Lab #4 Extraction
Separating Organic Acid from Neutral Compound
1. Unknown acidic (benzoic acid or salicylic acid) & neutral (naphthalene or biphenyl) 2. Dissolve unknown in ethyl acetate and pour into separators funnel 3. Extract ethyl acetate with NaOH (2x) --> Shake, release pressure 4-5x 4. Place undisturbed until layers separate 5. Drain lower layer out from bottom and top from top! - Top (ethyl acetate solution) - Lower (aqueous layer) 6. Dry Ethyl acetate layer --> Anhydrous MgSO4. Add small portion and swirl until traces of solid floating at top (water removed and solution is dry). - Decant liquid from dying agent onto watch glass - Solid left behind = neutral - Determine melting point to see identity 7. Recover acid form of organic acid --> Acid Base reaction to regenerate neutralized acid compound. 9 M Hal until white ppt forms - Filter and rinks with cold water - Measure melting point to determine identity
Which solution has the unknown organic acid?
Aqueous layer!!! Dissolved in this as its salt as NaBenzoate or NaSalicylate.
Where was the neutral component of the mixture at the end of your extraction?
C. Crystallized on the watch glass as solvent evaporated.
Organic Bases
Contain nitrogen atoms. TO be basic, nitrogen atom must have a lone pair to make bond with proton. When it becomes protonated, N becomes positively charged and more water-soluble.
Carboxylic Acid
Could become a salt. Stronger than phenols (weak acids) When it is deprotonated, it could be reversed by adding acid (HCl) tor provide protons. Phenols can do the same thing.
How do you determine which layer is which?
Density (data table)
Which solution contains the neutral organic compound?
Ethyl acetate; TOP
What must the solvents you pick NOT do?
MIX!!!
How do you get benzoic acid into water?
Must deprotenate by adding NaOH!!!! Salt is more polar, and therefore more water soluble than acid form!!!!
Which layer is always lighter?
Organic lighter than aqueous
Reactive Extraction
Polarity of molecules controlled by doing acid/base chemistry. - Changing polarity to change solubility ex) Benzoic acid extracted more rails into basic water than plain water.
Where was the acidic component of the mixture at the end of your extraction?
Precipitated with HCl and vacuum filtered.
Partitioning
Purification technique in organic labs
Liquid-Liquid Extraction
- Mix two compounds (water soluble and water insoluble) - Separated by adding water and organic solvent - Water and organic immiscible, so layers separated thus two compounds separated - Two layers formed (lowest density at top) *Two layers partition based on solubility (polar --> water layer & non polar --> Organic layer)*
_________ extraction involves changing the polarity (and therefore solubility) of a compound using acid/base chemistry.
Reactive
OH group attached to a Carbon in organic compound, but not C=O or benzene ring, then not acidic enough to be removed. Must be ATTACHED.
So acid-base extraction not possible!!!!
Why is benzoic acid more soluble in a basic aqueous solution than it is in neutral water?
The base deprotonates the carboxylic acid, and the anion form is more soluble than the neutral form.
Benzoic acid is more soluble in 5% aqueous sodium hydroxide than it is in water.
True
Extraction
Two solvents immiscible Dissolved compounds will have affinity for one solvent over another --> Extraction relies on principle to separate different compounds
Acid-Base extraction
Type of liquid-liquid extraction. - Different solubility levels in water and organic solvent - Organic solvent often doesn't dissolve well in water (ethyl acetate) - Separate organic compounds based on acid-base properties - Rests on assumption that most organic compounds soluble in water as IONS - Compounds easily made into ions by adding proton or removing proton (+ or -)
If 25 mL of dichloromethane is mixed with 25 mL of water, two layers will form and the ______ will be the bottom.
dichloromethane
If 25 mL of ethyl acetate is mixed with 25 mL of aqueous sodium hydroxide, two layers will form and the _________ will be the top.
ethyl acetate
Organic acids and bases in their ___________ form are soluble in organic solvents, but corresponding ________ are more water soluble. Therefore, converting acids and bases to _______ provides convenient tool to separate acidic, alkaline, and neutral compounds.
neutral, salt, salt
The ratio of concentrations of a solute in each layer is defined by the
partition coefficient, K
What piece of glassware is used to perform liquid-liquid extractions?
separatory funnel
In liquid-liquid extraction, separation of the compound of interest is based on its
solubility