Direct Diazotization Dyes

The group of direct dyes with aftertreatment includes direct dyes that, after being applied to the fiber by the usual method, are subjected one of the following aftertreatments (1) Aftertreatment with cationic auxiliaries, (2) aftertreatment with formaldehyde, 3) diazotization of the dye on the fiber and coupling with suitable components (diazotization dyes), and (4) aftertreatment with metal salts. 

The direct diazotization and preparation of azo-dyes in one electrochemical process was discovered by Lob.1 His method— an anodic process—is based on the following principle ... 

Azo-stilbene dyes formed by diazotization of a condensation product containing primary amino groups and coupling with azo dye coupling components, eg. Direct Brown 29 (Cl 40505) (6) ... 

Diazotization and formation of diazo dyes affords a general approach to pre-column derivatization, to be followed by direct phase or RP-HPLC with UVD or FLD. Thus,... 

Amino-6-nitrobenzthiazole [6285-57-0] and 2-amino-5,6- or 6,7-dichloro-benzthiazole [24072-75-1], [25150-27-0] are widely employed to give scarlet to ruby shades because of their facile accessibility by ring closure of 4-nitrophe-nylthiourea (e.g., 4) [20] or 3,4-dichlorophenylthiourea, respectively. In the latter case the resulting mixture of isomers is directly utilized for diazotization and transformed into the mixture of dye isomers 5. 

Coupling diazotized dehydrothio-p-toluidinesulfonic acid to resorcinol and subsequent coupling of diazotized aniline to the monoazo dye formed gives C. I. Direct Orange 18, 20215 [5915-59-3] (11), an important substantive dye. 

C. I. Direct Black 19, 35255 [6428-31-5] (19) is also an important dye. It is obtained by coupling two equivalents of j9-nitraniline to H acid, sulfhydrate reduction of the two nitro groups, and coupling of the bis-diazotized intermediate compound with two equivalents of m -phenylenediamine. 

C. I. Direct Yellow 12, 24895 [2870-32-8] 4,4 -Diaminostilbene-2,2 -disulfonic acid is bis-diazotized with an aqueous solution of sodium nitrite at 5°C. Next, phenol is dissolved in water, and sodium hydroxide solution and soda are added. To this solution is added the above bis-diazotized solution. Then, more 30 % sodium hydroxide solution is added. On the following morning, the solution is heated to 70 °C, and after addition of 30 % hydrochloric acid, the dye is salted out with rock salt. The damp press cake, ethanol, soda, 30 % sodium hydroxide solution, and ethyl chloride are kept in a closed stirrer vessel for 24 h at 100 °C (5 - 5.5 bar). The mixture is then cooled to 70 °C and transferred at its own pressure to a distilling vessel, from which the ethanol is distilled. After being cooled to 80 ° C, the mixture is suction filtered and dried at 100 °C. 

The urea bridge can also be introduced into direct dyes with 4,4 -diaminodi-phenylurea derivatives by means of bis-diazotization and coupling (see 25). 

Direct dyes containing one or more diazotizable amino groups in the dye molecule permit further diazotization on the fiber and subsequent coupling with a developer. 3-Naphthol can be used as a developer for orange, red, brown, blue, and black shades, and 1,3-phenylenediamine and 2,4-diaminotoluene for brown, gray, and black shades. 

The dialkylaminoalkyl residue may also be connected directly to the phenyl residue of the acetoacetanilide. By coupling with diazotized 2-(4-aminophenyl)-benzimidazole, a yellow dye suitable for paper is formed [15]. The dialkylaminoalkyl group may be connected to the N1 atom of 3-methylpyrazolone [16], to the amide nitrogen atom of Ar-phcnylpyrazolonc-3-carbonamide [17], to the N2 atom of 3-cyano-2,4,6-trisaminopyridine [18], or to the amino group of 2-amino-4,6-dihydroxypyridine [19],... 

Oxidation of dehydro tli i o-/ - to 1 u i dine su 1 fo nic acid with sodium hypochlorite [7] gives the yellow azo paper dye C.I. Direct Yellow 28, 19555 [8005-72-9] (10) without diazotization and coupling. 

Primuline, discovered by Green, was the first commercial yellow direct dye which could be diazotized on the fiber and coupled with washing is good, but its light fastness is unsatisfactory. Also, it is not... 

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 volume of diazotized aniline in cubic centimeters gives the per cent purity directly. Coupling should be carried out at 0°C. 

The nitrobenzene solution, together with the suspended solid material, is shaken with a mixture of 300 cc. water and 100 grams of ice, then twice with 100-cc. portions of cold water. The combined aqueous extracts are filtered through a moistened paper and then saturated with 200 grams of salt, whereupon sodium 2-naphthol-l-sulfonate is precipitated in colorless plates. Stirring is continued until all of the salt is dissolved, and the mixture is allowed to stand overnight, then filtered. The product is pressed out and washed twice with saturated salt solution. The filter cake is used directly for the preparation of 2-naphthyl-amine-l-sulfonic acid after tests have shown that it does not fluoresce in soda solution and does not yield a water soluble, orange red dye with diazotized aniline and thus does not contain isomeric naphtholsul-fonic acids. 

Various types of dyes are prepared from dehydrothiotoluidine. The free base or its sulfonic acid is diazotized and coupled with various naph-tholsulfonic acids such as, for example, e acid (l-naphthol-3,8-disul-fonic acid). The resulting dye is characterized by its high purity of color and can be discharged to a pure white. Such red direct dyes are sold under various names, and are usually referred to as dyes of the erika red type. (Erika Z is the combination from dehydxothioxylidine and e acid. l-Naphthol-3,6-disulfonic acid gives a very similar dye.) In addition to the true azo dyes from dehydrothiotoluidine, two other products are made which are important yellow dyes. One of these dyes is the naphthamine yellow NN (also called chloramine yellow) (Kalle), formed from dehydrothiotoluidinesulfonic acid by oxidation with sodium hypochlorite. The other is thiazole yellow or Clayton yellow, which is made by combining the diazo compound of dehydrothiotoluidinesulfonic acid with a second molecule of the same compound to form a diazoamino compound. 

The direct dye is applied in the manner already described according to whether it belongs to Class A, B, or C. After dyeing the goods are rinsed to remove all free colour and then diazotized in a fresh liquor either in another machine or in the same one. In order to ensure complete diazotiza-tion the following conditions must be fulfilled ... 

In producing the developed colours, the direct dyestuff is diazotized on tile fibre, and the diazonium compound couples with a suitable developer. With the coupled dyes the process is reversed. The cotton is dyed with a direct dye containing an amino or hydroxyl group and the dyed fibre is then treated with a solution of a diazotized base. An example is Benzo Para Deep Brown G (C.I. direct brown 152), (24),... 

The acrylic component can be left undyed quite easily because it has no affinity for those direct dyes which are classified as acetate reserving. There are also many diazotized and developed direct, as well as vat dyes which will dye the cellulose only. Disperse dyes can be used for acrylonitrile fibre, but they will stain the cotton or rayon component, and clearing with a solution containing 8 oz to 1 lb of potassium permanganate and 2 oz of sulphuric acid per 100 gallons at 30 C (86 F) for 15 minutes, will probably be necessary. The oxides of manganese will subsequently have to be removed with sodium bisulphite. 

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