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An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.
These catalysts initiate radical chain reactions, autoxidation that produce organic radicals that combine with oxygen to give hydroperoxide intermediates. Generally the selectivity of oxidation is determined by bond energies. For example, benzylic C-H bonds are replaced by oxygen faster than aromatic C-H bonds. [2]
Catalysts: There are two types of catalysts, positive and negative. Positive catalysts increase the reaction rate and negative catalysts (or inhibitors) slow down a reaction and possibly cause the reaction not occur at all. The purpose of a catalyst is to alter the activation energy.
A catalyst is able to reduce the activation energy by forming a transition state in a more favorable manner. Catalysts, by nature, create a more "comfortable" fit for the substrate of a reaction to progress to a transition state. This is possible due to a release of energy that occurs when the substrate binds to the active site of a catalyst ...
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The disadvantage with a copper catalysts is that it is very sensitive when it comes to sulfide poisoning, a future use of for example a cobalt- molybdenum catalyst could solve this problem. The catalyst mainly used in the industry today is a copper-zinc-alumina (Cu/ZnO/Al 2 O 3) based catalyst.
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An example of a positive non-linear effect is observed in the case of Sharpless epoxidation with the substrate geraniol. [7] In all cases of chemical reactivity exhibiting (+)-NLE, there is an innate tradeoff between overall reaction rate and enantioselectivity.