EMIL H. WHITE 191 



The Clie»iilunii)ics(cnt Reaction in Organic Solvents 



The hydrogen-peroxide— hmiinol systems discussed in the previous 

 section can be carried out without much change in solvents such as 

 acetone and ethanol. An interesting mixture from which a deep blue 

 light is obtained consists of luminol, hydrogen peroxide, ammonia, 

 a trace of copper, and glycerin as the solvent. When organic solvents 

 are used, alkyl hydroperoxides can be substituted for hydrogen per- 

 oxide if iron catalysts such as the iron-polyamine complexes (II) are 

 used; copper is not a catalyst under these conditions. These systems 

 are actually not much different than the corresponding ones in water. 



A major change in the chemiluminescent reaction occurs, however, 

 when certain weakly acidic, highly polar organic solvents are used; 

 only luminol, oxygen, and a base are required, and the light emis- 

 sion is superior to that observed in water. Dimethyl sulfoxide is the 

 best of the solvents that we have tested and dimethyl formamide is 

 the second best. The advantage of using solvents of this type is that 

 bases stronger than hydroxide ion can be used. We normally use 

 /-butoxide ion (j^repared from the alcohol and potassium metal); 

 with this base, the dianion of luminol is formed and, as will be shown 

 later, this ion can react directly with oxygen. 



Base 



Luminol + O2 > Light 



The reaction is thus similar in general outline to a number of other 

 chemiluminescent reactions (Fig. 8) (12, 14, 20) . 



These equations illustrate the interesting fact that in most, if not all, 

 chemiluminescent and bioluminescent reactions at room temperature, 

 oxygen is a reactant. (See McElroy and Seliger, this symposium) . 

 The ground state of oxygen is a triplet state, and the significance 

 of the oxygen requirement may be that, in these cases, adducts of 

 oxygen and the organic molecules are formed with no re\"ersal of 

 an electron spin; i.e., the adducts may be formed directly in a triplet 

 excited state. 



The products of the luminol chemiluminescence in dimethyl sulf- 

 oxide are nitrogen and 3-aminophthalate ion (Fig. 9) . The nitrogen 

 was identified and measured by gas-liquid chromatographic tech- 

 niques. The aminophthalate ion was determined as dimethyl 3- 

 aminophthalate; this ester was obtained in 89 per cent yield from 

 the successive treatment of the reaction mixture with hydrochloric 

 acid and diazomethane. Since the quantum yield for the reaction in 

 dimethyl sulfoxide was found to be 0.1 and since it is unlikely that 



