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Fisher Esterification Lab report...

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Fischer Esterification Project Introduction Esters happens to be chemical compounds that play a very significant role in the lives of people worldwide. According to Encyclopedia.com, naturally esters of organic acids in fruits and flowers enables them to have their distinctive odors. Mostly, they are synthesized in the laboratory and used by cosmetic industries. Nontheless, certain evaporative esters are used as solvents for paints, lacquers and varnishes. Scientifically, common fats and oils are combination of various esters like stearin, palmitin, and linolein, formed from the alcohol glycerol and fatty acids.( Encyclopedia.com) On the other hand, Fischer Esterification is a method used in synthesizing esters from carboxylic acids and alcohols. As depicted in Fig 1, it occurs with the liberation of water. The reaction is acid catalyzed and an inorganic acid as sulfuric acid can be used as a catalyst. [Williamson, 2011]. According to Le Chatelier’s Principle, the reaction is reversible since the position of equilibrium can be shifted to the right by either the addition or removal of excess reactants.

Fig 1: General representation of Fischer Esterification

[McMurry, 2016]

The mechanism as shown in (Fig 2) happens by the initial protonation of carboxyl group by the acid, followed by nucleophilic attack by the alcohol, proton rearrangement, loss of water and loss of catalyzing proton. The reversible reaction yields hydrolysis of the ester. [Williamson, 2011]

Fig 2: General Mechanism for Fischer Esterification [Williamson, 2011]

Objectives For this experiment, unknown samples of a carboxylic acid and an alcohol were given for the Fischer ester synthesis. Prior to the experiment, the molar masses of the reactants to be used were given and their refractive indices were taken so all the substances were known. Procedure

First, the refractive indices of the carboxylic acid and alcohol were recorded in a refractometer. 4.6g of the acid and 25mL of the alcohol were put in a 125-mL bottom flask. Then 3 mL of concentrated sulfuric acid and a magnetic spinner were added. A reflux condenser was attached to the top of the flask and an electric heater put on the bottom. With reflux, heating and stirring, the reaction took about 1 hour to occur. Afterwards, it was allowed to cool to room temperature. Fig 4: Experimental setting for the reaction

[Williamson, 2011]

For the workup part of this experiment, it comprises of organic extraction by adding the solution to a separatory funnel containing 50 mL of water and 35 mL of ether. It was the shaken thoroughly in order to decant the aqueous layer and to remove sulfuric acid and excess alcohol. The organic layer was rinsed with 25 mL of water, followed by 25 mL of 0.5 M sodium bicarbonate, saturated sodium chloride solution. It was dried with anhydrous calcium chloride pellets. The product was purified by simple distillation and its refractive index was obtained. [Williamson, 2011]

Results and Discussion

To identify unknown samples of carboxylic acid and alcohol, the molar masses and the refractive indexes were obtained and compared to reference values from literature. The table below displays the results that were obtained. The substance that corresponds with the data is Ethyl acetate, a mixture of ethanol and ethanoic acid. Based on what was produced, it matches with the refractive index that was obtained

Table 1: Experimental Data Sample

Molar Mass

Melting point (C)

Refractive Index

Proposed Substance

(literature) [Chemical Book]

CD79146

60.05 g/mol

104.1

1.369

Ethanoic Acid

BX57146

46.1 g/mol

-114.1

1.402

Ethanol

Product

106.15g/m ol

166

1.372

Ethyl acetate

The proposed structures and esterification reaction are shown in Fig.3: Ethanoic Acid + Ethanol

Ethyl acetate + H2O

Fig 3: Proposed Reaction for the Experiment In order to the accuracy of results, additional analysis of infrared spectroscopy, mass spectra, nuclear magnetic resonance could be taken. Unfortunately, we were unable to obtain tis data in the lab.

Conclusion In a nut shell, the refractive index and data that were retrieved showed that the unknown sample from the carboxylic acid and alcohol were ethanoic acid and ethanol. The Fischer reaction yielded Ethyl acetate, and from the refractive indexes that were obtained, it shows the experiment was successfully carried out. Also, if the data were further analyzed through NMR and mass spectra process, the accuracy of it would have been excellent.

References  "ester." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 19 Apr. 2018 .

● McMurry, J. Organic Chemistry. 9th ed. Cengage Learning, 2016. Print. ● Williamson, K.L. and Masters, K.M. Organic Experiments: Macroscale and Microscale Organic Experiments. 7th ed. N.p.: Thomas Brooks / Cole, 2017. Print. ● Chemical Book (Refractive Index Data)...