1.4- Dichloro-1,3-butadienes

There is a good synthesis of the C-unsubstituted 1-phenylarsole (34). The reaction of dilithiophenylarsine with the readily available mixture of isomeric 1,4-dichloro- 1,3-butadienes (33) gives 34 in 25% yield.13 The arsole 34 is easily converted to 1,1 -diarsaferrocene (8), while 1,1 -diphos-phaferrocene (7) can be prepared analogously, as shown in Scheme 4. The lack of availability and low stability of phenylstibine and phenylbismuthine limit extension to preparation of the heavier diheteroferrocenes. 

Phenylarsole (30) is available by condensation of dilithiophenylarsine with 1,4-dichloro-1,3-butadiene (Equation (25)). The reaction is nonstereospecific as either pure (Z,Z)- or (Z, )-isomer... 

Beilstein Handbook Reference) BRN 1698807 1,3-Butadiene, 2,3-dichloPO- 2,3-Dichlor-1,3-butadien 2,3-Dichloro-1,3-butadiene 2,3-Dichlorobuta-1,3-diene 2,3-Dichlorobutadiene 2,3-Dichloro-butadiene-1,3 EINECS 216-721-0. Uquid bp = 98 d O =... 

The concentration of (Z)-configuration varies indirectly proportional with the polymerization temperatnre whereas the other three configurations vary directly proportional with the polymerization temperature. The total amoimt of E-, 1,2-, and 3,4- configurations vary from 5% at —40°C to 30% of the total polymer backbone at 100°C polymerization temperatures. Other structvu-al studies have involved 2,3-dichloro- butadiene homopolymer (52), the free-radical random copolymer with methyl methacrylate (53) with chloroprene, and the alternating copolymer of sulfur dioxide with chloroprene (54). Petiaud and Pham studied the thermodynamics of the various modes of imit addition (55). 

Dichloro-butadiene to reduce the crystallization tendency, that is, the stiffness of the chain. 

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). 

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. 

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... 

Continuous polymerization in a staged series of reactors is a variation of this process (82). In one example, a mixture of chloroprene, 2,3-dichloro-l,3-butadiene, dodecyl mercaptan, and phenothiazine (15 ppm) is fed to the first of a cascade of 7 reactors together with a water solution containing disproportionated potassium abietate, potassium hydroxide, and formamidine sulfinic acid catalyst. Residence time in each reactor is 25 min at 45°C for a total conversion of 66%. Potassium ion is used in place of sodium to minimize coagulum formation. In other examples, it was judged best to feed catalyst to each reactor in the cascade (83). 

Fluorinaied dienophiles. Although ethylene reacts with butadiene to give a 99 98% yield of a Diels-Alder adduct [63], tetrattuoroethylene and 1,1-dichloro-2,2-difluoroethylene prefer to react with 1,3-butadiene via a [2+2] pathway to form almost exclusively cyclobutane adducts [61, 64] (equation 61). This obvious difference in the behavior of hydrocarbon ethylenes and fluorocarbon ethylenes is believed to result not from a lack of reactivity of the latter species toward [2+4] cycloadditions but rather from the fact that the rate of nonconcerted cyclobutane formation is greatly enhanced [65]... 

In a definitive study of butadiene s reaction with l,l-dichloro-2,2-difluoio-ethylene, Bartlett concluded that [2+4] adducts of acyclic dienes with fluorinated ethylenes are formed through a mixture of concerted and nonconcerted, diradical pathways [67] The degree of observed [2+4] cycloaddition of fluorinated ethylenes IS related to the relative amounts of transoid and cisoid conformers of the diene, with very considerable (i.e., 30%) Diels-Alder adduct being observed in competition with [2+2] reaction, for example, in the reaction of 1,1 -dichloro-2,2-difluoro-ethylene with cyclopentadiene [9, 68]... 

An important difference between conjugated and nonconjugated dienes is that the former compounds can react with reagents such as chlorine, yielding 1,2- and 1,4-addition products. Eor example, the reaction between chlorine and 1,3-butadiene produces a mixture of 1,4-dichloro-2-butene and 3,4-dichloro- 1-butene ... 

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 ... 

Polarization is found in reactions involving chlorides. 1,1-Dichloro-2,2-dimethylcyclopropane (26) reacts with lithium ethyl in benzene-ether solution (40°) giving mainly l-chloro-2,2-dimethylcyclopropane (27 X = H) and 3-methyl-l,2-butadiene (28) both of which are polarized (Ward et al., 1968). If n- or t-butyl lithium are used in the reaction, the butene produced by disproportionation shows only net polarization. 

Although the orbital-symmetry rules predict the stereochemical results in almost all cases, it is necessary to recall (p. 1070) that they only say what is allowed and what is forbidden, but the fact that a reaction is allowed does not necessarily mean that the reaction takes place, and if an allowed reaction does take place, it does not necessarily follow that a concerted pathway is involved, since other pathways of lower energy may be available.Furthermore, a forbidden reaction might still be made to go, if a method of achieving its high activation energy can be found. This was, in fact, done for the cyclobutene butadiene interconversion (cis-3,4-dichloro-cyclobutene gave the forbidden cis.cis- and rran.y, ra i -l,4-dichloro-1,3-butadienes,... 

Many of these cobalt complexes will catalyze the reduction of organic compounds by borohydride, hydrazine, thiols, etc. Cobalt cyanide complexes will catalyze the reduction of a,j8-unsaturated acids by borohydride (105) DMG complexes the reduction of butadiene and isoprene by borohydride, but not by H2 (124) Co(II) salen, the reduction of CHCI3 and CH3CCI3 to the dichloro compounds by borohydride (116) and cyanocobalamin, the selective reduction of -CCI2- by borohydride to -CHCl- in compounds such as aldrin, isodrin, dieldrin, and endrin without... 

