Question

Materials Available to Students in Lab:Solvents: acetone, ethanol, methanol, ethyl acetate, hexanes dichloromethane, and diethyl ether.

Aqueous Solutions: 1 M NaOH, 1 M HCl, 3 M NaOH, 3 M HCl, 1 M NaHCO3, saturated NaCl.

Special Glassware: TLC chambers and plates, separatory funnels

Step by step procedures for each scenario:

1.During an oxidation of benzyl alcohol to benzoic acid, a student did not have adequate time during the labperiod to let the reaction mixture stir long enough. Consequently, the benzoic acid he obtained was stillcontaminated with benzyl alcohol. Purify the benzoic acid and demonstrate its final purity.

2.An organic chemistry student reacted salicylic acid with an acid and methanol. The reaction did not haveenough time to allow the reaction to go to completion and the student ended up with a mixture of salicylicacidand methyl salicylate (oil of wintergreen). Recover the salicylic acid so you can reuse it again. Provide datatoshow that your salicylic acid is purified and recovered.

3.An organic chemistry student was attempting to synthesize 2-methoxynaphthalene from 2-napthol via anSN2reaction with methyl iodide and the reaction did not go to completion and the student ended up withmainlythe starting material and some product. Recover the 2-napthol so you can reuse it again. Provide datato showthat your 2-napthol is purified and recovered.

4.An organic chemistry student accidentally combined two unknown reagents as they had the same meltingpoint. However, further analysis showed that they now needed to be separated because they were actuallydifferent compounds: benzoic acid and 2-naphthol. Purify the benzoic acid, and provide the data that showsyour compound is pure.

5.An organic chemistry student attempted to synthesize o-toluic acid from o-chlorotoluene via a Grignardreaction and dry ice. The reaction did not go to completion and the student ended up with a mixture of o-toluicacid and o-chlorotoluene.Purify the o-toluic acid. Provide data to show that your compound is pure.

6.An organic chemistry student was attempting to synthesize N,N-diethyl-3-methylbenzamide from m-toluicacid and the reaction did not go to completion and the student ended up with a mixture of bothcompounds.Purify the m-toluic acid. Provide data to show that your compound is pure.

7.Benzaldehyde is used as the starting material for the synthesis of cinnamic acid. An organic chemistrystudent had made the mistake of stopping the reaction before it was complete and ended up with a mixture ofbenzaldehyde and cinnamic acid. Purify the cinnamic acid. Provide data to show your compound is pure.

8.Anilines can be reacted with sodium nitrite to be converted to aryl diazonium salts. These products can belater used in coupling reactions (i.e. Sandmeyer reaction) to further functionalize arenes. An organic chemistrystudent checked the purity of their 4-nitroaniline reagent prior to diazotonization only to discover it wascontaminated with naphthalene. Purify the 4-nitroaniline, and provide data to show your compound ispure.

Answer 1

You haven’t provided the experimental data for quantification. I will address the techniques used.

1) Benzoic acid and benzyl alcohol are both acidic in nature; however, benzoic acid is a stronger acid and reacts with a mild base like 1 M NaHCO₃ to give the sodium salt of benzoic acid, sodium benzoate. Benzyl alcohol doesn’t react with NaHCO₃.

The impure mixture is treated with 1 M NaHCO₃ when benzoic acid dissolves forming soluble sodium benzoate. The aqueous layer, containing sodium benzoate is extracted by solvent extraction technique and treated with 1 M HCl. This step converts sodium benzoate to benzoic acid which separates out as a solid. The solid benzoic acid is washed and dried to afford the pure compound.

2) Salicylic acid is a carboxylic acid while methyl salicylate is an ester. Being an acid, salicylic acid reacts with 1 M NaHCO₃. However, 1 M NaHCO₃ is a mild base and cannot cause hydrolysis of methyl salicylate. Consequently, the mixture is treated with 1 M NaHCO₃ when salicylic acid dissolves to form soluble sodium salicylate. Sodium salicylate is separated from methyl salicylate by solvent extraction technique and treated with 1 M HCl to give pure salicylic acid.

3) 2-napthol is faintly acidic and can be separated from 2-methoxynaphthalene (non-polar) by treatment with a strong base like 3 M NaOH. The mixture is treated with 3 M NaOH when 2-napthol dissolves, forming soluble the sodium salt of 2-napthol. The aqueous layer contains the sodium salt and is extracted from the organic layer which contains 2-methoxynaphthalene. The aqueous layer is just acidified with 3 M HCl which converts the sodium salt of 2-napthol to 2-napthol. 2-napthol is insoluble in the neutral medium and precipitates out as a solid. The solid is washed and dried with saturated NaCl solution to afford purified 2-napthol.

4) Benzoic acid and 2-napthol can be easily separated from each other since benzoic acid is a stronger acid and readily reacts with 1 M NaHCO₃. The mixture of the organic compounds was dissolved in an organic solvent and was extracted with 1 M NaHCO₃. Benzoic acid dissolves in 1 M NaHCO₃ forming sodium benzoate. The aqueous layer was separated from the organic layer by solvent extraction and acidified with 1 M HCl to give solid benzoic acid. The solid was separated, washed and dried to afford pure benzoic acid.

5) o-toluic acid is a carboxylic acid and reacts with 1 M NaOH. o-chlorotoluene is an aromatic halide and doesn’t react with 1 M NaOH. This difference in reactivity is exploited to separate o-toluic acid from o-chlorotoluene. The mixture of the organic compounds is dissolved in an organic solvent like dichloromethane and extracted with 1 M NaOH. Treatment of the mixture with 1 M NaOH converts o-toluic acid to soluble sodium methylbenzoate. The aqueous layer is separated and then acidified with 1 M HCl to give solid o-toluic acid. The crude material is dried and purified to give pure o-toluic acid.