CH3MgBr

CH3MgBr, or methylmagnesium bromide, is a simple Grignard reagent used as a versatile nucleophile in organic synthesis. It consists of a methyl group bound to magnesium bromide and is typically employed as a solution in dry ether solvents. The compound is highly reactive and must be prepared and used under strictly anhydrous, inert conditions.

Preparation and handling: CH3MgBr is prepared by reacting methyl bromide with elemental magnesium in dry ether solvents such as diethyl ether or tetrahydrofuran (THF). The reagent is moisture- and air-sensitive; exposure to water or oxygen leads to rapid quenching and heat release, forming methane and magnesium hydroxide. It is typically stored under inert gas in sealed, dry containers and used as a solution rather than as a neat solid.

Reactivity and scope: As a carbon nucleophile, CH3MgBr adds to carbonyl compounds to form new C–C bonds. Upon acidic workup, the resulting alkoxide is converted to an alcohol. Reactions with common carbonyl partners include:

- Formaldehyde (H2C=O): ethanol after workup.

- Acetaldehyde (CH3CHO): isopropanol after workup.

- Ketones (e.g., acetone, (CH3)2CO): tertiary alcohols such as tert-butanol after workup.

Reaction with carbon dioxide yields acetic acid after acidic workup, illustrating the one-carbon homologation capability of Grignard reagents. CH3MgBr also reacts with epoxides to give alcohols with the methyl group appended at the less substituted carbon.

Workup and applications: After completing the carbonyl addition, the reaction is quenched with water, ammonium chloride, or acetic acid, and the mixture is worked up to isolate the alcohol product. CH3MgBr is widely used to extend carbon skeletons in organic synthesis and to form secondary or tertiary alcohols from aldehydes or ketones, respectively.

Safety and limitations: CH3MgBr reacts violently with water and air; anhydrous conditions and proper ventilation are essential. The ether solvents are flammable, and the reagents are moisture-sensitive and air-sensitive, requiring careful handling and storage.