Diazotization Titration » PHARMACAREERS

Introduction

Diazotization is an organic reaction that involves the conversion of a primary aromatic amine into a corresponding diazonium salt. This process was first reported by the German industrial chemist Peter Griess in 1858. The general mechanism of the diazotization reaction involves the use of nitrous acid and another acid to treat aromatic amines, yielding the diazonium salt. Nitrous acid is typically generated from the reaction between sodium nitrite and another mineral acid, which is present in excess. In this article we will study Basic principles, methods and applications of diazotization reactions.

Table of Contents

Diazotization titrations

Diazotization titrations are a type of titration method that involves the conversion of primary aromatic amines into diazonium compounds. This process was first discovered in 1853 and was applied to the synthetic dye industry. The reaction mechanism was first proposed by Peter Griessi.

The principle of diazotization titration is that the given sample of primary aromatic amine will react with sodium nitrite to yield a diazonium salt in the presence of an acid (For example, HCl). The chemical reaction of this process is as follows.

R−NH2 + NaNO2 + HCl → R−N + ≡N−Cl–+ NaCl + H2O

Principles

Diazotization Reaction

The primary aromatic amine (the analyte) reacts with sodium nitrite (NaNO2) in acidic conditions to form a diazonium salt1234. The chemical reaction of this process is as follows.

R−NH2+NaNO2+HCl→R−N+≡N−Cl–+NaCl+H2O

Specific Reactions

Once the diazonium salt is formed, it can be further reacted with specific reagents to produce a measurable product. For example, these diazonium ions can react with various types of compounds, such as phenols or amines, to form colored azo dyes.

Endpoint Detection

The endpoint of the titration is detected when a change in color is observed. For example, starch iodide paper produces a blue color when it comes into contact with the endpoint1. The reaction is as follows.

I2 + starch mucilage → blue color end point

Temperature Control

The reaction is usually carried out at a low temperature (0-5 °C) to prevent the decomposition of the diazonium salt.

Excess Nitrous Acid Removal

In addition to nitrous acid, ammonium sulfate solution is added to remove excess nitrous acid.

These principles make diazotization titration a powerful tool in pharmaceutical analysis, such as determining sulphonamides.

Methods

Diazotization titrations can be of three primary methods.

Direct Method

This method involves treating the given amino group with an acid solution to yield the diazonium salts of diazonium compounds. This solution will be kept in the ice water to maintain the temperature between 0-5 °C. Now, titrate it with sodium nitrate and wait for the endpoint.

Indirect Method

The application of the indirect method of titration is for insoluble diazonium salts. In this method, we shall have to add the excess nitrous acid to the titration solution sample. As it is an insoluble diazonium salt, we have to titrate it against some other titrant.

Other Methods

The other method involves the conversion into diazo oxides rather than the diazo compounds, as they tend to be more stable.

Some of the factors that will affect the diazotization titration are as follows.

pH of NaNO2
The concentration of the acid that we will use for the titration
The temperature of the reaction
Time duration of the reaction

Applications

Diazotization titrations have several applications, particularly in the field of pharmaceuticals and chemical analysis.

Pharmaceuticals: Diazotization titration is used to determine the concentration of primary aromatic amines in pharmaceutical formulations. It ensures the quality and safety of pharmaceutical products. For example, sulphonamides are determined using this method. A sample of 1 mg of sulphonamide is accurately weighed and dissolved in 4ml of concentrated HCl and 10ml of distilled water. The 0.1 M Solution of Sodium Nitrite solution is then titrated with this solution after cooling to 15 °C.
Water and Wastewater Analysis: Diazotization titration can be used in the analysis of water and wastewater.
Food and Beverage Analysis: It can also be applied in the analysis of food and beverages.
Organic Chemistry: Diazotization titration is used in organic chemistry for the synthesis of various compounds.
Analysis of Dyes and Pigments: Diazotization titration is used in the analysis of dyes and pigments. Diazonium salts are used to produce water-fast dyed fabrics.
Nanotechnology: It is also applicable in nanotechnology.
Preparation of Various Compounds: It is also used in the preparation of hydrocarbons, aryl halide, aryl cyanide and aryl hydrazine.
Assay of Various Drugs: It is used in the assay of various drugs like benzocaine, procainamide, procaine, suramin, sodium salicylate, primaquine sulphate.

Summary

Diazotization titrations are a type of chemical analysis method that involves the conversion of primary aromatic amines into diazonium salts. The reaction is carried out in acidic conditions, typically using nitrous acid, which is generated from sodium nitrite and another mineral acid. The diazonium salts formed can then react with specific reagents to produce a measurable product. The endpoint of the titration is detected when a change in colour is observed.