Oxidation mechanistic studies

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. ... 

Rueping reported a combined photoredox- and palladium-catalyzed system that allows for the synthesis of 3-acylindole 101 under mild conditions starting from aniline lOO.This procedure obviates the need for large amounts of an external oxidant mechanistic studies showed the oxidation was achieved by either (1) the photoredox catalyst (in the absence of oxygen) or (2) an in situ formed superoxide anion (in the presence of oxygen and pho-toredox catalyst). This allows for the synthesis of oxidant-sensitive substrates and an improved scope (14AG(I)13264). 

The oxidation of terminal olefins to ketones with dioxygen is catalyzed by rhodium(I) phosphine complexes. The phosphine is co-oxidized to the phosphine oxide. Mechanistic studies show that the active intermediate contains a ir-bonded olefin and dioxygen is... 

In 2009, Fagnou et al. discovered a Rh(III)-catalyzed synthesis of substituted isoquinolines 45 by oxidative annulation between N-tBu aromatic aldimines and internal alkynes [28a]. The -Bu leaving group was eliminated as isobutene in the reaction process and avoided the generation of a mixture of isoquinolines. However, the substrate scope was limited to aldimines, and a stoichiometric amount of Cu(0Ac)2-H20 was used as an external oxidant. Mechanistic studies omitted the ort/zo-alkenylation/64 -electrocyclization/oxidation pathway, and intermediate H2 was crucial for the C-N reductive elimination to proceed (Eq. (5.44)). At the same time, Satoh and Miura groups also exploited a Rh(III)-catalyzed oxidative cyclization of N-H benzophenone imine and internal alkynes to give isoquinolines [28b]. Both aromatic and aliphatic alkynes were agreeable for this protocol, but a stoichiometric amount of the Cu(II) salt was required. 

Deuterium oxide (D2O) is water in which the protons ( H) have been replaced by their heav ler isotope deuterium ( H) It is readily available and is used in a vanety of mechanistic studies in organic chemistry and biochemistry When D2O is added to an alcohol (ROH) deuterium replaces the proton of the hydroxyl group... 

Oxidation Step. A review of mechanistic studies of partial oxidation of propylene has appeared (58). The oxidation process flow sheet (Fig. 2) shows equipment and typical operating conditions. The reactors are of the fixed-bed shell-and-tube type (about 3—5 mlong and 2.5 cm in diameter) with a molten salt coolant on the shell side. The tubes are packed with catalyst, a small amount of inert material at the top serving as a preheater section for the feed gases. Vaporized propylene is mixed with steam and ak and fed to the first-stage reactor. The feed composition is typically 5—7% propylene, 10—30%... 

J. W. Hastie and C. L. McBee, Mechanistic Studies ofFriphenylphosphine Oxide-Poly(ethylene terephthalate) and FelatedFlame Fetardant Systems, Feport NBSIF 75-741, Nad. Buieau of Standards Washington, D.C., 1975. 

Because transition metals even in a finely-divided state do not readily combine with CO, various metal salts have been used to synthesize metal carbonyls. Metal salts almost always contain the metal in a higher oxidation state than the resulting carbonyl complex. Therefore, most metal carbonyls result from the reduction of the metal in the starting material. Such a process has been referred to as reductive carbonylation. Although detailed mechanistic studies ate lacking, the process probably proceeds through stepwise reduction of the metal with simultaneous coordination of CO (90). 

A novel Af-oxide (595) was prepared by the solvolysis at room temperature of (594) in 1 1 water-dioxane. A kinetic and mechanistic study of this reaction was carried out. 

The reactions of copper salts with diacyl peroxides have been investigated quite thoroughly, and the mechanistic studies indicate that both radicals and carbocations are involved as intermediates. The radicals are oxidized to carbocations by Cu(II), and the final products can be recognized as having arisen from carbocations because characteristic patterns of substitution, elimination, and rearrangement can be discerned " ... 

During the course of these mechanistic studies a wide range of possible applications of this reaction have been revealed. When the reduction is carried out with lithium aluminum deuteride and the anion complex decomposed with water, a monodeuterio compound (95) is obtained in which 70% of the deuterium is in the 3a-position. Reduction with lithium aluminum hydride followed by hydrolysis with deuterium oxide yields mainly (70 %) the 3j5-di-epimer (96), while for the preparation of dideuterio compounds (94) both steps have to be carried out with deuterated reagents. ... 

This is undoubtedly the most prolific oxidation state for this group of elements. The stereochemistry of Ni" has been a topic of continuing interest (see Panel), and kinetic and mechanistic studies on complexes of Pd" and Pt" have likewise been of major importance. It will be convenient to treat Ni" complexes first and then those of Pd" and Pt"... 

