Sulfur Indophenols

Polysulfide Melt. Cl Sulfur Black 1 [1326-82-5] (Cl 53185), derived from 2,4-dinitrophenol, is the most important dye in this group which also includes the indophenol-type intermediates. The latter are appHed in the stable leuco form. The derived dyes are usually confined to violet, blue, and green shades. Other members of this group are intermediates capable of forming quinoneimine (10) or phenazone stmctures (11) that produce red-brown or Bordeaux shades ... 

The stmcture of indophenol-type sulfur dyes was studied (21) on Cl Sulfur Blue 9 made from the indophenol (13). This compound was purified and brominated to a tetrabromo derivative (14) identical with that obtained on hromin ation of Methylene Violet [2516-05-4] (15). 

Massaccesi reported the development of a two-phase titration method for the analysis of miconazole and other imidazole derivatives in pure form and in pharmaceutical formulation [14], To the sample (10 mg) are added 10 mL of water, 10 mL of 1 M-sulfuric acid, 25 mL of dichloromethane and 1 mL of 0.05% indophenol blue (C.I. No. 49700) in dichloromethane solution and the solution is titrated with 10 mM sodium dodecyl sulfate until the color of the organic phase changes from blue to pale yellow. Results obtained for the drug in pure form, tablets, suppositories, cream and lotion agreed with the expected values and the coefficient of variation (n = 6) were 0.3-0.35%. Imidazole and the other constituents of the pharmaceutical preparations did not interfere. 

By this method, sulfur dyes derived from 4-hydroxydiphenylamine are seen to be essentially identical. Similarly, the sulfur dye from 7-anilino-9-methyl-l,2,4-trichlorophenothiazin-3-one (21) and the sulfur dye from 4-anilino-4 -hydroxy-2-methyldiphenylamine (22) were compared and found to be almost identical, as was the related trichlorophenothiazinone derivative (23) from carbazole when compared with Hydron Blue indophenol, Cl... 

This class of compounds also includes phcnazone, phenothiazone, and phe-noxazone derivatives (12), and so these polysulfide melt dyes are also referred to as quinoneimine or indophenol sulfur dyes. 

Gnehm and Kaufler [4] showed that C.I. Sulphur Blue 9, 53430 [1327-56-6], which is prepared by sulfurization of the indophenol derivative 10 [Y = N(CH3)2], has the phenothiazone structure 12. 

The structure 15 can thus be regarded as the prototype of the polysulfide-melt dyes (quinoneimine or indophenol sulfur dyes) (Scheme 2.8). 

In this process, the reaction of the intermediates-essentially indophenols, chiefly in leuco form, or indophenol-like substances-with sulfur is effected by heating with alkali metal polysulfide in an aqueous or alcoholic medium under reflux. When monoethers of ethylene glycol or diethylene glycol (such as Carbitol) are used, the dye can be obtained in solution form after melting, without distillation and elimination of the solvent. Accordingly, these solvents are used chiefly in the preparation of ready-to-dye sulfur dye solutions. The addition of hydrotropic substances such as sodium xylenesulfonate improves the homogeneity of the melt and hinders sedimentation of the dye on storage. 

Sulfur blue dyes are often made using an organic solvent such as n-butanol, in what is known as the solvent reflux process. Examples are C.I. Sulfur Blue 9 and Sulfur Blue 13. In this case, intermediate structures are indophenols (e.g., 55). See Fig. 13.133. Similarly, sulfur dyes containing benzothiazine groups can be made from... 

Sulfur dyes, vat dyes (helindone), oxazines Indophenols. sulfur dyes Azo dyes (chrome)... 

Complex III - Complex III contains a diversity of electron carrying proteins. They include cytochrome b, iron sulfur centers, and cytochrome cl. Cytochrome b is the first of the heme-carrying proteins (Figure 15.6) involved in electron transport. Passage of electrons from cytochrome b to the iron sulfur centers can be blocked by antimycin A. Also, the artificial electron acceptor phenazine methosulfate can accept electrons from cytochrome b and 2,6-dichlorophenol-indophenol can accept electrons from the iron sulfur proteins (Figure 15.9). The crystal structure of the redox components of complex III from bovine heart mitochondria is shown in Figure 15.16... 

