Reactions of hydrocarbons

A number of related reactions of hydrocarbons are catalyzed by acidic oxide types of materials. These include the cracking of high molecular weight... 

Amm oxida tion, a vapor-phase reaction of hydrocarbon with ammonia and oxygen (air) (eq. 2), can be used to produce hydrogen cyanide (HCN), acrylonitrile, acetonitrile (as a by-product of acrylonitrile manufacture), methacrylonitrile, hen onitrile, and toluinitnles from methane, propylene, butylene, toluene, and xylenes, respectively (4). 

Methanol substitution strategies do not appear to cause an increase in exposure to ambient formaldehyde even though the direct emissions of formaldehyde have been somewhat higher than those of comparable gasoline cars. Most ambient formaldehyde is in fact secondary formaldehyde formed by photochemical reactions of hydrocarbons emitted from gasoline vehicles and other sources. The effects of slightly higher direct formaldehyde emissions from methanol cars are offset by reduced hydrocarbon emissions (68). 

H. Pines, W. M. StaUck, and H. B. Injovanovich, ed., Base-Cataly d Reactions of Hydrocarbons and Related Compounds, Academic Press, Inc., New York, 1977. 

The alkanoic acids, with the exception of formic acid, undergo typical reactions of the carboxyl group. Formic acid has reducing properties and does not form an acid chloride or an anhydride. The hydrocarbon chain of alkanoic acids undergoes the usual reactions of hydrocarbons except that the carboxyl group exerts considerable influence on the site and ease of reaction. The alkenoic acids in which the double bond is not conjugated with the carboxyl group show typical reactions of internal olefins. All three types of reactions are industrially important. 

Whereas this reaction was used to oxidize ethylene (qv) to acetaldehyde (qv), which in turn was oxidized to acetic acid, the direct carbonylation of methanol (qv) to acetic acid has largely replaced the Wacker process industrially (see Acetic acid and derivatives). A large number of other oxidation reactions of hydrocarbons by oxygen involve coordination compounds as detailed elsewhere (25). 

The overall reaction scheme by which high concentrations of aromatics are produced in Powerforming is rather complex. However, it can be broken down into four important and distinct types of reactions. In Figure 1, these four reactions are illustrated by the reactions of hydrocarbon feed components. 

Metal Catalyzed Skeletal Reactions of Hydrocarbons J. R. Anderson... 

D.G. Kelly, M. Salmeron, and G.A. Somorjai, The adsorption and reactions of hydrocarbons on molybdenum single crystal surfaces when clean and in presence of coadsorbed sulfur or carbon, Surf. Sci. 175,465 (1986). 

Avramoff et al. have already reported that the reaction of hydrocarbons such as toluene with tetramethylammonium tribromide (TMA Br3) in benzene, in the presence of benzoyl peroxide at room temperature gave benzylic bromination products (ref. 21). However, TMA Br3 is not easy to handle in comparison with the stable BTMA Br3 because of its hydroscopic character. Furthermore, as shown in their literature, a large excess of TMA Br3 is necessary to brominate arenes. 

For reviews of double-bond migrations, see Pines, H. Stalick, W.M. Base-Catalyzed Reactions of Hydrocarbons and Related Compounds , Academic Press NY, 1977, p. 25 ... 

Zeolites are used in various applications such as household detergents, desiccants and as catalysts. In the mid-1960s, Rabo and coworkers at Union Carbide and Plank and coworkers at Mobil demonstrated that faujasitic zeolites were very interesting solid acid catalysts. Since then, a wealth of zeolite-catalyzed reactions of hydrocarbons has been discovered. Eor fundamental catalysis they offer the advantage that the crystal structure is known, and that the catalytically active sites are thus well defined. The fact that zeolites posses well-defined pore systems in which the catalytically active sites are embedded in a defined way gives them some similarity to enzymes. 

Surface science studies have generated much insight into how hydrocarbons react on the surfaces of platinum single crystals. We refer to Somorjai [G.A. Somor-jai. Introduction to Surface Chemistry and Catalysis (1994), Wiley, New York] for a detailed overview. Also, the reactions of hydrocarbons on acidic sites of alumina or on zeolites have been studied in great detail [H. van Bekkum, E.M. Flanigan and J.C. Jansen (Eds.), Introduction to Zeolite Science and Practice (1991), Elsevier, Amsterdam],... 

Zeolites have led to a new phenomenon in heterogeneous catalysis, shape selectivity. It has two aspects (a) formation of an otherwise possible product is blocked because it cannot fit into the pores, and (b) formation of the product is blocked not by (a) but because the transition state in the bimolecular process leading to it cannot fit into the pores. For example, (a) is involved in zeolite catalyzed reactions which favor a para-disubstituted benzene over the ortho and meso. The low rate of deactivation observed in some reactions of hydrocarbons on some zeoUtes has been ascribed to (b) inhibition of bimolecular steps forming coke. 

Consequent to the work of many and employing such techniques as structure variation, isotopic tracers, and stereochemistry, a large number of different adsorbed hydro bon firagments have been identified as key intermediates in various reactions of hydrocarbons. Correlation of these spedes with similar polynuclear organometallic spedes has been of interest. However, the author feels that mechanistic understanding has lagged behind some other aspects of catalysis. 

H. Pines and W.M. Stalick, Base catalyzed reactions of hydrocarbons and related compounds. Academic Press N.Y. 1977. 

G. C. Bond, Metal-Catalysed Reactions of Hydrocarbons, Springer, New York, 2005, 231. 

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