Vinyl chloride chemical reactions

Acetylene (Figure 13.1) is widely used as a chemical raw material and fuel for oxyacetylene torches. It was once the principal raw material for the manufacture of vinyl chloride (see reaction 13.2.4), but other synthetic routes are now used. Acetylene is a colorless gas with an odor resembling garlic. Though not notably toxic, it acts as an asphyxiant and narcotic and has been used for anesthesia. Exposure can cause headache, dizziness, and gastric disturbances. Some adverse effects from exposure to acetylene may be due to the presence of impurities in the commercial product. 

During the polymeriza tion process the normal head-to-tad free-radical reaction of vinyl chloride deviates from the normal path and results in sites of lower chemical stabiUty or defect sites along some of the polymer chains. These defect sites are small in number and are formed by autoxidation, chain termination, or chain-branching reactions. Heat stabilizer technology has grown from efforts to either chemically prevent or repair these defect sites. Partial stmctures (3—6) are typical of the defect sites found in PVC homopolymers (2—5). 

Titanium carbide may also be made by the reaction at high temperature of titanium with carbon titanium tetrachloride with organic compounds such as methane, chloroform, or poly(vinyl chloride) titanium disulfide [12039-13-3] with carbon organotitanates with carbon precursor polymers (31) and titanium tetrachloride with hydrogen and carbon monoxide. Much of this work is directed toward the production of ultrafine (<1 jim) powders. The reaction of titanium tetrachloride with a hydrocarbon-hydrogen mixture at ca 1000°C is used for the chemical vapor deposition (CVD) of thin carbide films used in wear-resistant coatings. 

Vinyl chloride has gained worldwide importance because of its industrial use as the precursor to PVC. It is also used in a wide variety of copolymers. The inherent flame-retardant properties, wide range of plastici2ed compounds, and low cost of polymers from vinyl chloride have made it a major industrial chemical. About 95% of current vinyl chloride production worldwide ends up in polymer or copolymer appHcations (83). Vinyl chloride also serves as a starting material for the synthesis of a variety of industrial compounds, as suggested by the number of reactions in which it can participate, although none of these appHcations will likely ever come anywhere near PVC in terms of volume. The primary nonpolymeric uses of vinyl chloride are in the manufacture of vinyHdene chloride and tri- and tetrachloroethylene [127-18-4] (83). 

The first large-scale commercial oxychlorination process for vinyl chloride was put on-stream in 1958 by The Dow Chemical Company. This plant, employing a fixed-tube reactor containing a catalyst of cupric chloride on an active carrier, produced 1,2-dichloroethane from ethylene. The high temperatures involved in the reaction were moderated by a suitable diluent. The average heat output from the reaction is 116 kJ/mol (50,000 Btu/lb mol). 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Runaway reaction or polymerization—e.g., vinyl chloride monomer (Kim-E and Reid, The Rapid Depressurization of Hot, High Pressure Liquids or Supercritic Fluids, chap. 3, in M. E. Paulaitis et al., eds.. Chemical engineering at Supercritical Fluid Conditions, Ann Arbor Science, 1983, pp. 81-100)... 

Vinyl chloride is an important monomer for polyvinyl chloride (PVC). The main route for obtaining this monomer, however, is via ethylene (Chapter 7). A new approach to utilize ethane as an inexpensive chemical intermediate is to ammoxidize it to acetonitrile. The reaction takes place in presence of a cobalt-B-zeolite. 

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 aerobic degradation of chloroethene (vinyl chloride) by Mycobacterium aurum strain LI proceeded by initial formation of an epoxide mediated by an alkene monooxygenase (Hartmans and de Bout 1992). This reaction has also been demonstrated to occur with Methylosinus trichosporium, even though subsequent reactions were purely chemical (Castro et al. 1992b). 

PCDFs are also found in residual waste from the production of vinyl chloride and the chlor-alkali process for chlorine production. Factors favourable for the formation of PCDD/PCDFs are high temperatures, alkaline media, the presence of ultraviolet light, and the presence of radicals in the reaction mixture/chemical process (Fiedler, 1999 Hutzinger and Fiedler 1993). 

