What is a Grignard reagent?

Question

Addison Armstrong · Accepted Answer

Grignard reagents are organometallic reagents in which an hydrocarbyl residue is more or less directly bound to a magnesium metal centre. They offer one of the few means of #C-C# bond formation.

Given a few provisos (i.e. no protic functional groups, exclusion of water) an hydrocarbyl halide, #R-X#, may be metallated directly with magnesium metal: #R-X + Mg rarr R-MgX# The #R-MgX# reagent, formally alkyl (hydrocarbyl) magnesium halide, will react as a carbanion, #R^(delta-)""^(delta+)MgX#. Typically the reaction is performed in an ethereal solvent, #Et_2O#, or #"THF"#. The Grignard reagent is usually not isolated, but used directly, and added to aldehydes to give #2""^@# alcohols (after workup), #R-MgX + R'C(=O)H rarr RC(-OMgX)R'# to ketones to give #3""^@# alcohols, #R-MgX + R'C(=O)H rarr RC(-OMgX)R'# additionally, to dry ice in order to produce a carboxylate salt that has one more carbon than the Grignard residue: #R-MgX + CO_2 rarr RC(=O)(-OMgX)# In fact, still the best way to make a carboxylic acid is to pour your Grignard mixture directly onto dry ice, and step back. The Grignard reagent usually fails to react with alkyl halides to give direct #C-C# coupling, but there are reports of the use of copper salts to add to the Grignard to make an organocopper species that is capable of direct reaction with #RCH_2X#. To conclude, Grignard reagents offer ease of synthesis (of course, you can't be too ham-fisted), prodigious reactivity, and adaptability. We can exploit the water sensitivity of the Grignard if we want to label a hydrocarbon chain with deuterium, #""^2H#, or tritium labels, #""^3H# labels. #R-MgX + ""^2H_2O rarr R-""^2H + MgO""^2HX# As I've already mentioned, this is an inexpensive and effective way to label a hydrocarbyl chain, and it's a great way to get your indolent graduate students back to the lab bench and off the computer.

Ryan Andrews · Answer

undefined A Grignard reagent is an organomagnesium compound derived from the reaction between an alkyl or aryl halide and magnesium metal. These reagents are highly reactive and commonly used in organic synthesis to form carbon-carbon bonds. Grignard reagents play a crucial role in creating complex organic molecules.