Alcohols and carboxylic acids

Question 1

How does chain length affect alcohol solubility in water?

Answer 1

As chain length increases, the solubility decreases because a larger proportion of the molecule becomes non-polar and cannot form hydrogen bonds with the water molecules. The covalent tail becomes less able to penetrate the hydrogen-bonded water structure.

Immiscable layer of water and alcohol

Question 2

Describe the formation of alcohols from alkenes

Answer 2

Direct Hydration (reacts with water)
- Continuous process

Conditions:
- Phosphoric acid on silica gel catalyst
- 300°C
- 60-70atm

Question 3

Describe the formation of alcohols from fermentation

Answer 3

Fermentation of sugars and starch

Conditions:
- No air (Anaerobic conditions) to prevent microbial oxidation
- Optimum temperature of yeast used (37°C)
- Yeast catalyst

Fractional distillation to extract ethanol from the mixture.

Question 4

Benefits and drawbacks of direct hydration vs fermentation

Answer 4

Direct Hydration :)
- Continuous process thus lowers labour costs
- High atom economy (only one product)
- Faster

Fermentation :)
- Renewable

Direct Hydration :(
- Non-renewable crude oil to source ethene

Fermentation :(
- Slower
- Batch process has higher labour costs
- CO2 side product lowers atom economy
- Only produces 15% ethanol in the mixture; otherwise yeast is poisoned.

Question 5

Uses of alcohols

Answer 5

Biofuels
Solvents
Drinks

Question 6

Forming alkenes and trend of ease of forming

Answer 6

Dehydration (Elimination reaction)

Conditions:
- Temperature: 180
- Reflux
- Reagent: Concentrated sulphuric acid

Tertiary alcohols are more easily dehydrated than secondary and than primary because tertiary carbocation is much more stable.

However reaction cannot occur is the carbon adjacent to the carbon with OH has not hydrogens bonded.

Question 7

Describe the oxidation of primary alcohols

Answer 7

Oxidising agent:
- Acidified potassium dichromate
- Sulphuric acid (Acidifies)

Aldehyde
Conditions for partial oxidation:
- Distil out aldehyde as it forms to prevent further oxidation to carboxylic acid.
-Excess alcohol

Carboxylic acid
Conditions for full oxidation:
- Reflux
- Excess oxidising agent to ensure max yield of Carboxylic acid

Question 8

Describe the oxidation of Secondary alcohols

Answer 8

Forms a ketone (loss of a Hydrogen from Carbon and OH)

Oxidising agent:
- Acidified potassium dichromate
- Sulphuric acid (Acidifies)

Conditions for full oxidation:
- Reflux

Question 9

Why do tertiary alcohols not react with acidified dichromate?

Answer 9

There are no Hydrogens on the C-OH. C-C bond would fragment molecule if oxidised.

Question 10

Describe the colour change of acidified dichromate and primary and secondary alcohols

Answer 10

Orange to green

Question 11

Formation of an ester

Answer 11

Alcohol + Carboxylic acid <–> Ester + Water

Conditions:
- Sulphuric acid catalyst
- Reflux
- Anhydrous Zinc chloride absorbs the water produced to push the equilibrium right (increase ester yield)

Question 12

Naming an ester

Answer 12

-yl comes from alcohol next to the -O- bond

-anoate comes from carboxylic acid (incl. C=O bond)

Question 13

How to test for carboxylic acid?

Answer 13

Salt formation reactions with:
- Metal
- Alkalis
- Carbonates and hydrogen carbonates

CO2 is produced and can be collected and bubbled through limewater (Turns cloudy)

Question 14

Carboxylic acid and metal forms?

Answer 14

Salt ( metal ..-anoate) + H2(g)

Question 15

Carboxylic acid and sodium hydroxide/alkali forms?

Answer 15

Salt ( metal ..-anoate) + H2O(l)

Question 16

Carboxylic acid and carbonates form?

Answer 16

Ionic equation
2H+ (aq) + CO3^2- (aq) —> H2O(l) + CO2 (g)

Question 17

Carboxylic acid and hydrocarbonates form?

Answer 17

Ionic equation
H+ (aq) + HCO3- (aq) —> H2O(l) + CO2 (g)