A Naphthol orange

Aminonaphthol has been prepared by the reduction of 1.4-nitronaphthol by tin and hydrochloric acid 1 by the reduction with sodium amalgam of i,4-aminonaphthol-3,8-disul-fonic acid 2 or i,4-aminonaphthol-5-sulfonic acid 3 by the action of phenylhydrazine on 1,4-nitrosonaphthol.4 The more usual preparative method has been to start with a-Naphthol Orange (Orange I) and reduce it with stannous chloride.8... 

Water as the solvent. Water may be used to dissolve tropeolin 00, methyl orange, p-nitrophenol, sodium alizarine sulfonate, propyl-a-naphthol orange, nile blue, alizarine yellow, diazo violet, and tropeolin 0. 

Propyl-a-naphthol orange Cf. page 148 7.4-S.9 yellow - red Slotta and Franke... 

The hydrogen attached to the nitrogen atom (1) has no effect on the indicator properties, and may be replaced by alkyl groups. Slotta and Franks have determined the indicator characteristics of such substituted a-naphthol orange derivatives. Their findings are summarized in the following table. The color intensity of the alkaline form increases with the atomic weight of the... 

Propyl-a-naphthol orange has already been included in the list of recommended indicators. More exhaustive studies with this new indicator are still desirable however. It remains yet to be shown that the color intensity of the red form is less than that of cresol red which.possesses a similar transformation range. 

Azoic Dyes. These are used to produce cost-effective heavy yellow, orange, red, maroon, navy blue, brown, and black shades and are ptinted alongside other dye classes to extend the coloristic possibiUties for the designer. Two approaches are adopted. The common method ia the United States is to use both a naphthol derivative and a stabilized color base, usually in the form of a diazo imino compound in the same print paste. This mixture is soluble in dilute caustic soda and no coupling takes place at this stage. The dried prints are passed through steam at 100—105°C that contains acetic and/or formic acid vapor. As neutralization takes place on the print, the coupling occurs rapidly and the insoluble azoic dye is formed. 

B ) Coupling Orange T.—The procedure is the same as in (B) except that the alkaline solution of a-naphthol (Note 4) is cooled to 25 before adding the ice (Note 5). The azo dye in this case does not crystallize but forms a deep purple-red solution. 

The only practical method of preparing 1,4-aminonaphthol is from a-naphthol through an azo dye, the nitroso compound not being readily available. The majority of investigators have reduced technical Orange I with stannous chloride Mi.is.is.ir.is by the procedures discussed above, and benzeneazo-a-naphthol has been reduced by the same reagent. In order to make possible the use of crude, technical a-naphthol a method has been developed for the preparation of the benzeneazo compound, its separation from the isomeric dye coming from the d-naphthol present as well as from any disazo compound by extraction with alkali, and the reduction of the azo compound in alkaline solution with sodium hydrosulfite. The process, however, is tedious and yields an impure product. 

The sample is first dissolved in 2 M hydrochloric acid, and then 1 drop of this solution is placed on a white tile. One then adds 1 drop of a 1% sodium nitrite solution and 1 drop of a 4% 2-naphthol solution in 2M sodium hydroxide, and observes a red-orange color as a positive reaction. 

When this ceases, the liquid is filtered and the filtrate, which should be acid, cooled to about 150 and treated with 5-10 drops of a 10% aqueous sodium nitrite solution the acid is neutralised with sodium carbonate, cooling meanwhile, and to the liquid, which is turbid owing to the presence of zinc carbonate, are added 1-2 drops of alkaline a-naphthol solution (01 gram a-naphthol, 100 c.c. water, 5 c.c. of caustic soda solution of sp. gr. 1 35). If the spirit contains benzene or its homologucs, an orange-red coloration is produced in consequence of the formation of an azo-colouring matter from the a-naphthol and the diazo-compound of the aniline or analogous base. 

Unsubstituted polysaccharides do not appreciably absorb ultraviolet and visible radiation, but they can be made to do so intensely by combining them with chromophores and chromogens (e.g., a-naphthol, dihydroxynaph-thalein, anthrone, carbazole, phenol-sulfuric acid, 2-thiobarbituric acid, tolu-idine blue, diphenylamine, Congo red, aniline blue, and methyl orange), usually in acidic or basic media. Coloration is normally preceded by depoly-... 

Azoic dyes are also known as naphthol dyes, because all employ a naphthol component in their formation, and they can be produced in batch or continuous processes. Because they have a limited shade range, they are best known for their ability to provide economical wetfast orange and red shades on cotton. A generic azoic dye structure is shown in Fig. 13.4. 

Oil red is also a naphthol dye which contains one azo base, -N=N-, in the molecule like para red. It is a bright red powder, insoluble in water, soluble in alcohol and in acetone producing an orange red colour, it melts at l65°C, begins to vaporize at 270 C, and boils at 330 0. Oil red is more stable than para red against heat and is not so easily damaged. 

The dyestuffs from a-naphthol and diazo-compounds of the benzene series are orange or brown, while those from the a a-acid are mostly of a beautiful yjoraceaw-red tone. 

This dyestuff is prepared by action of paradiazobenzene-sulphonic acid on a-naphthol. Tlie free acid forms almost black leaflets, with a green reflex, which dissolve in concentrated sulphuric acid with a violet coloration. Its alkali salts are orange-yellow, and dissolve easily in water. The solutions become red with excess of alkali (distinction from /S-naphthol dyestuff s). 

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