Ethylene dehydrochlorination

Once the principal route to vinyl chloride, in all but a few percent of current U.S. capacity this has been replaced by dehydrochlorination of ethylene dichloride. A combined process in which hydrogen chloride cracked from ethylene dichloride was added to acetylene was advantageous but it is rarely used because processes to oxidize hydrogen chloride to chlorine with air or oxygen are cheaper (7) (see Vinyl polymers). 

Minor amounts of acetylene are used to produce chlorinated ethylenes. Trichloroethylene (trichloroethene) and perchloroethylene (tetrachloroethene) are prepared by successive chlorinations and dehydrochlorinations (see Chlorocarsons and chlorohydrocarsons). The chlorinations take place in the Hquid phase using uv radiation and the dehydrochlorinations use calcium hydroxide in an aqueous medium at 70—100°C. Dehydrochlorination can also be carried out thermally (330—700°C) or catalyticaHy (300—500°C). 

Dichloroethane, an important intermediate for vinyl chloride production, is produced by catalytic chlorination of ethylene in either vapor or Hquid phase or by oxychlorination of ethylene. Thermal dehydrochlorination of 1,2-dichloroethane produces vinyl chloride and coproduct hydrogen chloride. Hydrogen chloride is commonly recycled to an oxychlorination unit to produce 1,2-dichloroethane or is processed into sales-grade anhydrous or aqueous hydrogen chloride. 

Oxychlorination. This is an important process for the production of 1,2-dichloroethane which is mainly produced as an intermediate for the production of vinyl chloride. The reaction consists of combining hydrogen chloride, ethylene, and oxygen (air) in the presence of a cupric chloride catalyst to produce 1,2-dichloroethane (eq. 24). The hydrogen chloride produced from thermal dehydrochlorination of 1,2-dichloroethane to produce vinyl chloride (eq. 25) is usually recycled back to the oxychlorination reactor. The oxychlorination process has been reviewed (31). 

Ethyl chloride can be dehydrochlorinated to ethylene using alcohoHc potash. Condensation of alcohol with ethyl chloride in this reaction also produces some diethyl ether. Heating to 625°C and subsequent contact with calcium oxide and water at 400—450°C gives ethyl alcohol as the chief product of decomposition. Ethyl chloride yields butane, ethylene, water, and a soHd of unknown composition when heated with metallic magnesium for about six hours in a sealed tube. Ethyl chloride forms regular crystals of a hydrate with water at 0°C (5). Dry ethyl chloride can be used in contact with most common metals in the absence of air up to 200°C. Its oxidation and hydrolysis are slow at ordinary temperatures. Ethyl chloride yields ethyl alcohol, acetaldehyde, and some ethylene in the presence of steam with various catalysts, eg, titanium dioxide and barium chloride. 

Oxychl orin ation of ethylene has become the second important process for 1,2-dichloroethane. The process is usually incorporated into an integrated vinyl chloride plant in which hydrogen chloride, recovered from the dehydrochlorination or cracking of 1,2-dichloroethane to vinyl chloride, is recycled to an oxychl orin a tion unit. The hydrogen chloride by-product is used as the chlorine source in the chlorination of ethylene in the presence of oxygen and copper chloride catalyst ... 

In Japan, Toagosei is reported to produce trichloroethylene and tetrachloroethylene by chlorination of ethylene followed by dehydrochlorination. In this process the intermediate tetrachloroethane is either dehydrochlorinated to trichloroethylene or further chlorinated to pentachloroethane [76-01-7] followed by dehydrochlorination to tetrachloroethylene. Partially chlorinated by-products are recycled and by-product HCl is available for other processes. 

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. 

Chlorohydrin Process. Ethylene oxide is produced from ethylene chlorohydrin by dehydrochlorination using either sodium or calcium hydroxide (160). The by-products include calcium chloride, dichloroethane, bis(2-chloroethyl) ether, and acetaldehyde. Although the chlorohydrin process appears simpler, its capital costs are higher, largely due to material of constmction considerations (197). 

The monomer is produced from trichloroethane by dehydrochlorination Figure 17.2). This may be effected by pyrolysis at 400°C, by heating with lime or treatment with caustic soda. The trichlorethane itself may be obtained from ethylene, vinyl chloride or acetylene. 

The second step is the dehydrochlorination of ethylene dichloride (EDC) to vinyl chloride and HCl. The pyrolysis reaction occurs at approximately 500°C and 25 atmospheres in the presence of pumice on charcoal ... 

