Squaric acid

3,4- Dihydroxycyclobut -3 -ene-1 ,2-dione

Beige solid

Fixed

1.82 g · cm -3

Decomposition at 293 ° C

• PKS1 = 1.5
• PKa2 = 3.4

Soluble in water (20 g · l-1 at 20 ° C)

Risk

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The squaric acid is a descendant of cyclobutene, belongs to the group of oxocarbons and is related to the semisquare acid ( moniliformin ), the most acidic natural substance known. The salts of squaric acid hot Quadratate.

Representation

The first representation of squaric acid was carried out by reaction of chlorotrifluoroethylene with zinc. The resulting perfluorocyclobutene is reacted in ethanol to form 1,2- diethoxy- 3 ,3,4,4 -tetrafluoro -1 -cyclobutene. By acid hydrolysis eventually turn squaric acid.

Properties

The name of squaric acid is actually incorrect, since the four carbon atoms do not form a square due to different C -C bond lengths. In the crystalline state, the planar C4O4 subunits arrange via hydrogen bonds into a flat layer.

The high acidity ( PKS1 = 1.5, pKa2 = 3.4 ) of squaric acid can be, like, for example, in the delta, crocon or the rhodizonic, explained by resonance stabilization of the anion. The dianion of squaric acid is built completely symmetrical and shows no different C- C or C -O bond lengths:

As with the other above-mentioned anions of the acids ( oxocarbons ) is an aromatic system having from 2 π - electrons.

Use

The squaric acid is used in chemistry, industry and medicine.

Chemistry

• Squaric acid was [ VIV12O12 ( OCH3 ) 16 ( C4O4 ) 6 ] was used as a building block for the synthesis of novel poly - alkoxo - oxometallate derivatives, such as the K4. These ortho- Vanadinsäuremethylester was reacted with squaric acid and potassium hydroxide under solvothermal conditions.
• Also for the presentation of new organotin compounds squaric acid was used. In 2004, succeeded by the reaction of trimethyltin chloride, tributyltin chloride and dimethyltin dichloride with Dinatriumquadratat the synthesis of bis ( trimethyl) -, bis ( tributyltin) - or Dimethylzinnquadratat.

Industry

By increasing industrial importance are derived from squaric acid dyes squaraines.

Medicine

Besides Diphenylcyclopropenone ( DPCP ) is Quadratsäuredibutylester ( SADBE ) used for the treatment of hair loss. In the context of topical immunotherapy in treatment- resistant alopecia areata or alopecia totalis a targeted contact sensitization of the scalp occurs with dilute acid solution square.