3,4-Dihydroxy-3-cyclobutene-1,2-dione is used to produce diethoxy-cyclobutenedione by heating, pharmaceutical intermediates, squarylium dyes, and photoconducting squaraines; The dibutylester is used as a contact sensitizer in the treatment of alopecia and warts.
MacLean, E.J.; Wheatley, P.S Ferguson, G.; Glidewell, C. Self-templating of large rings by small rings in 4,4'-bipyridyl-3,4-dihydroxy-3-cyclobutene-1,2-dione (2/3). Acta Cryst. 1999, 55, 1892-1896.
Semmingsen, D.; Hollander, F.J.; Koetzle, T.F. A neutron diffraction study of squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione). J. Chem. Phys. 1977, 66, 4405.
Interesting dibasic acid, readily forming salts, acid chloride, esters, amides, etc. Esters of squaric acid have been used to synthesize chiral bioisosteres for the amino acid functionality: J. Org. Chem., 57, 6896 (1992).
For reviews of squaric acid and its derivatives, see: Synthesis, 1, 649, 869 (1978); 961 (1980). See also: J. Chem. Soc., Perkin 1, 263 (1993).
Gefahrenhinweise (EU): H315-H319-H317-H335
Causes skin irritation. Causes serious eye irritation. May cause an allergic skin reaction. May cause respiratory irritation.
Avoid breathing dust/fume/gas/mist/vapours/spray. Wear protective gloves and eye/face protection. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. IF INHALED: Remove to fresh air and keep at rest in a position comfortable for breathing. Store locked up. Dispose of contents/container in accordance with local/regional/national/international regulations.