Ethanol
Properties
| State | Liquid (volatile) |
| Color | Colorless |
| Solubility | Miscible with water in all proportions |
| Melting Point | -114.1°C |
| Boiling Point | 78.4°C |
About Ethanol
Ethanol is the smallest alcohol that humans have made deliberately — a two-carbon chain with a single OH group, dipole moment around 1.69 D, and a hydrogen-bonding network strong enough to make it fully miscible with water yet weak enough to give a 78.4 °C boiling point that fractional distillation can exploit. The miscibility is what makes ethanol such an effective bridge solvent: dissolve a polar salt or sugar in water, dissolve a non-polar substance in hexane, and use ethanol to push the two phases together for crystallizations and extractions. Industrial production splits cleanly into two routes. Fuel and beverage ethanol comes from yeast fermentation — Saccharomyces cerevisiae anaerobically converts glucose to two equivalents of ethanol and two CO2 with a theoretical yield of 51.1% by mass, hitting around 90% of theoretical in a well-run distillery. Industrial-grade synthetic ethanol is made by direct hydration of ethylene over phosphoric acid on silica at 300 °C and 70 bar, which is cheaper at scale but yields chemically identical product. Azeotrope chemistry is the classic teaching hook: ethanol and water form a minimum-boiling azeotrope at 95.6 wt% ethanol that distillation alone cannot break, which is why anhydrous "absolute" ethanol requires a third component (benzene historically, cyclohexane today) or molecular sieves. Ethanol's CNS depressant action is mediated by GABA-A receptor potentiation and NMDA receptor inhibition, with metabolism running through alcohol dehydrogenase to acetaldehyde and then aldehyde dehydrogenase to acetate — the ALDH2*2 polymorphism common in East Asian populations is the basis for the alcohol flush reaction.
Where you'll encounter it
If you've ever used hand sanitizer, run an HPLC column, fermented sourdough, or filled a flex-fuel vehicle, ethanol was the active material. In a synthesis lab it's the default recrystallization solvent for everything from caffeine to acetanilide, and the workup solvent for a thousand reactions where you want polar protic without committing to water. In a hospital pharmacy you'll see 95% ethanol stock for compounding tinctures and as the drug-of-choice infusion for methanol or ethylene glycol poisoning (it competes for ADH and lets the toxic alcohol clear renally). Practical detail every undergrad learns the hard way: "190 proof" ethanol from a chemical supplier already contains the 4.4% water from the azeotrope, so if your reaction is moisture-sensitive you need 200-proof from a freshly opened bottle stored over 3 Å sieves.
Common Uses
- Default recrystallization and extraction solvent in undergraduate and research organic chemistry
- Active ingredient in hand sanitizers (60-90% v/v gives optimal viral envelope disruption)
- Fuel oxygenate in E10 and E85 gasoline blends (lowers CO emissions, raises octane)
- Beverage alcohol in beer (4-6%), wine (10-14%), and distilled spirits (40%+)
- Pharmaceutical antidote infusion for methanol and ethylene glycol poisoning
- Process solvent in pharmaceutical tincture and herbal extract manufacturing
- Disinfectant for medical surfaces and skin antisepsis (70% v/v is the sweet spot)
- Carrier solvent in HPLC mobile phases and gas chromatography column conditioning
Safety Information
Highly flammable liquid (flash point 13 °C, autoignition 363 °C, explosive range 3.3-19% in air) — keep away from open flames, hot plates, and ungrounded transfers of larger volumes. GHS H225 (flammable liquid Category 2), H319 (eye irritation), H371 (CNS effects on inhalation). OSHA PEL is 1000 ppm (1900 mg/m3) as an 8-hour TWA, but the more realistic limit for chronic exposure is the ACGIH TLV of 1000 ppm STEL only. Acute oral toxicity in humans is well-characterized — LD50 is roughly 7 g/kg, blood levels above 0.4% are typically fatal. Chronic ingestion causes hepatic steatosis, cirrhosis, and Wernicke-Korsakoff syndrome via thiamine depletion.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.