Cationic Basic Dyes

Cationic dyes form positively charged dye ions by dissociation, and the positive electric charge is delocalized over the entire molecule. They are usually di- and triarylmethine dyes such as C.I. Basic Green 4, 42000 [569-64-2] (31), which are also known as triarylmethane dyes or triaryl carbenium ions [15], oxazine dyes such as C.I. Basic Blue 3, 51005 [2787-91-9] (32), orthiazine dyes. 

Cyclized di- or triarylmethine dyes are also known as acridine, xanthene, or thioxanthene dyes. Rhodamine GG (33), C.I. Basic Red 1, 45160 [989-38-8], is of the most interest for the paper industry. Rhodamine dyes dye paper in strongly fluorescent red shades. 

Low-molecular azo dyes, such as C.I. Basic Brown 1 (34), which bear basic groups are also classified in this category. 

This styryl dye 35 has very high color strength and dyes paper in brilliant yellow shades. 

Sulfur dyes are water-insoluble, macromolecular, colored compounds which are produced by bridging aromatic amines, phenols, and amino phenols with sulfur and/or sodium polysulfide [16], These dyes are of little interest for dyeing paper. Only C.I. Sulphur Black 1 (36), the most important dye of all in terms of volume, is used for special paper dyeings. 

---

Cationic (Basic) Dyes. These water-soluble cationic dyes are applied to paper, polyacrylonitrile (e g. Dralon), modified nylons, and modified polyesters. Their original use was for silk, wool, and tannin-mordanted cotton when brightness of shade was more important than fastness to light and washing. Basic dyes are water-soluble and yield colored cations in solution. For this reason they are frequently referred to as cationic dyes. The principal chemical classes are diazahemi-cyanine, triarylmethane, cyanine, hemicyanine, thiazine, oxazine, and acridine. Some basic dyes show biological activity and are used in medicine as antiseptics. 

Dyes are usually divided into water-soluble and water-insoluble groups. The water soluble group is further divided into anionic (acid) and cationic (basic) dyes. Gun 3 provides a comprehensive chart of the synthetic organic dyes. However, he does not address the resonant amphoteric dyes. The specific placement of the Rhodonines within his chart requires additional analysis and probably laboratory measurements to determine their relative level of amphoterism. The chart does not specifically delineate resonant dyes such as the Rhodonines. 

Synthetic dyes are mainly aromatic organic compounds, and they can be classified as cationic (basic dyes), anionic (direct, acid, and reactive dyes), or nonionic (disperse dyes) type [134]. Synthetic dyes are mainly used in the textile industries, but they have many other applications such as in printing, leather, papermaking, drug, and food industries [85]. Total world colorant production is estimated to be... 

Yoracryl. [Yorkshire Pat-Chem] Cationic basic dyes for acrylic, modified acrylic, and other fibers. 

Greater success was achieved by DuPont who copolymerized, the sodium salt of 5-sulfoisophthalic acid into PET to render the polymer dyeable with cationic (basic) dyes. Basic dyeable PET was successfully launched as Dacron 64 in the form of a low-pill staple product [64]. The presence of the sulfonate groups in the polymer chain also acts as an ionic dipolar cross-link and increases the melt viscosity of the polymer quite markedly. Thus, it is possible to melt-spin polymer with IV 0.56 under normal conditions, giving a low-pill fiber variant. The fiber also has a greater affinity for disperse dyes due to the disruption of the PET structure. Continuing this theme, there are deep dye variant PET fibers, often used in PET carpet yarns, which are copolymers of PET with chain-disrupting copolymer units like polyethylene adipate. They have less crystallinity and a lower Tg. therefore, they may be dyed at the boil without the use of pressure equipment or carrier at the cost of some loss of fiber physical properties. 

Mishra and Tripathy (1993) proposed a simplified classification as follows anionic (direct, acid, and reactive dyes), cationic (basic) dyes, and nonionic (disperse) dyes. There are many structural... 

Acid dyes are synthetic dyes typically applied to natural fibers, such as wool and silk, as well as to polymer-based fibers, such as polyamides and acrylics. The method of dyeing is through the use of dye baths, and chemical affixation occurs in part by the formation of salts between cationic and anionic functional groups in the fibers and dyes, respectively. Water-soluble basic dyes are also applied to the same class of substrates. But even though they are also cationic, basic dye baths require an acetic acid additive to promote uptake to the fibers. Hence, basic dyes can be tailored for use with cellulosic fiber-based materials. 

Nylon 6,6 can be made dyeable with cationic (basic) dyes as well by incorporating —SO3H or —COOH groups in the polymer. Cationic dyeable nylon is used mainly for styling purposes and has not been a major item in the stain-resist technology. 

