Angelic acid

Angelic acid (cis-2-methyl-2-butenoic acid) is an unsaturated aliphatic carboxylic acid that was discovered by Munich pharmacist Ludwig Andreas Buchner in 1842. Buchner isolated it from the carrot-like roots of the herb Angelica archangelica (garden angelica). According to lore, an archangel revealed the herb’s medicinal properties, hence the heavenly name.

Since its discovery, angelic acid and its esters have been found in other plants, such as Roman chamomile (Anthemis nobilis), sabadilla (Schoenocaulon officinale), and lovage (Levisticum officinale). It is often found together with its more thermodynamically stable trans isomer, tiglic acid¹.

In 1949, Robert E. Buckles* and Gene V. Mock at Iowa State University (Ames) reported the synthesis of tiglic acid by treating 2-hydroxy-2-methylbutyronitrile² with sulfuric acid, followed by hydrolysis. They then converted tiglic acid to angelic acid in a three-step process: (1) addition of bromine across the double bond; (2) reaction with potassium hydroxide to form 3-bromoangelic acid³; and (3) reduction with sodium amalgam to produce angelic acid. Six years later, Buckles, Mock, and Louis Locatell, Jr., wrote an extensive review of the chemistry of both isomers.

Angelic and tiglic acids are used primarily as their esters in such products as perfumes and flavorings. The angelic ester petasin⁴, originally discovered in the common butterbur plant (Petasites hybridus), is a sesquiterpene with potential medical uses.

Despite its name, angelic acid has a spicy—even pungent—odor and a biting, acidic taste. As shown in the hazard information table, it must be handled with care.

1. CAS Reg. No. 80-59-1.
2. CAS Reg. No. 4111-08-4.
3. CAS Reg. No. 35057-99-9.
4. CAS Reg. No. 26577-85-5.