CROTONIC 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 3 H 3 2 Ag. Lead acrylate, 

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

 lustre. 



2. Crotonic Add. 



C 3 H 5 .CO.OH. 



There are three isomeric acids of this composition 

 known. 



1. Crotonic acid, CIP: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 |3-oxy butyric 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. 



Trichorcrotonic 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 



