Diazomethane

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Diazomethane
Diazomethane
Diazomethane
Names
IUPAC name
Diazomethane
Other names
Azimethylene,
Azomethylene,
Diazirine
Identifiers
334-88-3 YesY
ChEBI CHEBI:73716 N
ChemSpider 9176 YesY
Jmol 3D model Interactive image
KEGG C19387 N
PubChem 9550
  • InChI=1S/CH2N2/c1-3-2/h1H2 YesY
    Key: YXHKONLOYHBTNS-UHFFFAOYSA-N YesY
  • InChI=1/CH2N2/c1-3-2/h1H2
    Key: YXHKONLOYHBTNS-UHFFFAOYAZ
  • N#[N+]-[C-]
Properties
CH2N2
Molar mass 42.04 g/mol
Appearance Yellow gas
Odor musty
Density 1.4 (air=1)
Melting point −145 °C (−229 °F; 128 K)
Boiling point −23 °C (−9 °F; 250 K)
hydrolysis[1]
Structure
linear C=N=N
polar
Vapor pressure {{{value}}}
Related compounds
Related functional groups;
compounds
 R-N=N=N azide),
R-N=N-R (azo);
R2CN2 R = Ph, tms, CF3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
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

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

File:Diazomethane preparation - Macro Diazald Kit.jpg
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]

File:Diazomethane Synthesis V.1.png
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

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

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

  1. ↑ ICSC 1256 - DIAZOMETHANE
  2. ↑ 2.0 2.1 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.; Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.; Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.; Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.; Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.; Lua error in package.lua at line 80: module 'strict' not found.
  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

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