Dichlorocarbene
Encyclopedia
Dichlorocarbene is a carbene
commonly encountered in organic chemistry
. This reactive intermediate
with chemical formula
CCl2 is easily available by reaction of chloroform
and a base such as potassium t-butoxide or sodium hydroxide dissolved in water. A phase transfer catalyst
, for instance benzyltriethylammonium bromide, is added to facilitate the migration of the hydroxide in the organic phase.
when reacted with sodium
in methanol
. and phenyl(trichloromethyl)mercury by thermal decomposition Dichlorodiazirine is an experimental dichlorocarbene precursor . It is stable in the dark at room temperature
and decomposes
into the carbene and nitrogen
gas by photolysis.
Dichlorocarbene can also be obtained by reaction of carbon tetrachloride
with elemental magnesium
with ultrasound chemistry . This method is tolerant to ester
s and carbonyl
compounds because it does not involve strong base
.
s in a formal [1+2]cycloaddition
to form geminal
dichlorocyclopropanes
which can subsequently be 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 based on the functionalization of cyclohexene.
In the Reimer–Tiemann reaction dichlorocarbene reacts with phenol to salicylaldehyde.
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 CBr2.
. It has been used in the synthesis of spiropentadiene
.
Carbene
In chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...
commonly encountered in organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
. This reactive intermediate
Reactive intermediate
In chemistry a reactive intermediate is a short-lived, high energy, highly reactive molecule. When generated in a chemical reaction it will quickly convert into a more stable molecule. Only in exceptional cases can these compounds be isolated and stored, e.g. low temperatures, matrix isolation...
with chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
CCl2 is easily available by reaction of chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
and a base such as potassium t-butoxide or sodium hydroxide dissolved in water. A phase transfer catalyst
Phase transfer catalyst
In chemistry, a phase transfer catalyst or PTC is a catalyst that facilitates the migration of a reactant from one phase into another phase where reaction occurs. Phase transfer catalysis is a special form of heterogeneous catalysis. Ionic reactants are often soluble in an aqueous phase but...
, for instance benzyltriethylammonium bromide, is added to facilitate the migration of the hydroxide in the organic phase.
Preparation
Other dichlorocarbene precursors are ethyl trichloracetateEthyl acetate
Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell and is used in glues, nail polish removers, and cigarettes...
when reacted with sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
in methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
. and phenyl(trichloromethyl)mercury by thermal decomposition Dichlorodiazirine is an experimental dichlorocarbene precursor . It is stable in the dark at room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
and decomposes
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...
into the carbene and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
gas by photolysis.
| Dichlorocarbene from dichloroaziridine |
|---|
Dichlorocarbene can also be obtained by reaction of carbon tetrachloride
Carbon tetrachloride
Carbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
with elemental magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
with ultrasound chemistry . This method is tolerant to ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s and carbonyl
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....
compounds because it does not involve strong base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
.
Reactions
Dichlorocarbene reacts with alkeneAlkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s in a formal [1+2]cycloaddition
Cycloaddition
A cycloaddition is a pericyclic chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction.Cycloadditions are usually described by the...
to form geminal
Geminal
In chemistry, the term geminal refers to the relationship between two functional groups that are attached to the same atom...
dichlorocyclopropanes
Cyclopropane
Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms...
which can subsequently be reduced to proper cyclopropane
Cyclopropane
Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms...
s or hydrolyzed to a cyclopropanone
Cyclopropanone
Cyclopropanone is an organic compound with molecular formula C3H4O consisting of a cyclopropane carbon framework with a ketone functional group. The parent compound is labile with melting point −90 °C and has been prepared by reaction of ketene with diazomethane at −145 °C...
in a gem halide hydrolysis. The preparation of dichlorocarbene from chloroform and its utility in synthesis was discovered by William von Eggers Doering
William von Eggers Doering
William von Eggers Doering was a Professor Emeritus at Harvard University and the former Chair of its Chemistry Department...
in 1954 based on the functionalization of cyclohexene.
| Dichlorocarbene formation and reaction with cyclohexene Cyclohexene Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes... |
|---|
In the Reimer–Tiemann reaction dichlorocarbene reacts with phenol to salicylaldehyde.
History
Dichlorocarbene as a reactive intermediate was first proposed by Anton Geuther in 1862 who viewed chloroform as CCl2.HCl and again by Hine in 1950 . Dichlorocarbene was first trapped by Doering in 1954.Related reactions
The Doering–LaFlamme carbon chain extension describes the conversion of alkenes to allenes (a chain extension) with magnesiumMagnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
or sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
metal through initial reaction of the alkene with dichlorocarbene. The same sequence is incorporated in the Skattebøl rearrangement
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 University of Oslo...
to cyclopentadienes. Dichlorocarbene also features in the Reimer–Tiemann reaction. Closely related is the more reactive dibromocarbene CBr2.
Chlorocarbene
The related chlorocarbene (ClHC) can be generated from methyllithium and dichloromethaneDichloromethane
Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...
. It has been used in the synthesis of spiropentadiene
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...
.