In this lab, a liquid-liquid extraction will be preformed to isolate 3 different compounds. Using acid base chemistry and polarity techniques, the compounds will be extracted from one another by moving them through various phases of polarity. Once the compounds are extracted, benzoic acid is tested for the partition coefficient.

This lab will help me implement uses of acid base chemistry and introduce its relationship to extraction of substances. 

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.  First we will dissolve the solid in ether, 2. Then we will mix in water and bicarbonate then separate layers, 3…after that we will....

1. First we will dissolve the solid in ether.

2. Then we will mix in water and bicarbonate then separate layers.

3. After that we will drain the aqueous layer into a flask and add water and bicarbonate.

4.  Mix again and extract the aqueous layer containing benzoic acid.

5. Precipitate the carboxylate from the aqueous solution and isolate the solid by filtration.

6. Extract the weak acid with sodium hydroxide then wash it with water and a saturated salt solution.

7. Precipitate the conjugate base from the hydroxide solution.

8. The, purify the neutral compound from the ether layer.

9. Lastly, set the solid aside to dry.

2.  In your own words describe the difference between an extraction step and a washing step.

An extracting step is when the major product is moved from one phase to another, polar to non-polar phases. This extracts the compound of interest from a solution.

In a washing step, its purpose is to remove impurities while keeping the compound of interest within the same phase.

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?

If the partition coefficient is a large number, it means it's more soluble in non-polar 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.

Answer below

B.  What weight of malononitrile would be recovered by extraction with (a) three 100 ml portions of ether; (b) one 300  ml portion of ether? Take a picture of your calculation and upload the picture. Show all work.

Answer below

C.  Which is better, to extract several times with small amounts of solvent or one time with a large amount of solvent?  

 It's better to extract several times with smaller amounts of solvent because the solute left in solution after 3 extractions than with 1 extraction with more solvent meaning the 3 extractions are more effective in removing the desired solute from solution.

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?

It's not necessary to record the exact amount of solvent used in activity two because its purpose is to test for solubility while in activity 1, chemicals are being extracted so exact measurements are required for proper extraction and analysis.

6.  The mixture contains two acids - why doesn’t the bicarbonate solution react with the weakly acidic phenol compound?

The bicarbonate solution is a weak base. As a weak base, it's not strong enough to react with the weak acid phenol compound as it doesn't have the strength to act as a proton acceptor, to pull a proton off the weakly acidic compound.

7.  Why is it important to wash an organic layer with water just after washing it with a strongly basic aqueous solution?

It's important to wash an organic layer after washing it with a strongly basic solution to further remove impurities and excess basic solution and neutralize the pH.

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.

When using a solid sample for a TLC analysis, the solid is grinded into a fine powder then combine with a solvent. It becomes a liquid making it effective for spotting on a TLC plate. 

*Assuming the initial mass is 1 gram, these would be the final masses or, disregarding masses, this is the ratio of what product is still in solution.

Activity 1

-2.5 grams of 1:1:1 mixture of benzoic acid/4-t-butylphenol/dimethoxybenzene was measured out.

-Approximately 30 mL of ether, 10 mL of sodium bicarbonate and 10 mL of water were added to the solution.

-The solution was combined in a separatory funnel.

-The separatory funnel was inverted about 30 times, with the pressure being released every 4-5 inversion by removing the stock cap.

-The solution was left to settle and the aqueous layer, the bottom layer, was removed into an Erlenmeyer flask.

-Another 10 mL of water and 10 mL of sodium bicarbonate was added into the separatory funnel and inverted like before.

-The aqueous layer was removed into the same flask.

-The pH of the aqueous layer was tested to be a pH of 5.

-Around 22 drops of 6 M HCl was added to the aqueous solution to get a pH of 3 and to precipitate benzoic acid.

-The solution was then left to cool in an ice bath to further precipitate benzoic acid crystals.

-10 mL of sodium hydroxide solution was added to the organic layer that remained in the separatory funnel.

-The inversion process described above was repeated followed by a wash with a saturated salt solution to ensure complete removal of the  aqueous layer with the  4-t-butylphenol from the organic layer. 

- The aqueous bottom layer was removed and HCl was added until it reached a pH of 2.

-The mixture was then set in ice to let cool and allow the crystals to precipitate.

-The ethyl layer containing the neutral compound was fried with magnesium sulfate.

-Once dried, the mixture was placed in a vacuum and on top of a burner to evaporate the solvent and causde precipitation of crystals.

-One the strong and weak acid were cooled, both the crystals were vacuum filtrated and left to dry.

Activity 2

-Weighed 0.5g of benzoic acid.

-The benzoic acid with 8 mL of DI water and 8 mL of dichloromethane were added into a centrifuge flask and inverted to mix the contents.

-A flask was pre-weighed then the dichloromethane layer was transferred into it using a pasteur pipette.

- The masses were taken for each step to determine the patron coefficient for benzoic acid.

