Ozone reaction with bromide

The enol acetate 77 of 3,4-dihydro-7-methoxy-5-methyl-l-(2l/)-naphthalenone was converted to the acid 78 by ozonolysis and hydrolysis and this by a Wittig reaction with a-methoxyethyltriphenyl-phosphonium chloride gave 79. Compound 79 was converted into 80 by a series of reactions, five in number, which in turn was converted into 81 by reaction with potassium in -butanol. The methyl ester of compound 81, one isomer of which was recognized as that having the correct stereo structure, was converted to 82 by heating with acetic anhydride and 10-camphorsulfonic acid. Subsequent steps involved ozonization, reaction with V,iV -carbonyldiimidazole, lactam formation, reaction with pyridinium bromide perbromide, reaction with sodium hydride, and a further series in which (+ )-oxodendrobine (83) was ultimately obtained. Reduction of the latter to ( )-dendrobine... 

This dry ozonation procedure is a general method for hydrox-ylation of tertiary carbon atoms in saturated compounds (Table 1). The substitution reaction occurs with predominant retention of configuration. Thus cis-decalin gives the cis-l-decalol, whereas cis- and frans-l,4-dimethylcyclohexane afford cis- and trans-1,4-dimethylcyclohexanol, respectively. The amount of epimeric alcohol formed in these ozonation reactions is usually less than 1%. The tertiary alcohols may be further oxidized to diols by repeating the ozonation however, the yields in these reactions are poorer. For instance, 1-adamantanol is oxidized to 1,3-adamantane-diol in 43% yield. Secondary alcohols are converted to the corresponding ketone. This method has been employed for the hydroxylation of tertiary positions in saturated acetates and bromides. 

Multiple-stage ozonization seems to be more effective than single-stage ozonization, both followed by biodegradation, for DOC ehmination in treatment of reservoir waters and secondary effluents of a domestic wastewater treatment plant . The fate of O3 in water ozonization consists of a fast reaction with the DOC and a slow first-order decay of unreacted O3. A method for optimization of a two-stage water ozonization process is based on control with a FIA unit, where the ozone concentration is continuously measured by oxidation of indigotrisulfonate(8) . The various fractions of DOC (in the ppm range) may react with the traces of bromide (sub-ppm) found in natural waters, as this anion... 

The 2,3-dihydrobenzo[6]selenophene (113) yields the oxide (114) on treatment with ozone. The oxide may be ring opened by treatment with sodium hydride and the product of the ring opening can be alkylated by reaction with benzyl bromide. Thermal rearrangement of the oxide yields a 15 85 mixture of compounds (115) and (116) (Scheme 15) (76JOC2503). 

For GC analysis, the salts of the lowest molecular weight acids present in ozonation products subjected to base-promoted hydrolysis have been converted to their benzyl esters by reaction with benzyl bromide (Bonnet et al. 1989). The salts of all acids produced have commonly been converted to the free acids, usually with the aid of a cation exchange resin. The acids have then been converted to methyl esters by reaction with diazomethane (Bonnet et al. 1989) or, more often, have been converted to trimethylsilyl (TMS) esters (Matsumoto et al. 1986, Taneda et al. 1989, Habu et al. 1990). Trimethylsilylation has the major advantage that alcoholic and phenolic hydroxyl groups are simultaneously converted to TMS ethers, thus greatly facilitating GC analysis. 

The Role of Oxygen. To define properly the role which 02 played in these ozonolysis reactions, nitrogen was occasionally used as the carrier gas for ozone. After ozonizing n-hexylmercuric bromide at 10°C with the usual 03—02 mixture, the reaction was repeated with 03—N2 (see Experimental). By comparing the reaction products from runs 6 and 7 (Table I), it can be readily seen that no product differences exist when N2 is substituted for 02. 

Greenwood91,92 demonstrated the formation of primary ozonides in the reaction of some reaction with liquid ozone gave products that formed glycols on mild reduction with isopropylmagnesium bromide. On the other hand, primary ozonides have not been detected with certainty in the case of cis-olefins.88 91 The reaction of cis-3-hexene,93 eis-2-butene, cis-2-pentene, and ethylene92 with ozone at —112° in pentane led to extremely explosive substances, which could be primary ozonides. In the... 

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. 

Theoretical considerations, the reference of Inglis (6), and the recommendations of Manley (11) suggested that the reaction of ozone with bromide at pH 2.0 be studied. The analytical scheme using bromide ion is based on the addition of potassium bromide to ozonated solutions at pH 2 followed by the addition of potassium iodide to reduce the bromine liberated by the ozone. 

Bromine is potentially able to interact with stratospheric ozone in the same manner as chlorine (Wofsy et al., 1975). The catalytic cycle for bromine is expected to be quite efficient, because its reaction with methane is slower than that of Cl atoms in addition, the reaction of OH with HBr is faster than that of OH with HC1. The major bromine compound in the troposphere is methyl bromide, which has a natural origin and occurs with a mixing ratio of about 10 pptv (see Table 6-14). This seems small enough to neglect bromine to a first approximation. 

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