Vinyl chloride transformation

Poly(vinyl chloride). PVC is one of the most important and versatile commodity polymers (Table 4). It is inherently flame retardant and chemically resistant and has found numerous and varied appHcations, principally because of its low price and capacity for being modified. Without modification, processibiUty, heat stabiUty, impact strength, and appearance all are poor. Thermal stabilizers, lubricants, plasticizers, impact modifiers, and other additives transform PVC into a very versatile polymer (257,258). 

Degradation of trichloroethylene by anaerobes via reductive dehalogenation can be problematic because a common product is vinyl chloride, a known carcinogen (Ensley 1991). In an anaerobic colunm operated under methanogenic conditions, 100% transformation of injected tetrachloroethylene and trichloroethylene to... 

Observations on the polymerization of readily polymerizable vinyl monomers such as styrene, vinyl chloride, and butadiene date back approximately to the first recorded isolation of the monomer in each case. Simon 2 reported in 1839 the conversion of styrene to a gelatinous mass, and Berthelot applied the term polymerization to the process in 1866. Bouchardat polymerized isoprene to a rubberlike substance. Depolymerization of a vinyl polymer to its monomer (and other products as well) by heating at elevated temperatures was frequently noted. Lemoine thought that these transformations of styrene could be likened to a reversible dissociation, a commonly held view. While the terms polymerization and depolymerization were quite generally applied in this sense, the constitution of the polymers was almost completely unknown. 

Under methanogenic conditions, a strain of Methanosarcina sp. transformed tetrachloroethene to trichloroethene (Fathepnre and Boyd 1988). In the presence of suitable electron donors snch as methanol, complete rednction of tetrachloroethene to ethene may be achieved in spite of the fact that the dechlorination of vinyl chloride appeared to be the rate-limiting step (Freedman and Gossett 1989). 

Double bonds having oxygen and halogen substituents are susceptible to epoxi-dation, and the reactive epoxides that are generated serve as intermediates in some useful synthetic transformations in which the substituent migrates to the other carbon of the original double bond. Vinyl chlorides furnish haloepoxides that can rearrange to a-haloketones. 

The BAT system operates based on principles of aerobic cometabolism. In cometabohsm, enzymes that the microbes produce in the process of consuming one particular compound (e.g., phenol) have the collateral effect of transforming another compound that normally resists biodegradation (e.g., chlorinated ethenes, especially lesser chlorinated ethenes such as dichloroethene or vinyl chloride). The BAT system operates under these principles by sorbing the chlorinated compounds from a vapor stream onto powdered activated carbon (PAC) where they are cometabolically transformed into a combination of end products, including new biomass, carbon dioxide, inorganic salts, and various acids. 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

Vinylidene fluoride is taken up rapidly via the pulmonary route in rats, but at equilibrium the mean concentration (by volume) in rats was only 23% of that in the gaseous phase. Metabolism proceeded very slowly and was saturable at exposure concentrations of about 260 mg/m Its maximum rate was 1% that of vinyl chloride and less than 20% that of vinyl fluoride there has been a report of an increase in the urinary excretion of fluoride in exposed rats. No alkylating intermediate was demonstrated after passage through a mouse-liver microsomal system. However, vinylidene fluoride inhibits mixed-function oxidase activity in vitro and, like similar halogenated compounds that are transformed to reactive metabolites, it alters rat intermediary metabolism, leading to acetone exhalation (lARC, 1986). 

The cis- and trans-dichloroethenes reacting by this addition mechanism are transformed more slowly than the tetra- and trichloroethenes that could form them and more slowly than the vinyl chloride that their reactions would form. Thus, these particular dichlorocompounds accumulate when microorganisms reduce tetra- and trichloroethene in anoxic environments contaminated by these solvents (see Glod et al., 1997b and references therein). Reduction reactions of 1,1-dichloroethene with the super-reduced corrinoids are more likely to form the very toxic product, vinyl chloride. 

Vinyl Chloride. Vinyl chloride is an important monomer in the manufacture of polyvinyl chloride and vinyl polymers. Two basic transformations are in commercial use.188-190 The catalytic hydrochlorination of acetylene, once an important... 

