Benzocaine - Ester Synthesis Online-2 PDF

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Benzocaine - Ester Synthesis Online Olivia pizzella 10/27/20 Dr. D’Amelia

Purpose : Recrystallization of Benzoic Acid from Water and Aspirin from Isopropyl Alcohol. Introduction : In this experiment we will be performing two recrystallization experiments: one will be the recrystallization of Benzoic Acid from Water and the other will be the recrystallization of aspirin from a regular aspirin tablet using isopropyl alcohol. After the recrystallization of these compounds the melting points of each recrystallized compound will be determined and perform a qualitative test for the phenol group (hydroxybenzene) using a 5% aqueous solution of Iron (lll) Chloride Ferric Chloride.

Observation / data : Mass (g) Experimental Melting Point (o C) PABA 0.1233 187.5 – 188.5 Benzocaine 0.0724 80 – 82 -

Molar Mass (g/mol) 137.14 165.19

The weight of the carboxylic acid is 1.321 g and the alcohol weight is in excess and the weight of the ester formed was 1.321 g.

Part 1 : Benzocaine -

Mechanism of formation of benzocaine from 4-aminobenzoic acid (PABA)

Benzocaine was reacted with ethanol and sulfuric acid, therefore became a catalyst. Benzocaine becomes a P-aminobenzoic acid then, undergoes acid-catalyzed esterification for benzocaine. The mechanism begins with the carbonyl oxygen of a carboxylic acid being protonated by a hydrogen from the sulfuric acid catalyst. The double bond is broken and the lone pair from the ethanol oxygen attacks the carbonyl carbon, from the back, forming a tetrahedral intermediate. The oxygen and new ethanol substituent have a positive charge. This causes the lone pairs on the sulfuric acid to attack the hydrogen on ethanol. Then the lone pairs on the hydroxyl group then attack a hydrogen atom from the sulfuric acid, this then forms water. The lone pair remaining on the hydroxyl group, forms a double bond with carbon and pushes off the water. The sulfuric acid then relieves the double bonded oxygen of the extra hydrogen, removing the unwanted positive charge. This process creates the final product of benzocaine. 1 . Discussion of reaction conditions and purification techniques -

The formation of benzocaine took place under acidic conditions. 0.120g of paminobenzoic acid, 1.2ml of ethanol and 0.10 ml of sulfuric acid were added to a 3ml conical vial, in that order, with a spin vane. The mixture was placed on a hot plate only the spin function was in use, and 0.10 ml of sulfuric acid was added. A water-cooled condenser was then inserted into the conical vial and the apparatus was heated on the hot plate. The solution was left untouched to boil for 60 minutes, allowing the reaction to full take place. Once the 60 minutes was over the benzocaine purifIcation process began. The conical vial was removed from the hot plate and allowed to cool. Once the solution was cooled, it was decanted into a 50ml beaker captaining 3.0ml of distilled water. Then 10% NaHCO3was added to the beaker until the solution presented a green color on orange, neutral pH paper. This indicated that the solution was slightly basic, and a precipitate formed. The precipitate was then collected using vacuum Filtration. It was washed three times using distilled water. This Enal product was denoted to be benzocaine.

Analysis of product 2.  Physical  appearance of product - Benzocaine should be white and flaky. It should be flat and chalky, and it would be white and or a tanish color 3.  Identification  of significant absorbances in the IR spectrum for both starting PABA and benzocaine The PABA has a strong peak at 1342.21 cm−1 telling us that a carbon oxygen single bond was present in the product. There was another strong bond present at 1282.34 cm−1 telling us that there was most likely a double bond between the carbon and oxygen present. After there was only one more strong speak at 768.91 cm−1 elling us there were sp3 hybridized carbons in the product .

For Benzocaine the first speak was at 1679.05 cm−1 indicating that a single bond present. The second peak was at 1271.92 cm−1 telling us there was a double bond present because of such a high peak. The last high peak was 770.09 cm−1 telling us there was a benzene ring. 4. Melting  point difference between PABA ( 4-Aminobenzoic acid) and Benzocaine - The melting range of the experimental benzocaine was found to be 80  – 82C.  The accepted melting range for pure benzocaine is 88.0- 89.0C. This supports that benzocaine is the sample collected from experimentation and that it contains little to no impurities because the experimental and accepted melting range are very similar. - The melting range of the experimental PABA was found to be  187.5 – 188.5C.  The accepted melting rang for 4-Aminobenzoic acid 187  to 189 °C - This also supports that 4-Aminobenzoic acid contains very little impurities because the experimental and accepted are in the same range 5.  Identifying  factors that differentiate product from reactant - The reactant, p-aminobenzoic acid contains a carboxyl acid, the product, benzocaine contains an ester. The reactant contained with the carboxylic acid, the IR spectrum of the reactant would show a strong broad peak. This would indicate the alcohol group. The product that contains an ester in the reactant. There were also no sp3 hybridized carbons in the product, the IR spectrum shows peaks in the 1500 cm−1 - 700 cm−1 range.. The spectrum of the reactant wouldn't have shown peaks in the range it did. 6. Discussion of the Proton and Carbon 13 NMR -

The H NMR presented in peaks for benzocaine. Two of these peaks were ignored because they were from the solvent, water and chloroform, not the actual product benzocaine. There were two doublets in the correct range indicating a benzene ring present. The single peaks represent the hydrogens bonded to saturated carbons in the product. The C13 NMR presented eight distinct signals for benzocaine; however, there was a signal resembling a multiplet. C13 NMR can only contain singlets, so therefore the multiplet was ignored. The singlets represented the carbon oxygen single bond. The singlet around 15 ppm represented the carbon at the end of the benzene ring. Lastly the singlets between 110-150 ppm represent the carbons in the benzene ring.

7. calculation  of percent yield g - 50.08% -

Part 2 : 4-Methoxy Benzoic acid - 1 butanol Describe the stoichiometric equation for your Direct Esterification reaction. Name the ester formed

2. Accepted Melting point for both starting carboxylic acid and product ester – cite reference - The accepted melting point for 4-methoxybenzoic acid is 182-185 °C

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“4-Methoxybenzoic Acid.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/4-Methoxybenzoic-acid The accepted melting point for 1 butanol is −89.8 °C -

“1-Butanol.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/263.

3. Physical Appearance of starting reactants and Ester product. - The appearance of the reactant should be white crystalline. The product should be colorless because of the conjugation 4. Identification of significant absorbances in the IR for both the starting carboxylic acid and ester product - the IR reactant that is 4-methoxy benzoic acid indicates- OH broad peak stretching frequency near 3300 - 3500 cm−1 also carbonyl stretching near 1680 - 1700 cm−1 because of conjugation. The IR absorbance of product does not shocos - OH stretching frequency, the carbonyl stretching frequency shows near 1715- 1720 cm−1 which is ester therefore it indicates product formation takes place. Determine % yield - 78.08%

Interpret Proton and Carbon NMR for your ester reaction product The ester group is present so the CH2 group which is attached to oxygen of carbonyl group shoes highly deshielding is also the methoxy group shows value. Molar mass 208g/mol The carbon NMR : C1: 13.8 , C2: 19.3 C3:30.6, C4:65.4, C5:166.6, C6:123.1, C7:160.4, C8:132, C9:133.8, C10:65.4 IR= 1710CM^-1 , 1745CM^-1...