Reactions of CIO

Evidence has recently been adduced by Clyne and Coxon410 that, at pressures of the order of a few torr, reaction (9) proceeds through the intermediate formation of the chlorine peroxy radical 

Clearly, this discovery has an important bearing on the kinetics of the decompositions of chlorine oxides and of the halogen-sensitized decompositions of oxides, e.g. 03 and N20. Johnston et alf21 have recently shown that an additional, pressure-dependent reaction occurs between two CIO radicals, viz 

The thermal decomposition of N20 catalyzed by the halogens, Cl2, Br2, I2, proceeds according to the rate law434 

Values for k are summarized in Table 30. Benson and Buss431 argue convincingly that the reaction catalyzed by Cl2 involves a Cl atom chain which consists either of 

This compound exists as the monomer (C103) in the gas phase and almos exclusively as the dimer in the liquid phase or solution. Paramagnetism of the liquid is probably not due to C103, as was once thought, but rather to traces of C102437. Qualitative studies have been made of the thermal and photochemical decomposition of C103438,439. 

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C16-0051. Describe experiments that could be done to demonstrate that the decomposition reaction of CIO anions (Problem 16.3) is reversible. 

P(OR)3, Sb(III), or Sn(II) is also extremely slow, so slow that complications attributable to the reaction of CIO with these... 

The reaction of CIO- with methyl chloride can only proceed via the Sn2 process. An inverse KIE of 0.85 is measured (Table 10.3). The reaction with /-butyl chloride presumably proceeds via an E2 mechanism (since Sn2 attack on the Cl substituted carbon is blocked) and the observed KIE of 2.31 (Table 10.3) is consistent with that conclusion. The isotope effects for both species are nearly the same as the effects measured in the condensed phase (compare Tables 10.3 and 10.4) and measure the relative contributions of the two paths. The results indicate that the E2 pathway becomes the dominant channel as the substrate becomes more sterically hindered. 

Chlorine nitrate is formed from the reaction of CIO with N02.) These reactions also occur when NaCl is in the aqueous phase, in competition with the hydrolysis of N205 and C10N02, i.e., above the deliquescence point of NaCl in sea salt (e.g., Behnke et al., 1997). Photolysis then generates chlorine atoms, e.g.,... 

This cycle accounts for 30% of the ozone loss due to halogens in the lower stratosphere, and the corresponding cycle for bromine for 20-30% (Wennberg et al., 1994). Reaction of CIO with HOz, reaction (28), produces HOC1 + 02 with a yield >95% at temperatures from 210 to 300 K however, at the lowest end of this temperature range, there is evidence for the produc-... 

The self-reaction of CIO has both a termolecular component shown as (43a) and a bimolecular component with three possible sets of products (Hayman et al., 1986 Nickolaisen et al., 1994 Horowitz et al., 1994) ... 

Laboratory studies of the uptake of CIO into sulfuric acid (Martin et al., 1979, 1980), taken in light of a deficit in the inorganic chlorine budget at 17 km after the Mount Pinatubo eruption, led Jaegle et al. (1996) to propose that a heterogeneous reaction of CIO on sulfuric acid aerosols to form perchloric acid, HC104, may also occur. 

As discussed in Section C.3, CIO, chemistry and BrOx chemistry are closely interrelated via the gas-phase reactions of CIO with BrO ... 

Approximately one-half of the total reaction of CIO and BrO results in the destruction of ozone. Other mechanisms exist, such as a catalytic cycles that are rate-limited by the reaction between CIO and O and between CIO and H02 (25), but the contribution from these reactions is small in the polar regions. 

CI2O3, generated in the reaction of CIO with CIO2, has a relatively short lifetime and is not expected to be an important reservoir for ClOx. ... 

However, the reaction of CIO with O3 has subsequently been shown to be slow . Furthermore, reaction (32) does not alter the rate law as it is followed by - ... 

Three important recent results by Clyne and Coxon , who used a flow system and followed CIO spectroscopically, help to resolve the mechanistic difficulties in the CI2-O3 system. These results are (/) the reaction of Cl with O3 produces CIO in the ground vibrational level in amounts comparable to the initial Cl concentration, the rate coefficient being in excess of 4x 10 l.mole . sec (it) the reaction of CIO with O3 is immeasurably slow and (Hi) the products of the reaction of two CIO radicals are predominantly Cl and ClOO, at least at low pressures (a further discussion of this reaction is found in Section 2.2.4). 

The conclusion that Cl atoms do not react with O2 conflicts with other findings as previously discussed, including those reported subsequently by Burns and Norrish and Stedman (cited in ref. 27). Furthermore, Iredale and Edwards found that the presence of H2 accelerated the decomposition of CI2O, which they felt could be attributed only to the reaction of CIO with H2. They suggested two reactions... 

To end this brief discussion on the reactions of chlorine species, we must consider the formation of other constituents such as ClOO, OCIO, CIONO2, HOC1, etc. Chlorine nitrate CIONO2, another important chemical reservoir for chlorine, is formed by the reaction of CIO with... 

Molina, L.T., and M.J. Molina, Production of CI2O2 from the self-reaction of CIO radical. J Rhys Chem 91, 433, 1987. 

The recombination and disproportionation reactions of CIO radicals have been investigated extensively on account of their relevance to the Os-destruction chemistry in the stratosphere [104 - 118], The reactions are expected to play a significant role in AP combustion also due to the potential high concentration of the CIO radical. In principle, the reactions may take place via at least two long-lived intermediates viz. 

Both CIO and OCIO, and their higher oxides of chlorine have been implicated in the formation of Os-hole in the antarctic stratosphere [122-135] at low temperatures, one of the major products of the reaction of CIO with OCIO is CI2O3, which may have several stable isomers under the stratospheric condition [131-135]. The stability of at least 3 isomers of CI2O3 (see below) have been predicted to be theoretically stable at low temperatures by several authors using different computational methods [136-... 

Bimolecular reactions of CIO and CIO are slow and can be neglected. The termolecular reaction 1 is facilitated at higher pressures, that is, larger M, and low temperature.) C1202 has been shown to have the symmetric structure ClOOCl (McGrath et al. 1990). Photolysis of ClOOCl has two possible channels ... 

The self-reaction of CIO leads to the C1202 dimer and not to the direct production... 

At conditions in the upper stratosphere, the characteristic time of reaction 4.30 for reaction of Cl is about 1 second and that of reaction 4.31 for reaction of CIO is approximately 1... 

The products of decay of CIO radicals reacted with added Hj at 300 K, but on addition of bromine, which acts as an effective scavenger through the rapid transfer reaction,Cl -I- Br -> BrCl -H Br, the CIO -I- Hg reaction was completely suppressed. Subsequently, Cl atoms were detected directly by atomic absorption spectrometry at 2 138-0 nm, as a product of the decay reaction of CIO radicals. The following scheme was proposed ... 

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