Dehydrogenation alkenes

Alkenylbenzenes are prepared by the various methods described m Chapter 5 for the preparation of alkenes dehydrogenation dehydration and dehydrohalogenation... 

In addition to the corresponding alkenes, dehydrogenation of butane and cyclohexane could result in butadiene and benzene, which are very stable conjugated unsaturated hydrocarbons. Therefore, it should be possible to attain high yields of butadiene or benzene. Indeed, the data in Table VII show that these products represent substantial fractions of the dehydrogenation products in most cases. 

Hydride derivatives are of interest in coimection with the catalytic properties of vanadium, for example, in alkene dehydrogenation or polymerization. Complexes with sulfhr-donor and possibly also nitrogen-donor atoms are relevant to the role played by vanadium in the poisoning of the Co Mo catalyst used for the hydrodesulfiirization of crude oU. ... 

Reed DW, Pohchuk DR, Buist PH, Ambrose SJ, Sasata RJ, Savile CK, Ross AR, Covello PS. Mechanistic study of an improbable reaction alkene dehydrogenation by the A12 acetylenase of Crepis alpina. J. Am. Chem. Soc. 2003 125 10635-10640. 

The product distribution depends on the mole ratio of the substrate alkene to hydrosilane. In the presence of a large excess of alkene, dehydrogenative hydrosilylation is apt to become the major process, as illustrated in equation (31). °... 

Dehydrogenation of alkanes is not a practical laboratory synthesis for the vast majority of alkenes The principal methods by which alkenes are prepared m the labo ratory are two other (3 eliminations the dehydration of alcohols and the dehydrohalo genation of alkyl halides A discussion of these two methods makes up the remainder of this chapter... 

Ca.ta.lysts, A small amount of quinoline promotes the formation of rigid foams (qv) from diols and unsaturated dicarboxyhc acids (100). Acrolein and methacrolein 1,4-addition polymerisation is catalysed by lithium complexes of quinoline (101). Organic bases, including quinoline, promote the dehydrogenation of unbranched alkanes to unbranched alkenes using platinum on sodium mordenite (102). The peracetic acid epoxidation of a wide range of alkenes is catalysed by 8-hydroxyquinoline (103). Hydroformylation catalysts have been improved using 2-quinolone [59-31-4] (104) (see Catalysis). 

The generation of caibocations from these sources is well documented (see Section 5.4). The reaction of aromatics with alkenes in the presence of Lewis acid catalysts is the basis for the industrial production of many alkylated aromatic compounds. Styrene, for example, is prepared by dehydrogenation of ethylbenzene made from benzene and ethylene. 

Like ethylene, propylene (propene) is a reactive alkene that can be obtained from refinery gas streams, especially those from cracking processes. The main source of propylene, however, is steam cracking of hydrocarbons, where it is coproduced with ethylene. There is no special process for propylene production except the dehydrogenation of propane. 

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

The first step in this preparation, the epoxidation of 1,4,5,8-tetra-hydronaphthalene, exemplifies the well-known selectivity exerted by peracids in their reaction with alkenes possessing double bonds that differ in the degree of alkyl substitution.12 As regards the method of aromatization employed in the conversion of ll-oxatricyclo[4.4.1.01-6]-undeca-3,8-diene to l,6-oxido[10]annulene, the two-step bromination-dehydrobromination sequence is given preference to the one-step DDQ-dehydrogenation, which was advantageously applied in the synthesis of l,6-metliano[10]annulene,2,9 since it affords the product in higher yield and purity. 

This section contains dehydrogenations to form alkenes and unsaturated ketones, esters and amides. It also includes the conversion of aromatic rings to alkenes. Reduction of aryls to dienes is found in Section 377 (Alkene-Alkene). Hydrogenation of aryls to alkanes and dehydrogenations to form aryls are included in Section 74 (Alkyls from Alkenes). 

Oxoreductases include enzymes such as dehydrogenases, oxidases and peroxidases which catalyse transformations such as oxidation of alcohols to carbonyls and dehydrogenation of functionalized alkanes to alkenes. 

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