Ozonolysis of alkynes

When treated with ozone followed by water, alkynes undergo oxidative cleavage to produce 

When a terminal alkyne undergoes oxidative cleavage, the terminal side is converted into carbon dioxide  

Decades ago, chemists used oxidative cleavage to help with structural determinations. An unknown alkyne would be treated with ozone followed by water, and the resulting carboxyUc acids would be identified. This technique allowed chemists to identify the location of a triple bond in an unknown alkyne. However, the advent of spectroscopic methods (Chapters 15 and 16) has rendered this process obsolete as a tool for structural determination. 

25 Draw the major products that are expected when each of the following alkynes is treated with O3 followed by H2O  

26 An alkyne with molecular formula C6H10 was treated with ozone followed by water to produce only one type of carboxylic acid. Draw the structure of the starting alkyne and the product of ozonolysis. 

Carboxylic acids are produced when alkynes are subjected to ozonolysis. 

Ozonolysis is sometimes used as a tool in structure determination. By identifying the carboxylic acids produced, we can deduce the structure of the alkyne. As with many other chemical methods of structure determination, however, it has been superseded by spectroscopic methods. 

PROBLEM 9.16 A certain hydrocarbon had the molecular formula C16H26 and contained two triple bonds. Ozonolysis gave CH3(CH2)4C02H and HO2CCH2CH2CO2H as the only products. Suggest a reasonable structure for this hydrocarbon. 

Section 9.1 Alkynes are hydrocarbons that contain a carbon-carbon triple bond. Simple alkynes having no other functional groups or rings have the general formula C H2 2- Acetylene is the simplest alkyne. 

Section 9.2 Alkynes are named in much the same way as aUcenes, using the suffix -yne instead of -ene. 

Recall that when carbonic acid is formed as a reaction product, it dissociates to carbon dioxide and water. 

Some Things That Can Be Made from Acetylene. . . But Aren t 

Acetylene had several uses around the time of World War I, primarily because it burned with a hot, luminous flame. The oxyacetylene torch and automobile and bicycle headlamps made by the Prest-O-Lite Company are representative of this period. 

In an attempt to find a route to acetylene other than from calcium carbide, Prest-O-Lite sponsored research carried out by George 0. Curme at Pittsburgh s Mellon Institute. Curme s research, which was directed toward converting the gases produced during petroleum refining to acetylene, led to methods better suited for making ethylene than acetylene. Viewed from our present perspective, Curme s petroleum-based 

What about acetylene Based on the reactions described in this chapter we can vi/rite the following equations, all of which lead to useful compounds. 

In fact, very little of each of these products is made from acetylene. Ethylene is the starting material for the preparation of vinyl chloride, vinyl acetate, and acetaldehyde. Propene is the starting material for acrylonitrile. 

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Ozonolysis of alkynes followed by hydrolysis gives similar products to those obtained from permanganate oxidation. This reaction does not require oxidative or reductive work-up. Unsubstituted carbon atoms are oxidized to CO2, and mono-substituted carbon atoms to carboxylic acids. For example, ozonolysis of 1-butyene followed by hydrolysis gives propionic acid and carbon dioxide. 

The importance of electron transfer in the mechanism of ozonolysis has been discussed <97JOC5934> and ozonolysis of 2-methylthio-3-methylbut-2-ene on polyethylene has allowed isolation of pure tetrarnethyl-l,2,4-trioxolane 123 <97MI543>. Solid-supported 1,2,4-trioxolanes have been prepared by ozonolysis and used for further transformations <97TL1043>. Ozonolysis of alkynes in the presence of carbonyl compounds affords access to... 

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