Preparation of Isoamyl Acetate

...

[pic 4]

Figure 2. Reflux Set-up

The Fischer esterification was conducted for this experiment at a reflux reaction. This is a method of heating liquid so that escaping vapor is condensed and returned to the liquid. The purpose of reflux is to use heat reaction mixtures without losing a volatile liquid. The condenser is used to heat a liquid in a container that catches and returns escaping vapor.

Esterification is a reversible reaction - the 'forwards' and 'reverse' reactions occur at the same time. This reaction balances out and will naturally find its “equilibrium point” where the forwards and reverse reactions occur at a certain proportion to each other, and all concentrations of reactants will remain the same. This is a reverse reaction principle called the Le Chatelier's principle. It states that the amount of ester produced in an equilibrium reaction might be increased either by using an excess of one of the reactants or by removing one of the products.

Concentrated sulfuric acid has the useful property of being the reaction’s dehydrating agent – which will absorb water molecules. This acts as the catalyst of the reaction When you add this to the reaction mixture, you lower the number of water molecules.

The extraction with saturated sodium chloride(NaCl) solution instead of plain distilled water is used because the bulk of the water in the solution can often be removed by swirling vigorously or "washing" the organic layer with saturated aqueous sodium chloride. The salt water works to pull the water from the organic layer to the water layer. This is because the concentrated salt solution wants to become more dilute and because salts have a stronger attraction to water than to organic solvents. Sometimes, a saturated aqueous solution of sodium chloride is called brine.

Volume of Isoamyl Alcohol

2.5 mL

Volume of Acetic Anhydride

2.6 mL

Weight of empty vial

17.5545 g

Wight of vial and sample

19.1411 g

Actual Yield

1.5866 g

Also, the use of sodium bicarbonate(NaHCO3) and anhydrous sodium sulfate(Na2SO4) was made for this experiment. A wash with a sodium bicarbonate was done to neutralize the excess acid and to remove any unreacted acetic anhydride. Mixing with anhydrous sodium sulfate, an organic salt, which decreases the solubility of the organic compounds in water thus assisting in the extraction by organic solvent.

Table 3. Data Table

The determination of limiting reagent, theoretical yield and percent yield was calculated using the data in Table 3:

- Determination of Limiting Reactant

(2.5mL isoamyl alcohol)[pic 5] [pic 6] [pic 7]

= 0.0229 mole of isoamyl acetate – LIMITING

(2.6mL acetic anhydride)[pic 8]

= 0.0276 mole isoamyl acetate- EXCESS

2. Theoretical Yield

(0.229 mole isoamyl acetate)[pic 9] = 2.98158 g isoamyl acetate

3. Percent Yield

[pic 10]

Some of the errors that might have occurred during the experiment could be one of this reasons including: (1) using unclean glass wares that made some side reactions; and (2) water may not have circulated fast enough during reflux and distillation methods.

CONCLUSION

Isoamyl acetate is the final product that was prepared from an Fischer esterification reaction of acetic anhydride and isoamyl alcohol. This was isolated by liquid-liquid extraction and drying over sodium carbonate, and then purified by distillation. The pure product had a viscous, pale yellow oil with a fruity odor. These esterification reactions are very slow in nature and need to be catalyzed by inorganic acids. Thus, the need of refluxing of reactants is done to increase the yield of the product.

REFERENCES

[1] Gilbert, J. & Martin, S. (2011). Experimental organic chemistry: A miniscale and microscale approach. USA: Cengage Learning.

[2] Jacobs, T., Truce, W., Robertson, G. (1974). Laboratory practice of organic chemistry. USA: Macmillan Publishing Co., Inc.

[3] Mayo, D., Pike, R., & Forbes, D. (2011). Microscale organic laboratory with multistep and multiscale syntheses. USA: John Wiley & Sons.

[4] Pavia, D., Lampman, G., Kriz, G. (2013) A microscale approach to organic laboratory techniques, 5th Ed. USA: Cengage Learning.

[5] Pike, D., Engel, R., Kriz, G., & Lampman, G. (2006). Introduction to organic laboratory techniques: A microscale approach. USA: Cengage Learning.

[6] Ping, Elizabeth. (2011, November). Isopentyl Acetate. Retrieved September 11, 2016 from the World Wide Web: http://www.academia.edu/7330446/Isopentyl_Acetate_Banana_Oil

[7] Williamson, K. & Masters, K. (2011). Macroscale and microscale organic experiments. USA: Brooks/Cole Cengage Learning.