Chlorine monoxide radical

In 1986 we proposed a cycle that involves the self reaction of chlorine monoxide radicals, without requiring free oxygen atoms to regenerate the chlorine atoms (14) ... 

Waters, J.W., J.C. Hardy, R.F. Jamot and H.M. Pickett (1981) Chlorine monoxide radical, ozone and hydrogen peroxide by microwave limb sounding. Science 214 61-64. 

Anderson, J.G., Margitan, J.J. and Stedman, D.H. (1977) Atomic chlorine and the chlorine monoxide radical in the stratosphere three in situ observations. Science, 198, 501. 

The chlorine radicals are the ozone-removing agents. They react with ozone to form chlorine monoxide radicals and molecular oxygen. The chlorine monoxide radicals then react with ozone to regenerate chlorine radicals. These two propagating steps are repeated over and over, destroying a molecule of ozone in each step. It has been calculated that each chlorine atom destroys 100,000 ozone molecules ... 

Anhydride of chloric acid, Cl20, is unknown. Oxides with even number of oxygen atoms are mixed anhydrides. Other chlorine oxides such as the radicals CIO, CIO, and CIO are known. Chlorine monoxide [14989-30-17, CIO, plays a key role in depletion of the o2one layer. 

Write the Lewis structure of each of the following reactive species, all of which are found to contribute to the destruction of the ozone layer, and indicate which are radicals (a) chlorine monoxide, CIO (b) dichloroperoxide, Cl—O—O—Cl ... 

FIGURE 1.8 Measured concentrations of the chlorine monoxide free radical (CIO) as well as 03 outside and inside the polar vortex on August 23, 1987 (adapted from Anderson, 1989). 

The hypothesis postulated that CFCs are photolyzed by UV in the stratosphere to halogenated carbon radicals and chlorine atoms and that the latter are capable of destroying ozone molecules via the intermediate formation of chlorine monoxide. The mechanism is complex but the essential steps, notably the regeneration of chlorine atoms which, in effect, are said to catalyze the destruction of stratospheric ozone, are summarized in Scheme l.8,9... 

The Airborne Submillimeter SIS Radiometer (ASUR), operated on-board the German research aircraft FALCON, measures thermal emission lines of stratospheric trace gases at submillimeter wavelength. Measurement campaigns with respect to ozone depletion in the Arctic winter stratosphere were carried out in yearly intervals from 1992-97 to investigate the distributions of the radical chlorine monoxide (CIO), the reservoir species hydrochloric acid (HC1), the chemically inert tracer nitrous oxide (N20), and ozone (O3). The high sensitivity of the receiver allowed to take spatially well resolved measurements inside, at the edge, and outside of the Arctic polar vortex. This paper focuses on the results obtained for CIO from... 

The next step, addition (equation 83) of molecular oxygen to C1CO, involves the intermediacy of the unstable chloroformylperoxy radical, which may readily dissociate (equation 84) to chlorine monoxide and carbon dioxide. 

The principal fate of the chlorine atom released is reaction with ozone to form the chlorine monoxide free radical which in turn reacts with atomic oxygen to regenerate the chlorine atom thereby forming a homo-... 

Figure 6 traces the major exchange reactions in the SOURCE — RADICAL RESERVOIR system. The dominant natural source of chlorine in the stratosphere is CH3CI the main synthetic contribution is from CCI4, CF2CI2 and CFCI3. Atomic chlorine and chlorine monoxide are... 

The chlorine atom is highly reactive toward 03 and establishes a rapid cycle of 03 destruction involving the chlorine monoxide (CIO) radical ... 

The dots are unpaired electrons resulting from bond cleavage.) Like many species with unpaired electrons (free radicals), atomic Cl is very reactive. It reacts with ozone to produce chlorine monoxide (CIO-), which then regenerates Cl atoms ... 

Acyl radicals can fragment with toss of carbon monoxide. Decarbonylation is slower than decarboxylation, but the rate also depends on the stability of the radical that is formed. For example, when reaction of isobutyraldehyde with carbon tetrachloride is initiated by t-butyl peroxide, both isopropyl chloride and isobutyroyl chloride are formed. Decarbonylation is competitive with the chlorine-atom abstraction. 

In summary the concentration of ozone in the polluted atmosphere is controlled by the intensity of sunlight and the ratio of nitrogen dioxide to nitric oxide. Hydrocarbons and other pollutants—such as aldehydes, ketones, chlorinated hydrocarbons, and carbon monoxide—react to form peroxy radicals. These, in turn, react with nitric oxide, causing the ratio [NOjjilNO] to increase. As a consequence of Equation 2-5, the ozone concentration also increases. 

Alkanes are fuels they burn in air if ignited. Complete combustion gives carbon dioxide and water less complete combustion gives carbon monoxide or other less oxidized forms of carbon. Alkanes react with halogens (chlorine or bromine) in a reaction initiated by heat or light. One or more hydrogens can be replaced by halogens. This substitution reaction occurs by a free-radical chain mechanism. 

Activated carbon is an active catalyst for the free radical chlorinations of hydrocarbons. Methane108, in the gas phase, and acetic acid109, in the liquid phase, are both chlorinated in its presence. Surface free radicals are claimed to play a major role in the mechanism of this reaction. A similar mechanism has been established for the active carbon catalyzed chlorination of indane in aqueous solution by quenching methods110. Trimm111 has reviewed the activity of carbon in chlorination of carbon monoxide, ethylene and toluene. 

Regeneration of atomic chlorine, essential for catalysis, does not take place by means of reaction 8 because of the very low concentration of atomic oxygen (reaction 1 does not happen in the dark ). However, reaction 14 with bromine monoxide does occur instead. Furthermore, dimerization (equation 18) of chlorine monoxide18 is followed by photolysis (equation 19) and dissociation (equation 20) of the chloroperoxy radicals which serve to release chlorine atoms19. Thus arises the now famous Antarctic ozone hole, a very significant depletion in ozone concentrations at altitudes of 15-20 km during the austral... 

The chloroformyl radical C1CO is less stable than FCO but nonetheless is of atmospheric significance due to its ability to participate in the oxidation of CO to C02. The first step of this process is the formation of Cl CO either by the addition (equation 81) of chlorine to carbon monoxide or by photolysis of phosgene (equation 82). 

---