Azo-dye

It is used as a first component in the preparation of azo-dyes, amlnoazo-dyes See azo-dyes, o-aminobenzoic acid See anthranilic acid. 

Prepared by reduction of 4-nitrophenol or 4-nitrosophenoi. Can be diazotized and used as a first component in azo-dyes. Chief outlet is for sulphur dyes in which it is fused with sodium polysulphides. L/sed as a photographic developer. 

It is an important dyestuffs intermediate. It condenses with chloroethanoic acid to give phenylglycine-o-carboxylic acid for the synthesis of indigo. It can be diazotized and used as a first component in azo-dyes it condenses also with chloroanthraquinones to give intermediates for anthraquinone dyes. 

Usually prepared from the corresponding sulphonic acids by alkali fusion, methylation of phenol or from the aminotoluene by treatment with nitrous acid followed by boiling. Both o- and p-cresol are used as end components in azo dyes. 

It was used as an end component in a few azo-dyes, but this use has been discontinued because of its carcinogenic character. 

Basic, forms a stable water-soluble dihydrochloride. Diazotization gives brown azodyes (Bismarck brown) owing to the coupling of the partially diazotized base with the excess of diamine. Is also used as an end component of many azo-dyes, readily coupling with one or two molecules of diazo compound. 

It is prepared by heating aniline sulphate for 8 hours at l C. It readily diazotizes and is used as first component in a large variety of azo dyes. 

The mixture of xylidines has been used as a first component of azo-dyes. The chief constituent of the mixture is m-xylidine (4-amino-1,3-xylene). It can be separated by crystallization from glacial ethanoic acid. It is also used for the preparation of azo-dyes. 

The behavior of insoluble monolayers at the hydrocarbon-water interface has been studied to some extent. In general, a values for straight-chain acids and alcohols are greater at a given film pressure than if spread at the water-air interface. This is perhaps to be expected since the nonpolar phase should tend to reduce the cohesion between the hydrocarbon tails. See Ref. 91 for early reviews. Takenaka [92] has reported polarized resonance Raman spectra for an azo dye monolayer at the CCl4-water interface some conclusions as to orientation were possible. A mean-held theory based on Lennard-Jones potentials has been used to model an amphiphile at an oil-water interface one conclusion was that the depth of the interfacial region can be relatively large [93]. 

Couple in alkaline solution with diazotised amines to give orange or red azo dyes. 

Azo-dye formation. Dissolve 2-3 drops of aniline in 1 ml. of cone. HCl and add 3 ml. of water. Shaike to dissolve any hydrochloride which may have separated and cool in ice. Add a few drops of 20% sodium nitrite solution. Add this cold diazonium solution to a cold solution of the phenol in an excess of aqueous NaOH solution. Solutions or precipitates of azo-dyes ranging in colour from orange through scarlet to dark red, according to the phenol used, are obtained. Note in particular that i-naphthol gives a brownish-red, 2-naphthol a scarlet precipitate. Catechol decomposes. 

Forms diazonium derivative which can be coupled with 2-naphthol or with dimethylaniline to form azo-dyes. 

The solution must be strongly acid in order to avoid the coupbng reaction between the undecomposed diazonium salt and the phenol (see under Azo Dyes). For the preparation of phenol and the cresols, the aqueous solution of the diazonium compound is warmed to about 50° at higher temperatures the reaction may become unduly vigorous and lead to appreciable quantities of tarry compounds... 

The azo dyes are not of any great practical value owing to their slight solubility in water. Th4 introduction of a sulphonic acid group into the molecide has no effect upon the colour, but renders the dye water-soluble—a fact of great commercial value. The simplest way of achieving this is to employ an amine, e.g., sulphanilic acid, in which the — OjH group is already present. 

Primary aromatic diamines cannot be diazotised (tetrazotised) and coupled normally. Thus o-])henylenediamiiie yields a triazole derivative and m-phenylenediamine gives an azo dye (Bismarck brown) by selfcoupling. 

Some reference to the use of nitrous acid merits mention here. Primary aromatic amines yield diazonium compounds, which may be coupled with phenols to yield highly-coloured azo dyes (see Section IV,100,(iii)). Secondary aromatic amines afford nitroso compounds, which give Liebermann a nitroso reaction Section IV,100,(v). Tertiary aromatic amines, of the type of dimethylaniline, yield p-nitroso derivatives see Section IV,100,(vii). ... 

The diazonium salt of 2-aminothiazole couples with 2-dimethylamino-4-phenylthiazole, giving the corresponding azo dye (194) (Scheme 123) used for dyeing synthetic fibers (404). 

Disperse azo dyes for dyeing polyester textile material... 

The colors of azo compounds vary with the nature of the aryl group with its substituents and with pH Substituents also affect the water solubility of azo dyes and how well they... 

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