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| Names | |
|---|---|
| IUPAC name Diazomethane | |
| Other names Azimethylene, Azomethylene, | |
| Identifiers | |
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3D model (JSmol) |
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| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.005.803 |
| EC Number |
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| KEGG |
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| UNII | |
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| Properties | |
| CH2N2 | |
| Molar mass | 42.04 g/mol |
| Appearance | Yellow gas |
| Odor | musty |
| Density | 1.4 (air=1) |
| Melting point | −145 °C (−229 °F; 128 K) |
| Boiling point | −23 °C (−9 °F; 250 K) |
| hydrolysis[1] | |
| Conjugate acid | Methyldiazonium |
| Structure | |
| linear C=N=N | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | toxic and explosive |
| GHS labelling: | |
  | |
| Danger | |
| H350 | |
| P201,P202,P281,P308+P313,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LC50 (median concentration) | 175 ppm (cat, 10 min)[3] |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | TWA 0.2 ppm (0.4 mg/m3)[2] |
REL (Recommended) | TWA 0.2 ppm (0.4 mg/m3)[2] |
IDLH (Immediate danger) | 2 ppm[2] |
| Related compounds | |
Relatedfunctional groups; compounds | R-N=N=N (azide), R-N=N-R (azo); R2CN2 R = Ph, tms, CF3 |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Diazomethane is an organic chemical compound with the formula CH2N2, discovered by German chemistHans von Pechmann in 1894. It is the simplestdiazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellowgas; thus, it is almost universally used as a solution indiethyl ether. The compound is a popularmethylating agent in the laboratory, but it is too hazardous to be employed on an industrial scale without special precautions.[4] Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagenttrimethylsilyldiazomethane.[5]
For safety and convenience diazomethane is always prepared as needed as a solution inether and used as such. It converts carboxylic acids to methyl esters andphenols into theirmethylethers. The reaction is thought to proceed via proton transfer from carboxylic acid to diazomethane to give amethyldiazonium cation, which reacts with the carboxylate ion to give the methyl ester and nitrogen gas. Labeling studies indicate that the initial proton transfer is faster than the methyl transfer step.[6] Since proton transfer is required for the reaction to proceed, this reaction is selective for the more acidic carboxylic acids (pKa ~ 5) and phenols (pKa ~ 10) over aliphatic alcohols (pKa ~ 15).[7]
In more specialized applications, diazomethane and other diazoalkyl reagents are used in theArndt–Eistert reaction and theBüchner–Curtius–Schlotterbeck reaction forhomologation of various compounds.[8][9]
Diazomethane reacts withalcohols orphenols in presence ofboron trifluoride (BF3) to givemethylethers.
Diazomethane is also frequently used as acarbene source. It readily takes part in1,3-dipolar cycloadditions.
A wide variety of routes have been developed for the laboratory production of diazomethane.[10] In general, the synthesis of these all involves the addition ofmethylamine to an electron-deficient species, before treatment withnitrite and mineral acid (nitrous acid) to form anN-methyl nitrosamide. Diazomethane is prepared by hydrolysis of an ethereal solution of theseN-methyl nitrosamides with aqueous base. Examples include:
Diazomethane reacts withalkaline solutions of D2O to give the deuterated derivative CD2N2.[20] This can be used forisotopic labeling studies.
The ease with which diazomethane explodes makes it too hazardous to handle in large quantities. Despite this, it can be used on an industrial scale using on-demandflow chemistry. In these processes the rate of production is matched by the rate of consumption, such that the amount of diazomethane present at any one time is very low.[21][4]
The concentration of CH2N2 can be determined in either of two convenient ways. It can be treated with an excess ofbenzoic acid in cold Et2O. Unreactedbenzoic acid is thenback-titrated with standard NaOH. Alternatively, the concentration of CH2N2 in Et2O can be determinedspectrophotometrically at 410 nm where itsextinction coefficient, ε, is 7.2.[citation needed]The gas-phase concentration of diazomethane can be determined usingphotoacoustic spectroscopy.[4]
Diazomethane is both isomeric andisoelectronic with the more stablecyanamide, but they do not interconvert.Many substituted derivatives of diazomethane have been prepared:
Diazomethane is toxic by inhalation or by contact with the skin or eyes (TLV 0.2 ppm). Symptoms include chest discomfort, headache, weakness and, in severe cases, collapse.[26] 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 fulminatingpneumonia.[27] Like any otheralkylating 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.[28] 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, exposed to intense light, alkali metals, or calcium sulfate. Use of a blast shield is highly recommended while using this compound.
Proof-of-concept work has been done withmicrofluidics, in which continuous point-of-use synthesis fromN-methyl-N-nitrosourea and 0.93 M potassium hydroxide in water was followed by point-of-use conversion withbenzoic acid, resulting in a 65% yield of the methyl benzoate ester within seconds at temperatures ranging from 0 to 50 °C. The yield was better than under capillary conditions; the microfluidics were credited with "suppression of hot spots, low holdup, isothermal conditions, and intensive mixing."[29]
The stable compoundcyanamide, whose minor tautomer iscarbodiimide, is an isomer of diazomethane. Less stable but still isolable isomers of diazomethane include the cyclic3H-diazirine and isocyanoamine (isodiazomethane).[30][31] In addition, the parentnitrilimine has been observed under matrix isolation conditions.[32]
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