Experiment 4 Notes: Isolation of Trimyristin from Nutmeg and Preparation of Myristic Acid from Trimyristin by Hydrolysis

Overview and Key Concepts

• Experiment 4 covers two connected tasks: isolation of trimyristin (a triglyceride) from ground nutmeg, and hydrolysis of trimyristin to prepare myristic acid.

• Chemical identities:

  • Trimyristin: propane-1,2,3-triyl tritetradecanoate; a triglyceride where glycerol is esterified with three myristic acid (tetradecanoic acid) groups. mp = $56-58^ emp C$.

  • Myristic acid: tetradecanoic acid; mp = $54-55^{e}C$ .

• Practical goals:

  • Part A: Isolate trimyristin from nutmeg (week 1).

  • Part B: Hydrolyze trimyristin under basic conditions to form glycerol and myristic acid, then purify to obtain pure myristic acid (week 2).

• Real-world relevance: illustrates classic edible fat chemistry, triglyceride hydrolysis (saponification) to yield fatty acids, purification, crystallization, and purity assessment by melting point. Also demonstrates safe solvent use, recrystallization, and simple yield calculations.

• Key safety and apparatus notes: micro-scale reflux setup, use of diethyl ether (highly flammable), ethanol, NaOH in ethanol, and acetone for recrystallization; use of petroleum ether for washing and extraction; filtration and vacuum techniques; careful handling of hot equipment and glassware.

Part A: Isolation of Trimyristin from Ground Nutmeg

• Objective: extract and isolate trimyristin from ground nutmeg.

• Materials (as listed):

  • Ground nutmeg, 2.0 g

  • Diethyl ether, 20 mL

  • 50 mL conical flask

  • Pasteur pipet

  • Cotton, 2 mm sand, 1 cm anhydrous Na2SO4 (drying agent)

  • Vacuum filtration setup with a pre-weighed 10–25 mL vacuum flask

  • Additional ether for rinsing: 0.5 mL

• Procedure (summary):

  • Mix 2.0 g ground nutmeg with 20 mL diethyl ether in a 50 mL conical flask.

  • Swirl and stir vigorously for 15 minutes to extract lipophilic materials (including trimyristin).

  • Prepare a filtration cartridge: pack with cotton, add 2 mm sand, and fill with ~1 cm of anhydrous Na2SO4.

  • Clamp the cartridge over a pre-weighed vacuum flask (10–25 mL).

  • Transfer the nutmeg/ether mixture onto the cartridge and collect the filtrate into the vacuum flask.

  • Rinse the extraction bottle with ~0.5 mL ether to ensure all product is collected.

  • Evaporate solvent to obtain a solid (crude trimyristin).

  • Weigh the crude product and save a small portion (a few mg) for melting point analysis.

• Purification by recrystallization:

  • Dissolve the crude solid in acetone (min amount, ~0.5 mL or less) by heating.

  • Cool to room temperature (RT), then further cool to 0 °C to crystallize.

  • Collect crystals by suction filtration.

  • Result: Pure trimyristin.

• Purity assessment: weigh purified trimyristin and calculate percentage yield based on initial nutmeg mass and the amount of trimyristin recovered.

• Key notes: recrystallization solvent choice (acetone) and gentle heating prevent decomposition; ensure dry nitrates/salts are removed to maximize yield.

• Calculations: Percentage yield (Part A)

  • Formula (as provided):
    ext{Yield of trimyristin} = rac{ ext{weight of trimyristin}}{ ext{weight of ground nutmeg}} imes 100 ext{%}

• Expected outcomes and mp correlation: mp of trimyristin is $56-58^ emp C$, and mp of isolated product should align with literature if pure.

Part B: Hydrolysis of Trimyristin to Myristic Acid

• Objective: hydrolyze trimyristin to obtain myristic acid via base-catalyzed saponification followed by acid workup and purification.

• Materials (as listed):

  • Trimyristin (crystallized product from Part A), 0.2 g

  • Ethanol, 2 mL

  • 10% NaOH, 2 mL

  • Boiling stones

  • Micro-reflux setup

  • 10% HCl, about 10 mL for acidification

• Procedure (summary):

  • In a 10-mL vial, combine 0.2 g trimyristin, 2 mL ethanol, and 2 mL 10% NaOH.

