Epoxidation of ethene

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. 12.11. Transition structures and /. values for epoxidation of ethene and substituted derivatives by dimethyloxirane. Reproduced from. /. Am. Chem. Soc., 119, 10147 (1997), by permission of the American Chemical Society. 

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. 

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 ) ... 

A fundamental issue in selective oxidation is the activation of C—H bonds that is always required for ODH (oxidative dehydrogenation) and oxo-functionalization and is detrimental for epoxidation. A particular case is silver [70] as catalyst, which can achieve highly selective epoxidation of ethene as well as highly selective dehydrogenation of methanol to formaldehyde although it is notably in both cases only the same metallic catalyst. We will return to this case in the next section, which deals with the multiplicity of active oxygen species. 

Several modifications of either the catalyst formulation or the process conditions were then reported, with remarkable improvements in performance being recorded. However, in all cases gas-phase promoters, be they organic halides or NOx, were necessary to have acceptable conversion and relatively stable performance. Carbon dioxide is also a promoter, since in the presence of CO2 the selectivity was improved, but the conversion considerably decreased. These features are clearly analogous to those applied in the industrial epoxidation of ethene. 

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... 

Multi-state epoxidation of ethene by cytochrome P450 A quantum cherrucal study. J. Am. Chem. Soc. 123, 3037-3047. 

MINDO/3 calculations carried out for the epoxidation of ethene by peroxyacids... 

The epoxidation of ethene-1,1 -diylbisphosphonic acid esters with 30% H2O2 in NaHCOj buffered solution yields esters of 2,2-oxiranediylbisphosphonic acid ... 

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

Both experimental and theoretical studies of the peracid epoxidation of ethene and alkyl-substituted olefins have suggested that a spiro transition structure is favored over a planar one. For example, DFT calculations indicated that the transition structure for the reaction of peroxyformic acid and ethene has the geometry shown in Figure 9.45. In this case the two C-0 distances are identical, indicating synchronous formation of the two C-O bonds. If the olefin is substituted with a methyl, methoxy, vinyl, or cyano group, however, the transition structure can become asynchronous, meaning that one C-0 bond has been formed to a greater extent than the other in the transition structure. ... 

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