Nitroxide chemistry. Part II. Reaction of bistrifluoromethyl nitroxide with some alkanes and alkenes; free-radical dehydrogenation of alkanes to alkenes

Abstract

Methane resists attack by bistrifluoromethyl nitroxide at room temperature, but hydrogen abstraction occurs with ethane [→ EtR, RCH₂·CH₂R, MeCOR; R =(CF₃)₂N·O throughout this paper], propane (→ PrⁱR, MeCHR·-CH₂R, Me₂CO), isobutane (→ Bu^tR, Me₂CR·CH₂R), isopentane (→ Me₂CREt, Me₂CR·CHRMe, RCH₂·-CRMeEt), and neopentane (→ Bu^tCH₂R, Bu^tCOR). Reaction of the nitroxide with 3-methylbut-1-ene at room temperature leads to rapid abstraction of the allylic tertiary hydrogen and formation of a 1 : 1 mixture of the isomeric butenes Me₂CR·CH:CH₂ and Me₂C:CH·CH₂R in almost quantitative yield. Addition predominates over hydrogen abstraction when isobutene, 2-methylbut-1-ene, 2-methylbut-2-ene, or tetramethylethylene is treated with bistrifluoromethyl nitroxide.

The alkane–nitroxide reactions are believed to involve olefin formation via hydrogen abstraction from the alkyl radicals formed initially. This was proved in the case of isobutane by trapping the isobutene formed with hydrogen chloride.