Mechanistic study under atmospheric

Mechanistic studies on the formation of PPS from polymerization of copper(I) 4-bromobenzenethiolate in quinoline under inert atmosphere at 200°C have been pubUshed (91). PPS synthesized by this synthetic procedure is characterized by high molar mass at low conversions and esr signals consistent with a single-electron-transfer mechanism, the Sj l-type mechanism described earlier (22). 

Complex 5 was more active than the well-known precious-metal catalysts (palladium on activated carbon Pd/C, the Wilkinson catalyst RhCl(PPh3)3, and Crabtree s catalyst [lr(cod)(PCy3)py]PFg) and the analogous Ai-coordinated Fe complexes 6-8 [29] for the hydrogenation of 1-hexene (Table 2). In mechanistic studies, the NMR data revealed that 5 was converted into the dihydrogen complex 9 via the monodinitrogen complex under hydrogen atmosphere (Scheme 4). 

Alkenes. The available kinetic and mechanistic data show that under atmospheric conditions the reaction of HO radicals with alkenes proceeds predominantly via addition of the HO radical to the carbon-carbon double bond(s) [30]. The energized HO-adducts which result are rapidly thermalized to yield HO-substituted alkyl radicals which, in turn, undergo subsequent free-radical reactions leading to the formation of molecular products. Thus, the possible reactions in the HO-inidated oxidation are, in many respects, analogous to those of alkyl radicals described in the preceding section. Product studies on these reactions have mainly been made by the FTIR method [109-112]. 

Direct Kinetic and Mechanistic Study of the OH-Dimethyl Sulfide Reaction Under Atmospheric Conditions... 

In the effort to find confirmation on Foote s original mechanistic proposal [84] and discriminate among these two different pathways, a great deal of experimental proofs were achieved. First of all, the DCA and/or 9-cyanoanthracene (CNA)-sensitized reactions on aryl-olefins were studied under inert atmosphere by flash spectroscopic techniques obtaining clear evident for the formation of both olefin radical cations and cyanoaromatic radical anions [95]. In the presence of oxygen, the cyanoaromatic radical anions were rapidly removed, supporting the very rapid formation of superoxide ion and so its direct involvement in these photoinduced oxygenations. 

An analysis of the aging process in the alkylation of benzene with ethylene over a rare earth-exchanged X zeolite (REX) (43) provides insight into the physicochemical phenomena operative. In this reaction, a catalyst lifetime of over 792 hours was observed at 204°, benzene ethylene molar ratio of 5, and pressure of 500 psig. Under similar conditions, but at atmospheric pressure, a drastic increase in the rate of catalyst aging was observed, with catalytic activity lasting only 2 to 3 hours. Subsequent mechanistic studies showed that most of the catalyst aging in this reaction could be attributed to complex, temperature-dependent side reactions of ethylene (44,44a). 

The kinetics and products of the gas-phase alkene-03 reaction have been studied extensively (Atkinson et al. 2000) and are reasonably well understood for a large number of the smaller alkenes. The major mechanistic issue concerns the fate, under atmospheric conditions, of the initially energy-rich Criegee biradical, which can be collisionally stabilized or can undergo unimolecular decomposition ... 

Cytochrome P-450 Catalyzed Reactions - Studies with 02 have established that the cytochrome P-450 mediated hydroxylation of camphor by the bacterial enzyme and the enzyme purified from rat liver results in the incorporation of atmospheric oxygen in the 5-exo-hydroxylation product. Cumene [ 02]hydroperoxide will transfer its peripheral oxygen atom to a variety of compounds which serve as substrates for mammalian cytochrome P-450. As expected, 02 served as the oxygen source for the bacterial cytochrome P-450 catalyzed epoxidation of 5,6-dehydrocamphor.N-Hydroxy-methylcarbazole, formed by the cytochrome P-450 catalyzed oxidation of N-raethylcarbazole, incorporates 0 exclusively from dioxygen. Under anaerobic conditions cytochrome P-450 may catalyze the intramolecular transfer of oxygen present in tertiary amine N-oxides. Mechanistic studies on S-dealkylation and S-oxidation reactions also have used tracer methods. ... 

Multlnuclear NMR studies at atmospheric pressure, i.e., under less extreme conditions, have yielded valuable structural and mechanistic information on transition metal carbonyl clusters and both the above limitations suffered by infrared spectroscopy have now been overcome by measuring high resolution NMR spectra at high pressure. Well-resolved NMR spectra, with excellent slgnal/nolse, have been obtained on the catalytic system involved In the formation of ethylene glycol. 

