The invention: The culmination of centuries of efforts to mimic the brilliant colors displayed in nature in dyes that can be used in many products.
The people behind the invention:
Sir William Henry Perkin (1838-1907), an English student in
Hofmann’s laboratory Rene Bohn (1862-1922), a synthetic organic chemist Karl Heumann (1850-1894), a German chemist who taught Bohn Roland Scholl (1865-1945), a Swiss chemist who established the correct structure of Bohn’s dye August Wilhelm von Hofmann (1818-1892), an organic chemist
Synthesizing the Compounds of Life
From prehistoric times until the mid-nineteenth century, all dyes were derived from natural sources, primarily plants. Among the most lasting of these dyes were the red and blue dyes derived from alizarin and indigo.
The process of making dyes took a great leap forward with the advent of modern organic chemistry in the early years of the nineteenth century. At the outset, this branch of chemistry, dealing with the compounds of the element carbon and associated with living matter, hardly existed, and synthesis of carbon compounds was not attempted. Considerable data had accumulated showing that organic, or living, matter was basically different from the compounds of the nonliving mineral world. It was widely believed that although one could work with various types of organic matter in physical ways and even analyze their composition, they could be produced only in a living organism.
Yet, in 1828, the German chemist Friedrich Wohler found that it was possible to synthesize the organic compound urea from mineral compounds. As more chemists reported the successful preparation of compounds previously isolated only from plants or animals, the theory that organic compounds could be produced only in a living organism faded.
One field ripe for exploration was that committed to exploiting the uses of coal tar. Here, August Wilhelm von Hofmann was an active worker. He and his students made careful studies of this complex mixture. The high-quality stills they designed allowed for the isolation of pure samples of important compounds for further study.
Of greater importance was the collection of able students Hofmann attracted. Among them was Sir William Henry Perkin, who is regarded as the founder of the dyestuffs industry. In 1856, Perkin undertook the task of synthesizing quinine (a bitter crystalline alkaloid used in medicine) from a nitrogen-containing coal tar material called toluidine. Luck played a decisive role in the outcome of his experiment. The sticky compound Perkin obtained contained no quinine, so he decided to investigate the simpler related compound aniline. A small amount of the impurity toluidine in his aniline gave Perkin the first synthetic dye, Mauveine.
Searching for Structure
From this beginning, the great dye industries of Europe, particularly Germany, grew. The trial-and-error methods gave way to more systematic searches as the structural theory of organic chemistry was formulated.
As the twentieth century began, great progress had been made, and German firms dominated the industry. Badische Anilin- und Soda-Fabrik (BASF) was incorporated at Ludwigshafen in 1865 and undertook extensive explorations of both alizarin and indigo. A chemist, Rene Bohn, had made important discoveries in 1888, which helped the company recover lost ground in the alizarin field. In 1901, he undertook the synthesis of a dye he hoped would combine the desirable attributes of both alizarin and indigo.
As so often happens in science, nothing like the expected occurred. Bohn realized that the beautiful blue crystals that resulted from his synthesis represented a far more important product. Not only was this the first synthetic vat dye, Indanthrene, ever prepared, but also, by studying the reaction at higher temperature, a useful yellow dye, Flavanthrone, could be produced.
The term vat dye is used to describe a method of applying the dye, but it also serves to characterize the structure of the dye, because all
William Henry Perkin
Born in England in 1838, William Henry Perkin saw a chemical experiment for the first time when he was a small boy. He found his calling there and then, much to the dismay of his father, who wanted him to be a builder and architect like himself.
Perkin studied chemistry every chance he found as a teenager and was only seventeen when he won an appointment as the assistant to the German chemist August Wilhelm von Hof-mann. A year later, while trying to synthesize quinine at Hof-mann’s suggestion, Perkin discovered a deep purple dye—now known as aniline purple or Mauveine, but popularly called mauve. In 1857 he opened a small dyeworks by the Grand Union Canal in West London, hoping to make his fortune by manufacturing the dye.
He succeeded brilliantly. His ambitions were helped along royally when Queen Victoria wore a silk gown dyed with Mauveine to the Royal Exhibition of 1862. In 1869, he perfected a method for producing another new dye, alizarin, which is red. A wealthy man, he sold his business in 1874 when he was just thirty-six years old and devoted himself to research, which included isolation of the first synthetic perfume, coumarin, from coal tar.
Perkin died in 1907, a year after receiving a knighthood, one of his many awards and honors for starting the artificial dye industry. His son William Henry Perkin, Jr. (1860-1927) also became a well-known researcher in organic chemistry.
currently useful vat dyes share a common unit. One fundamental problem in dyeing relates to the extent to which the dye is water-soluble. A beautifully colored molecule that is easily soluble in water might seem attractive given the ease with which it binds with the fiber; however, this same solubility will lead to the dye’s rapid loss in daily use.
Vat dyes are designed to solve this problem by producing molecules that can be made water-soluble, but only during the dyeing or vatting process. This involves altering the chemical structure of the dye so that it retains its color throughout the life of the cloth.
By 1907, Roland Scholl had showed unambiguously that the
chemical structure proposed by Bohn for Indanthrene was correct, and a major new area of theoretical and practical importance was opened for organic chemists.
Impact
Bohn’s discovery led to the development of many new and useful dyes. The list of patents issued in his name fills several pages in Chemical Abstracts indexes.
The true importance of this work is to be found in a consideration of all synthetic chemistry, which may perhaps be represented by this particular event. More than two hundred dyes related to Indan-threne are in commercial use. The colors represented by these substances are a rainbow making nature’s finest hues available to all. The dozen or so natural dyes have been synthesized into more than seven thousand superior products through the creativity of the chemist.
Despite these desirable outcomes, there is doubt whether there is any real benefit to society from the development of new dyes. This doubt is the result of having to deal with limited natural resources. With so many urgent problems to be solved, scientists are not sure whether to search for greater luxury. If the field of dye synthesis reveals a single theme, however, it must be to expect the unexpected. Time after time, the search for one goal has led to something quite different—and useful.
See also Buna rubber; Color film; Neoprene.
