Alcohols

Question 1

Making ETHANOL ~ hydration of ethene

Answer 1

ELECTROPHILIC ADDITION:

H2C=CH2(g) + H2O(g) —— CH3CH2OH(g)

Requirements:

• H3PO4
• 300 degrees
• 60 atm
• steam

REVERSIBLE ~ only 5% of ethene entering reactor is converted to ethanol.

UNREACTED gases are RECYCLED and the process runs continuously to give an overall conversion close to 100%.

Question 2

Making ETHANOL ~ Fermentation of glucose

Answer 2

C6H12O6(aq) — 2CH3CH2OH(aq) + 2CO2(g)

Reaction Conditions:
- Yeast
- 37 degrees
- Absence of oxygen

Question 3

USES of alcohols

Answer 3

• alcoholic drinks
• perfumes and aftershaves
• cleaning fluids

Question 4

Making METHYLATED SPIRITS
(denatured alcohol)

Answer 4

• ETHANOL is added to 10% METHANOL and a COLOURED DYE such as methyl violet (poisonous).
• The ETHANOL molecules are UNAFFECTED but the solution is TOXIC & UNDRINKABLE.

Used as a SOLVENT:

• remove paint
• fuel for camping stoves

Question 5

MP & BP of alcohols & the TREND as chain length increases.

Answer 5

RELATIVELY HIGH :
- Due to hydrogen bonding
- More energy is needed to overcome the strength of the hydrogen bonds.

The TREND:
- BP increase as chain LENGTH INCREASES
- MORE CONTACT POINTS
- Strength of London forces INCREASES
- Takes extra energy to overcome.

Question 6

VOLATILITY of alcohols compared to ALKANES

Answer 6

Volatility ~ how readily a substance vaporises.

• An alcohol is LESS volatile than an alkane containing the same number of carbon atoms.
• This is because EXTRA ENERGY has to be provided to overcome the strength of the HYDROGEN BONDS.

Question 7

SOLUBILITY of alcohols

Answer 7

• HYDROGEN BONDS form between WATER and the POLAR -OH group of alcohols
• This allows alcohols to be SOLUBLE/ MISCIBLE in water.

(methanol and ethanol are COMPLETELY soluble in water)

Question 8

The TREND in SOLUBILITY of alcohols

Answer 8

NON-POLAR HYDROCARBON CHAIN:

• unable to form hydrogen bonds with water molecules
• only forms LONDON forces

UNFAVOURABLE IMF to form with water:

• It is POLAR
• capable of forming hydrogen bonds

As the LENGTH of the hydrocarbon chain INCREASES:

• RATIO of London forces to hydrogen bonds INCREASES
• SOLUBILITY of alcohol DECREASES

Question 9

Primary, secondary and tertiary alcohols

Answer 9

PRIMARY : The carbon carry the -OH is bonded to 2 hydrogens and 1 carbon.

SECONDARY : The carbon carrying the -OH is bonded to 1 hydrogen and 2 carbons.

TERTIARY : The carbon carrying the -OH is bonded to NO hydrogens and 3 carbons.

Question 10

Partial oxidation of Primary Alcohols

Answer 10

Primary alcohol + [0] —- Aldehyde + water

REAGENTS & CONDITIONS:

• dil.H2SO4
• K2Cr2O7
• heat & distil immediately

OBSERVATION ~ orange to green

Question 11

Complete oxidation of Primary alcohols

Answer 11

Primary alcohol + 2[0] —- Carboxylic acid + H2O

REAGENTS & CONDITIONS:

• K2Cr2O7
• dil. H2SO4
• Heat under reflux

OBSERVATIONS ~ orange to green

Question 12

Reflux

Answer 12

The CONTINUAL boiling and condensing of a reaction mixture to convert ALL REACTANTS to PRODUCTS.

Question 13

Oxidation of secondary alcohols

Answer 13

Secondary alcohol+ [0] ——- ketone + H2O

REAGENTS & CONDITIONS:

• K2Cr2O7
• dil.H2SO4
• Heat under reflux

OBSERVATIONS ~ orange to green

• NO further OXIDATION possible due to the absence of hydrogen bonded to C=O

Question 14

Oxidation of TERTIARY alcohols

Answer 14

NO REACTION.

• No colour change
• Oxidation NOT POSSIBLE due to absence of hydrogen atoms attached to the carbon carry the -OH group
• WATER cannot be formed

Question 15

Esterification

Answer 15

Carboxylic acid + alcohol ——- ester + water

CONDENSATION ~ removal of water across the reactant molecules

CONDITIONS:
- heat under reflux
- c.H2SO4

Question 16

Dehydration of alcohols

Answer 16

Alcohol ——– Alkene + H2O

Groups REMOVED from alcohol:

• OH group
• One of the H atoms on the adjacent C

REAGENTS & CONDITIONS:

• c.H2SO4 / c.H3PO4
• 180 degrees

ELIMINATION ~ one mole of reactant gives two moles of product

Question 17

Alcohol ——————– Haloalkane

Answer 17

NUCLEOPHILIC SUBSTITUTION:

REAGENTS & CONDITIONS:

• heat under reflux
• c.H2SO4 / c.H3PO4
• NaX
• alcohol

CHOH + NaX + H2SO4 —— CHX + NaHSO4 + H2O

Question 18

Reagent Vs Reactant

Answer 18

REAGENT ~ the substance ‘taken off the shelf’ and added to the reaction flask to bring about a chemical reaction.

REACTANT ~ the actual species which participates in the reaction.

SOLVENTS & CATALYSTS are NOT classified as reactants as they are involved in the reaction but not consumed .