Apart from the UOP Pacol process, today s only other meaningful economic process is the Shell higher olefin process (SHOP) in which /z-olefins are produced by ethylene oligomerization. Until 1992 Hiils AG used its own technology to produce -60,000 t/year of /z-olefins by the chlorination of /z-paraffins (from Molex plant) and subsequent dehydrochlorination [13]. In the past, the wax cracking process (Shell, Chevron) played a certain role. In the Pacol and Hiils processes, olefins are obtained as diluted solutions in paraffin (Pacol to max. 20%, Hiils about 30%) without further processing these are then used for alkylation. In contrast, the SHOP process produces pure olefins. 

A PPV derivative which is twofold phenylsubstituted at the vinylene unit, poly(l,4-phenylene-l,2-diphenylvinylene DP-PPV), (71b) (see also the discussion of dehydrochlorination of unsymmetrically substituted para-xylylene dichlorides in Section 3.1) was first synthesized by Smets et al., using acid-catalyzed elimination of nitrogen from l,4-bis(diazobenzyl)benzene 83 [106]. The yellow products obtained are fully soluble in common organic solvents (toluene, chloroform, ethylene chloride, DMF, THF). 

Secondly, the carbon framework holding the exocyclic double bonds could be extended. This is demonstrated by naphtharadialene 5, a highly reactive intermediate which has been generated by thermal dehydrochlorination from either the tetrachloride 178 or its isomer 179106. Radialene 5 has not been detected as such in these eliminations rather, its temporary formation was inferred from the isolation of the thermolysis product 180 which was isolated in 15% yield (equation 25). Formally, 5 may also be regarded as an [8]radialene into whose center an ethylene unit has been inserted. In principle, other center units—cyclobutadiene, suitable aromatic systems—may be introduced in this manner, thus generating a plethora of novel radialene structures. 

It is evident that reactions of unsaturated polymers with bisnitrile oxides lead to cross-linking. Such a procedure has been patented for curing poly(butadiene), butadiene-styrene copolymer, as well as some unsaturated polyethers and polyesters (512-514). Bisnitrile oxides are usually generated in the presence of unsaturated polymers by dehydrochlorination of hydroximoyl chlorides. Cross-linking of ethylene-propylene-diene co-polymers with stable bisnitrile oxides has been studied (515, 516). The rate of the process has been shown to reduce in record with the sequence 2-chloroterephthalonitrile oxide > terephthalonitrile oxide > 2,5-dimethylterephthalonitrile oxide > 2,3,5,6-tetramethylterephthalo-nitrile oxide > anthracene-9,10-dicarbonitrile oxide (515). 

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. 

Vinyl chloride, formerly obtained from acetylene, is now produced by the transcatalytic process where chlorination of ethylene, oxychlorination of the by-product hydrogen chloride, and dehydrochlorination occur in a single reactor. 

Vinyl Chloride. A second process by which petroleum-derived ethylene may be employed in the production of polymeric products is by conversion to vinyl chloride and subsequent polymerization or copolymerization with other vinyl monomers. The process involves the reaction of ethylene with chlorine followed by catalytic dehydrochlorination of ethylene dichloride. 

Several aromatic diamines were prepared using DDT as starting compound. 4,4 -Diaminobenzophenone was prepared using a three-stage process, including dehydrochlorination of DDT, oxidation of the 1,1-dichloro-2,2-di-(4-chlorophenyl)-ethylene thus formed and amination of 4,4 -dichlorobenzophenone [20, 23] (Scheme 2.8). 

Nitration of DDT and its dehydrochlorination product 1,1 -dichloro-2,2-di-(4-chlorophenyl)-ethylene led to the formation of bis(3-nitro-4-chlorophenylene) compounds containing 1,1,1-trichloroethane and carbonyl bridging groups [19,20]. These compounds were converted to the corresponding bis(3-amino-4-chlorophenylenes) l,l-dichloro-bis-(3-amino-4-chlorophenyl)-ethylene and 3,3 -diamino-4,4 -dichlorobenzophenone in accordance with Scheme 2.9 [5, 22, 24]. 

The point (a) is demonstrated by the data in Table 11 for 2-halobutanes which give three products 1-butene, cis-2-butene and frans-2-butene. The differences in selectivities can be even larger than indicated by these data. The dehydrochlorination of 1,1,2-trichloroethane yields 1,2-dichloro-ethylene (I) and trans- and ci s-l,2-dichloroethylene (II). On silica—alumina, the value of the ratio I/II was 10 3, on alumina, 0.30 and on KOH— Si02,10 [66]. 

