Question

Explain Gomberg reaction with mechanism.

Answer 1

Hint: Gomberg reaction is known by the name of Gomberg-Bachmann reaction as this reaction is discovered by two scientists known as Gomberg and Bachmann. It is an aryl-aryl coupling reaction with the help of diazonium salt.

Complete answer: Gomberg reaction is basically start with the starting reactant diazonium salt and diazonium salt can be explained as a group of organic compounds which shares a common functional group represented by $R-{{N}_{2}}^{+}{{X}^{-}}$ where R can be any organic group may be alkyl or aryl and X is halogen.
The mechanism of Gomberg-Bachmann reaction can be explained as follows:
1. In the first step diazonium salt derivative is reacted with hydroxide ion and forms diazonium oxide which further reacts with $Ph{{N}_{2}}^{+}$ and forms a double ring compound.
2. After this loss of nitrogen gas is there which dissociates the molecule into two fragments out of which one is in the form of diazonium oxide and other one is a radical form of benzene.
3. After that diazonium gets reacted with benzene group and forms a biaryl group with the presence of aryl intermediate in this product i.e. H ion is present in this compound.
4. This H atom firstly gets reacted with $Ph{{N}_{2}}O$ which immediately form $Ph{{N}_{2}}OH$ which readily get lost from the compound and it forms biaryl product.
Mechanism can be shown as follows:

Note: Gomberg reaction is generally classified as coupling reaction; these are those reactions in which two fragments are joined together with the help of a metal catalyst. The most common coupling reaction is the cross coupling reaction.