Lab F Procedure DS

Lab F: Fischer Esterification

Objective: Synthesize Isopentyl acetate (banana oil) via an acid-catalyzed Fischer esterification between acetic acid and isopentyl alcohol (3-methyl-1-butanol).

Techniques:

1. Reflux,

2. Extraction,

3. Gravity Filtration,

4. Simple Distillation,

5. Boiling Point Determination.

Fischer Esterification Background

1. An acid-catalyzed equilibrium reaction between a carboxylic acid and an alcohol to form an ester and water.

2. Concentrated H₂SO₄ is the catalyst. The reaction is reversible.

3. Equilibrium is driven by using an excess of one reagent (acetic acid) and by refluxing.

4. Esters often have fruity odors.

Reaction Scheme

Reactants: 3-methyl-1-butanol (Isopentyl alcohol) + Glacial Acetic Acid. Catalyst: Concentrated H₂SO₄. Product: Isopentyl Acetate (banana oil) + Water. Reaction: HO-(CH₂)₂-CH(CH₃)₂ + CH₃COOH ⇌ CH₃COO-(CH₂)₂-CH(CH₃)₂ + H₂O.

Starting Materials in RB Flask

The provided 100 mL Round Bottom Flask contains: 15 mL of 3-methyl-1-butanol (isopentyl alcohol), 20 mL of glacial acetic acid (excess reagent), 2 mL of concentrated sulfuric acid (catalyst), and two boiling stones.

Safety: Concentrated Sulfuric Acid

Extremely corrosive! Causes severe burns. Wear safety goggles, gloves, and an apron at all times. Handle with extreme care.

Safety: Other Hazards

Glacial acetic acid is corrosive and has irritating vapors. Isopentyl alcohol is flammable. Work in the fume hood. The reaction mixture becomes very hot during reflux.

Step 1-2: Initial Setup

Obtain your pre-loaded 100 mL Round Bottom Flask. Clamp ONLY the neck of the flask to the ring stand.

Step 3-4: Reflux Setup

Set up the reflux glassware on the far right side of the fume hood. Place the smaller cloth heating mantle (from 'F' drawer) directly on the ring stand. Ensure the RB flask sits flush inside the mantle. Attach the water-cooled condenser to the flask. Check that water is flowing (CHWS = Chilled Water Supply, CHWR = Chilled Water Return) and the condenser feels cool. Have your TA check the setup. The TA will plug the heating mantle into the Variac (set to 65).

Step 5: Reflux Reaction

Cover the RB flask with foil to insulate for the first 5 minutes. Wait for the solution to reach a boil (this starts the 50-minute reflux period). Remove the foil and save it for the distillation later. Observe solvent vapors condensing. Check the condenser every 10 minutes to ensure it stays cold. If the heating mantle glows red, alert your TA immediately. Reflux for 50 minutes.

Step 5: Thinking Ahead - Prep Work

In the middle of the hood: Set up a 250 mL Separatory funnel on a ring stand with a 19/22 glass stopper. Have ready: 25 mL of 5% aqueous sodium bicarbonate (NaHCO₃), 5 mL of saturated NaCl (brine) solution. Cool 60 mL of tap water in an ice bath during the last 3 minutes of reflux. On the far left of the hood: Set up simple distillation glassware (vacuum adapter, 3-way distillation adapter, thermometer in adapter). Pre-weigh a vial and label it with your name, TA name, and lab section. Have ready a powder funnel with gravity filter paper and a 25 mL round bottom flask.

Step 6: Cool & First Extraction

After 50 min reflux, raise the clamped RB flask above the heating mantle. Let it cool in the hood for 10 minutes. Pour the reaction mixture (EXCLUDE boiling stones) into the separatory funnel. Slowly add 50 mL of the pre-cooled water to the funnel. Rinse the RB flask with 10 mL cold water and add it to the funnel. Gently shake the funnel. Drain the lower aqueous layer into a beaker labeled #1 "AQUEOUS WASTE".

