Nitric oxide addition reactions

The second direct reaction pathway, one-electron reduction of a target by nitric oxide, could occur only if the target was itself a strong oxidant, since nitric oxide does not readily give up its unpaired electron. Oxidation of nitric oxide would result in the formation of NO, which would rapidly nitrosate nucleophiles such as amines, sulfhydryls, or aromatics. In fact, the best one-electron oxidants would be radicals such as -NOi or hydroxyl radical or even ONOO itself. In such cases the net effect would be nitric oxide addition reactions (nitrosations), regardless of whether the mechanism is considered to be transfer of an electron from nitric oxide followed by attack of NO or simple radical-radical combination. Thus, under most conditions, one-electron reduction of a target by nitric oxide becomes a simple addition reaction. 

Nitric oxide addition reactions and nitrosations (often referred to as nitrosylations) are currently the subject of much debate. Evidence exists that nitrosation, particularly thiol nitrosation, serves to prolong the biological activity of nitric oxide by acting as a slow-releasing reservior (Stamler et al, 1992 Keaney et al., 1993). It has also been proposed that alteration of the redox state of critical thiols by nitric oxide may serve a signaling function (Sucher and Lipton, 1991 Lipton et al., 1993) quite distinct from the ability of nitric oxide to directly stimulate cGMP production. 

Production of nitric oxide (NO ), by hydroxylation of arginine, is a part of normal cell signalling. In addition to being a radical, and hence potentially damaging in its own right, nitric oxide can react with superoxide to form peroxynitrite, which in turn decays to yield the more damaging hydroxyl radical. Nitric oxide was first discovered as the endothelium-derived relaxation factor, and this loss of nitric oxide by reaction with superoxide may be an important factor in the development of hypertension. 

The nitrato-complexes [M(N03)s(PPh3)2] and [M(N03)a(NO)(PPh3)2] may be prepared by treating [M(CO)H(PPha)3] (M=Rh or Ir) with nitric acid. Mixed nitrato-nitro complexes such as [Ir(C0)Cl(PPh3)2(N03)(N02)] and [Rhg-(PPh3)4(N03)a(N02)2Cl] result from oxidative-addition reactions of N2O4 with... 

At room temperature, Htde reaction occurs between carbon dioxide and sodium, but burning sodium reacts vigorously. Under controUed conditions, sodium formate or oxalate may be obtained (8,16). On impact, sodium is reported to react explosively with soHd carbon dioxide. In addition to the carbide-forrning reaction, carbon monoxide reacts with sodium at 250—340°C to yield sodium carbonyl, (NaCO) (39,40). Above 1100°C, the temperature of the DeviHe process, carbon monoxide and sodium do not react. Sodium reacts with nitrous oxide to form sodium oxide and bums in nitric oxide to form a mixture of nitrite and hyponitrite. At low temperature, Hquid nitrogen pentoxide reacts with sodium to produce nitrogen dioxide and sodium nitrate. 

Sodium nitrite has been synthesized by a number of chemical reactions involving the reduction of sodium nitrate [7631-99-4] NaNO. These include exposure to heat, light, and ionizing radiation (2), addition of lead metal to fused sodium nitrate at 400—450°C (2), reaction of the nitrate in the presence of sodium ferrate and nitric oxide at - 400° C (2), contacting molten sodium nitrate with hydrogen (7), and electrolytic reduction of sodium nitrate in a cell having a cation-exchange membrane, rhodium-plated titanium anode, and lead cathode (8). 

Isoxazole-3-carbaldehyde has been obtained as a minor product from the reaction of acetylene with a mixture of nitric oxide and nitrogen dioxide (61JOC2976). Although 3-aryl-4-formylisoxazoles have been synthesized in good yields from the reaction of benzonitrile Af-oxides with 3-(dimethylamino)-2-propen-l-one (71S433), the parent member of the series, isoxazole-4-carbaldehyde, has never been reported. It may possibly be obtained by the addition of fulminic acid to 3-(dimethylamino)-2-propen-l-one. 

Another redox reaction leading to arenediazonium salts was described by Morkov-nik et al. (1988). They showed that the perchlorates of the cation-radicals of 4-A,A-dimethylamino- and 4-morpholinoaniline (2.63) react with gaseous nitric oxide in acetone in a closed vessel. The characteristic red coloration of these cation-radical salts (Michaelis and Granick, 1943) disappears within 20 min., and after addition of ether the diazonium perchlorate is obtained in 84% and 92% yields, respectively. This reaction (Scheme 2-39) is important in the context of the mechanism of diazotization by the classical method (see Sec. 3.1). 

Thus, nitric oxide seems to react in a complex manner. Simple addition to existing ions and initiation of new reactions, which might involve even carbon bond scission, seem to occur. At present our study of this system is incomplete. We have not been able to reconcile the complexity of the spectra with the findings of Meisels which are otherwise supported by our rate constant determinations. 

The catalytic activity of ln/H-ZSM-5 for the selective reduction of nitric oxide (NO) with methane was improved by the addition of Pt and Ir which catalyzed NO oxidation, even in the presence of water vapor. It was also found that the precious metal, particularly Ir loaded in/H-ZSM-5 gave a low reaction order with respect to NO, and then showed a high catalytic activity for the reduction of NO at low concentrations, if compared with ln/H-ZSM-5. The latter effect of the precious metal is attributed to the enhancement of the chemisorption of NO and also to the increase in the amount of NO2 adsorbed on in sites. 

