University of Mary Washington Chemically Active Extractions Lab Report

Extraction – Separation of Acidic, Basic, and Neutral CompoundsBackground reading
–
Mohrig Chapter 10 (Extraction)
Klein Chapter 3 (Acid/base reactions)
In this experiment you will separate a mixture of two organic compounds, then identify them by
their melting points. The unknowns will represent two of the following three groups: acid, base,
or neutral.
Safety
Ethyl ether is very volatile and highly flammable. Although it is not especially toxic, it does give
many people a headache. Keep the ethyl ether in the hood as much as possible and avoid any
source of ignition.
Some of the unknown organic compounds are toxic, and all may be irritating to some people.
Likewise, the acid and base solutions are irritating to the skin. Use gloves when handling all of
these solutions and when performing the extractions. If any of the solutions are spilled on the
skin, wash the affected areas thoroughly with cold water and soap.
Because pressure builds up in the separatory funnel during extractions and ethyl ether is more
volatile than most solvents, be sure to release the pressure frequently when shaking the funnel;
be careful where you point the funnel to avoid spraying yourself or a neighbor with the extraction
solutions.
NOTE: During the lab, make sure you clearly label each solution, and do not throw any
solutions away until the conclusion of the lab. A well-organized workspace is essential during
this lab. Every container should be labeled.
Procedure
1) Obtain an unknown mixture and record the unknown number in your notebook.
2) Dissolve the unknown in 50 mL of ethyl ether, and pour the solution into the separatory funnel.
3) Prepare 2 M aqueous HCl by diluting the desk reagent (6 M). Make sure you prepare enough
acid to complete all of step 4.
4). Extract the ether solution three times using a fresh 15 mL portion of 2 M aqueous HCl each
time. Drain off the aqueous layer after each extraction, and combine the three aqueous layers
in a labeled Erlenmeyer flask. For now, leave the ether solution in the separatory funnel. You
will return to it in step 7.
Isolation of unknown base
5) Add 3 M aqueous NaOH to the acidic aqueous layer from step 4 until the solution is basic to
litmus paper. Swirl the flask after each addition of base and test the pH frequently. If the
unknown contains an amine, the solution should become cloudy, and solid should form. Cool
this flask on ice and isolate the product by vacuum filtration. If no solid forms after cooling, you
likely (but not necessarily) do not have an amine. If an oil occurs, proceed to the back
extraction section. You will need to try both the isolation of unknown acid and isolation of
unknown neutral compound.
Isolation of unknown acid
6) Prepare 1.5 M aqueous NaOH from desk reagent (3M) by dilution. Make sure you prepare
enough to complete step 7.
7) Extract the original ether solution (from step 4) three times using a fresh 15 mL portion of
1.5 M aqueous NaOH each time. You can keep the ether layer in the funnel. Drain off the
aqueous layer after each extraction, and combine the three aqueous layers in a labeled
Erlenmeyer flask.
8) Add 6 M HCl to the aqueous layer in step 7 until the solution is acidic to litmus paper. Swirl
the flask after each addition of acid, and test the pH frequently. Be careful not to add a large
excess of acid. If the unknown contains a carboxylic acid, a fluffy, white precipitate will form
(unless there is an excess of water). Cool the flask on ice and isolate the product by vacuum
filtration. If no solid forms, you likely (but not necessarily) do not have a carboxylic acid. If you
did not have an unknown base, you will need to complete the isolation of neutral compound. If
you have a cloudy or oily layer, proceed to the back extraction.
Isolation of neutral compound
9) Wash the original ether layer (you set it aside in step 5) with one 15 mL portion of water.
Fresh ether may be added to the solution to replace any lost by evaporation. Drain off the
water and set it aside. Pour the ether layer into a clean, dry Erlenmeyer flask.
10) To dry the ether layer, add a tablespoon of MgSO4 to the ether solution, swirl the mixture,
and stopper the flask for 10 to 15 minutes. Tare an appropriately sized round bottom flask.
Label the flask with your name, the identity of this compound and the mass of the empty flask.
Remove the drying agent by gravity filtration using fluted filter paper in a powder funnel. Filter
the solution directly into the labeled round-bottomed flask. You may rinse the flask with a little
extra ether and pour the ether through the MgSO4. Use the rotary evaporator to concentrate
the ether in your round-bottomed flask.
After you have isolated your two compounds, scrape them out of the round bottomed flask and
store them, clearly labeled with your name and the compounds’ identity in your drawer on a
watch glass covered loosely with a paper towel. If you have the neutral compound, store it in a
small stoppered, labeled test tube. After one or two days, obtain the melting point range for
each compound and use the tables below to identify your compounds.
Back-extraction of compound from water (ONLY NECESSARY IF YOU HAD A CLOUDY
AQUEOUS LAYER THAT NEVER FORMED A SOLID)
11) Pour your aqueous mixture (from either step 5 or step 8) into a separatory funnel. Rinse
the flask with 5 – 10 mL of ethyl ether, and add this to the funnel. Complete the first extraction
by shaking the funnel as usual, draining off the aqueous layer, and pouring the ether layer into
a clean, dry Erlenmeyer flask. Return the aqueous layer to the separatory funnel, and extract
it with a fresh 15 mL portion of ether. Repeat this process with one more 15 mL portion of
fresh ethyl ether.
12) To dry the combined ether layers, add a tablespoon of MgSO4 to the ether solution, swirl
the mixture, and stopper the flask for 10 to 15 minutes. Label an appropriately sized round
bottomed flask with your name, the identity of this compound and the mass of the empty round
bottomed flask. Remove the drying agent by gravity filtration using fluted filter paper in a
powder funnel. Filter the solution directly into the labeled round-bottom flask. You may rinse
the flask with a little extra ether and pour the ether through the MgSO 4.
13) Evaporate the ether from the solution using the rotary evaporator. Weigh the isolated
product. Return to the lab to obtain and the melting point.
Postlab
Make sure that you include both IR spectra as part of your lab report, and neatly tabulate in
your lab notebook the important peaks in your IR spectra annotated with the type of stretch.
Clean up and Waste Disposal
Once you have your two solid compounds you may dispose of any remaining aqueous layers
by pouring them down the sink. Dispose of any remaining ether layers in the NONHALOGENATED organic waste jar. Dispose of MgSO4 by scraping it into the solid waste
container. Once scraped, filter paper may be disposed of in the trash.
Unknown Compounds for Chemically Active Extraction Lab
Please remember that you only have TWO components in your unknown.
Acids
m-toluic acid
Benzoic acid
p-anisic acid
Bases
p-chloroaniline
Ethyl 4-aminobenzoate
4-nitroaniline
Neutrals
Biphenyl
Benzil
Fluorene
Melting point (°C)
111
122
184
68 – 71
89
147 – 151
68
94 – 96
116
Name:_____________________
Section:_______
Chemically active extractions
1. Identify the components of your mixture.
Unknown number: _______
Component 1: ____________________
Component 2:____________________
2. Draw a flow diagram similar to the one presented in the PowerPoint presentation and notes
to show what you did during your extraction experiment and what your results were.
Include notes beside your diagram to describe the procedure and any problems
encountered. Do NOT show compounds that were not in your mixture.
3. How could you modify this experiment to separate a solid carboxylic acid (pKa ~ 4) from a
solid phenol (pKa ~ 10). You have available water, hexane, aqueous sodium bicarbonate
(pH ~ 8), aqueous sodium hydroxide (pH ~ 14), and aqueous acid (might be HCl, might be
H2SO4, it doesn’t matter).