Reduction reactions boron oxide

Elemental boron is produced by the reduction of boron oxide by magnesium to give boron and magnesium oxide. Write a balanced equation for this reaction. 

Research-grade material may be prepared by reaction of pelleted mixtures of titanium dioxide and boron at 1700°C in a vacuum furnace. Under these conditions, the oxygen is eliminated as a volatile boron oxide (17). Technical grade (purity > 98%) material may be made by the carbothermal reduction of titanium dioxide in the presence of boron or boron carbide. The endothermic reaction is carried out by heating briquettes made from a mixture of the reactants in electric furnaces at 2000°C (11,18,19). 

Preparation. The simplest method of preparation is a combination of the elements at a suitable temperature, usually ia the range of 1100—2000°C. On a commercial scale, borides are prepared by the reduction of mixtures of metallic and boron oxides usiag aluminum, magnesium, carbon, boron, or boron carbide, followed by purification. Borides can also be synthesized by vapor-phase reaction or electrolysis. 

Preparation. Boron carbide is most commonly produced by the reduction of boric oxide with carbon in an electric furnace between 1400 and 2300°C. In the presence of carbon, magnesium reduces boric oxide to boron carbide at 1400—1800°C. The reaction is best carried out in a hydrogen atmosphere in a carbon tube furnace. By-product magnesium compounds are removed by acid treatment. 

However, the reduction reactions in which a solid reducing agent is used usually give impure products. In this case, the product contains 80% to 95% boron that also contains magnesium and boron oxide as impurities. The boron produced in this way is a brownish-black form having a density of 2.37 g/cm3. 

Boron carbide is prepared by reduction of boric oxide either with carbon or with magnesium in presence of carbon in an electric furnace at a temperature above 1,400°C. When magnesium is used, the reaction may be carried out in a graphite furnace and the magnesium byproducts are removed by treatment with acid. 

In principle, oxidation could occur simultaneously during a HDH (reduction) reaction. For example any de-halogenated compounds could be oxidised to C02 in the anode compartment. Thus in the case of pentachlorophenol the phenol produced by the HDH could be oxidised at a suitable anode (e.g. boron-doped diamond) to C02 ... 

More than one boride phase can be formed with most metals, and in many cases a continuous series of solid solutions may be formed. Several methods have been used for the relatively large-scale preparation of metal borides. One that is commonly used is carbon reduction of boric oxide and the appropriate metal oxide at temperatures up to 2000 °C. Fused salt electrolysis of borax or boric oxide and a metal oxide at 700 1000 °C have also been used. Small-scale methods available include direct reaction of the elements at temperatures above 1000 °C and the reaction of elemental boron with metal oxides at temperatures approaching 2000 °C. One commercial use of borides is in titanium boride-aluminum nitride crucibles or boats for evaporation of aluminum by resistance heating in the aluminizing process, and for rare earth hexaborides as electronic cathodes. Borides have also been used in sliding electrical contacts and as cathodes in HaU cells for aluminum processing. 

Borides. Zirconium forms two borides zirconium diboride [12045-64-6] ZrB2, and zirconium dodecabotide [12046-91 -2] ZtB 2- Th diboride is synthesized from the elements, by vapor-phase coreduction of zirconium and boron hahdes, or by the carbothermic reduction of zirconium oxide and boron carbide boric oxide is avoided because of its relatively high vapor pressure at the reaction temperature. 

Boron carbide (B4C) is one of the hardest known materials with excellent properties of low density, very high chemical and thermal stability, and high neutron absorption cross-section. Bulk B4C is conventionally synthesized by high temperature (up to 2400 °C) reactions, such as the carbothermal reduction of boric acid or boron oxide. Nanocrystalline B4C was solvothermally synthesized in CCI4 at 600 °C (Reaction (32)). 

Preparation of the left-hand fragment, which incorporates the C-11 to C-13 portion of 18, utilizes the aldol reaction of / -boron enolate 10 with propionaldehyde to provide the a-hydroxy acid 11 in 85% yield and 100 1 stereoselectivity. Subsequent diazomethane esterification, O-silylations, DIBAL reduction, and Collins oxidation affords the optically pure aldehyde 12 in an overall yield of 75%. 

Fusion processes can be grouped into acid-base reactions (carbonates, borates, hydroxides, disulfates, fluorides, and boron oxide) and redox reactions (alkaline fusion agent plus oxidant or reductant). Common fluxes are listed in Table 4.2. Fluoride-pyrosulfate and carbonate-bisulfate fusions are used to decompose soil and fecal samples. 

One of the serious drawbacks of the Wittig reaction is the unavoidable production of triphenylphosphane oxide in stoichiometric quantities. Whilst its direct reduction with boron, aluminium or silicon hydrides would be possible, these reagents are too expensive for a viable process. In fact, distilled triphenylphosphane oxide is reacted with phosgene, generated in situ, to give the corresponding dichloride, which is then reduced with metals, like aluminium. [55]... 

The three basic steps in the palladium-catalysed Suzuki-Miyaura reaction involve oxidative addition, transmetalation, and reductive elimination. A systematic study of the transmetalation step has found that the major process involves the reaction of a palladium hydroxo complex with boronic acid, path B in Scheme 3, rather than the reaction of a palladium halide complex with trihydroxyborate, path A. A kinetic study using electrochemical techniques of Suzuki—Miyaura reactions in DMF has also emphasized the important function of hydroxide ions. These ions favour reaction by forming the reactive palladium hydroxo complex and also by promoting reductive elimination. However, their role is a compromise as they disfavour reaction by forming of unreactive anionic trihydroxyborate. A method for coupling arylboronic acids with aryl sulfonates or halides has been developed using a nickel-naphthyl complex as a pre-catalyst. It works at room temperature in toluene solvent in the presence of water and potassium carbonate. ... 

Metal borides are generally prepared by the direct reaction of the elanents at high temperatures or by the reduction of metal oxides or halides. Thus, reduction of mixtures of BjOj and metal oxides by carbothermic reaction yields metal borides. Reaction of metal oxides with boron or with a mixture of carbon and boron carbide is another route. Some metal borides are prepared by fused salt electrolysis (e.g. TaBj). Borides of IVA-VIIA elements as well as ternary borides have been reviewed by Nowomy [1], The method employed to prepare TiB starting with TiCl is interesting [2], TiCl and BCI3 react with sodium in a nonpolar solvent (e.g. heptane) to produce an amorphous precursor powder along with NaCl. NaCl is distilled off and the precursor crystallized at relatively low temperatures (-970 K). 

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