Ozone reaction with halogens

Calculations of ozone reactions with halogenated olefins in some cases resulted in saddle point cw-TS2 (NTSl, [12]). Its existence is not approved in all methods and not for all objects. In terms of UHF it has been found for ethylene and mono-substiments. In case of dihalogensubstituents for more reliable methods - CCSD (1,1-difluoethyle), CASSCF (1,1-dichloroethylene). This suggests that it is probably a calculation artifact, which should be additionally verified. For that purpose Gaussian 09, MOLPRO have been used. The verification was done in following way ... 

Ozone in the stratosphere is depleted by reactions with halogen atoms. Depletion of stratospheric ozone, commonly referred to as the ozone hole, usually occurs over the Earth s cold regions. The main source of chlorine atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds,1369 commonly called Freons, e.g. ... 

Although ozone (O3) is a reactive species among stable molecules in the atmosphere, partner molecules of homogeneous gas phase reaction are not so many. Important atmospheric reactions are reactions with halogen atoms in the... 

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

The oxidation scheme for halomethanes not containing a hydrogen atom is similar to that for those which do, except that it is not initiated by tropospheric reaction with hydroxyl radicals, since the fully halogenated methanes are unreactive. Consequently, substantial amounts of CFCs and halons are transported intact up into the stratosphere, where they absorb UV radiation of short wavelength and undergo photodissociation (equation 36) to a halogen atom and a trihalomethyl radical. The halogen atom Y may enter into catalytic cycles for ozone destruction, as discussed in the introduction. 

Besides the photochemical dissociation, ozone decays in oxidation-reduction reactions with different species. The stratospheric 03 reacts rapidly with nitric oxide and products of photodissociation of halogenated hydrocarbons (Figure 9.5). 

Ariya and her students are trying to determine what kinds of halogens exist in Earth s atmosphere, how quickly they are produced and degraded, and what their major sources are. As they find answers to these questions, they may be able to recommend ways to reduce halogens in the oceans and atmosphere. They may also develop ways to modify halogens reactions with ozone and other gases so that the halogens do less harm. 

Explosive reaction with alkenes + diiodomethane, sulfur dioxide. Reacts violently with bromine, water, nitro compounds. Ignites on contact with air, ozone, methanol, or hydrazine. Reacts violently with nonmetal halides (e.g., arsenic trichloride or phosphorus trichloride) to produce pyrophoric triethyl arsine or triethyl phosphine. To fight fire, do not use water, foam, or halogenated extinguishing agents. Use dty materials, such as graphite, sand, etc. When heated to decomposition it emits toxic fumes of ZnO. See also ZINC COMPOUNDS. 

Oxidation of disulfides with halogens may lead to sulfonyl chlorides or the much less stable bromides which afford sulfonamides. However, replacement of the sulfur function by halogen or complete desulfurization may also occur. Treatment of the sulfonyl chloride does not yield the expected esters but is the best way to prepare the sulfonic acids. Electrolytic oxidation of thiones affords a mixture of sulfonic acids and desulfurized compounds. The action of ozone on disulfides is a feasible but not very convenient reaction leading to sulfonic acids. Scheme 54 summarizes some of these relationships and the unusual nitration of the sulfonamide (147) (62BEp619423) for convenience the generalized triazole Tr is shown in... 

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