Squaric acid

Squaric acid[1]
Structural formula (carbon atoms omitted)
Structural formula (carbon atoms omitted)
Ball-and-stick-model
Ball-and-stick-model
Names
Preferred IUPAC name
3,4-Dihydroxycyclobut-3-ene-1,2-dione
Other names
Quadratic acid
Cyclobutenedioic acid
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.018.875 Edit this at Wikidata
EC Number
  • 220-761-4
UNII
  • InChI=1S/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H checkY
    Key: PWEBUXCTKOWPCW-UHFFFAOYSA-N checkY
  • InChI=1/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H
    Key: PWEBUXCTKOWPCW-UHFFFAOYAC
  • c1(c(c(=O)c1=O)O)O
Properties
C4H2O4
Molar mass 114.056 g·mol−1
Appearance white crystalline powder
Melting point > 300 °C (572 °F; 573 K)
Acidity (pKa) pKa1 = 1.5
pKa2 = 3.4
Hazards[2]
GHS labelling:
GHS05: Corrosive
Danger
H314
P260, P280, P301+P330+P331, P303+P361+P353, P304+P340+P310, P305+P351+P338
Flash point 190 °C (374 °F; 463 K)[3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Squaric acid, also called quadratic acid because its four carbon atoms approximately form a square, is a diprotic organic acid with the chemical formula C4O2(OH)2.[4]

The conjugate base of squaric acid is the hydrogensquarate anion HC4O−4; and the conjugate base of the hydrogensquarate anion is the divalent squarate anion C4O2−4. This is one of the oxocarbon anions, which consist only of carbon and oxygen.

Squaric acid is a reagent for chemical synthesis, used for instance to make photosensitive squaraine dyes and inhibitors of protein tyrosine phosphatases.

  1. ^ 3,4-Dihydroxy-3-cyclobutene-1,2-dione. Sigma-Aldrich
  2. ^ "SICHERHEITSDATENBLATT". 21 March 2021.
  3. ^ 3,4-Dihydroxy-3-cyclobutene-1,2-dione, 98+%. Alfa Aesar
  4. ^ Robert West (1980). "History of the Oxocarbons". In Robert West (ed.). Oxocarbons. Academic Press. pp. 1–14. doi:10.1016/B978-0-12-744580-9.50005-1. ISBN 9780127445809.