Squaric acid (FR-0532), is also called quadratic acid, because its four carbon atoms approximately form a square (cyclobutene). It is a highly acidic, white, high melting crystalline powder. Frinton Laboratories, Inc. offers this in small to medium quantities, as a free-flowing crystalline powder, melting at above 300°C and with purity higher than 99%.The symmetrical anion is stable due to resonance and forms many salts with metals. Squaric acid is the starting compound for many products, such as photosensitive squaraine dyes and inhibitors of protein tyrosine phosphatases. Squaric acid forms stable salts with many metallic elements as cobalt and iron. Medically it is widely used in the form of its dibutyl ester (SADBE, FR-0553) to treat dermatitis warts.