Question

What is Grignard reagent?

Answer 1

Hint: It is a nucleophilic reagent that acts like a very strong base in chemical reactions. Its unique properties are due to the carbon-metal bond present in it and because carbon is bonded to metal, it can form carbanions in chemical reactions but it is important to keep it away from the moisture.

Complete step by step answer:
Grignard reagent’s molecular formula is \[RMgX\]
Here R can be any alkyl group and X can be Cl, Br or I
Preparation:
Grignard reagent is prepared with the reaction of alkyl halide with Magnesium in presence of dry ether.
 \[RX+Mg\xrightarrow{ether}RMgX\]
Chemical properties:
Grignard is a very important reagent in chemistry as it can be used to form a variety of compounds.
On reacting with alkyl halide it forms higher alkanes.
\[RMgX+{{R}^{'}}X\to R{{R}^{'}}+Mg{{X}_{2}}\]
- On reaction with aldehyde followed by hydrolysis in acidic medium it forms secondary alcohols.
$R-MgCl+R-CHO\xrightarrow{{{H}_{3}}{{O}^{+}}}{{R}_{2}}CHOH$
On reaction with ketone followed by hydrolysis in acidic medium it forms tertiary alcohol
$R-MgCl+{{R}_{2}}C=O\xrightarrow{{{H}_{3}}{{O}^{+}}}{{R}_{3}}C-OH$
- From the above reactions you can clearly see that Grignard reagent can be used to prepare a variety of products.
- The important observation is the nucleophilic addition of Grignard reagent over the substrate as alkyl carbanion is a very strong base and powerful nucleophile, that’s with compounds containing carbonyl carbons it readily forms nucleophilic addition product and common thing over here is the acidic work up to form the final product, because the addition compound formed after the nucleophilic addition of Grignard reagent over substrate will easily gets hydrolyzed in acidic medium.

Additional Information :French chemist Victor Grignard discovered this reagent and won the 1912 Nobel Prize for that. From the scientist's name it is known as Grignard reagent.

Note: While preparing Grignard reagent it is important to have anhydrous condition because Grignard reagents react with water and form alkane. In fact with compounds containing active hydrogen like carboxylic acid, alcohol etc. it acts like a base and forms alkane.
$RMgX+{{H}_{2}}O\to RH+MgXOH$
\[RMgX+C{{H}_{3}}COOH\to RH+C{{H}_{3}}COOMgX\]
$RMgX+C{{H}_{3}}OH\to RH+C{{H}_{3}}OMgX$