Diazomethane

Diazomethane
IUPAC name Diazomethane
Identifiers
CAS number	334-88-3 Y
PubChem	9550
ChemSpider	9176 Y
KEGG	C19387 N
Jmol-3D images	Image 1
SMILES [N-]=[N+]=C
InChI InChI=1S/CH2N2/c1-3-2/h1H2 Y Key: YXHKONLOYHBTNS-UHFFFAOYSA-N Y InChI=1/CH2N2/c1-3-2/h1H2 Key: YXHKONLOYHBTNS-UHFFFAOYAZ
Properties
Molecular formula	CH2N2
Molar mass	42.04 g/mol
Appearance	Yellow gas
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
Main hazards	toxic and explosive
Related compounds
Related compounds	R2CN2 R = Ph, tms, CF3
N (verify) (what is: Y/N?) 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 the simplest of diazo compounds. In the pure form at room temperature, it is a 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.^[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

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 somewhat unstable and nowadays such compounds as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitroso-p-toluenesulfonamide (Diazald) are preferred.^[2]

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

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]}

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] 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.

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., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0351 ; Coll. Vol. 5: 351 
3. ^ P. G. Gassman and W. J. Greenlee (1988), "Dideuterodiazomethane", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0432 ; Coll. Vol. 6: 432 
4. ^ W. J. Middleton; D. M. Gale (1988), "Bis(Trifluoromethyl))diazomethane", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0161 ; Coll. Vol. 6: 161 
5. ^ L. I. Smith, K. L. Howard (1955), "Diphenyldiazomethane”", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0351 ; Coll. Vol. 3: 351 
6. ^ T. Shioiri, T. Aoyama, S. Mori, "Trimethylsilyldiazomethane", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv8p0612 ; Coll. Vol. 8: 612 
7. ^ X. Creary (1990), "Tosylhydrazone Salt Pyrolyses: Phenydiazomethanes", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv7p0438 ; 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