What is "squaric acid"

n. (context organic compound English) The compound ''3,4-dihydroxycyclobut-3-ene-1,2-dione'' derived from cyclobutene

Squaric acid, also called quadratic acid, because its four carbon atoms approximately form a square, is an organic compound with chemical formula .

The conjugate base of squaric acid is the hydrogensquarate anion CHO; and the conjugate base of the hydrogensquarate anion is the divalent squarate anion CO. 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.