CHEM 2212: Fischer Esterification Procedure Study Notes

CHEM 2212: Fischer Esterification Procedure Study Notes

Overview of Fischer Esterification

  • Definition: Fischer esterification is a chemical reaction that involves the reaction of a carboxylic acid with an alcohol to produce an ester and water, facilitated by an acid catalyst.

  • Objective: In this lab, we will combine glacial acetic acid with an unknown alcohol to synthesize an ester.

Materials Used

  • Glacial Acetic Acid: 5 mL

  • Unknown Alcohol: Identified by the code FE159234, 4 mL

  • Concentrated Sulfuric Acid: 1 mL, used as a catalyst

Procedure Steps

1. Preparation of Reaction Mixture

  • Measure out 4 mL of the unknown alcohol underneath a fume hood (snorkel) due to its strong odor.

  • Carefully cap the alcohol once measured.

  • Add the 5 mL of glacial acetic acid and 1 mL of concentrated sulfuric acid into a microwave vessel.

  • Insert a stirring bar into the vessel and seal the top with a thermal well.

2. Reflux Process

  • Place the vessel in a FlexiWave microwave instrument under safety shields.

  • Position the temperature probe through the cap and into the thermal well.

  • Ensure the vent is directed outside before sealing the safety shield.

  • The reflux will take place for 10 minutes.

3. Completion of Reflux

  • After the reflux, carefully open the microwave, remembering the order of actions:

    • Remove the brace

    • Extract the temperature probe with caution

    • Open the vessel in the fume hood to release any pressure.

4. Separation of Mixture

  • Transfer the reaction mixture into a separatory funnel.

  • Observe that the initially colorless liquid has turned dark purplish brown.

  • Note: The ester product will form its own layer, avoiding the typical extraction process. Instead, a series of washes will be performed.

  • First Wash: Add 10 mL of deionized water, swirl, and pour into the separatory funnel. A gentle shake is needed to mix and then vent.

5. Layer Separation

  • Allow the layers to settle for a couple of minutes. Observe two distinct layers:

    • Top Layer: Dark purple (ester layer)

    • Bottom Layer: Light pink/purplish (aqueous layer with impurities)

  • Drain the aqueous layer, retaining the ester layer.

6. Second Water Wash

  • Repeat the washing with another 10 mL portion of deionized water.

  • Observe color change; the dark purple becomes a milky yellow upon washing.

  • Drain the bottom aqueous layer again, ensuring to keep the ester layer.

7. Sodium Bicarbonate Washes

  • Conduct one or more sodium bicarbonate washes to neutralize any acids remaining.

  • First wash involves:

    • 10 mL of 5% sodium bicarbonate solution.

    • Observe carbon dioxide evolution, indicating reaction with residual acid.

    • Shake and vent, allowing the layers to separate before draining off the aqueous layer.

  • pH Testing: Use pH paper to check the aqueous layer, aiming for weak alkalinity, confirming neutralization of the acid.

  • A second wash may be conducted similarly to ensure pH reaches neutrality.

8. Brine Wash and Drying

  • Using 5 mL of saturated sodium chloride solution (brine), perform a drying wash to extract remaining water from the ester layer.

  • Allow layers to separate, then drain off the brine layer to leave the ester.

9. Drying with Sodium Sulfate

  • The ester is dried using a small amount (a spatula tip) of sodium sulfate.

  • Stir gently; the sodium sulfate will clump with any remaining water, indicating drying success.

10. Decantation

  • Using a pre-weighed beaker, carefully decant the ester solution, ensuring no sodium sulfate solids are transferred.

  • The odor of the ester should be noted, indicating fruity characteristics as may be identified by comparison.

11. Weighing Final Product

  • Weigh the final beaker with the ester and determine the weight of the ester by subtracting the initial weight of the beaker.

  • Example calculation: Weight of beaker plus product = 68.284 g, weight of beaker alone = 64.942 g => Total ester product = 3.342 g.

Characterization of Ester

  • IR Spectroscopy: Upon preparing the sample, run through IR to observe key peaks, particularly in the 3000 cm⁻¹ region for functional group identification.

  • NMR Spectroscopy: Utilize proton NMR (Pico spin instrument), adding TMS (tetramethylsilane) for reference.

  • Collect scans to refine the spectrum; peaks will give insights into structure and help identify the original alcohol.

Observations and Discussion

  • The transformation of a clear liquid into a dark purple/brown during reflux indicates effective reaction.

  • Color changes observed through washes to a yellow/orange suggest removal of impurities and formation of pure ester.

  • Careful documentation of all weights and measures, including indications of possible experimental error,
    (e.g., residual ester in the original flask).

Final Data Summary:

  • Initial volume of glacial acetic acid: 5 mL

  • Initial volume of unknown alcohol: 4 mL

  • Volume of concentrated sulfuric acid: 1 mL

  • Total washes: 2 x 10 mL deionized water, 2 x 10 mL sodium bicarbonate, 5 mL brine.

  • Final yield of the ester product: 3.342 grams

Important Notes for Lab Report:

  • Include signage of reactions, observations during washes, and any anomalies encountered.

  • belief that isopentanol is the alcohol used because the end ester has a strong banana scent

  • 5 mL 1.049 g/mL = 5.245 g
    4 mL     0.812 g/mL = 3.248 g
    5.245 g / 60.05 g/mol ~ 0.08734 mol

    3.248 g / 88.15 g/mol~ 0.03685 mol

    C5H12O
    0.03685 mol * 130.18 g/mol ~ 4.797 g