Ethane cleavage reaction

Iron complexes containing bidentate alkyl and aryl phosphorus ligands cleave a variety of C-H bonds under mild conditions, Hydrido acetylide complexes were prepared by oxidative addition of primary acetylenes in the Fe(DPPE)2 and the Fe(DMPE)2 systems [DPPE = bis(diphenylphos-phino)ethane, DMPE = bis(dimethylphosphino)ethane]. The Fe(DMPE)2 system also cleaves C-H bonds of activated methyl groups, aromatic compounds, and certain other sp hybridized molecules. The C-H cleavage reactions are reversible, resulting in equilibrium mixtures of isomeric products in many cases. Studies of substituted benzenes show that while product stability is favored by electron withdrawing substituents, steric effects play a predominant role in the determination of product distribution. 

A large proportion of the volatiles identified in vegetable oils are derived from the cleavage reactions of the hydroperoxides of oleate, linoleate, and linolenate (Section D). A wide range of hydrocarbons (ethane, propane, pentane and hexane) appears to be formed in soybean oil oxidized to low peroxide values. A number of volatiles identified in vegetable oils that are not expected as primary cleavage products of monohydroperoxides include dialdehydes, ketones, ethyl esters, nonane, decane, undecane, 2-pentylfuran, lactone, benzene, benzaldehyde and acetophenone. Some of these volatiles may be derived from secondary oxidation products, but the origin of many volatiles still remains obscure. However, studies of volatile decomposition products should be interpreted with caution, because the conditions used for isolation and identification may cause artifacts, especially when fats are subjected to elevated temperatures. 

The 1,4-dithian derivatives (148) and (149) have been isolated after the reaction of ethane-1,2-thiol with 2-chlorocyclohexanone and cr-bromoacetaldehyde diethyl acetal, respectively. A novel cleavage reaction, with the formation of complexes such as (150), was observed when 1,4-dithian reacted with [Fe2(CO),]. ... 

The rhodium-catalyzed successive C-C/C-O bond cleavage reaction of a cyclobutanone 77 containing a phenoxymethyl side chain was affected by the employed bidentate diphosphine ligand (Scheme 3.44) [53]. In the presence of [Rh(nbd)(dppe)]PF 5 (nbd, norborna-2,5-diene dppe, l,2-bis(diphenylphos-phino)ethane) (5 mol%) and diphenylacetylene (20 mol%), cyclobutanone 77 was transformed into the alkenoic ester 78 in 88% yield via C-C bond cleavage, P-oxygen elimination, and reductive elimination. In contrast, the [Rh(nbd)(dppp)]PFg-catalyzed (dppp, l,3-bis(diphenylphosphino)propane) reaction afforded cyclopentanone 79 in 81% yield through a rhodacyclohexanone species that was formed by 6-endo cyclization. The reaction of the cyclobutanone 77 catalyzed by [Rh(nbd)(dppb)]PFg (dppb, l,4-bis(diphenylphosphino)butane) led to exclusive formation of cyclopropane 80 via decarbonylation. 

The photochemical decarbonylation of ketones can be traced back to 1910 when acetone was photolysed in the gas phase to yield ethane and carbon monoxide. A radical process involving a-cleavage (Norrish type I reaction) and decarbonylation as two separate steps was proposed a few years later by Norrish and Appleyard (Scheme 1). Each of the two cleavage reactions has been the subject of numerous theoretical and mechanistic studies that have been covered in several reviews. 

Although reactions in which molecules are cleaved into two or more pieces have favorable entropy effects, many potential cleavages do not take place because of large increases in enthalpy. An example is cleavage of ethane into two methyl radicals. In this case, a bond of 79 kcal mol (330 kJ mol ) is broken, and no new bond is formed to compensate for this enthalpy increase. However, ethane can be cleaved at very high temperatures, which illustrates the principle that entropy becomes more important as the temperature increases, as is obvious from the equation AG = AH — TAS. The enthalpy term is independent of temperature, while the entropy term is directly proportional to the absolute temperature. 

Hydrogenolysis of butane was used to study the catalysis of the RhPt particles in mesoporous silica. This is a test reaction of reforming of alkanes in oil refinery, and methane, ethane, and propane are formed by the cleavage of terminal or central C-C bond (Scheme 1). 

When one of the aromatic groups of the triarylmethyl free radical is replaced by an alkyl group, a decrease in stability due to a loss of resonance stabilization is to be expected. The paramagnetism and reactions associated with these less stable radicals will therefore appear only when the ethane is heated well above room temperature, the dissociation being endothermic. The rate of formation, but not the equilibrium constant, is experimentally accessible for these radicals since the radical once formed is subject to rearrangement, cleavage, and disproportionation reactions ... 

This is a major achievement, mainly due to Basset and his group, in surface organometallic chemistry because it has been thus possible to prepare single site catalysts for various known or new catalytic reactions [53] such as metathesis of olefins [54], polymerization of olefins [55], alkane metathesis [56], coupHng of methane to ethane and hydrogen [57], cleavage of alkanes by methane [58], hydrogenolysis of polyolefins [59] and alkanes [60], direct transformation of ethylene into propylene [61], etc. These topics are considered in detail in subsequent chapters. 

This heme-dependent enzyme [EC 1.11.1.14], also known as diarylpropane peroxidase, diarylpropane oxygenase, and ligninase I, catalyzes the reaction of 1,2-bis(3,4-dimethoxyphenyl)propane-l,3-diol with hydrogen peroxide to produce veratraldehyde, l-(3,4-dimeth-ylphenyl)ethane-l,2-diol, and four water molecules. The enzyme brings about the oxidative cleavage of C—C bonds in a number of model compounds and also oxidizes benzyl alcohols to aldehydes or ketones. 

The photochemistry of biacetyl has been extensively studied, both in the vapor phase and in solution. In the vapor phase the products include carbon monoxide, ethane, methane, acetone, ketene, and 2,3-pentanedione. It has been shown that the primary process is cleavage of the carbon-carbon bond between the two carbonyl groups to yield acyl radicals, which on further reaction give the observed products.14,43... 

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