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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.
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
. Diazald in a solution of diglyme
and diethyl ether
reacts with a warm aqueous solution of sodium hydroxide
and the generated CH2
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.
The concentration of CH2
can be determined in either of two convenient ways. It can be treated with an excess of benzoic acid in cold Et2
O. Unreacted benzoic acid is then assayed using titration with standard NaOH. Alternatively, the concentration of CH2
O can be determined spectrophotometrically at 410 nm where its extinction coefficient, ε, is 7.2.
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.
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. CH2
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.