Lab Report: Preparation of Benzocaine by Esterification Reaction

Abstract

The aim of this experiment was to synthesize benzocaine, a local anesthetic, through an acid-catalyzed esterification reaction between 4-aminobenzoic acid and ethanol. The synthesized product's purity was analyzed using Fourier Transform Infrared Spectroscopy (FTIR), the percentage yield was calculated, and the melting point was measured. The experiment yielded a product with an 84% purity.

Introduction

Benzocaine, commonly known as Orajel, is a local anesthetic used for pain relief in medical and dental procedures. It belongs to the class of amino esters and amino amides, which are vital in modern medicine (Torrens and Castellano, 2006).

The history of local anesthetics traces back to the discovery of cocaine in the 1880s. However, cocaine's toxic and addictive properties led to the search for safer alternatives, resulting in the discovery of compounds like procaine, tetracaine, and benzocaine (Redman, 2011).

Benzocaine, with the chemical formula C₉H₁₁NO₂ and a molecular weight of 165.19 g/mol, inhibits sodium channels in neuronal membranes, preventing the transmission of action potentials and thereby reducing pain signals (R.

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Singh et al., 2020).

Benzocaine is commonly found in topical gels, creams, lozenges, and throat sprays, as it has poor water solubility and cannot be injected (L. Rahilly, 2015). This experiment aims to synthesize benzocaine through acid-catalyzed esterification of 4-aminobenzoic acid with ethanol, a process in which the carboxyl group of the acid reacts with the alcohol's hydroxyl group in the presence of a catalyst (K. Scott, 1995).

Materials and Methods

Materials

• 5mL round bottom flask
• 120mg 4-aminobenzoic acid
• 7.5mL absolute ethanol
• 1.25mL concentrated sulfuric acid
• Reflux apparatus
• 100mL Erlenmeyer flask
• 15mL distilled water
• 15mL sodium bicarbonate
• pH paper
• Vacuum filter

Method

1. Add 120mg of 4-aminobenzoic acid into a 5mL round bottom flask along with 7.5mL of absolute ethanol and boiling chips. Heat the mixture until the solid dissolves and then cool it in an ice bath.

2. After cooling, add 1.25mL of concentrated sulfuric acid drop by drop. Set up a reflux apparatus and reflux the mixture for 60 minutes.

3. Detach the apparatus and cool the mixture to room temperature. Transfer the mixture to a 100mL Erlenmeyer flask and add 15mL of distilled water. Allow the mixture to sit for one week.

4. In the following week, add saturated sodium bicarbonate drop by drop to the mixture to neutralize excess sulfuric acid. Use pH paper to check the pH; add more sodium bicarbonate if the pH is less than 8. Filter the mixture using vacuum filtration, washing the crystals with 1mL of water to ensure all the product is collected.

5. Dry the product in an oven for 20-30 minutes. Analyze the final product using FTIR spectroscopy.

Results and Calculations

Functional Group Assignments (cm^-1)

Calculations

The percentage of benzocaine obtained:

% Benzocaine = (Actual yield / Theoretical yield) x 100

Actual yield of 4-aminobenzoic acid:

Mass = 0.50g

Moles = Mass / Molecular weight (m.w) = 0.50 / 137.14 = 3.6x10^-3

Theoretical yield of benzocaine:

Molecular weight (m.w) = 165.19

Mass = Moles x m.w = 3.6x10^-3 x 165 = 0.594g

% Benzocaine = 0.5g / 0.594g x 100 = 0.84 x 100 = 84%

Discussion and Conclusion

The FTIR analysis of the synthesized benzocaine revealed characteristic peaks corresponding to functional groups, supporting the successful synthesis. In the fingerprint region, the C-O stretch (1280 cm^-1) and C=O stretch (1680 cm^-1) were identified, as expected for an ester like benzocaine (Fuliaş et al., 2013).

The calculated percentage yield of 84% indicates the efficiency and purity of the synthesis process. Any product loss can be attributed to the filtration step. Additional tests such as melting point determination can be performed to further assess impurities, as a sharp melting point range signifies high purity (C. Graham Brittain, 2009).

Other analytical techniques like Mass Spectroscopy (MS) and NMR can also be employed in future experiments to confirm purity and structural information. MS can determine the presence of nitrogen atoms based on mass values, while NMR can provide insights into proton arrangements and splitting patterns (ChemLibre, 2020; Users.wfu.edu, 2020).

Conclusion

This experiment successfully synthesized benzocaine through acid-catalyzed esterification. The FTIR analysis and percentage yield of 84% support the purity and efficiency of the synthesis. Future experiments should include additional purity tests, such as melting point determination, and comparison with industrial sources for a more comprehensive assessment of the synthesized product.

References

1. Torrens, F. and Castellano, G. (2006). Periodic Classification of Local Anesthetics (Procaine Analogues). International Journal of Molecular Sciences, 7(1), 13.
2. Singh R, Al Khalili Y. Benzocaine. [Updated 2020 Feb 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK541053/
3. Redman, M. (2011). Cocaine: What is the Crack? A Brief History of the Use of Cocaine as an Anesthetic. Anesthesiology and Pain Medicine, 1(2).
4. Louisa J. Rahilly DVM, DACVECC, Deborah C. Mandell VMD, DACVECC, in Small Animal Critical Care Medicine (Second Edition), 2015.
5. K. Scott, Separation of Liquid mixtures/pervaporation. Handbook of Industrial Membranes (Second Edition) 1995.
6. Chen, Y., Zou, C., Mastalerz, M., Hu, S., Gasaway, C. and Tao, X. (2015). Applications of Micro-Fourier Transform Infrared Spectroscopy (FTIR) in the Geological Sciences—A Review. International Journal of Molecular Sciences, 16(12), 30223-30250.
7. Prusty, K. (2020). Fourier Transform Infrared Spectroscopy - An Overview. Sciencedirect.com.
8. Fuliaş, A., Ledeţi, I., Vlase, G., Popoiu, C., Hegheş, A., Bilanin, M., Vlase, T., Gheorgheosu, D., Craina, M., Ardelean, S., Ferechide, D., Mărginean, O. and Moş, L. (2013). Thermal behaviour of procaine and benzocaine Part II: compatibility study with some pharmaceutical excipients used in solid dosage forms. Chemistry Central Journal, 7(1).
9. Paczkowska, M., Wiergowska, G., Miklaszewski, A., Krause, A., Mroczkowka, M., Zalewski, P. and Cielecka-Piontek, J. (2013). The Analysis Of The Physicochemical Properties Of Benzocaine Polymorphs.
10. C. Graham Brittain (2009). Using Melting Point to Determine Purity of Crystalline Solid, 1-2.
11. Chemistry LibreTexts. (2020). Nitrogen Rule.
12. Users.wfu.edu. (2020). 1H NMR - Splitting.