Reaction scheme for Fischer Esterification of p-aminobenzoic acid: Synthesis of Benzocaine.3
In 1890, a chemist named Ritsert, was the first to synthesis benzocaine and introduced it in the market in 1902. Benzocaine is a pain reliever and has many active over-the-counter ingredients. It is also used as a lubricant and topical anesthetic on intratracheal catheters and pharyngeal and nasal airways to obtund the pharynegeal and tracheal reflexesl.2 Sodium channel binds to benzocaine and stabilizes the neuronal membrane which decrease its permeability to sodium ions.1 In this experiment, the synthesis of benzocaine is carried out by the acid-catalyzed esterification of 4-aminobenzoic acid with ethanol.2 Theoretical Yield:
1.25g/MW 137 = .009 moles
20mL / MW46 =0.435 moles
.009 X 165.19 = 1.49g
The purpose of this experiment is to synthesize benzocaine by esterification using 4-aminobenzoic acid with ethanol.
There were several parts in the procedure of benzocaine beginning with a round bottom flask that was 50mL, was fitted with a stirring rod and 1.25g of p-aminobenzoic acid and 20mL of ethyl alcohol was added. While being stirred, 1.0mL of concentrated sulfuric acid was added drop wise. A precipitate was formed and dissolved when heated. The solution was then cooled to room temperature and stirred for an hour. Cautiously, 10% sodium carbonate was added drop wise until the ph was 8. A precipitate formed and the crude of benzocaine was collected by vacuum filtration and a Hirsh funnel was used. Cold water was used to wash in 3 mL portions, the crude was weighed and a percent yield and melting point was recorded.
| Weighed (g)
Benzocaine + Watch glass + Paper
The expected amount of benzocaine was 1.49g, the measured was...
References: and Citation:
1. Material Data Safety Sheet. Benzocaine. http://www.jtbaker.com/msds/englishhtml/b1236.htm (accessed June 17, 2009)
2. Reactions of Carboxylic Acids & Their Derivatives. History of Benzocaine. http://www.chemistry.mcmaster.ca/~chem2ob3/20b3_summer2004_exp4.pdf (accessed 2004)
3. CHE Lab Supplement. Fischer Esterification of p-aminobenzoic acid: Synthesis of Benzocaine, a local anesthetic. http://tigernet.campbellsville.edu/ics/icsfs/CHE_344_Draft_Lab_Supplement_Spr_2011.pdf?target=76a75934-3ba3-431f-b2af-53908c0081b8 (accessed 2011)
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