Oxidation by nitrous oxide

The reduced iron atoms of complex C, being inert to dioxygen, are readily oxidized by nitrous oxide into complex D to give adsorbed species of a-oxygen, Oa. As Figure 7.3 shows, the reversible redox transition Fc" <-> Fe provides the catalytic activity of FeZSM-5 both the oxidation cycle due to the oxygen transfer from N20 to a substrate and the decomposition cycle of N20 into N2 and 02 due to recombination of a-oxygen into the gas phase. The decomposition is an environmentally important process, and FeZSM-5 zeolites are considered to be the best catalysts for this reaction (see review [117] and references therein). 

We used HZSM-5 zeolites (Si02/AI203 = 40 - 120) and H[Ga]ZSM-5 zeolites (Si02/AI203 = 60) prepared by decationization of the Na-form with a 1 N aqueous solution of HCI. The preliminary activation of all catalyst samples was carried out at temperatures of 820 - 1120 K either in an Ar flow or in an air flow for 6 h. For comparison, we prepared the HZSM-5 zeolite modified by 2 wt % Cu (wet impregnation with a 1 M nitrate solution with further nitrate decomposition at 820 K in air) and tested this sample in the fluorobenzene oxidation by nitrous oxide. 

For example an elemental absorption line can be interfered by a molecular absorption line from reaction products of co-existing elements in the sample. In the case of Ba determination in the presence of Ca the elemental absorption line at 553.6 nm can be overlapped by a broad CaOH absorption band in the range 548.0 nm to 558.0 nm. In many cases such interference can be ehminated by replacing air as oxidant by nitrous oxide. The resulting higher flame temperature leads to the decomposition of the CaOH and ehmiriates the absorption band. 

Catalytic Oxidation by Nitrous Oxide in the Gas Phase 221 Table 7.4 Methane oxidation by N2O over 1.7% Mo03/Si02. ... 

Catalytic Oxidation by Nitrous Oxide in the Cas Phase 229 7.3.2.5 Hydroxylation of Alkanes and Benzene Derivatives... 

Below about 1125°C, the reaction rate of NO (as a 5% mixture in argon) with tantalum cannot be detected, but thereafter the rate increases rapidly with temperature. The oxidation by nitrous oxide (N2O) on an evaporated film of tantalum has been studied over the temperature range — 56-200°C. Fast dissolution and absorption of N2O occurred at — 56°C, accompanied by N2 evolution. Some incorporation of N2O also occurred. The rate of N2O absorption was independent of the pressure of the nitrous oxide. 

Chloroanisole and p-nitrophenol, the nitrations of which are susceptible to positive catalysis by nitrous acid, but from which the products are not prone to the oxidation which leads to autocatalysis, were the subjects of a more detailed investigation. With high concentrations of nitric acid and low concentrations of nitrous acid in acetic acid, jp-chloroanisole underwent nitration according to a zeroth-order rate law. The rate was repressed by the addition of a small concentration of nitrous acid according to the usual law rate = AQ(n-a[HN02]atoioh) -The nitration of p-nitrophenol under comparable conditions did not accord to a simple kinetic law, but nitrous acid was shown to anticatalyse the reaction. 

Hey and Osbond converted (18) to 5 6-benzoquinoline (19) with copper powder in dilute acid solution, reaction probably going through the dihydro compound (20) which was oxidized by nitrous acid in the... 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

There are few reports on the effects of nitrous oxide on dopaminergic neurotransmission. A study in mice showed that nitrous oxide inhalation produced a significant increase in locomotor activity that was antagonized in a dose-dependent fashion by the dopamine synthesis inhibitor a-methyl-/)-tyrosine (Hynes and Berkowitz 1983). Moreover, administration of the D2 antagonist haloperidol also reduced the locomotor activity induced by nitrous oxide (Hynes and Berkowitz 1983). These results suggest that excitatory effects induced by nitrous oxide may be also mediated by dopaminergic neurotransmission. However, other studies have reported that exposure to nitrous oxide resulted in decreased dopamine release by neurons in the striatum (Balon et al. 2002 Turle et al. 1998). 

Copper metal surface area was determined by nitrous oxide decomposition. A sample of catalyst (0.2 g) was reduced by heating to 563 K under a flow of 10 % H2/N2 (50 cm min"1) at a heating rate of 3 deg.min 1. The catalyst was then held at this temperature for 1 h before the gas flow was switched to helium. After 0.5 h the catalyst was cooled in to 333 K and a flow of 5 %N20/He (50 cm3mirr ) passed over the sample for 0.25 h to surface oxidise the copper. At the end of this period the flow was switched to 10 % H2/N2 (50 entitlin 1) and the sample heated at a heating rate of 3 deg.min"1. The hydrogen up-take was quantified, from this a... 

Hanson, C. et al., Proc. Int. Solvent Extr. Conf. (Liege), 1980, 2, paper 80-70 The solvent ( Butex ), an extractant in nuclear reprocessing may decompose violently in contact with nitric acid. Hydrolysis to butanol, followed by violent oxidation, catalysed by nitrous acid, is involved. 