  • Add boiling stones and set up a micro-reflux apparatus.

  • Reflux for 1 hour to hydrolyze the triglyceride to glycerol and sodium salts of the fatty acid.

  • After reflux, pour the reaction mixture into a beaker containing 10 mL of 10% HCl to acidify and release free fatty acids.

  • Swirl and then collect the solid by vacuum filtration to obtain crude product.

• Purification of crude product:

  • Transfer crude solid to a test tube and add 3 mL petroleum ether.

  • Purify by filtration through a Pasteur pipet containing cotton and Celite; collect filtrate.

  • Wash/flash with petroleum ether to remove nonpolar impurities.

  • Evaporate petroleum ether to yield crude myristic acid.

  • Weigh the crude product and determine the yield.

• Final purification: If needed, further purification to obtain pure myristic acid (e.g., additional crystallization); record mp for purity check.

• Expected Product: Myristic acid (mp $54-55^ emp C$).

• Calculations: Percentage yield for myristic acid (Part B)

  • Step 1: Determine moles, using masses and molar masses (MM):
    $n<em>{ ext{trimyristin}} = rac{m</em>{ ext{trimyristin}}}{M<em>{ ext{trimyristin}}}$ $n</em>{ ext{myristic ext{ acid}}} = rac{m<em>{ ext{myristic ext{ acid}}}}{M</em>{ ext{myristic ext{ acid}}}}$

  • Step 2: The theoretical moles of myristic acid produced from 1 mole of trimyristin is 3 (one for each ester group):
    $n<em>{ ext{theoretical ext{ (myristic acid)}}} = 3 imes n</em>{ ext{trimyristin}}$

  • Step 3: Percent yield (actual vs theoretical):
    ext{
    % yield of myristic acid} = rac{n{ ext{actual}}}{n{ ext{theoretical}}} imes 100 ext{ %} = rac{(m{ ext{myristic ext{ acid}}} / M{ ext{myristic ext{ acid}}})}{3 imes (m{ ext{trimyristin}} / M{ ext{trimyristin}})} imes 100 ext{ %}

  • Note: This calculation assumes complete hydrolysis and quantitative transfer/collection of products. Molar masses:

  • Trimyristin: $M_{ ext{trimyristin}}$ (need exact MM from a table)

  • Myristic acid: $M_{ ext{myristic ext{ acid}}} = 228.24 ext{ g/mol}$ (approx; use your course MM)

• Purity check by melting point (mp) of product:

  • Mixed melting point concept:

  • If the MP of a mixture is depressed and broad relative to a pure reference, the identity is confirmed as a mixture, indicating impurity or incomplete reaction.

  • If the mp is sharp and near the literature value for a pure substance, the material is likely pure.

  • In mixed-mp experiments, typical comparisons are with known standards to confirm identity.

  • General rule (from the notes):

  • Mixed mp concept: a depressed or broadened mp suggests non-identical materials; a sharp mp near literature value suggests the same material.

  • Specific guideline provided: If you weigh equal amounts of trimyristin and myristic acid and measure mp, the interpretation depends on the mp range:

    • If mp is wide and lower than $54^ emp C$, the hydrolysis reaction worked (product mixture present).

    • If mp is sharp (narrow), the hydrolysis reaction did not work (the mixture is not present or not formed).

    • In general, mp near literature value and sharp implies purity; a wide range and lower mp implies impurity.

  • Practical mp values used:

  • Trimyristin mp: $56-58^ emp C$

  • Myristic acid mp: $54-55^ emp C$

• Conceptual notes on the reaction mechanism:

  • Mechanism (base-catalyzed hydrolysis of a triglyceride) in two stages:
    1) Saponification: triglyceride + 3 NaOH → glycerol + 3 RCOO- Na+ (carboxylate salts of myristic acid).
    2) Acid workup: carboxylate salts + HCl → RCOOH (myristic acid) + NaCl; glycerol remains in solution or co-purifies depending on conditions.