Statistics for the production of basic dyes include those products hsted as cationic dyes, eg, cyanines, for dyeing polyacrylonitrile fibers and the classical triaryhnethane dyes, eg, malachite green, for coloring paper and other office apphcations (2,53). Moreover, statistics for triaryhnethane dyes are also hidden in the production figures for acid, solvent, mordant, and food dyes, and also organic pigments. Between 1975 and 1984, the aimual production of basic dyes in the United States varied from 5000—7700 t. However, from 1985—1990, aimual production of basic dyes varied from 5000—5700 t, and the annual sales value increased from 56 to 73 million per year. 

Dyes in these classes are generally basic dyes ie, the chiomophoie is cationic. Some stmctures have been sulfonated to acid dyes, eg, the Nigrosine, (Cl Solvent Black 5 Cl 50415), (8) to Cl Acid Black 2 [8005-03-6] (Cl 50420) (9). 

Cationic azo dyes carry a positive charge ia the chromophore portion of the molecule. The salt-forming counterion is usually a chloride or acetate. Cl basic dyes are ammonium, sulfonium, or oxonium salts. Commercial basic azo dyes for which chemical stmctures are revealed by U.S. producers are listed ia Table 15. 

Basic Orange 1 (130) (aniline coupled to 2,4-diamiaotoluene) and Basic Orange 2 (22) (aniline coupled to y -phenylenediamiae) are examples of amine salt type cationic azo dyes. The cation is formed by protonation under acidic conditions. Under neutral or alkaline conditions, these dyes behave more like disperse dyes. In 1988 the U.S. production of Cl Basic Orange 2 amounted to 132 tons. 

Basic Red 18 (131), Basacryl Red X-NL [14097-03-17 is an example of a pendant cationic azo dye, ia which a localized positive charge is not conjugated with the chromophoric system. /V-Kthy1-/V-(2-ch1oroethy1)ani1ine [92-49-9] reacts with trimethyl amine to form the ammonium salt coupler. The diazo component ia Basic Red 18 is 2-ch1oro-4-nitroani1ine [121 -87-9]. 

So-called delocalized cationic azo dyes are another type ia which the positive charge is delocalized (or distributed) across the dye cation. Basic Blue 54 (132) (2-amiao-6-methoxybenzothiazole coupled to /V, /V-dimethy1 ani1 ine and then quarternized with dimethyl sulfate) is an example of this class which can also be considered as a diazamethine dye. 

Basic Red 22 (134), which contains 1 part ia 7 of the yellowish red 1,4-dimethyl isomer, Basic Red 29 (135), and Basic Yellow 25 (136) are all examples of delocalized cationic azo dyes. Dyes of this type can also be synthesized by Hbnig s oxidative coupling reaction of heteroaromatic hydrazones with tertiary aromatic amines. 

Basic Dyes. These are usuaUy the salts of organic bases where the colored portion of the molecule is the cation. They are therefore sometimes referred to as cationic dyes. They are appHed from mild acid, to induce solubUity, and appHed to fibers containing anionic groups. Thein main outiet is for dyeing fibers based on polyacrylonitrile (see Fibers, acrylic). 

The compatibihty value is mainly related to the affinity of the dye for the particular fiber because for basic dyes on modified acryhc fibers there is htde possibihty for migration and therefore this does not play a significant part in determining compatibihty. The rate of dyeing of a specific mixture of dyes of the same compatibihty value is not determined by the value itself. The adsorption of cationic dyes is induenced by the presence of others in the dyebath the presence of cationic retarding agents and electrolytes also induences the rate of exhaustion. It is therefore possible to have a combination of dyes with a compatibihty value 5 that under specific dyebath conditions exhausts more rapidly than a combination based on dyes of compatibihty value 3. 

Basic (Cationic) Dyes. The use of basic dyes is confined mainly to acryUc textile fibers, acetate, and as complementary dyes for acid-modified polyester fibers that accept this class of dyes. 

In this work hybrid method is suggested to determine anionic surfactants in waters. It is based on preconcentration of anionic surfactants as their ion associates with cationic dyes on the membrane filter and measurement of colour intensity by solid-phase spectrophotometry method. Effect of different basic dyes, nature and hydrophobicity of anionic surfactants, size of membrane filter pores, filtration rate on sensitivity of their determination was studied. Various cationic dyes, such as Methylene Blue, Crystal Violet, Malachite Green, Rhodamine 6G, Safranin T, Acridine Yellow were used as counter ions. The difference in reflection between the blank and the sample was significant when Crystal Violet or Rhodamine 6G or Acridine Yellow were used. 

The name of this structural class ( quinoline ) in the Colour Index is not ideal because quinoline derivatives feature in other related classes, such as the methine basic dyes with a quinolinium cationic group. The class is more precisely associated with quinophthalone (1.15), the characteristic chromogen derived by condensation of quinoline derivatives with phthalic anhydride. This small class of yellow compounds contributes to the disperse, acid, basic and solvent ranges of dyes. 

Controversy has arisen at times [52] regarding the apparent synonymity of the terms basic dye and cationic dye . The Society of Dyers and Colourists defines a basic dye as characterised by its substantivity for the acidic types of acrylic fibres and for tannin-mordanted cotton , whereas a cationic dye is defined as one that dissociates in aqueous... 

---