Isobutyric acid, also known as 2-methylpropanoic acid or isobutanoic acid, is a

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

with structural formula ( CH₃)₂CH COOH. It is an

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

butyric acid Butyric acid (; from , meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl carboxylic acid with the chemical formula . It is an oily, colorless liquid with an unpleasant odor. Isobutyric acid (2-met ...

. It is classified as a short-chain fatty acid. Deprotonation or esterification gives derivatives called isobutyrates. Isobutyric acid is a colorless liquid with a somewhat unpleasant odor. It is soluble in water and organic solvents. It is found naturally in carobs ('' Ceratonia siliqua''), in vanilla, and in the root of ''

Arnica ''Arnica'' is a genus of perennial plant, perennial, herbaceous plants in the sunflower family (Asteraceae). The genus name ''Arnica'' may be derived from the Greek language, Greek ''wikt:arni, arni'', "lamb", in reference to the plants' soft, h ...

dulcis'', and as an ethyl

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

in croton oil.

Production

Isobutyric acid is manufactured by the oxidation of isobutyraldehyde, which is a byproduct of the hydroformylation of propylene. It can also be prepared by the high pressure hydrocarboxylation ( Koch reaction) from propylene: :CH₃CH=CH₂ + CO + H₂O → (CH₃)₂CHCO₂H Isobutyric acid can also be manufactured commercially using engineered bacteria with a sugar feedstock.

Laboratory methods

Many routes are known including the hydrolysis of isobutyronitrile with alkalis and the

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

of isobutanol with potassium dichromate in the presence of

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

. In the presence of proton donors, the action of sodium amalgam on methacrylic acid also gives isobutyric acid.

Reactions

The acid reacts as a typical carboxylic acid: it can form amide,

, anhydride, and chloride derivatives. Its acid chloride is commonly used as the intermediate to obtain the others. When heated with a chromic acid solution it is oxidized to

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

. Alkaline potassium permanganate oxidizes it to ''α''-hydroxyisobutyric acid, (CH₃)₂C(OH)-CO₂H.

Uses

Isobutyric acid and its volatile

esters In chemistry, an ester is a chemical compound, compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds c ...

are present naturally in a wide variety of foods and, at varying concentrations, can impart a range of flavors. The compound's safety as a food additive was reviewed by an

FAO The Food and Agriculture Organization of the United Nations; . (FAO) is a List of specialized agencies of the United Nations, specialized agency of the United Nations that leads international efforts to defeat hunger and improve nutrition ...

and WHO panel, who concluded that there were no concerns at the likely levels of intake.

Biology

In humans, isobutyric acid is a minor product of the gut microbiome and can also be produced by metabolism of its esters found in food. It has a characteristic odor like rancid butter (4-carbon organic compounds take the root, butyl, which is in turn from butyric which is in turn from the Latin word for butter and the Greek, βούτυρον) but anosmia for it has been reported in about 2.5% of people. The

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

of isobutyric acid in plants has been studied. Isobutyric acid, along with several other short-chain fatty acids collectively known as "copulins," is found abundantly in human vaginal secretions. Levels of isobutyric acid fluctuate throughout the

menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eg ...

, and it is hypothesized to act as an indicator of ovulatory status. Similar cycles are observed in chimpanzees.

References