Course: CHM 25501, Organic Chemistry (Purdue University) Difficulty: Introductory lab Prerequisites: Basic understanding of functional groups (alcohols, esters, carboxylic acids), familiarity with filtration and recrystallisation techniques.
This experiment teaches you how to isolate a single compound, trimyristin, from a complex natural source (nutmeg) using solvent extraction, then purify it by recrystallisation. It ties together three analytical techniques you will use repeatedly in organic chemistry: melting point determination, IR spectroscopy, and percent recovery calculations. If you can follow the logic here, you have the conceptual toolkit for most isolation-and-purification labs in the course.
Ground nutmeg is extracted with ethyl acetate to dissolve trimyristin (a fat/triglyceride). The extract is filtered, concentrated, and recrystallised to give pure trimyristin. Purity is confirmed by a narrow melting point range and by matching IR peaks to the expected ester functional group.
Trimyristin
A triglyceride (triester of glycerol and myristic acid) with molecular formula C₄₅H₈₆O₆. It is the principal fat in nutmeg, making up roughly 20 to 40% of nutmeg by mass. In simple terms, it is the specific fat molecule you are trying to pull out of nutmeg in this experiment.
Myristic acid (tetradecanoic acid)
A 14-carbon saturated fatty acid (C₁₄H₂₈O₂) with a carboxylic acid functional group. It is one of the three identical fatty acid chains esterified to the glycerol backbone in trimyristin. Think of it as the "arm" of the trimyristin molecule: three myristic acid chains hang off one glycerol core.
Glycerol (glycerine, 1,2,3-propanetriol)
A three-carbon triol (three hydroxyl groups) that forms the backbone of all triglycerides. Functional groups: three alcohol (–OH) groups. In simple terms, glycerol is the central scaffold that holds the three fatty acid chains together.
Recrystallisation
A purification technique in which a crude solid is dissolved in a hot solvent, then allowed to cool slowly so that pure crystals form while impurities remain dissolved. Think of it as letting only the "right" molecules lock into the crystal lattice while the wrong ones stay in solution.
Percent recovery (% recovery)
The mass of purified product obtained divided by the theoretical mass of product expected, multiplied by 100. It tells you how much of the target compound you managed to collect. In simple terms, it is your efficiency score for the extraction.
Melting point range
The temperature span over which a solid transitions to a liquid. A narrow range (1 to 2 °C) indicates high purity; a broad or depressed range suggests impurities. Think of it as a purity fingerprint: the sharper the melting point, the cleaner your compound.
IR spectroscopy (infrared spectroscopy)
An analytical technique that measures which infrared wavelengths a compound absorbs. Each functional group absorbs at characteristic frequencies (reported in cm⁻¹), so IR tells you which functional groups are present. In simple terms, it is a way of shining infrared light through your sample to see what chemical groups are in it.
Functional group
A specific arrangement of atoms within a molecule that determines its chemical reactivity and physical properties. Examples from this lab: ester (C=O and C–O in trimyristin), carboxylic acid (–COOH in myristic acid), alcohol (–OH in glycerol), and alkane (C–H chains).
Solvent extraction
The process of dissolving a target compound out of a mixture by adding a solvent in which the target is soluble but other components are not (or are less soluble). In simple terms, you pick a liquid that the compound you want will dissolve in, then wash it out of the solid mixture.
