Question

How would you prepare pentanal from the following starting materials?

(a) CH₃CH₂CH₂CH₂CH₂OH (b) CH₃CH₂CH₂CH₂CH=CH₂

(c) CH₃CH₂CH₂CH₂CO₂CH₃ (d) CH₃CH₂CH₂CH=CH₂

Short answer

Aldehyde is one of the types ofthe “carbonyl compound.” with the chemical formula R-CHO in which R is the alkyl or aryl group.

The most common method for the preparation of aldehyde are as follows:

• Hydrogenation of acyl chloride or acid chloride ( Rosenmund reduction)
• Reduction of nitriles and ester (Stephen reaction)
• From oxidation of hydrocarbon (Etard reaction)

Step-by-step solution

Step 1:Aldehyde Preparation

Aldehyde is one of the types ofthe “carbonyl compound.” with the chemical formula R-CHO in which R is the alkyl or aryl group.

The most common method for the preparation of aldehyde are as follows:

• Hydrogenation of acyl chloride or acid chloride ( Rosenmund reduction)
• Reduction of nitriles and ester (Stephen reaction)
• From oxidation of hydrocarbon (Etard reaction)

Step 2:Formation of Pentanal from Pentanol

To synthesize aldehyde pentanal is done by oxidizing primary alcohol pentanol; the reaction is often carried out using the Dess–Martin periodinane reagent ${\text{C}}_{\text{13}}{\text{H}}_{\text{13}}{\text{IO}}_{\text{8}}$in dichloromethane $\left({\text{CH}}_{\text{2}}{\text{Cl}}_{\text{2}}\right)$solvent at room temperature.

The formation of pentanal from pentanol is shown as follows:

Formation of pentanal by oxidation

Formation of Pentanal from Hexene

Alkene 1-hexene can be oxidized to one carbon less aldehyde pentenal by reacting it with (ozonolysis) followed by reductive workup reacting it with zinc hydronium ion$\left({\text{Zn/H}}_{\text{3}}{\text{O}}^{\text{+}}\right)$

The formation of Pentanal from Hexene is shown as follows:

Formation of pentanal by ozonolysis

Formation of Pentanal from ester

Ester methyl pentanoate can be reduced to form the aldehyde by reacting with the reducing agent Diisobutylaluminum hydride (DIBAH), followed by acidic work up to ${\text{(H}}_{\text{3}}{\text{O}}^{\text{+}}\text{)}$give the desired result aldehyde pentanal.

The formation of Pentanal from methyl pentanoate is shown as follows:

Formation of pentanal by reduction

Formation of Pentanal from pentene

alkene 1-pentene is converted to aldehyde pentanal is done in two steps as follows:

• In the first step, the Hydroboration-oxidation transforms 1-pentene (alkene) intopentanol (alcohols). It is done by adding water across the double bond on alkene.
• In the second step, pentanol (alcohols)is further oxidized by reacting with Dess–Martin periodinane reagent ${\text{C}}_{\text{13}}{\text{H}}_{\text{13}}{\text{IO}}_{\text{8}}$in dichloromethane $\left({\text{CH}}_{\text{2}}{\text{Cl}}_{\text{2}}\right)$solvent at room temperature to form the pentanal.

The formation of Pentanal from pentene is shown as follows:

Formation of pentanal by two times oxidation