Reference to this oxide is included here to indicate a possible complication that may appear in kinetic and mechanistic studies of sublimation-type reactions, since the vacuum dissociation of V2Os has been shown [655] to produce a variety of molecular entities V4Oi0, V6014, V6012, V408 and V204. Allowance for the complexity of the product mixture must be made in the design of experiments. 

Palladium(II) complexes provide convenient access into this class of catalysts. Some examples of complexes which have been found to be successful catalysts are shown in Scheme 11. They were able to get reasonable turnover numbers in the Heck reaction of aryl bromides and even aryl chlorides [22,190-195]. Mechanistic studies concentrated on the Heck reaction [195] or separated steps like the oxidative addition and reductive elimination [196-199]. Computational studies by DFT calculations indicated that the mechanism for NHC complexes is most likely the same as that for phosphine ligands [169], but also in this case there is a need for more data before a definitive answer can be given on the mechanism. 

A mechanistic study performed by the authors showed that CALB and EtOAc are required for racemization to take place. They claimed that enzyme-catalyzed oxidation of the amine substrate takes place, and a ketone intermediate is produced. The ketone reacts with the substrate to form an enamine. This process results in racemization of the substrate (Figure 4.34). It is not clear how the enzyme and EtOAc could dehydrogenate the amine. 

Mechanistic studies have shown that TBT and certain other forms of trialkyltin have two distinct modes of toxic action in vertebrates. On the one hand they act as inhibitors of oxidative phosphorylation in mitochondria (Aldridge and Street 1964). Inhibition is associated with repression of ATP synthesis, disturbance of ion transport across the mitochondrial membrane, and swelling of the membrane. Oxidative phosphorylation is a vital process in animals and plants, and so trialkyltin compounds act as wide-ranging biocides. Another mode of action involves the inhibition of forms of cytochrome P450, which was referred to earlier in connection with metabolism. This has been demonstrated in mammals, aquatic invertebrates and fish (Morcillo et al. 2004, Oberdorster 2002). TBTO has been shown to inhibit P450 activity in cells from various tissues of mammals, including liver, kidney, and small intestine mucosa, both in vivo and in vitro (Rosenberg and Drummond 1983, Environmental Health Criteria 116). 

Kinetic studies have been reported only for the oxidations by Hg(II) and Tl(III), although the oxidation by Pb(IV) is receiving mechanistic study at the present time. 

This Is also consistent with mechanistic studies on platinum electrodes. Although there are cases, such as In the oxidation of As(III) by platinum oxides (30), the predominating observation Is... 

For some of these reactions detailed mechanistic studies were carried out. As an example, in Scheme 5 the pathway suggested for 1.1-diphenylethylene oxidation with O2 into benzophenon [23] is shown. 

Catalysts include oxides, mixed oxides (perovskites) and zeolites [3]. The latter, transition metal ion-exchanged systems, have been shown to exhibit high activities for the decomposition reaction [4-9]. Most studies deal with Fe-zeolites [5-8,10,11], but also Co- and Cu-systems exhibit high activities [4,5]. Especially ZSM-5 catalysts are quite active [3]. Detailed kinetic studies, and those accounting for the influence of other components that may be present, like O2, H2O, NO and SO2, have hardly been reported. For Fe-zeolites mainly a first order in N2O and a zero order in O2 is reported [7,8], although also a positive influence of O2 has been found [11]. Mechanistic studies mainly concern Fe-systems, too [5,7,8,10]. Generally, the reaction can be described by an oxidation of active sites, followed by a removal of the deposited oxygen, either by N2O itself or by recombination, eqs. (2)-(4). 

Jusys Z, Behm RJ. 2001. Methanol oxidation on a carbon-supported Pt fuel cell catalyst—A kinetic and mechanistic study by differential electrochemical mass spectrometry. J Phys ChemB 105 10874-10883. 

Samjeske G, Miki A, Ye S, Osawa M. 2006. Mechanistic study of electrocatal3dic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy. J Phys Chem B 110 16559-16566. 

Aldehydes can be oxidized to carboxylic acids by both Mn(VII) and Cr(VI). Fairly detailed mechanistic studies have been carried out for Cr(VI). A chromate ester of the aldehyde hydrate is believed to be formed, and this species decomposes in the rate-determining step by a mechanism similar to the one that operates in alcohol oxidations.209... 

FIGURE 6.42 Oxidation of 3-oxa-chromanol 58 in the presence of 1 equivalent of water mechanistic study hy means of selectively deuterated starting material. The initially formed ortho-quinone dimethide 63 rearranges into styrene derivative 64, which then reacts with water to provide acetophenone 61. 

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