The M—(NO ) and M—(HNO) (M = Fe, Ru) complexes described in this work have been shown to be reactive under an oxygen atmosphere, either in nonaqueous or aqueous media, though no kinetic/mechanistic studies are available (13—15). Once the speciation of the NO /HNO complexes is known, there is an obvious need to make advances in the studies on this type of reactivity, particularly in biorelevant aqueous media, with a need of disclosing the similarities and differences with autoxidation reactions of = 7 complexes, like those described in Section 3.4 for [Fe(CN)sNO] and other related nonheme and heme-lMXsNO ions. 

Kinetic and mechanistic studies of the ozonolysis of alkenes under atmospheric conditions,... 

Yamamoto and colleagues were able to develop an additive-free palladium catalyst system for the oxidative carbonylation of alkynes [87, 88]. By using their palladium-phosphine catalyst in the presence of molecular oxygen, acetylene-carboxylates were formed under atmospheric pressure of CO at room temperature. A detailed mechanistic study was also carried out proposing a reductive elimination of a palladium species with methoxycarbonyl and alkynyl residues. The oxidation of Pd(0) to Pd(II) species was confirmed to proceed cleanly with... 

In 2016, Xu and coworker reported another TM-fee aerobic Al-alkylation method for anilines, some heteroarylamines, and sulfinamides with alcohols (Scheme 49) [209]. As described in their work, these amines are not effective substrates under anaerobic catalyst-free autocatalyzed conditions, so an oxidant has to be employed to initiate the reaction. Differing from Yao and Zhao s protocol by adding O2 to an argon atmosphere [208], they found that a catalytic amount of air is active enough to initiate the reaction. In addition to primary alcohols, secondary alcohols can also be used as the aUcyl source. In mechanistic studies, the authors observed that primary and secondary alcohols underwent different initiation processes, i.e., primary alcohols require the presence of the amine to facilitate the aerobic oxidation to... 

It is interesting to note that a mechanistic study carried out on the palladium-catalyzed biphasic carbonylation of iodobenzene has shown that an indirect route to produce benzoic acid involves benzoic anhydride [35]. For instance, isolation of [Pd(/x-OH)Ph(PPh3)l2 and further reaction with Phi under a CO atmosphere leads to [Pd(/u.-I)(COPh)(PPh3)]2, (PhC0)20... 

Consideration of the relative concentrations of various oxidants in the marine boundary layer leads to the conclusion that reaction with O3, along with CH3SOO adduct formation, is likely to be the dominant fate of the methyl thiyl radical under typical atmospheric conditions. The CH3S+O3 reaction has been the subject of several kinetic and mechanistic studies (see Table 3) the rate coefficient for this reaction has been found to exhibit a slight negative activation energy (295-367 K) and no dependence on pressure (75-325 Torr He) [59]. The mechanism of the CH3S-1-O3 reaction remains uncertain. The thermodynamically viable reaction channels include reactions (6a) to (6f) [61J ... 

An intriguing oxidative coupling of indoles with a-amino ketones can selectively afford a-aryl a-imino and a-aryl a-oxo carbonyl compounds under argon and air atmosphere, respectively (Scheme 2.8) [38]. The mechanistic studies demonstrated that stronger oxidizing conditions favored the hydrolysis process, and the traditional acidification hydrolysis is unlikely. Later, oxidative phosphonation and alkylation of a-amino ketones with diarylphosphine [39] and ethers [40] were reported. 

Kelly, T., V. Bossoulrot, I. Magneron, K. Wirtz, J. Treacy, A. MeUouki, H. Sidebottom, and G. Le Bras (2005), A kinetic and mechanistic study of the reactions of OH radicals and Cl atoms with 3,3,3-trifluoropropanol under atmospheric conditions, J. Phys. Chem. A, 109, 347-355. 

In addition to the thermal decomposition the photochemical reaction of geminal diazide 62 was also studied. Irradiation of an acetone solution of 62 under an inert gas atmosphere afforded a complex mixture of products which could not be separated or identified. However, if the reaction was carried out in the presence of oxygen the uracil derivative 66 was obtained in 48 % yield. Surprisingly, in addition to the oxidation of the CH2 group, the 6-diazidomethyl function was completely lost during the reation [91JCS(P1)1342]. At the present time no mechanistic explanation for this unusual behavior can be presented. On the other hand, photooxidation of compound 63 leads straightforward to compound 67 [91 JCS(P1)1342],... 

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