Reaction with chlorine atoms

Ashmore et have suggested both molecular and free radical paths 

Gilbert and Thomas estimated kxos from kinetic data on the reaction of HCI + NO2 (see section 4.7). At 354 °C they found fcjos = (6.6+2) x 10 ° P. mole. sec where M was a mixture of CI2, HCl, NO2 and NO, which compares favourably with the value obtained by Ashmore et al. 

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In homogeneous catalysis, both the catalyst and the reactants are in the same phase, i.e. all are molecules in the gas phase, or, more commonly, in the liquid phase. One of the simplest examples is found in atmospheric chemistry. Ozone in the atmosphere decomposes, among other routes, via a reaction with chlorine atoms ... 

Concern has been expressed over the destruction of ozone in the stratosphere brought about by its reactions with chlorine atoms produced from chlorofluoroalkanes that are persistent in the troposphere, and that may contribute to radiatively active gases other than COj. 

Langer, S., E. Ljungstrom, I. Wangberg, T. J. Wallington, and O. J. Nielsen, Atmospheric Chemistry of Di-fert-butyl Ether—Rates and Products of the Reactions with Chlorine Atoms, Hydroxyl Radicals, and Nitrate Radicals, Int. J. Chem. Kinet, 28, 299-306 (1996). 

Rudolph, J., R. Koppmann, and Ch. Plass-Diilmer, The Budgets of Ethane and Tetrachloroethene—Is There Evidence for an Impact of Reactions with Chlorine Atoms in the Troposphere Atmos. Enriron., 30, 1887-1894 (1996). 

Rudolph J., Koppmann R., and Plass-Dulmer C. (1996) The budgets of ethane and tetrachloroethene Is there evidence for an impact of reactions with chlorine atoms in the troposphere A/moi. Environ. 30, 1887—1894. 

With the exception of a-haloalcohols, the atmospheric lifetime of halogen substituted saturated alcohols is determined by their reaction with hydroxyl radicals. In laboratory experiments to simulate the atmospheric oxidation of halogen substituted alcohols, it is often convenient to use chlorine atoms, rather than OH radicals to initiate the oxidation. To aid in the design and interpretation of such experiments, a knowledge of the kinetics of reactions with chlorine atoms is desirable. Rate constants for the reactions of organic compounds with chlorine atoms are also useful because they can be used to estimate the rate constants of reactions with OH radicals. 

Iwasaki, E., Y. Matsumi, K. Takahashi, T.J. WaUington, M.D. Hurley, J.J. Orlando, E.W. Kaiser, and J.G. Calvert (2008a), Atmospheric chemistry of cyclohexanone UV spectrum and kinetics of reaction with chlorine atoms, Int. J. Chem. Kinet., 40, 223-229. 

This cycle is terrninated by the reaction of chlorine atoms with methane Cl + CH — HCl + CH3. The importance of this cycle depends on the avadabiLity of oxygen atoms and varies with altitude as well as the time of year it accounts for only 5% of the halogen-controUed loss at 15 km, but increases to 25% at 21 km. 

Oxidation. The chlorine atom [22537-15-17-initiated, gas-phase oxidation of vinyl chloride yields 74% formyl chloride [2565-30-2] and 25% CO at high oxygen [7782-44-7], O2, to CI2 ratios it is unique among the chloro olefin oxidations because CO is a major initial product and because the reaction proceeds by a nonchain path at high O2/CI2 ratios. The rate of the gas-phase reaction of chlorine atoms with vinyl chloride has been measured (39). 

Now that we have a model, we must check its consistency with various experiments. Sometimes such inconsistencies result in the complete rejection of a model. More often, they indicate that we need to refine the model. In the present case, the results of careful experiments show that the collision model of reactions is not complete, because the experimental rate constant is normally smaller than predicted by collision theory. We can improve the model by realizing that the relative direction in which the molecules are moving when they collide also might matter. That is, they need to be oriented a certain way relative to each other. For example, the results of experiments of the kind described in Box 13.2 have shown that, in the gas-phase reaction of chlorine atoms with HI molecules, HI + Cl — HC1 I, the Cl atom reacts with the HI molecule only if it approaches from a favorable direction (Fig. 13.28). A dependence on direction is called the steric requirement of the reaction. It is normally taken into account by introducing an empirical factor, P, called the steric factor, and changing Eq. 17 to... 

Molecules containing two or more chlorine atoms may be produced by the reaction of chlorine atoms or molecules with products generated in the earlier stage of the process. Product yields depend on irradiation conditions and can reach as high as 105 pmol.J-1. With bromine and iodine, not all of the individual steps of the reaction are exothermic. Therefore, a sustained chain reaction is not expected, and the yields are low. 

The chemiluminescent reaction with chlorine dioxide provides a highly sensitive and highly selective method for only two sulfur compounds, hydrogen sulfide and methane thiol [81]. As in the flame photometric detector (FPD), discussed below, atomic sulfur emission, S2(B3S -> ) is monitored in the wave-... 

Silicon tetrachloride undergoes addition with olefinic and acetylenic unsaturated hydrocarbons. In these addition reactions, one chlorine atom adds to one carbon atom of the double or triple bond while the rest of the unit —SiCls attaches to the other carbon atom forming a sihcon—carbon bond ... 

For example, Figure 5.11 shows typical results from a relative rate experiment on the reaction of chlorine atoms with some simple alkanes (Beichert et al., 1995). The chlorine atoms in this case were produced by the... 

Beichert, P L. Wingen, J. Lee, R. Vogt, M. J. Ezell, M. Ragains, R. Neavyn, and B. J. Finlayson-Pitts, Rate Constants for the Reactions of Chlorine Atoms with Some Simple Alkanes at 298 K Measurement of a Self-Consistent Set Using both Absolute and Relative Rate Methods, J. Phys. Chem., 99, 13156-13162 (1995). 

Table 6.4 summarizes the rate constants for the reactions of chlorine atoms with alkanes. Structure-reactivity relationships have again been developed for... 

TABLE 6.14 Some Reported Values of the Rate Constants for the Reactions of Chlorine Atoms with Some Alkenes at 1 atm Total Pressure and 298 K... 

Finlayson-Pitts, B. J., C. J. Keoshian, B. Buehler, and A. A. Ezell, Kinetics of Reaction of Chlorine Atoms with Some Biogenic Organics, Int. J. Chem. Kinet., 31, 491-499 (1999). 

Atomic chlorine reacts rapidly with DMS, with an overall rate constant of (3.3 + 0.5) X 10 1(1 cm3 molecule 1 s 1 at 298 K and 700 Torr total pressure (Stickel et al., 1992). As is the case for the OH reaction, the chlorine atom reaction proceeds by two reaction channels, one an abstraction and the other addition to the sulfur atom ... 

Syntheses of 5-halogenotetrazoles from metallic derivatives have met with mixed fortunes. Lithiation of 1-methyltetrazole followed by reaction at -60°C with bromine, iodine, or cyanogen bromide gave the 5-bromo and 5-iodo compounds in 36-55% yields (71CJC2139). 1,2-Disubstituted tetrazolium tetraphenylborates were lithiated in the 5-position, but subsequent reaction with chlorine or bromine failed to trap the anion. Instead, oxidation produced a radical cation, which abstracted a hydrogen atom from the solvent [91 AG(E)1162]. 

Rate-Constant Data from the Reaction of Chlorine Atoms with CO... 

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