Whole nutmeg is crushed and ground to increase surface area
Greater surface area allows more contact between the solid and the extraction solvent
Skipping grinding would mean slower, less complete extraction and lower yield
Ground nutmeg is extracted with ethyl acetate (a moderately polar organic solvent)
Trimyristin dissolves in ethyl acetate; many other nutmeg components do not
The mixture is gravity-filtered to remove insoluble solids (cell walls, fibre, pigments)
This is where significant product loss often occurs: trimyristin can get trapped in the filter cake alongside insoluble material
The filtrate is concentrated (solvent removed) to yield crude trimyristin
Crude trimyristin is purified by recrystallisation
Dissolve in a minimal amount of hot solvent, then cool slowly
Pure trimyristin crystallises out; impurities remain in solution
The purified crystals are collected by vacuum filtration
Percent recovery = (mass of purified trimyristin / theoretical mass of trimyristin in the nutmeg sample) x 100
The theoretical mass depends on the assumed trimyristin content of nutmeg, which ranges from about 20% to 40%
An additional correction factor of 0.75 is sometimes applied to account for incomplete extraction
Example from lab data:
Mass of nutmeg used: 7.927 g
Mass of purified trimyristin recovered: 0.043 g
At 24% assumption: (7.927 x 0.24) x 0.75 = 1.427 g theoretical, so recovery = 0.043 / 1.427 = 3.01%
At 40% assumption: (7.927 x 0.40) x 0.75 = 2.378 g theoretical, so recovery = 0.043 / 2.378 = 1.81%
A low percent recovery does not necessarily mean the product is impure; it means you lost material along the way
Loss of product during transfers between vessels
Trimyristin trapped in filter paper during gravity filtration (the most common culprit)
Incomplete extraction from the nutmeg
Losses during recrystallisation (some product stays dissolved in the cold solvent)
Interference from other compounds in nutmeg
Mitigation: filter in smaller portions so less product is trapped in the cake
Melting point is the primary non-spectroscopic measure of purity
A narrow melting point range (about 1 °C) indicates high purity
A broad or depressed range indicates impurities are present, because impurities disrupt the crystal lattice
Literature melting point of trimyristin: approximately 56 to 57 °C
IR confirms that the correct functional groups are present and that starting materials or contaminants are absent
You compare your observed peak positions to known characteristic frequencies for each functional group
Insoluble in water (trimyristin is nonpolar; water is polar)
Soluble in: ether, ethyl acetate, alcohol, chloroform, benzene, acetone, dichloromethane, ethanol
Water would be a poor extraction solvent because trimyristin simply will not dissolve in it
The choice of ethyl acetate as extraction solvent follows from the "like dissolves like" principle
Grinding increases surface area, which increases the rate and completeness of extraction
Unground nutmeg would require much longer extraction times and give lower yields
This is a direct application of the principle that reaction (or dissolution) rate depends on surface area of contact
\text{\% Recovery} = \frac{\text{mass of purified product}}{\text{theoretical mass of product}} \times 100Where theoretical mass = (mass of nutmeg) x (assumed fraction of trimyristin) x (correction factor, e.g. 0.75).
Compound | Vibration | Expected Range (cm⁻¹) | Example Observed (cm⁻¹) |
|---|---|---|---|
Glycerol | O–H stretch | 3500 to 3200 | 3150 to 3000 |
Glycerol | C–O stretch | 1320 to 1000 | 1031.04 |
Glycerol | C–H stretch | 3000 to 2850 | 2916.33 to 2848.70 |
Myristic acid | O–H stretch | 3300 to 2500 | 2000 to 2800 |
Myristic acid | C=O stretch | 1760 to 1690 | 1697.78 |
Myristic acid | C–O stretch | 1320 to 1000 | 1285.69 |
Trimyristin | C=O stretch (ester) | 1750 to 1735 | 1735.53 |
Trimyristin | C–O stretch | 1320 to 1000 | 1177.75 |
Trimyristin | C–H stretch | 3000 to 2850 | 2848.27 to 2913.98 |
The ester C=O in trimyristin appears at a higher frequency (around 1735 cm⁻¹) than the carboxylic acid C=O in myristic acid (around 1698 cm⁻¹). This difference is a reliable way to distinguish the two on an IR spectrum.
Glycerol: three –OH groups on a three-carbon chain (a triol)
Myristic acid: 14-carbon chain with a terminal –COOH (carboxylic acid)
Trimyristin: glycerol backbone esterified with three myristic acid chains, containing three ester linkages (C=O and C–O) and long alkane chains
Trimyristin and myristic acid are used in the cosmetics and food industries as emollients, emulsifiers, and stabilisers. The extraction and purification logic here (solvent extraction, recrystallisation, spectroscopic confirmation) is the same workflow used in pharmaceutical isolation of active compounds from plant material.
Students often think a low percent recovery means the product is impure. It does not. Recovery measures how much you collected, not how clean it is. You can have very pure product with very low recovery.
Students sometimes confuse the melting point range with the melting point value. The range (how many degrees between first and last crystal melting) indicates purity. The absolute value tells you which compound you have.
