INDUSTRIAL A N D ENGINEERING CHEMISTRY
December, 1926
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Commercialization of Synthetic Anthraquinone I n addition to the chromic acid oxidation of anthracene and the synthetic process based on the Friedel and Crafts reactions, it was inevitable that many variations of the anthracene process and other synthetic methods should be proposed. These, however, have been either impractical commercially or of limited application only. The choice, therefore, when a source of anthraquinone was needed in this country, was between the anthracene process and the synthesis through o-benzoylbenzoic acid. The anthracene process presented serious difficulties to the American manufacturer. The purihation and treatment of the anthracene before oxidation is a costly step, and the recovery of the reduced chromic acid liquors uneconomic. For the commercialization of the synthetic, process, on the other hand, the availability of two raw materials, phthalic anhydride and anhydrous aluminum chloride, was essential. Gibbs and Conover had discovered the air oxidation process for the production of phthalic anhydride from naphthalene.ll By passing naphthalene vapor mixed with air over a catalytic mass containing vanadium oxides, preferably at a temperature of between 350" and 500" C., phthalic anhydride is formed, together with small amounts of phthalic acid, benzoic acid, and naphthaquinones. The crude anhydride is purified by one or two sublimations.
Various processes were also being developed by Jacobson" and others for anhydrous aluminum chloride, the other raw material essential to the synthetic process. The chloride should preferably be as nearly pure as possible, of the correct physical form, and freshly prepared. With these materials available, and the chemistry of the reaction thoroughly investigated, the industry turned to synthetic anthraquinone as a source of an intermediate of consistent and exceedingly high purity, available in any quantity, and a t comparatively low cost. The actual process is described by HardingI3 as follows: The o-benzoylbenzoic acid is prepared by adding a solution of phthalic anhydride in benzene to a mixture of anhydrous aluminum chloride and benzene contained in a lead-lined, jacketed kettle. A temperature of 35" C. is maintained for about a half hour after all the reactants have been added. The temperature is then raised to the boiling point of benzene and maintained until hydrogen chloride is no longer evolved. The benzene is removed by steam distillation. After drying the o-benzoylbenzoic acid is converted into anthraquinone by treatment with 95 to 98 per cent sulfuric acid a t a temperature of from 110" to 150" C. The crude anthraquinone so obtained is finally purified by sublimation. There are some variations in the details of the present-day process but the basic principles remain unaltered. In addition to solving a serious problem for the American vat dye manufacturer, the development of the process adds still another product to a list already !ong, and headed by synthetic indigo, of products once obtained from natural sources and now produced synthetically. 11
11
U.S. Patent 1,285,117 (November 19, 1918).
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U. S. Patent 1,448,082 (February 13, 1923). Colov Trade J . , 9, 184 (1921).
Development of the Food Color Industry in the United States By W. C. Bainbridge H. KOHNSTAMM & Co., INC.,BROOKLYN, N. Y.
