Objective Statement: In this lab, I will learn about the extraction technique. Extraction is one of the many ways to purify an organic compound. Extraction helps to overcome the difficulty of removing water from a solution through boiling, instead solutes and other compounds can be used to create chemical reactions, isolate, and remove certain compounds like water to purify specific organic compounds.
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Compounds of Study:
Benzoic acid
Molecular Weight: 122.123 g/mol
Melting point: 122 degrees celsius
Boiling point: 250 degrees celsius
pka: 4.202 (H20), 11.02 (DMSO)
4-t-butylphenol
Molecular Weight: 150.221 g/mol
Melting point: 99.5degrees celsius
Boiling point: 239.8 degrees celsius
pka: 10.23
Dimethlybenzene
Molecular Weight: 138.166 g/mol
Melting point: 55 degrees celsius
Boiling point: 212.6 degrees celsius
pka: -4.5
Dichloromethane
Molecular Weight: 84.93 g/mol
Melting point: -96.7 degrees celsius
Boiling point: 39.6degrees celsius
Pre-Lab Questions:
1. Outline the steps activity #1, you do not need to write complete sentences but simply outline what you should be doing first, then second, etc. Below is an example of how you could outline the first few steps, you can copy this in your answer and then add the remaining steps
1. Dissolve the solid in ether.
2. Add in water and bicarbonate then separate layers
3. Drain the aqueous layer and add 10 mL of water and 10 mL of bicarbonate to the organic solution in the funnel.
4. Mix again, and drain the aqueous layer into the same flask as step 3.
5. Precipitate the carboxylate by adding droplets of 6M HCL in the aqueous layer and make sure the pH level is appropiate.
6. Vaccum filter the precipitate solution and let it dry.
7. Extract the weak acid from the organic layer by using 1.5 M sodium hydroxide. Using the same methods listed above, do not dilute further with sodium hydroxide.
8. Wash the ether layer with 10 mL of DI water, and then wash the ether layer with 10 mL of a saturated salt solution after two extraction steps.
9. Precipitate the conjugate base from the aqueous hydroxide solution. Use the same methods in Step 5 to accomplish this.
10. Purify the neutral compound from the ether layer. Do this by "drying" the ether layer using magnesium sulfate.
11. Set solid left over to dry.
2. In your own words describe the difference between an extraction step and a washing step.
In the extraction step, the desired compound is moved between layers. While the washing step keeps the desired compound in its current layer, and instead moves unwanted material to the other layer.
3. If the partition coefficient is a large number, does this mean that the compound is more soluble in water or more soluble in nonpolar organic?
A greater partition coefficient means that the substance has greater solubility in nonpolar organic substances.
4. To decide if it is better to extract multiple times with a small amount of solvent or extract once with a large amount of solvent considering the following scenario:
suppose a reaction mixture afforded 300 ml of an aqueous solution containing 30 g of malononitrile (CH2(CN)2) which is to be isolated by extraction with ether. The solubility of malononitrile in ether at room temperature is 20.0 g per 100 ml, and water is 13.3 g per 100 ml.
A. What is the partition coefficient of malononitrile? Take a picture of your calculation and upload the picture. Show all work.
k = 1.5 (see picture below)
B. What weight of malononitrile would be recovered by extraction with (a) three 100 ml portions of ether; and (b) one 300 ml portion of ether? Take a picture of your calculation and upload the picture. Show all work.
a) 21.11 g of malononitrile will be extracted b) 18.07 g of malononitrile will be extracted.
C. Which is better, to extract several times with small amounts of solvent or one time with a large amount of solvent?
Extracting several times will be better.
5. Why is it not necessary to record the exact amount of the organic solvent used in activity #2 but it is important to record the exact amount of organic solvent used in activity #1?
The organic solvent used in Activity #2 is to just dissolve the compounds into a liquid form for TLC. In Activity #1 the organic solvent is used for extraction of the compound so it needs to be a lot more precise to get effective results and not over or under-dilute solution.
6. The mixture contains two acids - why doesn’t the bicarbonate solution react with the weakly acidic phenol compound?
The bicarbonate is not strong enough to pull the proton off of phenol to make it react.
7. Why is it important to wash an organic layer with water just after washing it with a strongly basic aqueous solution?
Washing an organic layer with water helps to remove any polar or water-soluble impurities in the basic aqueous solution.
8. At the end of the lab, you will analyze your three solid products by TLC. Refer to lab #1 and explain how you prepare a solid sample for TLC analysis.
Dissolve the samples you want to run on TLC in vials containing volatile solvents that the samples are soluble in. Then you would spot the samples on a TLC plate using a micropipet and wait for the solvent to evaporate to leave the sample on the TLC plate.
Activity #1:
Added 2.49 g of 1:1:1 benzoic acid/4-t-butylphenol and dimethoxybenzene mixture and 33 mL of diethyl ether into a separatory funnel.
Added 10 mL of DI water and 10 mL of saturated 3M sodium Bicarbonate to the separatory funnel
Inverted the separatory funnel 15 times, releasing pressure every 5 inversions and letting the organic and aqueous layers settle apart.
