EMIL H. WHITE 189 



There is, furthermore, no evidence for the formation of the azo 

 compound XVII in the luminol chcmihuninescence. Albrecht (1) 

 and Rautsky (18) proposed that XVII was a reaction intermediate, 

 and both of them attempted to prepare XVII from knninol. They 

 were unable to isolate it because of its instability, and their tests 

 were run on the crude material. Albrecht's observations can be 

 accounted for by the presence of luminol in the crude samples which 

 he used, and this may also be the explanation for Kautsky's results. 

 We have examined the relatively stable azo compound XVIII (Fig. 5) 



Uv^JLc-N-N-C-\^ 



II - . .. 

 O H H O 



xrx 



Fig. 



and compared it with dibenzoylhydrazine (Fig. 5, XIX) , The hy- 

 drazide is chemiluminescent, but the azo compound is not. Further- 

 more, the products obtained from the two reactions are different. 

 Only benzoic acid was obtained from the hydrazide XIX, whereas 

 approximately equimolar amoinits of benzoic acid and benzaldehyde 

 were obtained from XVIII (Fig. 6) . 



O O 



" 11 



R-C-N=NtC.-R > RCOoH + No+ RCHO -»• OH 



er ^ 



T" '^ '7 



HO-^ Ht-O-H 



Fig. 6. 



The above discussion is intended to show that there is actually no 

 unambiguous experimental evidence supporting any of the mechan- 

 isms that have been proposed for the chemiluminescence of Luminol. 

 Practically the only facts available for a discussion of the mechanism 

 are the following: (1) oxygen is required (6) ; (2) the anion of 

 luminol is the reactant (K^ for luminol ^ 10-") (26) ; (.S) free 

 radicals are involved; and (4) nitrogen is a product of the reaction. 

 The requirement for radical intermediates is based largely on the 

 observation that radical chain stoppers inhibit the chemiluminescence 

 (5b, 23, 26) , and on experiments such as the following. A basic 



