Hydroxylamine ammonia oxidation

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

Kf., while not quantified experimentally, was recently introduced by Kirby and coworkers on the basis of product formation from O-attack at electrophilic P and C centers, as well as MO calculations incorporating the novel species, ammonia oxide, NH3+-0 . In common with other ambident nucleophiles, factors such as electronic, steric, kinetic and thermodynamic effects will determine actual extant pathways in a given system. Af-substituted hydroxylamines (see Scheme 1) can in principle partake of the equilibria shown in Scheme 2. Again, actual outcomes will be influenced by the aforementioned criteria. 

In a similar reaction, 2-(o-nitrophenyl)ethylamine (100) may be reduced in an ammonia buffer to the hydroxylamine and oxidized to the nitroso derivative, which condenses with the amino group to a dihydrocinnoline.160,161 It is also possible to prepare dihydrobenzo-l,2,3-triazinones on reduction of o-nitrobenzhydrazide, followed by oxidation of the hydroxylamine to a nitroso group, and 3-phenyldihydrobenzo-l,2,3-triazine (101) from N-phenyl-(V-(o-nitrobenzyl)hydrazine (100) in an analogous way161 [Eq. (78)]. 

Figure 18-19 The ammonia oxidation system of the bacterium Nitrosomonas. Oxidation of ammonium ion (as free NH3) according to Eq. 18-17 is catalyzed hy two enzymes. The location of ammonia monooxygenase (step a) is uncertain but hydroxylamine oxidoreductase (step b) is periplas-mic. The membrane components resemble complexes I, III, and IV of the mitochondrial respiratory chain (Fig. 18-5) and are assumed to have similar proton pumps. Solid green lines trace the flow of electrons in the energy-producing reactions. This includes flow of electrons to the ammonia monoxygenase. Complexes HI and IV pump protons out but complex I catalyzes reverse electron transport for a fraction of the electrons from hydroxylamine oxidoreductase to NAD+. Modified from Blaut and Gottschalk.315...

HAO catalyzes the four-electron oxidation of hydroxylamine to nitrite. " It is present in autotrophic nitrifying bacteria, like Nitrosomonas, which are obligate chemolithotrophs that use the oxidation of ammonia as their sole energy source. For each cycle of hydroxylamine oxidation, two electrons are returned for the initial step of ammonia oxidation and the other two are either transferred to the terminal oxidase via the components of the respiratory chain, or used to generate NADH by reverse electron transport. 

The immediate product of AMO is hydroxylamine, which is further oxidized by hydroxylamine oxidoreductase (HAO) to N02 (Eq. (5.2)). AOA apparently do not possess the hydroxylamine reductase gene, so the pathway of ammonia oxidation in these organisms must be quite different from that outlined here for AOB. Oxygen is also consumed by the terminal oxidase (Eq. (5.3)), as a result of electron transport generating ATP for cellular metabolism. 

As carried out industrially, the processes pose problems in almost all their aspects. The catalysts generally operate between 800 and 1100 °C and at very high space velocities (>100 000 h ) with contact times of the order of 10" — 10 s the question arises therefore whether the reactions are wholly surface catalysed, or whether surface initiated gas-phase reactions are important. Since there is a considerable reorganization of atoms in reactants during their conversion to products, the nature of the reaction intermediates has been the subject of considerable speculation over many years. Reaction theories for ammonia oxidation were named, prior to 1960, after the principle intermediate proposed, viz. the imide (NH), nitroxyl (HNO), and hydroxylamine (NH2OH) theories. Similarly, alternative theories for the Andrussow cyanide process have proposed methylene-imine (CH2=NH) and nitrosomethane (CH3.NO) as reaction intermediates. Modern techniques might now reasonably be expected to discriminate amongst these hypotheses. 

The ammonia-oxidizing bacteria oxidize ammonia to nitrous acid via hydroxyl-amine (NH2OH) (Lees, 1952 Hofman and Lees, 1953) ammonia is first oxidized to hydroxylamine by the catalysis of ammonia monooxygenase (AMO) (Dua et al., 1979 Hollocher et al., 1981). In this reaction, molecular oxygen is utilized. Then, hydroxylamine formed is oxidized to nitrous acid by the catalysis of hydroxylamine oxidoreductase (HAO). 

The oxidation of hydroxylamine by the ammonia-oxidizing bacteria is catalyzed by hydroxylamine oxidoreductase (Yamanaka and Sakano, 1980). The molecular... 

Hydroxylamine oxidoreductase was first purified by Hooper and Nason in 1965. They found that the enzyme catalyzed the reduction of horse ferricytochrome c with hydroxylamine but they found little nitrous acid formed as the result of the reaction nitrite formed was approximately 5% as much as cytochrome c reduced in 0.1 M glycine-NaOH buffer, pH 9.8. As the ammonia-oxidizing bacteria oxidize hydroxylamine to nitrite, they thought that one or more enzymes in addition to the oxidoreductase might participate in the oxidation of hydroxylamine to nitrite or additional factor(s) might be necessary for changing hydroxylamine to nitrite (Hooper et al., 1977). 

Alcaligenes faecalis has a hydroxylamine-oxidizing enzyme which differs from the enzyme of other heterotrophic nitrifying bacteria. In this bacterium, hydroxylamine is oxidized through pyruvic oxime (Fig. 3.6). Pyruvic acid derived from lactate, succinate, and other carboxylates reacts nonenzymatically with hydroxylamine formed from ammonia to form pyruvic oxime. This compound is oxidized to nitrite and pyruvic acid by the catalysis of pyruvic oxime dioxygenase (Ono et al., 1996, 1999). 

The growth of the chemolithoautotrophic bacteria can be inhibited by paraquat, because the bacteria have NAD(P) reductase. So it is rather mysterious that N. europaea is not affected by the compound at 4 pM. It will be attributable to hydrox-ylamine which is formed as an intermediate metabolite during the oxidation of ammonia by the bacterium that the inhibitory effect of paraquat is not observed with the bacterium. Hydroxylamine is a scavenger of superoxide anion (Elstner et al., 1975). Probably, N. europaea (and other ammonia-oxidizing bacteria) are exceptionally resistant to paraquat, but other chemolithoautotrophs all will be sensitive to paraquat. Therefore, we should take care not to disturb the soil bacteria when we use paraquat as a herbicide. 

Otte S, Schalk J, Kuenen JG, JettenMSM (1999) Hydroxylamine oxidation and subsequent nitrous oxide production by the heterotrophic ammonia oxidizer Alcaligenes faecalis. Appl Microbiol Biotechnol 51 255-261... 

Membrane-bound ammonia monooxygenase (AMO) has been isolated from ammonia-oxidizing bacteria, and has recently been isolated from Paracoccus denitrificansP This enzyme catalyzes not only oxygenation of ammonia to hydroxylamine but also hydroxylation and epoxidation of hydrocarbons. pMMO and AMO have high sequence identity, and are considered to be closely related to each other with respect to their structure and function. 

Ammonia. Ammonia oxidation yields two very important products, hydrazine and hydroxylamine, the latter of particular importance in caprolactam manufacture. 

Kinetic studies of the reaction between the a-nucleophile hydroxylamine and tri-2-pyridyl phosphate (TPP) (54) showed that an initial rapid reaction occurred via a general base-catalysed attack of TPP by the ammonia oxide tautomer of hydroxylamine TlgN -O to form a transient 0-phosphorylated derivative (55) (Scheme 19), which is trapped by the NH2OH in solution to generate diimide (56) and DPP (Scheme 20). 

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