Ozonolysis Techniques

The oxidation of double bonds in organic compounds and polymers in a non-aqueous solvent leads to the formation of ozonides which, when acted upon hy water, are 

Triphenyl phosphine is frequently used to assist this reaction. When applied to complex unsaturated organic molecules or polymers, this reaction has great potential for the elucidation of the microstructure of the unsaturation. Examination of the reaction products, for example by conversion of the carbonyl compounds to carboxylates then esters followed by gas chromatography (GC), enables identification of these products. 

An example of the value of the application of this technique to a polymer structural problem is the distinction between polybutadiene made up of consecutive 1,4-1,4 butadiene sequences (I), and polybutadiene made up of alternating 1,4 and 1,2 butadiene sequences (II), i.e., 1,4-1,2-1,4  

Upon ozonolysis, followed by hydrolysis, these in the case of 1,4-1,4 sequences produce succinaldehyde (CHO-CH2-CH2CHO) and in the case of 1,4-1,2-1,4 sequences produce formyl 1,6-hexane-dial  

Analysis of the reaction product for concentrations of succinaldehyde and 3-formyl-1,6-hexane-dial can showwhether the polymer is 1,4-1,4 or 1,4-1,2-1,4, or whether it contains both types of sequence. 

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Oxidation of alkenes with ozone followed by cleavage of the resulting ozonides to carbonyl compounds is widely used for the determination of structure of unsaturated compounds. The ozonolysis technique is described in detail in Section 2.17.4, p. 103. 

There are some interesting examples of selective ozonolysis in the terpene field. Limonene is ozonized at the 8,9- double bond in preference to the 1- double bond. This is indicated by the fact that the amount of formaldehyde found is almost equal to the amount of ozone introduced, up to 1 mole. In like manner, terpinolene yields acetone in an amount nearly equal to the ozone passed, up to 1 mole. -Pinene should add ozone readily and form formaldehyde and nopinone on ozonolysis. Practically none of these products can be obtained by ordinary ozonolysis techniques. The hydrogens alpha to the double bond, with probable additional activation from the general strain of the system, are so active to peroxidation by oxygen that little ozonide is formed, because of the large excess of oxygen present. 

Although the full significance of the reactions of ozone with diene rubbers was not to be appreciated until the mid-1940s its importance was recognized in part, by the early years of this century, with the ozonolysis techniques developed by Harries (see Chapters 1 and 2). Subsequently the reactions between olefins and ozone were studied by various workers and much of the experimental data obtained can be accounted for by a series of mechanisms proposed by Criegee (1951, 1954, 1955). The essential proposals are summarized below. 

Bromination appears to involve substitution rather than addition. Baldwin and Kuntz (I960) report that bromination of butyl rubber with elemental bromine is accompanied by the formation of large amounts of HBr. Using ozonolysis techniques it was found that unsaturation did not greatly change with bromination. It has thus been inferred (Makowski, 1%9) that the reaction proceeds by a free radical allylic substitution rather than by an ionic mechanism, e.g. 

The amount of 1,4-1,2-1,4 sequences in polybutadienes can be estimated from the amounts of the different ozonolysis products (Table 5.5) if one considers the amount of 1,4 structure not detected. Because the ozonolysis technique cleaves the centre of a butadiene monomer unit, one-half of a 1,4 unit remains attached to each end of a block of 1,2 units after ozonolysis these structures do not elute from the gas chromatographic column. Using random copolymer theory, the maximum amounts of these undetected 1,4 structures can then be calculated. Tanaka and coworkers [28] also discussed the determination by ozonolysis of 1,2 butadiene units in polybutadiene. 

A further example concerns the application of the ozonolysis technique to butadiene-propylene copolymers [153,158-160]. Samples of highly alternating copolymers of butadiene and propylene yielded large amounts of 3-methyl-l,6-hexane-dial when submitted to ozonolysis. The ozonolysis product from 4-methyl-cyclohexane-l (i.e., 3-methyl-l,6 hexane-dial ... 

The structure and carbon chain distribution of sodium vinylidenesulfonate (VOS) has been investigated by Hashimoto et al. [119] using NMR, IR, and chromatographic techniques. The double-bond distribution of VOS was determined using ozonolysis-reduction-GLC. The position of the sulfonic acid groups... 

There is a simple technique for drawing the products of an ozonolysis just split up each C=C bond into two C=0 bonds. Let s see an example of how this works ... 

Segal-Rosenheimer M, Dubowski Y (2007) Heterogeneous ozonolysis of cypermethrin using real-time monitoring FTIR techniques. J Phys Chem C 111 11682-11691... 

