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Additional recommended knowledge
It appears a white crystalline powder, and the melting point is 293 °C.
Medically, it can be used for the successful treatment of warts. It is also used treating alopecia areata or alopecia totalis/universalis (autoimmune hair loss) through topical immunotherapy involving the production of an allergic rash.
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. 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. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Squaric_acid". A list of authors is available in Wikipedia.|