Internal oxygen transfer

Inspection of models shows that this internal oxygen transfer is energetically favorable in the case of the 14,15-double bond by way of a 15-membered strain-free cyclic structure. The same sequence of reactions was also reported for the 5,6-dihydro derivative of 1. Internal epoxidation does not appear to be favorable in the case of a double bond in the 9,10-position of a peroxy acid (peroxyoleic acid). 

Checking the absence of internal mass transfer limitations is a more difficult task. A procedure that can be applied in the case of catalyst electrode films is the measurement of the open circuit potential of the catalyst relative to a reference electrode under fixed gas phase atmosphere (e.g. oxygen in helium) and for different thickness of the catalyst film. Changing of the catalyst potential above a certain thickness of the catalyst film implies the onset of the appearance of internal mass transfer limitations. Such checking procedures applied in previous electrochemical promotion studies allow one to safely assume that porous catalyst films (porosity above 20-30%) with thickness not exceeding 10pm are not expected to exhibit internal mass transfer limitations. The absence of internal mass transfer limitations can also be checked by application of the Weisz-Prater criterion (see, for example ref. 33), provided that one has reliable values for the diffusion coefficient within the catalyst film. 

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