Synthesis from the Elements

The iodine is then sublimed to the lower or right-hand portion of apparatus a or b, respectively, and two tubular furnaces arranged as to provide the temperature profiles shown. Insulation (Fiberfrax, Carborundum Co.) is used to cover the tops of the furnaces and especially the smaller horizontal tube in b. The hotter furnace is positioned so that sublimed or molten Lal3 which may overflow the crucible will not block the narrow tubes. The temperature of the metal end is run right up to 800°, with the I2 reservoir held at 110-130°. 

After some salt has formed and covered the metal, the I2 furnace temperature is increased to about 180°. The reaction will take 4-12 hr, depending on quantities and temperatures. The furnace around the I2 can be lowered occasionally to 

The most likely impurity is LaOI which has the PbFCl structure as do many of the other rare earth metal oxyiodides.3 The stronger 25% of the powder diffraction lines for LaOI (A), with intensities in parentheses, are 3.05(10), 2.92(8), 2.06(4), 1.72(5), 1.71(5). The powder pattern of Lal3 is not especially useful for establishing its purity unless all the lines from a high-resolution (Guinier) pattern are compared. 

The light yellow Lal3, melting point 778-779°, exhibits the PuBr3-type structure. The material is very sensitive to traces of both moisture and 02. The absence of cloudy appearance on the dissolution of Lal3 (and other rare earth metal trihalides) in absolute ethanol is not a good assurance of purity unless the material has been heated strongly to ensure the formation of crystalline LaOI (or other MOX phases) from absorbed moisture, hydroxide, etc. The same applies to the appearance of MOI in the powder pattern. 

Halides of the Lanthanides and Actinides, WHey-lnterscience, New York, 1968, p. 219. 

Inorganic Syntheses, Volume 22 Edited by Smith L. Holt, Jr. 11983 by Inorganic Syntheses, Inc. 

The tungsten crucible, about 3.2 cm diameter x5 cm high, is sealed within the apparatus, taking care that it rests either on a fairly flat tube end or on a silica support so that greater thermal expansion of tungsten will not lead to 

After some salt has formed and covered the metal, the furnace temperature is increased to about 180°. The reaction will take 4-12 h, depending on quantities and temperatures. The furnace around the can be lowered occasionally to judge progress. If excess I2 has been used, the iodine reservoir is cooled to — 80° after reaction is complete while the furnace around the salt is still at 200-300° and the 12 reservoir sealed off. If a slight deficiency of 12 has been used (or the reaction has been incomplete), the excess metal can be separated (and intermediate iodides allowed to disproportionate) through sublimation of the crude product in high vacuum (below). 

The Lal3 product obtained from either of the above routes is sufficiently pure for some purposes. However, some impurities will have been introduced by handling of the reactants. La especially, in the air. One may also choose to use a relatively poor grade of metal (with respect to nonmetals) for the synthesis, anticipating the purification afforded by the sublimation. Also, some reaction of Lal3 with fused silica to give Sil4 plus LaOI or a lanthanum silicate will 

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Hafnium Boride. Hafnium diboride [12007-23-7] HfB2, is a gray crystalline soHd. It is usually prepared by the reaction of hafnium oxide with carbon and either boron oxide or boron carbide, but it can also be prepared from mixtures of hafnium tetrachloride, boron trichloride, and hydrogen above 2000°C, or by direct synthesis from the elements. Hafnium diboride is attacked by hydrofluoric acid but is resistant to nearly all other reagents at room temperature. Hafnium dodecaboride [32342-52-2] has been prepared by direct synthesis from the elements (56). 

Other preparative methods include direct synthesis from the elements, reaction between gaseous hydrogen fluoride and titanium tetrachloride, and decomposition of barium hexafluorotitanate [31252-69-6] BaTiF, or ammonium, (NH 2TiFg. 

Titanium Dibromide. Titanium dibromide [13873-04-5] a black crystalline soHd, density 4310 kg/m, mp 1025°C, has a cadmium iodide-type stmcture and is readily oxidized to trivalent titanium by water. Spontaneously flammable in air (142), it can be prepared by direct synthesis from the elements, by reaction of the tetrabromide with titanium, or by thermal decomposition of titanium tribromide. This last reaction must be carried out either at or below 400°C, because at higher temperatures the dibromide itself disproportionates. 

