Alcohols - Organic (6)

Question 1

Halogenation reactions of Alcohols - give the equations and state conditions for:

1. Chlorination (2)
2. Bromination (5)
3. Iodination (5)

Answer 1

1. Add PCl₅

CH₃CH₂OH + PCl₅ = CH₃CH₂Cl + POCl₃ + HCl

2. Add KBr + 50% Conc. H₂SO₄ + heat

KBr + H₂SO₄ = KHSO₄ + HBr

CH₃CH₂OH + HBr = CH₃CH₂Br + H₂O

3. Add Red Phosphorous + Iodine + Heat under reflux

2P + 3I₂ = 2PI₃

CH₃CH₂OH + PI₃ = CH₃CH₂I + H₃PO₃

Question 2

Oxidation reaction of alcohols - Give reactions of these alcohols:

1. Primary (1)
2. Secondary (1)
3. Tertiary (1)
4. State the reagents and conditions (3)
5. State the colour change (1)

Answer 2

1. CH₃OH -> CH=O -> CHOOH
   Primary alcohol -> aldehyde (loses H) -> Carboxylic acid (Gains O)
2. CH₃CH₂(OH)CH₃ -> CH₃CH₂=OCH₃
   Secondary alcohol -> Ketone (loses H)
3. No easy oxidation
4. Reagents: Potassium Dichromate(VI) + dilute S
   Sulphuric acid + heat under reflux
5. Colour change from Orange to Green

Question 3

Explain the Dehydration of alcohols (3)

Answer 3

1. Add conc, Phosphoric acid
2. Similar to elimination reaction of haloalkane as OH and H from neighbouring C removed forming double bond
3. 2 products can be formed depending on placement of double bond