Diazomethane

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Diazomethane
Diazomethane
Diazomethane
Identifiers
CAS number 334-88-3 YesY
PubChem 9550
ChemSpider 9176 YesY
KEGG C19387 N
ChEBI CHEBI:73716 N
Jmol-3D images Image 1
Properties
Molecular formula CH2N2
Molar mass 42.04 g/mol
Appearance Yellow gas
Density 1.4 (air=1)
Melting point −145 °C (−229 °F; 128 K)
Boiling point −23 °C (−9 °F; 250 K)
Solubility in water hydrolysis[1]
Structure
Molecular shape linear C=N=N
Dipole moment polar
Hazards
R-phrases R12 R19 R22 R66 R67
S-phrases S9 S16 S29 S33
Main hazards toxic and explosive
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorine Special hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Related functional groups;
compounds
R-N=N=N azide),
R-N=N-R (azo);
R2CN2 R = Ph, tms, CF3
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Diazomethane is the chemical compound CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow gas; thus, it is almost universally used as a solution in diethyl ether. The compound is a popular methylating agent in the laboratory, but it is too hazardous to be employed on an industrial scale without special precautions.[2]

Use[edit]

For safety and convenience diazomethane is always prepared as needed as a solution in ether and used as such. It converts carboxylic acids into their methyl esters or into their homologues (see Arndt-Eistert synthesis). In the Büchner–Curtius–Schlotterbeck reaction diazomethane reacts with an aldehyde to form ketones.[3][4]

Buchner-Curtius-Schlotterbeck Reaction.

When diazomethane is reacted with alcohols or phenols in presence of boron trifluoride (BF3), methyl ethers are obtained.

Diazomethane is also frequently used as a carbene source. It readily takes part in 1,3-dipolar cycloadditions.

Preparation[edit]

Diazomethane laboratory preparation

Diazomethane is prepared by hydrolysis of an ethereal solution of an N-methyl nitrosamide with aqueous base. The traditional precursor is N-nitroso-N-methylurea, but this compound is itself somewhat unstable, and nowadays such compounds as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitroso-p-toluenesulfonamide (Diazald) are preferred.[5]

Preparation of Diazomethane.

CH2N2 reacts with basic solutions of D2O to give the deuterated derivative CD2N2.[6]

The concentration of CH2N2 can be determined in either of two convenient ways. It can be treated with an excess of benzoic acid in cold Et2O. Unreacted benzoic acid is then back-titrated with standard NaOH. Alternatively, the concentration of CH2N2 in Et2O can be determined spectrophotometrically at 410 nm where its extinction coefficient, ε, is 7.2.[citation needed] The gas-phase concentration of diazomethane can be determined using photoacoustic spectroscopy.[2]

Related compounds[edit]

Many substituted derivatives of diazomethane have been prepared:

  • The very stable (CF3)2CN2 (2-diazo-1,1,1,3,3,3-hexafluoropropane; b.p. 12–13 °C),[7]
  • Ph2CN2 (diazo(diphenyl)methane; m.p. 29–30 °C).[8]
  • (CH3)3SiCHN2 (trimethylsilyldiazomethane), which is commercially available as a solution and is as effective as CH2N2 for methylation.[9]
  • PhC(H)N2, a red liquid b.p.< 25 °C at 0.1 mm Hg.[10]

Safety[edit]

Diazomethane is toxic by inhalation or by contact with the skin or eyes (TLV 0.2ppm). Symptoms include chest discomfort, headache, weakness and, in severe cases, collapse.[11] Symptoms may be delayed. Deaths from diazomethane poisoning have been reported. In one instance a laboratory worker consumed a hamburger near a fumehood where he was generating a large quantity of diazomethane, and died four days later from fulminating pneumonia.[12] Like any other alkylating agent it is expected to be carcinogenic, but such concerns are overshadowed by its serious acute toxicity.

CH2N2 may explode in contact with sharp edges, such as ground-glass joints, even scratches in glassware.[citation needed] Glassware should be inspected before use and preparation should take place behind a blast shield. Specialized kits to prepare diazomethane with flame-polished joints are commercially available.

The compound explodes when heated beyond 100 °C, exposed to intense light, alkali metals, or calcium sulfate. Use of a blast shield is highly recommended while using this compound.

References[edit]

  1. ^ http://www.inchem.org/documents/icsc/icsc/eics1256.htm
  2. ^ a b Proctor, Lee D.; Warr, Antony J. (November 2002). "Development of a Continuous Process for the Industrial Generation of Diazomethane". Organic Process Research & Development 6 (6): 884–892. doi:10.1021/op020049k. 
  3. ^ Buchner, E.; Curtius, Th. (1885). "Synthese von Ketonsäureäthern aus Aldehyden und Diazoessigäther". Berichte der Deutschen Chemischen Gesellschaft 18: 2371–2377. doi:10.1002/cber.188501802118. 
  4. ^ Schlotterbeck, F. (1907). "The conversion of aldehydes and ketones through diazomethane". Berichte der Deutschen Chemischen Gesellschaft 40: 479–483. doi:10.1002/cber.19070400179. 
  5. ^ Reed, Donald E.; James A. Moore (1961). "DIAZOMETHANE". Organic Syntheses 41: 16. doi:10.15227/orgsyn.041.0016. 
  6. ^ P. G. Gassman and W. J. Greenlee (1988), Dideuterodiazomethane, Org. Synth. ; Coll. Vol. 6: 432 
  7. ^ W. J. Middleton; D. M. Gale (1988), Bis(Trifluoromethyl)diazomethane, Org. Synth. ; Coll. Vol. 6: 161 
  8. ^ L. I. Smith, K. L. Howard (1955), Diphenyldiazomethane", Org. Synth. ; Coll. Vol. 3: 351 
  9. ^ T. Shioiri, T. Aoyama, S. Mori, Trimethylsilyldiazomethane, Org. Synth. ; Coll. Vol. 8: 612 
  10. ^ X. Creary (1990), Tosylhydrazone Salt Pyrolyses: Phenydiazomethanes, Org. Synth. ; Coll. Vol. 7: 438 
  11. ^ Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.
  12. ^ LeWinn, E.B. "Diazomethane Poisoning: Report of a fatal case with autopsy", The American Journal of the Medical Sciences, 1949, 218, 556-562.

External links[edit]