What is Diazotization?

What is Diazotization?

Diazotization is the process of converting the primary amines which are aromatic into its diazonium salt. The diazonium salts are important synthetic products that can have coupling reactions to form as dyes and other reactions. In the process of diazotization we add sodium nitrate to a solution of the amine in an acid solution at about temperature between 0 to 5 degree C.

The diazotization reaction has many uses –

1. They are bright colours because of conjugated systems. Many are used as dyes. Eg- methyl red and pigment red. As printing also used in reactions.
2. An azo coupling process is also used to make drugs.
3. An azo coupling is the reaction between the diazonium compound and another compound which is aromatic that in turn produces an as compound. In this reaction the diazonium compound is also aromatic.

General properties and reactivity: The general properties of the diazonium compound is that they have strong electron withdrawing substituents. Thus the position of acidic protons her and also benzoic acids have greatly reduced pKa values as compared to their counterparts. Eg- the pKa for methanediazonium is less than 10. In terms of reactivity the chemistry of these sales are greatly dominated by their propensity to dediazotize. Here there is expulsion of dinitrogen gas. There are other methods of dediazotization and they are- electrode organic reduction. By mild reducing agents such as ascorbic acid, we can do it by some gamma radiation from solvated electrons in the water. This process can also include the photo induced electron transfer. Others are:

1. Reduction by metal cations, most commonly a salt.
2. Anion-induced dediazoniation where iodine gives electron transfer to the diazonium forming the aryl radical and an iodine radical.
3. Solvent-induced dediazoniation with solvent serving as electron donor.

Preparation:  The process here is called diazotization or diazotation. The reaction was first done by Peter Greiss in the year 1858. He discovered that several reactions of new class of compounds. The most common ones are diazonium salts which are prepared by treating aromatic amines with nitrous acids and additional acid. The nitrous acid is generated in the same flask from sodium nitrate and excess mineral acid.

Applications:

1. The basic application for Diazonium salts is that they are used for water based fast dying fabrics where the fabric is immersed in a solution of the diazonium compound then it is followed by the immersion in a coupler solution. Here the electron rich ring goes through electrophilic substitution. The vast major use of diazonium compound is used for Dye and Pigment industry for Fabrics.
2. The diazonium compounds are reagents for synthesis of organic compounds and specially for aryl derivatives.
3. These salts are very sensitive to light and they break down under the UV or violet light. This particular property is used for document reproduction. In this process, film is coated with a diazonium salt and then After its contact exposure with light, the diazo is converted to a stable azo dye with an aqueous coupler solution. A more common process uses a paper coated with diazo, coupler and an acid to encourage coupling. After exposure the image is developed by a vapor mixture of ammonia and water which forces it for
4. Safety process – some diazonium halides are most often explosive and dangerous and it has been recorded for many injuries and fatalities.
5. The nature of the anions effect the salt stability. Some of them like nitrobenzenediazonium is used for making explosives.
6. In the filed of Biochemistry – Alkanediazonium otherwise rarely encountered in organic chemistry, are known to have been treated as the causative agents in the carcinogens. Specifically, nitrosamines are thought to undergo metabolic activation to produce alkanediazonium species.
7. Grafting reactions- In a very important application in nanotechnology, the diazonium salts 4-chlorobenzenediazonium tetrafluoroborate is very efficiently used to functionalize single wall nanotubes.Hence to make the natures exfoliate they are then mixed with some ionic liquid in a mortar and pstle. The salt is then added to the potassium Carbonate and after the mixture is grinder then at room temperature the surface of the nanotubes are covered with chlorophenyl groups with an efficiency of 1 in 44 carbon atoms. These added ions prevent the nano tubes from forming intimate bundles due to large cohesive forces between them, which is a recurring problem in nanotube technology.