Alkanes from alkene hydrogenation

Catalytic hydrogenation produces alkanes from alkenes. 

Formation of I is thus the first step in the hydrogen transfer process that is necessary to produce aromatics (and alkanes) from alkenes. The 1500 cm infrared band may be associated with (I), although that has not yet been proved. 

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

Pyrolysis of alkanes is referred to as eraeking. Alkanes from the paraffins (kerosene) fraetion in the vapor state are passed through a metal ehamher heated to 400-700°C. Metallie oxides are used as a eatalyst. The starting alkanes are broken down into a mixture of smaller alkanes, alkenes, and some hydrogen. 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

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). 

Hence, the rate depends only on the ratio of the partial pressures of hydrogen and n-pentane. Support for the mechanism is provided by the fact that the rate of n-pentene isomerization on a platinum-free catalyst is very similar to that of the above reaction. The essence of the bifunctional mechanism is that the metal converts alkanes into alkenes and vice versa, enabling isomerization via the carbenium ion mechanism which allows a lower temperature than reactions involving a carbo-nium-ion formation step from an alkane. 

Usually, various quantities of alkane are found during the hydrogenolyses of oxacycloalkanes. This is especially so for the oxiranes on platinum metals in the presence of hydrogen. These alkanes presumably form from alkenes, which are formed from deoxygenation (Scheme 4.67). 

The initial step of the adsorption of cyclic sulfides on a Mo(100) surface is also the formation of adsorbed thiolate groups.395-397 Adsorbed alkyl thiolates decompose to adsorbed sulfur, carbon, and hydrogen on the clean Mo surface, but once the surface is deactivated by adsorbed sulfur, alkanes and alkenes evolve from the surface. Tetrahydrothiophene (34) and trimethylene sulfide decompose on Mo(110) to alkanes and alkenes by way of a common intermediate, which is proposed to be a surface thiolate (33). The thiolate undergoes hydrogenation or dehydrogenation, depending on the surface hydrogen concentration (Scheme 4.115).398 399... 

SMALL MOLECULE PRODUCTS. The small molecule products from irradiation of polymers include hydrogen, alkanes and alkenes, CO and CO2, SO2, H2O and HC1 depending on the chemical composition of the polymer. They may be partly evolved and partly trapped in the polymer according to their volatility, the sample dimensions and the temperature. 

Figure 19.9. Hydrogen transfer from alkanes to alkenes...

The distribution of volatile products of low molar mass from the irradiation of poly (olefin) s is strongly dependent on the nature of substituents (short-chain branches) on the backbone chain. Hydrogen is the main volatile product with smaller quantities of alkanes and alkenes. 

The history of the oxo reaction is also noteworthy. It was developed originally in Germany in the years following World War 1. At that time, the German chemical industry was faced with inadequate supplies of petroleum. Many German chemists therefore turned to research on ways by which hydrocarbons could be synthesized from smaller building blocks, particularly carbon monoxide and hydrogen derived from coal. The success achieved was remarkable and led to alkane and alkene syntheses known as the Fischer-Tropsch process ... 

In the transition from sp3 to sp2 and to sp hybridization of the valency of carbon, i.e. from alkanes to alkenes, and alkynes, the polarity of the CH bond is increased and the mobility of the hydrogen becomes greater. Electrons belonging to multiple bonds may take part in the formation of donor-acceptor complexes, and unsaturated hydrocarbons are stronger bases than saturated hydrocarbons. 

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