10 P - Organic Chemistry (Mcmurry)

Question

Question: Use a Grignard reaction to prepare the following alcohols.

1. 2-Methyl-2-propanol
2. 1-Methylcyclohexanol
3. 3-Methyl-3-pentanol
4. 2-Phenyl-2-butanol
5. Benzyl alcohol
6. 4-Methyl-1-pentanol

 

Step-by-Step Solution

Answer

(A)

(B)

(C)

(D)

(E)

(F)

Step-by-Step Solution Step 1: Alcohols from carbonyl compounds using Grignard reagents

Alcohols are prepared when carbonyl compounds are treated with Grignard reagents. Grignard reagents give different types of alcohol when they react with formaldehyde, aldehydes, and ketones.

Step 2: The preparation of 2-Methyl-2-propanol

(A) 2-Methyl-2-propanol is tertiary alcohol, and for synthesizing tertiary alcohol, the starting material used is a ketone. When ketone is treated with Grignard reagent (), tertiary alcohol is formed.

2-Methyl-2-propanol from ketone

 

When two or more alkyl groups attached to the carbon-containing –OH group are the same, tertiary alcohol can also be synthesized from ester and Grignard reagent.

2-Methyl-2-propanol from ester

Step 3: The preparation of 1-Methylcyclohexanol

(B) 1-Methylcyclohexanol is tertiary alcohol and is obtained when ketone is treated with the Grignard reagent. Thus, the reaction is shown as,

1-Methylcyclohexanol from ketone

Step 4: The preparation of 3- Methyl-3-pentanol

(C) 3-Methyl-3-pentanol is tertiary alcohol with two same alkyl groups attached to the carbon-containing OH group. So, either a ketone or an ester can be used as a starting material to obtain 3-Methyl-3-pentanol as a product.

 

3-Methyl-3-pentanol from ketone and ester

Step 5: The preparation of 2- Phenyl-2-butanol

(D) 2-Phenyl-2-butanol is a tertiary alcohol, and it is obtained when three possible ketones are treated with three possible Grignard reagents. The three possible reactions are shown below

2-Phenyl-2-butanol from different ketones

Step 6: The preparation of Benzyl alcohol

(E) Benzyl alcohol is a primary alcohol and it is obtained when formaldehyde is treated with the Grignard reagent. The reaction for the preparation of benzyl alcohol is shown as,

Benzyl alcohol from formaldehyde

Step 7: The preparation of 4-Methyl-1-pentanol

(F) 4-Methyl-1-pentanol is a primary alcohol, and it is also obtained when formaldehyde is treated with the Grignard reagent. The reaction for the preparation of 4-Methyl-1-pentanol is shown as,

 

4-Methyl-1-pentanol from formaldehyde