Архивы рубрики ‘DYE CHEMISTRY’

Triphenylmethane Dyes

Reduction takes place according to the scheme: (X)3OH + 2 ТіСІз + 2 HC1 2 ТіС14 + (Х)3Н + Н20 Titration is carried out to a colorless endpoint, which is usually very sharp. Knecht has titrated fuchsin, eosin, malachite green, acid green, aniline blue, rhodamine, and other dyes by this method. Safranine behaves exactly like […]


Determination of azo dyes is done most satisfactorily in the presence of sodium tartrate which prevents the precipitation of the difficultly solu­ble dye acids (e. g., benzopurpurin, see Knecht,105 pages 31-32). Yellow dyes cannot be easily titrated because titanium tartrate is strongly yellow in color. The reduction takes place quantitatively according to the equation: R—N=N—R’ […]

Titration of Methylene Blue

One mole of methylene blue (mol. wt. 319.6) requires two equival­ents of iron (112 grams) for reduction, and therefore 1 cc. titanium tri­chloride solution corresponds to: 0.007299 X 319.6 __ 0.02083 gram of methylene П2~ blue (C16H18N3SC1) For example, exactly 0.2 gram of methylene blue (zinc-free) is dis­solved in about 100 cc. water in a […]

Preparation of the Titanium Trichloride Solution

In principle, a known amount of ferrous iron is oxidized to ferric iron, and this is reduced with titanium trichloride using potassium thiocyan­ate as an indicator. As the ferrous salt, Knecht used iron ammonium sulfate (Mohr salt) and oxidized this to ferric sulfate with 0.02 N potassium permanganate in sulfuric acid solution. The resulting ferric […]

Principle of the Knecht Method

Titanium trichloride is an extremely easily oxidized material which dissolves in water to form a violet solution. On oxidation, it is con­verted to the colorless titanic acid, Ti(OH)4. Using a titanium tri­chloride solution of known strength, it is possible to reduce quantita­tively dyes of various classes, the endpoint being taken as the point where the […]

Volumetric Determination of Dyes by the Edmund Knecht. Reduction Method[73]

In many cases, testing a dye for color strength and tint by means of a dyeing test is replaced by a simple analysis by reduction with titanium trichloride (TiCl3) to determine the content of reducible substance present. This elegant method is usable for homogeneous products, but it fails if the dye being tested is a […]

Determination of 2 Naphthylamine-5,7-disulfonic. Acid in the Presence of 2-Naphthylarnine-6,8-. disulfonic Acid

The analysis of mixtures of these two acids is very simple. The mix­ture is first titrated with nitrite to determine the total of the two acids, and then the 2,5,7 acid is titrated with sodium hypobromite. The 2,5,7 add reacts smoothly in hydrochloric acid solution with sodium hypo­bromite, taking up two atoms of bromine, while […]

Determination of Naphtholmono — and — disulfonic Acids,. and Dihydroxynaphthalenemono — and — disulfonic Acids

Examplet Nevile-Winther Acid (l-ISaphthol-4-sulfonicAcid) (Molecular Weight 224) Coupling is carried out with a 0.1 N diazotized aniline solution, just as prescribed for H acid, and at the end the dye is salted out in the re­action dish so that the remainder of the naphtholsulfonic acid is easily determined. Starting out with a 2.24-gram sample, the […]

H acid—l-Amino-8*naphthol-3,6<diaul onic Acid

(a) Nitrite Value. (Calculated in terms of the acid sodium salt, mol. wt. 341.) A solution of 3.41 grams of H acid in 5 cc. 10 per cent soda ash solution is diluted to 250 cc., precipitated with 25 cc. concen­trated hydrochloric acid, and diazotized at 5°C. with 1N nitrite solution. H acid should give […]

Determination of Aminonaphtholsulfonic Acids

Two determinations are always made. In the first, the amount of nitrite which is used is measured to give the “nitrite value.” Then, the compound is titrated with diazonium solution to give the “coupling value.” If the two values agree, then it is known that the aminonaphthol­sulfonic acid has been correctly made. If, on the […]