Q4P - Organic Chemistry (Mcmurry)

Question

How would you carry out the following reactions? More than one step may be

required.

(a) 3-Hexyne  3-Hexanone

(b) Benzenem-Bromoacetophenone

(c) Bromobenzene Acetophenone

(d) 1-Methylcyclohexene  2-Methylcyclohexanone

Step-by-Step Solution

Answer

(a)

(b)

(c)

(d)

Step 1:Ketone Preparation

Ketone organic compounds come under the class of carbonyl compounds in which both sides of the carbonyl group alkyl or aryl group are attached.

 

Ketones are prepared mainly by three starting materials (substrate), which are as follows:

• By acyl chloride
• By nitriles
• From Benzene

Step 2:Formation of 3-Hexanone

Alkene 3-hexyne is converted to ketone 3-hexanone by hydrating the 3-hexyne to enol that immediately tautomerizes to ketone 3-hexanone, the reagent required for this conversion is aqueous acid $\left({\text{H}}_{\text{3}}{\text{O}}^{\text{ + }}\right)$ typically with a ${\text{HgSO}}_{\text{4}}$ mercury salt (catalyst).

The reaction of converting 3-hexyne to 3-hexanone is as follows:

                                           Formation of 3-Hexanone

Step 3: Formation of m-Bromoacetophenone

Benzene is converted to m-Bromoacetophenone in two steps which are the following:

 

• In the first step, the freidel craft acylation reaction is done on Benzene with the help of reagent acyl chloride $\left({\text{CH}}_{\text{3}}\text{COCl}\right)$ in the presence of Lewis acid aluminumchloride $\left({\text{AlCl}}_{\text{3}}\right)$ to form the acetophenone
• In the second step, the bromination of acetophenone takes place with the help of a reagent ${\text{Br}}_{\text{2}}{\text{/FeBr}}_{\text{3}}$electrophilic aromatic substitution reaction) that results in the formation of desired product, m-Bromoacetophenone.

The reaction of convertingBenzene to m-Bromoacetophenoneis as follows:

                               Formation of m-Bromoacetophenone

Step 4: Formation of Acetophenone

Bromobenzene is converted to acetophenone in the following steps:

 

• In the first step, bromobenzene is reacted with magnesium (Mg) to form the Grignard reagent phenyl magnesium bromide (PhMgBr).
• In the second step, phenyl magnesium bromide reacts with ethanal, followed by acidic work to form the 1-phenyl ethanol.
• In the last step, 1-phenyl ethanol is oxidized with the help of chromium trioxide $\left({\text{CrO}}_{\text{3}}\right)$, followed by an acidic workup to form the desired product, acetophenone.

 

 

The reaction of convertingbromobenzene to acetophenone is as follows:

                                       Formation of acetophenone

Step 5: Formation of 2-Methylcyclohexanone

1-methylcyclohexeneis converted to 2-methyl cyclohexanonein the two steps:

 

• In the first step, the Hydroboration-oxidation transforms 1-methylcyclohexene  (alkene)  into (1R,2R)-1,2-dimethylcyclohexanol (alcohols). It is done by adding water across the double bond on alkene.
• In the second step, (1R,2R)-1,2-dimethylcyclohexanol is oxidized with the help of ${\text{CrO}}_{\text{3}}$, followed by acidic workup to form the desired product2-methylcyclohexanone.

The reaction of converting1-methylcyclohexeneto2-methyl cyclohexanoneis as follows:

                          Formation of 2-methyl cyclohexanone.