  • Simplified schematic:
    ext{trimyristin} + 3 ext{NaOH}
    ightarrow ext{glycerol} + 3 ext{RCOO}^- ext{Na}^+ \[0.2em] 3 ext{RCOO}^- ext{Na}^+ + 3 ext{H}^+
    ightarrow 3 ext{RCOOH} + 3 ext{Na}^+

  • In practice: first hydrolysis under ethanol/NaOH, then acidify with HCl to obtain free fatty acid.

• Possible side reaction (in Part B):

  • ROH (alcohol) formation via base-catalyzed trans-esterification or hydrolysis side reactions, depleting the desired product.

  • The slide lists: ROH + NaOH → R-ONa + H2O as a potential side process.

Part A vs Part B: Conceptual Connections to Foundational Principles

• Lipid chemistry foundations:

  • Trimyristin is a triglyceride derived from glycerol and myristic acid; hydrolysis yields fatty acids and glycerol.

  • Hydrolysis is a type of ester cleavage; saponification uses strong base to form carboxylate salts, which are water-soluble.

• Purification principles:

  • Recrystallization exploits differences in solubility with a chosen solvent system (acetone here) to yield pure solids.

  • Vacuum filtration and Celite filtration help remove insoluble impurities and fine particulates.

• Purity assessment:

  • Melting point is used as a quick indicator of purity; a pure crystalline solid typically shows a sharp mp close to literature data.

  • Mixed-melting-point technique helps determine if two substances are the same material or mixtures.

• Real-world relevance:

  • Saponification is the basis for soap production; fatty acids are common fuel/industrial chemicals.

  • The exercise connects organic synthesis (ester hydrolysis), purification, and analytical techniques (melting point) in a compact lab workflow.

Apparatus and Conditions in the Micro-Scale Reflux System

• Micro-scale reflux components:

  • Water condenser (inlet water and outlet water lines)

  • Thermometer probe (to monitor reaction temperature)

  • Sand bath or hot plate with a sand bed for even heating

  • Ethanol as solvent (bp ≈ $78^ emp C$)

  • Reaction mixture heated to ~$70^ emp C$ in the boiling region; total reflux around ~$100-110^ emp C$ depending on setup

• Important notes:

  • For accurate reflux operation, ensure the condenser is cooled and water supply is stable.

  • The reaction medium is ethanol-based, and the viscosity/volatility of solvents impact heating control.

  • The setup is designed for small-scale experiments (micro-reflux) to minimize solvent usage and exposure.

Experimental Procedures: Week-by-Week Summary

• Part A (Week 1): Isolation of Trimyristin

  • Set up: 50 mL conical flask, reagents as above.

  • Extraction: Add 2.0 g ground nutmeg to 20 mL diethyl ether; agitate for 15 minutes.

  • Filtration preparation: Prepare a small cartridge with cotton, 2 mm sand, and drying agent (1 cm of anhydrous Na2SO4).

  • Filtration: Transfer mixture onto cartridge and collect filtrate in a pre-weighed vacuum flask.

  • Rinse: Use ~0.5 mL ether to rinse the flask and ensure maximum recovery.

  • Solvent removal: Evaporate solvent in the vacuum flask to obtain crude solid.

  • Collection: Weigh solid; reserve a portion for mp testing.

  • Purification: Recrystallize from acetone (0.5 mL or minimal solvent) by heating, then cooling to RT and 0 °C; collect crystals by suction filtration.

  • Final product: Pure trimyristin; weigh and compute percentage yield relative to ground nutmeg.

• Part B (Week 2): Hydrolysis of Trimyristin

  • Setup: 10-mL vial with 0.2 g trimyristin, 2 mL ethanol, 2 mL 10% NaOH; add boiling stones.

  • Reflux: Micro-reflux for 1 hour to hydrolyze the triglyceride to glycerol and sodium salts of myristic acid.

  • Acid workup: Pour mixture into 10% HCl solution (≈ 10 mL) to release free myristic acid; swirl.

  • Filtration: Collect crude solid by vacuum filtration.

