Ammonium reoxidation

The yield of hydroquinone is 85 to 90% based on aniline. The process is mainly a batch process where significant amounts of soHds must be handled (manganese dioxide as well as metal iron finely divided). However, the principal drawback of this process resides in the massive coproduction of mineral products such as manganese sulfate, ammonium sulfate, or iron oxides which are environmentally not friendly. Even though purified manganese sulfate is used in the agricultural field, few solutions have been developed to dispose of this unsuitable coproduct. Such methods include MnSO reoxidation to MnO (1), or MnSO electrochemical reduction to metal manganese (2). None of these methods has found appHcations on an industrial scale. In addition, since 1980, few innovative studies have been pubUshed on this process (3). 

Raffinate acid from the first cycle, containing approximately 7 to 14 g/L U Og is then reoxidized and re-extracted in the second, purification cycle using a solvent containing 0.3 Af D2EHPA and 0.075 AfTOPO. The loaded solvent is washed with iron-free acid to remove iron and then with water to remove extracted and entrained acid. The solvent is stripped with ammonium carbonate [506-87-6] to yield ammonium uranyl tricarbonate [18077-77-5] which is subsequendy calcined to U Og (yellow cake). The stripped solvent is regenerated with mineral acid before recycling (39). 

While their physiologic role is uncertain, L-amino acid oxidases of liver and kidney convert amino acids to an a-imino acid that decomposes to an a-keto acid with release of ammonium ion (Figure 29-6). The reduced flavin is reoxidized by molecular oxygen, forming hy-... 

Nitroso compounds are usually not obtained directly but rather by reoxidation of hydroxylamino compounds or amines. Hydroxylamino compounds are prepared by electrolytic reduction using a lead anode and a copper cathode [573], by zinc in an aqueous solution of ammonium chloride [574 or by aluminum amalgam [147], generally in good yields. 

The study of the mechanism of the fast SCR over V-W-Ti-0 catalysts was addressed first by Koebel and co-workers [65-68]. They suggested that (i) the reoxidation ofthe catalyst is rate determining at low temperature in the redox cycle of standard SCR catalyst, (ii) NO2 reoxidizes the catalyst faster than O2 the NO2-enhanced reoxidation of the catalyst was demonstrated by in situ Raman experiments, (hi) the reaction occurs via the nitrosamide intermediate in both standard and fast SCR and (iv) ammonium nitrate is considered an undesired side-product. 

Controlled rotation of the molecular rings has also been achieved in catenanes composed of three interlocked macrocycles. For example, catenane 42H26+ (Fig. 13.37) is made up of two identical macrocycles 2 interlocked with a cyclophane containing two bipyridinium and two ammonium units.44 Because of the type of the macrocycles used, the stable coconformation of 42H26+ is that in which the two rings surround the bipyridinium units (Fig. 13.37a, state 0). Upon addition of one electron in each of the bipyridinium units, the two macrocycles move on the ammonium stations (Fig. 13.37b, state 1) and move back to the original position when the bipyridinium units are reoxidized. 

Recently we presented (23) the results of an experimental study on the kinetics and mechanisms of the reaction of lepidocrocite (y-FeOOH) with H2S. With respect to the interaction between iron and sulfur, lepidocrocite merits special attention. It forms by reoxidation of ferrous iron under cir-cumneutral pH conditions (24), and it can therefore be classified as a reactive iron oxide (19). The concept of reactive iron was established by Canfield (19), who differentiated between a residual iron fraction and a reactive iron fraction (operationally defined as soluble in ammonium oxalate). The reactive iron fraction is rapidly reduced by sulfide or by microorganisms. 

Oxidation of alkenes to ketones.3 Both internal and terminal alkenes are oxidized by PdCl2 (with CuCl2 as reoxidant) in water-polyethylene glycol (PEG), serving as the phase-transfer catalyst as well as the solvent (9, 360, 376). This oxidation is more facile than that catalyzed by quaternary ammonium salts, which is applicable only to terminal alkenes. 

