Chloroprene from acetylene

Table 6.14 gives the main economic data concerning the production of chloroprene from acetylene and butadiene. 

Preparation of chloroprene from acetylene In this process, the following route is used ... 

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). 

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... 

Polychloroprene rubber (CR) is the most popular and versatile of the elastomers used in adhesives. In the early 1920s, Dr. Nieuwland of the University of Notre Dame synthesized divinyl acetylene from acetylene using copper(l) chloride as catalyst. A few years later, Du Pont scientists joined Dr. Nieuwland s research and prepared monovinyl acetylene, from which, by controlled reaction with hydrochloric acid, the chloroprene monomer (2-chloro-l, 3-butadiene) was obtained. Upon polymerization of chloroprene a rubber-like polymer was obtained. In 1932 it was commercialized under the tradename DuPrene which was changed to Neoprene by DuPont de Nemours in 1936. 

Calcott, a DuPont chemist, attempted to make polymers from acetylene, reasoning that if acetylene formed dimers and trimers, conditions could be found to produce polymers. He failed, but went to Carothers who had one of his chemists, Arnold Collins, work on the project. Collins ran the reaction described by Nieuwland, purifying the reaction mixture. He found a small amount of material that was not vinylacetylene or divinylacetylene. He set the liquid aside. When he came back, the liquid had solidified giving a material that seemed rubbery and even bounced. They analyzed the rubbery material and found that it was not a hydrocarbon, but had chlorine in it. The chlorine had come from HCl that was used in Nieuwland s procedure to make the dimers and trimers. The HCl added to the vinylacetylene forming chloroprene. 

Chloroprene, used for the production of neoprene rubber, is obtained by the dehydrochlorination of dichlorobutene. The latter is produced by the chlorination of 1,3-butadiene, which in turn is synthesized from acetylene. 

Another chlorinated compound which, like vinyl chloride, is used only in its polymeric form, is chloroprene (2-chloro-l,3-butadiene), which is polymerized to make neoprene, first produced in 1940. As far as is known (17) y the monomer is made commercially only from acetylene via addition of hydrochloric acid to monovinylacetylene in the presence of cuprous chloride, but syntheses from butylenes or butadiene have been described. The production of chloroprene exceeded 100,000,000 pounds per year at the wartime peak and has been somewhat lower since then, but in view of the many valuable properties of the neoprene rubber it will continue to be important. 

Production of chloroprene today is completely determined by demand for the polymer. The only other use accounting for a significant volume is the synthesis of 2,3-dichloro-1,3-butadiene, which is used as a monomer in selected copolymerizations with chloroprene. The original commercial production was from acetylene through mono-vinylacetylene. Since the 1960s, because of the increasing price of acetylene and decreasing price of butadiene, the latter has displaced acetylene as the feedstock in most countries (Kleinschmidt, 1986 Stewart, 1993). 

The polymerization of 2-chloro-l,3-butadiene(chloroprene), which is made from acetylene or 1,3-butadiene [284-287] is strongly exothermic (75kJ/mol). It can be initiated radically, anionically, cationically, or with Ziegler catalysts [288]. Only the free-radical process, which is usually run as an emulsion polymerization, is of technical importance [289-294]. Compared with polybutadiene and polyisoprene, polychloroprene features improved gasoline and aging resistance, low-temperature flexibility, and is less combustable [295-297]. 

There are two routes to chloroprene, a) starting from butadiene, b) starting from acetylene. 

Now there are at least six chloroprene plants worldwide. All but one of these plants produce chloroprene from butadiene. However, there is one remaining plant that produces chloroprene monomer using the original acetylene process as shown in Figure 4.27. 

Neoprene was manufactured via the acetylene route for many years. However, the technology is difficult and the starting material, acetylene, gradually increased in price over the years. By 1960 a second, less expensive method of chloroprene production had been developed and commercialized. The second, preferred method involves the production of chloroprene from butadiene via a chlorination step. 

Cuprous salts catalyze the oligomerization of acetylene to vinylacetylene and divinylacetylene (38). The former compound is the raw material for the production of chloroprene monomer and polymers derived from it. Nickel catalysts with the appropriate ligands smoothly convert acetylene to benzene (39) or 1,3,5,7-cyclooctatetraene (40—42). Polymer formation accompanies these transition-metal catalyzed syntheses. 

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. 

