Direct yellow dyes

Stilbene dyes of importance aie mosdy direct yellow dyes for ceUulosic fibers, especially paper. There have been several red and blue stilbene-containing dyes reported, but they have not (ca 1996) been developed to commercial importance. There are brown leather dyes which are stilbene-based. The most important stilbene dyes are those known siace the 1880s. The commercial importance of Direct Yellow 11 (1883), Direct Orange 15 (1888), Direct Yellow 4 (1886), and Direct Yellow 106 (1936) attest to the value, properties, and durabiUty of stilbene yellow dyes. 

Wastewater Treatment by Electrocoagulation, Table 1 Comparison of different treatment strategies for a synthetic contaminated aqueous solutirai of 1 mM phenol and 0.1 mM direct yellow dye 52... 

Coupling tetra2o (7) with o-cresol has been reported to give a dye (19) which is less alkah-sensitive than Direct Yellow 4 (Cl 24890) and to have better cold-water solubiUty than Direct Yellow 12 (Cl 24895) (18). One reference is made to a stilbene laser dye (10) and two each to dyes for 1ight-po1ari2ing films (34,35) and reprographic inks (36,37). 

Direct Yellow 4, Direct Yellow 11, Direct Yellow 106, and Direct Orange 15 are the most important stilbene dyes, accounting for most sales of this type. Estimated volumes and values for Hquid and powder forms appear in Table 3 (38). 

Oxidation of Aromatic Amines. The technically important dye Direct Yellow 28 (23) [10114-47-3] (Cl 19555) for cotton usage is manufactured by oxidation of dehydrothio- i ra-toluidinesulfonic acid sodium salt with sodium hypochlorite ia aqueous alkaline solutioa. 

DAS (11.7) is synthesised from 4-nitrotoluene-2-sulphonic acid (11.6) by the route outlined in Scheme 11.1. An important factor in the preparation of DAST brighteners in the purity necessary for good performance is the purity of the DAS used as starting material. At one time DAS made in this way contained significant amounts of yellow azoxy compounds similar to 11.8, which formed the main components of the obsolescent dye Sun Yellow (Cl Direct Yellow 11) made by the partial reduction and self-condensation of intermediate 11.6. Today the major manufacturers supply DAS essentially free from these undesirable impurities [37]. 

The yellow ink jet dyes (and pigments) are metal-free azo dyes, such as Cl Direct Yellow 132 and Cl Acid Yellow 23 (Tartrazine).48,49 Most of the magentas are azo dyes derived from H-acid (l-amino-8-naphthol-3,6-disulfonic acid), such as (62), and xanthenes, such as Cl Acid Red 52 and Cl Acid Red 289.48,49 Where high lightfastness is a requirement, a copper complex azo dye, Cl Reactive Red 23 (63), is used. However, such dyes are dull (see Section 9.12.3.2). Nickel complex PAQ dyes, such as (22), are claimed to be brighter and to have similar high lightfastness... 

Affinity values of the symmetrical disazo dyes Cl Direct Yellow 12 (3.6), Red 2 (3.8 X = CH3, Y = H) and Blue 1 (3.2) on cellophane have been measured recently under hydrostatic pressures up to 600 Mpa [120]. The affinity of Yellow 12 increased slightly but values for the other two dyes decreased considerably with increasing hydrostatic pressure (Table 3.23). The sulpho groups on the central stilbene nuclei of the Yellow 12 molecule tend to inhibit aggregation, whereas Red 2 and Blue 1 aggregate much more readily. The small increase in the affinity observed with Yellow 12 may indicate that isomerisation from the cis to the more stable Linns form may occur as the hydrostatic pressure is increased. 

The simplest monoazo dyes fail to meet these requirements, but by choosing intermediates known to confer substantivity and by building up the molecule to provide the necessary length and coplanarity (section 3.2.1), direct dyes can be produced from this class. Thus the highly substantive character of the benzothiazole nucleus is exploited in Cl Direct Yellow 8 (4-58), as is the alignment of the azo, ureido and acylamino groups in the substituted J acid coupling component of Cl Direct Red 65 (4-59). 

The thiazole ring system is found in many types of dye. Thiazole-containing sulphur dyes and primuline were considered in section 6.4-2. Quaternised dehydrothio-p-toluidine 6.133 is available as Cl Basic Yellow 1 (6.152). Other derivatives of this intermediate are used as direct dyes, such as Cl Direct Yellow 8 (4-58). The benzothiazole ring appears in various azo disperse dyes [14], quatemisation of which gives useful cationic dyes, an important example being Cl Basic Blue 41 (4.99). Another example containing a quaternised thiazole ring is Cl Basic Red 29 (4-102). 

