Ozonolysis compared

Conceptually closely related, cefroxadi ne (40) can be prepared by several routes, including one in which the enol (33) is imethylated with diazomethane as a key step. A rather more involved route starts with comparatively readily available phenoxymethylpenicillin sulfoxide benzhydryl ester (36). This undergoes fragmentation when treated with benzothiazole-2-thiol to give Ozonolysis (reductive work-up) cleaves the... 

The glass reaction vessel is equipped with a light source, photocell, and 550-nm filter to detect the indicator color change (red to pale yellow). The signal from the photocell is continuously monitored using a strip recorder. Quantification is obtained by comparison of the time required for ozonolysis of the sample compared to that required for a pure compound with known saturation. 

Compound 4 was epoxidized to give 15 (Scheme 3) and the MS fragmentation of 15 is given by the broken-line mlz (relative abundance). To ensure the location of the double bonds, the epoxidation and the MS of 15 was compared with the products of the ozonolysis identified by GC and MS (as marked by the broken lines)6. The use of the various derivatization products via oxidation, combined with other spectroscopic methods, is discussed in Section III. 

The UV/ozone process destroyed about 75% of the influent anthracene within about 2 min. The degradation rate was generally steady for about the first minute of treatment but decreased somewhat thereafter, perhaps indicating the buildup of scavengers reacting with hydroxyl radicals. The UV / ozone process decelerates the chemical reaction of the ozonolysis of anthracene with molecular ozone as compared with ozone treatment alone (Trapido et al., 1995). 

The structure of neodeoxyvomicine (CCL) follows from (a) the failure of ozonolysis to give any acetaldehyde, (b) the low pXa of 5.16, as compared with the high value of 7.4 for deoxyvomicine, (c) the resistance of Nb to quaternization. These three pieces of evidence support the presence of a double bond in the neo position. The position of the other double bond is given by the failure of neodeoxyvomicine to form a benzylidene derivative and by the UV-spectrum, which is similar to that of N-crotonyl-O-aminophenol (CCLIII) (201). 

Ozonolysis of Tetramethylene and cis-3,4-Dimethyl- 3 -hexene. A solution of tetramethylethylene (0.503 gram, 5.98 mmoles) and cis-3,4-dimethyl-3-hexene (0.692 gram, 6.17 mmoles) in 20 ml pentane was ozonized to 63% theoretical yield at —40°C. The product mixture was analyzed by GPC using an 8-ft 10% XF-1150 column at 85°C and a flow rate of 150 ml/minute. The mixture contained 25 mg acetone diperoxide, 36.7 mg l,l,4-trimethyl-4-ethyl-2,3,5,6-tetraoxacyclohexane, and 23.2 mg methyl ethyl ketone diperoxide as determined by GPC using an internal standard. Total yield of diperoxides was 14%. The diperoxides were identified by comparing mp, infrared, NMR, and GPC data with those of authentic samples. 

The total yield of diperoxides obtained is usually low. Presumably most of the available zwitterions end up as polymeric peroxides. In the ozonolysis of 7 and 8, for example, the total yield of diperoxides is 17.4%. The diperoxides were obtained in the ratio of 1 1.35 0.78 for 9 10 11 as compared with the statistically predicted ratio of 1 2 1. 

Ozonolysis Procedure. Ten ml of olefin solution were ozonized at 0°C with an oxygen-ozone mixture. The ozone concentration was sufficiently high 4% ) to make the ozonolyses possible with relatively low 02-03 flow rates ( 0.15 mmole 03/min) in order to prevent olefin loss by evaporation. Control experiments, performed with pure 02, indicated that no appreciable amount of olefin is lost by bubbling the gas in the olefin solution in time intervals comparable with those required for the actual experiments. 

Such a reaction course has indeed been verified by independent experiments. Upon treatment of acetyl bromide with ozone under conditions that were comparable with those used in the ozonolysis of the dibromo-... 

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. 

Another potential dark source of in the atmosphere, more particularly in the boundary layer, is from the reactions between ozone and alkenes. The ozonolysis of alkenes can lead to the direct production of the OH radical at varying yields (between 7 and 100%) depending on the structure of the alkene, normally accompanied by the co-production of an (organic) peroxy radical. As compared to both the reactions of OH and NO3 with alkenes the initial rate of the reaction of ozone with an alkene is relatively slow, this can be olfset under regimes where there are high concentrations of alkenes and/or ozone. For example, under typical rural conditions the atmospheric lifetimes for the reaction of ethene with OH, O3 and NO3 are 20 h, 9.7 days and 5.2 months, respectively in contrast, for the same reactants with 2-methyl-2-butene the atmospheric lifetimes are 2.0 h, 0.9 h and 0.09 h. 

Oxidation of Propylene by Ozone. Hydrocarbon ozonolysis is important in smog chemistry, but the details of this ozone chemistry are still poorly understood despite numerous investigations 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56). However, the ozonolysis of propylene is fairly well established as compared with the ozonolysis of internally bonded olefins. For example, the rate constant for propylene is uncertain by about 10% while for trans-2-hutene the reported rate constants vary by an order of magnitude 48, 49, 52, 55). This provided another reason to choose propylene as the prototype hydrocarbon in this analysis. 

Figure 5. Effect of ozonolysis. A calculation with = 0 (dashed lines) is compared with the reference calculation, ...

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