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

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

, 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 t ...

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 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

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

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

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

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic 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 soluble base has a pH greater than 7.0. The a ...

s to form

carmine Carmine ()also called cochineal (when it is extracted from the Cochineal, cochineal insect), cochineal extract, crimson Lake pigment, lake, or carmine lake is a pigment of a bright-red color obtained from the aluminium coordination complex, compl ...

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

pH indicator A pH indicator is a halochromism, halochromic chemical compound added in small amounts to a Solution (chemistry), solution so the pH (acidity or Base (chemistry), basicity) of the solution can be determined visually or spectroscopically by chang ...

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

dye Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy Fantasy is a genre of speculative fiction that involves supernatural or Magic (supernatural), magical ele ...

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 ...

, 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 German chemist and academic, and a major contributor to the birth of modern organic chemistry. He was a professor at Marburg and Leipzig. Kolbe was the first to apply t ...

and Rudolf Schmitt 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 w ...

(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 known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

and

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...

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 (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 4-Hydroxyphenyl compounds