SEPARATION OF COMPONENT MIXTURE

 

Liquid-liquid extraction is one of the most used methods for isolating an organic compound from a mixture.  This technique is commonly used to isolate and purify products from chemical reactions and is also used to isolate natural products.  The process can be categorized into two types of liquid-liquid extraction.  The first type takes advantage of the polarity of compounds and uses water to extract or “wash” an organic mixture by removing highly polar materials, such as inorganic salts, strong acids or bases, etc.    Second, acid and base extraction, takes advantage of chemical properties of compounds.  

Acid extractions are intended to separate basic compounds from an organic mixture.  Organic bases, amines, are converted to their corresponding cationic salts by reacting with acids.  These salts are then soluble in water and can be separated from the organic mixture. 

 

           

 

Base extractions have a concept similar to acid extractions.  They are intended to separate acidic compounds from an organic mixture.  Organic acids, carboxylic acids, are converted to their corresponding anionic salts by reacting with bases.  These anionic salts are usually soluble in water and can be extracted from the organic mixture.

 

                       

 

Purpose:  In this experiment you will be given a three-component mixture, an acid (benzoic acid), a base (ethyl- 4-aminobenzoate) and a neutral organic compound (9-fluorenone).  You will have to separate these three compounds individually from the mixture.

                             

 

benzoic acid                 ethyl-4-aminobenzoate              9-fluorenone

 

The key success for this experiment is to understand the chemical reactions that are taking place at each step of separations.  You will have to fill in the blank the products that result from the chemical reactions.

 

Required reading:  Mayo 94-108, B&F sections 4.1-4.2

Procedure:

 

  1. Weigh approximately 300 mg of the three-component mixture, which contains 100 mg of each: amine, carboxylic acid and neutral.  Place the solid into a 5 mL conical vial and add 2 mL of ethyl acetate.  Top the vial with a teflon disk (slippery teflon side facing in) secured with a screw cap and thoroughly shake its contents until the sample dissolves.  To this solution add 1 mL of 3M HCl.

 

  1. Cap the vial and thoroughly shake its contents to complete the reaction that selectively converts the amine to its water-soluble cationic salts.  Add a few drops of water if you see some precipitation in the vial.

 

 

Use structural formulas to answer the following questions as you perform the lab.

 

What are the compounds in the top organic layer?  __________________________

 

What is the compound in the bottom aqueous layer? __________________________

 

 

  1. In this 5mL conical vial, the bottom water layer refers to as solution A and the top ethyl acetate layer refers to as solution B.  Carefully transfer just solution A to a 3 mL conical vial using a Pasteur pipet.  To the 3 mL conical vial (solution A) add 1 mL of pure ethyl acetate (solution B1), cap and shake the vial.  Transfer just the lower layer (solution A) from this vial to a 10 ml beaker.  Combine the solution B’s into a clean flask and put that solution aside for now. 

 

  1. Add 6 M NaOH to this beaker (solution A) until the solution is basic to pH paper.  The appearance of a white cloudiness indicates the reformation of the desired compound.  Indicate the total volume of solution in your notebook.

 

  1. Collect the crystals using the Hirsch funnel.  Use cold water to rinse the flask. 

Why did you add the 6M NaOH?   _________________________________

 

What is the compound in the organic layer? _____________________________

 

  1. The yellow ethyl acetate solution (solution B’s) remaining in the vials transfers into the 5 mL vial.  Add 1 mL of pure water, shake its content and then allow the layers to settle.  Remove and discard the bottom aqueous layer. 

 

What is the purpose of washing the organic layer with 1 mL of water?_____________________________________

 

  1. Add 1 mL of 3 M NaOH into the 5 mL conical vial that has the yellow ether solution (Solution B’s).

 

 

What are the two main compounds that present in the solution B?  ___________________________________________________

 

  1. Cap and thoroughly shake the vial to allow completion of the reaction and the dissolution of the compounds in their respective solvents.  Allow the layers to separate.

 

Write the reaction (steps 8-9). ___________________________________________

 

What is the compound in the water layer? ________________________________

 

What is the product in the top organic layer?  _____________________________

 

  1.  Carefully transfer the bottom layer (solution C) to a 3 mL conical vial using a Pasteur pipet and the top layer refers as solution D.  To the 3 mL vial add one ml of ethyl acetate (solution D1).  Cap and shake its contents.  As before, transfer the lower layer (solution C), this time to a 10 mL beaker.  By now the contents of the beaker should be very pale or colorless.

 

  1. Add dropwise 6 M HCl to the beaker (solution C) until the mixture is acidic to pH paper.[1]  The appearance of white solid indicates the reformation of desired compound.

 

Calculate from the volume and concentration of NaOH previously added, at least how many mL of the 6 M HCl will be needed?  Show calculations.

 

 

 

 

 

 

 

Write the products of the reaction (after HCl is added).________________________

 

 

 

11.  Filter the solid using the Hirsch funnel.

 

What is the compound in the ethyl acetate?

 

  1. Combine the previous left yellow ethyl acetate layers (solution D’s) into a 5 mL conical vial.  Add 1 mL of water, cap and shake its contents.  Remove and discard the water layer with a pipette.  Dry the organic layer with Na2SO4[2] and evaporate the ethyl acetate on the sand bath or on the hot plate in the hood.[3]  Watch the solid and make sure that you don’t burn it. 

 

  1. For all three compounds, determine melting points and calculate the % recoveries.

 

Questions:

 

Use structural formulas to complete all the questions above.

 

Include a detailed flow chart to show how each extraction step works in your notebook.

 

References:

"Mayo": Mayo, D.W., Pike, R.M., Butcher, S.S. and Trumper, P.K. Microscale Techniques for the Organic Laboratory; Wiley: New York, 1991.

"B&F". Brown, W. H.; Christopher, S. F. Organic Chemistry, 3rd Ed., Harcourt College Publishers. San Diego, CA. 2002 

Created by Evan Thompson, revised by Shane Phillips on 1/21/98 then J. Almy January, 2001.  Revised by Nhu Y Stessman March 2006.

 

 


[1]  Use a stirring rod to transfer a droplet of the water to the pH paper for this test.

[2]     The term “to dry” an organic layer means to remove traces of water from the compounds you separate.  Drying is accomplished by passing the ether solution through a pipette containing anhydrous Na2SO4  (about 2 cm of Na2SO4) into a preweighed container.

[3]   Add the wooden splinter to the filtered solution before you put the solution on the sand bath or directly on the hot plate.