Vinylic chloride, elimination

Rgure 10.6 The direct chlorination step of the vinyl chloride process using a boiling reactor eliminates the washing and neutralization steps and the resulting effluents. (From McNaughton, Chem. Engg., December 12, 1983, pp. 54-58 reproduced by permission.)... 

Polymers can be classified as addition polymers and condensation polymers. Addition polymers are formed by iiitermolecular reactions of the monomeric units without the elimination of atoms or groups. An example is vinyl chloride, which can be made to combine with itself to yield polyvinyl chloride ... 

Photochemistry. Vinyl chloride is subject to photodissociation. Photexcitation at 193 nm results in the elimination of HCl molecules and Cl atoms in an approximately 1.1 1 ratio (69). Both vinyUdene ( B2) [2143-69-3] and acetylene have been observed as photolysis products (70), as have H2 molecules (71) and H atoms [12385-13-6] (72). HCl and vinyUdene appear to be formed via a concerted 1,1 elimination from excited vinyl chloride (70). An adiabatic recoil mechanism seems likely for Cl atom elimination (73). As expected from the relative stabiUties of the 1- and 2-chlorovinyl radicals [50663-45-1 and 57095-76-8], H atoms are preferentially produced by detachment from the P carbon (72). Finally, a migration mechanism appears to play a significant role in H2 elimination (71). 

Dehydrochlorination of bis(tnfluoromethylthio)acetyl chloride with calcium oxide gives bis(trifluoromethylthio)ketene [5] (equation 6) Elimination of hydrogen chloride or hydrogen bromide by means of tetrabutylammonium or potassium fluoride from vinylic chlorides or bromides leads to acetylenes or allenes [6 (equation 7) Addition of dicyclohexyl-18-crown-6 ether raises the yields of potassium fluoride-promoted elimination of hydrogen bromide from (Z)-P-bromo-p-ni-trostyrene in acetonitrile from 0 to 53-71 % In dimethyl formamide, yields increase from 28-35% to 58-68%... 

Braun and Schurek [9] assumed that during polymerization a reaction can occur between the polymer and free radicals that leads to the elimination of hydrogen chloride and formation of a double bond. The formation of HCl during the polymerization of vinyl chloride has been observed [10],... 

Besides simple alkyl-substituted sulfoxides, (a-chloroalkyl)sulfoxides have been used as reagents for diastereoselective addition reactions. Thus, a synthesis of enantiomerically pure 2-hydroxy carboxylates is based on the addition of (-)-l-[(l-chlorobutyl)sulfinyl]-4-methyl-benzene (10) to aldehydes433. The sulfoxide, optically pure with respect to the sulfoxide chirality but a mixture of diastereomers with respect to the a-sulfinyl carbon, can be readily deprotonated at — 55 °C. Subsequent addition to aldehydes afforded a mixture of the diastereomers 11A and 11B. Although the diastereoselectivity of the addition reaction is very low, the diastereomers are easily separated by flash chromatography. Thermal elimination of the sulfinyl group in refluxing xylene cleanly afforded the vinyl chlorides 12 A/12B in high chemical yield as a mixture of E- and Z-isomers. After ozonolysis in ethanol, followed by reductive workup, enantiomerically pure ethyl a-hydroxycarboxylates were obtained. 

The synthesis of enantiomerically pure propargylic alcohols is possible using the same methodology 43b. Thus, addition of (—)-[(l-chloro-2-phenylethyl)sulfinyl]-4-methylbenzene (14) to propan-al led to a mixture of the diastereomers 15A/15B (d.r. 44 56) which are easily separated by column chromatography. After thermal elimination of the sulfinyl group the vinyl chlorides 16A/16B were obtained as a mixture of E- and Z-oleftns. Elimination of hydrogen chloride was carried out with three equivalents of butyllithium, leading to enantiomerically pure 1 -phenyl-1-pentyn-3-ol. 

Aliphatic aldehydes and ketones can be converted to gem-dichlorides by treatment with PCI5. The reaction fails for perhalo ketones. " If the aldehyde or ketone has an a hydrogen, elimination of HCl may follow and a vinylic chloride is a frequent side product ... 

Change of base (pyridine, aniline, water) had no obvious effect on the steric course of the reaction (59). Rather surprisingly, it appears that the reactions of the cis and trans isomers of 1-bromopropene with the hydride [Co(CN)5H] give different products this eliminates an initial addition of Co—H to the double bond, since this would lead to the same product for the two isomers 105). Vinyl chloride apparently reacts only with [Co salen] , and not with the hydride, to form the CH2=CHCo complex 43) the same may be the case with the BAE complexes 40). 

The degree of vibrational excitation in a newly formed bond (or vibrational mode) of the products may also increase with increasing difference in bond length (or normal coordinate displacement) between the transition state and the separated products. For example, in the photodissociation of vinyl chloride [9] (reaction 7), the H—Cl bond length at the transition state for four-center elimination is 1.80 A, whereas in the three-center elimination, it is 1.40 A. A Franck-Condon projection of these bond lengths onto that of an HCl molecule at equilibrium (1.275 A) will result in greater product vibrational excitation from the four-center transition state pathway, and provides a metric to distinguish between the two pathways. 

