How do Grignard reagents react with alcohols? (2023)

FAQs

How do Grignard reagents react with alcohols? ›

The Grignard reagent reacts with aldehydes and ketones to form alcohol. The first step of the reaction is the nucleophilic addition of Grignard reagent to the carbonyl group to form an adduct. Hydrolysis of the adduct yields an alcohol ( R - C - OH ) .

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. Methyl magnesium bromide reacts with ethanol and methanol to form methane.

In their Grignard reactions, the carbon-oxygen pi bond is cleaved and a new C-C bond is formed, resulting in the formation of an alkoxide. These alkoxides can be subjected to an acidic workup to yield alcohols.

Therefore one mole of grignard reacts with one mol of alcohol to give 1 mole of alkane.

When Grignard reagents react with ethanol, due to nucleophilic nature it tends to extract the hydrogen atom attached with the hydroxyl group. The reaction between the ethanol and Grignard reagent is considered as an acid base reaction because alcohol acts as an acid while Grignard reagent acts as a base.

Aldehydes are more reactive towards the Grignard reagent or the nucleophilic substitution reaction than the ketone.

Grignard reagents do not typically react with organic halides, in contrast with their high reactivity with other main group halides. In the presence of metal catalysts, however, Grignard reagents participate in C-C coupling reactions.

Amines (except tertiary amine) react with Grignard's reagent to form hydrocarbons. Tertiary amine does not contain any acidic hydrogen. So, it can't react with Grignard's reagent.

The problem here is that Grignard reagents are strong bases, and will react with even weak acids (like alcohols). If we try to make a Grignard on a molecule with an acidic functional group, we'll end up destroying our Grignard instead.