Question

Alcohols cannot be used as a solvent for Grignard reagent. Give reason?

Answer 1

Alkyl or aryl magnesium halide is known as Grignard reagent (RMgX). “Grignard reagents are formed by the reaction of magnesium metal with alkyl or alkenyl halides”. Grignard reagent is extremely good nucleophile, reacts with electrophiles such as carbonyl compounds.

Complete step by step solution:
- The molecular formula of alcohol is R-OH.
- The alcohol contains an alkyl and –OH group.
- If alcohol undergoes ionization there are two parts going to form.
- One part is alkoxide anion and hydrogen cation.
- Alcohols and other similar compounds having active hydrogen in their molecules readily decompose Grignard reagents to respective alkanes and so they cannot be used as solvents for the latter. $C{{H}_{3}}MgBr+{{C}_{2}}{{H}_{5}}OH\xrightarrow{{}}C{{H}_{4}}+Mg(O{{C}_{2}}{{H}_{5}})Br$
- Due to formation of respective alkane by Grignard reagent upon reaction with alcohol, alcohols cannot be used as solvent for Grignard's reagent.
Therefore, diethyl ether or tetrahydrofuran is the suitable solvent for Grignard reagent.

Diethyl ether is a good solvent for Grignard reagents due to two reasons.

1. Ether is an aprotic solvent. (aprotic- incapable of donating proton)
2. Ether is a good solvating agent.

Therefore, ether or tetrahydrofuran are good solvents suitable for Grignard reagents.

Note: Don’t be confused with the words ethyl alcohol and ethanol. Both are the same.
Ethyl alcohol is frequently used as a solvent for alkyl halide substitution reactions like $SN_1$ and $SN_2$.