Metals, reaction with nitric oxide

Andrews and co-workers have used the matrix reaction between lithium atoms and some inorganic compounds to produce species of spectroscopic interest. Reaction of lithium with molecular oxygen [301] produces, in addition to the molecule Li02, the molecule LiO and a dimer Li2 02. Reaction with nitric oxide produced a nitroxide compound [302], but analysis of the infrared spectrum indicated that in this compound the lithium atom was bound to the oxygen atom (LiON), rather than to the nitrogen atom (LiNO), as would be expected by analogy with the known compounds HNO and RNO. The matrix deposition of lithium and nitrous oxide [303] leads to the formation of LiO and LijO. The other alkali metals have also been reacted in the same way with nitrous oxide [304]. Potassium, rubidium and caesium all led to the formation of the compounds MO and M2O. No sodium oxides were produced when sodium and nitrous oxide were co-deposited. This is to be compared with the mechanism advanced for the sodium-catalysed gas-phase reaction between N2O and CO, where sodium is assumed to react with N2O, (Section 4, ref. 

The above general description for the preparation of G-ORME from commercially available metallic gold is equally applicable to the preparation of ORMEs from the remaining Transition metals through reaction with nitric oxide (NO) gas. The Transition metals include platinum, palladium, rhodium, iridium, ruthenium, and osmium. Nitric oxide is unique in that it possesses the necessary chemical potential as well as the single unpaired electron. 

Ford, P.C. and Lorkovic, I.M. (2002) Mechanistic aspects of the reactions of nitric oxide with transition-metal complexes, Chem. Rev., 102, 993, and references therein. 

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. 

Redox reactions involving nitric oxide have important implications beyond their fundamental chemistry as demonstrated by the controversy in the biomedical literature regarding conditions under which generation of NO leads to the amelioration or the exacerbation of oxidative stress in mammalian systems (95). Oxidative stress is defined as a disturbance in the balance between production of reactive oxygen species (pro-oxidants) and antioxidant defenses (96). Reactive oxygen species include free radicals and peroxides as well as other reactants such as oxidative enzymes with metal ion sites in high oxidation states. The... 

In the presence of various metal ions, 2-(fluoroenone)benzothiazoline has been found to rearrange to A-2-mercaptophenylenimine, while a free radical mechanism involving the homolysis of C-S and C-N bonds has been invoked to explain the formation of 3-phenyl-1,2,4-triazole derivatives from the thermal fragmentation and rearrangement of 2-(arylidenehydrazino)-4-(5//)-thiazolone derivatives. The cycloadducts (36) formed from the reaction of 3-diethylamino-4-(4-methoxyphenyl)-5-vinyl-isothiazole 1,1-dioxide (34) with nitric oxides or miinchnones (35) have been found to undergo pyrolytic transformation into a, jS-unsaturated nitriles (38) by way of pyrrole-isothiazoline 1,1-dioxide intermediates (37). 

Nitric oxide also can be made by reactions of nitric acid, nitrate, or nitrite salts with metals, metal oxides, or sulfates. Several metals react with nitric acid liberating nitric oxide. (See Nitric Acid, Reactions). For example, action of 1 1 nitric acid on copper turnings forms nitric oxide ... 

Palladium is attacked by concentrated nitric acid, particularly in the presence of nitrogen oxides. The reaction is slow in dilute nitric acid. Finely divided palladium metal reacts with warm nitric acid forming paUadium(ll) nitrate, Pd(NOs)2. Hydrochloric acid has no affect on the metal. Reaction with boiling sulfuric acid yields palladium sulfate, PdS04, and sulfur dioxide. 

Although much of the biological literature focuses on nitrosating reactions of nitric oxide, chemically nitric oxide is a moderate one-electron oxidant, making formation of nitroxyl anion feasible under physiological conditions. The reduction potential to reduce nitric oxide to nitroxyl anion is +0.39 V, whereas it requires +1.2 V to oxidize nitric oxide to nitrosonium ion. Nitrosating reactions of nitric oxide are often mediated by conversion of nitric oxide to another nitrogen oxide species or by direct reaction with transition metals (Wade and Castro, 1990). 

The reaction of Co(tc-Cp)(CO)2 and of [Co(7t-Cp)NO]2 with nitric oxide in the presence of norbornene has been reported. In both cases the species shown in Figure 14 may be isolated in high yield.125 The mechanism of these three component syntheses could well be related to that of the NO insertion reactions (Scheme 2) in that here NO insertion might occur into the metal-carbon tt-bond of a cobalt-norbornene intermediate. 

The most familiar complexes in this class are Roussin s red and black salts140 obtained as a mixture from the reaction of iron(III) sulfide with nitric oxide and an alkali metal sulfide.141 The dimeric and diamagnetic red salt, K2[Fe(NO)2S]2 gives rise to a series of stable esters [Fe(NO)2SR]2 (R = Me, Et, Ph etc.) which are also diamagnetic, dark red and soluble in organic solvents. Some preparative routes142 to the red salt and its esters are shown in Scheme 3. 

In the presence of metal catalysts nitrosations using nitric oxide proceed rapidly and it is clear that a very powerful nitrosating species is produced. Rate measurements on the reaction of diethylamine with nitric oxide in the presence of Cu(II) salts indicated that a copper-nitrosyl complex was that species (Brackman and Smit, 1965). Many metal-nitrosyl complexes are now known... 

SAFETY PROFILE Poison by intravenous route. Lanthanum and other lanthanoids can cause delayed blood clotting leading to hemorrhages. Has caused liver injury" in experimental animals. The dust is a dangerous fire hazard when exposed to flame can react vigorously with oxidizing materials. Violent reaction with nitric acid, phosphoms (above 400°C), air, halogens. Moderately explosive in the form of dust when exposed to flame or by chemical reaction. Incompatible with H2O, C, N, B, Se, Si, S. See also RARE EARTHS and POWDERED METALS. 

Very dangerous fire hazard by spontaneous chemical reaction. Moderately explosive when exposed to flame. Explosive reaction with dichlorine oxide, silver nitrate, concentrated nitric acid, nitrogen trichloride, oxygen. Reacts with mercury(II) nitrate to form an explosive product. Ignition or violent reaction with air, boron trichloride, Br2, CI2, aqueous halogen solutions, iodine, metal nitrates, NO, NCI3, NO3, N2O,... 

The decomposition of the lower sulfides of the heavy metals and the recovery of the metal as soluble salts and of sulfur in the elemental form have been demonstrated for pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, molybdenite, and associated metals such as nickel and cobalt. Pyrite and chalcopyrite are higher sulfides and to be amenable to this treatment have to be thermally decomposed at 600-650 C prior to leaching. The reactions with nitric acid are exothermic, and are carried out below 1 atm and at around 100°C. In addition to the sulfides, this technique has been applied successfully to the extraction of nonferrous metals from partly oxidized sulfide ores, fayalite slags, copper scrap, and other intermediate products, such as residue from electrolytic zinc plats. 

The reactions of nitric oxide with metal cluster compounds themselves are complicated by the possibility of metal—metal bond cleavage. In the next example, the tri-iron compound shows very different reactivity from its ruthenium and osmium analogs (26-28) ... 

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