Benzocaine: Cocaine and New Melting Point

1605 Words Oct 9th, 2008 7 Pages
Experiment # 45: Benzocaine


The local anesthetic, benzocaine, was synthesized via the esterification of p-aminobenzoic acid with ethanol. The percent yield of crude product was determined to be 21% and the melting point was recorded at 86.2°C ± 0.2°C, with a 6.3% error from 92°C, the literature melting point of pure benzocaine. The crude product was then recrystallized to improve the purity of benzocaine and 57.4% was recovered. The new melting point range was measured at 89.1°C ± 0.3°C, which has a 3.15% error. The infrared spectrum of the recrystallized product was measured to further verify that the synthesized product was benzocaine.
The discovery of benzocaine as a local anesthetic came out of necessity to
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Next, 1mL plus an additional 10 drops of 10% sodium carbonate was added drop-wise to the beaker until the solution reached a pH of 8. The precipitate formed (crude benzocaine product) was collected via vacuum filtration and washed with water during the transfer into the Hirsch funnel. The product was allowed to dry for one week after which the mass and melting point of the crystals were measured.
The crude product was then recrystallized in a Craig tube over a warm water bath (60-70°C) by adding methanol drop-wise until the solid completely dissolved. Eight drops of hot waster were then added to reform the precipitate, followed by subsequent addition of 15 methanol drops to re-dissolve the precipitate. The solution was then chilled in an ice bath and “seeded” with a spatula to induce crystallization. The recrystallized product was then collected via gravity filtration using an air vacuum to accelerate the process. An analytical balance was used to determine the mass of the purified product. The crystals were collected in two capillary tubes and a MelTemp device was used to measure the new melting point. A sample of crystals was run through the IR spectrometer to obtain the infrared spectra for the purified benzocaine product. The data and calculations sheets are attached to the report.

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