Question

a) Please draw a separation scheme for the reactions.

b) Label all peaks for the IR and proton NMR. The product should be benzoic acid. Indicate which peak corresponds to which molecule of the product.

d) Identify type of reaction/mechanism. What are the molar ratio of the reactants? How do splitting pattern and integrations support product structure? Identify solvents or reagents on spectra.

Br + Mg ether, Br + Mgether MgBr MgBr Bromobenzene Phenylmagnesium bromide

(Right side)

(Left side)

Answer 1

The reaction mixture may contain unreacted bromobenzene, benzoic acid (product), ether and inorganic impurities in water. Hence the target product is separated using acid-base extraction. Benzoic acid is reacted with NaHCO4 to give sodium salt and made it to dissolve in water leaving behind bromobenzene and organic impurities. Further, the aqueous layer is acidified with HCl to give ppt of benzoic acid, and this ppt is separated using filtration. The filtrate contains water and inorganic impurities. And residue contains benzoic acid. That is further purified with recrystallization from hot water.

Reaction mixture Bromobenzene + Benzoic acid + Ether + watera Add some more ether and then extract with NaHCO3 solution. Aqueou Layer Organic Layer + Ether + organic impurity ONa Br + water Acidify with HCl solution filter the ppt Filtrate: water impurities from mixture + inorganic the reaction Reaction mixture may contain unreacted bromobenzene, benzoic acid (product), ether and inorganic impurities in water. Hence the target product is seprated using acid base extraction. Benzoic acid is reacted with NaHCO4 to give sodium salt and made it to dissolve in water leaving behind bromobenzene and organic impurities. Further the aqueous layer is acidified with HCl to give ppt of benzoic acid, and this ppt is seprated using filtration. The filtrate contains water and inorganic impurities. And resediue contains benzoic acid. That is further purified with recrystalization from hot water. OH benzoic acid PPT

b) IR: 2400-3300: broad peak -COOH 3072: sp2 C-H stretching 1678: C=O stretching The carbonyl peak is lowered as it is in conjugation with benzene ring. 1601: aromatic C=C stretching 1288: C-O stretching 804: OOP C-H bending Thus the compound contains carboxylic acid with aromatic ring. c) Total aromatic protons contains 5H, indicates it is monosubstituted benzene ring. a: 7.5ppm: 3H, multiplet: meta and para protons of carboxylic group b: 8.2ppm: 2H, ortho protons of carboxylic group c: 2.2ppm: 1H, May be due to impurity such as water it can show the broad peak with integration of 2H, but we can consider it as -COOH single proton. Thus the product is: SOHC benzoic acid