Drained the bottom aqueous layer into an Erhlenmeyer flask and added another 10 mL of DI water and 10 mL of sodium bicarbonate to the organic layer left in the separatory funnel. To remove the last little bit of aqueous solution within the organic solute.
Drained the bottom aqueous layer the second time from the separatory funnel into the same Erhlenmeyer flask as the first extraction. Extracting the acidic benzoic into the aqueous layer.
Added drops of 6M HCl in aqueous solution to lower pH to 3 to form a precipitate. After 26 drops no PP formed. Placed the solution on ice for 10 minutes.
White crystals formed and were removed from the solution through vacuum filtration and set aside to dry.
The organic layer formed in step 4 had 10 mL of 1.5M sodium hydroxide added to it in a separatory funnel.
Drained out the aqueous layer to a new flask, and repeated step 8.
Washed the organic layer with 10 mL of DI water and separated the DI into the aqueous layer flask.
Washed organic layer with 10 mL of saturated salt solution in the separatory funnel; flipped over 15 times, releasing pressure every 5 turns.
Added HCl in an aqueous flask as above until the solution turned cloudy and cooled on ice to form a precipitate. 18 drops of HCl
Vaccum filtered the solids out of the solution.
The drained organic layer had magnesium sulfate added to it until the magnesium no longer clumped together. Should swirl around like sand.
Gravity filtrated to remove magnesium sulfate.
Vaccum evaporated ether. Solid formed as ether was evaporated and cooled.
Results:
Strong Acid, Benzoic Acid Recovered(flakey white crystals):
-Mass recovered: .59g
-Experimental melting point: 127-132°C.
Weak Acid, 4-t-butylphenol Recovered(powdery grey crystals):
-Mass recovered: 0.73g
-Experimental melting point: 99-102°C.
Neutral, dimethoxybenzene Recovered(large opaque crystals):
-Mass recovered: 0.52g
-Experimental melting point: 41-43°C.
TLC Analysis:
Dimethoxybenzene
Dimethoxybenzene
Spot 1 (Pure): Rf = (4.8/6.) = 0.8
Spot 3 (Experi): Rf = (5/6.) = 0.83
4-t-butylphenol
4-t-butylphenol
Spot 1 (Pure): Rf = (4.1/6.5) = 0.63
Spot 3 (Experi): Rf = (5.0/6.5) = 0.77
Benzoic Acid
Benzoic Acid
Spot 1 (Pure): Rf = (5.9/6.5) = 0.91
Spot 3 (Experi): Rf = (6.2/6.5) = 0.95
Discussion/Conclusion:
A 100% recovery of all the masses, with a starting mass of 2.50 g would be .83g of each compound. The percent yield of dimethoxybenzene was 0.52g/ 0.833 x100 = 62.4% mass recovery; for 4-t-butyl phenol, 0.73g/0.833 x100 = 88.0% recovery; for benzoic acid, 0.59g/0.833 x100 = 71.1% recovery. The total mass recovered was 1.84g/ 2.49g x 100 = 73.9% total mass recovery. All recoveries are a bit lower than we would want but that would be due to compounds lost in water or not completely effective separation into their respective layers.
The data collected on the three experimental compounds' melting points helped to confirm the purity of the solids recovered. The experimental dimethoxybenzene had a range of 41-43°C, a little lower than the literature value of 55°C. The experimental benzoic acid had a range of 127-132°C, a little higher than the literature value of 122.3°C. The experimental 4-t-butylphenol had a range of 100-102°C, a bit higher than the literature value of 99.5°C. Most of the compounds were pretty close to their literature melting points, indicating pretty relative and mostly accurate purity. Dimethoxybenze's melting point had the greatest difference and that could mainly be because the solution was boiled out resulting in the greatest difference. The difference in boiling points higher and lower than the literature value was the result of impurities of the other compounds that were not completely extracted from the separatory or precipitation steps.
For TLC, all three compounds showed one major spot on the plate. They all did not have as compact or tight spots as their respective pure compounds but were still aligned in that the solids extracted were very similar to the pure examples. Along with their very similar Rf values across the board, I am very confident in the purity of the solids extracted in this lab. The only thing I did notice, is that I possibly left the TLC plates too long in their solvent systems as my Rf values are pretty high and the spots are stretched out on the paper.
Reflection:
This lab tied together a lot of the previous techniques learned about to understand acid-base chemistry for extraction. Using the different levels of acidity or basicity of the three compounds, successful extraction was possible from a 1:1:1 mixture and recovered for analysis. Using previous techniques of separation in a separatory funnel, precipitation forming, different forms of filtration, TLC, and melting point analysis were all used to yield the products and determine the purity of those products. A few issues that arose started with understanding the process of extracting each compound as parts for each next step depending on the previous steps' completion it was difficult to keep our station free of clutter and confusion. Another problem that arose was the evaporating of ether to yield the solid dimethoxybenzene. Dimethoxybenzene has a relatively low boiling point and we experience melting point depression due to the impurities left in the solution. Will pay more attention to my experiments as they happen in the next labs to accurately monitor my experiments.
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