The Fischer Esterification Experiment

Organic compounds that are classified into the ester group are commonly associated with very pleasant smelling fragrances. These esters can be synthesized by combining a carboxylic acid with an alcohol while using a mineral catalyst. By causing a reaction between ethanoic acid, more commonly known as acetic acid, and 3-methyl-1-butanol or isopentyl alcohol, the ester isopentyl acetate (3-methyl-1-butyl ethanoate) is produced. Isopentyl acetate is easily recognizable by the strong, “banana,” odor. This ester is used to give perfumes, foods, and beverages their fragrance and is a major component of banana oil. In order to synthesize isopentyl acetate, glacial acetic acid undergoes esterification with isopentyl alcohol.

Before the process of esterification can begin, the starting material acetic acid must be obtained. Acetic acid can either be found naturally or produced synthetically. In nature, this acid is found as a product of the oxidation of ethanol. Acetic acid is the major organic component of vinegar. If the sugars in apple cider or grape juice are allowed to ferment ethanol is formed initially, but prolonged fermentation leads to acetic acid. Acetic acid dissolves most simple organic compounds, and it has a convenient boiling point (118 C). In this experiment acetic acid is both the solvent and reactant. Using an excess of acetic acid also helps to drive the equilibrium toward the desired product (Mohrig, Hammond, Morrill, and Neckers). Once the method for producing acetic acid is known, we can add isopentyl alcohol in attempt to produce isopentyl acetate. By understanding the process involved in producing isopentyl acetate, a substantial amount of surplus can be produced allowin the extensive research that needs to be performed to truly understand the significance of this ester outside of the perfume and banana oil field.

Initially, the only thing given concerning the synthesis of the product was the structure and it”s respective common name. With this limited amount of information one has to come up with the reagents needed to form isopentyl acetate using the esterification process. Using basic knowledge about how esters are formed from combining a carboxylic acid and an alcohol, one can determine that isopentyl alcohol and glacial acetic acid are the reagents that would form isopentyl acetate via esterification.

Began by combing 16 ml of isopentyl alcohol and 22 ml of glacial acetic acid; These specific amounts were used because a limit (between 5g-10g) had been set on the amount of limiting reagent being used. In order for this reaction to take place, a catalyst was required so sulfuric acid was used. The process of esterification was started by assembling a reflux apparatus and beginning to heat this mixture at 60oC for an hour. While this mixture was heating, it changed from a foggy appearance dark yellow color almost immediately. Also, after about 8 minutes of boiling, an obvious odor of banana could be smelt. Upon removing this mixture after the hour of boiling was over, the sweet, fruity, banana smell was very strong and distinct and the solution was very dark yellow. After successful completion of forming this product, this mixture was put into a separatory funnel washed with 50 ml of distilled water and the lower aqueous layer was drained out, separating it from the upper organic layer.

This just described was necessary in order to remove the excess acid from the product. Then sodium bicarbonate was used in the same way that the water was used to separate further all the impurities that my compound was likely to have picked up. These steps were repeated until the layer that was being drained out could turn litmus paper blue. After this “work-up” part of the procedure, anhydrous calcium chloride was added as a drying agent and let to sit for 10-15 minutes. Next decant the product from the calcium chloride. Now, the only thing left to do is to remove impurities left in the compound. Using a ratovac to evaporate the remaining impurities did this. One should not only used the low vac, but also use the high vac to make sure that the only thing left in the flask is the actual product isopentyl acetate. After this long procedure was completed the product was weighed and the % yield was determined to be 38.322%.

The ester was then analyzed to determine structure and purity. This can be done by running a Gas chromatography (GC), a Nuclear Magnetic Resonance Spectrometry (NMR), and an infrared spectrometry (IR).

GC was a useful test to perform since the GC column in the machine has the ability to separate complex mixtures. As each of the components of the ester went through the column, peaks were recorded in order to calculate the retention time. The only drawback about this method to confirm my compound is that you have to have the results for a mixture that is proven to be isopentyl acetate and compare the results. Also, the set of experimental conditions must be the same. A sample of the product diluted in diethyl ether was entered into the GC at a temperature of 80oC and at a rate of 10o per minute. The chromatogram produced two main peaks. The first peak with a retention time of 1.844 was indicative of the diethyl ether. The second peak with a retention time of 2.150 was indicative of isopentyl acetate.

Since this method using GC is only useful in product identification when there is a known substance to compare it to, other methods such as NMR were used. NMR is useful in determining the actual positions of the H+ for in compounds. The NMR spectrum produced from this ester showed five different peeks indicating five different types of hydrogens. Peak A is a doublet and represents the hydrogens found on the two-methyl groups adjacent to one hydrogen. Peak B represents one hydrogen that is adjacent to eight hydrogens. Peak is a quadruplet, which means two hydrogens are split by the adjacent protons. Peak D Is a sing let which relates to the three hydrogens found on the carboxylic acid end of the molecule. Lastly peak E is a triplet found farthest down field meaning the hydrogens are deshielded by the oxgyens adjacent to them. In order to be accurate with analysis the NMR results should be compared to the one found in Sadtler.

By running an infrared spectrometry (IR) important information about the particular functional groups of a compound is obtained. This allows for the naming of an unknown compound by analyzing the different functional groups that makes up the specific compound. The regions in which the functional groups appear fall between 4000-1300 cm-1 on the spectra. Since the compound synthesized was an ester, the first thing one should look for on the spectra is a strong peak between 1800-1700 cm-1. The spectra did indeed have a strong peak at 1742.7cm-1 that is the carbon-oxygen double bond known as the functional group in esters. The alkyl carbon-hydrogen, part of the compound is represented by a peak around 2900 cm-1 on the spectra. The spectra results of the isopentyl acetate produced in class proved to be very similar to those found in Sadtler.

Being able to come up with the correct reagents needed to undergo the process of esterification when trying to form a specific ester was the main purpose of this lab. The starting products to form ester were isopentyl alcohol and glacial acetic acid. These two reagents won”t form the product alone so a sulfuric acid catalyst was necessary. After the reaction was completed, there was a Bi-product evident which was in this case, the water. Excess acetic acid was used in my reaction to drive the reaction to form the isopentyl acetate. Esters are very useful products because they give some perfumes, cosmetics, foods and beverages their sweet and fruity odor. Another main objective of this lab was to correctly use NMR, GC, and IR to confirm the synthesis of the ester. Since the process for forming isopentyl acetate is being practiced worldwide, maybe the best procedure in order to form a surplus of the product will be discovered so that research concerning other uses of isopentyl acetate will be able to be performed.

Bibliography

  1. Eagleson, Mary.ed. Consise Chemistry Encyclopedia. Walter de Gruyter and company, 1993.
  2. Lewis, Richard. J. Sr, ed. Hawley”s Condensed Chemical Dictionary. John Wiley and Sons incorporated, 1997.
  3. Snell, Foster Dee, ed. Snell-Ettre Encyclopedia of Industrial Chemical Analysis, v10. Interscience publishers, 1970.
  4. Mohrig, Hammond, Morrill, and Neckers. Experimental Organic Chemistry. W.H* Freeman and company, New York, New York 1998, pages 247-259.

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