What is glacial acetic acid

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Acetic acid: a product that everyone uses

Acetic acid is a product that everyone has had experience with, for example:

  • Wine becomes sour from standing for a long time
  • Salad sauces without acid taste bland
  • Verdigris is annoying and harmful to health
  • "Aspirin" helps with headaches

Acetic acid is involved in all of these observations. It is probably the most important organic acid, a carboxylic acid. The anhydrous acid is a pungent smelling, caustic liquid with a boiling point of 118 ° C. At 16.6 ° C it solidifies to form ice-like crystals, the so-called glacial acetic acid.

Already known to the ancient Egyptians

Acetic acid was already known to the ancient civilizations such as Egyptians, Assyrians and Chinese and used it as a preservative, as a drink, but also as a medicine. It was obtained by allowing wine or beer to stand in the air in clay jugs, i.e. to turn it into vinegar. The action of acetic acid bacteria (e.g. Acetobacter) produces vinegar in an aerobic biochemical process, i.e. under the influence of atmospheric oxygen, from liquids containing alcohol. The common name "vinegar" chemically stands for diluted acetic acid.

The large-scale production of acetic acid takes place through the catalytic conversion of methanol with carbon monoxide under pressure. The great importance of this so simply constructed chemical acid (world production approx. 5 million tons) results from its versatility. It is used for food, cleaning products and many large-scale applications.

Vinegar: universal food

Vinegar is used as an acidifier, seasoning and preservative and is marketed with an acid content of 5 to 15.5 g / 100 ml. The most important vinegars are wine, fruit or herb vinegars; Brandy vinegar is made from grain, sugar beet or potatoes.

Typical products of acidification with acetic acid are pickles, fish or meat marinades (sauerbraten), mustard, ketchup and of course the salad dressings. But it is not just the taste that is important; the preserving effect of acetic acid is also used. In an acidic environment, yeast and bacteria, for example, are inhibited in their growth and the food has a longer shelf life.

Also indispensable as a cleaning agent

This germ-inhibiting effect leads to another application, that of a cleaning agent. Germs do not like acidic environments, so there are cleaners containing acetic acid for cleaning kitchens and bathrooms. Lime stains (in English: "limescale", see graphic) can also be removed with vinegar. Base metals such as magnesium, calcium, zinc or iron dissolve in dilute acetic acid to form water-soluble salts, the acetates. Therefore, food containing vinegar should never be kept in metal containers. And marble, chemically calcium carbonate, must not be cleaned with acetic acid! Acetic acid reacts with copper in the air to form copper acetate, a green, harmful salt known as verdigris.

Ethyl acetate - an esterification product made from ethanol (alcohol) with acetic acid - will not necessarily be familiar with the chemical name, but who does not know the typical smell of this solvent, which is contained in nail polish remover or liquid glue, for example. Acetic acid produced on a large scale is used in the production of polymers such as polyvinyl acetate, cellulose acetate, paint base materials or adhesives.

In this graph from CompoundInterest, the formula and some of its applications are summarized. The website contains some additional explanations.

Products made from vinegar are also used in medicine

Another esterification product of acetic acid is particularly successful as a drug. The well-known compound acetylsalicylic acid, the active ingredient in the pain reliever aspirin, is obtained from acetic acid and salicylic acid. "Acetic clay" has been known for a long time as a remedy. It is the basic aluminum salt of acetic acid. The aqueous solution is recommended for anti-inflammatory compresses in wound treatment and helps with bruises and sprains.

The contribution was created by the Public Relations Working Group of the Senior Chemistry Experts, a specialist group of the Society of German Chemists.
Authors: Dr. Ingeborg Lenze, Dr. Ursula Kraska (edited by kjs)

In the series “What is actually…” we present chemical substances that everyone knows or uses in an easily understandable form. All articles in the series: https://faszinationchemie.de/chemie-ueberall