Alcohol (chemistry)

Alcohols are a class of organic compounds characterized by the presence of at least one hydroxyl (−OH) functional group bound to a saturated carbon atom. They range from simple substances like methanol and ethanol to complex ones like sugar alcohols and cholesterol, and their properties are strongly modified by the hydroxyl group, which confers hydrophilic characteristics and provides a site for many chemical reactions. The flammable nature of vapors from wine was noted by ancient philosophers such as Aristotle, Theophrastus, and Pliny the Elder, though the isolation of alcohol did not immediately follow. Early distillation techniques in Roman Egypt did not yield alcohol, but a key insight, attributed to the ninth-century scholar Jābir ibn Ḥayyān, was that adding salt to boiling wine increased the volatility of its vapors, enhancing flammability.

The distillation of wine is documented in Arabic works by al-Kindī, al-Fārābī, and al-Zahrāwī. By the twelfth century, Latin texts described producing aqua ardens by distilling wine with salt, and by the late thirteenth century, this substance was widely known among Western European chemists. Taddeo Alderotti later devised a method using repeated fractional distillation through a water-cooled still to achieve alcohol of 90% purity.

Etymology

The medicinal properties of ethanol were studied by Arnald of Villanova and John of Rupescissa, the latter viewing it as a life-preserving aqua vitae capable of preventing all diseases. The term "alcohol" itself derives from the Arabic kohl, a fine powder of antimony trisulfide used as an eyeliner. Its meaning expanded to include any distilled substance before narrowing to ethanol, and in modern chemistry, the class of compounds known as alcohols was formally recognized after 1850. The suffix -ol is used in IUPAC nomenclature for substances where the hydroxyl group is the highest priority functional group, while the prefix hydroxy- is used when a higher priority group is present.