How is ethanol prepared by methanal by using Grignard reagent?

Ethanol cannot be directly prepared from methanal (formaldehyde) using a Grignard reagent because Grignard reagents are typically used to synthesize alcohols by reacting them with carbonyl compounds like aldehydes and ketones. However, you can use a Grignard reagent to prepare a related alcohol, methanol, from formaldehyde.

Here's the general reaction for preparing methanol from formaldehyde using a Grignard reagent:

Formation of the Grignard reagent:

Start by preparing a Grignard reagent, typically by reacting an alkyl or aryl halide (such as methyl bromide, CH3Br) with magnesium (Mg) in anhydrous ether or another suitable solvent.
For example, if you use methyl bromide, the Grignard reagent formed would be methylmagnesium bromide (CH3MgBr).
Reaction with formaldehyde:

Next, you react the Grignard reagent with formaldehyde (methanal, HCHO) to form methanol (CH3OH):
CH3MgBr + HCHO -> CH3OH + MgBr2
The Grignard reagent, CH3MgBr, acts as a nucleophile and attacks the carbon atom in the carbonyl group of formaldehyde, resulting in the formation of methanol and magnesium bromide (MgBr2) as a byproduct. The reaction mixture is usually quenched with a weak acid or a proton source to ensure that the Grignard reagent is fully converted to the alcohol.

Keep in mind that this is just one way to prepare methanol using a Grignard reagent. Ethanol, on the other hand, is typically not synthesized directly from formaldehyde using Grignard reagents because ethanol has one more carbon atom than formaldehyde, and a different synthetic route would be required to introduce that additional carbon atom.