Ethylenes epoxidation

Alkylation reactions reveal a mechanistic aspect of the cuprate reactions different from that of addition reactions. Theoretical analyses of reactions of alkyl halides (Mel and MeBr) [123, 124] and epoxides (ethylene oxide and cyclohexene oxide) [124] with lithium cuprate clusters (Me2CuLi dimer or Me2CuLi-LiCl, Scheme 10.11) resolved long-standing questions on the mechanism of the alkylation reaction. Density functional calculations showed that the rate-determining step of the... 

Hardin BD, Niemeier RW, Sikov MR, et al Reproductive-toxicologic assessment of the epoxides ethylene oxide, propylene oxide, butylene oxide, and styrene oxide. Stand J Work Environ Health 9 94—102, 1983... 

Conversion of alkenes to epoxides The simplest epoxide, ethylene dioxide, is prepared by catalytic oxidation of ethylene, and alkenes are also oxidized to other epoxides by peracid or peroxy acid (see Section 5.7.2). 

Alkenes undergo a number of oxidation reactions in which the C=C is oxidized. The simplest epoxide, ethylene oxide, is prepared hy catalytic oxidation of ethylene with Ag at high temperatures (250 °C). 

This oxidation is unique, since only silver is capable of epoxidizing ethylene, and silver is active only in the oxidation of ethylene. A low-surface-area a-alumina is usually applied to support about 10-15% silver. Organic halides (1,2-dichloro-ethane, ethyl and vinyl chloride) are added as moderators, and additives (Cs, Ba) are also used to increase selectivity. At present selectivity in industrial oxidations is about 80%. 

The unique ability of silver to epoxidize ethylene lies in the fact that it adsorbs oxygen dissociatively, and that atomic oxygen formed at high oxygen coverage is weakly bound. The low activity of silver to activate C—H bonds is the key factor in the selectivity of epoxidation. 

Ethylene epoxidation Ethylene from coal Ethylene glycol... 

Epoxides are important intermediates in many industrial processes. For example, the reaction of the simplest epoxide, ethylene oxide, with water is employed to produce ethylene glycol, which is used in antifreeze and to prepare polymers such as Dacron. One method for the preparation of ethylene oxide employs an intramolecular nucleophilic substitution reaction of ethylene chlorohydrin ... 

Amines can also open epoxides. Ethylene oxide reacts with aqueous ammonia to give ethanolamine, an important industrial reagent. The nitrogen atom in ethanolamine is still nucleophilic, and ethanolamine can react further to give diethanolamine and triethanolamine. Good yields of ethanolamine are achieved by using excess ammonia. 

In spite of the CIDNP polarization pattern, we believe the sulfinyl mechanism can be dismissed. First, the SO bond in a sulfinyl radical is very strong. Using Benson s estimate for the heat of formation of the phenylsulfinyl radical (13 kcal/mol) [63] and standard values for the other relevant compounds [98], the S-0 bond energy is ca. 102 kcal/mol, whereas the C-S bond is some 35 kcal/mol weaker. Transfer of an O atom from phenylsulfinyl to a methyl radical is endothermic by 11 kcal/mol, and to epoxidize ethylene endothermic by 40 kcal/mol. (The relevance of the latter example will become clear below.) Furthermore, from the a-cleavage work discussed previously, it is clear that the expected product from reaction to an arylsulfmyl radical and a carbon radical is a sulfenic ester or disproportionation product. 

Multifunctional epoxides have been used predominantly as cross-linkers because of their electrophilic nature. Pentaerythritol tetraglycidyl ether, a tetrafunctional epoxide, was used originally by Alpert and Regnier (37). Pearson and Regnier (38) compared two difunctional epoxides, ethylene glycol diglycidyl ether and 1,4-butanediol diglycidyl ether. These multifunctional cross-linkers increased the hydrophilic nature of the support. 

EPOXIDATION ETHYLENE C2H4 ETHYLENE OXIDE C2H4O ETHYLENE GLYCOL, ANTIFREEZE POLYESTERS, SURFACTANTS 5.8... 

Preparation of an alcohol from an epoxide is shown below. The epoxide (ethylene oxide) ring opens when the nucleophile attacks the carbon-oxygen bond. Note the fact that the nucleophilic carbon is supplied by the Grignard reagent (methyl magnesium bromide). 

---