Uses of Grignard Reagent

Grignard reagents are exceptionally versatile: the alkyl group, being electron-rich, behaves as a carbanion/nucleophile and attacks the electron-poor centre of a polarised molecule, converting the Grignard reagent -- after a final aqueous acid work-up (H2O/H+) -- into almost every major class of organic compound: alcohols (primary, secondary or tertiary, depending on the carbonyl partner), aldehydes and ketones, carboxylic acids, esters, ethers, nitriles, and even the plain alkane. The TEN in …

(1) Primary alcohol: formaldehyde (HCHO) + RMgX gives an addition product that, on hydrolysis (H2O/H+), gives a primary alcohol + Mg(OH)X, e.g. + CH3MgI gives ethanol. (2) Secondary alcohol: any other aldehyde (e.g. acetaldehyde, CH3CHO) + RMgX, then H2O/H+, gives a secondary alcohol, e.g. + CH3MgI gives isopropanol. (3) Tertiary alcohol: a ketone (e.g. acetone) + RMgX, then H2O/H+, gives a tertiary alcohol, e.g. + CH3MgI gives tert-butanol. (4) Aldehyde: ethyl formate (HCOOC2H5) + one equivalent of RMgX, then H2O/H+, gives an aldehyde (e.g. + CH3MgI gives acetaldehyde); with EXCESS Grignard reagent the initially-formed aldehyde reacts further with a second equivalent to give a secondary alcohol instead. (5) Ketone: an acid …

(6) Carboxylic acid: solid CO2 (dry ice) + RMgX gives an addition product that, on hydrolysis (H+/H2O), gives a carboxylic acid, e.g. + CH3MgI gives acetic acid. (7) Ester: ethyl chloroformate (C2H5O-CO-Cl) + RMgX gives an ester, e.g. + CH3MgI gives ethyl acetate. (8) Higher ether: a halogenated ether (e.g. chlorodimethyl ether, CH3-O-CH2Cl) + RMgX gives a higher (unsymmetrical) ether. (9) Alkyl cyanide: cyanogen chloride (CNCl) + RMgX gives an alkyl cyanide, e.g. + CH3MgI gives methyl cyanide. (10) Alkane: any compound with an active (acidic) hydrogen -- water, an alcohol, an amine -- reacts with RMgX to give the alkane R-H directly, e.g. CH3MgI + H2O gives methane + MgI(OH), and CH3MgI + C2H5OH likewise gives methane + MgI(OC2H5). This last r …