Ozone with double bonds containing

The Interaction of Ozone with Double Bonds Containing Vinyl Bromide Moieties... 

The compound B formed must be, then, either a tertiary amine or an alkene. Its molecular formula does not contain "N (for nitrogen), which means it must be an alkene. In addition, the fact that B was cleaved into two products by ozone, acid, and zinc indicates the present of a double bond, for these reagents are the basis for the ozonolysis reaction, which cleaves compounds with double bonds into aldehydes and ketones. 

Ozone cracking is a physicochemical phenomenon. Ozone attack on olefinic double bonds causes chain scission and the formation of decomposition products. The first step in the reaction is the formation of a relatively unstable primary ozonide, which cleaves to an aldehyde or ketone and a carbonyl. Subsequent recombination of the aldehyde and the carbonyl groups produces a second ozonide [58]. Cross-linking products may also be formed, especially with rubbers containing disubstituted carbon-carbon double bonds (e.g. butyl rubber, styrene-butadiene rubber), due to the attack of the carbonyl groups (produced by cleavage of primary ozonides) on the rubber carbon-carbon double bonds. 

Based on these considerations, Croft prepared six formulations containing various combinations of NBR and NBR/PVC with CR and SBR and measured their oil, heat and ozone resistance, physical properties, and adhesion characteristics. Whereas the physicals are satisfactory for aU compounds, formulations based on NBR, NBR/PVC with CR performed better on heat and oil aging than the compounds containing SBR as shown in Tables 11.6 and 11.7. However, the adhesion is better with the latter compounds. It has been suggested that cuprous sulfide formed on the wire surface interacts with the double bond in SBR to provide the improvement in adhesion. 

The reaction of ozone with olefinic compounds is very rapid. Substiments on the double bond, which donate electrons, increase the rate of reaction, while electron-withdrawing substituents slow the reaction down. Thus, the rate of reaction with ozone decreases as follows polyisoprene > polybutadiene > polychloroprene [48]. The effect of substiments on the double bond is clearly demonstrated in Tables 15.2 and 15.3. Rubbers that contain only pendant double bonds such as EPDM do not cleave since the double bond is not in the polymer backbone. 

Since the main chain of NR contains unsaturation (residual double bonds) it, along with other unsaturated rubbers, is susceptible to attack by oxygen, ozone and light, and compounds therefore require protection against these agencies. 

Treatment of polyisobutylene (which contains terminal double bonds) with ozone followed by thermolysis produces polymeric radicals. Isobutylene-styrene block copolymer is formed when thermolysis is performed in the presence of styrene, but the process is not efficient because polystyrene and polyisobutylene homopolymers constitute more than half of the product [Cunliffe et al., 2001]. 

Ozone reacts with organics, attacking most kinds of double bonds. It reacts with ethylene forming ethylene ozonide, a cyclic compound containing three oxygen atoms ... 

The concentration of aqueous ozone can be determined by the decolorization of indigo trisulfate (X = 600 nm). The method is stoichiometric and extremely fast. The indigo molecule contains only one C = C double bond which can be expected to react with ozone directly and with a very high reaction rate (see Figure 2-7). 

Low-density lipids in the blood cause cholesterol deposits. Their presence and nature, including the position and number of double bonds, can be analyzed by means of ESI-MS techniques <2000JMP224>. Reverse-phase HPLC microsamples containing phospholipids were treated with bis(trimethylsilyl) trifluoroacetamide, then with methoxy-amine, and then exposed for 8 min to ozone gas at room temperature ESI-MS followed and showed the fragments corresponding to ozonides. 

Fig. 17.32. Oxidative cleavage of an asymmetric ketone with complementary regiose-lectivities. Lactone A is obtained by Baeyer-Villiger oxidation of menthone [2-methyl-5-(l- methylethyl)cyclo-hexanone]. Alternatively, one may first convert menthone into the silylenol ether B and cleave its C=C double bond with ozone to obtain a silyl ester containing an a-methoxyhydroperoxide group as a second functional group (which resembles the unstable structural element of the so-called ether peroxides cf. Figure 1.38). The latter is reduced with NaBH4tothe hydroxylated silyl ester C. The hydroxycarboxylic acid is obtained by acid-catalyzed hydrolysis. It cyclizes spontaneously to give lactone D.

Work on the pyridine-modified ozonization of tetramethylethylene showed that pyridine oxide is not-a product of ozonization (8). Most of the pyridine (— 90% ) remains unchanged during double bond cleavage. Only one mole of acetone, rather than two, is formed for each mole of olefin oxidized. Other work with a disubstituted olefin, trans-4-octene, showed that ozonides are formed in the reaction so that the reaction of pyridine with ozonide to form acid and aldehyde cannot occur (9). An NMR study of trans-4-octene ozonolysis in the presence of pyridine using 1,2-dichloroethane as the solvent shows that aldehyde and hydroxyl-containing material (carboxylic acid, peracid, and other OH species) are formed directly during double bond cleavage. 

Under somewhat milder conditions (200°C), the reaction does not proceed as far as removing the functional groups, and the result is merely the hydrogenation of multiple bonds [38,39]. This is an efficient means of structure elucidation, especially when combined with ozonolysis [40,41 ] to establish the locations of multiple bonds in the molecule. In ozonolysis the substance supposed to contain a double bond is dissolved in CS2, ozonized at about —70°C and the ozonide is reduced with triphenylphosphine to produce aldehydes and/or ketones characteristic of the moieties linked by the double bond. 

Another of the important uses of ozone is in reactions with many organic compounds, especially those containing double bonds,... 

---