Alcohols

n	Name	Formula	Notes
1	methanol	CH₃OH	Toxic — methylated spirits, antifreeze; can cause blindness or death if drunk
2	ethanol	C₂H₅OH	The alcohol in alcoholic drinks; biofuel; solvent
3	propanol	C₃H₇OH	Two isomers (1-ol, 2-ol); industrial solvents and antiseptics

All have:

• A chain of n carbons.
• An –OH group on one of those carbons.
• General formula CₙH₂ₙ₊₁OH (or equivalent CₙH₂ₙ₊₂O).

Properties:

• BPs are HIGHER than the equivalent alkanes — because –OH groups form hydrogen bonds between molecules.
  • Methanol BP 65 °C (vs methane −162 °C).
  • Ethanol BP 78 °C (vs ethane −89 °C).
• Soluble in water — also because of hydrogen bonding between –OH and water.

This solubility is why alcoholic drinks are mixtures of ethanol and water — they mix completely. Pure ethanol is sometimes called 'absolute alcohol'.

Route 1: Fermentation (biological)

Yeast contains enzymes that break sugar down into ethanol and CO₂:

$\text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{yeast}} 2\,\text{C}_2\text{H}_5\text{OH} + 2\,\text{CO}_2$

Conditions:

• Warm temperature (~25-37 °C — body temperature is optimal for yeast).
• Absence of oxygen (anaerobic).
• Yeast eventually dies when the ethanol concentration reaches ~15% — that's the natural maximum for fermented drinks like beer and wine.
• To make spirits (higher % alcohol), fermented liquid is then DISTILLED.

This is how all traditional alcoholic drinks are made: beer from barley, wine from grapes, rum from sugar cane. It's also how 'bioethanol' is produced for biofuel.

Route 2: Hydration of ethene (industrial)

$\text{CH}_2{=}\text{CH}_2 + \text{H}_2\text{O} \xrightarrow{\text{H}_3\text{PO}_4, \,300\,°\text{C}, \,60\,\text{atm}} \text{CH}_3\text{CH}_2\text{OH}$

Conditions:

• Phosphoric acid catalyst.
• 300 °C, 60 atm pressure.
• Continuous flow process — much higher throughput than fermentation.

Comparison:

Feature	Fermentation	Hydration
Feedstock	Sugar (renewable)	Ethene (from crude oil)
Conditions	Mild	Harsh (high T, P, catalyst)
Rate	Slow (days/weeks)	Fast (continuous)
Purity	Need to distill	High purity directly
Carbon-neutral?	Yes (CO₂ recently from atmosphere)	No (fossil source)
Better for environment	✓ (renewable)	✗ (uses oil)
Better for industrial scale	✗	✓ (fast, continuous)

Both methods are used industrially. Bioethanol (fermentation-route) is a popular renewable fuel in Brazil and the US.

As fuels:

• Pure ethanol burns cleanly: C₂H₅OH + 3 O₂ → 2 CO₂ + 3 H₂O.
• 'E10' petrol (UK, EU, US) contains 10% ethanol blended with petrol.
• Brazil runs many vehicles on pure ethanol or E85 (85% ethanol).
• Burning is essentially carbon-neutral if the ethanol came from fermentation (the CO₂ released was recently absorbed by the plant).

As solvents:

• Many medicines, perfumes, inks and cleaning products dissolve in ethanol but not in water. So ethanol is widely used as a solvent.
• Methanol is also a solvent (and an antifreeze).

As disinfectants and antiseptics:

• ~70% ethanol (or isopropanol = propan-2-ol) is the gold standard for surface and skin disinfection.
• Higher concentrations (95%+) work less well because they kill bacteria too fast — leaving a protective protein coat. ~70% is the sweet spot.

As alcoholic drinks:

• The cultural and economic role of ethanol-based drinks is enormous.
• But ethanol is a CNS depressant, addictive, damages the liver in heavy use, and is implicated in many social harms.

MYP criterion D classic: 'Evaluate bioethanol as a renewable transport fuel.' Strong answers cover renewability (positive), competition with food production for land (negative), CO₂ balance (close to neutral but depends on production process), and engine compatibility.