Experiment_9

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Feb 20, 2024

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CHM 2205L Exp.9 Esterification of p-aminobenzoic acid: Synthesis of Benzocaine July 28 th , 2017 Nicholas Tyndall Lab Partner: Abhi Ahuja Professor: Dr. Chandrasekhar Abstract The purpose of this experiment was to form benzocaine in the reaction of p- aminobenzoic acid, and ethanol. This was done, by mixing the reactants and the catalyst and having the reactants reflux and have the reaction go to completion, as well as using vacuum filtration to isolate the crystals from the solution. Also, IR Spectroscopy was used in this experiment to determine the functional groups in this final compound. The results of the experiment were that 0.5593g of Benzocaine was obtained the theoretical yield is 0.760g, so the percent yield of the compound was 73.60%. The melting point of benzocaine from the experiment was 88.5˚C- 90.2 ˚C, and the literature value was 88-90 °C, and because of the values being so close one is able to characterize and identify the powder compound as benzocaine. Introduction

The objective of this experiment was to use the carboxylic acid, p-aminobenzoic acid, and ethanol to form benzocaine. The importance of this experiment is that it is used to form other compounds such as Lidocaine and Novocaine, the only difference is that they use a different aromatic residue than benzocaine does to form. Medical uses of Benzocaine can be to reduce pain or discomfort caused by minor skin irritations, sore throat, sunburn; also used to numb the skin or surfaces inside the mouth, nose, throat, vagina, or rectum to lessen the pain of inserting a medical instrument such as a tube or speculum. 1 Experimental The equipment, methods, and procedures used can be found in the lab manual. 2 The only changes to the lab procedure was that reflux was allowed to occur for 45 minutes instead of for 1 hour. Results Table 1. Mass and Percent Yield Compound Initial Mass(g) Obtained Mass (g) Theoretical Mass (g) Percent Yield Benzocaine 0.6312g 0.5593g 0.760g 73.60% Table 2. Melting Point Compound Melting Point Lit. Melting Point Benzocaine 88.5˚C- 90.2 ˚C 88-90 °C 3 Discussion The appearance of benzocaine was a fluffy white powder that was obtained from the reaction. The melting point literature value is 88-90 °C, the value that was obtained from the experiment was 88.5˚C- 90.2 ˚C, so by melting point the 1 https://www.drugs.com/mtm/benzocaine-topical.html 2 Chandrasekhar. Experiment 9. Esterification of p-aminobenzoic acid: Synthesis of Benzocaine. (2017) 3 http://www.chemicalbook.com/ChemicalProductProperty_EN_CB1217951.htm

compound can be identify as benzocaine. With a percent yield of 73.60% from there being 0.5593g of benzocaine being obtained, and the theoretical yield being 0.760g. When analyzing the IR Spectrum, one can see that, there is a primary amine in the compound shown by there being multiple peaks between 3500-3300, instead of secondary amine which would have one peak in that range. Then the 1594 peak is there showing there is an aromatic compound. From 3000-2800 there are two more peaks from their being an alkyl substituents connected to the ester. The carbonyl causes a sharp peak at 1678, and the ester causes a sharp peak at 1272. Mechanism for the synthesis of benzocaine starts off with its two reagents and a catalyst, in the first step the oxygen molecule that is double bonded to the p- aminobenzoic acid, attacks the H in H-SO 4 H, this gives a now double bonded OH + connected to the p-aminobenzoic acid, and a SO 4 H. Then the electrons from the double bond go to the oxygen that is double bonded, so now there is an OH single bonded to the compound. Then the ethanol is added into carbon attached to the now single bonded OH group, that give a OCH 2 CH 3 + with a H bonded off of it. Next the electrons in the bond between the H and the OCH 2 CH 3 + go to the O so that it now become OCH 2 CH 3 and the H from the bonded is attacked by SO 4 H, to now give H-SO 4 H again. In the next step the oxygen from the original OH bond connected to the p-aminobenzoic acid, attacks the H in the H-SO 4 H bond. This then gives SO 4 H, and causes there to be OH 2 + . The electrons from the bond between the carbon and the OH 2 + go to the to OH 2 + group, as well as the OH group connected to the carbon give its electrons to the bond. This results in a double bond being formed with an OH + group connected to it, from there the SO 4 H group attacks the H connected to the OH + group. This leaves there just being an oxygen double bonded, and now an ester with an ethyl group connected to it and a reformed H-SO 4 H molecule because it is a catalyst so it could not have been synthesized in the reaction. With nothing affected the NH 2 throughout the reaction. The role of sulfuric acid was to catalyze the reaction. If the reaction was only the p-aminobenzoic acid and ethanol, then the reaction could not occur. Since sulfuric acid is a catalyst, it is not consumed in the reaction and stays in the flask. The solution goes through reflux for 45 minutes to allow the reaction to go all the way to completion. Sodium Carbonate is then used to neutralize the acidity of the sulfuric acid. The addition of the sodium carbonate caused the release of carbon dioxide gas and water vapor, leaving sodium sulfate, which is polar so it is not soluble in the solution. The liquid was then cooled in an ice bath to get the crystals to form because they would not form when the solution was at room temperature. The solution and crystals were then filtered through vacuum filtration, this was

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used to isolate the crystals, water was used as the rinse because the sodium sulfate is very soluble in water, leaving the benzocaine isolated by itself in the top of the filtration apparatus. Conclusion The objectives of the experiment were met, benzocaine was formed from the reactants and the catalyst. This was shown by melting point being 88.5˚C- 90.2 ˚C and the literature value being 88-90 °C, so the compound was able to be identified as benzocaine. The results also were that the yield of benzocaine compared to the theoretical was 72.90%. References 1 https://www.drugs.com/mtm/benzocaine-topical.html 2 Chandrasekhar. Experiment 9. Esterification of p-aminobenzoic acid: Synthesis of Benzocaine. (2017) 3 http://www.chemicalbook.com/ChemicalProductProperty_EN_CB1217951.htm Appendix (0.6312g)/(137.138g) = 0.00460mol (0.00460mol) (165.189g) = 0.760g % Yield = (Initial/ Theoretical) (100) 0.5593g/0.760g = 0.7290 0.7360 x 100 = 73.60%