| Diazomethane | |
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Diazomethane |
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| Identifiers | |
| CAS number | 334-88-3 |
| PubChem | 9550 |
| ChemSpider | 9176 |
| KEGG | C19387 |
| Jmol-3D images | Image 1 |
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| 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 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
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]
Contents |
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.
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.
Many substituted derivatives of diazomethane have been prepared:
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. 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.