Rate constants, removal chlorinated

A comparison has been made between the oxidations of uranium(iv) by halogens and the corresponding reactions of iron(n). Although the former reactions are thermodynamically more favoured and whereas those involving uranium(iv) are complementary those of iron(n) are not, the iron(ii) reactions are faster, and the variation in rate constants from chlorine to iodine 10 ) is greater for iron(n) than for uranium(iv) ( 10 ). The increase in rate constants from I2 to CI2 in both cases probably results from increasingly favourable entropy factors. The reduced rates for may be a consequence of the need to remove the less accessible S/ orbital electrons in this reductant compared with id in the case of iron(ii). 

The results of chain transfer studies with different polymer radicals are compared in Table XIV. Chain transfer constants with hydrocarbon solvents are consistently a little greater for methyl methacrylate radicals than for styrene radicals. The methyl methacrylate chain radical is far less effective in the removal of chlorine from chlorinated solvents, however. Vinyl acetate chains are much more susceptible to chain transfer than are either of the other two polymer radicals. As will appear later, the propagation constants kp for styrene, methyl methacrylate, and vinyl acetate are in the approximate ratio 1 2 20. It follows from the transfer constants with toluene, that the rate constants ktr,s for the removal of benzylic hydrogen by the respective chain radicals are in the ratio 1 3.5 6000. Chain transfer studies offer a convenient means for comparing radical reactivities, provided the absolute propagation constants also are known. 

For polychlorinated biphenyls (PCBs), rate constants were highly dependent on the number of chlorine atoms, and calculated atmospheric lifetimes varied from 2 d for 3-chlorobiphenyl to 34 d for 236-25 pentachlorobiphenyl (Anderson and Hites 1996). It was estimated that loss by hydroxy-lation in the atmosphere was a primary process for the removal of PCBs from the environment. It was later shown that the products were chlorinated benzoic acids produced by initial reaction with a hydroxyl radical at the 1-position followed by transannular dioxygenation at the 2- and 5-positions followed by ring fission (Brubaker and Hites 1998). Reactions of hydroxyl radicals with polychlorinated dibenzo[l,4]dioxins and dibenzofurans also play an important role for their removal from the atmosphere (Brubaker and Hites 1997). The gas phase and the particulate phase are in equilibrium, and the results show that gas-phase reactions with hydroxyl radicals are important for the... 

There are extensive data for the acid-catalyzed protiodesilylation of XCgELrSiMes in methanol-aqueous perchloric acid or acetic acid-aqueous sulphuric acid at 50°C225. Correlation analysis of the partial rate factors (relative rate constants) by means of the Yukawa-Tsuno equation (Section n.B) finds p = —5.3 and r+ = 0.65. These values are consistent with a relatively low demand for stabilization of the transition state by electron delocalization, i.e. the transition state is early along the reaction coordinate, p-NO2 is highly deactivating with / = 14 x 10 but 0-NO2 is even more deactivating, with / = 6.8 x 10-5. This contrasts with the deactivation order discussed above for nitration and chlorination (Table 6), and may be explained in terms of the early transition state, well removed from the Wheland intermediate. 

It is also clear that during periods of low surface ozone, chlorine atoms are a major reactant for hydrocarbons (e.g., Jobson et al., 1994 Solberg et al., 1996 Ariya et al., 1998). Figure 6.39, for example, shows the measured ratios of isobutane, n-butane, and propane during an ozone depletion event (Jobson et al., 1994). These particular pairs of hydrocarbons were chosen to differentiate chlorine atom chemistry from OH reactions. Thus isobutane and propane have similar rate constants for reaction with Cl but different rate constants for reaction with OH. If chlorine atoms are responsible for the loss of these organics, their ratio should remain relatively constant in the air mass, as indicated by the line marked Cl. Similarly, isobutane and n-butane have similar rate constants for removal by OH but different rate constants for reactions with... 