Kjeldahl method Ammonia produced by the oxidation of the enzyme by concentrated sulfuric acid is measured using the indophenol technique 0.5-1 Opg ml" ... 

The colorimetric Nesslerization method uses alkaline phenol and hypochlorite to react with ammonia to form indophenol blue in an amount proportional to the ammonia concentration. The blue color is intensified with sodium nitroprusside, and the concentration is measured using a calibrated colorimeter. The titration of basic ammonia is accomplished with standard sulfuric acid using a mixed indicator. Determination of ammonia may also be based upon the indophenol reaction adapted to automated gas-segmented continuous flow analysis. Potentiometric determination of ammonia is performed by ion-selective ammonia electrodes. 

The other dye classes are nitroso, carotene, xanthene, acridine, methine and polymethine, thiazole, indamine and indophenol, azine, oxazine, thiazine, sulfur, lactone, aminoketone, hydroxy-ketone, and natural organic coloring matters. 

Mapson (14) found that in solutions of pH 0.6 there is no significant condensation of formaldehyde with ascorbic acid. However, at this pH sulfides, sulfites, and thiol compounds combine readily with formaldehyde. He, therefore, proposed that the indophenol titration be carried out at pH 0.6 after the addition of formaldehyde to estimate ascorbic acid in the presence of the interfering sulfur compounds. 

The material to be analyzed is extracted with 5% metaphosphoric acid. The homogenate should be prepared in a dilution that will yield 0.04-0.10 mg. of ascorbic acid per milliliter. If it is suspected that sulfide, sulfite, or thiol compounds are present, an aliquot of the extract is brought to pH 0.6 by adding 50% sulfuric acid. Formaldehyde solution is then added until a concentration of 4% of formaldehyde is present. After waiting for 8 minutes, the solution is titrated with standardized indophenol reagent. If sulfide, sulfite, or thiol compounds are not present, the preliminary treatment with sulfuric acid and formaldehyde is omitted, and the metaphosphoric acid extract, which has a pH of about 1.2, is titrated with indophenol reagent. In either instance, the titration obtained is the initial value (A), which is later plotted as the total indophenol value. 

In these cases it is usually possible to explain why the color is formed. The reactions can be further classified, on the basis of the type of colored compound formed, into reactions leading to the formation of azo dyes, di- or triphenylmethane dyes, xanthene dyes, polymethine dyes, indophenols, etc. Azo dyes are formed, for example, in the reaction of diazonium salts and phenols (p. 192) or amines (p. 324), azomethines in the reaction of primary aromatic amines with aromatic aldehydes (p. 215), di- and triphenylmethane dyes in the reaction of aromatic aldehydes with aromatic hydrocarbons in concentrated sulfuric acid (p. 213), triphenylmethane dyes in the reaction of phenols with aromatic aldehydes or oxalic acid (p. 196), xanthene dyes in the reaction of anhydrides of dicarboxylic acids with resorcinol (p. 196), polymethine dyes are formed after the cleavage of the pyridine ring in the reaction of the glutaconaldehyde formed and barbituric acid (p. 378), indophenols on reaction of phenols with Gibbs reagent (p. 195), or 4-aminoantipyrine according to Emerson (p. 194), or on the Liebermann reaction (p. 195). 

In sulfuric acid and in the presence of nitrogen oxides, phenols give colored indophenols. In the reaction medium they give a blue or green solution, which after dilution with water turns red, and after alkalization becomes blue. A positive reaction is given by phenols with a free para-position, unless they are substituted with —OH, — NH2, — OCH3, — NO2, — CHO, — COOH, or — COCH3. For example, 3,5-xylenol, o-aminophenol, o-nitro-phenol, m-hydroxybenzaldehyde, m-hydroxybenzoic acid, and similar compounds do not react. 

Vat Blue 43 (Hydron Blue R) is a kind of sulfur dye that, unlike typical sulfur dyes, may be reduced by sodium hydrosulfite without destruction. To prepare Vat Blue 43, carbazole is condensed with p-nitrosophenol in sulfuric acid to give an indophenol, which is reduced and then fused with polysulfide. 

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