THE CHEMICAL ACTION OF LIGHT 267 



product (together with benzylic benzoate, see p. 261) on exposing 

 benzaldehyde containing traces of iodine to light. In the latter 

 case, only a small proportion of Ciamician and Silber's tetrameric 

 form could be isolated. 



IV. Condensations and Syntheses 



Closely allied with the changes involving polymerisation, 



that is the union of like molecules, are those in which the action 



involves the union of unlike molecules. Klinger in 1891 found 



that benzaldehyde, which easily polymerises in sunlight, also 



combines readily with other substances, such as quinone, under 



the same influence. In the case of quinone x the action is as 



follows : 



O OH 



,/^sCO . C 6 H5 

 + C 6 H 5 CHO - 



a 



OH 



Dihydroxybenzophenone. 



Acetaldehyde, in like manner, combines with quinone to form 

 dihydroxyacetophenone 2 (acetylquinol) : 



O OH 



1 + CH 3 .CHO -> f 



CO.CH3 



O OH 



Phenanthraquinone and benzaldehyde 3 interact as follows : 



& 



S-^COH 



CO 



I + C 6 H 5 CHO -> 

 -CO X\/ C • C0 • C « H 



s^s 



The addition of benzylic alcohol to benzophenone to form 

 triphenylglycol has already been dealt with in Section I. 

 Similar synthetic changes occur in the case of acetone in presence 

 of paraffinoid alcohols such as methylic and ethylic alcohol ; as 

 other changes also occur, these cases are dealt with in Section VII. 



1 Klinger and Standke, Ber. 1891, 24, 1340 ; Anna/en, 249, 237. 



' Klinger and Kolvenbach, Ber. 1898, 31, 12 14. 



8 Klinger and Standke, Ber. 1891, 24, 1340 ; Annalen, 249, 237. 



