. This yellow color was transferred to wool, silk, and nylon—all of which have an affinity for acid dyes. 

X-ray analysis of the washed specimen from which the yellow color leached out showed some slight diminishing of aluminum and virtually no sulfur, whereas sulfur was present in the remnant fabric. Although it is possible that sulfur was in some way connected with the yellow dyestuff molecule, it may also be that a sulfur-containing acid was used to affix the yellow dyestuff on the cloth. Acid dyes are so-named because they are set with acids, and sulfuric acid commonly was used at this time to serve this function (8-12). 

Titan yellow reagent titan yellow (also known as clayton yellow) is a water-soluble yellow dyestuff. It is adsorbed by magnesium hydroxide producing a deep-red colour or precipitate. Barium and calcium do not react but intensify the red colour. All elements of Groups I to III should be removed before applying the test. 

Fluorescein test Free bromine converts the yellow dyestuff fluorescein(I) into the red tetrabromofluorescein or eosin(II). Filter paper impregnated with fluorescein solution is therefore a valuable reagent for bromine vapour since the paper acquires a red colour. 

Both these sulphonic acids of amidoazobenzene, and especially the disulphonic acid, are valuable yellow dyestuffs, and the sodium salt of the latter comes into commerce as Acid Yellow or Fast Yellow. A further application of these acids is in the preparation of tetrazo-dyestuflFs, for example Biebrich- and Crocein-scarlets. 

Yellow dyestuffs are also obtained by action of diazotoluene-sulphonic acids on diphenylamine. 

This yellow dyestuff is obtained by heating paranitrotoluene-orthosulphonic acid with alkalies. It yields diamidostilbenesul-phonic acid on reduction, but whether it is azoxystilbene or whether a ring-formation between the methane-group and the azo-chain has taken place is doubtful [78, 79]. 

It produces a beautiful bluish-red shade on wool, and may be used in conjunction with yellow dyestuffs, giving fine scarlet tones. Its application in wool-dyeing has fallen off considerably since the introduction of the red azo-dyes. 

This compound is formed by melting phenanthrene-naphthazine-sulphonie acid (from phenanthrenequinone and a -naphthylene-diaminesulphonic acid) with caustic potash. It dissolves in concentrated sulphuric acid with a blue colour, which suddenly changes into bright red on dilution. Its sulphonic acid is a yellow dyestuff. 

For a considerable period chrysaniline was the only basic yellow dyestuff, and for this reason was largely used in cottondying. Wool and silk are dyed directly, cotton requires a taunin mordant. The shade produced is an orange-yellow, noteworthy for its fastness to light. 

These yellow dyestuffs, though of totally different origin, show some relationship in chemical properties, and possibly owe their tinctorial value to the same chromophor. In euxanthic acid this is a carbonyl group, which forms a ring with one oxygen atom and two benzene nuclei. 

Safflower, the petals of Carthamus tinciorius, c., contains, besides a yellow dyestuff, a red one, carthamine, which was of considerable importance before the introduction of the artificial dyestuffs. 

To prepare carthamin, safflower is washed with water to remove the yellow dyestuff, and is then extracted with dilute soda solution, and filtered. Cotton yarn is immersed in the alkaline solution, and the liquid acidulated with citric acid. The cotton takes up the carthamin, which is removed with soda solution, and precipitated with citric acid. Obtained in this manner carthamin forms a lustrous green powder, sparingly soluble iu water and ether, readily in alcohol. It dissolves in alkalies with yellowish-green colour. On fusion with potash it gives oxalic acid and para-oxy-benzoic acid. Carthamin dyes animal fibres and unmordanted cotton from a slightly acid bath. It produces a beautiful pink colour on silk. 

Lime yellow Lake produced by adsorbing auramine or other yellow dyestuff on a natural earth. 

Antimony salts, in acid solution, react with aromatic o-dihydroxy compounds (e.g., p3n ocatechol, pyrogBllol) to produce slightly soluble, white, or light yellow crystalline precipitates which can be formulated as cyclic esters of antimonous acid. The yellow dyestuff 9-methyl-2,3,7-trihydroxy-6-fluorone (I), which can be viewed as a derivative of pyrocatechol, forms a red antimonous compound (II). 

Members of the Berberidaceae are known to produce a yellow dyestuff extractable from the roots, of which the principal component is berberine q.v.). Other components include oxyacanthine, magnoflorine, berberrubine, berbamine, jatror-rhizine, columbamine, palmatine and isotetrandine (Schweppe, 1992). 

Various Rhamnus species produce a yellow dyestuff, generally extracted from the inrripe berries. These latter are typically referred to in the historical literature as yellow berries, buck-friom (. v.), French berries or Avignon berries (. v.). The dye is in turn used to produce various yellow lake pigments, often called pink in earher docinnentary sources. The term yellow berries was also apphed to the actual pigment produced from these berries, and came to replace the earher term pink (Harley, 1982). For a fuller discussion of the species involved, constituent compounds, substrates and alternative terminology, see the enhy for rhamnus. 

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