Diazotization titration | Notes

Diazotization titration | Notes

Diazotization titration


The process of forming diazonium compounds/salts are called diazotization. Diazotization titration Diazonium compounds/diazonium salts are a group of organic compounds sharing a common functional group with the characteristics structure of R -N2 – x-, Where R can be any organic Residue such as alkyl or aryl and X is on inorganic or organic anion search as a halogen.

The reaction was discovered by Peter Griese in 1858, who subsequently Discover several reactions of new compounds. This method is first used in the determination of dyes.

Diazonium salts have been developed as important intermediates in the organic synthesis of dyes.

Diazotization titration is carried out for the estimation of drugs containing a primary aromatic amino group.

Several drugs contain either primary aromatic amino groups or they can be converted to have such groups but simple reactions like hydrolysis or reduction.

And primary aromatic amine reacts with nitrous acid produced by the reaction of sodium nitrate in an acidic medium to form a diazonium salt.

The reaction is quantitative under the control conditions of temperature approximately 15 ° celsius and the endpoint can be detected when a small quantity of excess nitrous acid present at the endpoint gives color change with an indicator or by electronically.

It uses the Titrant – sodium nitrite hence the method is sodium nitrite titration/Nitrite titration.

3.4.1 Principal of diazotization titration

The first involves is the addition of sodium nitrite to hydrochloric acid cause the formation of nitrous acid

Nano2 + HCl → HONO + NACl

This nitrous acid diazotizes the aromatic amino group

R – NH2 + NaNo2 + HCl → R – N+ ≡ N Cl+ NaCl

After the endpoint excess nitrous acid formation by instant formation of blue color with starch iodide paper.


KI + HCl → HI + KCl

NaNo2 + HCl → HNO2 +NACl

2HI + 2HONO → I2↑ + 2NO + 2 H2O

– starch iodide paper is prepared by immersing a filter paper in starch mucilage and potassium iodide solution.

– the iodine form reacts with starch mucilage to give the blue color.

I2 + Starch → blue colour (endpoint)

The endpoint can be determined by the Dead stop endpoint and potentiometric technique.

3.4.2 Types / Method of diazotization titration

Direct titration 

  • These are carried out by treating one mole of the drug with 3 moles of acid solution.
  • Ice can be used to lower the temperature to about 0.50c to 1.1 Mili sodium nitrite is added in small amounts and titration is carried out.
  • The endpoint is determined by any one of the techniques as said before.

Reverse method 

  • In this method, a solution of amine and sodium nitrate is run into a solution of acid.
  • This method is used when the diazonium salt is insoluble.
  • eg. Napthylamine sulfonic acid form insoluble diazonium salts due to the formation of Zwitter ions.

Special method

  • Aminophenol is readily oxidized by nitrous acid to quinones.
  • For such substances, the titration is carried out in the presence of copper sulfate which forms Diazo oxide.
  • These diazo oxides are more stable and undergo coupling reactions.

3.4.3 Applications of diazotization titration

  • The first use of diazonium salt was to produce water-fast dye fabrics.
  • A more common process uses a proper coated with diaze.
  • Also applicable in nanotechnology
  • It is also used in the preparation of hydrocarbon, aryl halides, aryl cyanide, and aryl hydrazines.
  • Used in the assay of sulpha drugs like dapsone, sulphonamide, sulfacetamide sodium, Sulphadiazine, sulphamethoxazole, sulphadoxine, Sulphaphenazone, etc.
  • It is also used in the assay of various drugs life benzocaine, procainamide, sodium aminosalicylate primaquine sulfate, etc.

Written by: Ms.Mayuri Lendave (Ass. Professor- Pharmaceutical Analysis).

Gravimetric analysis