The earliest method for manufacturiag carbon disulfide involved synthesis from the elements by reaction of sulfur and carbon as hardwood charcoal in externally heated retorts. Safety concerns, short Hves of the retorts, and low production capacities led to the development of an electric furnace process, also based on reaction of sulfur and charcoal. The commercial use of hydrocarbons as the source of carbon was developed in the 1950s, and it was still the predominate process worldwide in 1991. That route, using methane and sulfur as the feedstock, provides high capacity in an economical, continuous unit. Retort and electric furnace processes are stiU used in locations where methane is unavailable or where small plants are economically viable, for example in certain parts of Africa, China, India, Russia, Eastern Europe, South America, and the Middle East. Other technologies for synthesis of carbon disulfide have been advocated, but none has reached commercial significance. 

Steam reforming of CH4 CH4 + H2O = CO + 3H2 NH3 synthesis from the elements Hydrogenation of CO and CO2 to form hydrocarbons (Fischer-Tropsch syndresis)... 

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 finely divided hydride produced by pyrolysis is pyrophoric in air, while synthesis from the elements produces a substantially air-stable product [1]. That prepared by reduction of butylmagnesium bromide with lithium tetrahydroalumi-nate is pyrophoric and reacts violently with water and other protic compounds [2], The hydride produced from magnesium anthracene has a very large specific surface area and is pyrophoric [3], In the context of use of the hydride for energy storage purposes, ignition and combustion behaviour of 100-400 g portions were studied, as well as the reaction with water [4],... 

The synthesis of chalcogenides such as those of the rare earth elements has traditionally been performed through the reaction of rare earth metals or oxides with a molten or vaporous chalcogen source in a high-temperature environment. Soft synthetic methods utilizing lower temperature conditions, such as hydrothermal or flux syntheses, can allow access also to thermodynamically metastable phases. Flux syntheses of R chalcogenides via an alkali poly-chalcogenide flux have been shown to be extremely versatile for the preparation of many new structures, some of which cannot be obtained by direct synthesis from the elements. 

Preparation of InAs by direct synthesis from the elements... 

Technetium(v) and Rhenium(v) Complexes.—Re2Tc5 has been obtained by ampoule synthesis from the elements at 800 °C, and its thermodynamic constants and X-ray diffraction characteristics determined/ Re2S3Cl4 has been identified in the Re—S—Cl system. Chloride complexes of technetium(v), K2[TcOCl5] and K2[TcO(OH)Cl4], have been obtained from a solution ofKTc04in HC1. "... 

The following data give a short historic survey on the first steps toward a synthesis of ammonia from hydrogen and nitrogen. In 1823, Eobereiner claimed to have achieved an ammonia synthesis from the elements (20). His experiments proved to be erroneous. In 1884, Ramsay and Young (21) showed that the catalytic decomposition of ammonia does not proceed quantitatively, a first indication for the exist-... 

Eu—As system. — Brixner. [227] has reported the preparation of arsenides, antimonides and tellurides of the type MA (M = rare earths, Sc, Y and A = As, Sb, Te) and has studied the structural and electrical properties of these compounds. The compounds were prepared by direct synthesis from the elements in an argon atmosphere. All compounds possess a grey metallic appearance and crystallize in the NaCl structure. The following physical properties on EuAs and EuSb are available [227]. 

Hydrogen chloride may be formed by direct synthesis from the elements. Although this method has been used on a commercial scale and yields a very pure product, it is not the one commonly used. It is far more convenient to treat sodium chloride with concentrated sulphuric acid. The volatile hydrogen chloride escapes from the reaction mixture and the reaction goes to completion. 

Mercuric sulphide is conveniently made by direct synthesis from the elements. Two modifications of this compound are known, one black, which is formed first in this preparation and also by precipitation of mercuric and sulphide ions the other a brilliant red (vermilion), which is more stable and into which the black form tends to change. 

These can be made by direct synthesis from the elements at 1000 °C. They have the NaCl structure and can be hydrolysed to NH3. 

The synthesis of borides often requires high temperatmes, involving difficulties in obtaining pme products while simultaneously using simple methods. Direct synthesis from the elements is of particular interest in fundamental research since high-pmity products can be obtained. Other processes are... 

For the synthesis of TeCl4 this latter reaction with direct use of TeCle as starting material is preferable to the synthesis from the elements. 

Several other methods are now employed industrially for the preparation of hydrocyanic acid. Synthesis from the elements is widely used. In this a mixture of hydrogen, carbon monoxide and nitrogen is passed through an electric arc, mixtures of nitrogen and hydrocarbons being sometimes employed, e.g., 20% methane, 10% hydrogen and 70% nitrogen. 

Synthesis from the Elements.— We may now consider methods for the formation of methane and in particular its synthesis from the elements. Though, as has been stated, hydrogen and carbon do not unite directly under ordinary laboratory conditions, they do unite directly when a mixture of the two elements is heated to 1200°, methane being the product. 

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