Benzoic Acid: Page 1THE GRIGNARD REACTION.PREPARATION OF BENZOIC ACIDTHE PROBLEM TO BE INVESTIGATED: Benzoicacidis synthesized by the use of an organometallicreagent, C6H5-Mg-Br, with CO2in aGrignard reaction.BACKGROUND INFORMATION: Organometallic compounds are important in life processes. One of thesignificant discoveries in organic chemistry is a series of reactions involving the Grignard reaction.Muchresearch elucidating the structures, mechanisms, and general application in organic synthesis has beenexpended. Classified as an addition reaction, a Grignard reagent and methanal(formaldehyde) produces -after workup - a primary alcohol. With any other aldehyde, the Grignard reaction yields a secondary alcohol,while a ketone or ester will afford a tertiary alcohol:CARBONYL REACTANT (electrophile)PRODUCTformaldehydeprimary alcoholaldehydesecondary alcoholketonetertiary alcoholestertertiary alcoholcarbon dioxidecarboxylic acidWhile benzoic acid may be obtained by alternative methods; e.g., permanganate or dichromate oxidation ofbenzyl alcohol or an alkyl-substituted benzene, or hydrolysis of benzonitrile, the Grignard reaction is a non-oxidative process. THE NATURE OF THIS INVESTIGATION: Grignard reagents must be produced under anhydrousconditionsand used immediately after preparation. The presence of protic mediasuch as water or alcohol willdecompose the Grignard reagent resulting in the formation of the corresponding hydrocarbon (Eq. 3). Additionof the nucleophilicR-(or, in this case,Ar-) group to the electrophiliccarbonyl group (O=C=O) also requiresanhydrous conditions. The importance of a protic-free (anhydrous) environment can not be overemphasized;for, failurein generating the Grignard reagent is often associated with the presence of protic material (Eq. 3).As in this experiment, a common impurity, biphenyl (R-R= C6H5-C6H5) may also result from a couplingreaction to form a different hydrocarbon (Eq. 4).
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