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

Yellow

Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...

 gas

Gas

Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

, thus it is almost universally used as a solution in diethyl ether

Diethyl ether

Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

. 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.

Use

For safety and convenience diazomethane is always prepared as needed as a solution in ether

Diethyl ether

Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

 and used as such. It converts carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s into their methyl ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

s or into their homologues

Homologous series

In chemistry, a homologous series is a series of compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and showing a gradation in physical properties as a result of increase in molecular size and mass...

 (see Arndt-Eistert synthesis

Arndt-Eistert synthesis

The Arndt-Eistert synthesis is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue and is considered a homologation process...

). In the Buchner-Curtius-Schlotterbeck reaction (1885) diazomethane reacts with an aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

 to form ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s. Diazomethane is also frequently used as a carbene

Carbene

In chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...

 source. It readily takes part in 1,3-dipolar cycloaddition

1,3-dipolar cycloaddition

The 1,3-dipolar cycloaddition, also known as the Huisgen cycloaddition or Huisgen reaction, is an organic chemical reaction belonging to the larger class of concerted, pericyclic cycloadditions. It is the reaction between a 1,3-dipole and a dipolarophile, most of which are substituted alkenes, to...

s.

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

N-Nitroso-N-methylurea

N-Nitroso-N-methylurea is a highly reliable carcinogen, mutagen, and teratogen. NMU is an alkylating agent, and exhibits its toxicity by transferring its methyl group to nucleobases in nucleic acids....

, 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.

CH₂N₂ reacts with basic solutions of ²H₂O to give the deuterated derivative C²H₂N₂.

The concentration of CH₂N₂ can be determined in either of two convenient ways. It can be treated with an excess of benzoic acid

Benzoic acid

Benzoic acid , C7H6O2 , is a colorless crystalline solid and the simplest aromatic carboxylic acid. The name derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as a food preservative and benzoic acid is an important precursor for the synthesis...

 in cold Et₂O. Unreacted benzoic acid

Benzoic acid

Benzoic acid , C7H6O2 , is a colorless crystalline solid and the simplest aromatic carboxylic acid. The name derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as a food preservative and benzoic acid is an important precursor for the synthesis...

 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.

Related compounds

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 (trimethylsilyldiazomethane
  Trimethylsilyldiazomethane
  Trimethylsilyldiazomethane, 3SiCHN2, is a diazo compound widely used as a less-explosive replacement for diazomethane.-Preparation:Trimethylsilyldiazomethane may be prepared from reacting methylmagnesium chloride with diphenyl phosphorazidate.-Uses:Trimethylsilyldiazomethane is a commercially...
  
  ), 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.

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. 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. 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.

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