Experiment 9: Synthesis of Organic Compounds

A. Synthesis of 1-phenylazo -2-naptholData and Results

3. Chemical Tests:Test Performed Observations

0.1M NaOH1.0M HClNH4OH

CH3COOH

Questions:1. What reactions are involved in the synthesis of 1-phenylazo -2-napthol?

A. DIAZOTIZATION Preparation of solution of diazonium salt and benzene diazonium chloride from

aniline.HCl or H2SO4

ANILINE + NaNO2 → PHENYLDIAZONIUM CHLORIDE +2 H2O

B. DIAZONIUM-COUPLING REACTION Diazonium salt attacks the carbon in the ortho- and para- positions with respect to

the activating group attached to the benzene.

1Chem 31.1 Experiment 9

1. Theoretical Yield:Actual Yield:Percent Yield:

2. Physical Properties of the ProductAppearance: mud blockColor: red orangeTexture: fineOdor: rugby

2. Write the reaction pathway and mechanism for the synthesis of 1-phenylazo -2-napthol.

3. Why should the temperature of the reaction mixture be kept in 5oC?

The diazonium salt will easily decompose back to aniline at temperature higher than 5oC.

4. Explain the principle behind the use of starch iodine paste in detecting excess nitrous acid.

Nitrous acid oxidizes iodide ion to form iodine. The iodide ion in starch reacts with nitrous acid to form a blue complex. The blue coloration on the starch iodine paste will indicate excess nitrous acid since all iodide has been oxidized.

5. Why is the rate of the phenyldiazonium ion with β-naphthol dependent upon the pH of the reaction medium?

If the acidity of the reaction medium is high, the amines will be converted to ions thus they cannot undergo aromatic substitution reaction slowing the coupling reaction.

Applications:

B. Synthesis of SoapData and Results

2Chem 31.1 Experiment 9

1. Theoretical Yield:Actual Yield:Percent Yield:

2. Physical Properties of the ProductAppearance: soft liquidColor: creamTexture: softOdor: fragrant

3. Chemical Tests:Test Performed Observations

pH

Calcium chloride white precipitate

Magnesium chloride white precipitate

Ferric chloride white precipitate

Oil with soap with layerOil with water no layers

Questions:1. What reactions are involved in the synthesis of soap?

A. ALKALINE HYDROLYSIS Reaction with water or dilute alkali of triglyceride (fat or oil).

B. Triglyceride is reacted with lye or other strong bases produce glycerol and fatty acid salts (soap)

→

2. Write the reaction pathway and mechanism for the synthesis of soap

The hydroxide ion from NaOH attacks the carbonyl group of the ester to give an

orthoester.

The orthoester rearranges to form a carboxylic ester and an alkoxide

Proton transfer takes place since the OR group is more basic than RCOOH. The products

formed are alcohol and salt.

3. Why was the dilute soap solution poured in a solution of sodium chloride in water?

3Chem 31.1 Experiment 9

The addition of NaCl solution to the soap solution will precipitate the soap.

4. Explain the result obtained when the dilute soap solution is treated with calcium chloride, magnesium chloride, and ferric chloride solutions.

5. How doe soap function as an emulsifying agent for oil in water? Draw a picture of an oil droplet and several soap molecules to illustrate your answer.

The long hydrocarbon chain of the soap is non-polar and hydrophobic while the "salt" end of the soap molecule is ionic and hydrophilic.

Applications:

Would soap be a reasonable choice for the emulsifying agent if the water were slightly acidic? Why?

No, because the soap will not be able to form a bridge between oil and water because of the H+ attached to the polar end of the soap instead of water so an emulsion will not occur. Detergent can be used in place of the soap since it can tolerate slightly acidic water.

C. Synthesis of AspirinData and Results

3. Chemical Tests:Test Performed ObservationsFerric Chloride no reaction

Questions:1. What reactions are involved in the synthesis of Aspirin?

4Chem 31.1 Experiment 9

1. Theoretical Yield:Actual Yield:Percent Yield:

2. Physical Properties of the ProductAppearance: crystallineColor: fineTexture: whiteOdor: vinegar-like

ESTERIFICATION acid-catalyzed reaction of a carboxyl (-COOH) group and an -OH group of an alcohol or

phenol to form a carboxylate ester

2. Write the reaction pathway and mechanism for the synthesis of Aspirin.

3. Explain why in the recrystallization of Aspirin the water should not be heated above 80°C.

Aspirin may decompose back into salicylic acid and acetic anhydride when the temperature is too high.

4. Explain the results obtained when Aspirin and salicylic acid were treated with Ferric chloride solution.

Ferric chloride reacts with phenol to give a purple solution and since salicylic acid has a phenol group, it is expected to give a positive result. When the synthesized aspirin gives purple solution upon the addition of ferric chloride then not all the salicylic acid were consumed.

Applications:

Aspirin and salol are both acidic substances. Which is the stronger acid? Which would be more easily hydrolyzed in an alkaline medium? Why?

Aspirin is more acidic than salol because of the stability of its conjugate base and its –COOH functional group. Aspirin will be hydrolyzed easily because it is acidic.

5Chem 31.1 Experiment 9