What Is Diazomethane?
Diazomethane is an organic compound with the molecular formula CH2N2.
It is classified as a diazo compound because it has a diazo group in its molecule. Diazomethane has the simplest structure among diazo compounds, and its CAS registration number is 334-88-3.
It has a molecular weight of 42.04, a melting point of -145°C, and a boiling point of -23°C. At room temperature, it exists as a yellow gas with a musty odor. It has a density of 1.4 (air = 1). It is highly explosive and may explode on impact, heat, light, or in the presence of alkali metals.
It reacts with water, but is relatively stable in ether or dioxane solutions. Otherwise, it is readily soluble in benzene, slightly soluble in ethanol and ethyl ether, but reacts slowly with alcohols and decomposes.
It is also harmful to the human body through skin irritation and inhalation, so it should be handled with care.
Uses of Diazomethane
The main uses of diazomethane include methylating agent, agrochemical raw material, and pharmaceutical raw material. In organic synthesis laboratories, it is used for reactions such as O-methylation of carboxylic acids and phenolic hydroxy groups (to produce methyl ether and methyl ester derivatives) and C-methylation via epoxidation of ketones, among others.
Because of its explosive nature, it is usually used in ether or dioxane solutions, which are prepared for use, but safer and easier-to-handle alternatives are very often used.
Characteristics of Diazomethane
Due to the delocalization of π-electrons, the Lewis structure of diazomethane is represented as a resonance mixture, and the molecular structure is a linear structure. It is a very unstable substance and, as mentioned above, can decompose explosively when subjected to shock, friction, or vibration.
Heating to 100°C or contact with rough surfaces are also factors that can induce explosion. Additionally, the presence of impurities or solids in undiluted liquids or concentrated solutions can also cause explosions under high-intensity light.
Types of Diazomethane
Diazomethane itself is not commercially available because it is a very unstable, dangerous, and difficult to handle substance. As mentioned above, it is usually used as an ether solution or dioxane solution, which is adjusted for use.
On the other hand, trimethylsilyl diazomethane ((CH3)3SiCHN2) is a stable, non explosive liquid with reactivity similar to that of diazomethane. Because it is easy to handle, it is also available commercially as a chemical reagent.
Except in special cases where diazomethane itself must be used, this is the most commonly used reagent, and it is also preferred from a safety standpoint. Trimethylsilyldiazomethane reagent products are usually 10% hexane solution, and are available in 5mL, 25mL, 100mL, etc. They are reagents that require refrigerated storage.
Other Information on Diazomethane
1. Synthesis of Diazomethane
Diazomethane, as mentioned above, is explosive, so it is used as an ether or dioxane solution, adjusted for use. The general method of synthesis is to react acylated or sulfonated N-methyl-N-nitrosamines with a concentrated aqueous alkaline solution.
The specific experimental operation can be obtained by the following flow.
- Prepare a two-layer beaker with an ether or dioxane layer on top of the concentrated aqueous alkali solution.
- Add a small amount of N-methyl-N-nitrosamine derivative while stirring under ice-cold conditions.
- Collect the diazomethane generated in the ether layer.
2. Chemical Reaction of Diazomethane
Diazomethane is a photolytic substance that produces methylene CH2. When reacted with acid chlorides, diazomethyl ketone or chloromethyl ketone is formed.
Reaction with active triple bonds of acetylenes and double bonds of ethylenes leads to 1,3-dipole addition reactions to form pyrazole or pyrazoline derivatives. It is also used in the ring expansion reaction of cyclic ketones in the Arndt-Eichstadt synthesis.
When used as an O-methylating agent for phenol or carboxylic acids, the reaction is generally carried out by stirring an ice-cold ether solution of an excess amount of diazomethane and adding it to a solution of phenol or carboxylic acid in small quantities.