In reoxidation by means of the air, the reduced sample may be exposed to ammonia vapour, which in many cases accelerates the reoxidation. If the colour does not reappear under these conditions, treatment with a cold, saturated potassium persulphate solution or with 1% ammonium persulphate solution is tried in accordance with the indications given for woollen fabrics (see p. 473). 

Finally, Kohl et al. used quaternary ammonium chlorides, e.g. benzyltrimethy-lammonium chloride, together with AICI3 and sodium chloride (working electrode Pt, counter electrode Pt wire, Al wire in melt). The addition of S OCI2 was required in order to reduce Na+. At — 2.4 V the deposition of sodium started and at —1.8 V the reoxidation was observed [5],... 

Because of the type of the macrocycles used, the stable conformation of 19 H26+ is that in which the two rings surround the bipyridinium units. Upon addition of one electron in each of the bipyridinium units, the two macrocycles move on the ammonium stations, and move back to the original position when the bipyridinium units are reoxidized. 

Sodium bromate, NaBrOs, a white crystalline compound, converts acyloins into a-diketones under forcing conditions [740]. More often, this reagent is used as a reoxidant of ammonium cerium nitrate [421], cerium sulfate [741], or ruthenium trichloride [741] in oxidations of alcohols to aldehydes [421] or carboxylic acids [741]. 

Ceric ammonium nitrate in water or in 50% acetic acid oxidizes ben-zylic alcohols at 90 °C in very good yields [420]. Only catalytic amounts of the reagent and sodium bromate as a reoxidant are needed to convert benzyl alcohol into benzaldehyde in 90% yield on heating in acetonitrile at 80 °C [421]. A similar result is obtained on treatment of benzyl alcohol with lead tetraacetate in pyridine at room temperature for a few hours (yield 85%) [442]. 

Ceric ammonium nitrate or ceric sulfate is used to oxidize saturated and unsaturated secondary alcohols to ketones. The ceric salts are used only in catalytic amounts with sodium bromate as a reoxidant (equation 241) [741]. 

The precipitate is largely freed of fluoride ions after filtration by extraction or recrystallization. After drying at 200°C, the ammonium diuranate is reductively decomposed by a H2/H2O mixture at ca 500°C to UyOg, which is then reduced with hydrogen at 500 to 800°C to uranium(IV) oxide. The reductive decomposition to U Og and its reduction can be carried out in a single step e.g. in a rotary kiln. Since the uranium(IV) oxide formed can be pyrophoric, it is weakly reoxidized. 

These mixed oxides can also be manufactured by mixing the uranium and nitrate solutions produeed during the reprocessing of spent nuclear fuels and converting these metal nitrate mixtures into a mixed oxide (coprecipitation). In this process the plutonium is first reoxidized, then gaseous ammonia and carbon dioxide are introduced into the aqueous nitrate mixture, whereupon ammonium uranyl-plutonyl carbonate is precipitated. This can be calcined to... 

The ceria sample used here was a medium-surface area sample (49 m. g-l) prepared in the laboratoiy by calcining at 873 K, for 4 h, a cerium hydroxycarbonate precipitate obtained by addition of ammonium carbonate to a solution of Ce(N03)3. To eliminate the residual carbonate, it was further treated with flowing H2 at 773 K for 4h, and finally reoxidized in air at 773 K for 4 h. The surface area of the ceria sample did not significantly change throughout the whole series of treatments applied in the present work. 

Chromophore modifications 1) Reduction with borohydride (modified from ref. 10). A solution of PC or isolated subunits (chromophore concentration 7-21/iM, 0.9M potassium phosphate, pH 7, 8M urea) was treated with NaBH (170 mM). After complete reduction (spectrum, 45 min) excess reductant was destroyed by glucose. For reoxidation experiments, the samples (lOOmM potassitim phosphate, pH 7, containing 70% ammonium sulfate to prevent protein degradation) were allowed to stand at room temperature in the dark for up to nine days. This was followed by recombination (if not yet done), denaturation (8M urea in lOOmM potassium phosphate, pH7) and renaturation as described below. 2) Photobleaching of the o-subunit (8/xM protein, 100 mM phosphate, 8M urea, pH 7.5) was... 

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