Chloroprene, chlorination

Chlorine (from the Greek chloros for yellow-green ) is the most abundant halogen (0.19 w% of the earth s crust) and plays a key role in chemical processes. The chlor-alkali industry has been in operation since the 1890s and improvements in the technology are still important and noticeable, for example, the transition from the mercury-based technology to membrane cells [60]. Most chlorine produced today is used for the manufacture of polyvinyl chloride, chloroprene, chlorinated hydrocarbons, propylene oxide, in the pulp and paper industry, in water treatment, and in disinfection processes [61]. A summary of typical redox states of chlorine, standard potentials for acidic aqueous media, and applications is given in Scheme 2. 

Vinyl or vinylidene chloride/acrylonitrile copolymers Chlorosulphonated polyethylene, vulcanised chloroprene, chlorinated butyl rubber... 

Chlorinated polyethylene Chlorinated polyvinylchloride Chloroprene, chlorinated rubber. Neoprene Chlorosulfonated polyethylene (or CSM)... 

Chloroprene, chlorinated polyethylene Chloroprene, chlorinated polyethylene Nitrile... 

Manufacture via this process has been completely replaced by chlorination of butadiene (3) (see Chlorocarbons and chlorohydrocarbons, chloroprene ElASTOT RS, synthetic, POLYCm OROPRENE). 

Calcium carbide has been used in steel production to lower sulfur emissions when coke with high sulfur content is used. The principal use of carbide remains hydrolysis for acetylene (C2H2) production. Acetylene is widely used as a welding gas, and is also a versatile intermediate for the synthesis of many organic chemicals. Approximately 450,000 t of acetylene were used aimuaHy in the early 1960s for the production of such chemicals as acrylonitrile, acrylates, chlorinated solvents, chloroprene, vinyl acetate, and vinyl chloride. Since then, petroleum-derived olefins have replaced acetylene in these uses. 

At one time, the only commercial route to 2-chloro-1,3-butadiene (chloroprene), the monomer for neoprene, was from acetylene (see Elastomers, synthetic). In the United States, Du Pont operated two plants in which acetylene was dimeri2ed to vinylacetylene with a cuprous chloride catalyst and the vinyl-acetylene reacted with hydrogen chloride to give 2-chloro-1,3-butadiene. This process was replaced in 1970 with a butadiene-based process in which butadiene is chlorinated and dehydrochlorinated to yield the desired product (see Chlorocarbonsandchlorohydrocarbons). 

Acetylene and hydrogen chloride historically were used to make chloroprene [126-99-8]. The olefin reaction is used to make ethyl chloride from ethylene and to make 1,1-dichloroethane from vinyl chloride. 1,1-Dichloroethane is an intermediate to produce 1,1,1-trichloroethane by thermal (26) or photochemical chlorination (27) routes. 

Chlorinated polyethylene (CPE) has excellent o2one, oil, and heat resistance. In addition chlorinated polyethylene has replaced chloroprene elastomers. CPE has a lower specific gravity than chloroprene compounds and produces compounds that are similar to CR in properties but with lower costs. In addition, due to high levels of chlorine in the polymer, the flame resistance of the compounds of CPE are high. 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

Chloroprene (qv), 2-chloro-1,3-butadiene, [126-99-8] is produced commercially from butadiene in a three-step process. Butadiene is first chlorinated at 300°C to a 60 40 mixture of the 1,2- and 1,4-dichlorobutene isomers. This mixture is isomeri2ed to the 3,4-dichloro-l-butene with the aid of a Cu—CU2CI2 catalyst followed by dehydrochlorination with base such as NaOH (54). 

Dicbloro-l,3-butadiene [1653-19-6] is a favored comonomer to decrease the regularity and crystallization of chloroprene polymers. It is one of the few monomers that will copolymerize with chloroprene at a satisfactory rate without severe inhibition. It is prepared from by-products or related intermediates. It is also prepared in several steps from chloroprene beginning with hydrochlorination. Subsequent chlorination to 2,3,4-trichloto-1-butene, followed by dehydrochlorination leads to the desired monomer in good yield if polymerization is prevented. 

The vinylacetylene [689-97-4] route to chloroprene has been described elsewhere (14). It is no longer practical because of costs except where inexpensive by-product acetylene and existing equipment ate available (see Acetylene-DERIVED chemicals). In the production of chloroprene from butadiene [106-99-0], there are three essential steps, chlorination, isomerization, and caustic dehydrochlorination of the 3,3-dichloro-l-butene, as shown by the following equations Chlorination... 

Chloroacetophenone (phenacyl chloride) Chlorbenzene (monochlorobenzene) o-Chlorobenzylidene malononitrile (OCBM) Chlorobromomethane/bromochloromethane 2-Chloro-l, 3-butadiene, see p-Chloroprene Chlorodiphenyl (42% chlorine)... 

Charcoal screenings, wet Charcoal, wet Chlorine azide Chlorine dioxide Chloroacetaldehyde Chloroacetone (unstabilized) Chloroacetonitrile Chloroformates, n.o.s. Chloroprene, uninhibited Chlorosulphonic acid Coal briquettes, hot Coke, hot Copper acetylide... 

Chemistry of polychloroprene rubber. Polychloroprene elastomers are produced by free-radical emulsion polymerization of the 2-chloro-1,3-butadiene monomer. The monomer is prepared by either addition of hydrogen chloride to monovinyl acetylene or by the vapour phase chlorination of butadiene at 290-300°C. This latter process was developed in 1960 and produces a mixture of 3,4-dichlorobut-l-ene and 1,4-dichlorobut-2-ene, which has to be dehydrochlorinated with alkali to produce chloroprene. 

Butadiene produces chloroprene through a high temperature chlorination to a mixture of dichlorohutenes, which is isomerized to 3,4-dichloro-1-hutene. This compound is then dehydrochlorinated to chloroprene ... 

At present it is believed that intermolecular chemical bonds are formed during the vulcanization of polychloroprene with ZnO not only due to the mobile chlorine in allyl position but also as a result of the reaction of the chlorine located directly at the double bond of the monomeric units chloroprene connected in the chain in 1,4-position as shown in the following scheme43. ... 

In the free radical polymerization of 1,3-dienes, 1,4 addition dominates 1,2 addition. The proportion of 1,2 (and 3,4 )units decreases in passing from butadiene to its methyl and chlorine substitution products isoprene, 2,3-dimethylbutadiene and chloroprene. The trans configuration of the 1,4 unit from butadiene is formed preferentially, the proportion of trans increasing rapidly with lowering of the polymerization temperature. 

Chloro pink, 9 310-311 Chloroplast transit peptide, 72 489 TV-Chloropolyacrylamides, 7 316 Chloroprene, 6 242, 246. See also 2-Chloro-1,3- butadiene from butadiene, 4 369 chlorocarbon/chlorohydrocarbon of industrial importance, 6 227t copolymerization of, 79 829-830 end use of chlorine, 6 134t removal in vinyl chloride manufacture, 25 642... 

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