Autoxidation


Autoxidation, which is a kind of degradation reaction, may be found in many different chemical fields. They are common in combustion reactions, drug degradation, and degradation of surfactants and fragrances, to mention only a few.

Advanced quantum mechanical (QM) computer simulations may be used to calculate how prone a molecule is to autoxidation and which part of the molecule is most sensitive to autoxidation. It is also possible to use QM computer simulations to find out how to increase or decrease the sensitivity of the molecule towards autoxidation, as well as to explore reaction mechanisms and the product stability.  When computer simulations are used correctly, they are a very powerful tool to support and to design experiments. Also, when used correctly, computer simulation results together with laboratory results are important for understanding the theory behind the reactions that are explored.

Today it is desirable to limit animal testing. Computer simulations do not replace animal experiments. However, the knowledge obtained from computer simulations together with laboratory work lead to increased understanding and helps to minimize the need for animal testing.

Wendelsbergs beräkningskemi has more than 15 years’ experience of these kinds of reactions. Some of  the published work is found here.

Autoxidation is a kind of chain reaction that takes place when a compound is exposed to oxygen and that generates peroxides and hydroperoxides, but also aldehydes and other kinds of products may be produced.

As in all chain reactions, the reaction product catalyzes the reaction. After initiation, the reaction becomes self-catalyzing and continues until termination where for example two radicals combines to form a stable product. The scheme below shows an overview of a simplified autoxidation reaction consisting of 4 steps, and where oxygen adds to 2-methyl-pentene.

Step 1 is the initiation step, in here represented by a radical “I•” that abstracts a hydrogen atom from 2-methyl-pentene, forming “IH” and a 2-methyl-pentene radical.
The propagation step consists of step 2 and step 3, i.e. the chain reaction itself, which continues until the reactants are finished or until two of the formed radicals react with each other instead of continuing the propagation.
Step 2 is the first part of the propagation step. In this step the oxygen molecule adds to the 2-methyl-pentene radical, forming a peroxy radical.
Step 3 is the second part of the propagation step. In this step a hydroperoxide is formed together with a new 2-methyl-pentene radical. The latter may then react according to step 2 again.
Step 4 is the terminating step where two radicals reacts and form a stable product.

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