The Livermore study used a 1.8 L upflow reactor, packed with a 1% w/w Pd/alumina catalyst, nominally 0.32 cm in diameter. (McNab and Ruiz 1998) The water supply consisted of groundwater from a well at the Livermore site and contained PCE (5-7 jig/L), TCE (500-600 tig/L), 1,1-DCE (15-25 pg/L), CT (8-15 fig/L), CF (4-10 gg/L), and 1,2-DCA (4-10 jrg/L). The water was first passed through an electrolyzer, which served as a source of hydrogen. With an average residence time of 2.3 minutes, the column showed >95% removal of chlorinated ethylenes (PCE, TCE and 1,1,-DCE) and CT. The apparent first order rate constants for all four compounds were approximately 72/hour. Chloroform was removed at a much slower rate (<32/hour) and 1,2-DCA removal was not significant. These results are also consistent with the batch studies of Lowry which showed rapid reaction of... 

Some reaction is found to occur between 0( D) atoms (produced from the photolysis of ozone at 253.7 nm and 25 C) and COCIF, as indicated by the high value of the quantum yield for ozone removal. However, no products were found (although analysis was not made for CO 2 which could be the major product), unlike the COCl 2 0( D) reaction, in which evidence was obtained for the formation of both CO and chlorine oxides [1038]. The rate constant for the reaction of COCIF with 0( D) atoms was estimated to be 2.8 times the value... 

Table III also shows that hydrogen and the chlorinated butanes are reduced substantially when ethyl chloride is irradiated in the presence of benzene. The other products are essentially unaffected by this additive. In the radiolysis of certain alkanes (4), benzene, added in small amounts, does not interfere with the fast ion-molecule reactions of primary ionic fragments or with free radical processes, but it will efficiently condense unreactive or long-lived ions in the system. It is reasonable to assume that this is also true for alkyl halide systems and that the reduction in product yields compared with the pure compound upon adding benzene may be attributed to the interception of unreactive ions. Since the rate constants for reactions of the expected primary ions with ethyl chloride are very large (see Table II), the concentration of benzene used in our experiments should not interfere with the initial fast ion-molecule reactions. For ethyl chloride ion-molecule reactions, C4Hi0C1+ is the only unreactive ion of appreciable abundance which is expected in this system at the elevated pressures used in the radiolysis experiments. Thus, the reduced product yields in the presence of benzene additive can be identified tentatively with the removal of this stable ion and the elimination of its resultant neutralization products.

The rate constants for HCFC removal show a correlation with respect to the chlorine content of the molecule. For molecules of the form RCXj- Cl, where R = H, CH3 or CF3 and X = H, F or a combination of the two, the reaction rate increases with n. For example, the reaction of 0( D) with HCFC-141b is faster than the reaction with HCFC-142b, and the reaction with HCFC-21 is faster than that with HCFC-22 This is consistent with an abstraction mechanism in which chlorine atom abstraction is preferred because of the weaker C—Cl bond. 

With increa. iing substitution of H for a halogen atom, the rate constant for removal of the remaining H atom decreases (see Table 4), and since abstraction or substitution of chlorine is an even slower process, the rate constants for CHCI3, CH2CI2, and CH3CI undoubtedly refer to H abstraction exclusively. At room temperature, the reaction of F with CHF3 is 100-fold slower than reaction with H2 or CH4. ... 

Table IX. First-Order Rate Constants for Removal/Destmction of Chlorinated Organic Compounds from Groundwater Using Sonication Alone, Vapor Stripping Alone, and Combined SonicationA apor...

It should be pointed out that a jet-type tubular turbulent reactor of similar design, instead of stirred tank reactors with mechanical stirrers, can and should be used at other stages of the process of chlorinated BR production, in particular, for the neutralisation of the modified polymer solution (the rate constant of the interaction between mineral acids and alkalis is k 10 1/mols), removal of salts and other substances from the chlorinated BR solution by water washing (extraction), removal of back solvent (extraction), and introduction of the stabiliser-antioxidant and adhesion reducing powder (mixing) into the polymer solution. 

Anderson, PC., and M.J. Kurylo (1979), Rate constant measurements for the reaction Cl - - CH2O - HCl + CHO, Implications regarding the removal of stratospheric chlorine, J. Phys. Chem., 83, 2055-2057. 

Benzene is to be chlorinated in the liquid phase in a kettle-type reactor operated on a steady-state basis. Liquid benzene is added continuously, and the liquid product and gaseous hydrogen chloride are removed continuously. The chlorine gas is bubbled continuously into the liquid reaction mixture in the kettle. The rate of reaction may be assumed large enough that there is no unreacted chlorine in the reaction products. Also, the concentrations of chlorine and HCl in the reaction mixture will be small. The density of the liquid mixture may be assumed constant. 

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