Absolute Ethanol

Absolute Ethanol (C₂H₅OH, >99% pure) is ethanol that has had nearly all water removed. Because ethanol forms an azeotrope with water at ~95.6% ethanol, it cannot be purified beyond this point by simple distillation. To obtain absolute ethanol, additional methods are used, such as:

  • Chemical drying agents (e.g., quicklime, calcium oxide, or molecular sieves)
  • Azeotropic distillation with benzene, cyclohexane, or other entrainers (though this is less common today due to toxicity concerns)

Application & Usage

Industrial & Chemical Applications

  • Powerful solvent: Used in the pharmaceutical, cosmetic, and chemical industries for dissolving both polar and non-polar substances
  • Chemical synthesis: Acts as a reagent, dehydrating agent, or intermediate in the production of esters, ethers, and other organic compounds.
  • Fuel & energy: Added to gasoline as a fuel additive or used in specialized alcohol-based fuels due to its high energy content and combustion efficiency

Pharmaceutical & Medical Uses

  • Excipient: Common in tinctures, elixirs, and vaccines for dissolving active ingredients.
  • Antiseptic & disinfectant: Its strong dehydrating properties make it effective for sterilizing lab equipment and medical instruments (though 70% ethanol is more effective for disinfection of microbes).
  • Endovascular therapy: Injected absolute ethanol is sometimes used as a sclerosant to deliberately occlude blood vessels in treatments of vascular malformations or tumors.

Laboratory Uses

  • Dehydrating agent: Used in sample preparation and histology (e.g., tissue dehydration before embedding).
  • Molecular biology: For DNA/RNA precipitation and purification.
  • Preservation: Helps stabilize and store biological specimens.

Cosmetic & Personal Care

  • Found in perfumes, lotions, and sprays, where its volatility helps deliver and preserve active ingredients.