Cooxidation not to be Confused with Catalysis: A Chemical Education Article to Physical-organic Chemists

Two substrates (A) and (B) are oxidized separately by an oxidant (Oxi) with the rate constants k1 and k2 and they are oxidized taken together (A + B) under similar conditions with a rate constant k3, if the value of k3 = (k1 + k2), then it is said to be an example of two reactions “going parallel”. If the value of k3 >>>> (k1 + k2), then the redox process is termed as “co-oxidation” (Hasan and Rocek 1972, JACS). In this process in the mixture the two substrates are oxidized synchronously by a direct three electron transfer route if the oxidant happens to be Cr(VI) and by a direct four electron transfer route if the oxidant happens to be Mn(VII) (Jagannadham et al., 1986, Oxidation Communications). It was realized that the essential condition of the synchronous oxidation of two substrates A and B is that one substrate must have two functional groups and the other must have one functional group or vice-versa. The compound with two functional groups must be a good chelating agent with the metal ion oxidant. A substrate (A) is oxidized by an oxidant (Oxi) with a rate a constant k4 and is oxidized in presence of a catalyst (Cat) with a rate constant k5, if k5 > k4 the redox process is termed as “catalyzed process”. It is to be noted that in the catalytic process the catalyst (Cat) is not oxidized and its concentration does not change during the reaction. It only increases the rate of oxidation with lower activation energies. If k5 = k4 it is to be understood that there is “no catalysis”. If k5 < k4 it is to be understood that the catalyst is called a negative catalyst or “inhibitor” and the reaction goes with higher activation energy. In this paper a lucid description is given for the two processes “co-oxidation” and “catalysis” with putative examples. Keyword: Cooxidation,Catalysis, Chemical education.