Fischer Esterification- Preparation of Benzocaine PDF

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Description

Name Razan Qamar Course Code and Section number CLAB 268-02 Experiment title Fischer Esterification- Preparation of Benzocaine

Data and Observations (typed or hand-written) 

Started with 1.070g p-aminobenzoic acid

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Ended with 0.920g benzocaine

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All solids dissolved within 30 minutes of adding 3ml of ethanol and around 0.5 ml of concentrated sulfuric acid.

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Red litmus paper turned blue after adding sodium carbonate to solution indicating its basic.

Calculations

Discussion of Results (one typed-page maximum) 1|Page

The purpose of this experiment is to synthesize benzocaine through an acid catalyzed Fischer esterification reaction with ethanol. The yield produced by using this procedure had a 76.4% yield, thus this procedure is efficient and effective. Fischer esterification utilizes an acid catalyst to facilitate the nucleophilic attack of the alcohol at the carbonyl carbon of the carboxylic acid to allow water to be the leaving group, since it is a better leaving group than the alcohol. With the addition of an acid, the amine group on the benzocaine will become protonated. The protonation creates a positive charge on the benzocaine molecule. Because of this, benzocaine will become soluble in a polar solvent. However, when the solution is returned to a more basic pH level which is why its required to add the 10% sodium carbonate, the amine will no longer be protonated. Thus, the benzocaine will no longer be soluble and will precipitate during neutralization and it can be isolated. It is also important to neutralize the sulfuric acid to prevent the reverse reaction. Since the maximum yield in any Fischer esterification is 67% but in this reaction, it was 76%, it could be from multiple reasons. As in any equilibrium processes, the reaction may be driven in one direction by adjusting the concentration of one of the either the reactants or products (Le Châtelier’s principle), which is why excess ethanol was used in this protocol. It also explains why absolute ethanol was used, since if it was dilute and contained water, it would push the reaction backwards. One other reason to why the yield was high was that the benzocaine product was not allowed to air dry to efficiently remove any water. The only thing I would change about this protocol is adding a step to give a few hours for the benzocaine crystals to fully dry to obtain a more accurate yield. To verify that our desired product was produced, we can run a GCMS and IR. Looking at the GCMS we can see the most notable peak will be (M)•* at 165(m/z) which is the same molecular weight of benzocaine. There is also a peak at M-29 which shows the loss of an ester radical in the compound. Looking at the IR, we see a strong signal around 3400cm-1 which indicates a nitrogen hydrogen bond and a signal around 1677cm-1 which shows the presence of an ester. In addition there was no spike around 3500cm-1, which indicates that our starting material which contained an OH group on the carboxylic acid was not present. This all shows that our reaction went successfully to completion and the protocol is indeed effective.

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