CKOTONIC ACID. 123 



acetic and formic acids. Treated with sodium amal 

 gam and water, it is converted into propionic acid. ^ It 

 combines with two atoms of bromine, without elimina 

 tion of hydrogen, forming an exceedingly unstable 

 acid. 



Its salts are all easily soluble in water, with the 

 exception of the silver salt C B Il 3 2 Ag.Lead acrylate, 

 (C 3 H 3 2 ) 2 Pb, crystallizes in thin needles of a silky 

 lustre. 



2. Crotonic Add. 

 C 4 H 6 2 = C 3 H 5 .CO.OH. 



There are three isomeric acids of this composition 

 known. 



1, Crotonic acid, CII 2 :CH.CH 2 .CO.OH. Is pro 

 duced by the oxidation of its aldehyde (p. 129); from 

 allyl cyanide by boiling with caustic potassa; and by 

 the destructive distillation of j3-oxybutyric acid. Fine, 

 fleecy needles or large plates, which fuse at 72 and 

 boil at 180-182. Nascent hydrogen converts it into 

 butyric acid, fusing potassium hydroxide into acetic 

 acid. 



Monochlorcrotonic acid, C 4 H 5 C10 2 . Is produced 

 by the action of zinc and hydrochloric acid on tri- 

 chlorcrotonic acid, and, together with another acid, 

 when phosphorus chloride is allowed to act on acetyl- 

 acetic ether (p. 82) and the product then treated 

 with water. Colorless crystals, easily soluble in water; 

 fusing point, 94-95. 



Tr ichor crotonic acid, C 4 H 3 C1 3 2 . Is formed by 

 the action of cold concentrated nitric acid on tri- 

 chlorcrotonic aldehyde (p. 129). Colorless, radiating 

 needles ; fusing point, 44 ; soluble in 25 parts water. 



Monobromcrotonic acid, C 4 H 5 Br0 2 , is formed by 

 boiling citradibrompyroracemic acid (see Pyroracemic 

 Acid) with watery solutions of the alkalies. Long, 

 flat needles, but slightly soluble in cold water. Fusing 

 point, 65 ; boiling point, 228-230 ; combines directly 



