Aurin (C.I. 43800), sometimes named rosolic acid or corallin is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

, forming

yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In the R ...

ish or deep-red crystals with

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...

ish metallic luster. It is practically insoluble in water, freely soluble in

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

. It is soluble in strong acids to form yellow solution, or in aqueous

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

s to form

carmine Carmine ()also called cochineal (when it is extracted from the cochineal insect), cochineal extract, crimson lake, or carmine lake is a pigment of a bright-red color obtained from the aluminium complex derived from carminic acid. Specific code n ...

red solutions. Due to this behaviour it can be used as

pH indicator A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...

with pH transition range 5.0 - 6.8. It is used as an intermediate in manufacturing of

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...

Synthesis

Aurin was first prepared in 1834 by the German chemist

Friedlieb Ferdinand Runge Friedlieb Ferdinand Runge (8 February 1794 – 25 March 1867) was a German analytical chemist. Runge identified the mydriatic (pupil dilating) effects of belladonna (deadly nightshade) extract, identified caffeine, and discovered the first coal ...

, who obtained it by distilling coal tar. He named it ''Rosölsäure'' or ''Rosaölsäure'' (red oil acid). In 1861, the German chemists

Hermann Kolbe Adolph Wilhelm Hermann Kolbe (27 September 1818 – 25 November 1884) was a major contributor to the birth of modern organic chemistry. He was a professor at Marburg and Leipzig. Kolbe was the first to apply the term synthesis in a chemical cont ...

and

Rudolf Schmitt Rudolf Schmitt (August 5, 1830 – February 18, 1898) was a German chemist who together with Adolph Wilhelm Hermann Kolbe discovered the Kolbe-Schmitt reaction. Biography Schmitt was born in the small village Wippershain in the Hesse-Kassel ...

presented the synthesis of aurin by heating oxalic acid and

creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types were ...

(which contains phenol) in the presence of concentrated sulfuric acid. (Gradually, chemists realized that commercial aurin was not a pure compound, but was actually a mixture of similar compounds.) Aurin is formed by heating of

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

and

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...

in concentrated sulfuric acid. : Aurinsynthese

Safety

Aurin may cause eye, skin, and respiratory tract irritation. Ingestion and inhalation should be avoided. Aurin was reported to have

endocrine disruptor chemical Endocrine disruptors, sometimes also referred to as hormonally active agents, endocrine disrupting chemicals, or endocrine disrupting compounds are chemicals that can interfere with endocrine (or hormonal) systems. These disruptions can cause c ...

(EDC) properties.

References

External links

MSDS at Oxford UniversityHistory of aurin in ''Heinrich Caro and the creation of modern chemical industry''
*{{Cite NIE, wstitle=Aurin, short=x Triarylmethane dyes PH indicators Phenol dyes Bis(4-hydroxyphenyl)methanes