Racemic acid is an old name for an optically inactive or

racemic In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...

form of

tartaric acid Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes but also in tamarinds, bananas, avocados, and citrus. Its salt (chemistry), salt, potassium bitartrate, commonly known as cream of ta ...

. It is an equal mixture of two mirror-image

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibili ...

(

enantiomers In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

), optically active in opposing directions. Racemic acid does not occur naturally in grape juice, although L-tartaric acid does. Tartaric acid's sodium-ammonium

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

is unusual among racemic mixtures in that during crystallization it can separate out into two kinds of crystals, each composed of one isomer, and whose macroscopic crystalline shapes are mirror images of each other. Thus,

Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist, pharmacist, and microbiologist renowned for his discoveries of the principles of vaccination, Fermentation, microbial fermentation, and pasteurization, the la ...

was able in 1848 to isolate each of the two enantiomers by laboriously separating the two kinds crystals using delicate tweezers and a hand lens. Pasteur announced his intention to resolve racemic acid in: * Pasteur, Louis (1848
"Sur les relations qui peuvent exister entre la forme cristalline, la composition chimique et le sens de la polarisation rotatoire"
while he presented his resolution of racemic acid into separate

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...

isomers in: * Pasteur, Louis (1850
"Recherches sur les propriétés spécifiques des deux acides qui composent l'acide racémique"
In the latter paper, Pasteur sketches from natural concrete reality

chiral polytope In the study of abstract polytopes, a chiral polytope is a polytope that is as symmetric as possible without being mirror-symmetric, formalized in terms of the Group action (mathematics), action of the symmetry group of the polytope on its Flag (g ...

s quite possibly for the first time. The optical property of tartaric acid was first observed in 1832 by Jean Baptiste Biot, who observed its ability to rotate

polarized light , or , is a property of transverse waves which specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. One example of a polarize ...

. It remains unknown whether

Arthur Cayley Arthur Cayley (; 16 August 1821 – 26 January 1895) was a British mathematician who worked mostly on algebra. He helped found the modern British school of pure mathematics, and was a professor at Trinity College, Cambridge for 35 years. He ...

or Ludwig Schläfli, or other contemporary mathematicians who studied polytopes, knew of the French work. In two modern-day re-enactments performed in Japan of the Pasteur experiment, it was established that the preparation of crystals was not very reproducible. The crystals deformed, but they were large enough to inspect with the naked eye (microscope not required).

References

{{Wiktionary Alpha hydroxy acids Chirality Dicarboxylic acids Food antioxidants Optical materials Racemic mixtures Stereochemistry Vicinal diols

See also

References