Solvent Extraction

CHE-231 Organic Chemistry University of Kentucky

ObjectivesA) To separate a mixture containing an acidic, basic, and neutral compound by liquid-liquid solvent extraction. B) To determine the purity of the separated compounds by recording their melting points and comparing to literature.

BackgroundSolvent Extraction: A technique commonly used in organic chemistry to separate compounds in a mixture, based on the differing solubility behaviors of the compounds. Two Methods: Solid-liquid extraction Liquid-liquid extraction

Background continuedLiquid-Liquid extractions require that the two liquids be immiscible when mixed together. Ex. Ether and H2O or Methylene Chloride and H2O

The densities will determine which layer is on top, and which is on bottom. (This is important when determining which layer contains which compounds)

Expressing the Solubility of a CompoundPartition Coefficient: [ X Solvent 2] Kp = [ X Solvent 1] When compound X is placed in a mixture of two immiscible solvents, it will be distributed between the two phases as a function of its relative solubility in each solvent.

Solubility Any substance (solid/ liquid) is soluble in another substance (liquid), only if their chemical nature is similar Polar substance is soluble in Polar solvent LIKE DISSOLVES LIKE!

Water Polar

N-Hexane Non-polar Ethanol Polar Miscible

Toluene Non-polar

Miscible

Water Soluble CompoundsA) Small molecules (5 carbons or less) with at least one polar functional group. Ex.

Amine

Acid

Ketone

Alcohol

Water Soluble Compounds continuedB) Larger molecules with more than one polar functional group (polyfunctional compounds, sugars, etc...) Ex.

Glucose

Water Soluble Compounds continuedC) Salts (ionic bonds) are soluble in water due to iondipole interactions. Ex. NaCl, KCl

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Water Insoluble CompoundsA) Molecules without polar functional groups. Ex. B) Monofunctional compounds with more than 5 carbon atoms. Ex.

Water Insoluble Compounds continued Compounds such as methylene chloride (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4) are insoluble in water; and are used for extraction from aqueous solutions. Although the presence of a chlorine atom attached to a carbon in a covalent C-Cl bond does lend some partial ionic character due to the electronegativity of the chlorine, it does not normally mean that such compounds are water soluble.

Type of compoundsA) Acid: Proton donor (Bronsted definition)

Acid (insoluble in H2O)

Base (abstracts most acidic proton)

Salt (H2O soluble Conjugate base)

Type of compounds continuedB) Base: Proton acceptor (Bronsted definition)

Acid Base (insoluble in H2O) (will be deprotonated) Salt (H2O soluble conjugate acid)

Type of compounds continuedC) Neutral Compounds Some examples: hydrocarbons, aldehydes, ketones, ethers, amides, esters.

What is our plan? Liquid-Liquid Extraction The compounds used:

Acid: Benzoic acid

Base: Ethyl 4-Aminobenzoate

Neutral: 9-Fluorenone

All insoluble in water

Outline of the ProcedureAr-COOHacid

Ar NH2Base

Dissolve in Ether(Et2O = ether)Ar-COOH Ar-NH2 Ar-H

HCl (aq) Et2O

Ar-H Neutral

Ar-COOH Ar-H Ar-NH3 + Cl-

Et2O Et2O

Ar-COOH Ar-H

NaOH (aq)

Ar-H Ar-COO Na+

Et2O H2O

Separate H2O H2OAr-NH3 + Cl-

Label: H2O w/Base

Outline of the Procedure continued...Et2O SeparateAr-COO Ar-H

Label: Et2O w/ Neutral

H2O

Na+

Label: H2O w/ Acid

** Now all three components are separated. Each component must now be isolated to reform and recover the original forms of the compounds Do not forget to label !!!

Recovery of Basic CompoundFilterAr-NH3 + Cl-

NaOH (aq)

Ar-NH2 (ppt)

Dry Weigh Product Calculate % recovery Record MP

H2O w/Base Reformation Reaction:

Deprotonation

Original H2O insoluble base is reformed (will crash out as a precipitate)

Recovery of Acidic CompoundFilterAr-COO Na+

HCl (aq)

Ar-COOH (ppt)

Dry Weigh Product Calculate % recovery Record MP

H2O w/ Acid

Reformation Reaction:

Protonation

Original H2O insoluble acid is reformed (will crash out as a precipitate)

Recovery of Neutral CompoundDry with Na2SO4 (collect in aAr-H

tare vial containing a boiling chip) Slowly evaporate Ether Cool and Weigh Compound Calculate % recovery Record MP

Et2O w/ Neutral

Reminders for Writing Lab Report Be sure to calculate the overall total % recovery and a % recovery for each component total four % recoveries. Different types of extraction techniques. How does the partition coefficient relate to this lab? How do you tell if something will be soluble? What makes a compound acidic, basic or neutral? How do we use this to change water solubility?

Some Friendly Reminders There is no handout for this experiment. Procedure is in the textbook. Refer to Experiment [4C]. Make sure to weigh original mixture (about 0.150 g) before you begin the extraction. Each compound should account for approximately 0.05 g of the original mixture. Always heat solvents with a boiling chip or stick. All the work must be your own only. For detail information on plagiarism refer to syllabus.

Friendly Reminders continued Have to dilute 6M HCl and 6M NaOH to 3M by using equal parts distilled water and either acid or base. Label, Label, Label!!! Always vent the vial after shaking. All lab work is to be performed in a hood. Make sure to dispose of all waste properly.

What do we need?

Add acid to the mixture of three compounds in ether

Which one is on top ------ Organic OR Aqueous?

Layer separation

Separation of Compounds(in Textbook pg. 74)

To reprecipitate basic component from aqueous solution, add aq. NaOH.

Help precipitation on Basic component

To the remaining organic layer, add aq. NaOH

Separation of Compounds(in Textbook pg. 74)

To reprecipitate acidic component from aqueous solution, add aq. HCl.

Now check the pH

Final products

Ethyl 4-Amino; benzoate

Benzoic acid;

9-Fluorenone