alizarin

[uh-liz-er-in]

alizarin, or 1,2-dihydroxyanthraquinone, mordant vegetable dye obtained originally from the root of the madder plant (Rubia tinctorum), in which it occurs as a glucoside. The term also includes a group of synthetic dyestuffs prepared from coal-tar derivatives. A method for the synthesis of alizarin was first discovered (1868) by Karl Graebe and Karl Liebermann, German chemists. With salts of metals the compound forms brilliant lakes, although by itself it is a poor dye. Turkey red is produced with an aluminum mordant, other shades of red with calcium and tin salts, dark violet with iron mordants, and brownish red with chromium. Purpurin, also used in dyeing, occurs with alizarin in madder and is produced synthetically.

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Alizarin

| Section8 = }} Alizarin is an organic compound that is historically important as a prominent dye. It is an anthraquinone originally derived from the root of the madder plant. In 1869, it became the first natural pigment to be duplicated synthetically. Alizarin is also the name for a variety of related dyes, such as "Alizarine Cyanine Green G" and "Alizarine Brilliant Blue R."

The word alizarin derives from the Arabic al-usara, juice.

History

Madder has been cultivated as a dyestuff since antiquity in central Asia and Egypt, where it was grown as early as 1500 BC. Cloth dyed with madder root pigment was found in the tomb of the Pharaoh Tutankhamun and in the ruins of Pompeii and ancient Corinth. In the Middle Ages, Charlemagne encouraged madder cultivation. It grew well in the sandy soils of the Netherlands and became an important part of the local economy.

By 1804, the English dye maker George Field had refined the technique to lake madder by treating it with alum, and an alkali, that converts the water-soluble madder extract into a solid, insoluble pigment. This resulting madder lake has a longer-lasting color, and can be used more versatilely, for example by blending it into a paint. Over the following years, it was found that other metal salts, including those containing iron, tin, and chromium, could be use in place of alum to give madder-based pigments of various other colors. This general method of preparing lakes has been known for centuries.

In 1826, the French chemist Pierre-Jean Robiquet found that madder root contained two colorants, the red alizarin and the more rapidly fading purpurin. The alizarin component became the first natural dye to be synthetically duplicated in 1868 when the German chemists Carl Graebe and Carl Liebermann, working for BASF, found a way to produce it from anthracene. About the same time, the English dye chemist William Henry Perkin independently discovered the same synthesis, although the BASF group filed their patent before Perkin by only one day.

The synthetic alizarin could be produced for a fraction of the cost of the natural product, and the market for madder collapsed virtually overnight. The principal synthesis entailed oxidation of anthraquinone-2-sulfonic acid with sodium nitrate in concentrated sodium hydroxide. Alizarin itself has been in turn largely replaced today by the more light-resistant quinacridone pigments developed at DuPont in 1958.

Applications

Alizarin red is used in a biochemical assay to determine, quantitatively by colorimetry, the presence of calcific deposition by cells of an osteogenic lineage. As such it is an early stage marker (days 10-16 of in vitro culture) of matrix mineralisation, a crucial step towards the formation of calcified extracellular matrix associated with true bone.

In clinical practice it is also used to stain synovial fluid to assess for basic calcium phosphate crystals.

Alizarin Crimson

At right is displayed the color alizarin crimson.

Alizarin crimson in human culture

Music

The color alizarin crimson is one of several mentioned in the 1967 song "Wear Your Love Like Heaven" by Donovan.

Alizarin crimson is mentioned in Karlheinz Stockhausen's 1966/67 musical composition Hymnen, where it is included in a spoken fugue where the names of dozens of different shades of red are intermingled as a symbol of the various forms of Communism that existed on the planet at that time.