Dichlorocarbene
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[[Image:Dichlorocarbene.gif|right|frame|Dichlorocarbene formation and reaction with [[cyclohexene]]]]'''Dichlorocarbene''' is a [[carbene]] commonly encountered in [[organic chemistry]]. This [[reactive intermediate]] with [[chemical formula]] CCl<sub>2</sub> is easily available by reaction of [[chloroform]] and a base such as [[potassium t-butoxide]] <ref>[[Organic Syntheses]], Coll. Vol. 5, p.874 (1973); Vol. 41, p.76 (1961).[http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p0874 Online Article]</ref> or [[sodium hydroxide]] dissolved in water. A [[phase transfer catalyst]] for instance [[ammonium salt|benzyltriethylammonium bromide]] is added to facilitate the migration of the hydroxide in the organic phase. Dichlorocarbene reacts with [[alkene]]s in a formal [1+2][[cycloaddition]] to form [[geminal]] [[cyclopropane|dichlorocyclopropanes]] which can subsequently be [[organic reduction|reduced]] to proper [[cyclopropane]]s or hydrolyzed to a [[cyclopropanone]] in a [[gem halide hydrolysis]]. The preparation of dichlorocarbene from chloroform and its utility in synthesis was discovered by [[William von Eggers Doering]] in 1954 <ref>''The Addition of Dichlorocarbene to Olefins'' W. von E. Doering and A. Kentaro Hoffmann [[J. Am. Chem. Soc.]]; '''1954'''; 76(23) pp 6162 - 6165; {{DOI|10.1021/ja01652a087}}</ref> based on functionalizion of cyclohexene. [[Anton Geuther]] in 1862 was the first to propose dichlorocarbene.
==Related reactions==
The '''Doering-LaFlamme carbon chain extension''' <ref>''A two-step of synthesis of allenes from olefins''
[[Tetrahedron]], Volume 2, Issues 1-2, '''1958''', Pages 75-79 [[William von Eggers Doering|W. von E. Doering]] and P. M. LaFlamme {{doi|10.1016/0040-4020(58)88025-4}}</ref>describes the conversion of alkenes to [[allenes]] (a chain extension) with [[magnesium]] or [[sodium]] metal through initial reaction of the alkene with dichlorocarbene. The same sequence is incorporated in the [[Skattebøl rearrangement]] to cyclopentadienes. Dichlorocarbene also features in the [[Reimer-Tiemann reaction]]. Closely related is the more reactive '''dibromocarbene''' CBr<sub>2</sub>.
== Synthetic methods ==
Other dichlorocarbene precursors are [[ethyl acetate|ethyl trichloracetate]] when reacted with [[sodium]] in [[methanol]] <ref>[[Organic Syntheses]], , Coll. Vol. 6, p.731 (1988); Vol. 54, p.11 (1974).[http://www.orgsyn.org/orgsyn/prep.asp?prep=cv6p0731 Online Article]</ref> and phenyl(trichloromethyl)mercury by thermal decomposition <ref>[[Organic Syntheses]], , Coll. Vol. 5, p.969 (1973); Vol. 46, p.98 (1966).[http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p0969 Online Article]</ref>
. Dichlorodiazirine is an experimental dichlorocarbene precursor <ref>''Dichlorodiazirine: A Nitrogenous Precursor for Dichlorocarbene'' Gaosheng Chu, Robert A. Moss, and Ronald R. Sauers [[J. Am. Chem. Soc.]], 127 (41), 14206 -14207, '''2005''' [http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/ja055656c DOI Abstract]</ref>. It is stable in the dark at [[room temperature]] and [[chemical decomposition|decomposes]] into the carbene and [[nitrogen]] gas by [[photolysis]].
:[[Image:Dichlorodiazirine.gif|Dichlorodiazirine synthesis]] <ref> a) Starting from [[phenol]] reaction with [[Cyanogen|cyanogen bromide]] to [[phenyl]] [[cyanate]] b) [[hydroxylamine]] reaction to the N-hydroxy-O-phenylisourea c) elevate hydroxyl group to [[leaving group]] by reaction with [[mesyl chloride]] to the [[mesylate]] d) [[intramolecular]] ring closure with [[sodium hypochlorite]] to the [[aziridine]] f) [[nitration]] with [[nitronium tetrafluoroborate]] g) [[nucleophilic substitution]] see proposed mechanism with [[caesium chloride]], [[ammonium salt|tetrabutylammonium chloride]] in [[ionic liquid]]</ref>
The reaction mechanism for the formation of dichloroaziridine is depicted below:
:[[Image:Aziridinemechanism.gif|Dichlorodiazirine: formation reaction mechanism]]
Dichlorocarbene can also be obtained by reaction of [[carbon tetrachloride]] with elemental [[magnesium]] with [[ultrasound chemistry]] <ref>''A Facile Procedure for the Generation of Dichlorocarbene from the Reaction of Carbon Tetrachloride and Magnesium using Ultrasonic Irradiation'' Haixia Lin, Mingfa Yang, Peigang Huang and Weiguo Cao [[Molecules (journal)|Molecules]] '''2003''', 8, 608-613 [http://www.mdpi.org/molecules/papers/80800608.pdf Online Article]</ref>. This method is tolerant to [[ester]]s and [[carbonyl]] compounds because it does not involve strong [[base (chemistry)|base]].
== External links ==
* [http://virtual.yosemite.cc.ca.us/smurov/carbene.htm Addition of dichlorocarbene to 2-methyl-1-buten-3-yne, laboratory procedure]
== References ==
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[[Category:reagents for organic chemistry]]