What are Grignard reagents? Give a chemical reaction for their preparation

Answer

### Step-by-Step Solution:

1. **Definition of Grignard Reagents**:
Grignard reagents are a class of organomagnesium compounds that have the general formula R-Mg-X, where R is an alkyl or aryl group, Mg is magnesium, and X is a halogen (such as bromine, chlorine, or iodine). They are highly reactive and are used extensively in organic synthesis.

2. **Preparation of Grignard Reagents**:
Grignard reagents can be prepared by the reaction of haloalkanes (alkyl halides) with magnesium metal in an anhydrous (dry) ether solvent. The reaction proceeds as follows:

**Chemical Reaction**:
\[ \text{R-X} + \text{Mg} \xrightarrow{\text{dry ether}} \text{R-Mg-X} \]
Where R-X is the haloalkane (for example, CH3CH2Br), and R-Mg-X is the Grignard reagent.

3. **Example Reaction**:
Let's consider the preparation of ethyl magnesium bromide (a Grignard reagent) from bromoethane:

\[ \text{CH}_3\text{CH}_2\text{Br} + \text{Mg} \xrightarrow{\text{dry ether}} \text{CH}_3\text{CH}_2\text{MgBr} \]

In this reaction, bromoethane (CH3CH2Br) reacts with magnesium (Mg) in the presence of dry ether to form ethyl magnesium bromide (C2H5MgBr), which is the Grignard reagent.