Step 7: Bicarbonate Extraction (Remove Acid)

Carefully add 25 mL of 5% NaHCO₃ to the separatory funnel. SWIRL GENTLY (DO NOT SHAKE YET) until most CO₂ bubbling ceases. When bubbling stops, stopper the funnel, gently shake, and frequently vent to release CO₂ pressure. Drain the lower aqueous layer into a new beaker labeled #2 "AQUEOUS WASTE". Check its pH with paper (should be orange or green, indicating neutrality).

Step 8: Brine Wash & Drying

TOGETHER, add 25 mL of water and 5 mL of saturated NaCl solution to the separatory funnel. Gently swirl. Drain the lower aqueous layer into Beaker #1 "AQUEOUS WASTE". Drain the top organic layer (contains the crude ester) into a 125 mL Erlenmeyer flask. Your TA will add 4 scoops of anhydrous calcium chloride (CaCl₂) drying agent to this flask. Swirl to dry the organic layer.

Step 9: Gravity Filtration & Distillation Setup

Gravity filter the dried organic solution into the clean, dry 25 mL Round Bottom Flask. Use the powder funnel and gravity filter paper; the CaCl₂ pellets will be trapped on the filter. Add 2 NEW boiling stones to the 25 mL RB flask. Set up a simple distillation apparatus with the pre-weighed, labeled vial as the receiver. Have your TA check the setup. The TA will plug in the heating mantle.

Step 10: Simple Distillation & Collection

Heat the distillation apparatus. As soon as the first drop of liquid distills into the vial, immediately record the temperature and start a 2-minute timer. Record the temperature again when the timer goes off (2 minutes later). STOP COLLECTING at this 2-minute mark. Lower/move the heating mantle away from the flask to stop the heat. Collect any liquid that boils below 125°C in a separate beaker for disposal.

Product: Isopentyl Acetate

The collected distillate is Isopentyl acetate. Literature boiling point: 142°C. Expected experimental boiling range: 125°C to 138°C. Determine the mass of the product in the pre-weighed vial. Record physical characteristics: appearance, color, fragrance (banana-like), phase (liquid).

Waste Disposal 1: Aqueous Waste

ALL aqueous waste from extractions (Beakers #1 and #2) must be disposed of into the special container labeled "Aqueous Waste (Fischer Lab)".

Waste Disposal 2: Solids & Solvents

Anhydrous CaCl₂ pellets and used gravity filter paper go into the biohazard box. Low-boiling distillate (collected below 125°C) goes into the "C, H, O Non-Halogenated" waste container. Used boiling stones go into the biohazard box. Used melting point capillary tubes go into the Red Sharps container.

Glassware Cleanup for Next Lab

Rinse the following glassware with ACETONE ONLY (NO WATER) in this order: All 125 mL Erlenmeyer Flasks, 250 mL beaker, All graduated cylinders, Buchner funnel, Vacuum filter flask, 50 mL RB flask, 50 mL beaker. Dispose of acetone waste appropriately.

Critical Note: Venting Separatory Funnel

During the NaHCO₃ extraction, CO₂ gas is produced. You MUST vent the funnel frequently by removing the stopper to release pressure. Failure to do so can cause the stopper to pop out violently, leading to loss of product and a hazardous situation.

Critical Note: Boiling Point Range

The boiling point range is critical for characterization. Record the temperature at the first drop and again exactly 2 minutes later. The product is collected within this 2-minute window, typically between 125°C and 138°C, due to thermometer calibration issues.

Critical Note: Driving Equilibrium

The equilibrium is driven toward the ester product by using a large excess of glacial acetic acid (20 mL vs. 15 mL of alcohol) and by refluxing for 50 minutes to increase the reaction rate and conversion.

Notebook Requirements

Record masses/volumes of reagents. Record observations during reflux and extractions (e.g., CO₂ bubbling). Record the boiling point range (start and 2-minute temperatures). Record the mass and physical characteristics (appearance, odor) of the final product. Calculate the percent yield.