Acetic acid, also known as ethanoic acid, is an organic chemical compound with the formula CH3COOH best recognized for giving vinegar its sour taste and pungent smell. Pure, water-free acetic acid (glacial acetic acid) is a colourless liquid that attracts water from the environment (hygroscopy), and freezes below 16.7°C (62°F) to a colourless crystalline solid. Acetic acid is corrosive, and its vapour causes irritation to the eyes, a dry and burning nose, sore throat and congestion to the lungs, however, it is considered a weak acid due to its limited ability to dissociate in aqueous solutions. Following is the sunnary of its general properties.
- Systematic Names: Acetic Acid
- Molecular Formula: CH3COOH
- Appearance: Colorless Liquid or Crystals
- Molecular Weight: 05 g/mol
- Melting Point: 5 oC
- Boiling Point: 1 oC
- pKa: 76
- EU Classification: Corrosive ( C )
Vinegar is as old as civilization itself, perhaps older. Acetic acid-producing bacteria are present throughout the world, and any culture practicing the brewing of beer or wine inevitably discovered vinegar as the natural result of these alcoholic beverages being exposed to air.The use of acetic acid in chemistry extends into antiquity. In the 3rd century BC, the Greek philosopher Theophrastos described how vinegar acted on metals to produce pigments useful in art, including white lead (lead carbonate) and verdigris, a green mixture of copper salts including copper(II) acetate. Ancient Romans boiled soured wine in lead pots to produce a highly sweet syrup called sapa. Sapa was rich in lead acetate, a sweet substance also called sugar of lead or sugar of Saturn, which contributed to lead poisoning among the Roman aristocracy. The 8th century Persian alchemist Jabir Ibn Hayyan (Geber) concentrated acetic acid from vinegar through distillation.
In the Renaissance, glacial acetic acid was prepared through the dry distillation of metal acetates. The 16th century German alchemist Andreas Libavius described such a procedure, and he compared the glacial acetic acid produced by this means to vinegar. The presence of water in vinegar has such a profound effect on acetic acid’s properties that for centuries many chemists believed that glacial acetic acid and the acid found in vinegar were two different substances. The French chemist Pierre Adet proved them to be identical. In 1847 the German chemist Hermann Kolbe synthesised acetic acid from inorganic materials for the first time. This reaction sequence consisted of chlorination of carbon disulfide to carbon tetrachloride, followed by pyrolysis to tetrachloroethylene and aqueous chlorination to trichloroacetic acid, and concluded with electrolytic reduction to acetic acid.
By 1910 most glacial acetic acid was obtained from the “pyroligneous liquor” from distillation of wood. The acetic acid was isolated from this by treatment with milk of lime, and the resultant calcium acetate was then acidified with sulfuric acid to recover acetic acid. At this time Germany was producing 10,000 tons of glacial acetic acid, around 30% of which was used for the manufacture of indigo dye.
The hydrogen (H) atom in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can be given off as an H+ ion (proton), giving them their acidic character. Acetic acid is a weak, effectively monoprotic acid in aqueous solution, with a pKa value of 4.8. Its conjugate base is acetate (CH3COO−). A 1.0 M solution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated.
Liquid acetic acid is a hydrophilic (polar) protic solvent, similar to ethanol and water. It can dissolve not only polar compounds such as inorganic salts and sugars, but also non-polar compounds such as oils and elements such as sulfur and iodine. It readily mixes with many other polar and non-polar solvents such as water, chloroform, and hexane. This dissolving property and miscibility of acetic acid makes it a widely used industrial chemical.
Acetic acid can be detected by its characteristic smell.
Production by region
Acetic acid is a very important commodity. Because of it’s versatile uses the production of acetic acid is increasing rapidly.
Production capacity is rapidly increasing in East Asia, also new plants are being set in Asia. The main companies producing acetic acid are Celanese (23 %)
and BP (21 %). BP is the fastest growing producer and 2/3 of world uses BP technology. Acetic acid production by region is statistically shown as below.
The overall production capacity of world is about 6.4 million tones. Out of which 1.42 million tones is produced in Europe. And 0.57 million tones are produces in UK.
Major uses of acetic acid
These wide uses are the cause of increasing world demand of acetic acid.