Question

Write the structure of the major organic product isolated from the reaction of 3-hexyne with ozone followed by hydrolysis. Enter the number of carbon present in the major product, i.e. ethane-2.

Answer 1

Oxidation of alkynes with the help of ozone gives diketones or acid anhydrides. If water is present during ozonolysis, then the acid anhydrides will undergo hydrolysis to give two carboxylic acids.

Complete step by step answer:
Ozonolysis is the organic chemical reaction where ozone is used to cleave the unsaturated bonds of alkenes, alkynes, azo compounds etc. It is a kind or organic redox reaction.
Ozone is a very reactive allotrope of oxygen and so it can cleave the carbon – carbon triple bonds and they are replaced by carbon – oxygen double bonds.
The process of ozonolysis follows the oxidative cleavage mechanism. Ozone not only cleaves the carbon pi bond, but also the carbon – carbon sigma bond.
Ozone attacks on the given reactant to form ozonide. The oxygen in this intermediate stage is then eliminated by zinc dust as zinc dust can form zinc oxide with the oxygen.
The final product may vary depending upon the type of the reactant and the workup.
The general mechanism for ozonolysis of alkynes is shown below.

Now let us consider the ozonolysis of 3-hexyne. 3-hexyne is a symmetrical alkyne.

Therefore, the major organic product formed by ozonolysis of 3-hexyne is propanoic acid and its structure is:

And the number of carbon atoms in propanoic acid is 3.

Note:
-Ozonolysis of alkenes yields alcohols, aldehydes, ketones or carboxylic acids.
-Ozonolysis of azo compounds yields nitrosamines.
-Ozone cracking is the ozonolysis of elastomers in which trace amounts of ozone present in the atmosphere creates cracks and breaks the double bond of the elastomers.