Question

A Grignard reagent and a ketone are reacted in ether solution and, followed by an acid workup, form a tertiary alcohol. Recall that Grignard reactions must be scrupulously dry in order to work effectively. A common method of drying glassware is to rinse with acetone prior to use.

1. Why is rinsing with acetone not suitable for the reaction stated in the question.
a) Magnesium does not dissolve in acetone.
b) Water dissolves in acetone. Adding acetone will add water to the reaction flask.
c) Magnesium dissolves in acetone. Adding acetone will remove a vital reactant from the flask.
d) Acetone is a ketone. Grignard reagents will react with acetone to make an unwanted byproduct.

Answer 1

Acetone cannot be used for rinsing in a Grignard reaction because it is a ketone and will react with the Grignard reagent, leading to unwanted byproducts.

Step-by-step explanation:

The reason why rinsing with acetone is not suitable for the reaction between a Grignard reagent and a ketone is d) Acetone is a ketone. Grignard reagents are highly reactive with carbonyl compounds, including ketones like acetone. If glassware is rinsed with acetone before a Grignard reaction, the acetone can react with the Grignard reagent, leading to the production of an unwanted byproduct instead of the desired tertiary alcohol. Thus, using acetone for rinsing can compromise the reaction's success.

Answer 2

Option-D (Acetone is a ketone. Grignard reagents will react with acetone to make an unwanted byproduct.) is the correct answer.

Step-by-step explanation:

Grignard reagents are formed by reacting alkyl halides in the presence of ether and dry atmosphere at controlled conditions. The rinsing of glassware is not suitable to be done with Acetone. This is because of the reactivity of Grignard reagents towards the carbonyl compounds.

In the scheme below it is assumed that a grignard reagent (ethyl magnesium bromide) was reacted with pentan-2-one to synthesise a tertiary alcohol (3-methylhexan-3-ol). But when the glassware is rinsed with acetone, some acetone left in glassware (like Round bottom flask) will react with the grignard reagent and will produce corresponding tertiary alcohol (2-methylbutan-2-ol in this assumption).