Q45E - Organic Chemistry (Mcmurry)

Question

How would you synthesize the following alcohols, starting with benzene and other alcohols of six or fewer carbons as your only organic reagents?

(a) 

(b) 

(c) 

(d) 

Step-by-Step Solution

Answer

(a) 

(b) 

(c) 

(d) 

Step 1: Synthesis of alcohols

The hydration of alkenes and the reduction of aldehydes, ketones, acids and esters leads to the formation of alcohols. The hydrolysis of halides can also generate alcohols. The hydroboration of alkenes can also generate alcohols.

Step 2: Synthesizing the alcohol starting with other alcohols

(a)In this reaction, ethanol reacts with ${\mathrm{PBr}}_3$ to form ethyl bromide. This product further reacts with Mg and ether to form ethyl magnesium bromide. This is the Grignard reagent used for the reaction.

Cyclohexanol reacts with ${\mathrm{CrO}}_3$and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form cyclohexanone. This further reacts with ethyl magnesium bromide and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form the given compound 1-ethylcyclohexanol. The reaction can be given as:

                      Reaction (a)

(b)In this reaction, 2-methylpentan-1-ol reacts with ${\mathrm{PBr}}_3$ to form 1-bromo-2-methylpentane. This further reacts with Mg and ether to form (2-methylpentyl) magnesium bromide. This is used as the Grignard reagent.

Methanol reacts with Periodinane and ${\mathrm{CH}}_2{\mathrm{Cl}}_2$ to form formaldehyde. This further reacts with the Grignard reagent formed above in the presence of ether and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form 3-methyl-hexan-1-ol. The reaction can be given as:

                         Reaction (b)

(c)Benzene reacts with ${\mathrm{Br}}_2$ and ${\mathrm{FeBr}}_3$ to form bromobenzene. This further reacts with Mg and ether to form phenyl magnesium bromide.

The alcohol, pentan-2-ol reacts with ${\mathrm{CrO}}_3$ and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form pentan-2-one.

Phenyl magnesium bromide reacts with pentan-2-one in the presence of ether and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form the compound 2-phenyl-pentan-2-ol. The reaction can be given as:  

(d)The Grignard reagent used in this reaction is ethyl magnesium bromide. 

The compound, 3-methylbutan-1-ol reacts with periodinane and ${\mathrm{CH}}_2{\mathrm{CI}}_2$ to form 3-methylbutanal. This compound reacts with ethyl magnesium bromide in the presence of ether and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form 5-methylhexan-3-ol. The reaction can be given as:  

Reaction (d)