Single-walled carbon nanotubes (SWNTs) induce the decomposition of four diacyl peroxides by single electron transfer (SET). Phthaloyl peroxide functionalizes SWNTs to the greatest extent of the four. It was also found that t-butoxy radicals add to SWNTs but that SWNTs fail to inhibit cumene autoxidation. Thus, SWNTs are reactive to alkoxy radicals but not to alkylperoxy radicals.The great potential value of functionalizing single-walled nanotubes (SWNTs) has led a number of workers to explore free radical attack on the sidewalls of these unique nanometersized objects. 1,2 The most common radical precursors are diazonium salts 3 and peroxides, 4-8 but other approaches are based on Fenton's reagent, 6 perfluoroalkyl iodides, 9,10 perfluoro azo compounds, 11,12 microwave discharge of ammonia, 13 and attack of growing polymer chains. 14 Presently, we report the kinetics of diacyl peroxide thermolysis in the presence of SWNTs, which reveal moderate to large rate accelerations attributed to induced decomposition. We further report the attack of t-butoxy radicals on SWNTs and the failure of SWNTs to inhibit the autoxidation of cumene.While studying the thermolysis of benzoyl peroxide (BP) with SWNTs, we noticed that the rate of gas evolution, as monitored by a pressure transducer, was accelerated by inclusion of purified, pristine HiPco SWNTs. 15 Thus, a solution of 75 mg BP in 10 mL ortho-dichlorobenzene (o-DCB) exhibited a 67% greater pressure rise over the course of 2 h at 80°C when SWNTs (5 mg) were included than a control experiment without SWNTs. This rate enhancement was confirmed by iodometric titration 16 of the BP remaining after thermolysis. All titration studies discussed below were performed in non-degassed o-DCB using purified HiPCo SWNTs batch no. 164-2 produced in the Rice University Carbon Nanotechnology Laboratory. 17 Comparison of non-degassed with degassed o-DCB gave essentially the same percent peroxide decomposition whether SWNTs were present or not. Figure 1 shows the percent BP consumed in 1 h at 80°C and 90°C in 50 mL o-DCB as the initial weight of SWNTs was increased from 0 to 5 mg. Although the rate enhancement due to SWNTs is apparent, a number of control experiments were required. The thermolysis of 0.006 M BP in o-DCB at 80°C is slow enough that hardly any decomposition (∼1%/hr) was detectable. We ran the thermolysis in benzene as a control and obtained about 6%/hr decomposition, corresponding to the rate reported in the literature. 18,19 Therefore o-DCB does not induce BP thermolysis as much as benzene does and no correction was needed for residual thermolysis at 80°C. (cf. Figure 1). However, at 90°C BP in o-DCB thermolyzes at a moderate rate, as evidenced by the 17% decomposed in 1 h even without added SWNTs. The steep rise in % BP consumed at low [SWNT] is seen in most runs where normal peroxide thermolysis was important. After this initial jump, BP consumption rises more or less linearly with increasing amounts of SWNTs.The same effect was observed in p-methoxybenzoyl peroxide (p-MeO-...
[reaction: see text] Although some aspects of azoxy group radical chemistry have been investigated, unhindered alpha-azoxy radicals remain poorly understood. Here we report the generation of alpha-azoxy radicals under mild conditions by irradiation of alpha-azoxy ketones 4a,b. These compounds undergo alpha-cleavage to yield radicals 5a,b, whose oxygen atom then recombines with benzoyl radicals to produce presumed intermediate 15. Formal Claisen rearrangement gives alpha-benzoyloxyazo compounds 8a,b, which are themselves photolabile, leading to both radical and ionic decomposition. The ESR spectrum of 5a was simulated to extract the isotropic hyperfine splitting constants, which showed its resonance stabilization energy to be exceptionally large. Azoxy compounds have been found for the first time to be good quenchers of triplet excited acetophenone, the main sensitized photoreaction of 7Z in benzene being deoxygenation. While this reaction has been reported previously, it was always in hydrogen atom donating solvents, where chemical sensitization occurred. The principal direct irradiation product of 4bZ and model azoxyalkane 7Z is the E isomer, whose thermal reversion to Z is much faster than that of previously studied analogues.
The azoxy functional group, though relatively uncommon, is found in several natural products and in liquid crystalline compounds. Azoxyalkanes are generally very stable to heat and light and are not subject to attack by radicals. Intramolecular radical reactions, however, can lead to cyclic aminyl nitroxides and hydrazyls, which rearrange further or undergo fragmentation. The azoxy group greatly stabilizes an attached carbon-centered radical but the chemistry of the resulting α-azoxy radicals is not completely understood.
A general method for the synthesis of g-nitro alcohols 1 via C-C-cross-coupling of nitro compounds 3 with silyl derivatives of nitro compounds 4, deoximination of resulting substrates and selective reduction of carbonyl group of ketones 2 is elaborated.
A New Strategy for the Synthesis of γ-Nitro Alcohols from Aliphatic Nitro Compounds. -Deoximation of previously reported adducts of two aliphatic nitro compounds with Jones reagent followed by reduction of the resulting ketone with BH3·THF provides a simple procedure for the synthesis of the title compounds. -(KUNETSKY, R. A.; DILMAN, A. D.; TSVAYGBOYM, K. P.; IOFFE*, S. L.; STRELENKO, Y. A.; TARTAKOVSKY, V. A.; Synthesis 2003, 9, 1339-1346; Zelinsky Inst. Org. Chem., Russ. Acad. Sci., Moscow 117913, Russia; Eng.) -Mais 47-074
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