Cerium halides

The compound cerium oxide (either Ce Oj or CeO ) is used to coat the inside of ovens because it was discovered that food cannot stick to oven walls that are coated with cerium oxide. Cerium compounds are used as electrodes in high-intensity lamps and film projectors used by the motion picture industry. Cerium is also used in the manufacturing and polishing of high-refraction lenses for cameras and telescopes and in the manufacture of incandescent lantern mantles. It additionally acts as a chemical reagent, a misch metal, and a chemical catalyst. Cerium halides are an important component of the textile and photographic industries, as an additive to other metals, and in automobile catalytic converters. Cerium is also used as an alloy to make special steel for jet engines, solid-state instruments, and rocket propellants. 

The ability of high-temperature ionic melts to dissolve various substances (e.g., metals, their oxides, etc.) is considered as one of their most important properties. In the case of scintillation single crystals based on alkali metal halides, definite halides-dopants (Til, cerium halides, etc.) are referred to as desirable admixtures, since they create levels in the forbidden zone of the dielectric matrix which are responsible for the luminescence. On the contrary, oxygen-containing admixtures are harmful, since their incorporation in the crystals causes a considerable decrease of their yield, radiation resistance, etc. 

Four years before isolating yttria, Mosander extracted lanthanum oxide as an impurity from cerium nitrate (hence the name from Greek XavOaveiv, to hide), but it was not until 1923 that metallic lanthanum in a relatively pure form was obtained, by electrolysis of fused halides. 

Other detrimental factors which should to be taken into account in the materials selection process include temperature cycling and the presence of halide gases. Specialist alloys containing rare earth element additions such as cerium, lanthanum and yttrium have been developed for use in certain environments up to 130°C. 

The first compound of this series, CeSI, was reported by Carter (68) in 1961, and later discussed by Dagron (93). It was obtained by the reaction of iodine with cerium sulfide at 430 C, or by direct synthesis from the elements at 500°C. This was the start of a detailed investigation of this group of compounds mainly by Dagron and co-workers. The present situation is presented in Table VII. No scandium compounds are known thus far, and the same is true for selenium and tellurium halides of these elements. 

The induced reduction of chlorate can be inhibited by iodide, bromide and chloride ions. The effectiveness of these ions is about 400 10 1 in the given order. The order and the magnitude of the effect agree fairly well with the catalytic activity of these ions in the arsenic(III)-cerium(IV) reaction. This inhibition by halides is presumably connected with the opening of a new two-electron route for the arsenic(III)-cerium(IV) reaction. 

Oxiranes undergo ring-opening with cerium(VI) ammonium nitrate and an excess of a quaternary ammonium halide to yield haloethanols [34], The reaction occurs with high regio- and stereo-selectivity, for example, / (+)-styrene oxide produces S(+)-2-chloro-2-phenylethanol in 85% yield with 96% ee. 

As a pure metal, cerium is unstable and will decompose rapidly in moist air. It also decomposes in hot water to form hydrogen. Its oxide compounds and halides are stable and have a number of uses. 

Cerium, samarium, and other lanthanide halides promote addition of ketene silyl enol ethers to aldehydes.54 Imines react with ketene silyl acetals in the presence of Yb(03SCF3)3. Preferential addition to the imine occurs even in the presence of aldehyde... 

Neodymium, along with lanthanum, cerium and praseodymium, has low melting points and high boiling points. The fluorides of these and other rare earth metals are placed under highly purified helium or argon atmosphere in a platinum, tantalum or tungsten crucible in a furnace. They are heated under this inert atmosphere or under vacuum at 1000 to 1500°C with an alkali or alkaline earth metal. The halides are reduced to their metals ... 

Metallic samarium is obtained by heating the oxide, Sm203 with lanthanum turnings or cerium in slight excess amounts in a tantalum crucible under high vacuum. The metal is recovered by condensation of its vapors at 300 to 400°C. The metal cannot be obtained by reduction of its halides, SmFs or SmCls, or by heating with calcium or barium. In such reduction, trihalides are reduced to dihalides, but not to the metal. 

Silica is reduced to silicon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous silicon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum halides, silica can be converted to silane in high yields by reaction with hydrogen (15). Silicon itself is not hydrogenated under these conditions. The formation of silicon by reduction of silica with carbon is important in the technical preparation of the element and its alloys and in the preparation of silicon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and silicate. At 800—900°C, silica is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce silica to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

Ammino-derivatives op Subgroup A—Derivatives of Titanium Kilts, Zirconium Salts, Cerium, and Thorium Halides. 

Reduction of RX.1 Alkyl halides, even alkyl fluorides, are reduced in high yield by LiAlH4/CeCl3 (3 1) in refluxing DME or THF. The actual reagent may be a low-valent cerium compound, since direct hydride attack is not involved. Under the same conditions phosphine oxides are reduced to phosphines. 

From the early 1960s onwards, the use of lanthanide (Ln) based catalysts for the polymerization of conjugated dienes came to be the focus of fundamental studies [31]. The first patent on the use of lanthanides for diene polymerization originates from 1964 and was submitted by Union Carbide Corporation (UCC) [32,33]. In this patent the use of binary lanthanum and cerium catalysts is claimed. Soon after this discovery by UCC, Throckmorton (Goodyear) revealed the superiority of ternary lanthanide catalyst systems over binary catalyst systems. The ternary systems introduced by Throckmorton comprise a lanthanide compound, an aluminum alkyl cocatalyst and a halide donor [34], Out of the whole series of lanthanides Throckmorton... 

Some of the applications of the organometallic compounds of lanthanides are as catalysts for (i) stereo specific polymerization of diolefins and in particular to obtain high yields of 1,4-ci.v-polybutadiene and 1,4-cw-polyisoprene and copolymer of the two monomers. The order of effectiveness of the rare earths as catalysts is Nd > Ce, Pr < Sm, Eu. The nature of halogen of the Lewis acid affecting the catalytic activity is in the order Br > Cl > I > F. Detailed work on the activity of cerium octanoate-AlR3-halide showed stereo specificity with cerium as the primary regulator. Cerium is thought to form jr-allyl or 7r-crotyl complexes with butadiene. 

A mixture of LiAlHi and CeCls is a powerful reducing agent, reducing unsaturated carbonyl compounds to allylie alcohols (in this case, anhydrous cerium chloride is a necessity). It will reduce phosphine oxides to phosphines, oximes to primary amines, and o ,jS-unsaturated carbonyl compounds to allylie alcohols. In particular, it reduces both aryl and alkyl halides to hydrocarbons. 

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