| Abstract
| - The oxidation of cyclohexane by the H2O2−trifluoroacetic acid system is revisited. Consistent witha previous report (Deno, N.; Messer, L. A. Chem. Comm. 1976, 1051), cyclohexanol forms initiallybut then esterifies to cyclohexyl trifluoroacetate. Small amounts of trans-1,2-cyclohexadiyl bis(trifluoroacetate) also form. Although these products form irrespective of the presence or absenceof O2, dual mechanisms are shown to operate. In the absence of O2, the dominant mechanism is aradical chain reaction that is propagated by CF3• abstracting H from C6H12 and SH2 displacementof C6H11• on CF3CO2OH. The intermediacy of C6H11• and CF3• is inferred from production of CHF3and CO2 along with cyclohexyl trifluoroacetate, or CDF3 when cyclohexane-d12 is used. In thepresence of O2, fluoroform and CO2 are suppressed, the reaction rate slows, and the rate lawapproaches second order (first order in peracid and in C6H12). Trapping of cyclohexyl radicals byquinoxaline is inefficient except at elevated (∼75 °C) temperatures. Fluoroform and CO2, telltaleevidence for the chain pathway, were not produced when quinoxaline was present in roomtemperature reactions. These observations suggest that a parallel, nonfree radical, oxenoid insertionmechanism dominates when O2 is present. A pathway is discussed in which a biradicaloid-zwiterionictransition state is attained by hydrogen transfer from alkane to peroxide oxygen with synchronousO−O bond scission.
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