Acetic Acid, with the chemical formula CH₃COOH, is one of the simplest and most widely used carboxylic acids. Also known as vinegar essence, it is the main component of edible vinegar and gives it its characteristic sour taste. At room temperature, acetic acid exists as a colorless liquid with a sharp and pungent odor. Due to its physical and chemical properties, it finds applications in many industries.

Structure

The molecular structure of acetic acid consists of a methyl group (−CH₃) and a carboxyl group (−COOH). These two groups are connected via a carbon–carbon bond. The carboxyl group is responsible for its acidity, as it can release a proton (H⁺) in aqueous solutions.

Properties

Physical state: Colorless liquid at room temperature
Melting point: 16.6°C – Below this temperature, it solidifies into crystalline form, known as glacial acetic acid
Boiling point: Approximately 118–119°C at 1 atm pressure
Odor: Strong, pungent, vinegar-like (irritating at high concentrations)
Solubility: Completely miscible with water, alcohols, ethers, and most polar organic solvents
Acidity: Weak acid with a pKa ≈ 4.76 – incompletely ionized in aqueous solutions
Corrosiveness: Corrosive at high concentrations, can cause chemical burns to skin and eyes
Flammability: Flammable; its vapors can form explosive mixtures with air
Density: Approx. 1.049 g/cm³ at 25°C

Applications

Acetic acid is widely used across various industries due to its versatility in reactions and functional properties:

Chemical Industry:

Production of Vinyl Acetate Monomer (VAM): For adhesives, resins, and polymers
Synthesis of Acetate Esters such as:
- Ethyl acetate: Solvent in nail polish removers, paints, adhesives
- Butyl acetate: Solvent in paints and inks
Production of Purified Terephthalic Acid (PTA): A precursor for PET in bottles and polyester fibers

Pharmaceutical Industry:

In the synthesis of drugs, antibiotics, and biologically active compounds

Textile Industry:

As a pH regulator and color fixative in dyeing and printing

Food Industry:

Used as a food additive (E260) to regulate acidity and act as a preservative
Main ingredient in vinegar and as a flavoring in sauces, pickles, and canned goods

Rubber and Plastics:

As a catalyst or reaction modifier

Other Uses:

In the production of insecticides and herbicides
As an industrial solvent for dissolving resins, paints, and oils

Advantages

High availability: One of the most abundantly produced organic acids on an industrial scale
Chemical versatility: Participates in esterification, polymerization, oxidation, and reduction reactions
Preservative capability: Its acidity inhibits microbial growth
Mild and controllable acidity: Suitable for sensitive formulations
Biodegradability: Rapidly decomposes in the environment to CO₂ and H₂O

Disadvantages

Corrosiveness: Dangerous to skin, eyes, and respiratory system at high concentrations
Strong, irritating odor: Vapors can cause coughing and irritation
Flammable: Vapors form explosive mixtures with air; must be stored away from open flames
High freezing point: Easily solidifies in cold climates
Inhalation toxicity at high concentrations: Can lead to pulmonary damage