Origin of byproducts during the catalytic autoxidation of cyclohexane.
The formation of byproducts during the Co(acac)2 and Cr(acac)3-catalyzed cyclohexane autoxidation is compared with the noncatalyzed thermal process. CoII ions seem to cause only a moderate perturbation of the reaction mechanism, causing a fast conversion of the cyclohexyl hydroperoxide via a redox cycle, rather than via abstraction of the alphaH-atom by chain carrying peroxyl radicals. Nevertheless, both the radical propagation and the CoII-induced decomposition of the hydroperoxide cause the formation of cyclohexoxy radicals that are partially transformed to 6-hydroxyhexanoic acid, the major primary byproduct for these systems. However, during the CoII-catalyzed reaction, the concentration of cyclohexanone increases much faster than that of the hydroperoxide, causing the ketone to take over the role of dominant byproduct source. A mechanism for the conversion of cyclohexanone to ring-opened byproducts is put forward. Cr(acac)3 seems to catalyze additional reactions, some of them probably leading directly to byproducts. Indeed, the evolution of (by)products is significantly different from the CoII-catalyzed and the thermal systems, in the sense that they all seem to be primary in origin.
Hermans
Ive
I
Centre for Surface Chemistry and Catalysis, Department of Microbial and Molecular Systems (M2S), K. U. Leuven, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium. ive.hermans@chem.ethz.ch
Peeters
Jozef
J
Jacobs
Pierre A
PA
D002208:Caproates / Q000737:chemistry; D002384:Catalysis; D002857:Chromium / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D003510:Cyclohexanes / Q000737:chemistry*; D003512:Cyclohexanones / Q000737:chemistry; D005609:Free Radicals; D006880:Hydroxy Acids; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010545:Peroxides; D013696:Temperature
D002208:Caproates; D003510:Cyclohexanes; D003512:Cyclohexanones; D005609:Free Radicals; D006880:Hydroxy Acids; D010545:Peroxides; D002857:Chromium; C049375:perhydroxyl radical; D003035:Cobalt; C039565:6-hydroxyhexanoic acid; C506365:Cyclohexane; C036468:cyclohexanone; D010100:Oxygen