1-Alkenes, liquid-phase oxidation

Liquid-Phase Oxidation of High Molecular Weight 1-Alkenes... 

Van Sickle DE, Mayo F, Arluck RM. Liquid-phase oxidation of cyclic alkenes. J Am Chem Soc 1965 87 4824 4832. 

Differences between copper and silver have been seen for the heterogeneously catalysed liquid-phase oxidation of cumene. Copper appears to initiate the reaction by decomposition of the hydroperoxide. The subsequent free-radical reaction occurs in the liquid phase. There is some evidence that silver initiates, this process via an adsorbed molecular oxygen species. If this is correct, this species is reacting in a different manner when compared to its reaction with gas-phase alkenes. In the latter, O—O bond cleavage occurs while the cumene oxidation mechanism would necessarily involve Ag—O bond cleavage. 

H.F.W.J. van Breukelen, M.E. Gerritsen, V.M. Ummels, J.S. Broens J.H.C. van Hooff (1997). Stud. Surf Sci. Catal., 105, Part A-C, 1029-1035. Application of CoAlPO-5 molecular sieves as heterogeneous catalysts in liquid phase oxidation of alkenes with dioxygen. 

The catalytic activity of various complex compounds of technetium was tested in the metathesis of olefins [17], epoxide ring opening reactions [18], epoxide ring formation by reaction of cyclohexene with fe/7-butylhydroperoxide [19,20], and the preferred production of tram-epoxides in the liquid phase oxidation of cw/tram-n-alkenes [21 j. 

Supercritical CO2 is a non-polar, aprotic solvent and promotes radical mechanisms in oxidation reactions, similar to liquid-phase oxidation. Thus, wall effects might occur as known, e.g. from olefin epoxidation with 02 or H202 which may decrease epoxide selectivities. The literature covers the synthesis of fine chemicals by oxidation either without catalysts (alkene epoxidation, cycloalkane oxidation, " Baeyer-Villiger oxidation of aldehydes and ketones to esters ), or with homogeneous metal complex catalysts (epoxidation with porphyrins, salenes or carbonyls ). Also, the homogeneously catalysed oxidation of typical bulk chemicals like cyclohexane (with acetaldehyde as the sacrificial agent ), toluene (with O2, Co +/NaBr ) or the Wacker oxidation of 1-octene or styrene has been demonstrated. 

Pb(C2H5)4 is employed as a chain-starter for the alkylation of alkanes or cycloalkanes by alkenes or cycloalkenes [697], and in the liquid-phase oxidation of alkylaromatic hydrocarbons to give hydroperoxides [892]. Pb(C2Hs)4 catalyzes the photochemical addition of HBr [661, 681] or of H2S or mercaptans to alkenes, such as propene [661, 679, 681], and it catalyzes the intermolecular condensation of arylalkanes in sunlight or on heating [684]. 

For the non-oxidative activation of light alkanes, the direct alkylation of toluene with ethane was chosen as an industrially relevant model reaction. The catalytic performance of ZSM-5 zeolites, which are good catalysts for this model reaction, was compared to the one of zeolite MCM-22, which is used in industry for the alkylation of aromatics with alkenes in the liquid phase. The catalytic experiments were carried out in a fixed-bed reactor and in a batch reactor. The results show that the shape-selective properties of zeolite ZSM-5 are more appropriate to favor the dehydroalkylation reaction, whereas on zeolite MCM-22 with its large cavities in the pore system and half-cavities on the external surface the thermodynamically favored side reaction with its large transition state, the disproportionation of toluene, prevails. 

However, beeause of the kinetie lability of eobalt(ll), heterogenized catalysts based on Co are suseeptible to metal leaehing during liquid phase reaetions and thus repeated use of such catalysts is not practical from a chemical point of view. In order to avoid this problem, use of catalysts based on cobalt(lll), whieh is substitutionally inert, may be expected to show more attraetive eatalytic properties for the same reaetions. As expeeted, substitutionally inert cobalt(lll) eomplexes have been shown to be eatalytieally very aetive, and henee attractive, for alkylaromatie oxidation [26]. Also, as we shall see later, a series of tetramerie eobalt(lll) complexes eapable of cycling oxidation states between 111 and IV has also been foimd to be effective as eatalysts for the oxidation of alkyl aromaties, aleohols and alkenes [5,15,27]. 

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