N THE early days of our existence the diet of the human
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race consisted largely of raw and uncooked food materials. The colorings that Nature had imparted to these products not only served to designate the species but also to gage their degree of freshness and wholesomeness. I n other words, our early ancestors soon became aware of the fact that the most tender and tasty grass was the greenest and that the most luscious and delicious berries were the reddest. But as civilization advanced and the culinary art developed, it was discovered that the natural freshness of the color and flavor of many of our foodstuffs suffered in the process of preparation. An esthetic desire was created to perpetuate the familiar and characteristic hues that had been destroyed in the process of cooking or preserving. Thus the art of tinting our food products was established. At first the juices of such vegetable products that lent themselves readily to extraction and concentration were employed. With few exceptions, these coloring matters were readily decomposed and the effects obtained were far from satisfactory. In order to get results, all types were used, including many poisonous mineral pigments, such as chrome yellow and quicksilver vermilion. Purified preparations of carminic acid, saffron, bixin, chlorophyl, turmeric, and certain derivatives of the lichens are among those that have stood the test of time and usage and still find application in this direction. With the advent of the coal-tar colors, the dyes employed for such purposes were greatly augmented. Wonderful
new effects were obtained that made Nature "ashamed of herself." Since shade was the governing factor in the choice of such colors, little thought was given to the poisonous qualities of these products. Not only were there toxic and physiological effects on the human tissues generally unknown, but little attempt was made to eliminate such impurities of manufacture as arsenic, heavy metals, and poisonous byproducts. First Attempts a t Standardization About 1880, the first serious thought was given to a standardization of the coloring matters required by the trade. This movement was the result of widespread public criticism of the methods spoken of above. After considerable study that involved many physiological tests, certain dyes were accepted and placed on the American market as harmless colors. It is strange that, despite the practices mentioned, there is very little record of any proved cases of color poisoning although they have been quite frequently mentioned in the press. Most of such cases were children whose illness was more the result of over-indulgence id sweets, than from the small amount of color consumed. There was one case, however, in which poisoning resulted from the use by a baker of chrome yellow in buns. Government Creates "Certified Colors" Although the reputable trade looked with favor upon the so-called harmless colors, and quite generally accepted them,
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I N D USTRISL -4SD ESGINEERING CHEMISTRY
the publicity that had been given the indiscriminate use of questionable products was not overlooked in the agitation that arose over the adulteration of foodstuffs and eventually resulted in government legislation. The passage of the Federal Food and Drug Act of June 30, 1906, brought the question of the use of coloring matters in food products under government supervision and resulted in a thorough investigation. In July, 1907, Food Inspection Decision No. 76 created “certified colors” and so legally terminated any further indiscriminate use of harmful varieties. Certified colors did not become a reality until careful scientific research and investigation established beyond a doubt their nontoxic qualities and the possibility of production in the highest state of purity. These observations and conclusions were the result of years of untiring effort on the part of eminent scientists augmented by a final thorough rechecking by our own government chemists. In this manner, after consideration under the jurisdiction of three Secretaries of Agriculture, “certified colors” were established. The procedure is described in Bulletin 147. Since thab time other colors have been added to the list but only after the same careful consideration. Recognition by foreign governments through the accep tance of these standards is worthy of comment and speaks well for American effort. The following seven colors were first placed on the list:
Vol. 18, No. 12
mentioned, some dyes were made in this country from intermediates wholly or partially of foreign origin. The bulk of the coal-tar colors used in the United States, however, was imported. Achievements Resulting from War Crisis
The outbreak of the World War in August, 1914, brought the realization that the supply of basic crude colors and intermediates was liable to be terminated. At first hope was held out that such a condition would be temporary, and it was a more logical course to await developments than to risk capital in any real endeavor to produce the necessary intermediates and dyes. The fear of foreign competition had to be considered. But as the intensity of the conflict increased with the passing months, and the supply of raw materials ceased to materialize, the seriousness of the situation was at last realized. The high standards of purity for food colors established by the U. S. Department of Agriculture and their wise decision that these requirements would not be lowered on account of the existing conditions made the problem a difficult one. With extinction almost a t hand, the industry made a determined effort to establish a permanent institution entirely domestic in character. The field was carefully surveyed and the requirements noted. Guided by former experiences and endeavors, an intensive program of research was started to Colour Index S . & J. make possible the manufacture of these cherished products. Amaranth 107 184 Since the naphthols were required in the synthesis of four 3R Ponceau 56 80 150 Orange I 85 of the permissible colors, their production was absolutely 773 Erythrosin 517 essential and efforts were concentrated in that direction. 