TWO DIFFERENT PRIMARY FOUR QUANTA PROCESSES 163 



photoxidation processes of the type (7.10a). In the second place, they 

 postulated that the intermediary catalyst, HZ, which reduces X to HX, , 

 is an organic hydroxyl compound, ROH. Upon its dehydrogenation to 

 a radical, RO, this catalyst was assumed to oxidize water, forming an 

 organic hydroperoxide, ROOH, which finally dismutates, restoring ROH 

 and liberating oxygen. This special mechanism of catalytic water 

 oxidation will be compared with the mechanism (7.4) in chapter 11 

 (page 189). The hypothesis of Franck and Herzfeld is represented by 

 the formulae (7.12) and the reaction scheme 7.VA. 



(7.12) 2 H2O + {CO2I "—^ {CH2OI + H2O + O2 



A characteristic assumption in scheme 7.VA is that all intermediary 

 products (designated by asterisks) are stabilized by one and the same 

 catalyst (Eb), to protect them from back reactions. The assumption of 

 a common effect of a catalyst on four different intermediates on the 

 "reduction side" of the primary photochemical process, and on one 

 intermediate "on the oxidation side" is not very plausible. The number 

 of different photochemical products requiring catalytic stabilization could 

 be reduced from five to two by combining (7.10a) with (7.8), instead 

 of with (7.7), thus arriving at a scheme similar to 7.V except for the 

 elimination of the intermediate oxidation-reduction system HY-Y — a 

 change which makes (CO2} a direct participant in the primary photo- 

 chemical process: 



(7.13a) 4X + 4HZ > 4 HX + 4 Z 



(7.13b) 4HX + 4{C02! ^4X4-4{HC02l 



(7.13c) 4Z + 4H2O )-4HZ + 2H2O + O2 



(7.13d) 4 {HCO2} > 3 CO2 + CH2O + H2O 



(7.13) 4 {CO2I + 4 H2O "-^ 3 CO2 + 3 H2O + {CH2O) + O2 



