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Primary and low explosives; glycerol trinitrate

Short answer

Primary explosives (e.g., lead azide) are extremely sensitive and used in detonators. Low explosives (e.g., black powder) deflagrate, producing a propelling effect for guns, rockets, and gentle blasting. GTN is made by nitrating glycerol with HNO₃/H₂SO₄ below 15°C; it is used in dynamite, cordite, blasting, and as a vasodilator.

What are primary and low explosives? Give the preparation and uses of glycerol trinitrate.

Primary explosives

Primary (initiating) explosives are extremely sensitive to heat, shock and friction and detonate even with a small spark. They are used in detonators and primers to start the explosion of secondary explosives. Examples: lead azide Pb(N₃)₂, mercury fulminate Hg(ONC)₂, lead styphnate.

Low explosives

Low explosives burn rapidly (deflagrate) instead of detonating; the burning front travels at a few metres per second up to about 400 m/s. The gases produced give a pushing (propelling) effect rather than a shattering one. They are used as propellants and for gentle blasting. Examples: black powder (gunpowder: KNO₃ + charcoal + S) and smokeless powder. Uses: firing bullets and shells, rocket propellants, quarrying soft rock, fireworks and safety fuses.

Preparation of glycerol trinitrate (GTN, nitroglycerine, TNG)

GTN is made by nitrating glycerol with a mixture of conc. HNO₃ and conc. H₂SO₄ (the sulfuric acid absorbs the water formed). The temperature is kept below 10–15 °C by cooling, because higher temperatures can cause an explosion.

CH₂OH                      CH₂ONO₂
|                          |
CHOH  + 3HNO₃ --H₂SO₄-->   CHONO₂  + 3H₂O
|                          |
CH₂OH                      CH₂ONO₂

The oily layer of GTN is separated, washed with water and sodium carbonate solution, and dried. It is a colourless to pale yellow oily liquid, very sensitive to shock, and explodes violently: 4C₃H₅(ONO₂)₃ → 12CO₂ + 10H₂O + 6N₂ + O₂

Uses

  • Making dynamite (absorbed in kieselguhr), blasting gelatin and gelignite.
  • Component of smokeless propellants such as cordite.
  • Blasting in mining and tunnelling.
  • In dilute form, a medicine (vasodilator) for angina.

✓ Answer checked by Claude Opus 5.5 (high effort)

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