When gardeners are considering how to kill weeds or do other organic procedures that use vinegar, they will on occasional be offered acetic acid products instead of actual vinegar, a fermented product. Here is information about acetic acid and why it is NOT a suitable substitute for vinegar.
acetic acid (əsç'tĭk), CH3CO2H, a colorless liquid that has a characteristic pungent odor, boils at 118°C, and is miscible (combines completely) with water in all proportions; it is a weak organic carboxylic acid (see carboxyl group). Also called ethanoic acid, glacial acetic acid, methane carboxylic acid. This product is a strong oxidizer and very caustic (corrosive to metals). For exposure to this product, OSHA advises that eyes and skin must be immediately irrigated (wash), extended breathing of the strong fumes requires respiratory support, and swallowing the acid requires immediate medical attention.
According to the Centers for Disease Control (CDC), symptoms of acetic acid exposure include irritation to eyes, skin, nose, throat; eye, skin burns; skin sensitization; dental erosion; black skin, hyperkeratosis; conjunctivitis, lacrimation (discharge of tears); pharyngeal edema, chronic bronchitis. The organs impacted most by acetic acid are the eyes, skin, respiratory system and teeth.
[Standard] vinegar is about 4-6% acetic acid in water. More concentrated solutions can be found in laboratory use, and pure acetic acid containing only traces of water is known as glacial acetic acid. (Source: Virginia Department of Health)
Glacial acetic acid is concentrated, 99.5% pure acetic acid; it solidifies at about 17°C to a crystalline mass resembling ice. Acetic acid is the major acid in vinegar; as such, it is widely used as a food preservative and condiment. For industrial use concentrated acetic acid is prepared from the oxidation of acetaldehyde. Acetic acid is also a product in the destructive distillation of wood. It reacts with other chemicals to form numerous compounds of commercial importance. These include cellulose acetate, used in making acetate rayon, nonflammable motion-picture film, lacquers, and plastics; various inorganic salts, e.g., lead, potassium, and copper acetates; and amyl, butyl, ethyl, methyl, and propyl acetates, which are used as solvents, chiefly in certain quick-drying lacquers and cements. Amyl acetate is sometimes called banana oil because it has a characteristic banana odor.
More from the Virginia DOH:
Acetic acid is the 33rd highest volume chemical produced in the United States. Acetic acid is used in the manufacture of acetic anhydride, cellulose acetate, vinyl acetate monomer, acetic esters, chloracetic acid, plastics, dyes, insecticides, photographic chemicals, and rubber. Other commercial uses include the manufacture of vitamins, antibiotics, hormones, and organic chemicals, and as a food additive. Typical concentrations of acetic acid occurring naturally in foods are 700 to 1,200 milligrams/kilogram (mg/kg) in wines, up to 860 mg/kg in aged cheeses, and 2.8 mg/kg in fresh orange juice.
The important takeaway for organic gardeners: There is acetic acid in vinegar (giving its characteristic odor) but there is no vinegar in acetic acid. Vinegar is made from fruit and alcohol. Glacial acetic acid is made from a petroleum based chemical and has none of the trace minerals found in vinegar. There is an attempt to continue to use it by some people because it is far cheaper than real vinegar.
Historically, white vinegar has been produced from the fermentation of foods such as sugar beets, potatoes, molasses or milk whey. Usually, the specific recipe depended on which food item was most readily available in a particular region.
Today, most white vinegar is made from the fermentation of grain alcohol (ethanol). This kind of alcohol doesn’t naturally contain many nutrients, so other ingredients such as yeast or phosphates may be added to kickstart the bacterial fermentation process.
An interesting aside from the University of Bristol School of Chemistry (UK): Formic acid is produced as a by-product in the manufacture of acetic acid. Formic acid is the source of the vinegary smell given off by ant hills. Isolated in 1671 by English naturalist John Ray, the name "Formic acid" comes from formica, the Latin name for "ants."
Formic acid is also present in a natural state in stinging nettles, and is is reponsible for the burning feeling on contact with them. It is also found in the stings and bites of many insects, including bees and ants, which use it as a chemical defence mechanism. When the ant contracts its poison gland, the formic acid stored in this gland passes in the sting and is propelled out in jets (up to a distance of one metre in some species!) toward the attackers of the ant. Since formic acid has a pH of ~2-3, the attackers usually flee, or are killed.
Formic acid produced commercially is a preservative and antibacterial agent. Beekeepers sometimes use it to kill a mite that attacks bees. There are also a lot of industrial production uses.