Pyrolysis. Vinyl chloride is more stable than saturated chloroalkanes to thermal pyrolysis, which is why nearly all vinyl chloride made commercially comes from thermal dehydrochlorination of EDC. When vinyl chloride is heated to 450°C, only small amounts of acetylene form. Litde conversion of vinyl chloride occurs, even at 525—575°C, and the main products are chloroprene [126-99-8] and acetylene. The presence of HCl lowers the amount of chloroprene formed. 

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 (boiling point 59.4°C, density 0.9583) is, chemically, a chlorovinyl ester of hydrochloric acid and can be manufactured by polymerizing acetylene to vinyl acetylene using a weak solution containing ammonium chloride (NH4C1), cuprous chloride (Cu2Cl2), and potassium chloride (KC1) as catalyst. The off-gas from the reactor has its water condensed out and is then fractionated. Aqueous hydrochloric acid at 35 to 45 °C is then reacted with the vinyl acetylene in the presence of cupric chloride to give chloroprene (2-chloro-l,3-butadiene). 

Wallace Carothers will be the subject of one of our Polymer Milestones when we discuss nylon in Chapter 3. Among his many accomplishments in the late 1920s and early 1930s, Carothers and his coworkers made a major contribution to the discovery and eventual production of the synthetic rubber, polychloroprene. It was synthesized from the diene monomer, chloroprene, CH2=CCI-CH=CHr Chloroprene, which is a very reactive monomer—it spontaneously polymerizes in the absence of inhibitors— was a product of some classic studies on acetylene chemistry performed by Carothers and coworkers at that time. In common with butadiene and iso-prene, in free radical polymerization chloroprene is incorporated into the growing chain as a number of different structural isomers. Elastomeric materials having very different physical and mechanical properties can be made by simply varying the polym-... 

As in steam cracking, a large number of by-products is produced. Some of them result from the consecutive reactions of the chlorination of vinyl chloride and of its derivatives obtained by dehydrochlorination (tri-, tetra-, pentachloroethane, perchloro-ethane, di-, trichloroethylene. perchloroethyleneX and the others from the hydrochlorination of vinyl chloride il.l-dichloroethane), while others result from decomposition reactions (acetylene, cokei or conversion of impurities initially present (hydrocarbons such as ethylene, butadiene and benzene, chlorinated derivatives such as chloroprene, methyl and ethyl Chlorides, chloroform, carbon tetrachloride, eta, and hydrogen) ... 

Discovered in 1930 by Carothers and Collins during their work on vinyl acetylene, chloroprene was also prepared in the same year from butadiene. But although it was developed industrially at the time from the dimer of acetylene, it was only in 1936 that Distugil built the first unit employing butadiene, the most widely used industrial method today. 

Poly(chloroprene) was one of the first synthetic elastomers. It came on the market in 1931, and was developed at the Du Pont factory as part of their search for elastomers for special areas of application. The industrial synthesis of the monomer became possible when Nieuwland discovered mono vinyl acetylene. Today, chloroprene is produced from monovinyl acetylene C4H4, butadiene butene C4H8, or butane C4Hio-... 

This route is analogous to the acetylene route to chloroprene as also were the polymerization methods employed. The properties of the resulting elastomer, Fluoroprene, were far from outstanding and production was soon discontinued. 

Details polychloroprene was Invented by DuPont scientists on April 17,1930 after Dr. Elmer K. Bolton of DuPont laboratories attended a lecture by Fr. Julius Arthur NIeuwland, a professor of chemistry at the University of Notre Dame. Fr. Nieuwland s research was focused on acetylene chemistry and during the course of his work he produced divinyl acetylene, a jelly that firms Into an elastic compound similar to rubber when passed over sulfur dichlorlde. After DuPont purchased the patent rights from the university, V fellace Carothers of DuPont took over commercial development of Nieuwland s discovery in collaboration with NIeuwland himself. DuPont focused on monovinyl acetylene and reacted the substance with hydrogen chloride gas, manu cturing chloroprene. ... 

From the very beginning up to the 1960s, chloroprene was produced by the older energy-intensive acetylene process using acetylene, derived from calcium carbide [3]. The acetylene process had the additional disadvantage of high investment costs because of the difficulty of controlling the conversion of acetylene into chloroprene. The modern butadiene process, which is now used by nearly all chloroprene producers, is based on the readily available butadiene [3]. 

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