Diazomethane
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Overview
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[1]
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 equivalent. 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. Diazomethane precursors
CH2N2 reacts with basic solutions of2H2O to give the deuterated derivative C2H2N2.[2]
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.
Other diazomethane compounds
Many substituted derivatives of diazomethane have been prepared:
- The very stable (CF3)2CN2 (b.p. 12–13 °C),[3]
- Ph2CN2 (m.p. 29–30 °C).[4]
- (CH3)3SiCHN2, which is commercially available as a solution and is as effective as CH2N2 for methylation.[5]
- PhC(H)N2, a red liquid b.p.< 25 °C at 0.1 mm Hg.[6]
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.[7] 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
- ↑ J. A. Moore; D. E. Reed “Diazomethane” Organic Syntheses Collective Volume 5, page 351
- ↑ P. G. Gassman and W. J. Greenlee “Dideuterodiazomethane” Organic Syntheses Collective Volume 6, page 432.
- ↑ W. J. Middleton; D. M. Gale “Bis(Trifluoromethyl))diazomethane” Organic Syntheses Collective Volume 6, page 161
- ↑ L. I. Smith, K. L. Howard “Diphenyldiazomethane” Organic Syntheses Collective Volume 3, page 351
- ↑ T. Shioiri, T. Aoyama, S. Mori “Trimethylsilyldiazomethane” Organic Syntheses Collected Volume, Volume 8, page 612.
- ↑ X. Creary “Tosylhydrazone Salt Pyrolyses: Phenydiazomethanes” Organic Syntheses, Coll. Vol. 7, p.438 (1990); Vol. 64, p.207 (1986).
- ↑ Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.