Dichlorocarbene is the

reactive intermediate In chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, s ...

with

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

CCl₂. Although this

chemical species A chemical species is a chemical substance or ensemble composed of chemically identical molecular entities that can explore the same set of molecular energy levels on a characteristic or delineated time scale. These energy levels determine the wa ...

has not been isolated, it is a common intermediate in

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...

, 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 ...

. 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 Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and al ...

. 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 rea ...

, 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 it releases CCl₂.

Phenyl(trichloromethyl)mercury Phenyl(trichloromethyl)mercury is an organomercury compound with the formula C6H5HgCCl3. It is a white solid that is soluble in organic solvents. The compound is used as a source of dichlorocarbene, e.g. in cyclopropanation reactions, illustr ...

decomposes thermally to release CCl₂. :PhHgCCl₃ → CCl₂ + PhHgCl Dichlorodiazirine, which is stable in the dark, decomposes into dichlorocarbene and

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

via

photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...

. 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 chemi ...

with

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

with ultrasound chemistry. This method is tolerant to

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

s 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 containi ...

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 ...

s in a formal +2 ycloaddition to form geminal 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 cyclopropanones 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. : Dichlorocarbene reaction cyclohexene

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 oily ...

. :

With amines

Dichlorocarbene is an intermediate in the carbylamine reaction. In this conversion, a dichloromethane solution of a primary amine is treated with

and aqueous

in the presence of

catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

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 In organic chemistry, the Doering–LaFlamme allene synthesis is a reaction of alkenes that converts them to allenes by insertion of a carbon atom. This name reaction is named for William von Eggers Doering and a co-worker, who first reported it. ...

entails the conversion of alkenes to

s (a chain extension) with

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

metal through initial reaction of the alkene with dichlorocarbene. The same sequence is incorporated in the Skattebøl rearrangement 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 wit ...

. It has been used in the synthesis of spiropentadiene.

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