Scheme 2.20 gives some examples of the application of the Julia olefination in synthesis. Entry 1 demonstrates the reductive elimination conditions. This reaction gave a good E.Z ratio under the conditions shown. Entry 2 is an example of the use of the modified reaction that gave a good E.Z ratio in the synthesis of vinyl chlorides. Entry 3 uses the tetrazole version of the reaction in the synthesis of a long-chain ester. Entries 4 to 7 illustrate the use of modified conditions for the synthesis of polyfunctional molecules. 

Figure 28.6 The direct chlorination step of the vinyl chloride process using a boiling reactor eliminates the washing and neutralization steps and the resulting effluents.

After a switch to a new poly/(vinyl chloride) (PVC) resin, a film residue was noted on the polished laminating plates used by a consumer product manufacturer. This residue needed to be identified so that the source of the contamination could be determined and eliminated. 

Several important classes of polar monomers have so far eluded copolymerization by the Pd(II) system. Vinyl chloride insertion, for example, leads to catalyst deactivation following P-halide elimination to form inert chloride species such as 1.32, as shown by Jordan [90], Similarly, attempted vinyl acetate copolymerization results in deactivation by an analogous acetate elimination process, although the ester chelate intermediate that forms after insertion also effectively shuts down the reaction [90], Therefore, -elimination of polar groups represents a significant and unresolved problem for late transition metal polymerization systems unless access of the metal to it is restricted. 

The use of transition metals for the facilitation of substitution reactions on vinylic carbon has proven to be quite successful. For example, vinylic chlorides in the presence of nickel(II) chloride react with trialkyl phosphites to substitute phosphorus for the halide (Figure 6.17j.71-72 While reminiscent of a direct Michaelis-Arbuzov reaction, including final dealkylation by a chloride ion, the reaction actually involves an addition-elimination process. It appears that chloride provides a more facile reaction than bromide, a characteristic noted in several reaction systems. 

Reaction of l,3-bis(methylthio)-2-methoxypropane with 2 moles of lithium diisopropylamide5 (or w-butyllithium) effects (a) the elimination of methanol to form l,3-bis(methylthio)propene and (b) the lithiation of this propene to generate l,3-bis(methylthio)allyllithium in solution. Its conjugate acid, l,3-bis(methylthio)propene, can be regenerated by protonation with methanol, and has also been prepared (a) in 31% yield by reaction of methylthioacetaldehyde with the lithio derivative of diethyl methylthiomethylphosphonate,5 (b) in low yield by acid-catalyzed pyrolysis of l,l-bis(methylthio)-3-methoxypropane,6 and (c) in low yield by acid-catalyzed coupling of vinyl chloride with chloromethyl methyl sulfide.7... 

A nucleophilic attack at an allene system of the type of 417 was described for the first time by Cainelli et al. [172], namely at 444 with the chloride ion as the nucleophile (Scheme 6.91). After the treatment of the mesylate 443 with triethylamine in the presence of lithium, sodium or tetrabutylammonium chloride, mixtures of the vinyl chlorides 445 and 447 were isolated in high yields. Since the reaction did not proceed in the absence of triethylamine, the first step should be a /3-elimination of methanesulfonic acid from 443 to generate 444, which would accept a chloride ion at the central allene carbon atom. A proton transfer to either allyl terminus of the anion thus formed (446) would lead to the products 445 and 447. 

Significant activation occurs during the microbial metabolism of trichloroethylene (TCE). This compound was once widely used and now represents a major contaminant of many aquifers. Because TCE is metabolized by many bacteria, its elimination by bioremediation is being actively pursued. However, a major product frequently encountered is vinyl chloride, a potent carcinogen ... 

In contrast to this direct chlorination there is the oxychlorination of ethylene using hydrogen chloride and oxygen, the other major method now used. Since the chlorine supply is sometimes short and it is difficult to balance the caustic soda and chlorine demand (both are made by the electrolysis of brine), hydrogen chloride provides a cheap alternate source for the chlorine atom. Most of the ethylene dichloride manufactured is converted into vinyl chloride by eliminating a mole of HCl, which can then be recycled and used to make more EDC by oxychlorination. EDC and vinyl chloride plants usually are physically linked. Most plants are 50 50 direct chlorinationroxychlorination to balance the output of HCl. 

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. 

Grohn and Vasiliu-Oprea (18,31,32,41) studied the grafting of several vinyl monomers on polyamide, mainly polycaprolactam. [Their work was summarized in the Simionescu and Vasiliu-Oprea book (73).] In each case, the polymer was first purified by extraction, dissolution and reprecipitation. The grinding was performed at 0.42 fraction packing and by using 16 mm diameter steel balls, at an amplitude of 1.75 mm and at 1420 rpm. With vinyl chloride the air was eliminated from the reaction jar and the monomer was introduced at up to two... 

Mg+" reacts with alkyl halides in the gas phase via a range of substrate-dependent pathways Not all halides are reactive—examples of unreactive substrates include methyl chloride, vinyl chloride, trichloro and tetrachloro ethylene. Reaction with ethyl chloride proceeds via an elimination reaction (equation 18) followed by a displacement reaction (equation 19). For larger alkyl halides, such as isopropyl chloride, chloride abstraction also occurs (equation 20). For multiply halogenated substrates such as carbon tetrachloride, oxidative reactions occur (equations 21 and 22), although organometallic... 

Vinyl chloride is readily absorbed through skin and is rapidly eliminated, either unchanged or as metabolites. The metabolism is catalyzed by cytochromes P-450, and vinyl chloride induces its own metabolism but also destroys cytochrome P-450. The tumor incidence in rats correlates... 

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