Lanthanum oxide fluoride

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

Anhydrous lanthanum fluoride also may be made by passing dry hydrogen fluoride over lanthanum oxide. This process, however, produces trace amounts of lanthanum oxyfluoride, LaOF. Highly purified material may be obtained by passing dry purified HF over molten fluoride in a platinum crucible. 

One of the most important uses of lanthanum compounds is in carbon arc lamps. In a carbon arc lamp, an electrical current is passed through the lamp electrode. The electrode is made of carbon and traces of other materials that have been added. The current causes the carbon to heat up and give off a brilliant white light. The exact color of the light depends on the other materials that have been added to the carbon. Lanthanum fluoride (Laf3) and lanthanum oxide (La203) are usually used for this purpose. 

The reaction of lanthanum(III) oxide fluoride, a-LaOF, with phosgene has been investigated as a function of time and temperature (430, 500 and 680 C) by t.g.a., followed by product analysis and characterization by powder X-ray diffraction [113]. This is a much more thorough study than those described above for the lanthanide oxide chlorides, and the results are summarized in Fig. 9.9. All the fluoride ends up as LaF (thus no significant quantities of COCIF or COFj can be formed), and the major product at each temperature is LaOCl. The product analysis is consistent with the following sequential reactions occurring [113] ... 

Some measurements of this property have been made in a range of electrically conducting polymers. These include epoxy resin/polyaniline-dodecylbenzene sulfonic acid blends [38], polystyrene-black polyphenylene oxide copolymers [38], semiconductor-based polypyrroles [33], titanocene polyesters [40], boron-containing polyvinyl alcohol [41], copper-filled epoxy resin [42], polyethylidene dioxy thiophene-polystyrene sulfonate, polyvinyl chloride, polyethylene oxide [43], polycarbonate/acrylonitrile-butadiene-styrene composites [44], polyethylene oxide complexes with sodium lanthanum tetra-fluoride [45], chlorine-substituted polyaniline [46], polyvinyl pyrolidine-polyvinyl alcohol coupled with potassium bromate tetrafluoromethane sulfonamide [47], doped polystyrene block polyethylene [38, 39], polypyrrole [48], polyaniline-polyamide composites [49], and polydimethyl siloxane-polypyrrole composites [50]. 

Marked differences are observed between the properties of the halides. The trifluorides are stable in air at room temperature and are non-hydroscopic. They are sparingly soluble in water with solubility product constants which vary from 10 for lanthanum to 10 for lutetium (DaDilva and Queimado, 1973). In liquid HF, the solubilities are less than 4x 10 mole/ (Ikrami et al., 1972). At high temperatures the trifluorides react with oxygen and moisture to form the oxide fluorides, ROF, which are stable in air at temperatures greater than 1000°C. Conversion of the fluorides to the oxides may be achieved by heating in steam at 1000°C (Stezowski and Eick, 1970). 

M. Takashima, S. Yonezawa, M. Leblanc, Synthesis and oxide ion conductivity of lanthanum-europium oxide fluoride, La2Eu203Fg, Solid State Ionics, 154-155, 547-553 (2002). 

The metallothermic reduction of the oxides by La produces the metals Sm, Eu, Tm, Yb, all having high vapour pressures. The reaction goes to completion due to the removal of the rare earths by volatilization from the reaction chamber (lanthanum has a low vapour pressure). The remaining rare earth metals (Sc, La, Ce, Pr, Nd, Y, Gd, Tb, Dy, Ho, Er, Lu) can be obtained by quantitative conversion of the oxides in fluorides, followed by reduction with Ca. The metallothermic reduction of the anhydrous rare earth chlorides could be also used to obtain La, Ce, Pr and Nd. The molten electrolysis can be applied to obtain only the first four lanthanide metals, La, Ce, Pr and Nd, because of the high reactivity of the materials that limits the operating temperatures to 1100°C or lower. 

Lanthanum in purified metallic state may be obtained from its purified oxide or other salts. One such process involves heating the oxide with ammonium chloride or ammonium fluoride and hydrofluoric acid at 300° to 400° C in a tantalum or tungsten crucible. This is followed by reduction with alkali or alkaline earth metals at 1,000°C under argon or in vacuum. 

C (190-196) and by the thermal decomposition of the trifluoride at 800°C in air (191, 197, 198). The lanthanum compound itself may also be prepared by hydrolysis of the trifluoride (199) and by the reaction of the oxide with molten sodium fluoride (200). On treatment with CFCI3 (201), it is converted back to the trifluoride. The cerium analog has been prepared from Ce02 by reaction with CeF3 at 2750°C (202) or with CeF3 and cerium metal at 900°C in a nickel tube (203). The infrared spectra of these solids have been reported (204). 

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