Sauer, Sustmann and coworkers59 have reported second-order rate constants for the reaction of trans-1 -substituted 1,3-butadienes with tetracyanoethylene (TCNE) in dichloro-methane at 20 °C their values are X, log 6 OMe, 7.935, vinyl, 5.456 Ph, 5.814 Me, 5.243 H, 3.228. The data were correlated with the CR equation the best regression equation is ... 

Examples 1,3-Butadiene 1,1-Dichloro-ethylene Isopropyl ether Other ethers Alkali metals Examples Most organic and inorganic materials are not peroxide forming... 

Scheme 6.71 Generation of l-oxa-3,4-cyclohexadiene (333) from 6,6-dichloro-3-oxabicyclo[3.1. OJhexane (332) by n-butyllithium and interception of333 by n-butyllithium, styrene, 1,3-butadiene, isopreneand 2,3-dimethyl-l,3-butadiene.

Dichlorination of tetramethylallene afforded 3-chloro-2,4-dimethyl-l,3-pentadiene as the single product, whereas the same reaction of 1,1-dimethylallene yielded a mixture of 2-chloro-3-methyl-l,3-butadiene, 2,3-dichloro-3-methyl-l-butene and 1,2-dichloro-3-methyl-2-butene, indicating the intermediacy of the 2-chloroallylic cationic intermediate 11 [13]. 

The reactions of l-t-butyl-3-methylallene with several alkenes, e.g. IV-phenylmalei-mide, acrylonitrile and methyl acrylate, afforded exclusively [4 + 2] cycloadducts of 1-t-butyl-l,3-butadiene, which had been formed from l-t-butyl-3-methylallene by a [1,3] sigmatropic rearrangement12. The reaction of l-t-butyl-3-methylallene with 1,1-dichloro-2,2-difluoroethene occurred more rapidly than the hydrogen shift, which allowed the... 

The reaction of 2,3-dimethyl-l,3-butadiene with an equimolar amount of chlorine in carbon tetrachloride at — 20 °C has instead been reported593 to give mainly trans-1,4-dichloro-2,3-dimethyl-2-butene and 2-chloromethyl-3-methyl-l,3-butadiene, arising from the loss of one of the acidic hydrogen atoms in the ionic intermediate (equation 28). 

Chlorination of olefins has also been achieved with SbCls in chlorinated solvents, which gives with mono-olefins vicinal dichloroalkanes by a syn addition. A concerted mechanism was initially proposed68 to rationalize this stereochemical behavior and the unexpectedly large amount of c -l,4-dichloro-2-butene found in the reaction of butadiene. In this case, however, because of orbital symmetry control it has been suggested that the addition occurs in an antarafacial direction69. 

Fig. 10.25. Reaction pathway of butadiene monoxide (10.102) in aqueous NaCl solution to yield l,2-dichloro-3,4-epoxybutane (10.111) [168], The sequence involves the intermediate...

Solvolysis of butadiene monoxide (10.102) in saline solution is a rather unexpected reaction that further documents this compound s reactivity [168]. In aqueous NaCl solution at physiological pH and temperature, butadiene monoxide disappeared rapidly to form 1,2-dichloro-3,4-epoxybutane (10.111, Fig. 10.25). There was a linear dependence of the rate of reaction on the Cl concentration (in the range investigated (34-135 mM)). The reaction pathway was described as slow solvolytic formation of the bu-tenylchloronium ion, followed by Cl attack to yield Cl2 and butadiene. Cl2 is then rapidly trapped by a second molecule of butadiene monoxide to form a different chloronium ion that also reacts with Cl to yield the final, stable dichloro product (10.111). The formation of 1,2-dichloro-3,4-epoxy-butane under physiological conditions is believed to be toxicologically significant. 

Methods of synthesis of 3-chloro- and 3,4-dichloro-thiophenes have usually involved tedious procedures in which tri- and tetra-chloro derivatives are dechlorinated by reductive or other methods. Gthanolic potassium hydroxide converted 2,3,4,5-tetrachlorothiophene into a 50 50 mixture of 2,4- and 3,4-dichlorothiophenes direct heating of the same tetrachloro substrate gave a mixture of 2,3- and 2,4-dichloro isomers (48JA1158). 3,4,5-Trichlorothiophene was readily prepared by the reaction of 1,1,2,3-tetrachloro-l,3-butadiene with sulfur (82JOU348). 

Polychloroprene is the polymer of 2-chloro-l,3 butadiene. Emulsion polymerization produces an almost entirely trans-1,4 polymer, which is highly crystalline. Less crystalline polychloroprenes are produced by incorporating several wt.% of 2,3-dichloro-l,3 butadiene into the polymer to break up crystalline sequences. 

Dichloro-l 3-butadiene [1653-19-6] M 123.0, b 41-43 /85mm, 98 /760mm. Crystd from pentane to constant melting point about -40 . A mixture of meso and d,l forms was separated by gas chromatography on an 8m stainless steel column (8mm i.d.) with 20% DECS on Chromosorb W (60-80 mesh) at 60 and 80ml He/min. [Su and Ache JPC 80 659 1976]. 

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). 

Vogel, E. (1979) Mutagenicity of chloroprene, 1 -chloro-1,3-Zrazw-butadiene. 1,4-dichlorobutene-2 and l,4-dichloro-2,3-epoxybutane to. Drosophila melanogaster. Mutat. Res., 61, 377-381... 

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