Chloroprene Monomer Production

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]. 

Butadiene is converted into monomeric 2-chlorobutadiene-1,3 (chloroprene) via 3,4-dichlorobutene-l involving reactions that are safe and easy to control. 

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Chloroprene monomer production starts with the catalytic conversion of acetylene to monovinylacetylene, which is purified and subsequently reacts with aqueous hydrogen chloride solution containing cuprous chloride and ammonium chloride to give chloroprene.61... 

Chloroprene monomer production starts with the catalytic conversion of acetylene to... 

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. 

The monomer solution makeup involves addition and solubilization of elemental sulfur and rosin (substituted diterpenes) in the chloroprene monomer. The water solution is made in a second vessel. Deionized water, sodium hydroxide, and a dispersant are mixed to form the water solution. The dispersant is a condensation product of naphthalene-sulfonic acid and formaldehyde. The monomer and water solutions are mixed with centrifiigal pumps to form an oil-in-water emulsion. The emulsion formed by virtue of formation of the sodiiun salt of rosin and resin components (abietic and dehydroabietic acids) having hydrophobic and hydrophilic ends. The large carbon-bearing portion of sodium abietate is hydrophobic and thereby solubilizes the monomer. The sodium carboxylate portion of sodium abietate is the hydrophilic end that extends into the aqueous phase and forms the electronic double layer that is critical to emulsion stability (84,85). In the patent example, the emulsion was added to the reactor and the temperatiu-e was increased to 40°C polymerization temperatiu-e (Table 3). 

Chloro 1 3 butadiene (chloroprene) is the monomer from which the elastomer neoprene IS prepared 2 Chloro 1 3 butadiene is the thermodynamically controlled product formed by addi tion of hydrogen chloride to vinylacetylene (H2C=CHC=CH) The principal product under conditions of kinetic control is the allenic chlonde 4 chloro 1 2 butadiene Suggest a mechanism to account for the formation of each product... 

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). 

Synthetic. The main types of elastomeric polymers commercially available in latex form from emulsion polymerization are butadiene—styrene, butadiene—acrylonitrile, and chloroprene (neoprene). There are also a number of specialty latices that contain polymers that are basically variations of the above polymers, eg, those to which a third monomer has been added to provide a polymer that performs a specific function. The most important of these are products that contain either a basic, eg, vinylpyridine, or an acidic monomer, eg, methacrylic acid. These latices are specifically designed for tire cord solutioning, papercoating, and carpet back-sizing. 

Chloroprene (2-chloro-1,3-butadiene), [126-99-8] was first obtained as a by-product from tbe synthesis of divinylacetylene (1). Wben a mbbery polymer was found to form spontaneously, investigations were begun tbat prompdy defined tbe two methods of synthesis that have since been the basis of commercial production (2), and the first successbil synthetic elastomer. Neoprene, or DuPrene as it was first called, was introduced in 1932. Production of chloroprene today is completely dependent on the production of the polymer. The only other use accounting for significant volume is the synthesis of 2,3-dichloro-l,3-butadiene, which is used as a monomer in selected copolymerizations with chloroprene. 

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. 

Except for the solvent process above, the cmde product obtained is a mixture of chloroprene, residual dichlorobutene, dimers, and minor by-products. Depending on the variant employed, this stream can be distiUed either before or after decantation of water to separate chloroprene from the higher boiling impurities. When the concentration of 1-chloro-1,3-butadiene [627-22-5] is in excess of that allowed for polymerisation, more efficient distillation is required siace the isomers differ by only about seven degrees ia boiling poiat. The latter step may be combiaed with repurifying monomer recovered from polymerisation. Reduced pressure is used for final purification of the monomer. All streams except final polymerisation-grade monomer are inhibited to prevent polymerisation. 

The process for manufacture of a chloroprene sulfur copolymer, Du Pont type GN, illustrates the principles of the batch process (77,78). In this case, sulfur is used to control polymer molecular weight. The copolymer formed initially is carried to fairly high conversion, gelled, and must be treated with a peptising agent to provide a final product of the proper viscosity. Key control parameters are the temperature of polymerisation, the conversion of monomer and the amount/type of modifier used. 

Butadiene is by far the most important monomer for synthetic rubber production. It can be polymerized to polybutadiene or copolymerized with styrene to styrene-butadiene rubber (SBR). Butadiene is an important intermediate for the synthesis of many chemicals such as hexa-methylenediamine and adipic acid. Both are monomers for producing nylon. Chloroprene is another butadiene derivative for the synthesis of neoprene rubber. 

Butadiene is not only the most important monomer for synthetic ruh-her production, hut also a chemical intermediate with a high potential for producing useful compounds such as sulfolane hy reaction with SO2, 1,4-hutanediol hy acetoxylation-hydrogenation, and chloroprene hy chlori-nation-dehydrochlorination. 

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. 

The manufacture of butadiene-based polymers and butadiene derivatives implies potential occupational exposure to a number of other chemical agents, which vary according to product and process, including other monomers (styrene, acrylonitrile, chloroprene), solvents, additives (e.g., activators, antioxidants, modifiers), catalysts, mineral oils, carbon black, chlorine, inorganic acids and caustic solutions (Fajen, 1986a.b Roberts, 1986). Styrene, benzene and toluene were measured in various departments of... 

Chloroprene is a monomer used almost exclusively for the production of polychloroprene elastomers and latexes. It readily forms dimers and oxidizes at room temperature. Occupational exposures occur in the polymerization of chloroprene and possibly in the manufacture of products from polychloroprene latexes. 

Table 6.1S summarizes the average commercial specihcationsbfdiloroprene produced from butadiene. Table 6.16 lists the main uses of chloroprene in Western Europe, the United States and Japan in 1984, and gives the production, production caparities and consumption of this monomer for these three geographic areas. 

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-... 

Except for the elimination of HCI, pyrolysis products of polychloroprene correspond rather well with those of isoprene. Besides the monomer and 3,7-dichloroocta-1,4,6-triene (which can be considered as a dimer of chloroprene), another compound found in appreciable levels in polychloroprene pyrolysate is 1-chloro-5-(1-chloroethenyl)-cyclohexene. This compound corresponds to diprene or 1-methyl-5-(1-methyivinyl)-cyclohex-1 -ene in the pyrolysate of polyisoprene. 

Clearly, this technique can be extended to Include other monomers polymerizable by free radical mechanisms and work has begun using chloroprene. It must be stressed, however, that the specificity and purity of the product Is largely controlled by the detailed kinetics of the radical polymerization process. In particular the prominence of chain transfer reactions and the nature of the termination step which will, of course, vary from monomer to monomer. 

For example, in one experiment, toluene, chloroprene, and tribu-tylphosphine were placed in a vessel, and a cyanoprene-toluene solution was aded dropwise at 0°C. The result was a 60% yield of a thermoplastic product with 14.2% nitrogen, corresponding to a chloroprene proportion of 17%. Analogous experiments were carried out with monomers such as styrene and isoprene, and with other catalysts. 

A considerable amount of work has also been done on the oxidation of the monomer and polymers of chloroprene. Chloroprene autoxidises rapidly, even at temperatures as low as 0°C, yielding a polymeric peroxide as the principle product [170,171]. The reaction has been found to be autocatalytic and, up to about 5 mole % oxidation, the mole % oxidation increased as the square of the time [170,172] above this extent of oxidation, the rate increased even more, apparently due to the subsequent reaction of the peroxide produced. The oxidations were so rapid that conventional initiators and inhibitors had less effect than could have been expected for less labile substrates. 

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