Epoxidation of ethylene

The selective epoxidation of ethylene by hydrogen peroxide ia a 1,4-dioxane solvent ia the presence of an arsenic catalyst is claimed. No solvent degradation is observed. Ethylene oxide is the only significant product detected. The catalyst used may be either elemental arsenic, an arsenic compound, or both. 

The epoxidation of ethylene on Ag is a reaction of great industrial importance which has been studied extensively for many decades. From a... 

S. Bebelis, and C.G. Vayenas, Non-Faradaic Electrochemical Modification of Catalytic Activity 6. The epoxidation of Ethylene on Ag/Zr02(8mol%)Y203,/. Catal. 138, 588-610 (1992). 

The catalytic epoxidation of ethylene on silver has been studied extensively over the last thirty years. The literature in this area is very broad and has been reviewed by several authors (2>2 3). In recent years considerable progress has been made towards a satisfactory understanding of the mechanism of this important and complex catalytic system. 

While chlorine is a poison for the ammonia synthesis over iron, it serves as a promoter in the epoxidation of ethylene over silver catalysts, where it increases the selectivity to ethylene oxide at the cost of the undesired total combustion to C02. In this case an interesting correlation was observed between the AgCl27Cl ratio from SIMS, which reflects the extent to which silver is chlorinated, and the selectivity towards ethylene oxide [16]. In both examples, the molecular clusters reveal which elements are in contact in the surface region of the catalyst. 

Another example of a famous organic chemical reaction being replaced by a catalytic process is furnished by the manufacture of ethylene oxide. For many years it was made by chlorohydrin formation followed by dehydrochlorination to the epoxide. Although the chlorohydrin route is still used to convert propylene to propylene oxide, a more efficient air epoxidation of ethylene is used and the chlorohydrin process for ethylene oxide manufacture has not been used since 1972. 

FIGURE 16. Transition structures for the epoxidation of ethylene with DMDO optimized at the MP2/6-31G level (TS-a) and at the B3LYP/6-31G level (TS-b, numbers in parentheses are at the QCISD/6-31G level)... 

The transition structures for the epoxidation of ethylene and propylene with peroxyformic acid and of ethylene with dioxirane and dimethyldioxirane calculated at the B3LYP, QCISD and CCSD levels are symmetrical with a spiro orientation of the electrophilic oxygen, whereas the MP2 calculations favor unsymmetrical transition structures. The geometries of the transition structures calculated using the B3LYP functional are close to those found at QCISD, CCSD, CCSD(T) levels as well as those found at the CASSCF(10,9) and CASSCF(10,10) levels for the transition structure of the epoxidation of ethylene. 

At that period of time, this rather primitive transition structure for the peracid epoxidation of ethylene was sufficiently novel to warrant publication as a communication Today, calculating transition structures for epoxidation of a variety of complex alkenes with the actual peracid used experimentally, such as meta-chloroperoxybenzoic acid m-CPBA), is commonplace . ... 

FIGURE 21. Selected geometrical parameters of the transition structures for the epoxidation of ethylene with peroxyformic acid calculated at the QCISD/6-31G, CCD/6-31G (in parentheses), B3LYP/6-31G (in square brackets) and MP2(FC)/6-31G (in curly brackets) levels... 

In industrial applications the achievement of higher activity and selectivity is of course desirable. However, beyond a certain point, they are not the driving forces for extensive research. For instance, current processes for epoxidation of ethylene to ethylene oxide on silver catalysts are so optimized that further increases in selectivity could upset the heat-balance of the process. Amoco s phthalic acid and maleic anhydride processes are similarly well energy-integrated (7). Rather than incremental improvements in performance, forces driving commercial research have been... 

Optimal Distribution of Silver Catalyst for Epoxidation of Ethylene... 

Fig.1 Doublet and quartet potential energy surfaces for the epoxidation of ethylene with Cp Cr(0)Cl2...

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