Ozone reaction with chlorine

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. 

Although technically a chlorine oxide, chlorine perchlorate is of little importance. When ozone reacts with chlorine dioxide, the reaction produces Cl2Og dichlorine hexoxide. 

Ozone can also be naturally destroyed through reactions with chlorine, nitrogen, and hydrogen. Eor example, chlorine can be a very effective destroyer of ozone via the following set of reactions. 

Oxidation of phenols with chlorine dioxide or chlorine produces chlorinated aromatic intermediates before ring rupture. Oxidation of phenols with either chlorine dioxide or ozone produces oxidized aromatic compounds as intermediates which undergo ring rupture upon treatment with more oxidant and/or longer reaction times. In many cases, the same nonchlorinated, ringruptured aliphatic products are produced using ozone or chlorine dioxide. 

The chlorine-containing product species (HCl, CIONO2, HOCl) are "inert reservoirs" because they are not directly involved in ozone depletion however, they eventually break down by absorbing solar radiation or by reaction with other free radicals, returning chlorine to its catalytically active form. Ozone is formed fastest in the upper stratosphere at tropical latitudes (by reactions 1 and 2), and in those regions a few percent of the chlorine is in its active "free radical" form the rest is in the "inert reservoir" form (see Figure 3). 

Typically, intense chemiluminescence in the UV/Vis spectral region requires highly exothermic reactions such as atomic or radical recombinations (e.g., S + S + M - S2 + M) or reactions of reduced species such as hydrogen atoms, olefins, and certain sulfur and phosphorus compounds with strong oxidants such as ozone, fluorine, and chlorine dioxide. Here we review the chemistry and applications of some of the most intense chemiluminescent reactions having either demonstrated or anticipated analytical utility. 

Nonhalogenated carboxylic acids are also common DBPs from chlorine, chloramines, ozone, and chlorine dioxide [10]. In addition to halogenation reactions that can occur (primarily with chlorine and chloramine), oxidation reactions also occur, and can produce carboxylic acids. There is generally not a concern for toxicity for them, as many are naturally present in foods. 

NDMA were observed in ozonated drinking water from Germany and came as a surprise because ozone does not form NDMA by reaction with natural organic matter. The chlorination products of NA -dimethylsulfamide have not been investigated yet. 

Bisphenol A, a compound highly used in the production of epoxy resins and polycarbonate plastics, forms monochloro-, dichloro, trichloro-, and tetrachloro derivatives when chlorinated [127], Its reaction with ozone produces as major transformation products, catechol, orthoquinone, muconic acid derivatives of bisphenol A, benzoquinone, and 2-(4-hydroxyphenyl)-propan-2-ol [128],... 

Ozone is the fourth strongest oxidant known to man and is more effective at sterilizing water than chlorine. Ozone s reaction with NO is a natural phenomenon that takes place in the upper atmosphere that depletes the ozone layer and creates acid... 

CFCs are nearly ideal substances for attacking ozone molecules and damaging the ozone layer. On the one hand, they tend to be very stable, even in the stratosphere. Many CFCs have half-lives of 100 years or more that means that once they have escaped into the upper atmosphere, they are likely to remain there for very long periods. On the other hand, some small number of CFC molecules do dissociate to form chlorine free radicals, with the ability to destroy ozone molecules. Although the number of CFC molecules that do dissociate is relatively small, the actual number is not important since chlorine free radicals that are generated in the process are used over and over again. That is, they are catalysts in the destruction of ozone and are not, themselves, used up in their reactions with ozone molecules. 

The importance of catalysts in chemical reactions cannot be overestimated. In the destruction of ozone previously mentioned, chlorine serves as a catalyst. Because of its detrimental effect to the environment, CFCs and other chlorine compounds have been banned internationally. Nearly every industrial chemical process is associated with numerous catalysts. These catalysts make the reactions commercially feasible, and chemists are continually searching for new catalysts. Some examples of important catalysts include iron, potassium oxide, and aluminum oxide in the Haber process to manufacture ammonia platinum and rhodium in the Ostwald synthesis of nitric... 

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... 

Fluorine chemistry in the stratosphere was also considered and it was concluded that ozone depletion by chlorine was > 104 more efficient than that by fluorine (Rowland and Molina, 1975 Stolarksi and Rundel, 1975). Since then, the kinetics of reaction of F atoms with 02 to form the F02 radical and its thermal decomposition have been measured (e.g., see Pagsberg et al., 1987 Lyman and Holland, 1988 Ellerman et al., 1994 and review in DeMore et al., 1997). The equilibrium constant for the F-F02 system... 

Atomic chlorine lowers the energy barrier of this reaction by providing an alternate pathway involving intermediate reactions, each having a lower activation energy than the uncatalyzed reaction. This alternate pathway involves two steps. Initially, the chlorine reacts with the ozone to form chlorine monoxide and oxygen ... 

Whenever a superficial modification is intended, keeping the graft copolymer in the same state of dispersion, special techniques can be employed, either creating active centers by high or low energy irradiation, or by chemical reactions with ozone, chlorine, bromine, dinitrogen trioxide or other reagents. 

The chemistry of ozone in aqueous solutions and the health effects are complex. It is clear that ozone reacts with water products in the water supply to form numerous disinfection byproducts. However, the general pattern that emerges from most studies is that the reaction byproducts of ozonation appear to be less toxic than those produced by chlorination. 

CFCs) and halons over the next decade, as mandated by the Montreal Protocol for the Protection of the Ozone Layer, will affect the chlorine burden of the stratosphere. Hydrochlorofluorocarbons (HCFCs) can be used as substitutes for the CFCs for a few decades without having a substantial impact on the chlorine burden of the stratosphere because they are primarily destroyed in the troposphere by reactions with OH before they are able to deliver the chlorine to the stratosphere. The elimination of CFCs and the temporary use of HCFCs into the early part of the next century must be carefully orchestrated to minimize the peak chlorine loading and promote the most rapid reduction of the chlorine burden of the stratosphere (56, 87). Another issue is the effects that perturbations to the reactive nitrogen abundances will have on the abundances of reactive chlorine. A better understanding and clarification of the direct heterogeneous conversions of chlorine species on both PSCs and sulfate aerosols are also needed. 

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