THE CHEMICAL ACTION OF LIGHT 269 



It seems probable that the acetonylurea is formed by the further 

 change of a-hydroxybutyramide under the influence of forma- 

 mide (produced from the hydrogen cyanide by addition of water, 

 HCN + H 2 = H . CO . NH 2 ), as follows : 



The formation of acetonylurea does not take place in darkness ; 

 the way in which the hydrogen liberated according to the 

 above equation is used up is not clear. a-Aminoisobutyric 

 acid is no doubt formed by hydrolysis of acetonylurea. Some 

 ammonic oxalate is also formed in the above case by hydrolysis 

 of hydrogen cyanide (or formamide), a change which also 

 involves liberation of hydrogen. 



2H.CO.NH, = H. 2 + ONH 4 .CO.CO.ONH 4 



An interesting synthesis of a substance having alkaloidal 

 properties is described by Paterno and Maselli, 1 who, by ex- 

 posing acetophenone dissolved in alcoholic ammonia to bright 

 sunlight, obtained a crystalline compound, Ci 8 Hi 8 N 2 ; apparently, 

 in the formation of this substance, two molecules of aceto- 

 phenone, two of ammonia and one of alcohol undergo condensa- 

 tion, water being eliminated. 



Other syntheses are considered in Section VII. 



V. Isomeric or Stereoisomeric Change 



In the case of compounds containing an ethenoid linkage, 

 light brings about very frequently the transformation of one 

 stereoisomeric form into another. Wislicenus 2 in 1895 observed 

 that in presence of traces of bromine maleic acid is rapidly 

 changed by sunlight into the more stable fumaric acid ; the same 

 change was found by Ciamician and Silber 3 to be brought about 

 by sunlight alone in either solid or dissolved maleic acid but 

 to take place more slowly in the absence of bromine. The 

 same is true of the analogous change of angelic into tiglic acid 



1 Gazzetta, 1912, 42, i. 65. 



a Ber. Verh. K. Ges. Leipzig, 1895, 489. 



3 Atti R. Accad. Lincei, 1903, 12, ii. 528 ; Ber. 1903, 36, 4266. 



