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Ester Reactions: Formation of Tertiary Alcohol from Ester using Grignard Reagents

Tertiary alcohols can be formed from esters using Grignard Reagents:

Ester Reactions: Formation of Tertiary Alcohol from Ester using Grignard Reagents image1.png

The carbon chain from the Grignard reagent (R) is added to the ester molecule twice.The “R” group is usually pretty small (think ethane to cyclohexane in size):

Ethane Addition Example

Ester Reactions: Formation of Tertiary Alcohol from Ester using Grignard Reagents image2.png

Cyclohexane Addition Example

Ester Reactions: Formation of Tertiary Alcohol from Ester using Grignard Reagents image4.png

The reaction mechanism is depicted below:

Ester Reactions: Formation of Tertiary Alcohol from Ester using Grignard Reagents image3.png

In the first step, the Mg-R bond breaks, sending that pair of electrons to attack the carbon atom that in between the oxygens on the ester molecule. This attack pushes electrons from the carbon-oxygen bond to the oxygen atom, allowing the R group to bond.

In the second step, the newly acquired lone pair electrons on the oxygen atom attack the carbon atom, reforming the double bond, and causing the single bonded oxygen to break its bond and leave the molecule.

In the third step, a second RMgX molecule comes and reacts with the now ketone molecule, causing the double bond to break and send electrons to the oxygen atom.

In the fourth step, the lone pair electrons on the negatively charged oxygen atom attack a proton on a nearby H3O molecule

There are many variations of Grignard reagents but all Grignard reagents will have an alkane chain, a Mg atom, and a halogen (Cl, Br).