Oxidation reactions metal halides

Several approaches have been used for the synthesis of heteroatomic chalcogen cations, including (a) direct oxidation of a mixture of two chalcogens with oleum, MF5 (M = As, Sb) or transition metal halides, (b) reaction of a chalcogen with a homoatomic cation of another chalcogen and (c) compro-portionation of the homoatomic cations of two different chalcogens. 

Higher-valent metal halides oxidize diaryl tellurium compounds to diaryl tellurium dihalides. Copper(II) halides can be generated in the reaction mixture from easily accessible copper(II) acetate and hydrohalic acids4. These halogenation reactions are convenient alternatives to the methods using corrosive elemental halogens or sulfuryl halides. 

Corrosion can also occur by a direct chemical reaction of a metal with its environment such as the formation of a volatile oxide or compounds, the dissolution of metals in fused metal halides. The reaction of molybdenum with oxygen and the reaction of iron or aluminum with chlorine are typical examples of metal/gas chemical reactions. In these reactions, the metal surface stays film-free and there is no transport of electrical charge.1 Fontana and Staehle2 have stated that corrosion should include the reaction of metals, glasses, ionic solids, polymeric solids and composites with environments that embrace liquid metals, gases, aqueous and other nonaqueous solutions. 

H, X = 0) may be prepared by the reaction of ethylene oxide with CO2 under pressure, at 140 °C, in the presence of alkali-metal halides.The reaction is catalysed by free anion, which is generated by the use of the complex between 18-crown-6 and Using complexes of this type, the compounds (233 X= 0 = Me, Ph, or CICH2 R = H or Me) have also been pre-... 

Removal of excess high oxidation state metal halide by reaction with a zero-valent metal. (From Matyjaszewski, K., et al.. Macromolecules, 30, 7348-7350,1997.)... 

The basic properties of metal hydroxides and oxides (basic anhydrides) make their reactions with the appropriate hydrohalic acid an excellent way to prepare metal halides. These reactions, shown in general in Equations (18.12) through (18.14), also extend to a variety of transition metal halides as well ... 

Element halides are alkylated by alkali metal organometallic derivatives. Depending on the stoichiometry, one, several or all the halides are substituted by alkyl groups. The number of introduced alkyl groups is sometimes larger than the number of halides on the element, which yields ate (i.e. anionic) complexes. With transition-metal halides, the reaction sometimes goes along with some reduction of the oxidation state of the transition metal. 

A chain mechanism is proposed for this reaction. The first step is oxidation of a carboxylate ion coordinated to Pb(IV), with formation of alkyl radical, carbon dioxide, and Pb(III). The alkyl radical then abstracts halogen from a Pb(IV) complex, generating a Pb(IIl) species that decomposes to Pb(II) and an alkyl radical. This alkyl radical can continue the chain process. The step involving abstraction of halide from a complex with a change in metal-ion oxidation state is a ligand-transfer type reaction. 

In view of the facile oxidation of 10.13a-c it is not surprising that some metathetical reactions with metal halides result in redox behaviour. Interestingly, lithium halides disrupt the dimeric structures of 10.13a or 10.13c to give distorted cubes of the type 10.14, in which a molecule of the lithium halide is entrapped by a Ei2[E(N Bu)3] monomer. Similar structures are found for the MeEi, EiN3 and EiOCH=CH2 adducts of 10.13a. In the EiN3 adduct, the terminal... 

The combination of hard (A) and soft (5) coordination in the 1,5-P2N4S2 ring system leads to a diversity of coordination modes in complexes with transition metals (Lig. 13.1). In some cases these complexes may be prepared by the reaction of the dianion [Ph4P2N4S2] with a metal halide complex, but these reactions frequently result in redox to regenerate 13.3 (L = S, R = Ph). A more versatile approach is the oxidative addition of the neutral ligand 13.3 (L = S) to the metal centre. 

Other routes include the high-temperature halogenation of metal oxides, sometimes in the presence of carbon, to assist removal of oxygen the source of halogen can be X2, a volatile metal halide CX4 or another organic halide. A few examples of the many reactions that have been used industrially or for laboratory scale preparations are ... 

Neutral carboranes and boranes react with transition-metal complexes forming metallocarboranes or metalloboranes, respectively. However, most metallocarboranes and metalloboranes are prepared from transition-metal halides and anionic carborane and borane species ( 6.5.3.4) or by reacting metal atoms and neutral boranes and carboranes. These reactions are oxidative addition reactions ( 6.5.3.3). 

Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

We have explored rare earth oxide-modified amorphous silica-aluminas as "permanent" intermediate strength acids used as supports for bifunctional catalysts. The addition of well dispersed weakly basic rare earth oxides "titrates" the stronger acid sites of amorphous silica-alumina and lowers the acid strength to the level shown by halided aluminas. Physical and chemical probes, as well as model olefin and paraffin isomerization reactions show that acid strength can be adjusted close to that of chlorided and fluorided aluminas. Metal activity is inhibited relative to halided alumina catalysts, which limits the direct metal-catalyzed dehydrocyclization reactions during paraffin reforming but does not interfere with hydroisomerization reactions. 

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

A final group of reactions are those involving water. A wide variety of materials such as the alkali metals light metals and their hydrides strong acids, such as sulphuric acid anhydrous metal oxides anhydrous metal halides and non-metal oxides ail react vigorously or violently with water under various circumstances. 

Rowley, A. T. et al., Inorg. Chem. Acta, 1993, 211(1), 77 Preparation of metal oxides by fusing metal halides with lithium oxide in a sealed tube leads to explosions if halide hydrates are employed, particularly lanthanide trihalide hydrates. The preparation succeeds with anhydrous halides. This will be purely a question of vapour pressure above an exothermic reaction the question is whether the vapour is water, or metal halide, and the reaction oxide formation, or hydration of lithium oxide. Like other alkali metal oxides, hydration is extremely energetic. 

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