Iridium oxide, decomposition

Iridium dioxide — Iridium oxide crystallizes in the rutile structure and is the best conductor among the transition metal oxides, exhibiting metallic conductivity at room temperature. This material has established itself as a well-known - pH sensing [i] and electrochromic [ii] material (- electrochromism) as well as a catalytic electrode in the production of chlorine and caustic [iii]. The oxide may be prepared thermally [iv] (e.g., by thermal decomposition of suitable precursors at temperatures between 300 and 500 °C to form a film on a substrate such as titanium) or by anodic electrodeposition [v]. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

Chloro-pentammino-iridium Hydroxide, [Ir(NH3)5Cl](OH)2, may be obtained by decomposition of the chloride with freshly precipitated silver oxide, or by warming the chloride with sodium hydroxide on a water-batli. The base is stable, absorbs carbon dioxide from the air, and only slowly decomposes on boiling with water. 

The reactions of butane-2,3-diol by HCF in alkaline medium using Ru(III) and Ru(VI) compounds as catalysts leads to similar experimental rate equations for both the reactions. The mechanism involves the formation of a catalyst-substrate complex that yields a carbocation for Ru( VI) or a radical for Ru(III) oxidation. The role of HCF is in catalyst regeneration. The rate constants of complex decomposition and catalyst regeneration have been determined.89 A probable mechanism invoving formation of an intermediate complex has been proposed for the iridium(III)-catalysed oxidation of propane- 1,2-diol and of pentane-1,5-diol, butane-2,3-diol, and 2-methylpentane-2,4-diol with HCF.90-92 The Ru(VIII)-catalyzed oxidation some a-hydroxy acids with HCF proceeds with the formation of an intermediate complex between the hydroxy acid and Ru(VIII), which then decomposes in the rate-determining step. HCF regenerates the spent catalyst.93... 

Metals or Metal Oxides. Explosions result on contact with Ni powder, Hg, colloidal Ag, thallium powder, Zn powder, PbO, Pb304, and Na202 violent decomposition occurs with barium peroxide, CuO, impure Cr03, iridium dioxide, Pb02, Mn02, and V205 and with Fe powder contaminated with a trace of Mn02.3... 

Hydroxylamine hydrochloride was used as an indicator for the determination of Co(acac)2. The absorbance of the resulting colored solution was measured at 590 nm . Iridium -diketonates were fluorinated oxidatively with BrFs in Freon 113, followed by decomposition in 6M HCl to IrCle and spectrophotometric determination at 488 nm. ... 

Iridium hexafluoride also proved able to oxidize CI2 The molar combining ratio is closer to 1 1 and, as in the case of PtFg, no evidence has been found for free chlorine fluorides in the product. Unfortunately the product is amorphous to X-rays the yellow solid is unstable at room temperature and decomposes ts. 231 to iridium pentafluoride [Z ] and a gaseous decomposition product, other than chlorine, that has not been identified. Should the Raman and infrared studies presently being carried out prove the presence of ClJlIrFe] in the adduct then it would follow that (irFi) > —144 kcahmole . ... 

The reaction of divalent metals, such as copper, nickel, and so on, with dioxetanes in methanol leads to clean catalytic decomposition into carbonyl fragments/ The reaction rates increase with increasing Lewis acidity of the divalent metal and indicate, therefore, typical electrophilic cleavage of the dioxetane. On the other hand, univalent rhodium and iridium complexes catalyze the decomposition of dioxetanes into carbonyl fragments via oxidative addition. 

A range of metals and metal oxides catalyze the reduction of NO. The most successful reducing agent is synthesis gas since the catalytic process is relatively fast 184), unlike the catalyzed decomposition of NO to N2 and O2. The observed nitrogen-containing products depend on the catalytic system used Pd- and Pt-based catalysts convert NO to NH3 184) whereas iridium and ruthenium systems minimize ammonia production and convert nitric oxide to dinitrogen. 

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