--- title: "Plastic explosive; TNT preparation; detonator" subject: "Engineering Chemistry" chapter: 7 key: "semester_2/engineering_chemistry:plastic-explosive-tnt" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/plastic-explosive-tnt site: BCT Engineering --- # Plastic explosive; TNT preparation; detonator Engineering Chemistry · Chapter 7: Explosives - Asked in: 2074 Bhadra, 1+2+2 marks - Video: [Synthesis of TriNitroToluene & PentaErythritolTetraNitrate.](https://www.youtube.com/watch?v=uL6-_SYaid0) — Chemistry for better tomorrow - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/plastic-explosive-tnt - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7 ## Question What is plastic explosive? How can you prepare TNT from benzene? Why does detonator require for the explosion of TNT? ## Short answer Plastic explosives are mouldable putty-like mixtures of high explosive (e.g., RDX) and plasticiser. TNT is prepared from benzene via Friedel-Crafts methylation to toluene, then stepwise nitration with HNO₃/H₂SO₄. TNT requires a detonator because it is insensitive to shock and needs a strong shock wave to initiate detonation. ## Answer #### Plastic explosive **Plastic explosives** are high explosives (such as RDX or PETN) mixed with a plasticiser (oil, wax, polymer) to form a putty-like mass that can be moulded by hand into any shape. They are safe to handle, stable, waterproof, and need a detonator. Examples: C-4 (about 91% RDX), Semtex, PE-4. #### Preparation of TNT (2,4,6-trinitrotoluene) TNT is made by the stepwise nitration of toluene with a mixture of conc. HNO₃ and conc. H₂SO₄ (H₂SO₄ is a dehydrating agent, giving NO₂⁺). Toluene itself is obtained from benzene by Friedel–Crafts methylation (benzene + CH₃Cl, anhydrous AlCl₃). ```text C₆H₆ + CH₃Cl --AlCl₃--> C₆H₅CH₃ + HCl (toluene) C₆H₅CH₃ --HNO₃/H₂SO₄, 30°C--> mononitrotoluene --HNO₃/H₂SO₄, 60°C--> dinitrotoluene --HNO₃/oleum, 100-110°C--> 2,4,6-trinitrotoluene ``` ```text Structure of TNT (ring carbons C1 to C6) CH₃ | .----C1---. O₂N--C2 C6--NO₂ | | C3 C5 '---C4----' | NO₂ ``` The product is washed with water and dilute sodium carbonate and recrystallised from alcohol. It is a pale yellow crystalline solid, m.p. 81 °C. Decomposition: 2C₇H₅N₃O₆ → 3N₂ + 5H₂O + 7CO + 7C #### Need for a detonator TNT is very stable and insensitive to heat, shock and friction. If lit, it burns quietly with a sooty flame and does not explode. The activation energy for its explosive decomposition is high, so a strong shock wave is needed to start it. A **detonator** (containing a sensitive primary explosive such as lead azide or mercury fulminate) gives this initial shock, which starts the detonation of the whole mass. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a plastic explosive? A. A low explosive made from plastics B. A liquid explosive absorbed in kieselguhr C. A high explosive (RDX/PETN) mixed with a plasticiser to form a putty-like mass that can be hand-moulded D. A primary explosive used in detonators Answer: C. Plastic explosives such as C-4 and Semtex are RDX/PETN with oil, wax or polymer, safe and mouldable. (Key point: Plastic explosive) 2. Which reagent mixture is used to nitrate toluene to make TNT, and what is the role of H2SO4? A. Dilute HNO3 + dilute H2SO4; H2SO4 acts as a reducing agent B. Conc. HNO3 alone; H2SO4 is not needed C. Conc. HNO3 + conc. H2SO4; H2SO4 is a dehydrating agent that helps give NO2+ D. Conc. HCl + conc. H2SO4; H2SO4 supplies the nitro group Answer: C. TNT is made by stepwise nitration of toluene with conc. HNO3 and conc. H2SO4; the sulfuric acid removes water and helps form NO2+. (Key point: Nitrating mixture) 3. How is the toluene needed for TNT obtained from benzene? A. Nitration of benzene with HNO3 B. Sulfonation of benzene with H2SO4 C. Hydrogenation of benzene with Ni D. Friedel-Crafts methylation using CH3Cl and anhydrous AlCl3 Answer: D. Benzene + CH3Cl with anhydrous AlCl3 gives toluene and HCl. (Key point: Source of toluene) 4. Why does TNT not explode when simply lit? A. It is very stable and insensitive to heat, shock and friction, so it only burns with a sooty flame B. It contains no oxygen at all C. It is a gas that escapes quickly D. Its melting point is too low Answer: A. TNT has a high activation energy for explosive decomposition, so ordinary ignition just makes it burn quietly. 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