Strong Acid, Benzoic Acid(flakey, shiny, white crystals):

Mass: 0.29 grams

% yield = (experimental mass/ original mass) * 100%

=(0.29/2.5)*100%

= 11.6%

Starting melting at 123.0°C

Stopped melting at  124.9°C

Weak Acid, 4-t-butylphenol:(powdery, dull, small crystals):

Mass: 0.63 grams

% yield = (experimental mass/ original mass) * 100%

= (0.63/2.5) *100 

= 25.2%

Starting melting at 89.7°C

Stopped melting at 91.6°C

Neutral, dimethoxybenzene(Large, dull, thin crystals):

Mass: 0.41 grams

% yield = (experimental mass/ original mass) * 100%

=(0.41/2.5)*100%

= 16.4%

Starting melting at 50.8°C

Stopped melting at 52.3°C

TLC analysis:

solvent: 9ml hexane 1 mL ethyl acetate

Spot 1- pure benzoic acid

Spot 2- experimental benzoic acid

Spot 3- pure 4-t-butylphenol

Spot 4- experimental 4-t-butylphenol

Spot 5- pure dimethoxybenzene

Spot 6- experimental dimethoxybenzene

Parton Coefficient:

Mass of the pre-weighed flask: 95.1 grams

Mass of the flask and water: 102.9 grams

Concentration of water = 102.9-95.1 = 7.8 grams/8 mL= 0.98 g/mL

Mass of pre-weighed flask: 111.4

Mass of flask, dichloromethane, and benzoic acid: 120.8 grams

Concentration of dichloromethane = 120.8-111.4= 9.4 grams/8 mL= 1.17 g/mL

Partition  coefficient = (g/mL of organic solvent)/(g/mL of water) = (1.17/0.98)=1.19

This extraction process of various chemicals was analyzed with many techniques to determine how effective the method was and how pure the compounds were.

First, looking at the masses of each compound collected, it is obvious not all the compound was purified as the masses in total don't add up to the starting mass and the masses vary amongst the compounds with the lowest being 11.6% yield and the highest being a 25.2% yield. In a perfect experiment, the % yields would add up to 100% demonstrating that all the compounds were effectively extracted. Also, the percent yields would be similar because the starting ratio of the compound was 1:1:1. This shows that this extraction method worked best for the weak acid as it had the highest % yield of the three compounds.

Next, examining the melting points, It's obvious that some of the substances weren't fully pure. A fully pure substance has a melting point within 3°C of the literature value. Benzoic acid had a starting melting point of  123.0°C and an end of 124.9°C while its literature melting point is 122.3°C. The extracted 4-t-butylphenol had a starting melting point of 89.7°C and an ending melting point of 91.6°C with a literature value of 99.5°C. The neutral compound had a starting melting point of 50.8°C and an ending melting point of 52.3°C with a literature value of 54-56°C. Benzoic acid and dimethoxybenzene had accurate melting points within 3 degrees of their literature values. Although they were within an accurate range, their melting points could've been closer to the literature value which could signify impurities within the compound. 4-t-butylphenol was not within an accurate melting point range which signifies that it is impure and wasn't properly extracted.

Looking at the TLC plate, It shows a certain level of purity within the compounds as well as impurities that remained. Examining spots 1 and 2 for benzoic acid, the pure compound had an Rf of 0.42 while the experimental compounds had an Rf of 0.33. This leads me to believe some of the compound was extracted but impurities remained. 4-t-butylphenol, spots 3 and 4, had a pure Rf of 0.40 and an experimental Rf of 0.36. Looking at the Rf value and the spots, some of the compounds were accurately isolated but, a large impurity remained leading to two distinct spots on the plate. Lastly, dimethoxybenzene which made up spots 5 and 6, had a pure Rf of 0.66 and an experimental Rf of 0.54. According to these numbers and the various spots on the experimental line of the TLC plate, some of the pure compound was isolated but many impurities remained.

Lastly, the patron coefficient for benzoic acid was 1.19. This reflects the solubility of the substance in polar vs. non-polar compounds. This makes sense as benzoic acid is more soluble in an organic solvent which means its coefficient should be greater than 1.

Overall, This extraction experiment proved to be somewhat effective for purifying the 3 compounds. Through the analysis, it was demonstrated that some of the pure compounds were effectively extracted but, lots of impurities remained.

is experiment, the compounds were isolated but purified to the desired extent. The mass collected and impurities shown throughout the analysis showed this was somewhat ineffective in isolating and purifying the three compounds. In a future experiment, I would repeat each analysis technique several times to make sure the analysis is correct in portraying the purity of these compounds. I would also do multiple washing and extracting steps to make sure the compound fully emerged into the dichloromethane layer.

Throughout this lab, I learned a lot about the solubility of various compounds and how to use acid/base chemistry to isolate substances. Learning these extraction techniques was new to me and I can see their usefulness in removing compounds from each other using topics learned in class.