Save A solution of a carbonyl compound is added to a Grignard reagent. See gallery below The Grignard reaction is an organometallic chemical reaction in which alkylvinylor aryl - magnesium halides Grignard reagents add to a carbonyl group in an aldehyde or ketone.
The addition of the Grignard reagent to a Grignard reaction typically proceeds through a six-membered ring transition state. Grignard reactions will not work if water is present; water causes the reagent to rapidly decompose. So, most Grignard reactions occur in solvents such as anhydrous diethyl ether or tetrahydrofuran THFbecause the oxygen in these solvents stabilizes the magnesium reagent.
The reagent may also react with oxygen present in the atmosphere. This will insert an oxygen atom between the carbon base and the magnesium halide group. Usually, this side-reaction may be limited by the volatile solvent vapors displacing air above the reaction mixture.
However, chemists may perform the reactions in nitrogen or argon atmospheres. In small scale reactions, the solvent vapors do not have enough space to protect the magnesium from oxygen.
Making a Grignard reagent[ change change source ] Grignard reagents are formed by the action of an alkyl or aryl halide on magnesium metal. Typical solvents are diethyl ether and tetrahydrofuran. Oxygen and protic solvents such as water or alcohols are not compatible with Grignard reagents.
The reaction proceeds through single electron transfer. First, there is an induction period during which reactive magnesium becomes exposed to the organic reagents. After this induction period, the reactions can be highly exothermic.
Alkyl and aryl bromides and iodides are common substrates.
Chlorides are also used, but fluorides are generally unreactive, except with specially activated magnesium, such as Rieke magnesium. Many Grignard reagents, such as methylmagnesium chloridephenylmagnesium bromideand allylmagnesium bromide are available commercially in tetrahydrofuran or diethyl ether solutions.
These methods weaken the layer of MgO that covers the magnesium.
They expose the magnesium to the organic halide to start the reaction that makes the Grignard reagent. Mechanical methods include crushing of the Mg pieces in situ, rapid stirringor using ultrasound sonication of the suspension.
Iodinemethyl iodideand 1,2-dibromoethane are commonly employed activating agents. Chemists use 1,2-dibromoethane because its action can be monitored by the observation of bubbles of ethylene.
Also, the side-products are innocuous:The reaction between Grignard reagents and methanal. In methanal, both R groups are hydrogen. Methanal is the simplest possible aldehyde.
Assuming that you are starting with CH 3 CH 2 MgBr and using the general equation above, the alcohol you get always has the form. The Grignard reaction is an important tool in the formation of carbon–carbon bonds.   It also can form carbon– phosphorus, carbon– tin, carbon– silicon .
The Grignard reaction is an important means of preparing organic compounds from smaller precursor molecules. For this work, Grignard was awarded the Nobel Prize in Chemistry in jointly with fellow Frenchman Paul Sabatier. The Grignard reaction of an allylic Grignard reagent to a ketone appears to be straightforward, but there are two ketone moieties.
There is no reason to believe that the reaction would be selective for one carbonyl unit in preference to the other, so at least two different products should result. MECHANISM OF GRIGNARD REACTION * The first step in the Grignard reaction is the nucleophilic addition of Grignard reagent to the polar multiple bond to give an adduct which upon hydrolytic workup gives the final product like alcohol.
The mechanism . Grignard Reaction Grignard Reagents. The Grignard Reaction is the addition of an organomagnesium halide (Grignard reagent) to a ketone or aldehyde, to form a tertiary or secondary alcohol, respectively.