Diazomethane

Diazomethane
IUPAC name	Diazomethane
Identifiers
CAS number	[334-88-3]
SMILES	C=[N+]=[N-]
Properties
Molecular formula	CH2N2
Molar mass	42.04 g/mol
Density	1.4 (air=1)
Melting point	-145 °C
Boiling point	-23 °C
Structure
Molecular shape	linear C=N=N
Dipole moment	polar
Hazards
R-phrases	R12 R19 R22 R66 R67
S-phrases	S9 S16 S29 S33
Related compounds
Related compounds	R2CN2 R = Ph, tms, CF3
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Diazomethane laboratory preparation

Diazomethane is the chemical compound CH₂N₂. It is one of the more common diazo compounds. In the pure form at room temperature, it is a famously explosive yellow gas, but 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 a technical scale without special precautions.^[1]

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 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 cycloadditions.

Preparation^[2]

Diazomethane is prepared by hydrolysis of an etheric solution of an N-methyl nitrosamide with aqueous base. The traditional precursor is N-Nitroso-N-methylurea, however this compound is somewhat unstable, and nowadays such compounds as N-methyl-N'-nitro-N-nitrosoguanidine (MMNG) and N-methyl-N-nitroso-p-toluenesulfonamide (Diazald) are preferred.

CH₂N₂ reacts with basic solutions of ²H₂O to give the deuterated derivative C²H₂N₂.^[3]

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 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.

Related compounds

Many substituted derivatives of diazomethane have been prepared:

• The very stable (CF₃)₂CN₂ (b.p. 12–13 °C),^[4]
• Ph₂CN₂ (m.p. 29–30 °C).^[5]
• (CH₃)₃SiCHN₂ (trimethylsilyldiazomethane), which is commercially available as a solution and is as effective as CH₂N₂ for methylation.^[6]
• PhC(H)N₂, a red liquid b.p.< 25 °C at 0.1 mm Hg.^[7]

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.^[8] 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. ^[9]

CH₂N₂ may explode in contact with sharp edges, such as ground-glass joints, even scratches in glassware. 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.

References

1. ^ L.D. Proctor, A.J. Warr, Org. Proc. Res. Dev., 2002, 6, 884–92. The authors report on a continuous process capable of generating 50-60 tons/year while the total inventory at any point in time is less than 80 g.
2. ^ J. A. Moore; D. E. Reed (1973). "Diazomethane". Org. Synth.; Coll. Vol. 5: 351. 
3. ^ P. G. Gassman and W. J. Greenlee (1988). "Dideuterodiazomethane". Org. Synth.; Coll. Vol. 6: 432. 
4. ^ W. J. Middleton; D. M. Gale (1988). "Bis(Trifluoromethyl))diazomethane". Org. Synth.; Coll. Vol. 6: 161. 
5. ^ L. I. Smith, K. L. Howard (1955). "Diphenyldiazomethane”". Org. Synth.; Coll. Vol. 3: 351. 
6. ^ T. Shioiri, T. Aoyama, S. Mori. "Trimethylsilyldiazomethane". Org. Synth.; Coll. Vol. 8: 612. 
7. ^ X. Creary (1990). "Tosylhydrazone Salt Pyrolyses: Phenydiazomethanes". Org. Synth.; Coll. Vol. 7: 438. 
8. ^ Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.
9. ^ 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

• MSDS diazomethane
• Sigmaaldrich technical bulletin (PDF)
• Sigma-Aldrich diazomethane applications and commercial availability of (Diazald) precursor
• The Buchner-Curtius-Schlotterbeck reaction @ Institute of Chemistry, Skopje, Macedonia