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Suppose I have a phenyl Grignard and methyl benzoate.
If I react the two, can I expect benzophenone and a triphenylmethoxide ion as my products?
I ask because I know that Grignards react with ketones and aldehydes. So as the benzophenone is generated, couldn't more Grignard attack the benzophenone as well as the original reactant?
Expected products and mechanism shown below:
Reaction of a Grignard reagent with an ester is a standard method for producing tertiary alcohols where at least two of the substituents (the "$\small\ce{R_2}$" group attached to the Grignard) are the same. Judicious choice of the starting ester allows for the preparation of a tertiary alcohol where all 3 substituents are the same. Alternately, you could react 3 equivalents of the Grignard with a cheap dialkyl carbonate (a "double" ester, if you will) to obtain a tertiary alcohol where all 3 groups are the same.
Typically a slight excess of Grignard reagent is used and the tertiary alcohol is produced after acid work-up. If an excess of Grignard is not used then a mixture (ugh!) of ester, intermediate ketone and alcohol may result.
Yes, that is exactly what happens. And since ketones are typically more reactive than esters, you should expect that the tertiary alcohol (after workup) will be the predominant product.
In order to access the ketone, add the Grignard to a nitrile, which will give an imine (after protonation) that can be hydrolyzed to a ketone. Alternatively, add the Grignard to an aldehyde and oxidize the resulting alcohol to the ketone.
