Ethyl bromide (bromoethane, C₂H₅Br) is prepared from ethyl alcohol (ethanol, C₂H₅OH) by substituting the hydroxyl group (–OH) with a bromine atom. The most common methods are reaction with hydrobromic acid (HBr) in the presence of H₂SO₄, or reaction with phosphorus tribromide (PBr₃). This is a nucleophilic substitution reaction.
Ethyl bromide (C₂H₅Br) is prepared from ethyl alcohol (C₂H₅OH) by nucleophilic substitution.
Method 1 — with HBr: C₂H₅OH + HBr → C₂H₅Br + H₂O (H₂SO₄ catalyst, heat).
Method 2 — with PBr₃: 3C₂H₅OH + PBr₃ → 3C₂H₅Br + H₃PO₃.
The –OH group in ethanol is replaced by –Br (bromine).
IUPAC name of ethyl bromide is bromoethane.
Ethyl bromide is a colourless liquid with boiling point 38.2°C.
It is used as an alkylating agent and to make Grignard reagents.
PBr₃ method gives cleaner product than the HBr/H₂SO₄ method.
C₂H₅OH + HBr → C₂H₅Br + H₂O
Conditions: Concentrated H₂SO₄ as catalyst; heat
Alternatively using NaBr + H₂SO₄: NaBr + H₂SO₄ → NaHSO₄ + HBr (HBr generated in situ) C₂H₅OH + HBr → C₂H₅Br + H₂O
Word equation: Ethanol + Hydrobromic acid → Ethyl bromide + Water
This is an SN1 or SN2 nucleophilic substitution reaction where the –OH group is replaced by –Br.
3C₂H₅OH + PBr₃ → 3C₂H₅Br + H₃PO₃
Conditions: Anhydrous conditions, room temperature or gentle heating
This method is preferred because: • It avoids the use of concentrated H₂SO₄ (which can cause side reactions) • The reaction is cleaner and gives better yield • PBr₃ can be generated in situ: 2P + 3Br₂ → 2PBr₃
Word equation: 3 Ethanol + Phosphorus tribromide → 3 Ethyl bromide + Phosphorous acid
Ethyl bromide (bromoethane) properties: • Chemical formula: C₂H₅Br or CH₃CH₂Br • IUPAC name: Bromoethane • Molecular weight: 108.97 g/mol • Physical state: Colourless liquid at room temperature • Boiling point: 38.2°C • Density: 1.46 g/mL (denser than water) • Solubility: Slightly soluble in water; miscible with organic solvents • Smell: Ether-like odour
Ethyl bromide is used in organic synthesis as an alkylating agent and in manufacturing pharmaceuticals.
Ethyl bromide is used in:
Grignard reagent preparation: C₂H₅Br + Mg → C₂H₅MgBr (ethyl magnesium bromide) This is important in organic synthesis for forming C–C bonds.
Ethyl bromide is prepared by two methods: (1) Reacting ethyl alcohol with HBr in presence of concentrated H₂SO₄: C₂H₅OH + HBr → C₂H₅Br + H₂O; (2) Reacting with PBr₃: 3C₂H₅OH + PBr₃ → 3C₂H₅Br + H₃PO₃. The –OH group is replaced by –Br in both cases.
C₂H₅OH + HBr → C₂H₅Br + H₂O (using HBr and H₂SO₄ catalyst). Or: 3C₂H₅OH + PBr₃ → 3C₂H₅Br + H₃PO₃ (using phosphorus tribromide).
It is a nucleophilic substitution reaction (SN1 or SN2). The hydroxyl group (–OH) in ethanol is replaced by a bromine atom (–Br). The Br⁻ ion acts as a nucleophile attacking the carbon bearing the –OH group.
The IUPAC name of ethyl bromide (C₂H₅Br) is bromoethane. It is also written as CH₃CH₂Br — an ethane molecule with one hydrogen replaced by bromine.
PBr₃ is preferred because it avoids concentrated H₂SO₄ which can cause side reactions like dehydration of ethanol to form ethene or ether. PBr₃ gives a cleaner reaction with higher yield at milder conditions.
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