Glyceryl Trinitrate (Nitroglycerine)
Formula: C3H5O3(NO2) or C3H5N3O9
Other Name: Nitroglycerine
Preparation
Glyceryl trinitrate is prepared by slowly adding glycerol to a chilled mixture of concentrated sulphuric acid (H₂SO₄) and concentrated nitric acid (HNO₃). The reaction mixture is then poured carefully into ice-cold water. Nitroglycerine separates as a heavy oily liquid, which is purified by washing several times with cold water.
Test for Purity
- Appearance: It is a pale yellow, thick liquid. The slight yellow color is due to nitrate impurities.
- Free Nitrate Test: When treated with Griessmann nitrate reagent, the sample develops a yellow-orange color that is compared with a standard solution.
Assay (Estimation)
The assay mainly identifies the nitrate content. Two approaches are commonly used:
1. Colorimetric Method
- The powdered sample is mixed with phenol-2,4-disulphonic acid.
- Ammonia is added, producing a yellow color.
- The color intensity is compared with a standard potassium nitrate solution.
- The major limitation: matching the yellow color accurately can be difficult.
2. Instrumental Colorimetry
- The test sample reacts with the reagent, producing a measurable color.
- The absorbance is measured in a colorimeter.
- The same process is done for a standard solution for comparison.
Uses
- Used in manufacturing dynamite and blasting gelatin (safer explosive materials).
- Given in tablet form for heart diseases such as angina (chest pain).
- Used in heart failure and during heart surgeries.
- Available as an ointment for treating anal fissures (painful cracks in the anal lining).
- Acts as a nitrate vasodilator — it relaxes blood vessels and improves blood flow.
Detailed Notes:
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