How to Prepare Benzoic Acid
Benzoic acid (C7H6O2) is a weak acid that is a crystalline solid at room temperature. It has many applications in industrial chemistry, primarily as a precursor in the synthesis of other chemicals. Benzoic acid is named after gum benzoin, which was first used to produce benzoic acid in 1556. The dry distillation of gum benzoin was the only method of preparing benzoic acid until the discovery of other techniques beginning in the 19th century.
Instructions
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Produce benzoic acid by partially oxidizing toluene with oxygen and using cobalt or manganese naphthenates as a catalyst. This is a common method of preparing benzoic acid commercially, as the reagents are cheap and the reaction has a high yield.
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Synthesize benzoic acid in the laboratory. This is a common exercise for college students since the reagents aren't highly toxic. These methods typically consist of recrystallizing benzoic acid from solution by using solvents such as acetic acid, benzene, ethanol or petroleum ether.
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Hydrolyze benzonitrile (C6H5CN) and benzamide (C6H5CONH2). Benzoic acid can be prepared from these similar molecules by splitting water (H20) into hydrogen (H+) and hydroxide (OH-) ions. Essentially, the hydroxide ion replaces the amide (NH2-) group in the reagent to produce benzoic acid.
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Produce benzoic acid through the disproportionation of benzaldehyde (C6H5COH) as follows: C6H5COH + OH- ' C7H7O2 + C6H5COH => C7H6O2 (benzoic acid) + C7H6O (benzyl alcohol). The benzyl alcohol can then be removed by distillation.
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Carbonate bromobenzene by carbonating the bromide ion. The magesium bromide ion may then be removed with hydrochloric acid as follows: C6H5MgBr + CO2 ' C6H5CO2MgBr. C6H5CO2MgBr + HCl ' C6H5CO2H + MgBrCl.
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