Grignard reaction product involving a ketone

[chris_0101]

Homework Statement

Basically I have to show the product of this reaction:

Homework Equations

Grignard reaction mechanism:
The conversion of a ketone to an alcohol

The Attempt at a Solution

My attempt of this reaction produces an alcohol with two ethyl groups attached to the central carbon as well as a phenyl group and an OH group attached to the central carbon, so the IUPAC name would be 3-phenyl-3-pentanol.

However, the answer is:

Can someone please explain why the reaction produced an alkene instead of an alcohol. I do not know why this occurred and need some clarification. Also, when does this extra step occur.

Thanks.

 

[pmsrw3]

Think a little about step 3.

 

[chris_0101]

What occurs is step 3? I know that the H2SO4 is deprotonated to become HSO4. This produces the alcohol part of the compound, which is what I got. I am going to assume that deprotonation of HSO4 occurs, thus producing water and the alkene as shown in the answer. Is this right?

 

[pmsrw3]

Look up "dehydration". Sulfuric acid is a powerful dessicant.

 

[DeeNos]

The Grignard reaction, also known as the Grignard reagent synthesis, is a chemical reaction involving the addition of an organomagnesium halide (Grignard reagent) to a ketone or aldehyde, resulting in the formation of a tertiary alcohol. However, it is important to note that the reaction can also produce an alkene as a byproduct under certain conditions.

The most common cause of an alkene byproduct in a Grignard reaction is the presence of excess Grignard reagent or prolonged reaction times. This can lead to the over-reduction of the ketone, resulting in the formation of an alkene instead of an alcohol.

In order to prevent the formation of an alkene byproduct, it is important to carefully control the amount of Grignard reagent used and the reaction time. Additionally, certain ketones may be more prone to over-reduction than others, so it is important to choose the appropriate ketone for the reaction.

In the case of your specific reaction, it is possible that the excess Grignard reagent or prolonged reaction time led to the formation of the alkene byproduct. It is important to carefully analyze the conditions of the reaction and make adjustments as needed in order to achieve the desired product.