Synthesis_of_isoamyl_acetate.pdf

Colleen Samantha Dioquinoa, Christopher Jay Robidillob Abstract Esters are prepared in many ways and one of which is through fischer esterification. This reaction involves carboxylic under acidic condition with alcohol. This experiment aimed to synthesize isoamyl acetate and understand preparing ester’s mechanism. The test compounds underwent reflux, distillation, extraction and vacuum filtration. Through an acid, acetic acid could serve as a substrate. This could easily be attacked by isoamyl alcohol, thus producing isoamyl acetate. Work up was done through the conjugate base. Assumed by-products of this reaction was water and sulfuric acid which was removed after simple distillation. This experiment had produced a considerable yield of isoamyl acetate. Keywords:

ester,

fischer

esterification,

isoamyl

acetate,

mechanism,

substrate

another acid and an alcohol, this would undergo fischer esterification process. Esters are prepared through SN2 reaction, acid chloride or fischer esterification. Carboxylic acids and its derivatives are usually the source of ester. When these are treated with strong base and alkyl halide, these will produce esters. Acid chlorides reacted with alcohol would readily yield ester since chlorines are good leaving group. Moreover, carboxylic acid, if treated with

This experiment aims to:  

Synthesize isoamyl acetate Understand the mechanism of preparing ester

The test compounds used and produced in this experiment are in Table 1.

a. CHM146L student, School of CHE-CHM-BE-MSE, Mapua Institute of Technology b. CHM146L professor, School of CHE-CHM-BE-MSE, Mapua Institute of Technology

Table 1-test compounds

Test Compounds Name Isoamyl alcohol

Sodium Bicarbonate Glacial acetic acid

Structure

NaHCO3

NaCl Sulfuric acid

Magnesium sulfate

Isoamyl acetate

The reagents were prepared by the laboratory assistant before the experiment was performed.

Figure 2

The hydroxyl group is converted into water to a better leaving group. The oxygen at another hydroxyl group would give its lone pair to form a π bond to expel water as a leaving group. The positive charge on oxygen would be deprotonated by the conjugate base.

When isoamyl alcohol was mixed with acetone and sulfuric acid, isoamyl acetate had been formed after refluxing the mixture. The carbonyl oxygen was first protonated using the acid. Isoamyl alcohol would function as a nucleophile and attacks the carbonyl carbon. To remove the positive charge on oxygen, the conjugate base would deprotonate oxygen. Figure 3

When the product was distilled, there were some liquid that were collected at 105ºC. This was assumed to be water from the last extraction of the isoamyl acetate. Table 2-Data

Figure 1

Data Weight of crude product Weight of pure product Percent yield

8.41 g 7.28 g 86.56%

From table 2, the weight of the crude product is 8.41g but after crystallization, the weight decreased to 7.28 g. This is a considerable

percent yield due to the presence of excess sulfuric acid that wasn’t neutralized by 5% aqueous sodium bicarbonate since the acid was concentrated.

The acetic acid was made less stable through sulfuric acid which had protonated the carbonyl group. Since the carbonyl group is weak, it could be attacked by isoamyl alcohol to produce ester. The positive charge on oxygen was relieved through hydrogen sulfate, conjugate base. The hydroxyl group was made water to become a stable leaving group. The experiment had produced a high yield of isoamyl acetate. The remaining percent might have been caused by the error brought by distillation and the excess sulfuric acid that wasn’t neutralized by the aqueous sodium bicarbonate. I would strongly recommend that the base must be much stronger than 10% sodium bicarbonate to reduce wasted chemicals since the extraction was done nine times.

[1] Klein, D. (2012). Organic Chemistry. USA: Wiley [2]

Mayo, Dana W. Microscale Organic Laboratory. John Wiley & Sons, Inc. 1999

[3] Williamson, Kenneth L. Macroscale and Microscale Organic Experiments. D. C. Healh and Company. [4]

Schoffstall, Allen M. Microscale and Miniscale Organic Chemistry Laboratory nd Experiments. 2 ed. Mcgraw hill publication. 2004. th

[5] Solomon and Fryhle. Organic Chemistry. 8 Edition. Prentice hall.