{{Chembox | ImageFile = 1,3-Cyclobutandion Struktur.svg | ImageSize = | ImageAlt = | PIN = Cyclobutane-1,3-dione | OtherNames = |Section1={{Chembox Identifiers | CASNo1 = 78675-98-6 | index1_label = 3-hydroxycyclobut-2-enone | CASNo = 15506-53-3 | index_label = 1,3-cyclobutanedione tautomer | ChemSpiderID = 25456 | ChemSpiderID1 = 10004000 | DTXSID1 = DTXSID30473940 | PubChem = 27357 | PubChem1 = 11829353 | QID1 = Q82303641 | StdInChI=1S/C4H4O2/c5-3-1-4(6)2-3/h1-2H2 | StdInChIKey = PZQGSZRQKQZCOJ-UHFFFAOYSA-N | SMILES = C1C(=O)CC1=O | InChI1=1S/C4H4O2/c5-3-1-4(6)2-3/h1,5H,2H2 | InChIKey1 = IHXWECHPYNPJRR-UHFFFAOYSA-N | SMILES1 = C1C(=CC1=O)O }} |Section2={{Chembox Properties | C = 4|H=4|O=2 | MolarMass = | Appearance = colorless or white solid | Density = 1.12 g/cm<sup>3</sup> | MeltingPtC = 119-120 | MeltingPt_notes = | BoilingPtC = | BoilingPt_notes = | Solubility = }} |Section3={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} }} '''1,3-Cyclobutanedione''' is an organic compound with the formula {{chem2|(CH2)2(CO)2}}. It is an isomer of 1,2-cyclobutanedione. The compound would be of little interest except that its tautomer is a subunit in some commercial dyes.

In solution, 1,3-cyclobutanedione exists in equilibrium with a less stable tautomer, called '''squaraine''', 3-hydroxycyclobut-2-enone.<ref>{{cite journal |doi=10.1021/jp9030915 |title=Thermochemical Properties and Contribution Groups for Ketene Dimers and Related Structures from Theoretical Calculations |date=2009 |last1=Morales |first1=Giovanni |last2=Martínez |first2=Ramiro |journal=The Journal of Physical Chemistry A |volume=113 |issue=30 |pages=8683–8703 |pmid=19572711 |bibcode=2009JPCA..113.8683M }}</ref> Squaraine dyes are, formally at least, derivatives of squaraine. In such dyes, the ene-one tautomer predominates. [[File:Tautomerization1,3-cybutanedione.svg|thumb|left|280px|1,3-cyclobutanedione and its enol tautomer.]] The mixture of tautomers can be prepared by hydrolysis of 1-ethoxycyclobutene-3-one, which is prepared from the cycloaddition of ethoxyacetylene to ketene. <ref>{{cite journal |doi=10.1021/ja00878a051 |title=Cyclobutane-1,3-Dione |date=1962 |last1=Wasserman |first1=Harry H. |last2=Dehmlow |first2=Eckehard V. |journal=Journal of the American Chemical Society |volume=84 |issue=19 |pages=3786–3787 |bibcode=1962JAChS..84.3786W }}</ref>

==Substituted derivatives== A variety of substituted 1,3-Cyclobutanediones form upon spontaneous dimerization of disubstituted ketenes.<ref>{{cite book |doi=10.1002/9780470771600.ch8 |chapter=Synthetic uses of ketenes and allenes |title=Ketenes, Allenes and Related Compounds: Vol. 1 (1980) |date=1980 |last1=Brady |first1=William T. |pages=279–308 |isbn=978-0-470-77160-0|series=PATAI'S Chemistry of Functional Groups|editor=Saul Patai }}</ref> 2,2,4,4-Tetramethylcyclobutanedione is thus formed by dehydrochlorination of isobutyryl chloride:<ref>{{citation|surname1=R. Huisgen, P. Otto|periodical=J. Am. Chem. Soc.|title=The mechanism of dimerization of dimethylketene|volume=90|issue=19|pages=5342–5343|date= 1968|doi=10.1021/ja01021a090|bibcode=1968JAChS..90.5342H }}</ref> :{{chem2|(CH3)2CHCOCl + Et3N -> (CH3)2C\dC\dO + Et3NHCl}} :{{chem2|2 (CH3)2C\dC\dO -> (CH3)2C)2(C\dO)2 }}

Ketene itself dimerizes mainly to give the lactone called diketene as well as a small amount of 1,3-cyclobutanedione.

==Related compounds== *Moniliformin, a naturally occurring derivative of 3-hydroxycyclobut-2-enone

==References== <references />

{{DEFAULTSORT:Cyclobutanedione, 1,3-}} Category:Cyclobutanes Category:Cycloalkanones Category:Diketones