acid dissociation constant than tiglic acid, in accordance to usually observed trends. Angelic acid reacts with hydrobromic acid and bromine producing bromovaleric and dibromovaleric acids, respectively, with a yield of 60–70%. Chlorovaleric and iodovaleric acids are obtained using hydrochloric and hydroiodic acids, respectively. The salts of angelic acid are called angelates. Angelates of alkaline earth metals 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. Roman chamomile, in which esters of angelic and tiglic acids are the principal components, was used as a sedative and tonic, and as a medicine against nervous problems, fever, colic, heartburn, loss of appetite, gout, headache and other health disturbances. References Enoic acids Hemiterpenes