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 R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...

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

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Is ...

of ''n''-

butyric acid Butyric acid (; from grc, βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl carboxylic acid with the chemical formula CH3CH2CH2CO2H. It is an oily, colorless liquid with an unp ...

. 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

carob The carob ( ; ''Ceratonia siliqua'') is a flowering evergreen tree or shrub in the Caesalpinioideae sub-family of the legume family, Fabaceae. It is widely cultivated for its edible fruit pods, and as an ornamental tree in gardens and lands ...

s (''

Ceratonia siliqua The carob ( ; ''Ceratonia siliqua'') is a flowering evergreen tree or shrub in the Caesalpinioideae sub-family of the legume family, Fabaceae. It is widely cultivated for its edible fruit pods, and as an ornamental tree in gardens and lands ...

''), in

vanilla Vanilla is a spice derived from orchids of the genus '' Vanilla'', primarily obtained from pods of the Mexican species, flat-leaved vanilla ('' V. planifolia''). Pollination is required to make the plants produce the fruit from whic ...

, and in the root of ''

Arnica ''Arnica'' is a genus of perennial, herbaceous plants in the sunflower family (Asteraceae). The genus name ''Arnica'' may be derived from the Greek '' arni'', "lamb", in reference to the plants' soft, hairy leaves. ''Arnica'' is also known by th ...

dulcis'', and as an ethyl

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

in croton oil.

Production

Isobutyric acid is manufactured by the oxidation of isobutyraldehyde, which is a byproduct of the

hydroformylation Hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of a formyl group (CHO) and a hydrogen atom to a carbon-carbon ...

propylene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...

. It can also be prepared by the high pressure

hydrocarboxylation Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbo ...

(

Koch reaction The Koch reaction is an organic reaction for the synthesis of tertiary carboxylic acids from alcohols or alkenes. The reaction is a strongly acid-catalyzed carbonylation using carbon monoxide, and typically occurs at high pressures ranging from 50 ...

) 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 Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysi ...

of isobutyronitrile with

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

s and the

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

of isobutanol with potassium dichromate in the presence of

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

. 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 In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...

, anhydride, and

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

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 formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...

. Alkaline

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

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

Uses

Isobutyric acid and its volatile

esters In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

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 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 Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the ...

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 Anosmia, also known as smell blindness, is the loss of the ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be due to a nu ...

for it has been reported in about 2.5% of people. The

metabolism Metabolism (, from el, μεταβολή ''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 ...

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 make pregnancy possible. The ovarian cycle controls the production and release of eggs ...

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

References