Grignard reagents can act as both a nucleophile and a base. Consequently, what w
ID: 743116 • Letter: G
Question
Grignard reagents can act as both a nucleophile and a base. Consequently, what would you expect to happen if that during the preparation of the phenylmagnesium bromide Grignard reagent:
a) water was present
b) carbon dioxide was present
Explanation / Answer
Grignard reagents react with water to produce alkanes. This is the reason that everything has to be very dry during the preparation above. CH3CH2MgBr + H20 --> CH3CH3 + MgBrOH The inorganic product, Mg(OH)Br, is referred to as a "basic bromide". You can think of it as a sort of half-way stage between magnesium bromide and magnesium hydroxide. Grignard reagents react with carbon dioxide in two stages. In the first, you get an addition of the Grignard reagent to the carbon dioxide. Dry carbon dioxide is bubbled through a solution of the Grignard reagent in ethoxyethane, made as described above.
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