10 Naphthol yellow S 4 Indigotin 692 1180 The first results were limited batches of a questionable de670 Light green S. F. 435 gree of purity that required considerable refining. With the advent of alpha- and beta-naphthols, the production of Purification of Dyes naphthol yellow S and “R” salt was assured. The latter The high standards of purity called for made the commer- product was the object of considerable study before a degree cial production of these products a difficult undertaking. of purity was attained that was entirely satisfactory. The purification of dyes of the desired types was undertaken. Alpha-naphthylamine, aniline, and xylidine were proThis procedure involved the removal of organic impurities, duced in like manner, and so led to the synthesis of naphisomeric and other colors, and inorganic contaminations. thionic acid, sulfanilic acid, and cumidine. With these interCrude dyes from every source of supply were studied, but all mediates available, the manufacture of 3R Ponceau, amawere found to be of inferior quality. Most of these products ranth, and orange I was possible. The domestic production were of foreign origin, although several of the dyes were of phthalic anhydride and resorcin made possible the manuproduced in this country from imported intermediates. facture of erythrosin. Indigo and tartrazin followed in a Considerable research and analytical effort were necessary like manner. before the commercial production of colors of the required The story concealed in the above achievements is long and degree of purity was possible. The information thus gathered not unlike the one that has been told many times in conwas very helpful in later years when the “American chemist” nection with the birth of the American dye industry. In was called upon to meet a great crisis. During the period just mentioned very important work this particular case the resulting products had in addition to equal the high standards of purity prescribed by law or was done on the production of the sulfonic acids of betameet rejection for the purpose intended. naphthol and other intermediates that entered into the As time went on, the supply and purity of the necessary colors in question. This was prompted by the desire to produce dyes of greater purity and eliminate many steps of intermediates increased. The manufacture of the finished purification. These efforts resulted in improving the quality dyes through larger batches assured more uniform products of those produced in this country. Analytical chemistry and made possible the lowering of the cost of production. Light green S. F. yellowish was not obtained in certified form also benefited. Many methods of separation, identification, until some time later. This was due to the difficulties of and assay of the colors and impurities in question had to be manufacture and the raising of the requirements. Two oilevolved. Because certain objections were raised by the trade against the use of naphthol yellow S, tartrazin was added soluble colors known as 0. B. and A. B. yellow, Colour Index 61 and 22, were added to the list since 1914 and were promptly to the list. produced by the food color manufacturers. The last addiStatus of.Industry between 1907 and 1914 tion was guinea green, Colour F d e x 666, in 1922. This The period from 1907 to 1914 saw the certified color busi- color was also made available in a comparatively short space ness firmly established and accepted by the trade and public of time. as a constructive move. Although an effort for independence Present Condition of Industry had manifested itself in a material way, we were still deThe certified color business is now firmly established and pendent upon foreign agencies for our commercial supply of basic intermediates such as beta-naphthol, phthalic can boast of a greater and superior line of products of truly anhydride, dimethylaniline, cumidine, etc. As previously American manufacture. The high standards of purity have
December, 1926
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
not only been met, but are excelled in most of the goods placed on the market. By 1921 the volume of the business amounted to about 140,000 pounds and has increased since that time. These colors are mainly used in the ice-cream, confectionery, and soft-drink trade. Education and legislation have practically eliminated the use of color to mask inferiority or impart a “bloom of youth” to the salmon or chicken that had grown hoary with age in the cold-storage plant. The standards of fixed by law for the colors are fully described in the pub!ications of the U. s. Department of Agriculture. Briefly stated, they are as follows : (1) Arsenic content must be less than 1/700,000. ( 2 ) Must be free from heavy metals according t o the authorized test.
(3)
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Must be structurally true to type.
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~ ~ O ’ ’ ~ ~ ’ ~ ~ ; ~ ~ ~ p ; f with other ( 5 ) Decomposed dyes and other organic impurities must be reduced to a minimum, (6) Insoluble matter must in no case exceed 0.3 per cent.
As stated before these requirements are than met by the producers today. The list now contains an assortment of colors that fully meets the esthetic requirements in the tinting of our confectionery and other products, including many of the demands of the cosmetic trade. Authentic certified colors bearing the official lot number and the name of a reputable manufacturer are products that have met the high standards of purity demand by the Government and Can be used with impunity.
