3.3.2 Reactions of Haloalkanes

Question 1

Why are haloalkanes more reactive than alkanes?

Answer 1

Haloalkanes have electronegative halogens causing polarity within molecule

Question 2

What are the 2 key reactions haloalkanes undergo?

Answer 2

Nucleophilic substitution
- Halogen substituted for another atom / group of atoms
- Products are usually alcohols, amines and nitriles

Elimination
- Hydrogen halide eliminated during reaction
- Alkene formed

Question 3

How are alcohols formed from haloalkanes?

Answer 3

• OH- is nucleophile
• Aqueous NaOH or KOH with ethanol is used
• Warmed
• Hydrolysis reaction
• Water can be used as nucleophile but very slow because only partial charge, compared to OH- which is a full negative charge

Question 4

Measuring rate of Hydrolysis

Answer 4

Question 5

How are nitriles formed from haloalkanes?

Answer 5

• CN- cyanide as nucleophile
• Ethanolic solution of KCN in ethanol is heated under reflux
• Produces nitrile
• Reaction is useful to increase length of carbon chain, because an extra carbon atom is added

Question 6

Ho are amines formed from haloalkanes?

Answer 6

• NH3 nucleophile
• Ethanolic acid of excess ammonia in ethanol heated under pressure with haloalkane
• Primary amine formed

Question 7

Nucleophilic Substitution Mechanism with OH-

Answer 7

Question 8

Nucleophilic Substitution Mechanism with NH3

Answer 8

Question 9

Nucleophilic Substitution Mechanism with CN-

Answer 9

Question 10

How do elimination reactions work?

Answer 10

• hydrogen halide lost
• Haloalkane heated with ethanolic NaOH causing C-X bond to break heterolytically
• X- ion formed and alkene

Question 11

Elimination Mechanism for haloalkanes

Answer 11

Question 12

What product forms?

Answer 12

Dependent on reaction conditions

NaOH (hot, ethanol) elimination occurs forming alkene

NaOH (warm, aqueous) nucleophilic substitution occurs and alcohol formed