Hydrolysis of alkyne to Aldehyde and Ketone
Alkyne hydration is not easy like hydration of alkene. Alkyne react with water in presence of mercuric sulphate (HgSO4) and dilute sulfuric acid at 333K. Carbonyl compounds are given as products. Carbonyl compounds are categorized as aldehyde are ketone. Dilute sulfuric acid and mercuric sulfate are behaved as catalysts in hydrolysis of alkyne.
Addition of water molecule to alkyne
Both hydrogen atoms of H2O are attached to a one carbon atom and oxygen atom is added to the other carbon atom. We will discuss how these oxygen and hydrogen atoms are connected to carbon atoms in next section of this tutorial.
Where to H2O molecule is added?
Now, we want to know which carbon atom will take two hydrogen atoms and which carbon atom will take oxygen atom. There is no case if alkyne is a symmetrical one. But in case of unsymmetrical alkyne, addition of water occurs according to Morkovnikv's rule.
According to the Markovnikv's rule
Hydrogen is attached to the carbon atom which has most hydrogen atoms. Oxygen is added to the other carbon atom which have less number of hydrogen atoms.
Alkyne hydrations are important in organic conversions to convert alkynes to aldehydes ketones. As an aldehyde, ethanal the only aldehyde can be produced from hydrolysis of alkyne.
Alkyne hydrolysis examples
Examples of hydrations of alkyne with dilute sulfuric acid and mercuric sulphate (HgSO4) are explained below.
Ethyne hydration
Ethyne, dilute H2SO4 and HgSO4 react to give ethanal. We don't need to apply markovnikv's rule to decide addition places of hydrogen and oxygen. This is the only reaction giving an aldehyde in alkyne hydration.
Propyne hydration
Propyne, dilute H2SO4 and HgSO4 react to give propanone. Propanone is a ketone compound.
2-butyne hydration
2-butyne, dilute H2SO4 and HgSO4 react to give 2-propanone.
Alkyne hydration mechanism
First, water molecule is added to the triple bond. The intermediate product of this reaction is very unstable. Then triple bond is converted to double bond. Therefore, as soon as this intermediate compound converts into carbonyl compound (aldehyde or ketone). Hydration of ethyne will give ethanal which is an aldehyde compound. All other hydrations of alkynes will give ketones.
Propyne hydration gives propanone
Questions of hydrolysis of alkene and alkyne
What is the reaction of HgSO4, H2SO4 with alkynes?
Alkenes hydration is done by HgSO4, H2SO4 and H2O. HgSO4, H2SO4 are behaved as catalysts. HgSO4 is used because hydrolysis of alkyne is difficult than hydrolysis of alkenes.
alkyne to ketone
Except ethanal, all other alkynes are conveeted to ketones in hydrolysis of alkynes.
converting butyne to ketone
Butyne, the alkyne with four carbon atoms can be converted to a ketone from hydrolysis by HgSO and dilute H2SO4. As the product, butanone (ketone) is given
alkyne to aldehyde
Only ethyne is possible to convert to aldehyde (ethanal) from hyrolysis.
What are the products of hydration of ethene
Ethanol is only product of hydration of ethene. Dilute H2SO4 is used for hydrolysis of ethene.
Questions
Chch + dil H2SO4/HgSO4
As product, CH3CHO (ethanal) is given.