Dichlorocarbene

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Dichlorocarbene
Wireframe model of dichlorocarbene Dichlorocarbene-from-MW-2001-2D.png
Wireframe model of dichlorocarbene
Ball and stick model of dichlorocarbene Dichlorocarbene-from-MW-2001-3D-balls.png
Ball and stick model of dichlorocarbene
Names
Preferred IUPAC name
Dichloromethylidene
Other names
Carbon(II) chloride

Carbon dichloride
Carbonous chloride
Dichloro-λ2-methane

Dichloromethylene

Contents

Identifiers
3D model (JSmol)
1616279
ChEBI
ChemSpider
200357
MeSH Dichlorocarbene
PubChem CID
UNII
  • InChI=1/CCl2/c2-1-3
    Key: PFBUKDPBVNJDEW-UHFFFAOYAT
  • [C](Cl)Cl
Properties
CCl2
Molar mass 82.91 g·mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Highly reactive
Related compounds
Related compounds
C2Cl4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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. This bent diamagnetic molecule rapidly inserts into other bonds.

Preparation

Dichlorocarbene is most commonly generated by reaction of chloroform and a base such as potassium tert-butoxide or aqueous sodium hydroxide. [1] A phase transfer catalyst, 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. [2]

Phenyl(trichloromethyl)mercury decomposes thermally to release CCl2. [3]

PhHgCCl3 → CCl2 + PhHgCl

Dichlorodiazirine, which is stable in the dark, decomposes into dichlorocarbene and nitrogen via photolysis. [4]

(a) Cyanogen bromide (b) hydroxylamine (c) mesyl chloride (d) sodium hypochlorite (e) nitronium tetrafluoroborate (f) caesium and tetrabutylammonium chlorides in an ionic liquid Dichlorocarbene from dichloroaziridine.svg
(a) Cyanogen bromide (b) hydroxylamine (c) mesyl chloride (d) sodium hypochlorite (e) nitronium tetrafluoroborate (f) caesium and tetrabutylammonium chlorides in an ionic liquid

Dichlorocarbene can also be obtained by dechlorination of carbon tetrachloride with magnesium with ultrasound chemistry. [5] This method is tolerant to esters and carbonyl compounds because it does not involve strong base.

Reactions

With alkenes

Dichlorocarbene reacts with alkenes in a formal [1+2]cycloaddition to form geminal dichlorocyclopropanes. These can be reduced to cyclopropanes or hydrolysed to give cyclopropanones by a geminal halide hydrolysis. Dichlorocyclopropanes may also be converted to allenes in the Skattebøl rearrangement.

Dichlorocarbene reaction cyclohexene.svg

With phenols

In the Reimer–Tiemann reaction dichlorocarbene reacts with phenols to give the ortho-formylated product. [6] e.g. phenol to salicylaldehyde.

Reimer-Tiemann Reaction Scheme.png

With amines

Dichlorocarbene is an intermediate in the carbylamine reaction. In this conversion, a dichloromethane solution of a primary amine is treated with chloroform and aqueous sodium hydroxide in the presence of catalytic amount of the phase-transfer catalyst. Illustrative is the synthesis of tert-butyl isocyanide: [7]

Me3CNH2 + CHCl3 + 3 NaOH → Me3CNC + 3 NaCl + 3 H2O

History

In 1835, the French chemist Auguste Laurent recognised chloroform as CCl2HCl (then written as C8Cl8H4Cl4) [lower-alpha 1] in his paper on analysing some organohalides. Laurent also predicted a compound seemingly consisting of 2 parts dichlorocarbene which he named Chlorétherose (possibly Tetrachloroethylene, which was not known to exist at the time.) [8]

Dichlorocarbene as a reactive intermediate was first proposed by Anton Geuther in 1862 who viewed chloroform as CCl2.HCl [9] Its generation was reinvestigated by Hine in 1950. [10] The preparation of dichlorocarbene from chloroform and its utility in synthesis was reported by William von Eggers Doering in 1954. [11]

The Doering–LaFlamme allene synthesis entails 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.

