Reduction using aluminum powder

Reduction with aluminum powder, for example, in the preparation of benzanthrone, or of quinizarin from purpurin (seldom used). 

The reactor used for the aluminothermic reduction of niobium pentoxide is shown schematically in Figure 4.17 (A). It is a steel pipe, lined on the inside with alumina and provided with a pipe cap. The charge, consisting of stoichiometric amounts of niobium pentoxide and aluminum powder, is blended and loaded in the lined pipe, and covered with alumina. The cap is closed and the reaction initiated by placing the loaded bomb in a gas-fired furnace, preheated to 800 °C, and by raising the temperature of the furnace to 1100 °C. 

Ferroniobium can be produced from the ore pyrochlore in batch process by thermal reduction in a refractory-bned steel or preferably an electric furnace reactor. Aluminum powder is used as a reducing agent. A mixture of niobium... 

The checker experienced difficulty with the dithionite reduction but obtained good results using metallic aluminum powder in aqueous alkali in the reduction step. It is suggested that a difference in purity of the reagent sodium dithionite, as obtained in the two countries, may account for the differing results. 

Grobe and Hegge demonstrated that aluminum powder in fV-methylpyrrolidinone (NMP) can also be used for the reduction of bromotrifluoromethane in the presence ofchlorotrimethyl-silane to produce trimethyl(trifluoromethyl)silane, a method more convenient than the modified Ruppert procedure. The C Br bond of bromochlorodifluoromethane is selectively reduced by aluminum powder in. V-methylpyrrolidinone in the presence of ehlorotrimethylsilane giving (chlorodifluoromethyl)trimethylsilane in 80% isolated yield. The process appears to involve a two-electron reduction of the C Br bond of bromochlorodifluoromethane followed by trapping of the resulting CFjCU" anion by chlorotrimethylsilane. Aluminum powder, corresponding to a net consumption of two electrons per mole of bromochlorodifluoromethane. is needed for the reduction. 

Highly reactive aluminum powders,5 chromium powders,8 and tin powders85 have been produced by the reduction of metal salts in ethereal or hydrocarbon solvents. However, very limited use of these metals to date precludes any discussion of their usefulness in organic and organometallic synthesis. 

Zero-valent indium can also be generated in situ by reduction of indium(III) halide with metallic zinc or aluminum [141] or even tin [142]. Thus,)3-trifluoro-methylated homoallylic alcohols have been prepared in high yields and with excellent stereoselectivity using indium powder [143] or a mixture of InClj/Sn [144]. 

In the Goldschmidt reaction, mentioned in Chapter VI, a metal oxide is reduced by aluminum powder to the free metal. The reaction is useful for obtaining transition metals, such as vanadium, chromium, and manganese, which are too reactive to be produced by reduction of their oxides with hydrogen. The reaction... 

Synthetic applications of dithietane 35 are not limited to its use as a source of hexafluorothioacetone. This compound is also a valuable precursor for the synthesis of a variety of fluorinated sulfur-containing derivatives. For example, the pyrolysis of 35 at 325 C results in the high-yield formation of (CF3)2C=C(CF3)2. The reaction of 35 with PhaP was found to be a convenient route to (Ph)3P=C(CF3)2, which was used for the preparation of l,l-bis(trifluoromethyl) alkenes and CF2=C(CF3)P(0)(0R)2. Recently reported transformation of fluorinated thietanes involves reductive ring expansion to substituted dihydrothiophenes. For example, the treatment of compound 47 with aluminum powder in the presence of a catalytic amount of PbCl2 resulted in an interesting ring expansion process leading to the formation of compound 48 in excellent yield (Scheme 2.23). Readily available fluorinated cycloadducts 49... 

The earliest commercial methods used slurry polymerizations with liquid hydrocarbon diluents, like hexane or heptane. These diluents carried the propylene and the catalyst. Small amounts of hydrogen were fed into the reaction mixtures to control molecular weights. The catalyst system consisted of a deep purple or violet-colored TiCls reacted with diethyl aluminum chloride. The TiCb was often prepared by reduction of TiCU with an aluminum powder. These reactions were carried out in stirred autoclaves at temperatures below 90 °C and at pressures sufficient to maintain a liquid phase. The concentration of propylene in the reaction mixtures ranged between 10-20%. The products formed in discrete particles and were removed at 20-40% concentrations of solids. Unreacted monomer was withdrawn from the product mixtures and reused. The catalysts were deactivated and dissolved out of the products with alcohol containing some HCl, or removed by steam extraction. This was followed by extraction of the amorphous fractions with hot liquid hydrocarbons. 

A novel aluminothermic reduction lithium process was developed, which used LiiCOs, AI2O3 and CaO as raw materials, and aluminum powder as reductant Metal lithium and aluminum hydroxide as by-product were obtained in the process. 

Based on the results, the optimmn proportions of materials are cement aluminmn powder water sand melamine silica fume superplasticizer equal to 1.0 0.004 0.35 1.4 2.0 0.25 0.007. However, the optimum proportions of materials for the studied by [4] were cement, sand, water, fly ash, aluminum powder, and melamine equal to 1.0 0.8 0.75 0.3 0.0035 0.9. Therefore, the used of melamine plastic more than previous study (about 122%) for non-load-bearing lightweight concrete according to ASTM C129 lype II standard. Also, the dry density of non-load-bearing hghtweight concrete was reduction by 36.4% in comparison with the previous study. 

Vapor—sohd reactions (13—17) are also commonly used ia the synthesis of specialty ceramic powders. Carbothermic reduction of oxides, ia which carbon (qv) black mixed with the appropriate reactant oxide is heated ia nitrogen or an iaert atmosphere, is a popular means of produciag commercial SiC, Si N, aluminum nitride [24304-00-3], AIN, and sialon, ie, siUcon aluminum oxynitride, powders. 

Lithium aluminum hydride, LiAIH4/ is another reducing agent often used for reduction of aldehydes and ketones. A grayish powder that is soluble in ether and tetrabydrofuran, LiAlH4 is much more reactive than NaBH4 but also more dangerous. It reacts violently with water and decomposes explosively when heated above 120 °C. 

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