Isobutyric acid

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Isobutyric acid, also known as 2-methylpropanoic acid, is a short-chain carboxylic acid with the formula (CH3)2CHCOOH. It is a colorless liquid with a strong, unpleasant odor and dissolves in water and many solvents. It is an isomer of butyric acid and occurs naturally in foods such as carobs and vanilla, and as an ethyl ester in croton oil.

How it is made and where it comes from:
- Industrially, it is produced by oxidizing isobutyraldehyde, a byproduct of propylene chemistry.
- It can also be made by other chemical routes, including high-pressure hydrocarbon reactions (Koch process) and certain bacterial systems using sugars.
- It can be found or produced via various practical routes in chemistry and industry.

What it does and how it reacts:
- Like other carboxylic acids, it can form derivatives such as amides, esters, anhydrides, and acid chlorides.
- Its acid chloride is a common intermediate for making other compounds.
- It can be oxidized to acetone with strong oxidants; alkaline permanganate can convert it to alpha-hydroxyisobutyric acid.

Uses and safety:
- Isobutyric acid and its esters contribute to flavors in foods.
- Safety reviews by international health organizations have found no concerns at typical levels of intake.
- In humans, it is a minor product of gut microbes and can come from the metabolism of esters found in food.

Odor and biology:
- It has a distinctive rancid-butter odor; most people can smell it, though about 2.5% may not (anosmia).
- Its metabolism has been studied in plants.
- Isobutyric acid is also found in human vaginal secretions as part of a group of fatty acids; its levels vary during the menstrual cycle and may indicate ovulatory status, with similar patterns seen in chimpanzees.