Angelic acid is a monocarboxylic unsaturated organic acid, mostly found in the plants of the family

Apiaceae Apiaceae or Umbelliferae is a family of mostly aromatic flowering plants named after the type genus ''Apium'' and commonly known as the celery, carrot or parsley family, or simply as umbellifers. It is the 16th-largest family of flowering plants ...

. It is a volatile solid with a biting taste and pungent sour odor. It is the ''

cis Cis or cis- may refer to: Places * Cis, Trentino, in Italy * In Poland: ** Cis, Świętokrzyskie Voivodeship, south-central ** Cis, Warmian-Masurian Voivodeship, north Math, science and biology * cis (mathematics) (cis(''θ'')), a trigonome ...

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. Iso ...

of 2-methyl-2-butenoic acid, which easily converts to the ''trans'' isomer, tiglic acid, upon heating or reaction with inorganic acids. The reverse transformation occurs much less readily. The salts and esters of angelic acid are called angelates. Angelic acid

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 ar ...

s are the active components of herbal medicine used against a wide range of various health disturbances including pains, fever,

gout Gout ( ) is a form of inflammatory arthritis characterized by recurrent attacks of a red, tender, hot and swollen joint, caused by deposition of monosodium urate monohydrate crystals. Pain typically comes on rapidly, reaching maximal intensit ...

, heartburn, etc.

Name and discovery

Angelic acid was first isolated by the German pharmacist Ludwig Andreas Buchner (1813–1897) in 1842 from the roots of the garden plant angelica (''

Angelica archangelica ''Angelica archangelica'', commonly known as garden angelica, wild celery, and Norwegian angelica, is a biennial plant from the family Apiaceae, a subspecies of which is cultivated for its sweetly scented edible stems and roots. Like several oth ...

''), which gave the acid its name.

Occurrence

Angelic acid occurs in the roots of many plants, especially of the family

. These plants include ''

'', ''

Peucedanum ostruthium ''Peucedanum ostruthium'' or ''Imperatoria ostruthium'', masterwort, is a species of flowering plant in the family Apiaceae. It is native to the mountains of Central and Southern Europe, but has been widely introduced outside its native range. ...

'' (masterwort), '' Levisticum officinale'' (lovage), '' Euryangium sumbul'' and '' Laserpitium latifolium''. In the latter plant, it is present in the resin called laserpicium, and the oil of carrot also contains angelic acid. Sumbul plants might contain not angelic acid itself, but a larger complex which breaks into angelic acid upon processing. The acid can also be extracted from the oil of

chamomile Chamomile (American English) or camomile (British English; see spelling differences) ( or ) is the common name for several plants of the family Asteraceae. Two of the species, ''Matricaria recutita'' and ''Anthemis nobilis'', are commonly us ...

flowers, and 85% of Roman chamomile (''

Anthemis nobilis ''Chamaemelum nobile'', commonly known as chamomile (also spelled camomile), is a low perennial plant found in dry fields and around gardens and cultivated grounds in Europe, North America, and South America. Its synonym is ''Anthemis nobili ...

'') oil consists of esters of angelic and tiglic acids;Ernest Smal
Culinary herbs
National Research Council Canada, 2006, p. 288 it also contains isobutyl angelate and amyl angelate. The acid content is highest in ''Angelica archangelica''William Allen Miller, Herbert McLeo
Elements of Chemistry
Vol. 3: Chemical physics, p. 958 where it is about 0.3%.Rudolf Fritz Weis
Weiss's herbal medicine
Thieme, 2001, pp. 46, 91, 236

Properties

Angelic acid is a volatile solid with a biting taste and pungent sour odor. It crystallizes in colorless monoclinic prisms which dissolve rapidly in alcohol or hot water and slowly in cold water. Angelic and tiglic acid are ''

'' and ''trans'' isomers of 2-methyl-2-butenoic acid, respectively. The former can be entirely converted to the latter by boiling for about 40 hours, by reaction with sulfuric and other acids, by heating with a base to a temperature above 100 °C, or simply by storing the acid for about 25 years. The reverse transformation occurs much less readily; it can be induced by ultraviolet light, but not with visible light. The conversion rate is low and only 0.36 g of angelic acid could be obtained from 13 g of tiglic acid after 43-day irradiation with a 500-watt lamp. Being the ''cis'' isomer, angelic acid has a lower melting point and higher acid dissociation constant than tiglic acid, in accordance to usually observed trends. D. Nasipur
Stereochemistry of Organic Compounds: Principles and Applications
New Age International, 1994, , p. 192 Angelic acid reacts with

hydrobromic acid Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. ...

and bromine producing bromovaleric and dibromovaleric acids, respectively, with a yield of 60–70%. Chlorovaleric and iodovaleric acids are obtained using

hydrochloric Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestiv ...

and

hydroiodic acid Hydroiodic acid (or hydriodic acid) is an aqueous solution of hydrogen iodide (HI). It is a strong acid, one that is ionized completely in an aqueous solution. It is colorless. Concentrated solutions are usually 48% to 57% HI. Reactions Hyd ...

s, respectively. The salts of angelic acid are called angelates. Angelates of

alkaline earth metal The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are al ...

s ''M'' have a general formula M(C₅H₇O₂)₂ and form white, water-soluble crystals.

Applications

The angelic acid esters of sesquiterpene alcohols, such as petasin, are the active chemical behind the strong pain-relieving and spasmolytic action of extracts from the plant

butterbur ''Petasites'' is a genus of flowering plants in the sunflower family, Asteraceae, that are commonly referred to as butterburs and coltsfoots.Roman chamomile, in which esters of angelic and tiglic acids are the principal components, was used as a

sedative A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but t ...

and tonic, and as a medicine against nervous problems, fever, colic, heartburn, loss of appetite, gout, headache and other health disturbances.

References

{{reflist, 2 Enoic acids Hemiterpenes