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Diazotization Reaction

May 11, 2013

Introduction to Diazotization reaction

Peter Griess, a German chemist, discovered in 1858 that aromatic primary amines such as aniline, toluidine etc., when treated with nitrous acid form aromatic diazo-compounds. They are represented by the general formula Ar2X, where Ar is phenyl radical or its derivative and X is a nucleophilic group.

Definition for Diazotization reaction

The name derived from –di meaning two and azo (from French azote) meaning nitrogen; indicating thereby the presence of two nitrogens per phenyl radical. These compounds are unstable and highly reactive and serve as useful intermediates in the synthesis of a large number of aromatic compounds and azo-dye stuffs. They may be divided into two classes, depending upon the chemical nature of group X.The process of formation of diazonium salt by the interaction of aromatic primary amine, sodium nitrite and an inorganic acid at low temperatures, preferably around 0˚C is known as Diazotization reaction.

Preparation of diazonium salt by Diazotization reaction:

Aromatic diazonium salts are prepared by dissolving aromatic primary amine in excess of mineral acid like HCl or sulfuric acid and then adding calculated amount of sodium nitrite dissolved in water. The temperature is maintained between 0-5˚C since most of the diazonium salts decomposes at high temperatures. The diazonium salt so formed remains in solution. While, the diazonium salts are unstable and explosive substances, they are not isolated in solid form but are used directly in aqueous solution. It can also be isolated from aqueous solution by addition of alcohol or ether in which they are insoluble.Fig 1 illustrates the example for diazotization reaction

diazotization reaction

General physical characteristics of Diazotization reaction:

Aromatic diazonium salts are generally colorless, crystalline compounds. On exposure to air they turn brown or dark in color.

They are readily soluble in water, sparingly soluble in alcohol and acetic acid, and insoluble in ether.

They are unstable, highly reactive compounds. Most of them, particularly nitrates, are dangerously explosive in the solid state.

Their aqueous solution is neutral to litmus but conducts electricity due to the presence of ions.

They form stable double salts with inorganic compounds.

Spectroscopic properties of Diazotization reaction: The triple bond in the aromatic diazonium salts between nitrogen atoms exhibits an absorption band in I.R. region near 2260 cms-1.

General physical characteristics of Diazotization reaction:

Aromatic diazonium salts are generally colorless, crystalline compounds. On exposure to air they turn brown or dark in color.

They are readily soluble in water, sparingly soluble in alcohol and acetic acid, and insoluble in ether.

They are unstable, highly reactive compounds. Most of them, particularly nitrates, are dangerously explosive in the solid state.

Their aqueous solution is neutral to litmus but conducts electricity due to the presence of ions.

They form stable double salts with inorganic compounds.

Spectroscopic properties of Diazotization reaction: The triple bond in the aromatic diazonium salts between nitrogen atoms exhibits an absorption band in I.R. region near 2260 cms-1.

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