Ozone reaction with iodide

O ne. Air pollution (qv) levels are commonly estimated by determining ozone through its chemiluminescent reaction with ethylene. A relatively simple photoelectric device is used for rapid routine measurements. The device is caHbrated with ozone from an ozone generator, which in turn is caHbrated by the reaction of ozone with potassium iodide (308). Detection limits are 6—9 ppb with commercially available instmmentation (309). 

As inert as the C-25 lactone carbonyl has been during the course of this synthesis, it can serve the role of electrophile in a reaction with a nucleophile. For example, addition of benzyloxymethyl-lithium29 to a cold (-78 °C) solution of 41 in THF, followed by treatment of the intermediate hemiketal with methyl orthoformate under acidic conditions, provides intermediate 42 in 80% overall yield. Reduction of the carbon-bromine bond in 42 with concomitant -elimination of the C-9 ether oxygen is achieved with Zn-Cu couple and sodium iodide at 60 °C in DMF. Under these reaction conditions, it is conceivable that the bromine substituent in 42 is replaced by iodine, after which event reductive elimination occurs. Silylation of the newly formed tertiary hydroxyl group at C-12 with triethylsilyl perchlorate, followed by oxidative cleavage of the olefin with ozone, results in the formation of key intermediate 3 in 85 % yield from 42. 

Chemical/Physical. Anticipated products from the reaction of methyl iodide with ozone or OH radicals in the atmosphere are formaldehyde, iodoformaldehyde, carbon monoxide, and iodine radicals (Cupitt, 1980). With OH radicals, CH2, methyl radical, HOI and water are possible reaction products (Brown et al., 1990). The estimated half-life of methyl iodide in the atmosphere, based on a measured rate constant for the vapor phase reaction with OH radicals, ranges from 535 h to 32 wk (Garraway and Donovan, 1979). 

SAFETY PROFILE Poison by intravenous route. Moderately toxic by ingestion and intraperitoneal routes. Human teratogenic effects by ingestion developmental abnormalities of the endocrine system. Experimental teratogenic and reproductive effects. Mutation data reported. Explosive reaction with charcoal + ozone, trifluoroacetyl hypofluorite, fluorine perchlorate. Violent reaction or ignition on contact with diazonium salts, diisopropyl peroxydicarbonate, bromine pentafluoride, chlorine trifluoride. Incompatible with oxidants, BrFs, FCIO, metallic salts, calomel. When heated to decomposition it emits very toxic fumes of K20 and I . See also IODIDES. 

The oceans acts as a one-way sink for atmospheric ozone due to the high reactivity of the gas with components in the surface water. The dominant reaction at the surface appears to be with iodide ions and unidentified organic surfactants (Garland et al., 1980). Given that this reactivity makes the sea a perfect sink,... 

As indicated by Equation 1, a standard procedure for ozone recommends the addition of iodide ions and the titration of the liberated iodine. There is a serious problem in interpreting the results of the iodide reaction The quantity of iodine liberated is pH dependent. Inglis (6) reported that acid solutions gave more than one molecule of iodine per molecule of ozone. He tried bromide in normal nitric acid but obtained decreasing amounts of bromine from aliquots of the original ozone solution with time, while the iodine liberated from iodide remained constant. He concluded that the bromide-bromine reaction was unsatisfactory. Alder and Hill (1) found that ozone decomposes, according to its ultraviolet spectrum, faster than the decreasing ability of the same solution to liberate iodine from iodide. They concluded that a decomposition product of ozone, the hydroperoxyl ion, liberates iodine from iodide in the absence of ozone. 

The 300 ml. of ozone solution from the scrubber is divided and analyzed in various ways. When crystals of iodide are added to an aliquot of the ozone solution at pH 2.0, much more iodine is liberated than when a second aliquot of the solution is first adjusted to pH 7.0 and iodide is added. Also, more iodine is produced at pH 7.0 than at pH 9.0. The solution with iodide at pH 9.0 liberated an amount of iodine equivalent to the amount of ferrous ion oxidized to the ferric ion at pH 2.0. This agrees with the observations of Manley (11). Observation of the ozone and iodide equation indicated that the newly liberated oxygen or some intermediary substance might be responsible for the increasing iodine as the hydrogen ion concentration increases. An experiment was designed to determine the difference in the concentration of dissolved oxygen after the reaction of ozone with iodide at pH 2.0 and 9.0... 

Pathway 1 (eq 6a) shows no oxygen-atom transfer and the production of r, as discussed for the H202 reaction (eq 3). The I+ can form a variety of products, in particular I2 from excess T as discussed for the H202 reaction. The [I-03] intermediate should break down to oxygen and hydroxide on H20 and anion attack. The reaction of ozone with iodide to form I2 is quantitative in the presence of excess T and can be used for the analysis of ozone (43). In seawater this process seems less likely to occur because I" is a trace constituent. 

Because 03 does not penetrate the ocean microlayer from the atmosphere, its reactions are significant only in the microlayer. The reaction of iodide with ozone has been documented at the surface microlayer of the ocean... 

---