Dichlorocarbene is the reactive intermediate with chemical formula CCl₂. Although this chemical species has not been isolated, it is a common intermediate in organic chemistry, being generated from

chloroform Chloroform, or trichloromethane, is an organic compound with formula C H Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to PTFE. It is also a precursor to various ref ...

. This bent diamagnetic molecule rapidly inserts into other bonds.

Preparation

Dichlorocarbene is most commonly generated by reaction of

and a base such as potassium ''tert''-butoxide or aqueous sodium hydroxide. A

phase transfer catalyst In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of heterogeneous catalysis. Ionic reac ...

, for instance benzyltriethylammonium bromide, facilitates the migration of the hydroxide in the organic phase. :HCCl₃ + NaOH → CCl₂ + NaCl + H₂O

Other reagents and routes

Another precursor to dichlorocarbene is ethyl trichloroacetate. Upon treatment with

sodium methoxide Sodium methoxide is the simplest sodium alkoxide. With the formula , it is a white solid, which is formed by the deprotonation of methanol. Itis a widely used reagent in industry and the laboratory. It is also a dangerously caustic base. P ...

it releases CCl₂. Phenyl(trichloromethyl)mercury decomposes thermally to release CCl₂. :PhHgCCl₃ → CCl₂ + PhHgCl Dichlorodiazirine, which is stable in the dark, decomposes into dichlorocarbene and nitrogen via photolysis. Dichlorocarbene can also be obtained by dechlorination of

carbon tetrachloride Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVACR) is an organic compound with the chemic ...

with magnesium with ultrasound chemistry. This method is tolerant to esters and

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...

compounds because it does not involve strong base.

Reactions

With alkenes

Dichlorocarbene reacts with

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, a ...

s in a formal +2 ycloaddition to form

geminal In chemistry, the descriptor geminal () refers to the relationship between two atoms or functional groups that are attached to the same atom. A geminal diol, for example, is a diol (a molecule that has two alcohol functional groups) attached to ...

dichlorocyclopropanes. These can be reduced to

cyclopropane Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself i ...

s or hydrolysed to give

cyclopropanone Cyclopropanone is an organic compound with molecular formula (CH2)2CO consisting of a cyclopropane carbon framework with a ketone functional group. The parent compound is labile, being highly sensitive toward even weak nucleophiles. Surrogates o ...

s by a

geminal halide hydrolysis Geminal halide hydrolysis is an organic reaction. The reactants are geminal dihalides with a water molecule or a hydroxide ion. The reaction yields ketones from secondary halides or aldehydes from primary halides. Reaction mechanism The first par ...

. Dichlorocyclopropanes may also be converted to

allene In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon centres (). Allenes are classified as cumulated dienes. The parent compound of this class is propadiene, which ...

s in the

Skattebøl rearrangement The Skattebøl rearrangement is an organic reaction for converting a geminal dihalo cyclopropane to an allene using an organolithium base. This rearrangement reaction is named after its discoverer, Lars Skattebøl, Professor emeritus at the Univers ...

. :

With phenols

In the Reimer–Tiemann reaction dichlorocarbene reacts with

phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...

to give the ortho-

formylated In biochemistry, the addition of a formyl functional group is termed formylation. A formyl functional group consists of a carbonyl bonded to hydrogen. When attached to an R group, a formyl group is called an aldehyde. Formylation has been identi ...

product. e.g. phenol to

salicylaldehyde Salicylic aldehyde (2-hydroxybenzaldehyde) is the organic compound with the formula (C7 H6 O2) C6H4CHO-2-OH. Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oi ...

. :

With amines

Dichlorocarbene is an intermediate in the

carbylamine reaction The carbylamine reaction (also known as the Hoffmann isocyanide synthesis) is the synthesis of an isocyanide by the reaction of a primary amine, chloroform, and base. The conversion involves the intermediacy of dichlorocarbene. Illustrative is th ...

. In this conversion, a dichloromethane solution of a primary amine is treated with

and aqueous sodium hydroxide in the presence of catalytic amount of the

phase-transfer catalyst In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of heterogeneous catalysis. Ionic reac ...

. Illustrative is the synthesis of ''tert''-butyl isocyanide: :Me₃CNH₂ + CHCl₃ + 3 NaOH → Me₃CNC + 3 NaCl + 3 H₂O

History

Dichlorocarbene as a reactive intermediate was first proposed by Anton Geuther in 1862 who viewed chloroform as CCl₂^.HCl Its generation was reinvestigated by Hine in 1950. The preparation of dichlorocarbene from chloroform and its utility in synthesis was reported by

William von Eggers Doering William von Eggers Doering (June 22, 1917 – January 3, 2011) was the Mallinckrodt Professor of Chemistry at Harvard University. Before Harvard, he taught at Columbia (1942–1952) and Yale (1952–1968). Doering was born in Fort Worth, Tex ...

in 1954.''The Addition of Dichlorocarbene to Olefins'' W. von E. Doering and A. Kentaro Hoffmann

J. Am. Chem. Soc. The ''Journal of the American Chemical Society'' is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the ''Journal of Analytical ...

; 1954; 76(23) pp 6162 - 6165;

Related reactions

The Doering–LaFlamme allene synthesis entails the conversion of alkenes to

s (a chain extension) with magnesium or sodium metal through initial reaction of the alkene with dichlorocarbene. The same sequence is incorporated in the

to cyclopentadienes. Closely related is the more reactive dibromocarbene CBr₂.

Chlorocarbene

The related chlorocarbene (ClHC) can be generated from methyllithium and

dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with w ...

. It has been used in the synthesis of

spiropentadiene Spiropentadiene, or bowtiediene, is a hydrocarbon with formula C5H4. The simplest spiro-connected cycloalkene, it is very unstable—decomposing even below −100 °C—due to its high bond strain and does not occur in nature. I ...

References

{{Reflist

External links

Addition of dichlorocarbene to 2-methyl-1-buten-3-yne, laboratory procedure
English translation of 1969 Polish patent on preparation of dichloropropane derivatives Carbenes