Diazomethane

Azimethylen

Yellow, smelling of damp leaves gas

Gaseous

1.45 g · cm -3

-145 ° C

-23 ° C.

• Decomposition in water
• Soluble in ethanol, diethyl ether and benzene

Risk

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Diazomethane ( CH2N2 sum formula ), also called Azimethylen, the easiest diazo compound. It is a frequently used in the laboratory and the methylating agent is used in particular for the preparation of methyl esters from carboxylic acids and of cyclopropanes from alkenes. Its technical application is very limited due to the high toxicity and reactivity.

Representation

Diazomethane can be prepared by reaction of N-methyl -nitroso compounds such as N -methyl-N -nitrosourea or N-methyl -N-nitroso -p-toluenesulfonamide with bases such as sodium or potassium hydroxide in diethyl ether. It first forms a diazotate, which is decomposed by the base in diazomethane and water. The diazomethane was distilled from the ether. Another postulated mechanism describes a 1,3 - acyl shift with a base-catalyzed cleavage.

Properties

The molecular structure of diazomethane can be described by three resonance structures:

The isomeric diazirine ring compound whose structure was initially assigned to the diazomethane, has completely different physical and chemical properties. Other isomeric forms of diazomethane are Isoknallsäureamid ( H2N -NC) and Isodiazomethan ( HCNNH ), which are stable only in komplexstabilisiertem state.

At room temperature, diazomethane is a yellow gas that smells of damp leaves. It is both as a gas or as a liquid extremely explosive. Therefore, it is usually prepared as a solution in diethyl ether and used. The ethereal solution is not stable, the diazomethane decomposes slowly under nitrogen discharge. Risk of explosion especially in contact with rough glass surfaces and metals. Diazomethane reacts with alkali metals, calcium chloride, copper powder and explosive sodium sulphide.

His characteristic chemical reaction is the methylation, reacts with diazomethane with suitable nucleophiles under nitrogen discharge.

Toxicity

Diazomethane is toxic and carcinogenic in animal experiments. The main route of diazomethane are the respiratory tract, where it reacts directly with the tissue. Acute, it causes burns, a chronic toxicity, little is known.

Use

Diazomethane is a powerful and methylating agent is used exclusively as a solution in diethyl ether in a smaller scale. It is a very strong electrophile and, with N2 a good leaving group. It is particularly suitable for the simple and effective preparation of methyl esters of carboxylic acids. Methylation is possible, in contrast to other methylations in weak acids. Furthermore, it can be used for ring extensions, the [ 1,3] -dipolar cycloaddition reactions are Arndt Eistert homologation for extension of carbon chains to another carbon atom and used.

If one uses boron trifluoride as a catalyst, as can be converted with diazomethane alcoholic hydroxyl groups (-OH) in methoxy groups ( - OCH3). Phenols react with diazomethane, however, even without boron trifluoride catalyst.

The addition of diazomethane to the C = C double bonds, such as acrylonitrile in the formation of pyrazoline ring.