It has been suggested (Gabr et al. 1995) that nitric oxide (NO ), which is, of course, a radical, bleaches (3-CAR presumably by forming addition complexes. However, when we completely exclude oxygen from the system we found no evidence of an interaction between NO and 3-CAR (unpublished). Therefore, the observed reaction by Gabr et al. may have been due to nitrogen dioxide (N02 ). 

Productive bimolecular reactions of the ion radicals in the contact ion pair can effectively compete with the back electron transfer if either the cation radical or the anion radical undergoes a rapid reaction with an additive that is present during electron-transfer activation. For example, the [D, A] complex of an arene donor with nitrosonium cation exists in the equilibrium with a low steady-state concentration of the radical pair, which persists indefinitely. However, the introduction of oxygen rapidly oxidizes even small amounts of nitric oxide to compete with back electron transfer and thus successfully effects aromatic nitration80 (Scheme 16). 

Formation of the bicyclic lithiated intermediate 8 is considered to be a two-step process whereby the nitrogen atom of nitric oxide attaches to the Cl atom of propynyllithium. Addition of a second molecule of nitric oxide gives intermediate 8 that on reaction with water produces 5-methyl-l,2,3-oxatriazole 3-oxide 9 (Scheme 1). Calculated, optimized geometry and bond lengths for stmcture 9 together with calculated infrared (IR) and Raman spectra are reported <2005JOC5045>. 

As mentioned earlier, when NO concentration exceeds that of superoxide, nitric oxide mostly exhibits an inhibitory effect on lipid peroxidation, reacting with lipid peroxyl radicals. These reactions are now well studied [42-44]. The simplest suggestion could be the participation of NO in termination reaction with peroxyl radicals. However, it was found that NO reacts with at least two radicals during inhibition of lipid peroxidation [50]. On these grounds it was proposed that LOONO, a product of the NO recombination with peroxyl radical LOO is rapidly decomposed to LO and N02 and the second NO reacts with LO to form nitroso ester of fatty acid (Reaction (7), Figure 25.1). Alkoxyl radical LO may be transformed into a nitro epoxy compound after rearrangement (Reaction (8)). In addition, LOONO may be hydrolyzed to form fatty acid hydroperoxide (Reaction (6)). Various nitrated lipids can also be formed in the reactions of peroxynitrite and other NO metabolites. 

The NO/NO+ and NO/NO- self-exchange rates are quite slow (42). Therefore, the kinetics of nitric oxide electron transfer reactions are strongly affected by transition metal complexes, particularly by those that are labile and redox active which can serve to promote these reactions. Although iron is the most important metal target for nitric oxide in mammalian biology, other metal centers might also react with NO. For example, both cobalt (in the form of cobalamin) (43,44) and copper (in the form of different types of copper proteins) (45) have been identified as potential NO targets. In addition, a substantial fraction of the bacterial nitrite reductases (which catalyze reduction of NO2 to NO) are copper enzymes (46). The interactions of NO with such metal centers continue to be rich for further exploration. 

Despite intense study of the chemical reactivity of the inorganic NO donor SNP with a number of electrophiles and nucleophiles (in particular thiols), the mechanism of NO release from this drug also remains incompletely understood. In biological systems, both enzymatic and non-enzymatic pathways appear to be involved [28]. Nitric oxide release is thought to be preceded by a one-electron reduction step followed by release of cyanide, and an inner-sphere charge transfer reaction between the ni-trosonium ion (NO+) and the ferrous iron (Fe2+). Upon addition of SNP to tissues, formation of iron nitrosyl complexes, which are in equilibrium with S-nitrosothiols, has been observed. A membrane-bound enzyme may be involved in the generation of NO from SNP in vascular tissue [35], but the exact nature of this reducing activity is unknown. 

The addition of nitric oxide markedly increases280 the rate of N2Os decomposition. In terms of the accepted mechanism, NO removes NOa in the very rapid reaction (29), thereby preventing reassociation. The stoichiometric equation is now... 

The homogeneous reaction was found to be catalysed by small percentages of nitric oxide and acetylene dichloride without any detectable change in the overall stoichiometry. This observation suggests the occurrence of additional initiation processes of the type... 

These are analogous to the reactions postulated for hydrocarbon systems by Laidler et al.115,176. With certain hydrocarbons there is almost no inhibition region, and the main effect of nitric oxide is to accelerate the rate of decomposition as in the present instance. Further work on this interesting aspect of the decomposition of S2F10 is obviously desirable. In addition, attention should be given to the effects of inert gases on the orders of the individual reactions in the above mechanism, and on the rate of the heterogeneous reaction. 

As mentioned, the addition of a small amount of water to the bomb ensures that the vapor phase remains saturated throughout the experiment, so that liquid water is produced in the combustion reaction. It also ensures that the mixture of nitric oxides formed by the oxidation of the N2 will be converted to NOjT(aq), which is simple to determine. 

---