Oxidation in-situ

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

Nitrile A-oxides, under reaction conditions used for the synthesis of isoxazoles, display four types of reactivity 1,3-cycloaddition 1,3-addition nucleophilic addition and dimerization. The first can give isoxazolines and isoxazoles directly. The second involves the nucleophilic addition of substrates to nitrile A-oxides and can give isoxazolines and isoxazoles indirectly. The third is the nucleophilic addition of undesirable nucleophiles to nitrile A-oxides and can be minimized or even eliminated by the proper selection of substrates and reaction conditions. The fourth is an undesirable side reaction which can often be avoided by generating the nitrile A-oxide in situ and by keeping its concentration low and by using a reactive acceptor (70E1169). 

Hi) Preparation of isoxazoles from nitrile N-oxides The reaction between a nitrile //-oxide and an alkyne is so facile that it is usually sufficient to leave an ether solution of the reactants at room temperature to obtain the desired isoxazole in good yield. The reaction is in general sensitive to the size of the substituent on the alkyne but not on the nitrile -oxide. In the case of poorly reactive alkynes, the difficulty may be overcome by generating the nitrile -oxide in situ and keeping its concentration low. 

An interesting combination of enzymatic with non-enzymatic transformation in a one-pot three-step multiple sequence was reported by Waldmann and coworkers [82]. Phenols 125 in the presence of oxygen and enzyme tyrosinase are hydroxylated to catechols 126 which are then oxidized in situ to ortho quinones 127. These intermediates subsequently undergo a Diels-Alder reaction with inverse electron demand by reaction with different dienophiles (Table 4.19) to give endo bicyclic 1,2-diketones 128 and 129 in good yields. 

Nitrobenzene reacts with the O-trimethylsilyl ketene acetal 663 in the presence of tris(dimethylamino)sulfur(trimefhylsilyl)difluoride (Me2N)3S(Me3SiF2) (TASF) to give the O-silylated adduct 1007 a, which can be oxidized in situ, e. g. by bromine, to give the 4-substituted nitrobenzene 1008 in an overall yield of 79% [87] (Scheme 7.28). With less hindered ketene-acetals, however, mixtures of ortho- and para-substituted nitrobenzenes are obtained. Yet, on reaction of 4-fluoronitroben-zene with the cyclic O-trimethylsilyl ketene acetal 1009 the ortho-substitution product 1010 is obtained in 79% yield [87]. 

Room temperature CO oxidation has been investigated on a series of Au/metal oxide catalysts at conditions typical of spacecraft atmospheres CO = 50 ppm, COj = 7,000 ppm, H2O = 40% (RH) at 25 C, balance = air, and gas hourly space velocities of 7,000- 60,000 hr . The addition of Au increases the room temperature CO oxidation activity of the metal oxides dramatically. All the Au/metal oxides deactivate during the CO oxidation reaction, especially in the presence of CO in the feed. The stability of the Au/metal oxide catalysts decreases in the following order TiOj > FejO, > NiO > CO3O4. The stability appears to decrease with an increase in the basicity of the metal oxides. In situ FTIR of CO adsorption on Au/Ti02 at 25 C indicates the formation of adsorbed CO, carboxylate, and carbonate species on the catalyst surface. 

Naval Facilities Engineering Service Center, Chemical Oxidation, In-Situ Technology Web Page. Available atportal.navfac.navy.mil, 2006. 

Another important catalytic reaction that has been most extensively studied is CO oxidation catalyzed by noble metals. In situ STM studies of CO oxidation have focused on measuring the kinetic parameters of this surface reaction. Similar to the above study of hydrogen oxidation, in situ STM studies of CO oxidation are often conducted as a titration experiment. Metal surfaces are precovered with oxygen atoms that are then removed by exposure to a constant CO pressure. In the titration experiment, the kinetics of surface reaction can be simplified and the reaction rate directly measured from STM images. 

The study of the intramolecular nitrile oxide—allene cycloaddition shows, in particular, that dehydration of nitroallene 339 by PhNCO, generates a nitrile oxide in situ, which gives isoxazoline 340 (Scheme 1.36). Thus, the reaction of the more remote double bond with the formation of six-membered ring prevails (405). 

Conjugate addition of RN02 to enones. Primary nitroalkanes and a, (3-enones when activated by alumina form conjugate addition products that are oxidized in situ by alkaline hydrogen peroxide to 1,4-diketones. A similar reaction of nitromethane with a vinyl ketone provides 1,4,7-triketones. 

Butenolides.1 2-Alkylfurans can be converted into 5-alkyl-2(3//)-butenolides by lithiation followed by alkylation with C1B(0CH,)2. The products are unstable, but are oxidized in situ by m-chloroperbenzoic acid exclusively to the butenolides 2. 

