Dyes and dyeing

Preparation of an Azo Dye Methyl Orange (Section 629). —Dissolve 10 grams of sulphanilic acid and 3 grams of anhydrous sodium carbonate in 150 cc. of water. To the solution first add 4 grams of sodium nitrite dissolved in 20 cc. of water, and then a mixture of 7 cc. of concentrated hydrochloric acid and 10 cc. of water. (Eq.) Dissolve 6 cc. of dimethylani- 

The salt may be purified by recrystallization from hot water (about 150 cc). Filter the boiling solution in the way described in 10, page 6. The yield should be about 12 grams. 

Dissolve a little methyl orange in water and add alternately to the solution dilute hydrochloric acid and dilute sodium hydroxide as long as a change in color is observed. (Eqs.) 

Dissolve about 0.2 gram of methyl orange in about 10 cc. of dilute hydrochloric acid, add about 1 gram of zinc dust and boil 

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Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

Modem hair colorants can be divided into temporary, semipermanent, and permanent systems. These categories are characterized by the durabiUty of the color imparted to the hair, the type of dye employed, and the method of apphcation (see Dyes and dye intermediates). 

Make acid yields coumaUc acid when treated with fuming sulfuric acid (19). Similar treatment of malic acid in the presence of phenol and substituted phenols is a facile method of synthesi2ing coumarins that are substituted in the aromatic nucleus (20,21) (see Coumarin). Similar reactions take place with thiophenol and substituted thiophenols, yielding, among other compounds, a red dye (22) (see Dyes and dye intermediates). Oxidation of an aqueous solution of malic acid with hydrogen peroxide (qv) cataly2ed by ferrous ions yields oxalacetic acid (23). If this oxidation is performed in the presence of chromium, ferric, or titanium ions, or mixtures of these, the product is tartaric acid (24). Chlorals react with malic acid in the presence of sulfuric acid or other acidic catalysts to produce 4-ketodioxolones (25,26). 

Acetates. Anhydrous iron(II) acetate [3094-87-9J, Ee(C2H202)2, can be prepared by dissolving iron scraps or turnings in anhydrous acetic acid ( 2% acetic anhydride) under an inert atmosphere. It is a colorless compound that can be recrystaUized from water to afford hydrated species. Iron(II) acetate is used in the preparation of dark shades of inks (qv) and dyes and is used as a mordant in dyeing (see Dyes and dye intermediates). An iron acetate salt [2140-52-5] that is a mixture of indefinite proportions of iron(II) and iron(III) can be obtained by concentration of the black Hquors obtained by dissolution of scrap iron in acetic acid. It is used as a catalyst of acetylation and carbonylation reactions. 

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