Halogenoalkanes

Halogenoalkanes production: free radical substitution

Reagents: Cl₂ or Br₂

Conditions: UV light

Halogenoalkanes production: electrophilic addition of an alkane with a halogen

Reagents: X₂

C₂H₄ + X₂ → C₂H₄X₂ (dihalogenoalkane)

Halogenoalkanes production: electrophilic addition of an alkane with a HX

Reagents: HX (g)

Conditions: room temp

C₃H₆ + HBr → C₃H₇Br

Halogenoalkanes production: Substituion of an alcohol with HX

Reagents: HX

Conditions: KX with H₂SO₄ or H₃PO₄ to make HX

Halogenoalkanes production: Substituion of an alcohol with PCl₃

Reagents: PCl₃

Conditions: heat

3C₂H₅OH + PCl₃ → 3C₂H₅Cl + H₃PO₃

Halogenoalkanes production: Substituion of an alcohol with PCl₅

Reagents: PCl₅

Conditions: room temp

C₂H₅OH + PCl₅ → C₂H₅Cl + POCl₃ + HCl

Halogenoalkanes production: Substituion of an alcohol with SOCl₂

Reagents: SOCl₂

Conditions: no conditions

C₂H₅OH + SOCl₂ → C₂H₅Cl+ HCl + SO₂

Nucleophilic substitution: +NaOH (aq) → alcohol

Reagents: NaOH (aq)

Conditions: heat

C₂H₅Br + NaOH (aq) → C₂H₅OH + NaBr

Nucleophilic substitution: + KCN → nitrile

Reagents: KCN

Conditions: heat

C₂H₅Br + KCN → C₂H₅CN (propanenitrile) + KBr

Nucleophilic substitution: + NH₃ → amine

Reagents: NH₃

Conditions: heat under pressure

C₂H₅Br + NH₃ → C₂H₅NH₂ (ethanamine) + HBr

Nucleophilic substitution: aq AgNO₃ in ethanol to identify halogen present

water in aq AgNO₃ hydrolyse halogenalkanes

C₂H₅Br + :OH^- → C₂H₅OH + :Br^-

X^- reacts with Ag⁺ to form ppt

Elimination reaction: make alkene

Reagents: NaOH (ethanolic)

Conditions: heat

C₂H₅Br + NaOH (ethanolic) → C₂H₆ + NaBr + H₂O

S_N¹ mechanism

• 2 step

• tertiary halogenoalkenes react via S_N¹

• secondary halogenoalkanes react via both mechanisms

S_N² mechanism

primary halogenoalkanes react via S_N²

secondary halogenoalkanes react via both mechanisms

halogenoalkanes reactivity

more reactive down the group as the C-X bonds get weakers and more easier to break down the group

→ halogens atomic radius increase down the group

→ weaker attraction between shared e- and nuclei