Crocein

Schaffer s acid, CioHg04S. 2-hydroxy-7-naphthalene sulphonic acid. Obtained by sulphonating 2-naphthol with a small amount of sulphuric acid at a higher temperature than is used for the preparation of crocein acid. A valuable dyestuff intermediate. 

Cristsll, c., = Kristall, fete. CzocflDScrocein scarlet. CKrtc -lAi Zj n. croton, resin. -61, n. croton oil. 

Fig. 3.130. HPLC chromatograms of the test mixture detected by DAD (270 nm, upper lane) by APCI-MS-TIC (middle) and by ESI-MS-TIC (lower lane). Peak identification l=benzene sulphonic acid sodium salt 2=2-naphtalene sulphonic acid sodium salt 3=2-anthraquinone sulphonic acid sodium salt 4 = sulphorhodamine D sodium salt 5=crocein orange G 6=eriochrome black T 7=2,6-anthraquinone disulphonic acid disodium salt 8 = 1,5-naphtalene disulphonic acid disodium salt 9 = azophloxine 10 = 1,2-benzene disulphonic acid dipotassium salt. Reprinted with permission from G. Socher et al. [178].

Mixtures of minium with other colours or with white substances, heightened in colour by artificial organic dyes (usually eosin, cochineal scarlet, crocein, ponceau and the like), or, in some cases, white substances (barium sulphate) coloured with lakes of artificial organic dyes, are often sold as imitations or substitutes of cinnabar and vermilion. 

The hydroxyl radical attack on aromatic structures appeared also to be an important step in the photocatalytic destruction of a series of other dye molecules including Crocein orange G, methyl red, Congo red and Alizarin... 

The first product formed by the actio of concentrated sulfuric acid on/3-naphthol is 2-naphthol-l-sulfonic acid (page 199). This compound, however, is very unstable and rearranges, even in the cold, in the presence of excess sulfuric acid, to form 2-naphthol-8-sulfonic acid (Bayer acid, croceine acid), and this in turn rearranges, only partially in the cold but completely at higher temperatures, into 2-naphthol-6-sulfonic acid (Schaeffer acid). 

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. 

One of these (the a-sulphonic acid or crocein-acid) is best obtained at a low temperature. By further heating with sulphuric acid it goes over into the )9- or Schaeffer s acid, which was prepared by Schaeffer a long time ago. These acids are distinguished... 

From the facts that azo-dyes from Schaeffer s acid differ but little in shade and solubility from those obtained from -naphthol, and that simple /3-naphthol azo-compounds on sulphonation always yield derivatives of Schaeffer s acid, and never those of crocein-acidj it may naturally be concluded that the azo-group enters in the same position both in /S-naphthol and in Schaeffer s acid. This is the a-y position. 

The acid soluble in alcohol and salt-solution (G-acid of Meister, Lucius, and Briining, 7-acid of Cassella and Co.) behaves very like, /3-naphthol-a-monosulphouic acid (crocein acid), and must be regarded as a derivative of the latter, as it is formed quantitatively on further sulphonation of crocein acid., It may also be obtained from Schaeffer s acid (this is contradicted by some chemists), and Armstrong gives it the following formula —... 

The sulphonic acids of this compound come into commerce as Biebrich and Crocein scarlets, according to the position of the sulpho-group. 

This body [61] is known as CroceTn Scarlet 3B, and although not producing fast shades is used, in cotton-dyeing. Crocein Scarlet 7 B is a dyestuff of somewhat bluer shade, and is obtained from orthoamidoazotoluenesulphonic acid in the same manner. The tetrazo-dyes prepared from y3-naphthol- -sulphonic acid give soluble crystalline calcium salts, while those from the other acid give amorphous and insoluble calcium salts. 

By the action of concentrated sulphuric acid on y3-naphthyl-amine two monosulphonic acids are first formed, 9-naphthylaminc-a-sulphonic acid (corresponding to the crocein acid from -naph-thol), and the yS-naphthylamine-7-sulphonic acid. 

Azo-dyes prepared by interaction of a diazo-compound and a pbenol are insoluble in waterj and therefore of no practical value. For this reason a sulpho-group is introduced (see p. 34), and this produces the solubility necessary for their application in ordinary dyeing processes. These sulphonated azo-dyes have a considerable affinity for wool and silk, but (with the exception of those of the tetrazo-series) are not easily fixed on cotton. Cotton may be dyed with certain azo-dyes of the Crocein series, hut the shades produced are not fast to washing. 

Diazot. Aniline + croceine acid (0-NaphthdL sulphonic acid)... 

Broenner acid Casella s acid Chicago acid (SS acid) chromotropic acid Cleve s acid crocein (Bayer s acid) epsilon acid G acid... 

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