Purification and Thin-Layer Chromatographic Analysis of Caffeine
Purpose of the Experiment: The intention of the experiment is to use solvent extraction methods to separate a mixture containing a carboxylic acid and a neutral compound. Once recovered, the solids were purified by recrystallization and examined by thin-layer chromatography, and their identities were derived by melting point and infrared (IR) spectroscopy.
Extraction is a procedure that selectively dissolves one or more of the mixture compounds into a proper solvent. Extraction refers to the moving of compounds from one liquid solvent to another liquid solvent.
A compound can be disconnected from impurities in a solution by extracting the compound from the first solvent into a second solvent. The compound must be more soluble in the second solvent than in the first solvent, and the impurities must be insoluble in the second solvent. Also the two solvents must not be soluble in one another because they need to produce two separate layers. The two layers are shaken to mix.
This mixing helps the moving of the dissolved compound from one layer to another. Once the transfer procedure is finished, the layers form again.
This time the separated layers separate the desired compound from the impurities. Washing is the reverse procedure, in which the impurities are moved to the second solvent, leaving the sought after compound in the first solvent. The aqueous, carboxylic acid, solvent used is polar and the organic, ether, solvent is non-polar.
The more dense solvent is the bottom layer. In this case the aqueous water is on the bottom layer and the ether is on the top. Density is one way to differentiate each layer but the identities still have to be confirmed.
A general rule of solubility is like dissolves like. Non-polar compounds, most organic compounds, are more soluble in non-polar solvents than in polar solvents.
Ionic and polar compounds are more soluble in polar solvents like water. Ionic forms of the organic compound can be produced by reacting them with aqueous bases, NaOH in this experiment. This converted the acid to a water-soluble carboxylate anion by deprotonating the carboxylic acid. Because an ionic compound is made in this reaction, the product is soluble in water but not soluble in ether.
So this product will extract into the aqueous layer. The other compound does not react with NaOH and remains dissolved in the non-polar ether.
The separatory funnel separates the aqueous layer from the organic layer. The carboxylic acid is recovered by neutralizing the aqueous solution containing the carboxylate anion with hydrochloric acid. To recover the organic compound, we dried the non-polar organic layer by adding Na2SO4 and evaporated the solvent under vacuum filtration. As the solvent evaporated, the organic compound remained.
To recrystallize the acid from the aqueous layer, we reversed the reaction above by adding some acid to the aqueous layer.
This neutralized the NaOH, and the ionic salt is made back into the acid. After the compounds dried, we measured the mass of each separate compound. Finally, we measured the melting point of the unknown and the acid. We deliberated on the purity by comparing the experimentally measured melting point with the known values. Also we used IR spectroscopy to determine what our acid and unknown organic compound could be.
Chemical| Molecular weight| Melting point| Boiling point| Density| Hazard| Diethyl Ether| 74.
12 g/mol| -116. 3 C| 34. 6 C| 0. 7134 g/cm3| Extremely flammable, harmful to skin| Sodium Hydroxide| 39. 99 g/mol| 318 C| 1388 C| 2. 13 g/cm3| Harmful to skin and eyes| Water| 18.
00 g/mol| 0. 00 C| 100 C| 1. 00 g/cm3| n/a| Sodium Sulfate| 142. 04 g/mol| 884 C | 1429 C | 2. 66 g/cm3| irritant| Hydrochloric Acid (6M)| 36.
46 g/mol| -59. 0 C| 108 C| 1. 098 g/cm3| irritant| Acetone| 58. 08 g/mol| -95. 0 C| 56 C| 0.
791 g/cm3| Extremely flammable, Toxic| Acetic Acid | 60. 05 g/mol| 16. C| 118 C| 1. 049 g/cm3| irritant| Ethyl Acetate| 88. 1 g/mol| -83.
6 C| 77. 1 C| 0. 897 g/cm3| Low toxicity| Procedure: The procedure was laid out exactly as we performed it in the Organic Chemistry Laboratory manual on pages 3-6. (Freeman, 2010). The only difference was in isolating the neutral compound; we did not place a boiling stick or stone in the Erlenmeyer flask and work in a hood to evaporate the ether using a steam bath or hot-water bath.
Part 2. 2 of the Extraction experiment is outlined and performed the exact way that the book describes. (Freeman, 2010).
Data: The percent error is found by taking the experimental value and subtracting the true value and then dividing that number by true value and multiplying that number by 100. The determined mass of the two labeled watch glasses is shown in the following table as well as the % Error of the melting points: Weight of Filter Paper | Weight of Filter Paper with Organic Crystals| Weight of Filter Paper with Acidic Crystals| % Error Value for Organic Melting Point| % Error Value for Acid Melting Point| Melting Point of Organic Compound| Melting Point of Acidic Compound| 0. 82 grams| 0.
682 grams| 0. 567 grams| -0. 5%| 0%| 99. 0 C| 110-111 C| Rf values are found by taking the distance traveled by the compound and dividing it by the distance traveled from origin to the solvent front.
The TLC that was performed in the second part of this experiment in week two yielded the following Rf values: Distance traveled by Acid| Distance traveled by Organic compound| Distance to the Solvent Front| Rf Value for Acid| Rf Value for Organic compound | 3. 8cm| 4.
2cm| 5. 7cm| 0. 667| 0. 7368| The last resort that we used to determine our unknown compounds was the Infrared spectroscopy (see attached reports). In comparing the IR spectroscopy spectra reports provided to us with our unknown’s reports, I believe that our unknown organic compound is Phenanthrene and our unknown inorganic substance to be 3-methylbenzoic acid or m-toluic acid.
The peaks between 1500 and 2000 look alike and the peaks in the OH region between 2500 and 3000 appear to be the same for the acids.
The Carbon double bond to Oxygen stretch in peak 1700 is also similar to the spectra for the known m-toluic acid that was provided to us. For the unknown organic solution, it most resembles Phenanthrene when compared to the provided spectra reports especially for the peaks between 650 and 1000. With the evidence gathered and explained in my report, it is safe to assume that our inorganic substance is m-toluic acid and the organic substance is Phenanthrene. This is proven through the IR spectroscopy, similar or exact melting point range, and the solubility and density of the polar and non-polar substances.
The percent error for the unknown organic substance was slightly off.
This could be due to impurities or human error. I enjoyed doing this experiment. It was very straight forward and showed us how the extraction method and recrystallization method work together to separate mixtures. I would use more of the unknown compounds so that I could produce more crystals to use in the experiment. Also I would do the experiment slower and more careful just to see if the percent error for the organic substance could be reduced to 0%.