Chlorination of butadiene

In a related process, 1,4-dichlorobutene was produced by direct vapor-phase chlorination of butadiene at 160—250°C. The 1,4-dichlorobutenes reacted with aqueous sodium cyanide in the presence of copper catalysts to produce the isomeric 1,4-dicyanobutenes yields were as high as 95% (58). The by-product NaCl could be recovered for reconversion to Na and CI2 via electrolysis. Adiponitrile was produced by the hydrogenation of the dicyanobutenes over a palladium catalyst in either the vapor phase or the Hquid phase (59,60). The yield in either case was 95% or better. This process is no longer practiced by DuPont in favor of the more economically attractive process described below. 

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

Another process, involving chlorination of butadiene, hydrolysis of the dichlorobutene, and hydrogenation of the resulting butenediol, was practiced by Toyo Soda in Japan until the mid-1980s (144). 

Liquid-phase chlorination of butadiene in hydroxyhc or other polar solvents can be quite compHcated in kinetics and lead to extensive formation of by-products that involve the solvent. In nonpolar solvents the reaction can be either free radical or polar in nature (20). The free-radical process results in excessive losses to tetrachlorobutanes if near-stoichiometric ratios of reactants ate used or polymer if excess of butadiene is used. The "ionic" reaction, if a small amount of air is used to inhibit free radicals, can be quite slow in a highly purified system but is accelerated by small traces of practically any polar impurity. Pyridine, dipolar aptotic solvents, and oil-soluble ammonium chlorides have been used to improve the reaction (21). As a commercial process, the use of a solvent requites that the products must be separated from solvent as well as from each other and the excess butadiene which is used, but high yields of the desired products can be obtained without formation of polymer at higher butadiene to chlorine ratio. 

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. 

The industrial use of 1,3-dienes and of their electrophilic reactions has strongly stimulated the field in recent years. Because of the low cost of butadiene, abundantly available from the naphtha cracking process, very large scale applications in the synthesis of polymers, solvents and fine chemicals have been developed, leading to many basic raw materials of the modem chemical industry. For example, the primary steps in the syntheses of acrylonitrile and adiponitrile have been the electrophilic addition of hydrocyanic acid to butadiene24. Chlorination of butadiene was the basis of chloroprene synthesis25. 

Besides butadiene, another important monomer for the synthetic elastomer industry is chloroprene, which is polymerized to the chemically resistant polychloroprene. It is made by chlorination of butadiene follow by dehydrochlorination. As with most conjugated dienes, addition occurs either 1,2 or 1,4 because the intermediate allyl carbocation is delocalized. The 1,4-isomer can be isomerized to the 1,2-isomer by heating with cuprous chloride. 

Hexamethylenediamine, 1,6 Hexanediamine (HMDA). H2N(CH2) NH2 mw 116.24, N 24.10% silk-like leaves, mp 42° bp 205° (subl), sol in water si sol in h eth. Prepd by hydrogenation of adiponitrile over Raney Ni or Co chlorination of butadiene then reactn with NaCN hydrogenation. Acute local irritant-mod flame hazard. Used in high polymer synth as a cross-linking agent (Refs 1, 3 4)... 

In the production of chloroprene from butadiene, there are three essential steps liquid- or vapour-phase chlorination of butadiene to a mixture of 3,4-dichloro-l-butene and l,4-dichloro-2-butene catalytic isomerization of 1,4-dichloro-2-butene to 3,4-dichloro-l-butene and caustic dehydrochlorination of the 3,4-dichloro-l-butene to chloroprene. By-products in the first step include hydrochloric acid, 1-chloro-1,3-butadiene, trichlorobutenes and tetrachlorobutanes, butadiene dimer and higher-boiling products. In the second step, the mixture of l,4-dichloro-2-butene and 3,4-dichloro-l-butene isolated by distillation is isomerized to pure 3,4-dichloro-l-butene by heating to temperatures of 60-120°C in the presence of a catalyst. Finally, dehydrochlorination of 3,4-dichloro-l-butene with dilute sodium hydroxide in the presence of inhibitors gives crude chloroprene (Kleinschmidt, 1986 Stewart, 1993 DuPont Dow Elastomers, 1997). 

The indirect hydrocyanation of butadiene as practiced by du Pont (/) involved the electrolysis of sodium chloride, formation of sodium cyanide from HCN using the NaOH, chlorination of butadiene to give 1,4-dichloro-but-2-ene, chloride displacement with sodium cyanide, and subsequent hydrogenation, as indicated in Eqs. (l)-(5), with the net result of Eq. 6. 

