Classification Systems for Dyes

Dyes may be classified according to chemical structure or by their usage or application method. The former approach is adopted by practicing dye chemists, who use terms such as azo dyes, anthraquinone dyes, and phthalocyanine dyes. The latter approach is used predominantly by the dye user, the dye technologist, who speaks of reactive dyes for cotton and disperse dyes for polyester. Very often, both terminologies are used, for example, an azo disperse dye for polyester and a phthalocyanine reactive dye for cotton. 

The classification used in this chapter maintains the backbone of the Colour Index classification, but attempts to simplify and update it. This is done by showing the structural interrelationships of dyes that are assigned to separate classes by the Colour Index, and the classification is chosen to highlight some of the more recent discoveries in dye chemistry [4], 

Usage Classification. It is advantageous to consider the classification of dyes by use or method of application before considering chemical structures in detail because of the dye nomenclature and jargon that arises from this system. 

Classification by usage or application is the principal system adopted by the Colour Index [5], Because the most important textile fibers are cotton and polyester, the most important dye types are those used for dyeing these two fibers, including polyester-cotton blends (see Chapter 4). Other textile fibers include nylon, polyacrylonitrile, and cellulose acetate. 

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The classification system that is most commonly used for colorants is the one initiaJIy developed by the UK Dyer s Company (now transformed into the Society of Dyers and Colourists, SDC), with the first volume of the Colour Index produced in 1924. More recently the Colour Index (Cl) has been pubhshed on CD-ROM and as an on-line web version, which makes it much more manageable to access. It is now recognised as an exhaustive international classification system for dyes and pigments and is pubhshed by the Bradford (UK)-based Society of Dyers and Colourists in partnership with the American Association of Textile Chemists and Colourists (AATCC). 

Dye manufacturers are now considering the environmental impact of the dyes they are producing, in addition to the traditional considerations of economy, higher wet fastness, and high tinctorial value [55]. Most dyes that might potentially cause damage to the environment have been eliminated from commerce. Surprisingly, there is no environmental classification system for dyes, and weU over half are of undisclosed structure. Dyestuffs can be synthesized based on safer intermediates. 

A principle focus of this book is the classification of dyes by chemical structure. This is certainly not the only possible classification scheme for dyes ordering by application properties, e.g., naming according the substrate to be dyed is another alternative. Neither of these two categories can be used with the exclusion of the other one, and overlap is often inevitable. Nevertheless, for this book it was decided to make the chemical structure of dyes the main sorting system. 

A useful classification of sensitizing dyes is the one adopted to describe patents in image technology. In Table 1, the Image Technology Patent Information System (ITPAIS), dye classes and representative patent citations from the ITPAIS file are Hsted as a function of significant dye class. From these citations it is clear that preferred sensitizers for silver haUdes are polymethine dyes (cyanine, merocyanine, etc), whereas other semiconductors have more evenly distributed citations. Zinc oxide, for example, is frequendy sensitized by xanthene dyes (qv) or triarylmethane dyes (see Triphenylmethane and related dyes) as well as cyanines and merocyanines (see Cyanine dyes). 

Another important limitation is the practical necessity of limiting the number of groupings that are established. In practice this works out so that only a small portion of the totality of logically valid classes and subclasses are set up. Dyestuffs, for example, might be classified on the basis of their chemical constitution, materials which they are used to color, methods of application, and the color imparted. When the classification is affected on the basis of chemical constitution, then a person who may be interested in dyes as chemical substances finds that his purpose is served very well. On the other hand, such classification may provide little assistance to a searcher who is interested in finding all the dyes used to color a certain type of material such as cellulose ester textiles. In establishing a classification system based on fixed compartments, arbitrary decisions must be made as to the basis for classification. If such decisions are in line with the user s... 

It is possible to classify dyes by using the Color Index that classifies dyes according to a dual system. An assigned number defines the chemical class and a generic name identifies the usage of application. However, it is convenient to use the application classification used by the U.S. International Trade Commission for application classes ... 

Classification by application or usage is the principal system adopted by the color index (Cl) [6]. The classification of dyes according to their usage is summarized in Table 8.1, which is arranged according to the Cl apphcation classification. It shows the principal substrates, the methods of apphcation, and the representative chemical t5q>es for each apphcation class [7, 8]. 

CAS 6408-78-2 EINECS/ELINCS 229-068-1 Synonyms 1-Amino-9,10-dioxo-4-phenylamino-9,10-dihydroanthracene-2-sulfonic acid, sodium salt 2-Anthracenesulfonic acid, 1-am i no-9,10-d i hyd ro-9,10-d i oxo-4-(phenylamino)-, monosodium salt Cl 62055 Classification Azobenzene Empirical C2oHi4N2NaOsS Properties M.w. 417.39 Toxicology Irritating to eyes, skin, and respiratory system TSCA listed Uses Dye for wool, silk, polyamide, leather, and soaps... 

Classification Amine salt Empirical C6H7NO V2H2O4S Toxicology TSCA listed Uses Colorant in hair dyes intermediate for prep, of oxidation color systems Trade Name Synonyms Rodol EGS [Lowenstein Dyes Cosmetics http //www.Jh lowenstein. com] p-Aminophenol sulfate CAS 63084-98-0 EINECS/ELINCS 263-847-7 Synonyms 4-Aminophenol sulfate Bis [(4-hydroxyphenyl) ammonium] sulfate Cl 76550 Classification Amine salt Empirical CsHtNO y2H204S Toxicology TSCA listed Uses Colorant in hair dyes intermediate for prep, of oxidation color systems Trade Name Synonyms Rodol PS [Lowenstein Dyes Cosmetics http //www.Jh lowenstein. com]... 

Classification Substituted aromatic amine salt Empirical C6H7N3O2 2CIH Properties M.w. 225.36 Uses Colorant in hair dyes intermediate for prep, of oxidation color systems Trade Name Synonyms Rodol 4GP t[Lowenstein Dyes Cosmetics http //www.Jhlowenstein. com]... 

Tallow trimethyl ammonium chloride. See Tallowtrimonium chloride Tallow trimethyl ammonium methosulfate. See Tallowtrimonium methosulfate Tallow trimethylene diamine. See Tallowaminopropylamine Tallowtrimonium chloride CAS 8030-78-2 7491-05-2 68002-61-9 EINECS/ELINCS 232-447-4 Synonyms Quaternary ammonium compds., tallow alkyl trimethyl, chlorides Tallow trimethyl ammonium chloride Trimethyl tallow ammonium chloride Classification Quaternary ammonium salt Formula [R-N(CH3)3]" Cr, R rep. alkyl groups derived from tallow Properties Cationic Toxicology TSCA listed Uses Antistat, preservative, surfactant in cosmetics dispersant external antistat for plastics emulsifier in corrosion inhibitor formulations for oil field brines and HCI acidizing systems textile softener, dyeing aid ... 

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