Alcohols Flashcards
Two methods to produce ethanol
- Direct hydration of Ethene
- Fermentation of glucose
Direct hydration equation, reagents and conditions
Reagent: H2O
• Conditions: Conc. H3PO4 catalyst
High temperature (200-450 °C)
High pressure (50-100 atm)
Mechanism = first ethene attracted to H+ then H2O to produce Ethanol
Fermentation equation and condition
C6H12O6 → 2CH3CH2OH + 2CO2
• Conditions: Yeast catalyst
No air
Temperature of 30-40 °C
Explain why neither a low temperature nor a high temperature is suitable for this
reaction.
Temperature too low: reaction too slow
Temperature too high: destroys or denatures yeast enzyme
Why is fermentation a carbon neutral fuel?
Photosynthesis → Fermentation → Combustion
1. Photosynthesis:
6CO2 + 6H2O → C6H12O6 + 6O2
2. Fermentation:
C6H12O6 → 2CH3CH2OH + 2CO2
3. Combustion:
2CH3CH2OH + 6O2 → 4CO2 + 6H2O
• 6CO2 are taken in during photosynthesis
• A total of 6CO2 are released during fermentation and combustion of ethanol
Reasons why bioethanol is not really a carbon neutral fuel
Planting
• Harvesting
• Transport
• Extracting sugar
• Distilling ethanol solution
• Fertiliser production
Advantages and disadvantages of fermentation
Advantages Disadvantages
Glucose is renewable source
Lower temperatures require less
energy
Simpler equipment required is cheaper
Land used to grow crops is not
available for food crops
Ethanol is impure and must be
distilled to purify
Low yield
Rate is slow
Batch production method is difficult to
automate
Advantages and disadvantages of direct hydration
Advantages Disadvantages
High-purity ethanol produced
Continuous production
Fast rate of reaction
Crude oil is not renewable
High temperature and pressure
requires a lot of energy (expensive)
Hi-tech equipment required
(expensive)
Primary Alcohol → Aldehyde
Reagent: Acidified K2Cr2O7
Conditions: Heat under distillation
Uses 1 (o) and produces 1 H2O
Aldehyde → Carboxylic Acid
Reagent: Acidified K2Cr2O7
Conditions: Heat under reflux
Uses 1 (o) and no H2O produced
Primary Alcohol → Carboxylic Acid
Reagent: Acidified K2Cr2O7
Conditions: Heat under reflux, excess oxidising agent
CH3CH2OH + 2[O] → CH3COOH + H2O
Oxidation of Secondary Alcohols
Produce ketones
Acidified K2Cr2O7
Conditions: Heat under reflux or distillation
Uses 1(o) and produces 1H2O
Oxidation of Tertiary Alcohols
Tertiary alcohols can’t be oxidised.
Reflux apparatus
Distillation apparatus
Purpose of anti-bumping granules
Prevent large vigourous bubbles
Why is distillation used when producing an aldehyde from a primary alcohol?
Distillation allows the aldehyde to escape the reaction mixture and prevents
further oxidation
Two ways to reduce maximum yield of aldehyde
Call ethanol as it’s distilled off
Heat at the boiling point
Test for aldehyde
Reagent used to test for aldehydes: Tollen’s reagent
• Observation when aldehyde present: Silver mirror forms
• Observation when aldehyde not present: No visible change
Reagent used to test for aldehydes: Fehling’s solution
• Observation when aldehyde present: brick-red precipitate
• Observation when aldehyde not present: No visible change
Test for carboxylic acid
Reagent used to test for carboxylic acids: • Observation when carboxylic acid present: • Observation when carboxylic acid not present: Na2CO3
effervescence
No visible change
