Olefins by hydrogenation

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

Epoxidation. 1,1,3,3-Tetrachloroacetone can mediate the epoxidation of olefins by hydrogen peroxide in the same way as hcxafluoroacctonc (9, 244-245). It has the advantage that it is probably less toxic, and it is inexpensive and commercially available. The actual oxidant presumably is the hydroperoxide 1, which is converted during the epoxidation into the unstable hydrate (2), from which the tctrachloroacetone can be recovered in >70% yield. Monosubstitutcd alkenes are epoxidized in low yields by this method more highly substituted alkenes are epoxidized in 65 85% yield (VPC).1... 

It was also shown that the ratio of oxidized alcohol to oxidized Fe2+ could be greater then one. Baxendale and Wilson (1957) showed that hydroxyl radical initiating the chain polymerization of olefins by hydrogen peroxide was the same process as the rapid oxidation of glycolic acid. Merz and Waters (1947) confirmed that simple water-soluble alcohols are oxidized rapidly by Fenton s reagent. The primary alcohols are oxidized to aldehydes, which are further oxidized at comparable rates by exactly the same mechanism. Merz and Waters proposed a mechanism of chain oxidation of alcohols and aldehydes by sodium persulfate, hydrogen peroxide, and an excess of ferrous salt as follows ... 

EPOXIDATION OF OLEFINS BY HYDROGEN PEROXIDE-ACETONITRILE cw-CYCLOOCTENE OXIDE... 

Equilibrium protonation to give the carbonium ion can be observed in 80 % (v/v) methanol—water containing buffers. Proton removal from the carbonium ion (pX ca. 2.7 in this solvent) by acetate and chloroacetate is thermodynamically favourable but occurs with rate coefficients of 19.1 and 4.7 1 mole-1 sec-1, respectively, which are well below the values which would be found for normal proton transfer. Protonation of the olefin by hydrogen ion is thermodynamically favourable but occurs slowly with rate coefficient 23 1 mole-1 sec-1. These results clearly show that protonation of olefinic carbon belongs to the category of slow proton transfers. 

C. Venturello, E. Alneri. M. Ricci, A new, effective catalytic system for epoxidation of olefins by hydrogen peroxide under phase-transfer conditions, J. Org. Chem. 48, 3831— 3833 (1983). 

T. Sakamoto, C. Pac, Selective epoxidation of olefins by hydrogen peroxide in water using a polyoxometalate catalyst supported on chemically modified hydrophobic mesoporous silica gel. Tetrahedron Lett. 41 (2000) 10009. 

We shall now consider briefly results obtained from the hydrogenation of 2-butyne in the liquid phase, using alcohol as solvent and Pd-BaS04 as catalyst (59). In this study cfs-2-butene was the only detectable product until the complete removal of the alkyne, the subsequent removal of the olefin by hydrogenation was accompanied by very fast isomerization. These results are in complete harmony with those obtained from the gas phase reaction and thus the mechanism of this reaction must be very similar in both the gas and liquid phases. 

Hydroxylation of olefins by hydrogen peroxide in the presence of osmium tetroxide leads to cis-glycols because a cyclic osmic ester is formed as intermediate and the cis-glycol is formed by hydrolysis of that intermediate. Other catalysts afford fraws-hydroxylation, which occurs by way of an intermediate epoxide.138... 

Oxidation of olefins by hydrogen peroxide and catalytic amounts of osmium tetroxide is effected in anhydrous tert-butyl alcohol (Milas reagent139), ether,122 aqueous methanol,140 or acetone.141 Also, tert-butyl hydroxyperoxide may be used in place of hydrogen peroxide.142... 

It is well known that saturation of olefins by hydrogen transfer is a major reaction occurring in commercial catalytic cracking. 

Many isomerization reactions occur by double-bond migration. Two common mechanisms of double-bond migration are (Parshall and Ittel, 1992) (1) equilibration between internal and terminal olefins by hydrogen migration and (2) interconversion between branched and linear chains of an olefin. Another mechanism of olefin isomerization is the shift of an allylic hydrogen from the 3- to the 1-position. We confine our discussion to the more important doublebond migration mechanism. 

Venturello, C., Alneri, E. and Ricci, M. (1983). A New, Effective Catalytic System for Epoxi-dation of Olefins by Hydrogen Peroxide under Phase-Transfer Conditions, J. Org. Chem., 48, pp. 3831-3833. 

Figure 32. Two mechanisms of isomerization of olefins by hydrogen transfer,...

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