Aluminum dehydration catalyst

The widely used Moifatt-Pfltzner oxidation works with in situ formed adducts of dimethyl sulfoxide with dehydrating agents, e.g. DCC, AcjO, SO], P4O10, CCXTl] (K.E, Pfitzner, 1965 A.H. Fenselau, 1966 K.T. Joseph, 1967 J.G. Moffatt, 1971 D. Martin, 1971) or oxalyl dichloride (Swem oxidation M. Nakatsuka, 1990). A classical procedure is the Oppenauer oxidation with ketones and aluminum alkoxide catalysts (C. Djerassi, 1951 H. Lehmann, 1975). All of these reagents also oxidize secondary alcohols to ketones but do not attack C = C double bonds or activated C —H bonds. 

The vapor-phase esterification of ethanol has also been studied extensively (363,364), but it is not used commercially. The reaction can be catalyzed by siUca gel (365,366), thoria on siUca or alumina (367), zirconium dioxide (368), and by xerogels and aerogels (369). Above 300°C the dehydration of ethanol becomes appreciable. Ethyl acetate can also be produced from acetaldehyde by the Tischenko reaction (370—372) using an aluminum alkoxide catalyst and, with some difficulty, by the boron trifluoride-catalyzed direct esterification of ethylene with organic acids (373). 

Dihydropyran (DHP), having an atmospheric boiling point of 86 °C and a very limited solubility in water (3 g in 100 g of water at 20 °C), can be produced from tetra-hydrofurfuryl alcohol by dehydration and ring expansion over an aluminum oxide catalyst at... 

Phosphates are also active dehydration catalysts [6,8,9]. Although a mixed (El and E2) mechanism has been reported [24], most of these materials and particularly BPO4 have typical El behavior [25-27]. The involvement of the carbocatio-nic intermediate results in a complex mixture of isomeric alkenes [27,28] and intramolecular and intermolecular dehydration (alkene and ether formation, respectively) are often parallel processes. For example, aluminum phosphates with P/Al < 1 yield a mixture of alkenes and ethers whereas those with P/Al > 1 give alkenes selectively [6,29]. Dehydration activity usually correlated with surface acidity [29-31]. The strongly acidic sites of AIPO4 were found to promote alkene formation [26]. 

The reaction requires a dehydrating catalyst, which, for reactions in the liquid phase, is an acid substance this is usually a concentrated mineral acid, but may also be an organic sulfonic acid, acid salt, or halogen compound such as boron trifluoride, zinc chloride, or aluminum chloride. For etherification in the gaseous phase the alcohol vapor is passed over a solid catalyst such as A1203, Ti02, or dehydrated alum.656... 

The necessary dehydrating catalysts such as aluminum oxide, kaolin, bauxite, aluminum phosphate, and mixed catalysts of similar composition require temperatures of 250-500° and pressures of several hundred atmospheres. The special apparatus and catalysts needed render this method of only industrial interest, the more so as only compounds of simple structure can be submitted to such drastic conditions and, on a laboratory scale, the amines that can be obtained in this way can be prepared more conveniently by other methods. 

On the basis of the above hypothesis, the mechanism of dehydration of ethanol and diethyl ether on aluminum oxide and aluminum silicate catalyst can be represented by the following scheme ... 

Dehydration Catalysts. In the production of amines from alcohols and ammonia or from alcohols and various amines, catalysts prepared by dehydrating alumina or silica gel are generally used. For specific reactions, these catalysts are promoted with various metals, their oxides or salts. For example, a dehydration catalyst has been made by incorporating aluminum phosphate in alumina gel prior to dehydrating the gel. An amination catalyst made by treating absorptive alumina with calcium and copper nitrates, followed by calcination and then reduction with hydrogen in a vapor-phase reactor, was used to produce an excellent yield of mono-methylaniline from aniline and methanol. ... 

The usage of metal sulfates as catalysts is not new. In 1901, aluminum sulfate was used as the dehydration catalyst for the formation of 2-methylpropene from 2-methyl-2-propanol (29) and, in 1923, as the hydration catalyst for the formation of ethanol from ethylene 30). 

Cyanopyridines are prepared by passage of nicotinic or isonicotinic acid, their ammonium salts, or amides over a dehydration catalyst at 350° in the presence of ammonia. Boron phosphate and aluminum phosphate are mentioned specifically as catalysts. ... 

Aluminum chloride, 60, 61 Diels-Alder catalyst, 144 Friedel-Crafts acylation catalyst, 91-100 MA complex, 212 Aluminum, diethyl chloride, 345 Aluminum oxide, dehydrating catalyst, 87 Aluminum phenoxides, MA polymerization reactant, 273... 

Other Higher Oleiins. Linear a-olefins, such as 1-hexene and 1-octene, are produced by catalytic oligomerization of ethylene with triethyl aluminum (6) or with nickel-based catalysts (7—9) (see Olefins, higher). Olefins with branched alkyl groups are usually produced by catalytic dehydration of corresponding alcohols. For example, 3-methyl-1-butene is produced from isoamyl alcohol using base-treated alumina (15). 

The reaction is cataly2ed by all but the weakest acids. In the dehydration of ethanol over heterogeneous catalysts, such as alumina (342—346), ether is the main product below 260°C at higher temperatures both ether and ethylene are produced. Other catalysts used include siUca—alumina (347,348), copper sulfate, tin chloride, manganous chloride, aluminum chloride, chrome alum, and chromium sulfate (349,350). 

Used industrially as a chlorinating agent, dehydrating agent, catalyst, in the manufacture of pharmaceuticals, and in aluminum metallurgy. 

Pure alumina catalyst prepared either by hydrolysis of aluminum isopropoxide or by precipitation of aluminum nitrate with ammonia, and calcined at 600-800°, contains intrinsic acidic and basic sites, which participate in the dehydration of alcohols. The acidic sites are not of equal strength and the relatively strong sites can be neutralized by incorporating as little as 0.1 % by weight of sodium or potassium ions or by passing ammonia or organic bases, such as pyridine or piperidine, over the alumina. 

Natural clay catalysts were replaced by amorphous synthetic silica-alumina catalysts5,11 prepared by coprecipitation of orthosilicic acid and aluminum hydroxide. After calcining, the final active catalyst contained 10-15% alumina and 85-90% silica. Alumina content was later increased to 25%. Active catalysts are obtained only from the partially dehydrated mixtures of the hydroxides. Silica-magnesia was applied in industry, too. 

Dehydration and dehydrogenation combined utilizes dehydration agents combined with mild dehydrogenation agents. Included in this class of catalysts are phosphoric add, silica-magnesia, silica-alumina, alumina derived from aluminum chloride, and various metal oxides. 

Most alcohols also will dehydrate at fairly high temperatures in the presence of solid catalysts such as silica gel or aluminum oxide to give alkenes or ethers. The behavior of ethanol is reasonably typical of primary alcohols and is summarized in the following equations ... 

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