Chlorohydrin epoxidation process

Ethylene oxide was originally manufactured by the two step chlorohydrin epoxidation process. This technology is no longer used, but is of historical interest, as it was the method by which ethylene oxide was first produced commercially. In this process, ethylene is reacted with chlorine to form a chlorohydrin intermediate which is then transformed to ethylene oxide by heating with calcium hydroxide. The chemistry is illustrated in equations (1) and (2) ... 

Dehydrochlorination to Epoxides. The most useful chemical reaction of chlorohydrins is dehydrochlotination to form epoxides (oxkanes). This reaction was first described by Wurtz in 1859 (12) in which ethylene chlorohydria and propylene chlorohydria were treated with aqueous potassium hydroxide [1310-58-3] to form ethylene oxide and propylene oxide, respectively. For many years both of these epoxides were produced industrially by the dehydrochlotination reaction. In the past 40 years, the ethylene oxide process based on chlorohydria has been replaced by the dkect oxidation of ethylene over silver catalysts. However, such epoxides as propylene oxide (qv) and epichl orohydrin are stiU manufactured by processes that involve chlorohydria intermediates. 

For many years ethylene chlorohydrin was manufactured on a large iadustrial scale as a precursor to ethylene oxide, but this process has been almost completely displaced by the direct oxidation of ethylene to ethylene oxide over silver catalysts. However, siace other commercially important epoxides such as propylene oxide and epichlorohydrin cannot be made by direct oxidation of the parent olefin, chlorohydrin iatermediates are stiU important ia the manufacture of these products. 

The most important chemical reaction of chi orohydrin s is dehydrochloriaation to produce epoxides. In the case of propylene oxide. The Dow Chemical Company is the only manufacturer ia the United States that still uses the chlorohydrin technology. In 1990 the U.S. propylene oxide production capacity was hsted as 1.43 x 10 t/yr, shared almost equally by Dow and Arco Chemical Co., which uses a process based on hydroperoxide iatermediates (69,70). More recentiy, Dow Europe SA, aimounced a decision to expand its propylene oxide capacity by 160,000 metric tons per year at the Stade, Germany site. This represents about a 40% iacrease over the current capacity (71). 

Hodgson et al. showed that a series of bis- and tris-homoallylic terminal epoxides underwent intramolecular cydopropanation to give a range of bicydic alcohols. A short asymmetric synthesis of sabina ketone based on this chemistry was demonstrated (Scheme 5.20). A practical advantage with this process is that the volatile epoxides can be replaced with readily available chlorohydrins, an extra... 

The disadvantage of the chlorohydrin process is the use of toxic, corrosive, and expensive chlorine the major drawback of the peroxide process is the formation of co-oxidates in larger amounts than the desired PO. The direct epoxidation of propylene using 02 (i.e., partial oxidation of propylene) from air has been recognized as a promising route. 

The epoxidation of propylene to propylene oxide is a high-volume process, using about 10% of the propylene produced in the world via one of two processes [127]. The oldest technology is called the chlorohydrin process and uses propylene, chlorine and water as its feedstocks. Due to the environmental costs of chlorine and the development of the more-efficient direct epoxidation over Ti02/Si02 catalysts, new plants all use the hydroperoxide route. The disadvantage here is the co-production of stoichiometric amounts of styrene or butyl alcohol, which means that the process economics are dependent on finding markets not only for the product of interest, but also for the co-product The hydroperoxide route has been practiced commercially since 1979 to co-produce propylene oxide and styrene [128], so when TS-1 was developed, epoxidation was looked at extensively [129]. 

An example of a whole-cell process is the two-step synthesis of an enantiopure epoxide by asymmetric reduction of an a-chloro ketone (Scheme 6.4), catalyzed by recombinant whole cells of an Escherichia coli sp. overexpressing an (R)-KRED from Lactobacillus kefir and GDH from Thermoplasma acidophilum, to the corresponding chlorohydrin, followed by non-enzymatic base-catalyzed ring closure to the epoxide [17]. 

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. 

Epoxidaiion of HPG. The reaction scheme for the epoxidation of HPG is shown in Figure 1. The generation of oxyanion II in toluene is assisted by (solid) KOH and QAS. II reacts rapidly with ECH to produce the 1,2-chlorohydrin of HPG, III. Dechlorohydrogenation of III proceeds immediately under the prevailing reaction conditions with formation of epoxide IV and KC1. The process can conveniently be monitored by HPLC. Completion is indicated when I is depleted. 

To understand and comparev the mechanisms and rates of polyester formation in catalyzed copolymerization, processes taking place in the system epoxide-anhydride without any initiator are described. In this review, copolymerization in the absence of compounds that do not occur in the initial reaction mixture is regarded as a non-catalyzed reaction. This means that the presence of alcohols, phenols or acids is not excluded. These compounds may be considered as copolymerization catalysts however, because of their possible occurrence in the polymerization system they are not regarded as initiators. The presence of OH groups in epoxy compounds, especially in resins where they occur as chlorohydrines (I), monoethers (II), and diethers of glycerol (III)... 

As with the previous studies in this section, no chloroform or HC1 was employed in the isolation process, which might otherwise convert the corresponding epoxides to these chlorohydrins. The fungus Phomopsis sp., which was found growing on the plant Adenocarpus foliolosus, produces the sesquiterpene acid 296 (534). 

Because most natural halogenated steroids are chlorohydrins, which are usually accompanied by the corresponding epoxide, one must ensure that the former are not artifacts formed during the isolation process. 

There are several alternatives to the polluting chlorohydrin route. One is the styrene monomer propene oxide (SMPO) process, used by Shell and Lyondell (Figure 1.6a) [14]. It is less polluting, but couples the epoxide production to that of styrene, a huge-volume product. Thus, this route depends heavily on the styrene market price. Another alternative, the ARCO/Oxirane process, uses a molybdenum... 

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 ... 

The industrial production of ethylene and propylene oxides was historically dependent on the chlorohydrin process, a multistep procedure that proceeds via the stoichiometric reaction of propylene (or ethylene) with chlorine and water to yield a mixture of chlorohydrin isomers (only one for ethylene) and hydrochloric acid. The epoxide is formed upon reaction of the chlorohydrins with calcium or sodium hydroxide. All the chlorine used in the process eventually ends up as chlorinated organic and inorganic by-products (Equation B2). 

Currently the chlorohydrin process is only used for the epoxidation of propylene, where it still accounts for some 48% of world installed capacity. The yields are 88-89%. In most cases, the plant is integrated with a chloro-alkali facility that supplies both the required chlorine and sodium hydroxide. The recycle to the electrolysis cells of the brine solution produced in the dehydrochlorination step has been considered but not applied, most probably, for technical and economic reasons. In general the aqueous solution of calcium or sodium chloride is disposed of. 

Our previous discussion makes it unnecessary to indicate how compounds XVIII and XIX yield XVII, from which we derive III and IV as well as II. Amusingly enough, when a stronger base (KOH) is used in lieu of potassium carbonate, compound IV is converted to cyclopentene V in moderate yield. A completely different process reminiscent of a semibenzylic acid rearrangement sets in, in contrast to the epoxidation reaction experienced by chlorohydrin XVIII under the same conditions (see Scheme 46.3). 

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