Chapter 10
Diazotization Titration
Introduction
- This titration involves the conversion of the primary aromatic amine to a diazonium compound by the reaction with sodium nitrite. This process was first discovered in 1853 and the reaction mechanism was first proposed by Peter Griessin. Initially, this method was applied to the synthetic dye industry. In this method, the primary aromatic amine is reacted with the sodium nitrite in acidic medium to form a diazonium salt.
Principle:
- The principle involved in diazotization titration is that the primary aromatic amine present in the sample reacts with the sodium nitrite in the presence of acid such as hydrochloric acid to obtain a diazonium salt.
R — NH2 * NaNO2 + HCI —+ R — N* - N — CI- + NaCI + H2O
- Sodium nitrite is added to the solution of amine in the presence of acid at 0-5°C, which gives HNO z. The amine reacts with the nitrous acid to form nitrosamine followed by the tautomerization and the water molecule is lost to form the diazonium ion.
Conditions for Diazotization
The major two conditions influencing diazotization reaction are:
(1) Rate of titration(2) Temperature of the solution
Rate of Titration:
- The rate of reaction for amino compounds with HONO differs. On the basis of rate of reactions amines are classified as slowly diazotisable and fast diazotisable amines. Slowly diazotisable amines include compounds containing sulpha groups, nitrous oxide group, or carboxylic group in aromatic ring besides aromatic ring are slow diazotisable compounds. Example: Isomeric nitro aniline, sulphanilic acid and anthranilic acid. Fast diazo Isable compounds do not contain any substituent group other than amino group but sometimes they may contain —CH3 or —OH group along with NHz group. Example: Aniline, toluidine and aminophenol. To increase the rate of reaction for slow dizotisable compounds, some techniques are employed which include addition of KBr to the solution and allowing titration reaction with sufficient time (5-10 minutes) to make the complete reaction with amine.
Temperature of the Solution:
- Temperature is the second major parameter that affects the reaction. Elevated temperature may decompose the formed diazonium compounds and thus lead to any side reactions. Hence, the titration is to be carried out at low temperature (0-50°C).
Applications of Diazotization Titration
- Analysis of sulphonamides: The primary aromatic amino group present in sulphonamides group of compounds is reacted with sodium nitrite to form diazonium compounds. Example: phthalylsulphathiazole and succinyl sulphathiazole.
- Analysis of Dapsone, Benzocaine, Procaine hydrochloride, Calcium amino salicylate, Sodium amino salicylate, Sulphacetamide tablet, Sulphadoxine and all sulpha drugs.
- Analysis of Dapsone, Benzocaine, Procaine hydrochloride, Calcium amino salicylate, Sodium amino salicylate, Sulphacetamide tablet, Sulphadoxine and all sulpha drugs.
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