Diazo

Diazo compounds are a group of organic chemical compounds having the general structural formula R1R2C = N = N; while R1 and R2 are carbon-containing radicals or hydrogen. The simplest diazo compound is diazomethane. The diazo compounds were discovered in 1858 by Peter Griess.

Properties

Diazo compounds are isolable but highly reactive toxic compounds that are often used as synthetic intermediates. Simple diazo compounds are volatile and explosive. Diazo compounds with N2 have a very good leaving group ( formation of gaseous nitrogen). Reactions with diazo compounds must be carried out at low temperatures, as diazo compounds easily decompose ( elimination of N2). Aromatic diazo compounds are usually more stable than aliphatic. They show a stable, internal dipole character, which can be described by two resonance structures; this is a an ylide.

Use in reactions

Diazo compounds can be used as, for example, in Alkylierungmittel esterification or the formation of ethers, owing to their high price and because they are difficult to handle, generally, however, only in the laboratory.

For example, diazomethane is used as a methylating agent for compounds with sufficiently acidic hydrogen:

In the reaction in the first step, the acidic proton is transferred to the diazomethane, which forms a Methandiazonium ion [ H3C -N2 ]. A nucleophile or as in this case an anion - RCO2 reacts further with elimination of N2.

Alcohols with substituents which show a - I effect, which increase the acidity of the OH group, can relatively easily react with diazomethane. The unactivated alcohols can not be distinguished directly methylate or only in the presence of silica gel.

Diazo compounds are important as a source for carbenes, which are formed by the splitting off of N2.

Production

Diazo compounds, due to their instability usually prepared in situ, ie directly before the actual reaction.

• Diazomethane prepared from N- methyl -N-nitroso -p-toluenesulfonamide

The resulting diazomethane is continuously distilled off.

• Nitrosation of glycine (see azo coupling )

• Oxidation of hydrazones

This variant is suitable for aromatic compounds. The oxidizing agent eg PbO2, Ag2O, HgO or CrO2 is used.