Q3P - Organic Chemistry (Mcmurry)

Question

How would you prepare pentanal from the following starting materials?

(a) CH₃CH₂CH₂CH₂CH₂OH (b) CH₃CH₂CH₂CH₂CH=CH₂

(c) CH₃CH₂CH₂CH₂CO₂CH₃ (d) CH₃CH₂CH₂CH=CH₂

Step-by-Step Solution

Answer

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

Step 3: 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

Step 4: 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

Step 5: 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