Nitric oxide autoxidation

Kharitonov, V., Sundquist, AR, and Sharma, VS (1994). Kinetics of nitric oxide autoxidation in aqueous solution. J Biol Chem 269(8) 5881-5883. 

Destruction of nitric oxide by superoxide in the buffers is more likely to account for the short half-life of nitric oxide in vitro. Superoxide dismutase (15-100 U/ml) substantially increased the apparent half-life of EDRF, strongly suggesting that superoxide contributes to the short biological half-life of nitric oxide. In the perfusion cascade bioassay system, the buffers are bubbled with 95% oxygen, contain 11 mM glucose as well as trace iron plus copper contamination and are incubated under the weak ultraviolet (UV) radiation of fluorescent lights. These are prime conditions for the autoxidation of glucose to form small amounts of superoxide in sufficient amounts to account for the short half-life of nitric oxide in nanomolar concentrations. The rate of reaction between superoxide and nitric oxide is 6.7 X 10 M sec L The shortest half-life of nitric oxide measured is approximately 6 sec. To achieve a half-life of 6 sec, the steady state concentration of superoxide would only need to be 17 pM, calculated as ln(2)/ (6 sec X 6.7 X 10 M" sec )-... 

HOC1 also reacts readily with nitrite (NOj), which is the autoxidation product of nitric oxide (NO). HOC1 and NOj react to form reactive intermediates CI-NO2, and/or CF-ONO, which are capable of nitrating, chlorinating, and dimerizing tyrosine residues. 

Ford, P. C., Wink, D. A., and Stanbury, D. M, (1993). Autoxidation kinetics of aqueous nitric oxide. FEES Lett. 326, 1-3. 

Fritz Haber (Breslau, 9 December 1868-Basel, 29 January 1934) studied in Berlin, Heidelberg and Charlottenberg, and worked at first on organic chemistry. In 1894 he became assistant to Bunte at the Technical High School at Karlsruhe, where he became associate professor (1898) and (1906) professor of technical chemistry. Whilst at Karlsruhe he investigated the synthesis of ammonia from its elements (1905, 1915) which afterwards (with the collaboration of Carl Bosch) led to the development of the manufacture of synthetic ammonia by the Badische Co. at Ludwigshafen, although the reaction under pressure (the technical process) was first carried out by Nernst (see above). In 1911 Haber became director of the Kaiser Wilhelm Institute of Physical Chemistry and Electrochemistry at Berlin-Dahlem. He received the Nobel Prize in 1919. He worked on chemical equilibria in flames (1895 f.), the electrolytic reduction of nitrobenzene (1898 f.), autoxidation (1900 f.), the synthesis of nitric oxide in the electric arc (1908 f.), and on many branches of electrochemistry. His books contain useful material, the one on thermodynamics an unsuccessful approach to the Nernst heat theorem. 

The reaction (Equation 7.10), together with subsequent reoxidation of nitric oxide with oxygen, constitutes the reduction-oxidation cycle for the catalytic autoxidation with NO. On the basis of the understanding of the interaction of nitrosonium with aromatic donors [15], hydroquinones are expected to strongly shift the equilibrium (Equation 7.3) to favour the nitrosonium complex in conformity with enhanced donor properties of the aromatic substrates. Accordingly, the oxidation of hydroquinone with NO proceeds via the nitrosonium nitrate ion pair. The overall two-electron oxidation of hydroquinone to quinone by 2 equivalent NO probably proceeds via successive one-electron steps. The labelling studies in the process... 

The various methods that are used for the production of aromatic acids from the corresponding substituted toluenes are outlined in Figure 1. The first two methods -chlorination/hydrolysis and nitric acid oxidation - have the disadvantage of relatively low atom utilization (ref. 13) with the concomitant inorganic salt production. Catalytic autoxidation, in contrast, has an atom utilization of 87% (for Ar=Ph) and produces no inorganic salts and no chlorinated or nitrated byproducts. It consumes only the cheap raw material, oxygen, and produces water as the only byproduct. 

Consequently, as a result of increasing environmental pressure many chlorine and nitric acid based processes for the manufacture of substituted aromatic acids are currently being replaced by cleaner, catalytic autoxidation processes. Benzoic acid is traditionally manufactured (ref. 14) via cobalt-catalyzed autoxidation of toluene in the absence of solvent (Fig. 2). The selectivity is ca. 90% at 30% toluene conversion. As noted earlier, oxidation of p-xylene under these conditions gives p-toluic acid in high yield. For further oxidation to terephthalic acid the stronger bromide/cobalt/manganese cocktail is needed. 

In one approach cyclohexane is autoxidized to a mixture of cyclohexanol and cyclohexanone in the presence of a Co or Mn naphthenate catalyst. This mixture is subsequently oxidized to adipic acid using nitric acid as the oxidant in the presence of a Cu Vv catalyst. An alternative method using dioxygen in combination with Co or Mn in HOAc gives lower selectivities to adipic acid (70% vs 95%). Alternatively, autoxidation in the presence of stoichiometric amounts of boric acid produces cyclohexanol as the major product, which is subsequently oxidized to adipic acid using HNO3 in the presence of Cu Vv. The latter step produces substantial amounts of N2O as a waste product. 

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