Tulevski GS, Miao Q, Fukuto M, Abram R, Ocko B, Ffindak R, Steigerwald ML, Kagan CR, Nuckolls C (2004) Attaching organic semiconductors to gate oxides in situ assembly of monolayer field effects transistors. J Am Chem Soc 126 15048-15050... 

Pyridazine shows a high dipolarophilic activity to benzonitrile oxide. Generation of this nitrile oxide in situ in diethyl ether at 0°C in the presence of 3 equiv of pyridazine affords a stable mono-cycloadduct 92 in 70% yield. In solution, upon standing in contact with the air, the cycloadduct is slowly oxidized to pyridazin-3(2//)-one. The monocycloadduct is still reactive toward benzonitrile oxide and its exposure to 2 equiv of the nitrile oxide affords mainly the bis-cycloadduct 93 (Figure 10) <1996T6421>. 

Extensive studies on diastereoselectivity in the reactions of 1,3-dipoles such as nitrile oxides and nitrones have been carried out over the last 10 years. In contrast, very little work was done on the reactions of nitrile imines with chiral alkenes until the end of the 1990s and very few enantiomerically pure nitrile imines were generated. The greatest degree of selectivity so far has been achieved in cycloadditions to the Fischer chromium carbene complexes (201) to give, initially, the pyrazohne complexes 202 and 203 (111,112). These products proved to be rather unstable and were oxidized in situ with pyridine N-oxide to give predominantly the (4R,5S) product 204 in moderate yield (35-73%). 

Can be used to enhance the performance of several in situ technologies, including bioremediation, in situ chemical oxidation, in situ thermal treatments, and in situ solidification. 

An alternative route to such 6-(l-hydroxyalkyl)-substituted pteridines including 106 is from 2,4,5-triamino-6-butoxypyrimidine 107 and 2-formyloxiranes 108 in which the stereochemical properties are emphasized by the inclusion of the 17-steroidal ester <1992S303>. L-Biopterin 106 was synthesized from the oxirane 108 and 107 via a 5,6-dihydropteridine intermediate which was oxidized in situ to afford the product (Scheme 21). Syntheses of oxiranes and the condensation mechanism in the context of molecular orbital calculations were discussed. The field has been reviewed <1998H(48)1255>. 

Acetaldehyde thus formed is oxidized in situ to acetic acid. Decomposition may also take place through other pathways. Ethyl alcohol can be an important primary product which cooxidizes rapidly.870 871... 

The degree of unsaturation of the heterocyclic product depends on the nature of the five-carbon starting material pentane-1,5-diones yield dihydro compounds (151 —> 152) (which are sometimes oxidized in situ) pentane-1,3,5-triones (153) give y-pyrones (154 Z = 0) by dehydration, and y-pyridones (154 Z = NH) by the action of ammonia. 

Quite independently of Cornforth s efforts, a similar approach was designed and executed by Stevens and coworkers (75JA5940, 76T1599). The isoxazoles were synthesized by one of the three routes outlined in Scheme 25, in which primary nitro compounds are transformed into nitrile oxides by dehydration with either phosphoryl chloride or phenyl isocyanate, or else the same oxides were formed by dehydrogenation with LTA (syn product) or NBS (syn and anti). Reaction of the unstable nitrile oxides in situ with an appropriately substituted alkyne then afforded the isoxazole (294). 

Carbon nucleophiles in general react at the least hindered position. Thus 1,3-ketones add to 2,6-diphenylthiopyrylium salts to give the expected 4-substituted 4H-products, but if the diketone is part of a six-membered ring it is further oxidized in situ to the thiopyrany-lidene product, while the other adducts require treatment with ferricyanide to convert them to the unsaturated products (76CB1549). 

Addition of silyl enol ethers to nitroarenes2 In the presence of 1 equiv. of TASF, silyl enol ethers add to nitroalkenes to form unstable ortho and/or para nitronates, which are oxidized in situ by Br2 or DDQ to nitroaryl carbonyl compounds. The position of substitution depends on the substitution pattern of the arene and the size of the silicon reagent. With less hindered silyl derivatives ortho addition is strongly favored. 

Use ol a stronger reducing agent such as lithium aluminum hydride or sodium borohydride would generate the corresponding alcohols. whereas an oxidative workup with hydrogen peroxide would cause the carbonyl compounds to be oxidized in situ to carboxylic acids. 

A carbocation stabilized on a to a hydroxy group—that is a protonated ketone—is generated by cleavage of a carbon-carbon bond. This also leads to the formation of an aldehyde, which is oxidized in situ to a carboxylic acid. 

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