HENRY UNSCHITZ 



175 



(U 

 I. 

 ■p 



</> 



o 



E 



o 



X 



X 



o 



1_ 

 <u 



Q- 



2.0 



/.5_ 



l.O 



0.5 _ 



_4.0 



_3.0 



-2.0 



-1.0 



■p 



1/1 



o 



E 



o 



h- 



C 



N 



/oo 



200 JOO 



TTme (minutesj 



400 



500 



Fig. 1. Decomposition of tetralin hydroperoxide (uncatalyzed and catalyzed) and 

 zinc tetraphenyloporphine, in /-butyl benzene, at 148°C. 



tion and luminescence-time data, read from these curves, as well as 

 specific rate constants for the various decays. These constants were 

 obtained by first establishing values of the actual rates at various 

 times by drawing tangents to the curves of Fig. 1, and then dividing 

 these rates by suitable powers of the corresponding reagent concen- 

 trations. In Table 1, the intensity of luminescence is measured by 

 the photometer galvanometer. This intensity is itself a rate (of 

 photon emission in photometer units) and thus may be compared 

 directly with the chemical rates. Correction is made in Table 1 for 

 the uncatalyzed decomposition of peroxide, by making the dubious 

 assumption that the uncatalyzed rate applies also in the presence of 

 active porphyrin. In the case presented, this correction is small and 

 introduces no essential change in the kinetic characteristics. 



1. Rate lotus. It is evident from Table 1 that the peroxide de- 

 composition rate accurately parallels the luminescence intensity (/) . 

 Both rates show good second-order kinetics (first order in both per- 

 oxide and porphyrin) over most of the course of reaction, and both 