Thus, RP-HPLC-MS has been employed for the analysis of sulphonated dyes and intermediates. Dyes included in the investigation were Acid yellow 36, Acid blue 40, Acid violet 7, Direct yellow 28, Direct blue 106, Acid yellow 23, Direct green 28, Direct red 79, Direct blue 78 and some metal complex dyes such as Acid orange 142, Acid red 357, Acid Violet 90, Acid yellow 194 and Acid brown 355. RP-HPLC was realized in an ODS column (150 X 3 mm i.d. particle size 7 /.an). The composition of the mobile phase varied according to the chemical structure of the analytes to be separated. For the majority of cases the mobile phase consisted of methanol-5 mM aqueous ammonium acetate (10 90, v/v). Subsituted anthraquinones were separated in similar mobile phases containing 40 per cent methanol. The flow rate was 1 ml/min for UV and 0.6 ml/min for MS detection, respectively. The chemical structure of dye intermediates investigated in this study and their retention times are compiled in Table 3.28. It was found that the method is suitable for the separation of decomposition products and intermediates of dyes but the separation of the original dye molecules was not adequate in this RP-HPLC system [162],... 

Many azo dyes which are insoluble in dilute hydrochloric acid can be titrated directly in presence of Rochelle salt. Since Rochelle salt forms a compound with titanium, which is pale yellow in dilute solution, this method is inapplicable for the estimation of yellow dyes. 

Stilbene dyes contain the stilbene structural moiety (C6H5C=CC6H5) but are synthesized from 4- nitrotoluene-2-sulfonic acid. Direct yellow stilbene dyes for dyeing paper are probably the most commercially important. 

Kinetic studies in sediment/water systems with Direct Red 2, Acid Black 92, Acid Red 4, Acid Red 18, and Direct Yellow 1 lead to linear and biphasic plots of dye loss over time. For all but Direct Yellow I, dye loss was usually preceded by a lag or adaptation phase. Acid Black 92 and Direct Red 2 were transformed completely in less than 24 and 48 hours, respectively, but Acid Yellow 151 and Direct Yellow 1 showed half-lives of greater than 2 years. The rapid initial drop in concentration of all dyes observed, with the exception of Acid Red 18, was presumed to be due to sorption. Tests to determine the effect of pH on... 

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. 

C. I. Direct Yellow 50, 29025 [3214-47-9] (26) is obtained, for example, by phosgene treatment of two equivalents of the aminoazo dye prepared from diazo-tized 2-aminonaphthalene-4,8-disulfonic acid coupled to w-toluidine. 

There are a number of yellow substantive dyes synthesized by this principle. Example C. I. Direct Yellow 41, 29005 [8005-53-6] (29) is obtained by phosgene treatment of an equimolar mixture of bases A (sulfanilic acid— cresidine) and B (jt>-nitroaniline—> salicylic acid and reduction of the N02 group). The mixture additionally contains the two corresponding symmetrical dyes. 

Compared to direct azo dyes, the direct anthraquinone dyes have lower tinctorial strengths and are therefore far less economical to use. They have lost most of their importance. Only a few special green dyes have retained their importance. Direct green cotton dyes can be produced by coupling a blue bromamine acid dye and a yellow azo dye via ureido or diaminotriazine bridges. 

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],... 

In streptocyanine dyes both ends of the methine chain are joined directly to nitrogen atoms, and a double enamine structure is thus present. The dyes are extremely susceptible to hydrolysis, particularly if they contain secondary nitrogen atoms. Stable dyes are obtained if the nitrogen is part of a heterocyclic ring system. Streptocyanine dyes are brilliant yellow dyes that dye polyacrylonitrile and acid-modified polyamide fibers with outstanding lightfastness [1],... 

Walther obtained the first direct dyes by self-condensation of 4-nitrotoluene-2-sulfonic acid. So-called Sun Yellow is a mixture of different components, depending on the concentration of sodium hydroxide, the temperature, and the duration of the reaction. Oxidation of the intermediate dye and subsequent reduction with iron and hydrochloric acid gives 4,4 diaminostilbene-2,2 -disulfonic acid, which is used for fluorescent whitening agents and azo dyes. The shades are mostly yellow to red. The structure of Direct Yellow 11, 40000 [65150-80-3] (13 is one of the main components) probably contains a mixture of stilbene, azo, and/or azoxy groups. 

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. 

Nitro dyes are the most important class of direct hair dyes they are substituted derivatives of nitrobenzene or nitrodiphenylamine [3, Nitro and Nitroso Dyes]. By proper selection of donor groups and substitution site on the benzene ring, a spectrum of dyes from yellow to blue violet can be prepared [9, pp. 247-250], [40] (Scheme 3). 

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