Another major chlorinated hydrocarbon is vinyl chloride. For many years acetylene was the sole raw material for the production of vinyl chloride by a catalytic fixed bed vapor-phase process. This process is characterized by high yields and modest capital investment. Nevertheless, the high relative cost of acetylene provided an incentive to replace it in whole or in part by ethylene. The first step in this direction was the concurrent use of both raw materials. Ethylene was chlorinated to di-chloroethane, and the hydrogen chloride derived from the subsequent dehydrochlorination reacted with acetylene to form additional vinyl chloride. 

This process is shown schematically in Figure 7. The ethylene part of the feed reacts with chlorine in the liquid phase to produce 1,2-di-chloroethane (EDC) by a simple addition reaction, in the presence of a ferric chloride catalyst (9). Thermal dehydrochlorination, or cracking, of the intermediate EDC then produces the vinyl chloride monomer and by-product HC1 (1). Acetylene is still needed as the other part of the over-all feed, to react with this by-product HC1 and produce VCM as in the all-acetylene route. 

POLYVINYLIDENE CHLORIDE. [CAS 9002-86-2J. A stereoregular, thermoplastic polymer is produced by the free-radical chain polymerization of vinylidene chloride (H>C=CCIi) using suspension or emulsion techniques. The monomer lias a bp of 31.6°C and was first synthesized in 1838 by Regnault. who dehydrochlorinated 1,1.2-trichloroethane which he obtained by the chlorination of ethylene. The copolymer product has been produced under various names, including Saran. As shown by the following equation, the product, in production since the late 1930s, is produced by a reaction similar to that used by Regnault nearly a century earlier ... 

The leading derivative of ethylene dichloride is vinyl chloride [75-01-4] monomer (VCM), which is subsequently used to produce poly(vinyl chloride) and chlorinated hydrocarbons. Vinyl chloride is obtained by dehydrochlorination of ethylene dichloride in the gas phase (500-600°C and 2.5-3.5 MPa). 

Ethylene oxide has been produced commercially by two basic routes the ethylene chlorohydrin and direct oxidation processes. The chlorohydrin process was first introduced during World War I in Germany by Badische Anilin-nnd Soda-Fabrik (BASF) and others (95). The process involves the reaction of ethylene with hypochlorous acid followed by dehydrochlorination of the resulting chlorohydrin with lime to produce ethylene oxide and calcium chloride. Union Carbide Corp. was the first to commercialize this process in the United States in 1925. The chlorohydrin process is not economically competitive, and was quickly replaced by the direct oxidation process as the dominant technology. At the present time, all the ethylene oxide production in the world is achieved by the direct oxidation process. 

The investigations of Lucas and his coworkers with 2,3-disubstituted butanes have contributed much to the clarification of the mechanism of ring closure and ring opening of ethylene oxides and ethylene imines. D-Mreo-2,3-Butanediol (XV) is converted into a chlorohydrin (XVII) via the diacetate (XVI).24 In the formation of the chlorohydrin (XVII) a Walden inversion occurs.26 The dehydrochlorination of XVII with... 

On the other hand dehydrochlorinated polyvinylchloride li > and polimethyl-jS-chlorvinyl-ketone 74> catalyze the autoxidation of hydrocarbons, and the activities are related to the semiconductive properties of the catalysts. Recently it has been shown that entirely inert polymers like polyethylene, polypropylene and polyftetrafluoro) ethylene are rather efficient catalysts for the oxidation of te-tralin 75>. 

This route has largely been superceded by a route involving chlorination and dehydrochlorination of ethylene or vinyl chloride and, more recently, by a route involving oxychlorination of two-carbon (C2) raw materials. 

For many years the manufacture of ethylene oxide was carried out by chlorohydrin formation followed by dehydrochlorination to the epoxide. 

The process is combined with the process in which hydrogen chloride is produced by thermal dehydrochlorination of ethylene dichloride. 

Thus, vinyl chloride is manufactured by the thermal dehydrochlorination of ethylene dichloride at 95 percent yield at temperatures of 480 to 510°C under a pressure of 50 psi with a charcoal catalyst. 

Vinyl chloride is usually prepared by the oxychlorination (dehydrochlorination) of ethylene. 

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