Experiment 33B.docx - Formation of Benzoic Acid through a...

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Formation of Benzoic Acid through a Grignard Reaction The objective of this experiment is to perform a grignard reaction to produce benzoic acid. In this experiment, magnesium is added to 1-bromobenzene to form phenyl magnesium bromide. The reaction mixture is then added to dry ice to sublime the carbon dioxide, forming benzoic acid and a by-product, biphenyl. The by-product is isolated by extraction using a separation funnel, and the isolated benzoic acid is then recrystallized using hot water to purify the sample. The mechanism for the formation of benzoic acid from 1-bromobenzene is shown below :
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The reaction is started combining 1-bromobenzene and 0.15g magnesium and diethyl ether under anhydrous conditions. The reaction cannot be exposed to any moisture until the grignard reagent is completely formed. Diethyl ether is the key solvent to use when preparing the phenyl magnesium bromide. This is due to the two lone pairs on the oxygen of the diethyl ether. The partial charge on the magnesium is then stabilized from these lone pairs and promotes the reaction. Diethyl ether works best in nucleophilic addition reactions, as the ether functional group does not react with most reactants. The grignard reagent has an alkyl group, this group behaves almost like a carbanion, an
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