190 



LIGHT AND LI IE 



aqueous solution of luminol (pH ca. 11) is dark both at room 

 temperature and at 75° C. When a small amoimt of a free-radical- 

 forming compound such as azoisobutyronitrile, or better, benzoyl 

 peroxide is added to the hot solution, light is emitted. The emis- 

 sion maximum is at the same wave length (430 niyu,) as the emission 

 from the hydrogen-peroxide-based chemiluminescence. Oxygen gas 

 is required for light production, and this system is therefore very 

 similar to the oxygen-ferricyanide system mentioned earlier. Our 

 working hypothesis for the chemiluminescence in the water systems, 

 based on these facts, is given in Fig. 7. 



N-H 



NH2 O 



NH2 O 



O2 



NH2 O 



Fig. 7. Reatlion scheme lor the clieiiiihuninesteiue ol liiminol hi water. 



A rather different approach to the study of chemiluminescence has 

 been made by several investigators interested in sensitized chemi- 

 luminescence (21) . This phenomenon involves the transfer of energy 

 from an excited molecule to a "foreign" molecule which subsequently 

 emits a photon. There seems to be no evidence, however, that this 

 can occur with the excited species in the luminol reaction (29) . 



It is apparent that the study of chemiluminescence in water sys- 

 tems has not been very successful. Part of the difficulty can be at- 

 tributed to the use of powerful oxidizing agents that degrade the 

 products which one might normally want to isolate. A system which 

 is free of hydrogen peroxide and oxidizing agents consists of luminol, 

 hot 30^% potassium hydroxide, and oxygen. The efficiency of this 

 system is, however, very low. To date, we have been able to carry 

 out efficient chemiluminescent reactions under mild conditions only 

 in organic solvents. 



