Ozone with alkynes

The reactions of ozone with alkynes are essentially slower than those with alkenes. This is shown by the values of rate constants, which are lower in the case of alkynes due to the higher activation energy. Alkanes react very slowly with O3 and thus, they are unimportant in atmospheric processes. 

Olefins with hindered double bonds may be transformed stereospecifically to oxiranes by treatment with ozone. The epoxidation of propylene has been achieved with alkoxyalkyl-hydroperoxides obtained by the ozonization of olefins in the presence of alcohol.The yield depends on whether the alcohol is a primary, secondary, or tertiary one. The low-temperature (—70°) epoxidation of olefins with a yield of about 30% has been performed with electrophilic intermediates produced in the course of the ozonization of alkynes these intermediates are probably five-membered cyclic trioxides. This epoxidation is almost totally stereospecific. 

Ozonation of Alkynes. Reactions of alkynes with ozone afford either carboxylic acids or, if reductive procedures are used, a-dicarbony 1 compounds. For the production of carboxylic acids, MeOH has been shown to be superior to CH2CI2 as reaction solvent. As with alkenes, a number of reducing agents can be used to produce a-dicarbonyl compounds. An easy option which results in high yields of a-dicarbonyl compounds involves the addition of Tetracyanoethylene directly to an ozonation reaction mixture as an in situ reducing agent (eq 16). ... 

Oxygenated alkynes also can be ozonated. The reaction of ozone with alkynyl ethers followed by reductive workup provides a convenient method for the production of a-keto esters in moderate yields (eq 19). ... 

R is hydrogen, alkenyl, or alkyne. In remote tropospheric air where NO concentrations ate sometimes quite low, HO2 radicals can react with ozone (HO2 + O3 — HO + 2 O2) and result in net ozone destmction rather than formation. The ambient ozone concentration depends on cloud cover, time of day and year, and geographical location. 

Alkynes, like alkenes, can be cleaved by reaction with powerful oxidizing agents such as ozone or KMnC, although the reaction is of little value and we mention it only for completeness. A triple bond is generally less reactive than a double bond and yields of cleavage products are sometimes low. The products obtained from cleavage of an internal alkyne are carboxylic acids from a terminal alkyne, CO2 is formed as one product. 

Treating alkynes with ozone or with basic potassium permanganate leads to... 

Further chemistry of alkenes and alkynes is described in this chapter, with emphasis on addition reactions that lead to reduction and oxidation of carbon-carbon multiple bonds. First we explain what is meant by the terms reduction and oxidation as applied to carbon compounds. Then we emphasize hydrogenation, which is reduction through addition of hydrogen, and oxidative addition reactions with reagents such as ozone, peroxides, permanganate, and osmium tetroxide. We conclude with a section on the special nature of 1-alkynes— their acidic behavior and how the conjugate bases of alkynes can be used in synthesis to form carbon-carbon bonds. 

Ozonium Ion (H03+). Ozone is a resonance hybrid of canonical structures 50a-50d.135 Ozone does in fact act as a 1,3-dipole—that is, either as an electrophile or a nucleophile. The electrophilic nature of ozone has been recognized for a long time in its reactions with alkenes, alkynes, arenes, amines, phosphines,... 

B-5. Which alkyne yields butanoic acid (CH3CH2CH2C02H) as the only organic product on treatment with ozone followed by hydrolysis ... 

The mechanism and kinetics of the atmospheric oxidation of alkynes, initiated by OH radicals, have been studied particularly to determine the role of alkyne oxidation in tropospheric ozone formation. A general mechanism for OH-initiated oxidation of alkynes has been developed with the aid of thermodynamic calculations. In general, the significance of atmospheric alkynes to the formation of tropospheric ozone was found to be smaller than for alkanes and alkenes, due to the absence of the hydroxy peroxy-forming product channel in the OH-initiated atmospheric oxidation of alkynes.227... 

Both internal and terminal alkynes are oxidatively cleaved with ozone to give carboxylic acids. 

I2 DMSO, " MeRe03/H202, " as well as by electrooxida-A ruthenium complex with a small amount of trifluoroacetic acid converts internal alkynes to the a-diketone. Ozone generally oxidizes triple-bond compounds to carboxyhc acids (19-9), but a-diketones are sometimes obtained instead. Selenium dioxide (Se02) with a small amount of H2SO4 oxidizes alkynes to a-diketones as well as arylacetylenes to a-keto acids (ArC=CH ArCOCOOH). " ... 

Many combinations of atoms are conceivable, among them azides, nitrones, nitrile oxides, and ozone. As these systems have four tt electrons, they are analogous to dienes, and cycloadditions with alkenes and alkynes are allowed [4 + 2] reactions. These are discussed in Section 10.3. 

Applications of tetracyanoethylene have been reviewed recent information on molecular complexes, ozonization of alkenes and alkynes (the Criegee reaction), and reactions with ketones is included. Dicyanoketene has been prepared in situ from 2,5-diazido-3,6-dicyano- and 2,6-diazido-3,5-dicyano-l,... 

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