Reaction of Acetic Anhydride and Isopropyl Alcohol

.

2008

Joshua BaileyChem 213 Section 3

3/19/2008

Introduction

Many esters with a low molecular weight have very pleasant odors. A few

examples are isoamyl acetate which has the odor of bananas, methyl salicylate which

smells like wintergreen, and ethyl butyrate which has the odor of pineapple. Esters are

also involved in biological activities. An example of such a case is vitamin C. The

purpose of this lab is to synthesize isopropyl acetate from acetic anhydride and isopropyl

alcohol. The product obtained will be analyzed by infrared spectroscopy, refractive

index, and gas chromatography. The data obtained in lab will be compared to literature

values to determine if the desired product was obtained.

Data Analysis

Mass of isopropyl acetate: 3.56 g

Refractive Index: 1.376

IR of Isopropyl Acetate

Peak (cm -1 ) Represents2983 C-H (aldehyde)2942 C-H (aldehyde)2884 C-H (aldehyde)1738 C=O (ester)1246 C-O (ester)

Discussion

When an anhydride reacts with an alcohol and is catalyzed by an acid the process

of esterfication takes place. The general reaction for this process is shown in figure 1.

The products obtained are an ester and a carboxylic acid. The complex mechanism of

this reaction occurs over six steps.

The first step of this reaction is protonation of the ester carbonyl (figure 2). This

makes it more electrophillic which in turns makes it more susceptible to nucleophillic

attack.

After the ester carbonyl is protonated the nucleophile is then able to attack the molecule

(figure 3). For this experiment the nucleophile isopropyl alcohol was used.

To neutralize the positive charge created by this nucleophillic addition the oxygen is

deprotonated (figure 4).

The oxygen in the middle of the compound becomes protonated (figure 5). This results

in -COOCH3 becoming a good leaving group. Once the leaving group has been created

the molecule splits in two (figure 6).

The deprotonation of figure 6 gives isopropyl acetate (figure 7).

Three different techniques were used to determine if the product obtained was

isopropyl acetate. The techniques used were infrared spectroscopy, refractive index, and

gas chromatography. The IR peaks obtained in lab were 2983 cm-1, 2942 cm-1, 2884 cm-

1, 1738 cm-1, and 1246 cm-1. The literature value of IR peaks for isopropyl acetate are

2984 cm-1, 2944 cm-1, 2884 cm-1, 1758 cm-1, and 1248 cm-1. The IR obtained in lab

showed many similarities to the literature IR of isopropyl acetate. The refractive index

was also obtained from the product. The refractive index was determined to be 1.376.

The literature value for the refractive index of isopropyl acetate is 1.377. The GC

obtained from lab showed the product was very pure. Using all this information it was

determined that isopropyl acetate was successfully synthesized.

Conclusion

The goals of the lab were successfully accomplished. Isopropyl acetate was

successfully synthesized in lab. This was determined by infrared spectroscopy, refractive

index, and GC. The refractive index of isopropyl acetate was found to be 1.376. The

actual refractive index of isopropyl acetate is 1.377. The percent yield of the product was

51.5%.

References

Smith, Janice G. Organic Chemistry. 1st ed. New York: McGraw-Hill, 2006. 798.

Mohrig, Jerry R., Christina N. Hammond, and Paul F. Shatz. Techniques in Organic Chemistry. 2nd ed. New York: Craig Bleyer, 2006. IR table.

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