Ozonides with hydrogen peroxide

Perfluoroalkyl ethylene, CF3(CF2CF2) CH=CH2, obtained by dehalogena-tion of perfluoroalkylethyl iodide, is treated with ozone to give ozonides. Oxidative cleavage of the ozonides with hydrogen peroxide yields perfluoroalkanoic acids [132]. 

The hydrogenolysis of 0-0 linkages is involved in the hydrogenation of peroxides, hydroperoxides, and ozonides. Decomposition may occur catalytically in the absence of hydrogen, as was observed in as early as 1818 by Thenard with hydrogen peroxide in the presence of platinum. 

The oxidative cleavage of ozonides to carboxylic acids is achieved with hydrogen peroxide in sodium hydroxide solution [97], in formic acid... 

The oxidative decomposition of ozonides is further accomplished by their treatment with hydrogen peroxide [97] in the presence of formic acid [95, 99] or acetic acid [102, 103] or with silver oxide and nitric acid [77] (equations 109-112). 

Conjugated dienes (and compounds that behave like conjugated dienes in the Diels-Alder reaction) react with singlet oxygen to form cyclic peroxides as if molecular oxygen acted as a dienophile. The yields of the peroxides, prepared by photochemical oxidation [13, 55] or by chemical oxidations with hydrogen peroxide and sodium hypochlorite, alkaline hydrogen peroxide and bromine, alkaline salts of peroxy acids [14, 26], or the ozonide of triphenyl phosphite [29], are comparable. 

Better yields are often obtained when ozone is used for oxidative cleavage of olefins to carboxylic acids or of cycloalkenes to dicarboxylic acids. Olefinic double bonds are very much more easily attacked by ozone than are aromatic systems, so that arylethylene derivatives can be successfully treated with ozone without appreciable effect on the ring. If the ozonide which is formed initially is decomposed with water, the aldehyde is obtained together with hydrogen peroxide and other products ... 

Fig. 8.3 Ozonolysis allows the cleavage of alkene double bonds. According to the Criegee mechanism the primary ozonide (POZ) is rapidly transformed into the more stable secondary ozonide (SOZ). Depending on the work-up, different products may be isolated. Oxidative work-up with hydrogen peroxide leads to carboxylic acids/ketones, while reductive work-up with either dimethyl sulfide or sodium borohydride gives aldehydes/ketones or alcohols, respectively...

Determination of ozone in aqueous solution is perhaps the most problematic for a variety of reasons (1) ozone is unstable (2) ozone is volatile and easily lost from solution and (3) ozone reacts with many organic compounds to form products such as ozonides and hydrogen peroxide that are also good oxidants. Careful study of the use of iodometric methods for the determination of ozone in aqueous solution has revealed that the stoichiometric ratio of ozone reacted with iodine produced in the reaction varies from 0.65 to 1.5, depending on pFI, buffer composition and concentration, iodide ion concentration, and other reaction conditions. As a result, iodometric methods are not recommended. Ozone can be determined iodimetrically by addition of an excess of a standard solution of As(III), followed by titration of the excess As(III) with a standard solution of iodine to a starch endpoint. Methods using DPD, syringaldazine, and amperometric titrations have also been developed. 

If the focus is on the C=C unit of 2,3-dimethyl-2-butene, the dipolar addition reaction cleaves the first bond (the n-bond), and the rearrangement of the 1,2,3-trioxolane to the 1,2,4-trioxolane cleaves the second bond (the c-bond). The conversion of an alkene to an ozonide is known as ozonolysis, and it is an example of an oxidative cleavage reaction. The ozonide is usually not isolated, but a second chemical step is performed in the same flask. When treated with hydrogen peroxide, the products of this reaction are 2-propanone (acetone) and a second molecule of acetone. This statement is phrased this way because an unsymmetrical alkene will give two different ketones. In effect, the C=C unit is cleaved and each carbon is oxidized to a C=0 unit. The mechanism described for this reaction is consistent with known chemistry of ketones and aldehydes and other carbonyl-bearing functional groups. A full discussion of carbonyl chemistry will be presented in Chapters 17 and 19. 

Reaction of an alkene with ozone leads to a 1,2,3-trioxolane, which rearranges to a 1,2,4-trioxolane (an ozonide). Subsequent treatment with hydrogen peroxide or with dimethyl sulfide leads to an aldehyde, ketone, or carboxylic acid product. When an ozonide contains a C-H unit, oxidation with hydrogen peroxide leads to a carboxylic acid, but reaction with dimethyl sulfide leads to an aldehyde 51, 52, 53, 54, 78,82,83,117. 

Oxidative cleavage of an alkene with ozone leads to an ozonide. Reductive workup with dimethyl sulfoxide or zinc and acetic acid gives ketones and/or aldehydes. Oxidative workup with hydrogen peroxide gives ketones and/or carboxylic acids. Oxidative cleavage of 1,2-diols with periodic acid or with lead tetraacetate gives aldehydes or ketones. 

Write out the 1,2,3-trioxolane and ozonide expected when cyclohexene reacts with ozone. Write out the reaction and name the final product formed when that ozonide reacts with hydrogen peroxide. 

Oxidation of the ozonides, usually with hydrogen peroxide (H2O2), leads either to ketones or carboxylic acids (see Fig. 10.24). The structure of the product again depends on the structure of the ozonide, which itself depends on the structure of the original alkene (Fig. 10.59). 

Aldehydes are easily oxidized to carboxylic acids under conditions of ozonide hydroly SIS When one wishes to isolate the aldehyde itself a reducing agent such as zinc is included during the hydrolysis step Zinc reduces the ozonide and reacts with any oxi dants present (excess ozone and hydrogen peroxide) to prevent them from oxidizing any aldehyde formed An alternative more modem technique follows ozone treatment of the alkene m methanol with reduction by dimethyl sulfide (CH3SCH3)... 

Oxygen Compounds. Although hydrogen peroxide is unreactive toward ozone at room temperature, hydroperoxyl ion reacts rapidly (39). The ozonide ion, after protonation, decomposes to hydroxyl radicals and oxygen. Hydroxyl ions react at a moderate rate with ozone (k = 70). 

There is some information concerning the reaction of ozone with chemicals under aqueous conditions. The information available suggests that double-bond cleavage takes place, just as it does under nonaqueous conditions, except that ozonides are not formed. Instead, the zwitterionk intermediate reacts with water, producing an aldehyde and hydrogen peroxide. In addition to double-bond cleavage, a number of other oxidations are possible. Mudd et showed that the susceptibility of amino acids is in the order cysteine, tryptophan, methionine. 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

Acid-catalyzed condensation of bicyclic ozonides with aldehydes and ketones, in the presence of hydrogen peroxide, leads to the formation of bicyclic peroxide analogs of acetals in low yields, as shown in equation 91 for the condensation of the ozonide of 1-phenylcyclopentene (266) with benzaldehyde. The structure of compound 267, with the preferred ring conformation as shown, was determined by XRD analysis . The same method served to demonstrate that the condensation compound 16c is unique, with structure 254 . 

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