Progress in the Development and Manufacture of Vat Colors in America By 0. M. Bishop and J. H. Sachs F,. I. D U PONTDE
NBMOURS & Co., WILMINGTON, DEL.
Y T H E term “vat color” is meant a dyestuff that in its stable form is insoluble in water and in dilute alkaline or acid solutions, but which on alkaline reduction passes into a form which is readily soluble in dilute alkali. In former times the reduction of indigo was brought about by fermentation, and from the fact that this process was carried out in large wooden or earthenware containers called vats the term “vat color” is derived. In the reduced form these colors are substantive to animal or vegetable fibers, and because in this form they are so unstable the simple process of allowing free access of air to the dyed fibers is sufficient to oxidize the color into its original insoluble form. This class of colors, which has been known from antiquity, includes both indigo, the king of dyestuffs, and the muchprized Tyrian purple of the Phoenicians. The former, in spite of the accomplishments of the synthetic organic chemists, still retains its premier position. The latter, synthesized and catalogued early in the twentieth century, has long since succumbed to colors which are much its superior in shade and fastness. With the advent of the synthetic organic chemist came the downfall of the natural dyestuffs. The extract of leaf, bark, and root was replaced by thz magic touch of chemistry upon the vegetation of geological age, stored up within the earth awaiting the key that would unlock its riches to mankind. The madder industry of southern Europe was overthrown in 1869 by the work of Caro and Liebermann in Germany and Perkin in England on the constitution and synthesis of alizarin. Likewise, about twenty-five years later the long and painstaking work of Bayer on the constitution of indigo bore fruit in the first successful commercial production of this color. As early as 1882, when Bayer and Drewson’s synthesis from o-nitrobenzaldehyde promised success on a commercial scale, the attention of the foremost color manufacturers in Germany was directed towards this goal. Thousands upon thousands of dollars were spent in research work. Other thousands were poured out in plant development. That these thousands were not spent in vain can be appreciated by the fact that, whereas in 1895 Germany imported indigo to the extent of about five millions of dollars, in 1905 she exported indigo to the extent of almost seven millions of dollars. Plant sites in Germany
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covering perhaps 50 acres had won an economic race against 500,000 acres devoted to the culture of indigo in Asia. At the beginning of the present century indigo and its substitution products were the only known vat colors of commercial importance. Scarcely one year of the new century had elapsed, however, when Rohn brought forth the epoch-making discovery of indanthrene and flavanthrene. These were vat colors, differing from indigo in that they possessad not only a different carbon skeleton but also a different chromophore-namely, that of anthraquinone. At this time there was no I. G. in Germany and competition between the various color manufacturers was keen. They all took up the scent of new vat colors. In 1905, Friedlaender discovered thioindigo. The way was therefore open in two directions for the synthesis of new and varied colors of this class. It thus comes about that even a t the present time practically all of the known vat colors can be divided into two groups-the indigoids and the anthraquinones. During the next ten years an enormous number of new products were uncovered, the majority of which were of no commercial importance. However, many of them possessed valuable properties and were thercfore commercially produced and marketed by the Badische Company under the name Indanthrene: by the Rayer Company under the name Algol; by the Meister, Lucius & Briining Company under the name of Helindon; by the Society of Chemical Industry, Basle, under the names of Ciba and Cibanone; and finally by the Cassella Company under the name of Hydron. According to the Norton’s census, during the fiscal year of 1913-1914 there were imported into the United States 1,232,002 pounds of fifty-eight different anthraquinone vat colors and 305:171 pounds of thirty-six different indigoids, indigo itself excluded. In Table I are given the twelve colors imported in the largest amounts in that year. Table I Indigo Indanthrene blue GCD Indanthrene blue R S Indanthrene yellow G Indanthrene green B Indanthrene violet R R Indigo MLB (brominated indigo) Indanthrene golden orange R Indanthrene black B Helindone pink Indanthrene claret B extra Helindone violet B
Pounds 8,507.359 478.980 187,379 75,192 72,227 68,419 53,610 50,496 50.034 39,393 28,728 28,607