Closely related is the more reactive dibromocarbene CBr2.

Chlorocarbene

The related chlorocarbene (ClHC) can be generated from methyllithium and dichloromethane. It has been used in the synthesis of spiropentadiene.

See also

Explanatory notes

  1. It was common for French chemists of 19th century to write molecular weights twice, seemingly Laurent also counted 2 molecules of chloroform. Combined with the inaccurate molecular weight of carbon in the early 19th century (considered half of what it really is), these resulted in a count of 8 carbons for 2 molecules of chloroform.

Related Research Articles

<span class="mw-page-title-main">Allenes</span> Any organic compound containing a C=C=C group

In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon atoms. Allenes are classified as cumulated dienes. The parent compound of this class is propadiene, which is itself also called allene. A group of the structure R2C=C=CR− is called allenyl, while a substituent attached to an allene is referred to as an allenic substituent. In analogy to allylic and propargylic, a substituent attached to a saturated carbon α to an allene is referred to as an allenylic substituent. While allenes have two consecutive ('cumulated') double bonds, compounds with three or more cumulated double bonds are called cumulenes.

<span class="mw-page-title-main">Ketone</span> Organic compounds of the form >C=O

In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.

<span class="mw-page-title-main">Elimination reaction</span> Reaction where 2 substituents are removed from a molecule in a 1 or 2 step mechanism

An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one- or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as the E1 reaction. The numbers refer not to the number of steps in the mechanism, but rather to the kinetics of the reaction: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism.

<span class="mw-page-title-main">Imine</span> Organic compound or functional group containing a C=N bond

In organic chemistry, an imine is a functional group or organic compound containing a carbon–nitrogen double bond. The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bonds. Imines are common in synthetic and naturally occurring compounds and they participate in many reactions.

<span class="mw-page-title-main">Aluminium chloride</span> Chemical compound

Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms a hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are colourless crystals, but samples are often contaminated with iron(III) chloride, giving them a yellow colour.

The Hofmann rearrangement is the organic reaction of a primary amide to a primary amine with one less carbon atom. The reaction involves oxidation of the nitrogen followed by rearrangement of the carbonyl and nitrogen to give an isocyanate intermediate. The reaction can form a wide range of products, including alkyl and aryl amines.

In organic chemistry, the Wurtz reaction, named after Charles Adolphe Wurtz, is a coupling reaction in which two alkyl halides are treated with sodium metal to form a higher alkane.

An isocyanide is an organic compound with the functional group –N+≡C. It is the isomer of the related nitrile (–C≡N), hence the prefix is isocyano. The organic fragment is connected to the isocyanide group through the nitrogen atom, not via the carbon. They are used as building blocks for the synthesis of other compounds.

<span class="mw-page-title-main">Hemiaminal</span> Organic compound or group with a hydroxyl and amine attached to the same carbon

In organic chemistry, a hemiaminal is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: −C(OH)(NR2)−. R can be hydrogen or an alkyl group. Hemiaminals are intermediates in imine formation from an amine and a carbonyl by alkylimino-de-oxo-bisubstitution. Hemiaminals can be viewed as a blend of aminals and geminal diol. They are a special case of amino alcohols.

<i>N</i>,<i>N</i>-Dicyclohexylcarbodiimide Chemical compound

N,N′-Dicyclohexylcarbodiimide (DCC or DCCD) is an organic compound with the chemical formula (C6H11N)2C. It is a waxy white solid with a sweet odor. Its primary use is to couple amino acids during artificial peptide synthesis. The low melting point of this material allows it to be melted for easy handling. It is highly soluble in dichloromethane, tetrahydrofuran, acetonitrile and dimethylformamide, but insoluble in water.

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.

