Question

Which one of the following would not be a suitable solvent for Grignard reagent?
A.\[C{H_3}C{H_2}OC{H_2}C{H_3}\]​, diethyl ether
B.Tetrahydrofuran (THF)
C.\[C{H_3}C{H_2}OH\], ethanol
D.They would all be suitable solvent

Answer 1

Hint: Ethanol has acidic hydrogen, when we use ethanol as solvent it will react with grignard reagent, so it cannot be used as solvent in grignard synthesis. Ether is an aprotic solvent and the bond between R - Mg is highly polar. Ether has a lone pair of electrons which benzene does not have.

Complete answer:
A Grignard reagent of Grignard compound is a chemical compound which has a general formula R−Mg−X, where X is a halogen and R is an organic group, which is normally an alkyl or an aryl. Two examples of Grignard reagents are methylmagnesium chloride \[Cl - Mg - C{H_3}\] and phenylmagnesium bromide (\[{C_6}{H_5}\])−Mg−Br. They are a subclass of the organomagnesium compounds.
Grignard compounds are popular reagents in organic synthesis for creating new carbon-carbon bonds. For example, when they are reacted with another halogenated compound R'−X' in the presence of a suitable catalyst, they typically yield R−R' and the magnesium halide MgXX' as a byproduct; and the latter is insoluble in the solvents normally used. In this aspect, they are similar to organolithium reagents.
Ether is an aprotic solvent and the bond between R - Mg is highly polar. Ether has a lone pair of electrons and is a great solvating agent. So, the Grignard reagent can be formed only in a good solvent but not in a nonpolar solvent whereas ethanol has acidic hydrogen, when we use ethanol as solvent it will react with grignard reagent, so it cannot be used as solvent in grignard synthesis.

Therefore, the correct answer is option (C).

Note: Ether is used as a solvent because it is aprotic and can solvate the magnesium ion because a Grignard reaction involves the reaction of an alkyl (or aryl halide) with magnesium metal to form an alkyl magnesium halide.
 \[R - X + Mg \to R - MgX\]
Diethyl ether is an especially good solvent for the formation of Grignard reagents for two reasons.