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Diazomethane is the chemical compound CH₂N₂. In the pure form at room temperature, it is a yellow gas, but it is almost universally used as a solution in diethyl ether. It is one of the more common diazo compounds. It is also toxic and potentially explosive.

Preparation

CH₂N₂ is usually prepared as a solution in diethyl ether and used for converting carboxylic acids into their methyl esters or into their homologues (see Arndt-Eistert synthesis). In the Buchner-Curtius-Schlotterbeck reaction (1885) diazomethane reacts with an aldehyde to form ketones. Diazomethane is also frequently used as a carbene source. It readily takes part in 1,3-dipolar cycloaddition reactions. Diazomethane is prepared in the laboratory at mmol scale from precursors such as Diazald or N-methyl-N-nitroso-p-toluenesulfonamide and MNNG or 1-methyl-3-nitro-1-nitrosoguanidine. Diazald in a solution of diglyme and diethyl ether reacts with a warm aqueous solution of sodium hydroxide and the generated CH₂N₂ is collected by distillation. Diazomethane is liberated from a solution of MNNG in diethyl ether by addition of aqueous potassium hydroxide at low temperatures.

Another possible way of the diazomethane synthesis is the basic hydrolysis of N-Nitroso-N-methylurea.

CH₂N₂ reacts with basic solutions of²H₂O to give the deuterated derivative C²H₂N₂.

Assay

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 assayed using titration 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.

Related compounds

Many substituted derivatives of diazomethane have been prepared:

• The very stable (CF₃)₂CN₂ (b.p. 12–13 °C),
• Ph₂CN₂ (m.p. 29–30 °C).
• (CH₃)₃SiCHN₂, which is commercially available as a solution and is as effective as CH₂N₂ for methylation.
• PhC(H)N₂, a red liquid b.p.< 25 °C at 0.1 mm Hg.

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. CH₂N₂ may explode when in contact with ground-glass joints or when heated to about 100.0 °C. Consequently specialized, scratch-free glassware and a blast shield should be employed for its use.

References

External links

• MSDS diazomethane
• Sigmaaldrich technical bulletin
• The Buchner-Curtius-Schlotterbeck reaction @ Institute of Chemistry, Skopje, Macedonia
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