3.5 Alcohols
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General formula of alkanes
C₂ₙH₂ₙ₌₂
Functional group of alcohols
R-O-H
How can alcohols be classified?
Primary, secondary or tertiary (based on the number of carbon atoms attached directly to the C bonded to oxygen)
Why do alcohols have relatively high melting and boiling points?
They form hydrogen bonds
Why are alcohols with a low Mr soluble in water?
They form hydrogen bonds with the water molecules
Reagent for the hydration of alkenes
Steam
Conditions for the hydration of alkenes
• 300°C • 60atm • Phosphoric acid catalyst (H₃PO₄)
Uses of alcohols
• Feedstock for chemical processes • Solvents • Alcoholic drinks • Fuels
Methods for industrial preparation of ethanol
Fermentation and hydration of alkenes
Process for fermentation
• Carbohydrates from crops are broken down into sugar • Sugars converted to ethanol by anaerobic respiration • Ethanol is separated from the mixture with fractional distillation
Reagents for fermentation
• Glucose • Yeast (catalyst)
Conditions for fermentation
• 30-40°C • Aqueous • Anaerobic
Products of fermentation
Ethanol + Carbon dioxide
Why is fermentation carried out under anaerobic conditions?
This prevents oxidation of ethanol to form ethanoic acid
Why is a temperature around 35°C used for fermentation
This is a compromise between maximising rate of reaction and avoiding denaturing enzymes
When does the fermentation reaction stop?
Around 15% ethanol (higher concentrations of ethanol damage the yeast enzymes)
Quality of ethanol produced through hydration of alkenes
Pure
Quality of ethanol produced from fermentation
Impure
Rate of reaction of hydration of alkenes
Very fast
Rate of reaction of fermentation
Very slow
What type of process is hydration of alkenes?
Continuous
What type of process is fermentation?
Batch
Raw materials for the hydration of alkenes
Crude oil
Biofuel
A fuel derived or produced from renewable biological sources