As shown in Figure 1.17, there are three possible dichloroethylene compounds, all clear, colorless liquids. Vinylidene chloride forms a copolymer with vinyl chloride used in some kinds of coating materials. The geometrically isomeric 1,2-dichloroethylenes are used as organic synthesis intermediates and as solvents. Trichloroethylene is a clear, colorless, nonflammable, volatile liquid. It is an excellent degreasing and dry-cleaning solvent and has been used as a household solvent and for food extraction (for example, in decaffeination of coffee). Colorless, nonflammable liquid tetrachloroethylene has properties and uses similar to those of trichloroethylene. Hexachloro-butadiene, a colorless liquid with an odor somewhat like that of turpentine, is used as a solvent for higher hydrocarbons and elastomers, as a hydraulic fluid, in transformers, and for heat transfer. 

In cases where sorptive equilibrium is reached rapidly and transformation is much slower, the aqueous phase concentration of contaminant may show a rapid initial decrease due to adsorption followed by a slower decline due to transformation. Under these conditions, the kinetic model represented by Eq. (16) is sufficient to describe the kinetics of transformation after the initial data have been excluded. This approach has been taken for TCE [168], vinyl chloride [176], and probably in many other studies where the exclusion of initial rate data was not clearly documented. 

Vinyltributylstannanes are smoothly transformed, stereoselectively, to vinyl chlorides (equation 150)972. 

A synthesis of benzotriquinacene 396) has recently been described (Scheme 63).36s 366 Vinylmagnesium chloride transformed ketone 380 into vinyl alcohol 393 whose dehydration gave 2-vinyltriquinacene 394). Addition of dimethyl acet-ylenedicarboxylate to 394 followed by dehydrogenation led to adduct 395 which underwent ready saponification and copper-catalyzed decarboxylation to give 396. 

Dissection of the chemical structure of jamaicamides A-C led to the speculation that these metabolites derive from a mixture of polyketides (nine acetate units), amino acids (t-Ala and p-Ala), and the S-methyl group of methionine. To map out the biosynthetic subunits of these molecules, isotopically labeled precursors were supplied to I. majuscula JHB, and the labeling patterns discerned by NMR spectroscopy (Figure 6.12). From these experiments, insights were gained into the biochemical transformations that produce the jamaicamides, especially the mechanism of formation of the vinyl chloride group [157]. 

Reactive substituents can undergo chemical transformations [9], Particularly in ionic polymerizations, the number of possible reactions of the monomeric molecules is broadened considerably. This limits the possibility of employing some polymerization types. So, for example, vinyl chloride (VC) cannot be polymerized on cationic or carbanionic centres because these would be destroyed by reaction with Cl— bonds in the polymer. Technically, the most important representatives of simple vinyl monomers are VC, methyl methacrylate (MMA) and acetronitrile (AN). Other monomers of this class, though important and interesting, need not be mentioned at this stage. They will be discussed in the pertinent parts of the text. 

Each year, hundres of thousands of tons of vinyl chloride are polymerized in the world. Commensurate attention is thus paid to studies of its polymerization. Vinyl chloride is one of those monomers that are transformed to polymer by a complicated mechanism. Poly(vinyl chloride) is soluble neither in its own monomer nor in the common solvents. Its formation is therefore connected with the appearance of a solid phase the process has the character of precipitation polymerization. This greatly complicates the kinetics of solution and bulk (suspension) polymerization. 

Vinylsilanes may be prepared from the corresponding ketones by formation of the hydrazone followed by Shapiro reaction, quenching the vinylic anion with chlorosilanes. An equally effective process derives the vinylsilane from the vinyl chloride, in turn prepared simply from the ketone. The crucial oxidative transformation may be achieved in two ways. Firstly, ozonolysis in dichloromethane/methanol at approximately 0 C followed by reductive work-up affords the a-hy xy ketone, e.g. (96) to (97), via the intermediates (98) and (99). The outcome of the reaction varies with the solvent and work-up conditions, but using the combination indicated, good yields of the desired products are available. 

Degradative Transformation of Poly(vinyl chloride) under Mild Oxidative Conditions... 

Another non-isohypsic transformation, addition of halogens to a double bond, is probably the oldest known reaction of unsaturated compounds. It is widely used for both industrial and laboratory purposes. The products formed, 1,2-dihaloalkanes, are valuable for conversion into vinyl halides (such as vinyl chloride monomers for the production of PVC) or alkynes ... 

Carvalho A, Hancock G, Saunders M. (2006) The reaction products of the 193 nm photolysis of vinyl bromide and vinyl chloride studied by time-resolved Fourier transform infrared emission spectroscopy. Phys Chem Chem Phys 8 4337-T346. 

One interesting example is provided by transformation of the vinyl chloride derivative XXXIII into XXXIV.No matter how one takes the product apart, the result will continue to be puzzling. 

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