Indophenols

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. 

The process is commonly carried out in jacketed stainless steel vessels with stirrer and reflux condenser. As in dry fusion, dehydrogenation reactions give off hydrogen sulfide, which is absorbed in caustic soda solution. 

The crude melt for powdered grades is then processed in a similar way to the dry-fusion product. 

All quinoneimine derivatives are commonly called indophenols by dye manufacturers, even though they are often indoanilines or indamines. The following methods can be used to prepare indophenols [4]  

1) Oxidation of the starting materials with hypochlorite at 0°C, with Mn02, or with dichromate. 

---

The colorations produced in this reaction arise from the action of nitrous acid on the phenol, giving />-nitrosophenol (I) which then reacts with excess of phenol to form an indophenol (II) which is an acid-base indicator ... 

Phosphatase Test. The phosphatase [9001-78-9] test is a chemical method for measuring the efficiency of pasteurization. AH raw milk contains phosphatase and the thermal resistance of this enzyme is greater than that of pathogens over the range of time and temperature of heat treatments recognized for proper pasteurization. Phosphatase tests are based on the principle that alkaline phosphatase is able, under proper conditions of temperature and pH, to Hberate phenol [108-95-2] from a disodium phenyl phosphate substrate. The amount of Hberated phenol, which is proportional to the amount of enzyme present, is determined by the reaction of Hberated phenol with 2,6-dichloroquinone chloroimide and colorimetric measurement of the indophenol blue formed. Under-pasteurization as well as contamination of a properly pasteurized product with raw milk can be detected by this test. 

The other method is less accurate but more rapid and involves direct Nessleri2ation of the sample for colorimetric deterrnination. Other colorimetric indicators with more sensitivity, such as indophenol, have been used in place of Nessler s reagent. Ion-selective electrodes have also found use in analysis for trace ammonia (93). 

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). 

Metallic additions to the melt, usually in the form of copper sulfate, brighten the shade of certain dyes, such as the Bordeaux range made from phenazones and the greens made from the indophenols the metal forms a complex with the dye. However, copper-containing dyes cannot be appHed to material that requires vulcanization. 

Additional Chromophores. Other types of dyes that have been studied as chromophores in dye developers include rhodamine dyes, azamethine dyes, indophenol dyes, and naphthazarin dyes (21). Cyanine dyes, although not generally stable enough for use as image dyes, have also been incorporated in dye developers (31). 

Dyes, quinone type used for anthraquinones, indamines, indoarulines, indophenols, and miscellaneous quinones (see Dyes, anthraquinone). 

Primary amines and substances with reactive methylene groups react with 1,2-naphthoquinone-4-sulfonate to yield intensely colored p-quinoid derivatives, which, in the case of aryl amines, are indophenol dyes [12, 13]. 

Fig. 3.12 The dependence on pH of the oxidation-reduction potential for c0x = cRcd (1) 6-dibromphenol indophenol, (2) Lauth s violet, (3) methylene blue, (4) ferricytochrome c/ferrocytochrome c, (5) indigo-carmine... 

---