Containing Cationic Groups Basic Dyes

Basic (cationic) dyes contain cationic groups which are ionized in the dyebath. They are applied to acrylics, nylon, polyester, and paper and are most often azo, anthraquinone, triarylmethane, quinoline, thiazine, methine, oxazine, and acridine types. 

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 chemical structures of synthetic dyes show considerable variety. They generally contain more than one aromatic group, condensed aromatic substructures or heterocyclic rings (pyrazolone, thiazole, acridine, thiazine, oxazine) which are mainly hydrophobic, and, frequently, a polar basic or cationic group which is strongly hydrophilic. Due to these structural characteristics, they readily bind both to polar adsorptive and apolar reversed-phase (RP) chromatographic supports, making their successful separation difficult. As the synthetic dyes are not volatile... 

Basic (or cationic) dyes They contain quaternary amine groups in their molecular structure. Examples of basic dyes are azo basic dyes (e.g. Basic Red 22) and cationic anthraquinone dyes (e.g. Basic Blue 47). Figure 4.3.3 shows the chemical structure of two of these semi-permanent dyes. 

ACID DYES Commercial acid dyes contain one or more sulfonate groups, thereby providing solubility in aqueous media. These dyes are apphed in the presence of organic or mineral acids (pH 2—6). Such acids protonate any available cationic sites on the fiber, thereby making possible bonding between the fiber and the anionic dye molecule. Wool, an animal fiber, is an amphoteric coUoid, possessing both basic and acidic properties because of the amino and carboxylic groups of the protein stmcture. In order to dye such a system, coulombic interactions between the dye molecule and the fiber must take place ie, H2N" -wool-COO + H2N" -wool-COOH. The term acid dye is appHed to those that are capable of such interactions. Acid dyes... 

Cationic Formaldehyde Condensation Resins. An appreciable improvement in wet-fastness properties is obtained by aftertreating the dyeings with polymeric condensation resins containing strongly basic groups. This leads to the formation of insoluble salts from resin cation and dye anion. 

The removal of three cationic dyes Basic Blue 3 (3), Basic Violet 3 (4) and Basic Violet 10 (5) from aqueous solutions using the P-GD polymer obtained by crossUnking with EP in the presence of carboxymethylcellulose was reported this GD polymer (denoted polymer P) contains hydroxyl and carboxylic groups [37-39]. 

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