Coal tar dyes

At about the same time a thorough study was undertaken by the Department of Agriculture to determine which dyes, if any, were safe for use in foods and what restrictions should be placed on thek use. This monumental task eventually included a study of the chemistry and physiology of the then nearly 700 extant coal-tar dyes as well as the laws of various countries and states regarding thek use in food products. Most of this investigation was done under the guidance of Dr. Bernard C. Hesse, a German dye expert (17). 

Piesendy, all ceitified colois aie factory-piepaied materials belonging to one of several different chemical classes. Although a few such as D C Blue No. 6 (indigo) are known to exist in nature, certified colors owe their commercial importance to their synthetic production. Because of the starting materials used in their manufacture in the past, certified colors were once known as coal-tar dyes. Today, since most of the raw materials used in their preparation are obtained from petroleum, this term no longer appHes. 

In the United States the use of coal-tar dyes ia eye makeup is geaerally prohibited. The use of permanent and temporary hair colorants (Tables 16 and 17) and of organic dyes and their lakes is precluded. As a result, only iasoluble inorganic pigments can be used (Table 9). The sensitivity of the eye... 

Commonly, various soluble synthetic dyes ( coal tar dyes ) and insoluble pigments are used. Commonly used pigments are the iron oxides. 

A minor precedent for premarket testing of chemicals in the 1938 law had been established, on a voluntary basis, shortly after the 1906 law had gone into effect, with respect to coal-tar dyes used to color foods (98). The new drugs clause of 1938, in its turn, became a more significant precedent for later laws requiring the establishment of safety before the release of pesticide chemicals (1954), food additives (1958), color additives (1960), and medical devices (1976) (99, 100). In 1962, by the Kefauver-Harris Amendments, the Congress added the requirement that proof of efficacy be demonstrated before a new drug could be released. 

Coal tar dyes first came on the market in the late 1850 s, and within a few years had virtually replaced natural dyestuffs in the textile trade. Almost from the first, these same dyes... 

Hesse complained that even if one could get an industrial representative to speak of harmless coal tar dyes, he could not be trusted to give an honest answer. A Dr. Schweitzer of the Elberfeld company gave Hesse a list of some forty-three colors... 

The use of any dye, harmless or otherwise, to color or stain a food in a manner whereby damage or inferiority is concealed is specifically prohibited by law. The use in food for any purpose of any mineral dye or any coal-tar dye, except those coal-tar tyes hereinafter listed, will be grounds for prosecution. Pending further investigations now underway and the announcement thereof, the coal-tar dyes hereinafter named, made specifically for use in foods, and which bear a guarantee from the manufacturer that they are free from subsidiary products and represent the actual substance the name of which they bear, may be used in foods. In every case a certificate that the dye in question has been tested by competent experts and found to be free from harmful constituents must be filed with the Secretary of Agriculture and approved by him" (21). 

Uncertified coal-tar dyes are likely to contain arsenic and other poisonous material, which, when used in food, may render such food injurious to health and, therefore, adulterated under the law. 

Goldwater LJ, Rossa Af) Kleinfeld M Bladder tumors in a coal tar dye plant. Arch Environ Health 11 814—817, 1965... 

FS Jiin, SL Ah, HJ Dalang. Analysis of food coal-tar dyes in commercial dairy product, soft drink, child food, pickle and vegetarian food. J Food Drug Anal 3(1) 65 -73, 1995. 

The discussion above has addressed the assessment of a product s colour or perceived colour in basic terms. In the next two sections, methods to determine which coloured compounds are present in a product will be addressed. For the purpose of this chapter, the section on synthetic dyes will cover the analysis of the water-soluble dyes, or so-called coal tar dyes, and the section on natural pigments will cover the anthocyanin pigments, such as grape skin extracts, and the carotenoid-based materials, even if they are of synthetic origin. 

Bulk powders are made in considerable variety, but they consist always of nitrocellulose fibers which are stuck together but are not completely colloided. Some contain little else but nitrocellulose others contain, in addition to potassium and barium nitrates, camphor, vaseline, paraffin, lampblack, starch, dextrine, potassium dichromate or other oxidizing or deterrent salts, and diphenylamine for stabilization, and are colored in a variety of brilliant hues by means of coal-tar dyes. In the United States bulk powders are manufactured by one or the other of two processes, either one of which, however, may be modified considerably the materials are incorporated under wooden wheels, grained, and partially gelatinized, or the grains arc formed in a still where a water suspension of ptdped nitrocellulose is stirred and heated with a second liquid, a solvent for nitrocellulose which is volatile and immiscible with water. 

With the remainder of the liquid, mixed with io c.c. of 10% potassium bisulphate solution and a few drops of acetic acid, two or three strands of well-defatted wool are heated on a water-bath for a long time. In presence of coal-tar dyes, the wool is coloured red, the colour persisting after washing with water. 

The artificial organic colouring matters form the large class known as coal-tar dyes. 

Naphthalene (C qHq) is a condensed aromatic compound obtained from coal tar. It has a relatively low melting point (80.2°C b.p. 217.9 )i sublimes readily on warming, and exerts sufficient vapor pressure at room temperature to be readily detectable by its characteristic odor. It is a chemical intermediate or feedstock in the synthesis of a large number of derivatives (e.g., phthalic, anthranilic, hydroxy-, amino- and sulfonyl-), compounds used in the production of the coal tar dyes. 

Color fastness is important in textiles. It is a measure of how well the dye is attached to fabric (substrate). In the early 1900s a new class of coal-tar dyes, known as the indanthrenes, was invented. Some blue indanthrenes displaced indigo, because they were fester to light and washing, and brighter. The most important of these colorants, collectively known as vat dyes, is vat jade green. 

During the 1800s, chemists discovered about half of the 100 known elements. After 1850, organic chemicals, such as coal-tar dyes, drugs, nitroglycerin explosives, and celluloid plastics were developed and manufactured. The two World Wars created needs for new and improved chemical processes for munitions, fiber, light-weight metals, synthetic rubber,... 

The recently discovered methods of producing iron and steel, such as the processes of Bessemer, Siemens, Gilchrist-Thomas, etc., cut to a minimum at relatively small costs the formerly arduous processes. The making of alizarin, a red dye-stuff extracted from coal-tar, requires but a few weeks, and this by means of already existing coal-tar dye-producing installations, to yield the same results which formerly required years. It took a year for the madder to mature, and it was customary to let the roots grow a few years more before they were processed.8... 

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