<span class="mw-page-title-main">Reimer–Tiemann reaction</span> Chemical reaction for ortho-formylation of phenols

The Reimer–Tiemann reaction is a chemical reaction used for the ortho-formylation of phenols. with the simplest example being the conversion of phenol to salicylaldehyde. The reaction was first reported by Karl Reimer and Ferdinand Tiemann.

<i>tert</i>-Butyllithium Chemical compound

tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as solutions in hydrocarbons (such as pentane); it is not usually prepared in the laboratory.

<span class="mw-page-title-main">Alkyl nitrite</span> Organic compounds of the form R–O–N=O

In organic chemistry, alkyl nitrites are a group of organic compounds based upon the molecular structure R−O−N=O, where R represents an alkyl group. Formally they are alkyl esters of nitrous acid. They are distinct from nitro compounds.

In chemistry, dehydrohalogenation is an elimination reaction which removes a hydrogen halide from a substrate. The reaction is usually associated with the synthesis of alkenes, but it has wider applications.

The carbylamine reaction is the synthesis of an isocyanide by the reaction of a primary amine, chloroform, and base. The conversion involves the intermediacy of dichlorocarbene.

The Sharpless oxyamination is the chemical reaction that converts an alkene to a vicinal amino alcohol. The reaction is related to the Sharpless dihydroxylation, which converts alkenes to vicinal diols. Vicinal amino-alcohols are important products in organic synthesis and recurring pharmacophores in drug discovery.

tert-Butyl isocyanide is an organic compound with the formula Me3CNC (Me = methyl, CH3). It is an isocyanide, commonly called isonitrile or carbylamine, as defined by the functional group C≡N-R. tert-Butyl isocyanide, like most alkyl isocyanides, is a reactive colorless liquid with an extremely unpleasant odor. It forms stable complexes with transition metals and can insert into metal-carbon bonds.

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.

<span class="mw-page-title-main">Phenyl(trichloromethyl)mercury</span> Chemical compound

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, illustrated with tetrachloroethylene as a substrate, the product being hexachlorocyclopropane:

References

  1. "2-Oxa-7,7-dichloronorcarane". Organic Syntheses. 41: 76. 1961. doi:10.15227/orgsyn.041.0076.
  2. "1,6-Methano[10]annulene". Organic Syntheses. 54: 11. 1974. doi:10.15227/orgsyn.054.0011.
  3. "Phenyl(trichloromethyl)mercury". Organic Syntheses. 46: 98. 1966. doi:10.15227/orgsyn.046.0098.
  4. Gaosheng Chu; Robert A. Moss; Ronald R. Sauers (2005). "Dichlorodiazirine: A Nitrogenous Precursor for Dichlorocarbene". J. Am. Chem. Soc. 127 (41): 14206–14207. doi:10.1021/ja055656c. PMID   16218614.
  5. 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 2003, 8, 608-613 Online Article
  6. Wynberg, Hans (1960). "The Reimer-Tiemann Reaction". Chemical Reviews. 60 (2): 169–184. doi:10.1021/cr60204a003.
  7. Gokel, G.W.; Widera, R.P.; Weber, W.P. (1988). "Phase-transfer Hofmann carbylamine reaction: tert-butyl isocyanide". Organic Syntheses. 55: 232. doi:10.15227/orgsyn.055.0096.
  8. Auguste Laurent, Note sur les Chlorure, Bromure et Iodure d'Aldehydène (1835), Annales de Chimie et de Physique, p. 327
  9. Ueber die Zersetzung des Chloroforms durch alkoholische Kalilösung Annalen der Chemie und Pharmacie Volume 123, Issue 1, Date: 1862, Pages: 121-122 A. Geuther doi : 10.1002/jlac.18621230109
  10. Carbon Dichloride as an Intermediate in the Basic Hydrolysis of Chloroform. A Mechanism for Substitution Reactions at a Saturated Carbon Atom Jack Hine J. Am. Chem. Soc., 1950, 72 (6), pp 2438–2445 doi : 10.1021/ja01162a024
  11. 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