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Experiment 21:

Experiment 21:. ESTERS: SYNTHESIS AND FRAGRANCE. Objectives:. To synthesize an ester from acetic acid with isoamyl alcohol under reflux. To purify your product through acid-base extraction and simple distillation.

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Experiment 21:

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  1. Experiment 21: ESTERS: SYNTHESIS AND FRAGRANCE

  2. Objectives: • To synthesize an ester from acetic acid with isoamyl alcohol under reflux. • To purify your product through acid-base extraction and simple distillation. • To identify and analyze the purity of your compound using GC analysis. • To identify your product by analyzing the NMR and IR spectra.

  3. Before coming to lab… • Review these techniques: • Reflux • Acid-Base Extraction • Simple distillation • Drying over MgSO4 • GC Analysis

  4. FISCHER ESTERIFICATION • Fischer esterification is an acid catalyzed nucleophilic acyl substitution. • Net effect is the replacement of an –OH of a carboxylic acid with the –OR of an alcohol to produce an ester. • It is an equilibrium reaction with an unfavorable Keq, thus we can improve product yield in several ways: • Use an excess of the alcohol reactant. • Use an excess of the carboxylic acid reactant. • Remove water as it forms.

  5. FISCHER ESTERIFICATION • Carboxylic acids are not reactive enough to undergo nucleophilic addition directly. • By using sulfuric acid as a catalyst, the carbonyl group oxygen is protonated to give the carboxylic acid a positive charge. This makes it more reactive.

  6. MECHANISM 1. Protonation of the carbonyl oxygen activates the carboxylic acid… 1 2. …toward nucleophilic attack by the alcohol… 2 3. … yielding a tetrahedral intermediate. 3 4. Transfer of a proton from one oxygen to another yields a second tetrahedral intermediate… 4 5 6 5…and converts the OH group into a good leaving group. 6. Loss of a proton and expulsion of H2O regenerates the acid catalyst and gives the ester product.

  7. OVERVIEW • Synthesize product ester under reflux. • Neutralize acetic acid with 10% NaHCO3. • Extract in ether, then wash with 10% NaHCO3. • Dry organic layer. • Perform simple distillation to remove ether from product. • Obtain final product mass, calculate % yield, prepare GC sample.

  8. EXPERIMENTAL PROCEDURE(SYNTHESIS) • Combine acetic acid, isoamyl alcohol and sulfuric acid in a 25 mL round bottom flask. • Clamp flask to ring stand and add 3 boiling chips. • Place water cooled condenser on top of flask, with a CaSO4 drying tube in the top. • Heat to reflux. Reflux 30 minutes. • Cool to room temp. • Add 10% NaHCO3 slowly to flask. CaSO4 tube 25mL

  9. EXPERIMENTAL PROCEDURE(PURIFICATION) • Transfer liquid to separatory funnel. • Rinse reaction flask with ether and transfer to separatory funnel. • Wash the organic layer with 10% NaHCO3. • Transfer the organic layer to a clean flask. • Dry over MgSO4. • Transfer liquid to a preweighed 50 mL round bottom flask. • Clamp flask to ring stand. 125 mL 50mL 50mL

  10. EXPERIMENTAL PROCEDURE(PRODUCT ISOLATION) • Set up a simple distillation apparatus, using a 25 mL round bottom as the receiving flask. • Collect all distillate that boils under 40oC. • Record distillation range, Ti-Tf. • Allow reaction flask to cool to room temperature. • Reweigh 50 mL flask to determine final product mass (actual yield) and calculate % yield. • Prepare GC sample. 50mL PRODUCT!!! 25mL WASTE SOLVENT

  11. Table 21.1

  12. Table 21.2

  13. EXPERIMENTAL PROCEDURE(IR ANALYSIS)

  14. Table 21.3

  15. EXPERIMENTAL PROCEDURE(NMR ANALYSIS)

  16. SAFETY CONCERNS CAUTION: H2SO4 is a STRONG ACID!

  17. WASTE MANAGEMENT • All aqueous washes from the extraction can be flushed down the drain with plenty of water! • Ester product and distilled ether should be placed in the bottle labeled, “ORGANIC WASTE (Esters)”.

  18. CLEANING • Clean round bottom flasks and distillation glassware with wash acetone only! • Separatory funnel and all other glassware should be cleaned with soap, water, and a brush if necessary, followed by a wash acetone. • DO NOT return any glassware to lab drawer dirty or wet!

  19. LABORATORY NOTEBOOK(Pre-lab) • OBJECTIVE(Must clearly state…) • What compounds will be made and how • How the compounds will be purified • How the purity of the product will be determined • CHEMICAL EQUATION • Include the chemical equation from the top of page 177. • TABLE OF PHYSICAL DATA (Complete the following table using a site listed on WWW Links ONLY. Wikipedia is unacceptable!) • REFERENCE TO PROCEDURE (Must include…) • full title including edition and author names • page numbers where actual procedure can be found

  20. LABORATORY NOTEBOOK(In-lab) • DATA/CALCULATIONS • Initial volumes of isoamyl alcohol and acetic acid used • Distillation range • Weight of 50 mL round bottom flask • Weight of 50 mL round bottom flask + product • Final product weight • Physical state and color of product • GC vial slot # • Theoretical yield calculation (not just value!) • % yield calculation (not just value!) • Example of an adjusted area % calculation (not just value!) • EXPERIMENTAL PROCEDURE • In paragraph form, BRIEFLY describe the procedure that you actually followed during the lab. • Paragraph must be written in PAST TENSE, PASSIVE VOICE. • Include any volumes or weights of chemicals used during the experiment. • Include any mistakes, accidents or observations if applicable.

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