Hexachloroiridic acids

Iridium (IV) chloride hydrate (hexachloroiridic acid) [16941-92-7 (6H2O) 207399-11-9 (XH2O)] M 334.O+H2O. If it contains nitrogen then repeatedly concentrate a cone HCl solution until free from nitrogen, and dry free from HCl in a vac over CaO until crystals are formed. The solid is very hygroscopic. [J Am Chem Soc 53 884 1931 Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Vol II 1592 7965.]... 

Hexachloroiridic acid trimethyl phosphite Sec. alcohols from ketones Stereospecific reduction... 

Insoluble iridium dioxide from the sodium peroxide fusion is dissolved in aqua regia, oxidized with nitric acid, and precipitated with ammonium chloride as impure ammonium hexachloroiridate(IV), To purify this salt, it is necessary to redissolve the compound and precipitate out the... 

A 100-mL, two-necked flask with 24/40 T joints is charged with potassium hexachloroiridate(IV) (2.0 g, 4.1 mmole), concentrated hydrochloric acid (10... 

Many other cations of transition metals have been employed for the oxidation of sugars. For example, the oxidation of aldoses by hexachloroiridate(IV)183,184 and tetrachloroaurate(III)183,185 in hydrochloric acid led to the corresponding aldonic acids or aldonolactones. The observed... 

Palleschi et al. [38] reported the use of a composite electrode obtained by mixing SWCNTs and mineral oil in a ratio 60/40 % w/w (carbon/oil). Comparable backgroimd currents were obtained with CPE and CNTPE when CNTs were not pretreated, increasing in a factor of 100 after CNTs pretreatment. The authors reported a significant improvement on the electrochemistry of dopamine, serotonin, 5-Hydroxytiyptamine and other compormds like caffeic acid, ferricyanide, sodimn hexachloroiridate (111) and catechol. 

Hence, the first clearcut evidence for the involvement of enol radical cations in ketone oxidation reactions was provided by Henry [109] and Littler [110,112]. From kinetic results and product studies it was concluded that in the oxidation of cyclohexanone using the outer-sphere one-electron oxidants, tris-substituted 2,2 -bipyridyl or 1,10-phenanthroline complexes of iron(III) and ruthenium(III) or sodium hexachloroiridate(IV) (IrCI), the cyclohexenol radical cation (65" ) is formed, which rapidly deprotonates to the a-carbonyl radical 66. An upper limit for the deuterium isotope effect in the oxidation step (k /kjy < 2) suggests that electron transfer from the enol to the metal complex occurs prior to the loss of the proton [109]. In the reaction with the ruthenium(III) salt, four main products were formed 2-hydroxycyclohexanone (67), cyclohexenone, cyclopen tanecarboxylic acid and 1,2-cyclohexanedione, whereas oxidation with IrCl afforded 2-chlorocyclohexanone in almost quantitative yield. Similarly, enol radical cations can be invoked in the oxidation reactions of aliphatic ketones with the substitution inert dodecatungstocobaltate(III), CoW,20 o complex [169]. Unfortunately, these results have never been linked to the general concept of inversion of stability order of enol/ketone systems (Sect. 2) and thus have never received wide attention. 

Ammonium hexachloroiridate(IV) can be prepared by the metathesis of sodium hexachloroiridate(IV) with ammonium chloride or by the addition of ammonium chloride to either a solution of iridium(IV) hydroxide in hydrochloric acid or of iridium(IV) chloride. Although many workers have prepared sodium hexachloroiridate(IV) by chlorinating mixtures of sodium chloride and iridium, few exact data are available concerning optimum temperatures, reaction times, and yields. 

Hydrogen hexachloroiridate(IV) hexahydrate (17.4 g, 34 mmol) is added to a mixture of ethanol (160 ml) and concentrated hydrochloric acid (20 ml). The mixture is refluxed for 2 h until the color turns from brown to green. After cooled to room temperature, an ethanol solution (70 ml) of triisopropylphosphine (18 ml) is slowly added to the mixture with vigorous stirring. The mixture is refluxed for 4 h and allowed to stand overnight at 0 °C. The resulting purple crystals of [PH Pr3][IrCl4(P Pr3)2] are filtered, washed with cold ethanol, and dried under vacuum. Yield 16 g (58 %). 

