Squaric acid

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Reference= [ [http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/123447?cm_mmc=PubChem-_-public%20database-_-products-_-products 3,4-Dihydroxy-3-cyclobutene-1,2-dione] at Sigma-Aldrich]
ImageFile=Squaric acid.svg
ImageSize=120px
IUPACName=3,4-Dihydroxycyclobut-3-ene-1,2-dione
OtherNames=Quadratic acid
Section1=Chembox Identifiers
CASNo=2892-51-5
PubChem=17913
SMILES=C1(=C(C(=O)C1=O)O)O
Section2=Chembox Properties
Formula=C₄H₂O₄
MolarMass=114.06 g/mol
Appearance=
Density=
MeltingPt=
BoilingPt=
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Section3=Chembox Hazards
MainHazards=
FlashPt=
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RPhrases = R36/37/38 R43
SPhrases = S26 S36

Squaric acid, also called quadratic acid, because its four carbon atoms approximately form a square, is an organic compound with chemical formula carbon₄hydrogen₂oxygen₄. It is one of the oxocarbonic acids (acids that have an oxocarbon anion as their conjugate base). Squaric acid is also used to synthesize photosensitive squaraine dyes and inhibitors of protein tyrosine phosphatases.

Chemical properties

Squaric acid is a white crystalline powder with a melting point of 293 °C. Structure of squaric acid is not a perfect square, as the carbon–carbon bond lengths are not quite equal.

The high acidity with pKa = 1.5 for the first proton and pKa = 3.4 for the second is attributable to resonance stabilization of the anion. [ "New Aromatic Anions. III. Molecular Orbital Calculations on Oxygenated Anions" Robert West, David L. Powell J. Am. Chem. Soc.; 1963; 85(17); 2577-2579.] Because the negative charges are equally distributed between each oxygen atom, the dianion of squaric acid is completely symmetrical (unlike squaric acid itself) with all C-C and C-O bond lengths identical.

The original synthesis started from reaction of 1-chloro-1,2,2-trifluoroethylene with zinc to perfluorocyclobutene. This compound was converted to 1,2-diethoxy-3,3,4,4-tetrafluoro-1-cyclobutene with ethanol. Hydrolysis gives the squaric acid. [cite journal | title = Hydrolysis Reactions of Halogenated Cyclobutene Ethers: Synthesis of Diketocyclobutenediol | author = J. D. Park, S. Cohen, and J. R. Lacher | journal = J. Am. Chem. Soc. |year = 1962 | volume = 84 | issue = 15 | pages = 2919–2922 | doi = 10.1021/ja00874a015]

Medical uses

Medically, it can be used for the treatment of warts.Fact|date=October 2008 It is also used treating alopecia areata or alopecia totalis/universalis (autoimmune hair loss) through topical immunotherapy involving the production of an allergic rash.Fact|date=October 2008

See also

* Cyclobutene

References