Students often believe the O–H stretch in a carboxylic acid looks the same as the O–H stretch in an alcohol on IR. It does not. The carboxylic acid O–H is characteristically broad and extends from roughly 3300 down to 2500 cm⁻¹, while an alcohol O–H is a broader, rounder peak centred around 3200 to 3550 cm⁻¹.
Students sometimes assume that water could work as an extraction solvent because it is cheap and safe. Trimyristin is nonpolar and will not dissolve in water, so water fails entirely for this purpose.
⚠️ Be able to calculate percent recovery given mass of nutmeg, assumed trimyristin content, correction factor, and mass recovered.
⚠️ Know how to interpret a melting point range in terms of purity, not just identity.
⚠️ Be able to distinguish ester C=O (around 1735 cm⁻¹) from carboxylic acid C=O (around 1700 cm⁻¹) on an IR spectrum.
⚠️ Explain why ethyl acetate is a suitable extraction solvent and water is not (like dissolves like).
⚠️ Explain why grinding the nutmeg improves extraction yield (surface area).
⚠️ If asked about detecting starting materials in a synthesised product by IR, know the characteristic peaks: ester C=O for trimyristin, carboxylic acid C=O for myristic acid, broad O–H for glycerol.
True or false: A low percent recovery always means your product is impure.
False. Recovery and purity are independent measures.
Fill in the blank: The ester C=O stretch in trimyristin appears at approximately ______ cm⁻¹.
1735
True or false: Water is a good solvent for extracting trimyristin from nutmeg.
False. Trimyristin is nonpolar and insoluble in water.
Fill in the blank: A narrow melting point range of about 1 °C indicates that the sample has high ______.
Purity
True or false: Grinding the nutmeg before extraction decreases the yield.
False. Grinding increases surface area and improves yield.
Q: You recover 0.043 g of trimyristin from 7.927 g of nutmeg. Assuming nutmeg is 24% trimyristin and applying a 0.75 correction factor, what is your percent recovery?
A: Theoretical mass = (7.927 x 0.24) x 0.75 = 1.427 g. Percent recovery = (0.043 / 1.427) x 100 = 3.01%.
Q: Your purified trimyristin has a melting point range of 55.5 to 56.5 °C. What does this tell you about purity?
A: A range of 1 °C is narrow, indicating the sample is relatively pure. The range is close to the literature value for trimyristin (approximately 56 to 57 °C), which also supports correct compound identity.
Q: Why is ethyl acetate chosen as the extraction solvent rather than water?
A: Trimyristin is nonpolar and therefore insoluble in water (a polar solvent). It is soluble in ethyl acetate, a moderately polar organic solvent. "Like dissolves like" governs solvent choice.
Q: On an IR spectrum, how would you distinguish trimyristin from myristic acid?
A: Trimyristin shows an ester C=O stretch at approximately 1735 cm⁻¹. Myristic acid shows a carboxylic acid C=O stretch at approximately 1698 cm⁻¹, along with a broad O–H stretch from 3300 to 2500 cm⁻¹ that is absent in trimyristin.
Q: If you synthesised trimyristin from glycerol and myristic acid but the reaction was incomplete, what IR peaks would reveal the presence of unreacted starting materials?
A: Unreacted glycerol would show a broad O–H stretch around 3200 to 3500 cm⁻¹. Unreacted myristic acid would show both a broad O–H stretch (3300 to 2500 cm⁻¹) and a carboxylic acid C=O at approximately 1698 cm⁻¹. These peaks would be absent if only pure trimyristin were present.
Q: What experimental error most likely explains a low percent recovery, and how could you mitigate it?
A: Product loss during gravity filtration, where trimyristin becomes trapped in the filter cake with insoluble material. Filtering in smaller portions reduces the amount of product trapped.
This lab connects directly to the broader topic of lipid chemistry and ester hydrolysis: trimyristin is a triglyceride, and understanding its structure prepares you for saponification reactions (base-catalysed hydrolysis of fats to make soap), which may appear later in the course.
The IR interpretation skills practised here carry over to every subsequent lab that uses spectroscopic identification, particularly distinguishing carbonyl subtypes (ester vs carboxylic acid vs ketone vs aldehyde).
The principles of solvent extraction and recrystallisation are foundational techniques you will reuse in nearly every organic chemistry lab, including Grignard reactions, aldol condensations, and natural product isolations.
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