Overview

Acetic acid, also called ethanoic acid (CH3COOH), is a simple organic compound in the carboxylic acid family. It is the principal acid in vinegar, present with water and other minor components. In pure form it is a colorless liquid with the characteristic sharp, sour odor and taste associated with vinegar. For a concise classification see carboxylic acid and for its relation to vinegar see vinegar.

Structure and physical properties

Chemically, acetic acid contains a methyl group (CH3-) attached to a carboxyl group (-COOH). It is a weak acid in water, typically dissociating partially to give the acetate ion and a proton; a common reference value for its acidity is the pKa near 4.8. Important physical figures include a melting point near 16.6 °C and a boiling point near 118 °C, so concentrated acetic acid can freeze at cool room temperatures and boil at a higher temperature than water. For quick reference to these properties see melting point and boiling point. The sour taste and smell are described further at taste and smell. Dilute aqueous solutions have acidic pH values (pH references vary with concentration).

History and production

Acetic acid has been known since antiquity because it is produced naturally during fermentation and is the active component of many traditional condiments. The name derives from the Latin acetum, meaning vinegar. Historically it was obtained by distilling fermented liquids; modern production uses chemical synthesis and biological fermentation at industrial scale.

Common uses and examples

Acetic acid and its derivatives have a broad range of applications in food, industry and laboratories. Typical roles include:

  • Food: dilute acetic acid is the preservative and flavoring in table vinegar and pickles; it is permitted as a food additive where it is listed with the E number E260 or simply as acetic acid (food additive).
  • Salts and buffers: salts such as sodium acetate, potassium acetate and calcium acetate are useful in food processing and as buffering agents; see acetate salts.
  • Preservation: acetate-based formulations are used for preserving vegetables and other foods (preserving food), including traditional pickling of vegetables.
  • Industrial chemistry: acetic acid is a feedstock for producing polymers and chemical intermediates, and it is used as a solvent and reagent in organic synthesis.

Safety, handling and distinctions

At household concentrations (vinegar, typically 4–8% acetic acid) the compound is safe for culinary use but can irritate sensitive tissues. Concentrated glacial acetic acid is corrosive and can cause chemical burns and harmful vapors; proper protective equipment and ventilation are required when handling it. Important conceptual distinctions include the difference between acetic acid (the molecular acid), the acetate ion (its deprotonated form), and acetyl groups (a two-carbon fragment used in organic chemistry).

For concise technical or regulatory details consult specialized sources: general chemistry entries at carboxylic acid, safety summaries at water-related data and material safety resources, and food additive databases at the referenced E-number pages.