C.I. Direct Red

D.T. Sponza and I. Mustafa, Toxicity and intermediate of C.I. Direct Red 28 dye through sequential anaerobic/aerobic treatment. Proc. Biochem., 40 (2005) 2735-2744. 

Reagents. The dyes used in this study (see Figure 1) were obtained from the following sources Congo Red (Colour Index (C.I.) Direct Red 28, C.I. No. 22120) A. D. Mackay Inc. ... 

This system resolved the aniline peak (retention time (rt) = 2.67 min) from the benzidine peak (rt = 2.27 min) as can be seen in Figure 2. Other potential interferences were selected for study by looking at the expected fragments from the reduction of various dyes. Reduced dye samples were spiked with aniline (rt = 2.67 min), -aminophenol (rt = 1.97 min), -phenylenediamine (rt = 1.93 min) and -nitroaniline (rt = 3 16 min). None of these materials interfered with the detection of the benzidine peak. To determine if other types of dyes might interfere with the analysis, two sets of filters were spiked at low and high levels separately with C.I. Direct Red 28 (13 7 yg and 137 yg), C.I. Direct Blue 53 formulation (o-tolidine-based) (21.2 yg and 212 yg) and C.I. Direct Blue 8 formulation (o-dianisidine-based)(23.3 yg and 233 yg). 

Based on the analyses of these liquid samples an approximation of amount of the benzidine-containing dye compound in a particular dye formulation could be made using molecular weight calculations. For 30 samples of C.I. Direct Red 28 formulation (molecular weight (Mr) = 696) at the... 

C.I. Direct Red 28. Duncan s multiple range test indicated that the recovery on day 1 was significantly different from the other three analyses at days 7, 14 and 28. Analyses at days 7, 14, and 28 were not significantly different. With... 

The repeatability and stability studies were done at concentration levels which preliminary evidence on liquid samples had shown to be reproducible within 10% CV. However, this was not the case for three of the dyes (C.I. Direct Red 28, C.I. Direct Brown 95, and C.I. Direct Black 38). In this situation, the lowest analytically quantifiable limit (LAQL) had to be redefined. From the results of the repeatability study, the second highest level was the logical choice for this redefined LAQL. A second abbreviated stability study was conducted with C.I. Direct Red 28, C.I. Direct Black 38, and... 

This method has been used to analyze both symmetrical (C.I. Direct Red 28 and C.I. Direct Blue 6) and unsymmetrical (C.I. Direct Black 38 and C.I. Direct Brown 95) benzidine-based dyes. Based on this work, the application of the method to other benzidine-based dyes should be straightforward. When field samples are submitted for benzidine-based dye analysis, bulk samples of the dyes present in the sample also should be submitted. With these bulk samples, the analyst should be able to determine if this method is applicable to the various dyes submitted and if any interferences are present. The method presently has not been tested on field samples. An existing sampling method (J 3) for azo dyes and diazonium salts should be directly applicable to this method with a change from a cellulose ester to a Teflon filter. This change is necessary to insure quantitative recovery of the sample from the filter. 

Examples From 4-aminoazobenzene-4 -sulfonic acid and benzoyl I-acid, the important red dye C. I. Direct Red 81,28160 [2610-11-9] (12) is obtained. 

With the increasing popularity of the continuous method of dyeing in the paper industry, new direct dyes were developed with particularly good cold-water solubility without any impairment to the substantivity. Improvements of this kind with regard to substantivity and solubility can be seen in the further development of the widely used, but only moderately soluble, cotton dye C.I. Direct Red 81, 28160 [2610-11-9] (4). 

If the benzoyl group is exchanged for 1,3,5 trichlorotriazine and the residual chlorine atoms are treated with, e.g., monoethanolamine, C.I. Direct Red 253, [142985-51-1] (5) is obtained, which has both higher substantivity and better solubility. 

For example, if 2-amino-5-naphthol-7-sulfonic acid is bridged with phosgene, highly substantive orange to red paper dyes such as C.I. Direct Orange 102, 29156 [i6598-63-6] (13) and C.I. Direct Red 239, [28706-25-4] (14) are formed with suitable diazo components. 

The metabolism of the benzidine-based dyes C.I. Direct Red 28, C.I. Direct Blue 6, C.I. Direct Brown 95, and C.I. Direct Black 38 was studied in Rhesus monkeys. After ingestion of the dyes, benzidine and monoacetylbenzidine could be detected as metabolites in the urine. This indicated that the dyes had been converted to benzidine [29], Recent in vitro studies on C. I. DirectBlue 14 show that bacteria isolated from healthy human skin have reductase activity and are able to cleave the dye into the corresponding arylamine, in this case 3,3 -dimethylbenzi-dine [30],... 

Suitably substituted direct dyes can be converted to metal complexes. In this regard, Cu is the metal of choice and examples are C.I. Direct Blue 218, C.I. Direct Red 83, and C.I. Direct Brown 95. About 5% of all azo direct dyes are metal complexes and unlike most direct dyes, these dyes have good lightfastness, as would be anticipated. 

The high temperature stability of direct dyes is an important consideration if one wishes to use these dyes as the colorant for cotton when dyeing a polyester/cotton blend at 130°C.20 The key to success is to choose dyes that are resistant to hydrolysis. Suitable dyes include C.I. Direct Yellow 105, C.I. Direct Orange 39, and C.I. Direct Blue 80, whereas unsuitable dyes include C.I. Direct Yellow 44, C.I. Direct Red 80, and C.I. Direct Red 83. A quick examination of the structures... 

Type E1 D-+E1 Synthesis. Dyes of this type require the conversion of an aryldiamine to a tetrazonium compound (one that has two diazonium groups), in a process know as tetra-zotization. See Fig. 13.93, which involves environmentally friendly alternatives to benzidine. Following tetrazotization, one tetrazonium molecule reacts with two coupler molecules to produce the target dye, examples of which are provided in Fig. 13.94 (11 C.I. Direct Red 28 (Congo Red), 12 C.I. Direct Yellow 12, and 13 C.I. Acid Yellow 42). Disazo dyes prepared this way include dye 14 (C.I. Direct Blue 15), which is converted to the important bis-copper complex, C.I. Direct Blue 218 (see Fig. 13.95). 

Fig. 13.100), for C.I. Direct Red 83. In this case the target dye is prepared by metallization after the coupling step. 

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