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A novel class of catalysts for alkane oxidation with molecular oxygen was examined. N-Hydroxyphthalimide (NHPI) combined with Co(acac)(n)() (n = 2 or 3) was found to be an efficient catalytic system for the aerobic oxidation of cycloalkanes and alkylbenzenes under mild conditions. Cycloalkanes were successfully oxidized with molecular oxygen in the presence of a catalytic amount of NHPI and Co(acac)(2) in acetic acid at 100 degrees C to give the corresponding cycloalkanones and dicarboxylic acids. Alkylbenzenes were also oxidized with dioxygen using this catalytic system. For example, toluene was converted into benzoic acid in excellent yield under these conditions. Ethyl- and butylbenzenes were selectively oxidized at their alpha-positions to form the corresponding ketones, acetophenone, and 1-phenyl-1-butanone, respectively, in good yields. A key intermediate in this oxidation is believed to be the phthalimide N-oxyl radical generated from NHPI and molecular oxygen using a Co(II) species. The isotope effect (k(H)/k(D)) in the oxidation of ethylbenzene and ethylbenzene-d(10) with dioxygen using NHPI/Co(acac)(2) was 3.8.

We performed first-principles calculations to simulate the grain boundary decohesion in ferromagnetic bcc iron ͑Fe͒ ⌺3͑111͒ symmetrical tilt grain boundaries by progressively adding solute atoms ͓sulfur ͑S͒ or phosphorous ͑P͔͒ to the boundaries. We show that there are two mechanisms of decohesion: ͑i͒ fracture surface stabilization with reference to the grain boundary by the segregated solute atoms without interaction between them, and ͑ii͒ grain boundary destabilization by a repulsive interaction among the segregated and neighboring solute atoms. It is found that the dominant mechanism for the S-induced decohesion is the former ͑i͒, while that for P is the latter ͑ii͒. This difference makes P a much weaker embrittling element comparing with S because the mechanism ͑ii͒ simultaneously brings about the reduction of the grain boundary segregation energy.

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