Aluminium oxide production

The purification of diethyl ether (see Chapter 4) is typical of liquid ethers. The most common contaminants are the alcohols or hydroxy compounds from which the ethers are prepared, their oxidation products (e.g. aldehydes), peroxides and water. Peroxides, aldehydes and alcohols can be removed by shaking with alkaline potassium permanganate solution for several hours, followed by washing with water, concentrated sulfuric acid [CARE], then water. After drying with calcium chloride, the ether is distilled. It is then dried with sodium or with lithium aluminium hydride, redistilled and given a final fractional distillation. The drying process should be repeated if necessary. 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

The inorganic sorbents act as catalysts in all this [3,4]. Hie pH also probaUy plays a role. Reactions that do not otherwise occur are observed on add silka gd [3] or basic aluminium oxide layers. Reactions of this type have also been obsoved for amino [6-8] and RP phases [9]. The products of reaction are usually fluorescent and can normally be used for quantitative analysis since the reactions are reprodudble. 

Owing to its excellent thermal and mechanical stability and its rich chemistry, alumina is the most widely used support in catalysis. Although aluminium oxide exists in various structures, only three phases are of interest, namely the nonporous, crys-tallographically ordered a-Al203, and the porous amorphous t]- and y-Al203. The latter is also used as a catalyst by itself, for example in the production of elemental sulfur from H2S (the Claus process), the alkylation of phenol or the dehydration of formic acid. 

Table 3 Aluminium oxide-promoted synthesis of furoxanes from a-nitro-oximes Substrate Product (294) Time (h)...

Uranium Arsenide, U3As4, may be obtained i by passing hydrogen over a fused mixture of sodium uranous chloride and sodium arsenide. It is a greyish powder which readily burns in the air. Sometimes it is obtained in a pyrophoric condition. An aluminium-containing product results when the aluminothermic process, using an oxide of uranium and arsenious oxide, is employed. The purest arsenide is obtained, in the crystalline form, when a mixture of hydrogen and arsenic vapour is passed over sodium uranium chloride. It is rapidly decomposed by nitric acid. 

Today we use aluminium in very large quantities. The annual production in the world is 19.5 million tonnes. The commercial extraction of aluminium has been made possible by two scientists, working independendy of each other, who discovered a method using electrolysis. The two scientists were Charles Martin Hall (USA), who discovered the process in 1886, and the French chemist Paul Heroult, who discovered the process independendy in the same year. The process they developed, often called the Hall-Heroult process, involves the electrolysis of aluminium oxide (alumina). The process involves the following stages. 

To the remaining solution 50 ml of ether and 50 ml of water are added. The water layer is separated and extracted with ether. The ethereal layer is washed with a 2 N hydrochloric acid solution, subsequently with a saturated sodium bicarbonate solution, and then with water. The ethereal solution is dried and evaporated to dryness. The resulting crude reaction product is dissolved in a mixture of benzene and petroleum ether (1 3) and chromatographed over aluminium oxide. The 84-17p-hydroxy-oestrene obtained after chromatographic purification has a melting point of 80°-90°C and 95°-100°C after repeated crystallization from petroleum ether. 

Our catalyst for the isomerization of alkenes is going to be HC1 absorbed on to solid alumina (aluminium oxide, AI2O3) and the isomerization is to occur during a reaction, the addition of HC1 to an alkyne, in which the alkenes are formed as products. In this reaction the oxalyl chloride is first mixed with dried alumina. The acid chloride reacts with residual water on the surface (it is impossible to remove all water from alumina) to generate HC1, which remains on the surface. 

Esterase EP10 from Pseudomonas marginata was supplied by Prof. Schwab from the Department of Biotechnology at the Graz University of Technology (Stubenrauch et al., 1995). Carbon dioxide (99.95 % (v/v), 35 ppmy water) was purchased from Linde. The aluminium oxide sensor is a product of PANAMETRICS. 

Phosphaallenes can be synthesized in the same way as 1,3-diaryl-substituted allenes following an aluminium-catalyzed propargyl rearrangement. Using sodium hydroxide-activated aluminium oxide (125), the synthesis is suitable on an enlarged scale without any detectable by-products [Eq. (63)]. A similar proton migration within a coordinated phosphaalkyne was reported recently (126). 

A commercial synthesis of 2,6-diphenylphenol is reported by Hay at General Electric, USA811. First, cyclohexanone was condensed with 50% sodium hydroxide at 150-190 °C giving the 2-mono- and the 2,6-disubstituted cyclohexanone derivatives. In the second step, after removal of water and sodium hydroxide, these are dehydrogenated at 300-350 °C with a palladium aluminium oxide catalyst for 20 minutes (e.g. 45 % total yield of 2,6-diphenyl-phenol). It is a useful compound in technical production and has been studied by Hay and coworkers 82) (see also 83,84)). Polymeric diphenylphenol ethers ( Tenas ) 85) or copolymers with polystyrene ( Normyl ) have been produced on a large scale by General Electric e.g. as thermoplasts 86). 

A polymeric condensation product of aluminium oxide and aspirin which contains about 83% of total salicylates. 

Mechanism The aluminium alkoxide complex A (of starting alcohol and aluminium alkox-ide) reacts with ketone (hydrogen acceptor) to form aluminium coordination complex B. Transfer of hydrogen takes place via a cyclic transition state to give the oxidized product ketone of the starting alcohol and aluminium alkoxide C, which releases 2-propanol (Scheme 7.12). 

---