Exp 8 - Preparation Of Benzyl Acetate 29121

OBJECTIVES: This experiment aims to: - Synthesize benzyl acetate through Fischer Esterification occurring through a nucleophilic acyl substitution mechanism - Successfully use the reflux technique to synthesize benzyl acetate - Understand mechanism involved in the reaction - Evaluate efficiency of Fischer Esterification as a method of synthesizing esters INTRODUCTION: Esters are some of the most widespread naturally-occurring compounds. Many esters are responsible for the fragrance of flowers and fruits like bananas, raspberries, and peaches and are also the primary constituent of fats and oils. Esters are usually formed from acid-catalyzed condensation of a carboxylic acid and an alcohol where the two molecules combine to form a bigger molecule. This type of reaction is called a nucleophilic acyl substitution. Fischer Esterification is the most useful method in synthesizing esters because of its relatively high yield. This process is done by using a carboxylic acid and an alcohol in the presence of an acid catalyst. In this reaction, the carboxylic acid is activated with an acid to make the acyl carbon more electrophilic. Thus, the alcohol can attack the acyl carbon and the deprotonation of the acyl oxygen forms the ester. PRELAB QUESTIONS: 1. How is the yield of the reaction maximized? How is the hydrolysis of benzyl acetate back to benzyl alcohol and acetic acid prevented? Explain.  To maximize the yield of the reaction, the reaction mixture is washed with water to remove unreacted benzyl alcohol and excess acetic acid. A second wash with bicarbonate is also utilized to remove any remaining traces of acetic acid. The ester must also be removed immediately as it forms. Another way to drive the reaction forward is to add an excess of acetic acid because it is easier to remove after the reaction. Because esterification is a reversible reaction, it is important to remove compounds such as water and strong bases that aid in inducing the reverse of esterification or hydrolysis process. These compounds are removed during the purification stage of the crude product. 2. What is the use of the sodium bicarbonate wash? What gas is produced upon the addition of sodium bicarbonate into the organic layer?  The sodium bicarbonate wash removes any remaining trace of acetic acid. It is also used to neutralize any unreacted acid. Sodium bicarbonate is a weaker acid thus its reaction with the unreacted acid catalyst will produce carbonic acid which dissociates into water and carbon dioxide. Thus, sodium bicarbonate must be added before removing the aqueous layer in the last washing and before drying the organic layer. Carbon dioxide is the gas produced. 3. What is the use of sodium chloride in the sodium chloride wash?  Sodium chloride increases the ionic strength of the aqueous layer. Therefore, the separation of the aqueous and organic layer will be easily observed. Sodium chloride also aids in removing polar impurities and water from the crude ester. 4. Where would you expect the organic layer to be in each of the three washing steps?  For the first wash with 15mL cold water, the organic layer is at the bottom of the separatory funnel because the benzyl acetate is denser than water. Thus, the organic layer is drained into an Erlenmeyer flask. For the second and third wash, the organic layer is at the top of the separatory funnel because sodium bicarbonate and sodium chloride both have higher densities than benzyl acetate. Therefore, they sit at the bottom of the funnel and are drained through the stopcock. 5. What are the qualitative tests to the presence of benzyl acetate and benzyl alcohol? What constitutes a positive test result?

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The Hydroxamic Acid test can help the presence of an ester in the benzyl acetate product. A positive result is seen if the test produces a redviolet solution. Meanwhile, a Chromic Acid test is used to check for the presence of an alcohol. A positive result is indicated by the presence of blue-green precipitate. If the Chromic Acid test results in a positive test result, then the benzyl acetate product still contains traces of benzyl alcohol and was not fully synthesized.

REAGENTS: REAGENTS Benzyl Acetate (IUPAC) [C9H10O2]

PHYSICAL AND CHEMICAL PROPERTIES Molecular Weight: 150.18 g/mol Boiling Point: 213oC Melting Point: -51oC Density: 1.05 g/cm3 Solubility: 3.1 mg/mL (25oC) in water Appearance: Colorless liquid with pear-like odor, bitter-pungent taste

Acetic Acid (IUPAC) [C2H4O2]

Molecular Weight: 60.052 g/mol Boiling Point: 117.9oC Melting Point: 16.6oC Density: 1.05 g/cm3 Appearance: Colorless liquid or crystals with a sour, vinegar-like odor

Sodium Bicarbonate / Sodium hydrogen carbonate (IUPAC) [NaHCO3]