  • Purification of crude product: Transfer crude to 3 mL petroleum ether in a test tube; filter through a pipet with cotton and Celite; rinse with petroleum ether; evaporate solvent to yield crude myristic acid.

  • Final steps: Weigh the crude product; calculate percent yield; optionally further purification to obtain pure myristic acid.

Data Interpretation and Notes on Purity Assessment

• Melting point data:

  • Trimyristin mp: $56-58^ emp C$ (solid, crystalline material)

  • Myristic acid mp: $54-55^ emp C$

• Mixed melting point tests:

  • If mixing trimyristin and myristic acid yields a mp that is depressed and broadened, the mixture indicates presence of both substances and partial hydrolysis has occurred.

  • If the mp is sharp and near the literature value for one component, that indicates purity of that component.

• Decision rules for Part B mp test (as given):

  • If mp is wide and lower than $54^ emp C$, hydrolysis worked (mixture present).

  • If mp is sharp, hydrolysis did not work (one pure component only).

  • In general:

  • sharp mp near literature value => compound pure

  • wide mp depressed mp => compound impure

• Practical mp expectations:

  • The use of equal masses for mixed mp helps identify if hydrolysis produced separate components (trimyristin + myristic acid) or if one component remains dominant.

Quick Reference: Formulas and Calculations (LaTeX)

• Yield (Part A):
  ext{ % yield of trimyristin} = rac{ ext{weight of trimyristin}}{ ext{weight of ground nutmeg}} imes 100 ext{ %}

• Moles and theoretical yield (Part B):
  $n<em>{ ext{trimyristin}} = rac{m</em>{ ext{trimyristin}}}{M<em>{ ext{trimyristin}}}$ $n</em>{ ext{myristic ext{ acid}}} = rac{m<em>{ ext{myristic ext{ acid}}}}{M</em>{ ext{myristic ext{ acid}}}}$
  $n<em>{ ext{theoretical ext{ (myristic acid)}}} = 3 imes n</em>{ ext{trimyristin}}$
  ext{ % yield of myristic acid} = rac{n{ ext{actual}}}{n{ ext{theoretical}}} imes 100 ext{ %} = rac{(m{ ext{myristic ext{ acid}}} / M{ ext{myristic ext{ acid}}})}{3 imes (m{ ext{trimyristin}} / M{ ext{trimyristin}})} imes 100 ext{ %}

• Reaction schematic (hydrolysis):
  $ext{trimyristin} + 3 ext{NaOH} <br>ightarrow ext{glycerol} + 3 ext{RCOO}^{-} ext{Na}^{+}$
  $3 ext{RCOO}^{-} ext{Na}^{+} + 3 ext{H}^{+} <br>ightarrow 3 ext{RCOOH} + 3 ext{Na}^{+}$

• Important constants (examples):

  • Ethanol bp ≈ $78^ emp C$

  • Trimyristin mp ≈ $56-58^ emp C$

  • Myristic acid mp ≈ $54-55^ emp C$

Practical Notes and Tips

• Drying and drying agents: ensure Na2SO4 is anhydrous to maximize extraction efficiency; avoid moisture that can affect recrystallization.

• Recrystallization: choose solvent in which the compound has differential solubility at RT vs hot; acetone is effective for trimyristin in this protocol.

• Purification steps are crucial for accurate mp and yield measurements; do not skip vacuum filtration or Celite filtration when crude mixtures contain unwanted solids.

• Safety reminders: handle diethyl ether and petroleum ether with care (highly flammable); work in a well-ventilated area; wear appropriate PPE; dispose of chemical waste according to institutional guidelines.

Connections to Foundational Principles and Real-World Context

• Saponification and ester hydrolysis under basic conditions demonstrates a standard method to convert triglycerides into glycerol and fatty acids, which is central to soap production and fat chemistry.

• The purification workflow (extraction, filtration, recrystallization) reflects general strategies used in organic synthesis to obtain pure products from natural sources or reaction mixtures.

• Melting point and mixed-melting-point techniques provide simple, rapid purity and identity checks, essential for validating synthetic outcomes without advanced instrumentation.

• The exercise reinforces calculating yields from mass measurements and molar relationships, a core skill in stoichiometry and process chemistry.