Procedure

Benzocaine is the trade name because that the neighborhood anesthetic well-known cg-tower.comically together ethyl p-aminobenzoate, i m sorry is discovered in plenty of creams and also ointments offered in the therapy of pain due to sunburn, minor burns, cuts, scrapes and insect bites. Benzocaine is structurally analogous to Cocaine, Lidocaine, and also Novocaine (shown below) and is ready by the esterification the p-aminobenzoic acid v ethanol.1 note that esterification reactions have the right to be substantially influenced by the concentration of beginning materials and products in solution, as described by Le Chatelier’s Principle.

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Focus Questions

Choose among the emphasis questions below.

What room the minimum molar equivalents of ethanol that have the right to be used in the esterification reaction and still obtain benzocaine product? (review Le Chatelier’s Principle) What room the preferably molar equivalents of water that have the right to be current in the esterification reaction and also still achieve benzocaine product? (review Le Chatelier’s Principle) have the right to the concentration that para-aminobenzoic acid be increased, fairly than ethanol, to rise the amount of benzocaine product derived from the reaction? (review Le Chatelier’s Principle) What is the impact if a sterically bulky alcohol, such together isopropanol, is provided rather than ethanol in the esterification reaction?

Creativity is encouraged. If you have actually a various idea because that a focus question please talk about it v your GSI prior to proceeding.

Before lab discuss your focus question with your tiny group and also answer the questions uncovered on the group experimental design sheet at the connect here. The paper is also listed in the sources folder ~ above CTools.


Reagents:

p-aminobenzoic acid ethanol concentrated H2SO4 10% sodium carbonate solution

Place 0.360 g that p-aminobenzoic acid and also 3.60 mL that ethanol in a 10-mL conical flask. Include a magnetic spin vane and also stir the mixture to dissolve the hard acid. Through stirring, add 0.30 mL of focused sulfuric acid dropwise (CAUTION! sulfuric acid reacts violently v water, is a corrosive, and also causes severe burns). Enhancement of sulfuric acid causes precipitation the the hydrogen sulfate salt of p-aminobenzoic acid, yet this precipitate will dissolve during the complying with reflux duration as the hydrogen sulfate salt that the acid is converted into the hydrogen sulfate salt the the ester. To prepare for reflux, attach a water-cooled condenser and also heat the mixture so that it boils gently for 60-75 minutes. (Note the quantities right here may need to be changed depending on your plans be sure to check all calculations with your GSI if you are unsure)

Depending on just how you’ve transformed the reaction conditions the reaction might take more or much less time. You can monitor the progression of the reaction through TLC. To collect a little sample from the refluxing mixture carefully lift increase the dry tube at the optimal of the reflux condenser and lower a lengthy glass pipette down right into the mixture. Over there is no must use a bulb to withdraw the solution, because a small drop that the reaction mixture will be normally wick up into the end of the pipette. Use the pipette directly to spot your TLC plate.

When the reaction is complete, remove the reaction device from the heat and allow it to cool. Making use of a Pasteur pipet, carry the solution to a little Erlenmeyer flask containing around 3 mL the water. The reaction mixture must dissolve completely in the water, due to the fact that the ethyl p-aminobenzoate is in the form of the hydrogen salt. ~ the solution has cooled to room temperature, include the 10% salt carbonate solution dropwise to neutralize the cooled reaction mixture. As the pH that the solution rises carbon dioxide will be produced and also evolve as gas bubbles out of the solution. Continue to add the salt carbonate till the gas evolution ceases and the pH is above 8. At this allude the sulfuric acid is fully neutralized, and the ethyl p-aminobenzoate precipitates.

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Collect the precipitation crude ethyl p-aminobenzoate through vacuum filtration making use of a Hirsch funnel. Use added portions of water to assist in transporting the crystals come the funnel and wash the crystals v water on the funnel. Dry the crystals overnight and also determine the melt point. Pure Benzocaine melts at 92 °C (here you deserve to save a little sample to dry overnight for determination of the melting allude and continue with recrystallization that the bulk of the sample immediately). The crude product can be recrystallized native a mixture of ethanol and water.