Epoxidation chlorine effect

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

C. Karavasilis, S. Bebelis, and C.G. Vayenas, In Situ Controlled Promotion of Catalyst Surfaces viaNEMCA The Effect of Na on the Ag-Catalyzed Ethylene Epoxidation in the Presence of Chlorine Moderators, J. Catal. 160, 205-213 (1996). 

The reaction is insensitive to steric effects, but kj increases with the number of alkyl substituents although it is not influenced by position of the alkyl groups (unlike oxidation by TI(III)) . In these respects Cr(VI) oxidation resembles bromination, chlorination and epoxidation and a symmetrical transition state of the type depicted is favoured. 

Gao and Friend showed that chlorine is an effective promoter for enhancing the selectivity of styrene epoxidation on Au(l 11) by inhibiting secondary oxidation [247]. 

This procedure is general for the conversion of epoxides to dichlorides with inversion of configuration at each of the two carbons and, in effect, provides a method for the cis-addition of chlorine to a double bond.2 ci.v-1,2-Dichlorocyclohcxane has also been prepared from 1,2-epoxycyclohexane and sulfuryl chloride,3 but the stereospecificity of the reaction appears to be extremely sensitive to reaction conditions, and the yield is lower than that obtained by the method described here. Other methods give cis-1,2-dichlorocyclohexane contaminated with considerable amounts of the trans -isomer. This method has been used to convert cis- and trans-4,5-epoxyoctanes to meso- and d/-4,5-dichlorooctanes, respectively, and trans-7,8-epoxyoctadecane to fhreo-7,8-dichloro-octadecane. These conversions were carried out on smaller amounts of material, and the products were purified by column chromatography on silica gel. Yields were 51-63%. 

The first report on the coordination polymerisation of epoxide, leading to a stereoregular (isotactic) polymer, concerned the polymerisation of propylene oxide in the presence of a ferric chloride-propylene oxide catalyst the respective patent appeared in 1955 [13]. In this catalyst, which is referred to as the Pruitt Baggett adduct of the general formula Cl(C3H60)vFe(Cl)(0C3H6),CI, two substituents of the alcoholate type formed by the addition of propylene oxide to Fe Cl bonds and one chlorine atom at the iron atom are present [14]. A few years later, various types of catalyst effective for stereoselective polymerisation of propylene oxide were found and developed aluminium isopropoxide-zinc chloride [15], dialkylzinc-water [16], dialkylzinc alcohol [16], trialkylalumi-nium water [17] and trialkylaluminium-water acetylacetone [18] and trialkyla-luminium lanthanide triacetylacetonate H20 [19]. Other important catalysts for the stereoselective polymerisation of propylene oxide, such as bimetallic /1-oxoalkoxides of the [(R0)2A10]2Zn type, were obtained by condensation of zinc acetate with aluminium isopropoxide in a 1 2 molar ratio of reactants [20-22]. 

Our calculations have shown that an electron-withdrawing substituent increases the reactivity of a protonated epoxide by weakening the adjacent C—O bond107, accordingly, the chlorine in vinyl chloride has a positive effect with regard to factor (c) above. On the other hand, since the epoxidation of the olefin occurs by reaction with an electrophilic form of... 

The catalyst derived from chlorine displacement was effective in the base catalysed ring-opening of epoxides to form monoglycerides.[16] The other TBD-derived catalyst (from epoxide ring-opening) was also found to be active in the Knoevenagel reaction, the Michael addition and the base catalysed epoxidation of alkenones.[15] Results in the epoxidation reaction were of particular interest, as this leads to highly labile and... 

The ring-closure mechanism of 2-chloroethanol has been studied on the basis of kinetic and equilibrium chlorine isotope effects. Epoxidation of the terminal double bond of farnesyl acetate has been achieved via the bromohydrin, obtained with NBS. A stereospecific method has been elaborated for the preparation of 1-alkynyloxiranes, starting from the monotosylate ester of acetylenic diols. 1-Alkynyloxiranes are also formed from a-hydroxy quaternary ammonium salts in alkaline medium (Eq. 57). ... 

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