Vinyl chloride rate constants

In the case of vinyl chloride, the addition of Zy to the monomer phase lends to an increase in rate from low conversions on (Fig. 12). This result is in accordance with the results of Ugelstad et al. (1967) who found that tbe rate of polymerization of vinyl chloride, at constant particle number, increased when the reaction was carried out at subsaturation pressures. 

Hydrolysis of 1,2-dichloroethane under alkaline and neutral conditions yielded vinyl chloride and ethylene glycol, respectively, with 2-chloroethanol, and ethylene oxide forming as the intermediates under neutral conditions (Ellington et al, 1988 Jeffers et al, 1989 Kollig, 1993). The reported hydrolysis half-life in distilled water at 25 °C and pH 7 is 72.0 yr (Jeffers et al, 1989), but in a 0.05 M phosphate buffer solution the hydrolysis half-life is 37 yr (Barbash and Reinhard, 1989). Based on a measured hydrolysis rate constant of 1.8 x 10 at 25 °C and pH 7, the half-life is 71.5 yr (Jeffers and Wolfe, 1996). 

Photolytic. Irradiation of vinyl chloride in the presence of nitrogen dioxide for 160 min produced formic acid, HCl, carbon monoxide, formaldehyde, ozone, and trace amounts of formyl chloride and nitric acid. In the presence of ozone, however, vinyl chloride photooxidized to carbon monoxide, formaldehyde, formic acid, and small amounts of HCl (Gay et al, 1976). Reported photooxidation products in the troposphere include hydrogen chloride and/or formyl chloride (U.S. EPA, 1985). In the presence of moisture, formyl chloride will decompose to carbon monoxide and HCl (Morrison and Boyd, 1971). Vinyl chloride reacts rapidly with OH radicals in the atmosphere. Based on a reaction rate of 6.6 x lO" cmVmolecule-sec, the estimated half-life for this reaction at 299 K is 1.5 d (Perry et al., 1977). Vinyl chloride reacts also with ozone and NO3 in the gas-phase. Sanhueza et al. (1976) reported a rate constant of 6.5 x 10 cmVmolecule-sec for the reaction with OH radicals in air at 295 K. Atkinson et al. (1988) reported a rate constant of 4.45 X 10cmVmolecule-sec for the reaction with NO3 radicals in air at 298 K. 

The effect of pressure on polymerization, although not extensively studied, is important from the practical viewpoint since several monomers are polymerized at pressures above atmospheric. Pressure affects polymerization through changes in concentrations, rate constants, and equilibrium constants [Ogo, 1984 Weale, 1974 Zutty and Burkhart, 1962], The commercial polymerizations of most gaseous monomers (e.g., vinyl chloride, vinylidene chloride, tetrafluoroethylene, vinyl fluoride) are carried out at very moderate pressures of about 5-10 MPa (1 MPa = 145 psi), where the primary effect is one of increased... 

Reaction with pyridine leads to the formation of a UV-active pyridinium ylide. Rate constants for the alkylcarbene reaction(s) can be extracted from the intercept of the linear correlation of feobs for ylide formation versus the pyridine concentration. Consider first the 1,2-H shift that converts chloromethylcarbene (48) into vinyl chloride (Scheme 7.17). The LFP experiments show that the H shift occurs with k= 1.2 — 3.0 X 10 s in isooctane, cyclohexane, or dichloroethane at 21-25 The rearrangement is fast, but not ultrafast carbene (48) has a lifetime... 

A large number of accurate rate constants are known for addition of simple alkyl radicals to alkenes.33-33 Table 2 summarizes some substituent effects in the addition of the cyclohexyl radical to a series of monosubstituted alkenes.36 The resonance stabilization of the adduct radical is relatively unimportant (because of the early transition state) and the rate constants for additions roughly parallel the LUMO energy of the alkene. Styrene is selected as a convenient reference because it is experimentally difficult to conduct additions of nucleophilic radicals to alkenes that are much poorer acceptors than styrene. Thus, high yield additions of alkyl radicals to acceptors, such as vinyl chloride and vinyl acetate, are difficult to accomplish and it is not possible to add alkyl radicals to simple alkyl-substituted alkenes. Alkynes are slightly poorer acceptors than similarly activated alkenes but are still useful.37... 

Zhang, J., Hatakeyama, S., Akimoto, H. (1983) Rate constants of the reaction of ozone with ra .s-l,2-dichloroethene and vinyl chloride in air. Inti. J. Chem. Kinet. 15, 655. 

In the vicinity of glass transition, both Eqs. (47) and (48) become Eqs. (42) and (43), respectively. The calculated dependence of the physical aging rate on temperature for polystyrene (PS), poly(vinyl chloride) (PVC), and poly(vinyl acetate) (PVAc) is shown in Fig. 17. There are five parameters (e, p, f xr, 7 ) in Eqs. (23), (2), (15) and (19). We have chosen p = 1/2. ft = 1/30, and xr = 30 min for these linear polymers in our theoretical calculation. The other two parameters r. = h and Tr are listed in Table 1. The calculation reveals that the Struik exponent (p) increases from zero above 7 to a constant below Tg, and then decreases to zero at 200 K below Tg. The three polymers all show a similar type of temperature dependence of physical aging rate, which compares well with the reported observations (see Fig. 15 of Ref. 2). 

Bamford et al. [157] were the first to observe the acceleration of vinyl monomer polymerization caused by inorganic salt addition. They polymerized acrylonitrile dissolved in dimethyl-formamide with 2,2 -azobisisobutyronitrile. The reaction rate was increased by the addition of LiCl. The observed effect was ascribed to the increase of the rate constant and interpreted by complex formation between lithium chloride and the nitrile group of the radical. 

The rate constants of propagation in bulk polymerizations of several alkenes initiated by y-rays are presented in Table 15. The rate constant of propagation of isobutene is estimated to be 1000 times lower in chlorinated solvents than in bulk [134]. The rate constant of vinyl ether propagation decreases a few times by adding only 1 mol% of methylene chloride [238]. This may be due to either an error in the estimate of Gh or to specific interactions between growing carbenium ions and solvent molecules both explanations assume that much less reactive, but still conducting carbenium ions are formed. Nevertheless, recently determined rate constants of propagation of isopropyl and isobutyl vinyl ethers initiated with trityl salts [217] are within a factor of 2 of those calculated from y-irradiated systems. 

In glacial acetic acid, Ogg and Nozaki found that the second-order rates of brominatioii of allyl chloride, vinyl bromide, and allyl nitrile gave rate constants which were proportional to the concentrations of LiBr or LiCI in solution, the latter being nearly twice as effective as the former. Although the authors interpreted this as a third-order reaction involving Br or Cl ,... 

Closely related to these investigations, Breslow and co-workers studied the Diels-Alder reaction of CP with methyl vinyl ketone (MVK) in water-like solvents, ethylene glycol and formamide, in the presence of lithium salts. They found clear differences and similarities between water and these two solvent systems. In the absence of Li salts, the second-order rate constant for the reaction at 20 °C increased in formamide ( 2 = 3184 X 10 m s" ), and even more in ethylene glycol (480 x 10 m" s" ), relative to a polar solvent such as methanol (75.5 x 10 m" s ) or non-polar solvent such as isooctane (5.940.3 x 10 m s ). The reactions in both polar solvents were faster in the presence of LiC104 than in the presence of LiCl, although the perchlorate ion has less salting-out effect than chloride ion in water [41]. 

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