Hexachloroiridates(IV) may be prepared by (i) chlorinating a mixture of iridium powder and an alkali metal chloride (ii) in solution, by the addition of an alkali metal chloride to a suspension of hydrous Ir02 in aqueous HC1 or (iii) by the oxidation of [IrCl ] " by O2 in acidic media. Oxidation by Oj probably occurs via reaction (122), with = + 0.21 V. Fine" has suggested that the reverse of reaction (122) occurs in alkaline media. The black crystalline sodium salt Na2[IrCls] is water soluble, and is the usual starting material for the synthesis of other iridium(IV) coordination complexes. The resonance Raman spectrum of (NBu4)2[IrCle] reveals anomalous polarization of all bands this has been ascribed to Jahn-Teller distortions present in the excited electronic state. The single-crystal electronic spectra of various [IrCl ] " salts have also been reported." ... 

A decade later Cleare and GriflBth (13) reported that the reaction of concentrated hydrohalic and formic acids with hexachloroiridate(IV) results in the formation of diamagnetic needle crystals of [Ir2( 00)4X4] " stoichiometry which exhibit metallic reflections. In accord with the work of Malatesta and Canziani (12), they prepared the bromo complexes as well as complexes containing different cations, but they did not prepare complexes containing more than four halides. To account for the observed diamagnetism, they proposed a planar tetranuclear structure based on the structure of the isoelectronic Re4(CO)ie ion (14). 

Recently Krogmann et al. (516) reported that the reaction of formic acid and hexachloroiridate(IV) yields Iri(CO)2ClJ via a series of reduction (Eqs. 57 and 60) and substitution (Eq. 58 and 59) reactions. Formation of [AsPh4]-... 

The nature of hexachloroiridate(rv) in solution has been examined. In neutral or weakly acidic media, the reaction IrCle Ir may take place, but it occurs spontaneously in solutions of pH 11, with evolution of a gas and a colour change from reddish-brown (Ir ) to pale yellow-green (Ir ")- The equilibrium ... 

Several studies have focussed on different methods of oxidizing D-glucose to D-gluconic acid or its lactone. These Include observations on the use of hexachloroiridate and tetrachloroaurate (radi-... 

Hexachloroiridate(iv).—The stopped-flow technique has been used in investigations of the oxidation of several benzenediols. In the reactions with 1,2-diols, the reactions are first-order with respect to each reactant but independent of [H+] and of added [IrClg] ". The wide range of standard redox potentials (0.729 V for 4-methyl-1,2-dihydroxybenzene to 0.955 V for 4,5-dihydroxybenzene-l,3-disulphonic acid) allows correlation of standard free energy variations with reactivities. The reaction proceeds via formation of a semiquinone radical, and a plot of AG against AG ° shows marked curvature. A similar mechanism is postulated for the reactions of quinols and it is of interest that the data on all the diols so far studied may be... 

Potassium hexachloroiridate(IV) and potassium hexacyanoferrate(III) were obtained commercially and used directly. Tris-(2,2-bipyridyl)iron(II) perchlorate was synthesized according to Reference 13. Catechol(1,2-di-hydroxygenzene), L dopa(3- 3,4-dihydroxyphenyl)alanine), and tiron(l,2-dihydroxybenzene-3,5 disulphonic acid) were obtained commercially. 

The oxidation of L-tyrosine by hexachloroiridate(lV) exhibits first-order dependence on both Ir(IV) and L-tyrosine. The reaction rate increases with increase in ionic strength and decreases with increase in acidity. Dityrosine has been identified as the main product, activation parameters have been evaluated, and a mechanism has been suggested. DFT study of the oxidation of a guanine nucleotide by platinum(lV) indicated that a key step in the mechanism is electron transfer from guanine to platinum(lV). It has been shown that out of several different Pt(lV)-guanine adducts, one which is formed from replacement of an axial chlorine ligand in the platinum(lV) complex undergoes oxidation more easily. The oxidation of adenine is found to be more difficult as it involves disruption of an aromatic jt system. ... 

---