Iridium chloride reduction

Another reduction process, catalyzed by iridium chloride, is characterized by very high axiatiequatorial product ratios for cyclohexanones and apparently involves hydride transfer from isopropanol.197... 

The PGM concentrate is attacked with aqua regia to dissolve gold, platinum, and palladium. The more insoluble metals, iridium, rhodium, mthenium, and osmium remain as a residue. Gold is recovered from the aqua regia solution either by reduction to the metallic form with ferrous salts or by solvent-extraction methods. The solution is then treated with ammonium chloride to produce a precipitate of ammonium hexachloroplatinate(IV),... 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

An interesting method to produce water-soluble iridium nanoparticles was proposed by Chaudret and coworkers [13]. Here, aqueous soluble iridium nanoparticles were synthesized by the chemical reduction of iridium trichloride with sodium borohydride in an aqueous solution of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (Scheme 15.2). The precursor reduction was assisted by sonication, while the gradual conversion of Ir(lll) ions to lr(0) nanoparticles was followed using UV spectroscopy. The use of a molar surfactant Ir ratio of 10 proved sufficient to obtain stable aqueous soluble iridium nanoparticles however, if the molar surfactant Ir ratio used was <10 then agglomeration was observed in solution after several days. TEM analysis of the iridium nanoparticles revealed a monodispersed size distribution and a mean diameter of 1.9 0.7nm (Figure 15.2). 

Finally, in connection with the comments of Dr. Gordon, we have looked at the reduction of chlorate by hexachloroiridate. The final products, of course, are hexachloroiridate and chloride. The reaction is stoichiometric. So far, no tracer experiments have been done to try to identify any of the unstable intermediates but both of the iridium species are well known to be substitution inert, and the reaction surely involves a one-electron reduction of chlorate. 

The main methods of reducing ketones to alcohols are (a) use of complex metal hydrides (b) use of alkali metals in alcohols or liquid ammonia or amines 221 (c) catalytic hydrogenation 14,217 (d) Meerwein-Ponndorf reduction.169,249 The reduction of organic compounds by complex metal hydrides, first reported in 1947,174 is a widely used technique. This chapter reviews first the main metal hydride reagents, their reactivities towards various functional groups and the conditions under which they are used to reduce ketones. The reduction of ketones by hydrides is then discussed under the headings of mechanism and stereochemistry, reduction of unsaturated ketones, and stereochemistry and selectivity of reduction of steroidal ketones. Finally reductions with the mixed hydride reagent of lithium aluminum hydride and aluminum chloride, with diborane and with iridium complexes, are briefly described. 

Vanadium predpitates the metal from solutions of salts of gold, silver, platinum, and iridium, and reduces solutions of mercuric chloride, cupric chloride and ferric chloride to mercurous chloride, cuprous chloride, and ferrous chloride, respectively. In these reactions the vanadium passes into solution as the tetravalent ion. No precipitation or reduction ensues, however, when vanadium is added to solutions of divalent salts of zinc, cadmium, nickel, and lead. From these reactions it has been estimated that the electrolytic potential of the change, vanadium (metal)—>-tetravalent ions, is about —0 3 to —0 4 volt, which is approximately equal to the electrolytic solution pressure of copper. This figure is a little uncertain through the difficulty of securing pure vanadium.5... 

Ruthenium(VI)-catalysed oxidation of propane-1,2-diol, cyclohexane-1,2-diol, and propanetriol by alkaline HCF(III) exhibits a zero-order dependence on HCF(III) and first-order dependence on Ru(VI) and the rate increased with a decrease in alkali concentration. The reaction showed a Michaelis-Menten type of behaviour with respect to the reductant. A tentative mechanism has been proposed.63 In the ruthenium(in)-catalysed oxidation of sulfanilic acid by HCF(III) in alkaline medium, the proposed ruthenium(III) active species is [Ru(H20)50H]2+.64 Iridium(III) chloride-catalysed oxidation of diethylene glycol by alkaline HCF(III) is proposed to proceed through complex formation.65... 

II. 5).204,205 Unsupported iridium catalysts have been prepared by reducing an iridium oxide of Adams type at 165°C under a stream of hydrogen206 or by reducing iridium hydroxide, prepared by addition of lithium hydroxide to an aqueous solution of irid-ium(III) chloride, at 80-90°C and 8 MPa H2.204 Unsupported and supported iridium catalysts may also be prepared by reduction of iridium(IV) chloride with sodium boro-hydride.207 It is noted that the catalytic activity of deactivated iridium can be almost completely regenerated by treatment with concentrated nitric acid.205... 

Ammonium Chloriridite, (NH4)sIrCl6.Aq., prepared either by reduction of ammonium chloriridate or by decomposing the sodium salt with concentrated ammonium chloride solution,9 yields dark, olive-green, orthorhombic prisms,10 which readily dissolve in water.11 It is probably the monohydrate, (NH4)3IrCl6.H20.12 Upon ignition, metallic iridium alone remains, in spongy form. The decomposition begins to be appreciable just above 200° C. 

Homobimetallic iridium(I) complexes containing the binucleating PNNP ligand undergo oxidative addition and reductive elimination reactions with acetyl chloride and methyl iodide. Thus,... 

Selective reduction to hydroxylamine can be achieved in a variety of ways the most widely applicable systems utilize zinc and ammonium chloride in an aqueous or alcoholic medium. The overreduction to amines can be prevented by using a two-phase solvent system. Hydroxylamines have also been obtained from nitro compounds using molecular hydrogen and iridium catalysts. A rapid metal-catalyzed transfer reduction of aromatic nitroarenes to N-substituted hydroxylamines has also been developed the method employs palladium and rhodium on charcoal as catalyst and a variety of hydrogen donors such as cyclohexene, hydrazine, formic acid and phosphinic acid. The reduction of nitroarenes to arylhydroxyl-amines can also be achieved using hydrazine in the presence of Raney nickel or iron(III) oxide. ... 

Among the complexes which may function in this way are pentacyano-cobaltate ion, iron pentacarbonyl, the platinum-tin complex, and iridium and rhodium carbonyl phosphines. It has been suggested that with tristriphenylphosphine Rh(I) chloride, a dihydride is formed and that concerted addition of the two hydrogen atoms to the coordinated olefin occurs (16). There are few examples of the homogeneous reduction of other functional groups besides C=C, C=C, and C=C—C=C penta-cyanocobaltate incidentally is specific in reducing diolefins to monoolefins. 

Iridium can be separated from Rh and Pt owing to the fact that the anionic Ir chloride complex is precipitated with Ag [7]. Precipitation methods have been proposed also for separation of Rh from Ir and Pt [28]. Rhodium(III) may be separated from iridium(IV) by reduction to the metal [iridium being reduced only to Ir(III)] with Cu powder in 1 M HCl or sodium borohydride (NaBH4)] [29,30]. Iridium can also be separated from Rh and Ru by flotation of the ion-associate formed by the chloride complex of Ir(IV) with a cationic... 

Serious interference in the determination of iridium is caused by Rh and Pt. The selectivity of the method can be improved by preliminary separation of Ir(IV) by extraction with tetraphenylarsonium chloride (CHCI3). If large amounts of Pt, Pd, Ru and Os are present, it is advisable to separate these metals, e.g., by selective reduction of Pt to the metal, extraction of Pd as its dimethylglyoximate, and distillation of Ru and Os as the tetroxides. 

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