2.5 ALCOHOL

E. ALCOHOL

Functional group
• Hydroxyl group ( -OH )

General formula
• CnH2n+1OH (n=1,2,….)

2.5 Analysing alcohols
State the general formula of alcohols | Identify the functional group of alcohols

Number of Name Molecular Structural Formulae
Carbon Formulae

1 Methanol CH3OH

2 Ethanol C2H5OH

2.5 Analysing alcohols
List the names and the molecular formulae of the first four alcohols

Number of Name Molecular Structural Formulae
Carbon Formulae

3 Propanol / C3H7OH
Propan-1-ol

4 Butanol / C4H9OH
But-1-ol

2.5 Analysing alcohols
List the names and the molecular formulae of the first four alcohols

C3H7OH Isomers of Alcohols

Difference position of -OH

Propanol / Propan-1-ol Propan-2-ol

2.5 Analysing alcohols
Draw structural formulae for isomers of propanol (C3H7OH) and butanol (C4H9OH)

C4H9OH Isomers of Alcohols

Difference position of -OH

Alkyl group, Butan-2-ol
CH3
Butanol / Butan-1-ol

2-methylbutan-1-ol 2-methylbutan-2-ol

2.5 Analysing alcohols
Draw structural formulae for isomers of propanol (C3H7OH) and butanol (C4H9OH)

Industrial Production of Ethanol

Industrial production of ethanol
• Two main process:

(a)From sugar and starch by fermentation
(b)From petroleum fraction by hydration

2.5 Analysing alcohols
Describe the industrial production of ethanol

1. Fermentation

C6H12O6 → 2C2H5OH + 2CO2

• From sugar & starches
• Yeast added
• Left in warm place (absence of oxygen)-

anaerobic
Temperature = 18 – 20 °C
Catalyst = yeast (zymase)
Other condition = absence of oxygen

2.5 Analysing alcohols
Describe the industrial production of ethanol

2.5 Analysing alcohols
Describe the preparation of ethanol in the laboratory

2. Hydration

C₂H₄ + H2O → C2H5OH

• From petroleum fractions
Temperature = 300 °C
Pressure = 60 atm
Catalyst = phosporic acid, H3PO4

2.5 Analysing alcohols
Describe the industrial production of ethanol

Solubility Colour Boiling point

• Simple • Colourless • Low boiling
alcohols are liquid at room point
very soluble temperature compare to
in water water

• Because has Odour
–OH group
• Very sharp
smell

State Physical Highly
properties of volatile
• C1 to C11 are
liquid at room alcohol
temperature

2.5 Analysing alcohols
State the physical properties of ethanol

Chemical properties of alcohols

Combustion
(a) Complete combustion: produce CO2 + H2O

C2H5OH + 3O2 → 2CO2 + 3H2O

2.5 Analysing alcohols
Describe the chemical properties of ethanol

2.5 Analysing alcohols
Describe the chemical properties of ethanol

Oxidation reaction
• React with the oxidation agent:

a) acidified potassium manganate(VII), KMnO4
(purple → colourless)

b) acidified potassium dichromate(VI), K2Cr2O7
(orange → green)

C2H5OH+ 2[O] → CH3COOH + H2O

Ethanol Ethanoic acid

2.5 Analysing alcohols
Describe the chemical properties of ethanol

The formation:
[carbon atom, C contains –OH was added with 1 more O]

2.5 Analysing alcohols
Describe the chemical properties of ethanol

2.5 Analysing alcohols
Describe the chemical properties of ethanol



Dehydration
• Removal of water molecule from alcohol

molecule

C2H5OH → C2H4 + H2O

Ethanol Ethene

• Method:

(a) Heated under reflux at 180 °C with excess
concentrated H2SO4 or

(b) Pass over a heated catalyst (porcelain chips,
porous pot, Al2O3

2.5 Analysing alcohols
Describe the chemical properties of ethanol

The formation:

2.5 Analysing alcohols
Describe the chemical properties of ethanol

Pass over a heated catalyst
(porcelain chips, porous pot, Al2O3)

2.5 Analysing alcohols
Describe the chemical properties of ethanol



Heated under reflux at 180 °C with
excess concentrated H2SO4

2.5 Analysing alcohols
Describe the chemical properties of ethanol

Uses of alcohols

As a solvent in
• Perfumes, cosmetics, toiletries
As a thinner in
• Lacquer, varnish, shellac, ink
As a cleaner for
Compact disc, video cassette recorder head
As a fuel
• Clean fuel, biofuel, gasohol

2.5 Analysing alcohols
Explain with examples the uses of alcohols in everyday life

As a raw material in manufacture of
• Vinegar, fibre, explosive, plastic
As a raw material to make pharmaceutical

products
• Tincture, antiseptic, cough syrup, rubbing

alcohol

2.5 Analysing alcohols
Explain with examples the uses of alcohols in everyday life