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.[4] Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagent trimethylsilyldiazomethane.[5]

Simplest diazo compound and methylating agent

IUPAC name

Other names

3D model (JSmol)
ECHA InfoCard 100.005.803
EC Number
  • 206-382-7
  • InChI=1S/CH2N2/c1-3-2/h1H2 Y
  • InChI=1/CH2N2/c1-3-2/h1H2
  • N#[N+]-[C-]
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)
linear C=N=N
Main hazards toxic and explosive
GHS pictograms
GHS Signal word Danger
P201, P202, P281, P308+P313, P405, P501
NFPA 704 (fire diamond)

Lethal dose or concentration (LD, LC):
175 ppm (cat, 10 min)[2]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 0.2 ppm (0.4 mg/m3)[3]
REL (Recommended)
TWA 0.2 ppm (0.4 mg/m3)[3]
IDLH (Immediate danger)
2 ppm[3]
Related compounds
Related functional groups;
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 YN ?)
Infobox references
Chemical compound

. . . Diazomethane . . .

For safety and convenience diazomethane is always prepared as needed as a solution in ether and used as such. It converts carboxylic acids to methyl esters and phenols into their methylethers. The reaction is thought to proceed via proton transfer from carboxylic acid to diazomethane to give methyldiazonium cation, which reacts with the carboxylate ion to give the methyl ester and nitrogen gas. Labeling studies indicate that the initial proton transfer is faster than the methyl transfer step.[6] Since proton transfer is required for the reaction to proceed, this reaction is selective for the more acidic carboxylic acids (pKa ~ 5) and phenols (pKa ~ 10) over aliphatic alcohols (pKa ~ 15).[7]

In more specialized applications, diazomethane and homologues are used in Arndt-Eistert synthesis and the Büchner–Curtius–Schlotterbeck reaction for homologation.[8][9]

Büchner-Curtius-Schlotterbeck Reaction.

Diazomethane reacts with alcohols or phenols in presence of boron trifluoride (BF3) to give methylethers.

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

. . . Diazomethane . . .

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. . . Diazomethane . . .

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