Liquid-phase chlorination of butadiene in the presence of BU3N affords a mixture of 1,2-and 1,4-addition products. Kinetic measurements suggest two independent mechanisms the 1,2-adduct is formed by the attack of BU3N.CI2 on the butadiene.Cl2 -complex, whereas formation of the 1,4-adduct involves Bu3N-stabilization of the -complex99-101. 

Toya Soda 86 -88) has studied the anodic chlorination of butadiene in aprotic electrolytes (e.g. CHjCN and Fe, Ce, and Ca chlorides). 

Antimony(V) chloride (SbClj) and molybdenum(V) chloride (Mods) can react spontaneously with alkenes to give predominantly the corresponding cir-1,2-dichlorides (equation 11). The reaction probably proceeds through a successive insertion and reductive elimination sequence. The chlorination of butadiene with SbCb and copper(ll) chloride results preferentially in the formation of (Z)- and ( )-... 

A conjugated double bond system undergoes 1,4-addition (Thiele s rule) for example, butadiene and an equimolar quantity of bromine yield 1,4-dibromo-2-butene (90%). On the other hand, chlorination of butadiene in the liquid or vapor phase furnishes about equal amounts of 1,2-and 1,4-addition products. Other polyfunctional compounds resulting from this method of preparation include dihalogenated acids, esters, aldehydes, and ketones. < The addition of bromine to unsaturated ethers yields dibromo ethers which are used as intermediates in the synthesis of olefins (method 21) and olefinic alcohols (method 99) ... 

Another example is the vapor-phase chlorination of butadiene, which gives a mixture of dichlorobutenes of which 3,4-dichloro-l-butene (12) is the only desired isomer for the chloroprene synthesis [23, 24] (cf. eq. (14)). It is easily boiled off from the cis/trans 1,4-dichloro-2-butenes (123 vs. 155 °C). The migratory isomerization of residual 1,4-isomers 11 is effected by Cu complexes and seems to operate through -olefin/ -allyl intermediates. The chloride probably migrates via the copper center, but no mechanistic details are available. 

Derivation Addition of cold hydrochloric acid to vinylacetylene, chlorination of butadiene. 

Derivation (1) Reaction of adipic acid and ammonia (catalytic vapor phase) to yield adiponitrile, followed by liquid-phase catalytic hydrogenation. (2) Chlorination of butadiene followed by reaction with sodium cyanide (cuprous chloride catalyst) to 1,4-dicyanobutylene and hydrogenation. 

The reaction of olefinic compounds with chlorine whereby addition takes place at the double bond has been known for some time. Ethylene dichloride and propylene dichloride are produced by reaction of ethylene or propylene with chlorine (27). A number of articles (23, 24, 31), which review the methods of production of ethylene dichloride, are available. The manufacture of dichloropropane in Germany by reaction of propylene with chlorine in the presence of light was reported by Sergeys (68). High yields of dichlorobutene may be obtained by the vapor phase chlorination of butadiene (73). 

In Japan, the techniques industrialized employ butadiene. Mitsubishi uses acetoxy-lation, and Toro Soda employs the chlorination of butadiene by the following reactions ... 

A monomer chemically similar to epichlorohydrin is obtained by the chlorination of butadiene with subsequent oxidation to l,2-di(chloromethyl) ethylene oxide. Depending on catalysts such as R2Mg/ H2O or R2Zn/ H2O, the monomer can be polymerized to cis or irons polymers ... 

Polychloroprene is dependent on chloroprene (2-chloro-l,3-butadiene), which is mostly produced from the chlorination of butadiene. 

In the past, acetylene has been dimerized and reacted with hydrogen chloride to form the chloroprene monomer for the polymerization of polychloroprene rubber. However, this synthesis route is not used as much now compared to the direct chlorination of butadiene, the preferred synthesis route. 

Later, a still shorter hexanedinitrile synthesis was discovered that used 1,3-butadiene as a starting material. Chlorination of butadiene furnished a mixture of 1,2- and 1,4-dichlorobutene (Section 14-6). This mixture can be... 

Small quantities of hexachloroethane are produced by direct chlorination of ethane. Chlorobutadienes may be obtained by chlorination of butadiene hexa-chlorobutadiene occurs as a by-product in the heavy ends of many of the processes described above, from which it may be isolated. 

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