Molecular Weight: 84.007 g/mol Boiling Point: 851oC Melting Point: 50oC Density: 2.1 g/cm3 Solubility: 8.7 g/100mL (20oC) of water Appearance: White crystalline powder or granules, odorless, saline and slightly alkaline taste Molecular Weight: 58.44 g/mol Boiling Point: 1465oC Melting Point: 800.7oC Density: 2.17 g/cm3 Solubility: 36.0 g/100g (25oC) of water Appearance: Colorless to white crystalline solid, salty taste

Sodium Chloride (IUPAC) [ClNa]

Sulfuric Acid (IUPAC) [H2SO4]

Molecular Weight: 98.079 g/mol Boiling Point: 337oC Melting Point: 10.31oC Density: 1.84 g/cm3 Solubility: miscible (20oC) in water

SAFETY PRECAUTIONS Skin and eye irritant: flush with water for at least 15 mins. then get medical assistance Ingestion (hazardous): do not induce vomiting unless instructed by medical personnel Inhalation (hazardous): to fresh air, give oxygen, seek medical assistance Combustible Skin and eye irritant: flush with water if Serious skin : Wash with disinfectant soap and cover contaminated skin with antibacterial cream. Seek medical aid Ingestion (hazardous): do not induce vomiting unless instructed by medical personnel Inhalation (hazardous): remove to fresh air, give oxygen, seek medical assistance Skin and eye irritant: flush with water if Ingestion: do not induce vomiting unless instructed by medical personnel Inhalation: remove to fresh air, give oxygen, seek medical assistance Skin and eye irritant: flush with water if Serious skin : Wash with disinfectant soap and cover contaminated skin with antibacterial cream. Seek medical aid Ingestion: do not induce vomiting unless instructed by medical personnel Inhalation: remove to fresh air, give oxygen, seek medical assistance Skin and eye irritant (very hazardous): flush with water if Serious skin : Wash with disinfectant soap and cover contaminated skin with anti-

Appearance: Odorless colorless oily hygroscopic liquid

bacterial cream. Seek medical aid Ingestion (very hazardous): do not induce vomiting unless instructed by medical personnel Inhalation (very hazardous): remove to fresh air, give oxygen, seek medical assistance

REFERENCES: Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry. Quezon City: Office of Research and  Publications, Ateneo de Manila University; 2005. [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2005 March 25 [updated 2017 March 26; cited 2017 March 26]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/benzyl_acetate  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 26]. Available from: http://www.sciencelab.com/msds.php?msdsId=9923066   [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2004 September 16 [updated 2017 March 25; cited 2017 March 26]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/acetic_acid  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 19]. Available from: http://www.sciencelab.com/msds.php?msdsId=9922769   [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2005 March 27 [updated 2017 March 25; cited 2017 March 26]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/sodium_bicarbonate  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 26]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927258  [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2005 March 25 [updated 2017 March 25; cited 2017 March 26]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/sodium_chloride  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 26]. Available from: http://www.sciencelab.com/msds.php?msdsId=9927593  [Author Unknown]. Pubchem compound database [Internet]. USA: National Centre for Biotechnology Information;  2004 September 16 [updated 2017 March 25; cited 2017 March 26]. Available from:  https://pubchem.ncbi.nlm.nih.gov/compound/sulfuric_acid  [Author Unknown]. Sciencelab.com [Internet]. USA: Sciencelab.com, Inc.; unknown first publication [cited 2017  March 26]. Available from: http://www.sciencelab.com/msds.php?msdsId=9925146  De Guzman JV. Scribd [Internet]. Unknown Place: Scribd Inc.; 2015 April 08 [cited 2017 March 26]. Available from:  https://www.idoub.com/doc/295968779/SYNTHESIS­OF­BENZYL­ACETATE­THROUGH­FISCHER­ ESTERIFICATION­REACTION  -

PROCEDURES: 

Pour 5.5mL of acetic acid and 3-5 drops (~0.2mL) of concentrated sulfuric acid into RBF. Slowly add 4.5mL of benzyl alcohol into mixture and swirl it.

Attach water condenser vertically over mouth of round bottom flask. Check setup for leaks and heat RBF to slow boil. Continue heating RBF over low-medium heat for an hour..

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Secure setup with clamps on neck of RBF and on body of condenser Regulate heat in order to prevent formation of solid byproducts

Let mixture in RBF cool down and decant into separatory funnel. Wash RBF with 15mL cold water and use to wash mixture in separatory fun

Drain organic layer into clean and dry Erlenmeyer flask and discard aqueous layer. Wash organic layer with 10mL 5% NaHCO3 and then with 10mL 10% NaCl.

Decant organic layer into Erlenmeyer flask and dry over sodium sulfate. Distill it if necessary and store in scintillating vial. Perform qualitative tests.

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The order of the organic and aqueous layers in separatory funnel changes throughout experiment due to changing density of aqueous layer Make sure layers are properly identified