392 



SCIENCE 



[N. S. Vol. XXXVI. No. 926 



CH, CHa CHb CH, 

 I I I I 



CO + CHOH=C.OH— COH. 



I I I I 



CH3 CH3 CH3 CHa 



In the aromatic series benzophenone and 

 benzyl alcohol give triphenylethylene gly- 

 col, together with other products: 



C„H, 



C„H, 



CO + CH20H=C0H— CHOH. 

 II II 



C0H5 CoHj C,H, C„H5 



This was the first case in which this con- 

 densation has been observed; others were 

 afterwards studied by Paterno, who re- 

 placed the benzyl alcohol by several other 

 aromatic substances. The observations of 

 Klinger showed that the aldehydes also 

 underwent condensations, and this has 

 since been confirmed by Benrath. 



To get an idea of the variety of photo- 

 chemical reactions we may confine our- 

 selves to a systematic study of the ketones 

 and alcohols. In ordinary organic chem- 

 istry the reactions often take place in some 

 definite way ; but the photochemical reac- 

 tions often furnish surprises and proceed 

 along quite different lines. From the very 

 first experiments we knew that benzophe- 

 none did not form addition products with 

 ethyl alcohol, but was converted into pina- 

 cone at the expense of the alcohol, which 

 was oxidized to aldehyde. Proceeding with 

 the study of aliphatic ketones, similar to 

 acetone, Tve have this year discovered a 

 remarkable fact. Methylethylketone con- 

 denses with itself and forms the paradike- 

 tone, reducing itself at the same time to 

 secondary butyl alcohol: 



CHa CH3 CHa CHa 



II II 



3CHj CH, CH— CH 



1=1 +1 I 



CO CHOH CO CO 

 II II 



CHa CHa CHa CH3. 



Of course the synthesis of diketones by 

 light could not be an isolated reaction; we 

 had previously noticed the formation of 

 diacetyl: acetonylacetone is found, as we 

 now know, among the products of acetone 

 in solution in ethyl alcohol and it is also 

 possible that the metadiketones, such as 

 acetylacetone for instance, may be pre- 

 pared photochemically. These reactions 

 have a special importance on account of 

 the special character of the diketones and 

 their tendency to change in all sorts of 

 ways. From them derivatives of benzene 

 can be obtained as well as of pyrrazol and 

 isoxazol, of quinoline, of furfurol, of thio- 

 phene and of pyrrol. In regard to this 

 last change I wish to remind you that 

 tetramethylpyrrol corresponds to the para- 

 diketone previously referred to. If I dare 

 to be reckless, as you may see I am at this 

 moment, contrary to my custom, but per- 

 haps urged thereto unconsciously by the 

 American genius which heeds no obstacles, 

 I may refer to the relations between the 

 polysubstituted pyrrols with alcohol rad- 

 icals and chlorophyll, and I may see in 

 these reactions the possibility of the syn- 

 thesis of this fundamental substance by 

 means of an artificial photochemical proc- 

 ess. Its formation in plants, like its func- 

 tion, is due to a photochemical process; 

 we do not know, however, whether and in 

 what measure light enters into all the syn- 

 thetic plant reactions, from which orig- 

 inate the various substances which we find 

 in plants. The research should proceed 

 together in the two fields; phytoehemistry 

 and photochemistry will be of great help 

 one to another. Industrially this coopera- 

 tion might have a great future: the raw 

 materials obtained from the plants might 

 be refined through artificial photochemical 

 processes. 



Lately we have been interested intensely 

 by the changes that some substances of the 