Chemical/Physical. A glass bulb containing air and 1,1-dichloroethane degraded outdoors to carbon dioxide and HCl. The half-life for this reaction was 17 wk (Pearson and McConnell, 1975). Hydrolysis of 1,1-dichloroethane under alkaline conditions yielded vinyl chloride, acetaldehyde, and HCl (Kollig, 1993). The reported hydrolysis half-life at 25 °C and pH 7 is 61.3 yr (Jeffers et al., 1989). 

Unstable chemicals are subject to spontaneous reactions. Situations where unstable chemicals may be present include the catalytic effect of containers, materials stored in the same area with the chemical that could initiate a dangerous reaction, presence of inhibitors, and effects of sunlight or temperature change. Examples include acetaldehyde, ethylene oxide, hydrogen cyanide, nitromethane, organic peroxides, styrene, and vinyl chloride. 

Vinyl chloride is a chemical used in the manufacture of plastics, which is carcinogenic and causes various toxic effects, including liver injury and damage to the bones and skin. Liver hemangiosarcomas are produced in animals and humans. Vinyl chloride undergoes metabolic activation by cytochrome P-450 to an epoxide, which may interact with DNA and form adducts (ethenodeoxyadenosine and ethenodeoxycytidine), which leads to mutations. These can be detected in white cells, and a mutant p21 ras protein can be detected in the serum of exposed workers. Also, reaction with GSH occurs. 

The production of vinyl chloride monomer is only a part of PVC production. Polymerization of the monomer completes the process. Commercially, it is a batch operation by one of three methods suspension, emulsion, or bulk. In all three methods, the chemical reaction is a free radical-initiated chain reaction. Peroxides or redox systems generally are used to provide the initial free radicals. 

Ethene and ethane account for 80% of the mass of the hydrocarbons identified as products. Trace amounts of methane and acetylene are also produced (Orth and Gillham, 1996). The reduction of PCE forms cis-1,2-dichloroethylene (DCE), frans-l,2-DCE, 1,1-DCE, vinyl chloride, ethylene, dichloroacetylene, acetylene, ethene, ethane, chloroacetylene, methane, and several alkenes ranging from C3 to C6. The trace amounts of dichloro-ethylene and vinyl chloride formed during the reduction of PCE and TCE are further reduced (Burris et al., 1995). Reaction rates vary with substrate, chemical, and microbiological conditions. Selected f1/2 values are provided in Table 13.3. 

A graph circle is a final sequence of the edges in which no node except the starting point occurs twice. A graph for the isomerization reaction has one circle, whereas that for vinyl chloride synthesis contains two circles. Every route of a chemical reaction corresponds to a graph s circle and vice versa. The number of independent reaction routes is equal to the number of elements in the basis of circles. It permits us to determine independent reaction routes from the graph type. 

Sodium hydroxide has many different uses in the chemical industry. Considerable amounts are used in the manufacture of paper and to make sodium hypochlorite for use in disinfectants and bleaches. Chlorine is also used to produce vinyl chloride, the starting material for the manufacture of polyvinyl chloride (PVC), and in water purification. Hydrochloric acid may be prepared by the direct reaction of chlorine and hydrogen gas or by the reaction of sodium chloride and sulfuric acid. It is used as a chlorinating agent for metals and organic compounds. 

Figure 10.11 shows an integrated plant for producing EDC and vinyl chloride from ethylene, chlorine, and air. In this process, vinyl chloride (VCM) is produced by the thermal cracking of EDC. The feed EDC may be supplied from two sources. In the first source, ethylene and chlorine are reacted in essentially stoichiometric proportions to produce EDC by direct addition. In the second source, ethylene is reacted with air and HC1 by the oxychlorination process. Ideally, both processes are carried out in balance, and the oxychlorination process is used to consume the HC1 produced in the cracking and direct chlorination steps. The chemical reactions are... 

A polymer is a large molecule built up by a repetition of small simple chemical units. These large molecules are formed by the reaction of a monomer.72 For example, the monomer for the plastic polyvinyl chloride (PVC) is vinyl chloride. When the vinyl chloride monomer is subjected to heat and pressure it undergoes a process called polymerization (Table 1.3) the joining together of many small molecules in repeat units to make a very large molecule. Structural representations of the monomer repeat unit and polymer are shown below. 

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