Jason Gleditsch's Writing Sample

 

Preparation of Benzocaine by an Esterification Reaction

Jason Gleditsch
2-17 -08

Introduction:

The coca shrub (Erythroxylon coca), which grows wild in the Peruvian Andes mountains, is notorious for being the source of cocaine and other strong drugs, but it is also the source of some weaker local anesthetics like benzocaine. This product of the coca shrub is used in many topical pain relieving ointments. Some of these ointments include oral ulcer medications like those produced by Blistex and Orejel. It is also used in some anti-itching ointments, hemorrhoid ointments, and some pain relief sprays. To make benzocaine in the lab, a Fischer esterification reaction of 4-aminobenzoic acid and ethanol is used (Figure 1.1). In this experiment this reaction will be performed and an infrared spectrograph and melting point will be taken to insure that benzocaine (Figure 1.2) was produced successfully.

Figure 1.1: Fischer Esterification to Create Benzocaine

 

Data:

Mass of Product = 0.314g
Theoretical Yield = 0.578g
% Yield = 54.3%
Melting Point = 88°C

Table 1.1: Benzocaine IR

 

Observed Peak (cm -1)

Standard Peak (cm -1)

Type of Bond

~2900

2990-2850

C-H

1281.18, 1311.24

1300-1000

C-O

1680.27

1850-1630

C=O

3418.05-3215.58

3500-3150

N-H

846.22

860-800

p-Aromatic

 

Duscussion:

In this experiment a Fischer esterification was used to create benzocaine. A Fischer esterification reaction is a six step reaction (Figure 1.3). In the first step the acid catalyst protonated the carbonyl oxygen, which created a positive charge on the oxygen atom. The electrons in the π-bond then moved to the oxygen atom to balance the charge. This created a positive charge on the carbon and one of the lone pairs of electrons on the oxygen of the ethanol formed a bond with the carbonyl carbon. The oxygen atom on the ethanol was then deprotonated by the conjugate base of the acid catalyst. The acid catalyst then protonated the OH group, that was on the carboxylic acid, to make it a better leaving group. The newly formed H2O group then leaved leaving a positive charge on the carbon, which was balance in the same step by one of the lone pairs on the oxygen on the other OH group which created a π-bond with the carbon again. This created a positive charge on the oxygen and the conjugate base then deprotonated the OH group balancing the charge on the oxygen atom. This reaction yielded benzocaine and water.

Once the product was produce a melting point was measured to identify the product and to test for purity. If the melting was not the literature melting point, which was obtained from the MSDS sheet for benzocaine, of 89°C then the product was not pure and would have to be recrystallized. The melting point for the product produced from the esterification was 88°C which confirmed the identity and that the product was close to pure and a recrystallization was not necessary.

An infrared spectrogram (IR) was the taken of the product to further confirm its identity. On the IR five distinctive peaks were observe and labeled with the corresponding functional group (Table 1.1). A peak showed up at about 2900cm -1 which was in the range of the literature peak (2990-2850cm -1) for a C-H bond. The peak’s wave number could not be determined exactly because the computer was unable to label it because the peak was so strong. More peaks showed up at 1281.18 and 1311.24cm -1 which fall into the literature peak range (1300-1000cm -1) for the C-O bond and another peak at 1680.27cm -1 which corresponds with the literature peak range (1850-1630cm -1) for the C=O bond. There were also peaks in the range of 3418.05-3215.58cm -1 which corresponds with the range in the literature for the N-H bond (3500-3150cm -1). Another peak showed up at the wave number 846.22cm -1 which corresponds with the literature peak range (860-800cm -1) for an aromatic region that has substituents in the para position.

 

Conclusion:

From the IR and the melting point it can be concluded that benzocaine was successfully synthesized with a percent yield of 54% and rather pure. The reason for the discrepancy in the melting point might be that there is still some reactant in the product or other impurities. Some possible reasons for the low percent yield might be that not all of the product was retrieved from the filter, some solvent was lost during the refluxing, and some of the reaction was lost when it foamed over the edge of the flask during the addition of the sodium bicarbonate.

Figure 1.2: Structure of Benzocaine

Figure 1.3: Mechanism for the Esterification of 4-aminobenzoic Acid and Ethanol