Epoxidation ethene with

Kursawe, a., Honicke, D., Epoxidation of ethene with pure oxygen as a model reaction for evaluating the performance of microchannel reactors, in Proceedings of the 4th International Conference on Microreaction Technology, IMRET 4,... 

Fig. 14 Stationary-point structures for the epoxidation of ethene with hydrogen peroxide in the absence and in the presence of one molecule of HFIP, optimized at RB3LYP/6-31+ G(d,p) (selected bond lengths in A RB3LYP/6-311++G(d,p) results in parentheses)...

A modest increase in the rate of alkene epoxidation by peroxy acid in benzene occurs on addition of TCA or TFA.183 Calculations predict a much lower activation barrier for epoxidation of ethene with fully protonated peroxyfonnic acid (A/v = 6.4kcalmof ) ... 

ARCO patents describe various approaches for the development of catalysts able to selectively epoxidize olefins other than ethene with oxygen. In all the catalyst formulations claimed, the main active component is supported silver, doped with various components [31a,b]. In the earlier patents, the best results reported were propene conversion 4.5%, selectivity for PO 59-61%, with a catalyst composition of 54% Ag, 2% K, 0.5% Mo, supported over calcium carbonate. Molybdenum was used to increase the selectivity (but the addition of Mo also caused a decrease in propene conversion). 

Although epoxidation of ethene with O2 over Ag catalysts has been industrially applied for many years, the catalysts used for this process typically show poor selectivity in the epoxidation reaction of propene, yielding mainly... 

Calculated transition structure for the epoxidation of ethene with peroxyformic acid. The numbers indicate distances in A (Adapted from reference 269.)... 

A more efficient agent than peroxy compounds for the epoxidation of fluoro-olefins with nonfluonnated double bond is the hypofluorous acid-acetomtrile complex [22] Perfluoroalkylethenes react with this agent at room temperature within 2-3 h with moderate yields (equation 13), whereas olefins with strongly electron-deficient double bond or electron-poor, sterically hindered olefins, for example l,2-bis(perfluorobutyl)ethene and perfluoro-(l-alkylethyl)ethenes, are practically inert [22] Epoxidation of a mixture of 3 perfluoroalkyl-1-propenes at 0 C IS finished after 10 mm in 80% yield [22] The trifluorovinyl group in partially fluorinated dienes is not affected by this agent [22] (equation 13)... 

The degradation of vinyl chloride and ethene has been examined in Mycobacterium sp. strain JS 60 (Coleman and Spain 2003) and in Nocardioides sp. strain JS614 (Mattes et al. 2005). For both substrates, the initially formed epoxides underwent reaction with reduced coenzyme M and, after dehydrogenation and formation of the coenzyme A esters, reductive loss of coenzyme M acetate resulted in the production of 5-acetyl-coenzyme A. The reductive fission is formally analogous to that in the glutathione-mediated reaction. 

The direct attack of the front-oxygen peroxo center yields the lowest activation barrier for all species considered. Due to repulsion of ethene from the complexes we failed [61] to localize intermediates with the olefin precoordinated to the metal center, proposed as a necessary first step of the epoxidation reaction via the insertion mechanism. Recently, Deubel et al. were able to find a local minimum corresponding to ethene coordinated to the complex MoO(02)2 OPH3 however, the formation of such an intermediate from isolated reagents was calculated to be endothermic [63, 64], The activation barriers for ethene insertion into an M-0 bond leading to the five-membered metallacycle intermediate are at least 5 kcal/mol higher than those of a direct front-side attack [61]. Moreover, the metallacycle intermediate leads to an aldehyde instead of an epoxide [63]. Based on these calculated data, the insertion mechanism of ethene epoxidation by d° TM peroxides can be ruled out. 

Figure 14. Energies (in kcal/mol) of intermediates with Ti(T)2-02) or TiOOH groups and the corresponding TSs of ethene epoxidation, relative to the energy of 13c + C2H4.

For Ti, hydroperoxo complexes exhibit lower activation barriers than the corresponding peroxo species. Peroxo complexes of Ti and Cr can be considered as inert in epoxidation. Hydroperoxo species may be competitive with di(peroxo) compounds in the case of Mo. For the system MT0/H202 the di(peroxo) complex CH3Re0(02)2-H20 was found to be most stable and to yield the lowest TS for epoxidation of ethene, in line with experimental findings. However, olefin epoxidation by Re monoperoxo and hydroperoxo complexes cannot be excluded. 

Peroxynitrous acid, which has an estimated lifetime of 1-3 s at neutral pH, has been studied through ab initio calculations that suggest that peroxynitrous acid, per-oxyformic acid, and dimethyldioxirane have, despite diverse 0—0 bond energies, similar activation energies for oxygen-atom transfer." The transition-state structures for the epoxidation of ethene and propene with peroxynitrous acid are symmetrical with equal or almost equal bond distances between the spiro oxygen and the carbons of the double bond. 

Highly fluorinated ethenes react readily with oxygen to yield epoxides, polymeric peroxides, perfluorocyclopropane, and, by rearrangement, fluorinated acetyl halides carbonyl fluoride and carbon dioxide are undesired byproducts, the amount of which is dependent on the method used. 

In studies of the reactions of 1.1 -difluoroethene, trifluoroethene, and perfluoroethene, the mechanism of ozonide, epoxide, and cyclopropane formation have been studied.84 Unusually stable ozonides 46A and B are prepared by treating mono- and bis(fluoroalkyl)cthenes with ozone85 at room temperature or on heating the substrate to which ozone is introduced. The rates are approximately 1()10 slower than that for the nonfluorinated analogs. Mono-perfluoroalkylated ethene seems to react several times more rapidly than the bis-perfluoroalkylated ethene.85... 

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