14.2 - Reactions of Alcohols

Question 1

What does the combustion of alcohols produce?

Answer 1

Combustion is exothermic

• Produces carbon dioxide and water in a plentiful supply of oxygen

Question 2

What is the oxidising agent used in the oxidation of alcohols and what is it represented by?

Answer 2

Acidified potassium dichromate (VI)
Kr2Cr2O7 with H2SO4 - orange

Represented by ‘O’ or [O]

Question 3

What happens to the colour of the orange oxidising agent solution if the alcohol is oxidised?

Answer 3

orange > green

Cr2O7(2-) > Cr(3+)

oragne dichromate (VI) ions > green chromium (III) ions

Question 4

What happens during the oxidation of primary alcohols?

Answer 4

• Oxidised to aldehydes or carboxylic acids.

- Products depend on reaction conditions as aldehydes are oxidised to carboxylic acids.

Question 5

How are aldehydes made as the product of primary alcohol oxidation and what colour is the solution?

Answer 5

1) Gently heat the primary alcohol with ‘O’
2) Forms an aldehyde

• To ensure a carboxylic acid is not formed, the aldehyde is distilled out of the reaciton mixture as soon as it is formed.

Dichromate (VI) oxidises to produce a GREEN SOLUTION

Question 6

What is reflux?

Answer 6

Continuous heating of a sample, vapours condensed & returned to the vessel until reaction is complete.

Anti-bumping granules are used to prevent violent flash boiling

Question 7

How are carboxylic acids made as the product of primary alcohol oxidation and what colour is the solution?

Answer 7

• Heat the primary alcohol strongly under reflux with excess ‘O’
• Excessive heating ensures all the alcohol and formed aldehydes completely
• Reflux is used to obtain carboxylic acid as in distillation, solution doesn’t stay in the condenser long enough to oxidise from alcohol>aldehyde>carboxylic acid

Question 8

What happens during the oxidation of secondary alcohols?

Answer 8

• Oxidised to ketones using ‘O’
• Heat under reflux
• Orange to green

Question 9

What happens during the oxidation of tertiary alcohols?

Answer 9

They do not oxidise

- Stay orange

Question 10

What happens during the dehydration of alcohols?

Answer 10

• It is an elimination reaction
• A water molecule is removed

Heat alcohol under reflux with phosphoric/sulfuric acid
Products: Alkene and water

Question 11

What happens during the substitution of an alcohol?

Answer 11

Alcohols react with hydrogen halides to form haloalkanes

R-OH + NaX > (H2SO4 reflux) H-X + NaHSO4

H-X + R-OH > R-X + H2O