PRACTICAL 4: CARBOXYLIC ACIDS, ESTERS AND AMIDES

Aim: To prepare a sample of ester and to investigate the physical properties of ester.

Hypothesis: Ester can soluble in organic solvent but insoluble in polar solvent.

Variables:-

Manipulative: Different types of solventRespond: Solubility Constant: Volume and concentration of solvent

Operation definition:

Materials/apparatus:

absolute ethanol, glacial ethanoic acid, concentrated sulphuric acid, 5% aqueous sodium bicarbonate solution, oil, water, sodium chloride solution, beaker, distillation flask, tap funnel, round bottomed flask, conical flask, measuring cylinder, thermometer, Liebig condenser, Bunsen burner, retort stands and clamps, tripod stand, stopper with two holes, wooden block.

Procedure:

A. To investigate the physical properties of ester

1. About 2 cm3 of ethyl ethanoate was poured into a test tube. The smell of the ester noted.2. About 5 cm3 of distilled water was added to the ester and the mixture is shaken well. The solubility of the ester in water was noted.3. Steps 1 to 2 were repeated using acetone and methylated spirits consecutively to replace distilled water.

Results:

Solvent Observation Inference Water Double layer form

Insoluble in waterEster insoluble in polar solvent

Acetone No double layer formSoluble in acetone

Ester soluble in organic solvent

Methylated spirits

No double layer formSolubke in methylated spirits

Ester soluble in organic solvent

B. To prepare a sample of ester

1. About 50 cm3 of absolute ethanol was mixed with 50 cm3 of glacial ethanoic acid flask into a

250 ml round-bottomed flask.2. 10 cm3 of concentrated sulphuric acid was added to the content of the flask while swirling.

Several boiling chips was added to the mixture. 3. The apparatus was set up as shown in Figure 1.4. The mixture was heated under reflux for 1 hour.5. The heating source was removed and the mixture allowed to cool to room temperature.6. The cooled mixture was poured into a separatory funnel and 25 cm3 cold water was added. The

separatory funnel was shaked. 7. The lower aqueous layer was separate from the upper organic layer. The aqueous layer was discard.8. 25 cm3 5% aqueous sodium bicarbonate solution was added and the separatory funnel was shaked and the lower layer was discard.9. Procedure 8 was repeated.10. 25 cm3 of water was added and the separatory funnel was shaked. The aqueous layer was

discard.11. 5 cm3 of saturated aqueous calcium chloride was added. The mixture was stir gently and the

aqueous layer discard.12. The organic layer was observed and smelted.

Figure:

water bath

Water in

Water out

Figure 1: Preparation of esterDiscussions:

For this activity we needed to investigate the physical properties of ester, which are when we mixed up the ester and water, acetone and methylated spirits. From the data that we collect in the table, we can define that when we mixed up some ester in water, we define that double layer will form. This is because the ester it is not soluble in water due to ester insoluble in polar solvent. Although the double layer is not appearing clearly, we can see the differences between the top of the layer and the bottom part. It is ester and water. Unlike when we mixed up some ester in acetone, there was no double layer formed. This is because due to ester is soluble in organic solvent, so that ester is soluble in acetone. The result and founded is the same as methylated spirits. No double layer formed because ester is soluble in organic solvent.

Esters participate in hydrogen bonds as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding makes them more water-soluble than their parent hydrocarbons. However, the limitations on their hydrogen bonding also make them more hydrophobic than either their parent alcohols or their parent acids. Their lack of hydrogen-bond-donating ability means that ester molecules cannot hydrogen-bond to each other, which, in general, makes esters more volatile than a carboxylic acid of similar molecular weight. Volatile esters, particularly carboxylate esters, often have a pleasant smell and are found in perfumes, essential oils, and pheromones, and give many fruits their scent.

Question1. Explain the meaning of esterification reaction?

Esterification reaction is conversion of an acid into an ester by combination with

an alcohol and removal of a molecule of water.

2. Write a balanced chemical equation to represent the reaction between ethanoic acid and ethanol.CH3 CHCOOH + CH3CH2OH H2SO4 CH3COOCH2CH3+ H2O

3. What is the function of the concentrated sulphuric acid in this experiment?The concentrated H2SO4 removes water from the products and is a dehydrating

agent.

4. Explain another method of preparing ethyl ethanoat.

Esters can also be made from the reactions between alcohols and either acyl

chlorides or acid anhydrides.

Making esters from alcohols and acyl chlorides (acid chlorides)

If we add an acyl chloride to an alcohol, we get a vigorous (even violent) reaction

at room temperature producing an ester and clouds of steamy acidic fumes of

hydrogen chloride.

For example, if we add the liquid ethanoyl chloride to ethanol, we get a burst of

hydrogen chloride produced together with the liquid ester ethyl ethanoate.

Making esters from alcohols and acid anhydrides

The reactions of acid anhydrides are slower than the corresponding reactions

with acyl chlorides, and you usually need to warm the mixture.

Taking ethanol reacting with ethanoic anhydride as a typical reaction involving an

alcohol:

There is a slow reaction at room temperature (or faster on warming). There is no

visible change in the colourless liquids, but a mixture of ethyl ethanoate and

ethanoic acid is formed.

5. What is the function of 5% aqueous sodium bicarbonate solution in this experiment?Sodium bicarbonate is used to neutralize the acidic catalyst and the excess of

ethanoic acid

6. Explain the use of calcium chloride solution in this experimentRemove the excess of ethanol

7. Compare the solubility of ethyl ethanoate in water, acetone and methylated spirits. Explain your observation.Ethyl ethanoate is most soluble in methylated spirit, followed by water and

acetone. Most of ethyl etahanoate structure is organic part. Hence, it is most

soluble in organic solvent such as methylated spirit. Ethyl ethanoate is also a

polar solute, so it must be soluble in water and acetone. But, water is more polar

than acetone. That's why water is a good solvent for ethyl ethanoate compare to

acetone but less good when comes to methylated spirit. One more thing, ethyl

ethanoate can form hydrogen bond with water. That makes it forms stronger

bond with water compare to acetone.

8. Name the ester produced from an esterification reaction between butanoic acid and ethanol.Propyl ethanoat

9. Write a balanced chemical equation to represent the reaction above.CH3 CH2CHCOOH + CH3CH2OH H2SO4 CH3 CH2CHCOO CH2CH3+ H2O

Conclusion: Ester can soluble in organic solvent but insoluble in polar solvent. Hypothesis accepted.

References:

1. http://en.wikipedia.org/wiki/Ester

2. Science notes given by Pn. Halina Bt. Kasmani