Unsaturated acids may be split chemically at their double bonds. Permanganate-periodate oxidation has been used to produce the corresponding carboxylic acids, while an alternative technique of ozonolysis results in the formation of aldehydes and aldehyde esters. All these reaction products may be identified by GLC and the information used to determine the position of the double bond in the original fatty acid. 

On an exam you may be asked to determine the structural formula of the starting alkene given the ozonolysis products. A useful technique is to work backward from the products of ozonolysis. By cutting off the oxygens and then combining the two pieces, you get the starting alkene. 

The reaction of alkenes with ozone constitutes an important method of cleaving carbon-carbon double bonds.138 Application of low-temperature spectroscopic techniques has provided information about the rather unstable species that are intermediates in the ozonolysis process. These studies, along with isotope labeling results, have provided an understanding of the reaction mechanism.139 The two key intermediates in ozonolysis are the 1,2,3-trioxolane, or initial ozonide, and the 1,2,4-trioxolane, or ozonide. The first step of the reaction is a cycloaddition to give the 1,2,3-trioxolane. This is followed by a fragmentation and recombination to give the isomeric 1,2,4-trioxolane. The first step is a... 

Novel practical methods using various reagents, such as [Co(OAc)Br],1355 sulfur trioxide,1356 or ds-dioxoruthenium complexes,1357 were developed to transform alkynes to 1,2-diketones. Radical-catalyzed aerobic oxidation using A-hydro-xyphthalimide combined with a transition metal (Co, Cu, or Mn) affords a,P-acetylenic ketones in good yields.1358 Oxidation by the HOF. acetonitrile complex yields diketones, ketoepoxides, or cleavage products.1359 Ozonolysis of acetylenes combined with trapping techniques affords to isolate various derivatives.1360,1361 New information for the ozonolysis of acetylene was acquired by quantum-chemical investigatons.1362... 

The selectivity of the ozone reaction in pure solvent or water-solvent systems is known from early studies conducted by chemists under analytical and preparative aspects (Bailey, 1958). Inert solvents (e. g. pentane, carbon tetrachloride) provide an opportunity to produce and study oxidation products of the ozonolysis, such as ozonides at low temperatures (Criegee, 1975). Only in the last two decades have ozonation techniques been developed and studied that utilize the higher ozone solubility, enhanced mass transfer rates, higher reaction rates etc. to be found in water-solvent systems. 

Different solid-phase techniques for the synthesis of C-terminal peptide aldehydes have gained much attention and allowed greater accessibility to such compounds. Solid-phase techniques have been used to synthesize peptide aldehydes from semicarbazones, Weinreb amides, phenyl esters, acetals, and a, 3-unsaturated y-amino acids)47-50,60 63 The examples presented below use unique linkers to enhance the automated efficiency of C-terminal peptide aldehyde synthesis)47 For instance, the reduction of phenyl esters led to the aldehyde as the major product, but also a small amount of alcohol)50 The cleavage of u,p-unsaturated y-amino acids via ozonolysis yielded enantiomeric pure C-terminal peptides)49,61 The semicarbazone from reduction of peptide esters technique laid the initial foundation for solid-phase synthesis. Overall, Weinreb reduction is an ideal choice due to its high yields, optical purity, and its adaptability to a solid-phase platform)47 ... 

A solid-phase technique that uses an N-protected u,p-unsaturated y-amino acid proved to be effective for ozonolysis due to its ethylenic functionality. The linker was prepared from the Wittig reaction between (ethoxycarbonylethylene)triphenylphosphorane and either the Boc or Fmoc N-protected a-amino aldehyde. The Boc or Fmoc protecting group was removed and the chain was elongated by standard BOP coupling 49,52 53 61 The peptide-resin was then cleaved by ozonolysis, which afforded the desired aldehyde 49 ... 

In a follow up full publication to the work above, Harrison et al. showed that using porous thin films as described above, pattern transfer could be accomplished in both Si and Ge substrates as well [23]. While an entire three-inch Si wafer was patterned using this technique, practical limitations, such as in etch anisotropy, were reported. In this paper, an effective technique for confirming porosity in these films was demonstrated. After ozonolysis of these thin films, an overlayer of PS remained at the surface of these porous samples. By using a low power CF4 RIE followed by periodic SEM analysis, this layer could be slowly etched to reveal thus revealing the cylindrical pores (now observed as trenches). Also, the authors showed that the low power CF4 etch did not result in significant surface roughness. 

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