Pellenberg [114] analysed soils and river sediment for silicone content by nitrous oxide-acetylene flame atomic absorption spectrophotometry. He showed that total carbon and total carbohydrates both correlate well with silicone content and the correlation between sedimentary silicone and presumed sewage material is good enough to suggest silicone as a totally synthetic, specific tracer for sewage in the aquatic environment. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3) so-called neutral diazotization or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. 

Ph,P)4Pd(0) and quaternary ammonium salts catalyse the oxidation of benzylic halides by nitrous oxide in a basic medium into O-benzylic ethers of the corresponding aryl aldoximes, ArCH=NOCH2Ar (20-40%) [21 ]. The procedure does not have a great synthetic appeal. 

The oxidation of alkenes by nitrous oxide on silver at 350°C has been studied from the viewpoint of structure effects on rate by Belousov, Mulik, and Rubanik (J40), and very good correlations of Type B have been found with ionization potentials and with the rate of oxidation by atomic oxygen (series 110 and 111). 

Notte, P.P. (2000) The AlphOx process or the one-step hydroxylation of benzene into phenol by nitrous oxide. Understanding and tuning the ZSM-5 catalyst activities. Top. Catal., 13, 387-394. 

Some phenolic substrates are readily nitrated with nitric acid of 5 % concentration or lower. Such reactions are catalyzed by nitrous acid either already present in the nitric acid or from initial oxidation of the phenolic substrate. Reaction of the substrate with nitrous acid... 

Nitrous oxide exerts a variety of its adverse effects by oxidizing vitamin Bn and rendering it inactive as a coenzyme in many essential metabolic processes. One vitamin dependent enzyme in particular, methionine synthetase, is involved in cell division and is necessary for DNA production. Adverse reproductive and hematologic effects caused by nitrous oxide are thought to be due to inactivation or dysfunction of methionine synthetase resulting in impairment of cell division. 

Laboratory studies have indicated an increasing number of further processes for which iron oxides may be used as catalysts. A sodium promoted iron oxide on a support of Si02 catalyses the gas phase oxidation (377-427 °C) by nitrous oxide, of pro-pene to propene oxide (Duma and Honicke, 2000). Ferrihydrite or akaganeite can be used to catalyse the reduction (at 55-75 °C) by hydrazine, of aromatic nitro compounds to aromatic amines (which are the starting materials for a huge range of chemicals) these Fe oxides have the potential to provide a safe and economical pathway to the production of these important organics (Lauwiner et al., 1998). 

The bishydrazones of the 1,2-diketones from inositols have also been converted into triazoles.222,223 The conversion of arylosazones into the corresponding osotriazoles requires the presence of an oxidant, and it is obvious that simple removal of aniline from the osazone, as suggested by the equation, is not involved. In addition to copper(II) sulfate, the reagent most commonly used, other oxidizing heavy-metal salts, such as ferric sulfate and chloride,224 and mercuric acetate,223 have been used, as well as halogens225 and nitro-sulfonates.226 The osazone acetates are converted into osotriazoles by nitrous acid,227 which decomposes the unacetylated osazones to the aldosuloses228 and the osazone formazans are cyclized with warm... 

Methyl groups in the 2-, 4- or 6-position of pyrimidine are also more reactive. In addition to typical reactions such as condensation with benzaldehyde, selenium dioxide oxidation and halogenation, they can be converted into oximino groups by nitrous acid, and undergo Claisen condensation with (C02Et)2. In the reaction of 2,5-dimethylpyrimidine with benzaldehyde, only the electrophilic 2-methyl group reacts preferentially to yield the 2-styryl derivative (631). In quinazolines partial double bond fixation makes a methyl group in the 4-position more reactive than that in the 2-position. 

These form derivatives with carbonyl compounds and can be acylated, sulfonylated, eliminated by mild oxidation [e.g. (762 Y = NHNH2) + CuS04 + AcOH — (762 Y = H)]. They are converted by nitrous acid into azides as in benzenoid chemistry. 

Far less is known about the oxidative behaviour of dihydro-1,4-oxazines, -benzoxazines and -benzothiazines, although it has been observed that dihydro-1,4-benzothiazine itself is oxidatively ring opened by nitrous acid to the diazonium salt (104 Scheme 44) (49JCS278). 

Biogenic silicon (BSI) was determined, with minor modifications, by the method of DeMaster (17). As adapted, the technique involved time-course leaching of <20-mg samples of particulate matter in 30 mL of 1.0% Na2C03 in a water bath at 85 °C. Silica in leachates was quantified either colorimetrically (Technicon autoanalyzer procedure) or by nitrous oxide flame atomic absorption. A high-temperature catalytic-combustion technique (Perkin Elmer 240C) was used for particulate organic carbon determinations. Particulate inorganic (carbonate) carbon was measured on the same instrument by CO 2 evolution after treatment of the particles with phosphoric acid. 

M. A. Hunter13 showed that platinum electrodes are not polarized by nitrous oxide, and he estimated that the oxidation potential of nitrous oxide is about... 

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