Lab 4: Separating Acids and Neutral Compounds by Solvent Extraction

What is extraction?

selectively dissolves one or more compounds into an appropriate solvent

What is the key for extraction?

two solvents must be immiscible

What is washing?

removes impurities from one solvent to a second solvent

What does immiscible mean?

liquids not able to be mixed

What is the rule for dissolving?

like dissolves like

What does the lab manual state about solubility?

all compounds are soluble to some extent in every solvent

How much transfer will be carried out by extraction in this lab?

only small amounts because there cannot be 100% transfer

In an extraction, what is typically the polar and nonpolar solvent?

water is polar solvent, and ether or hydrocarbon is nonpolar solvent

Nonpolar compounds are typically more soluble in what type of solvents?

nonpolar solvents

Since water tends to be the denser of the two solvents, which layer is it usually?

bottom layer

What do you do if you are unsure which layer is the aqueous water layer?

perform drop test; introduce 1-2 drops of water just below surface of the top layer

If the water drop mixes, what does that indicate about the aqueous layer?

the top layer is the aqueous layer

If the water drop falls to the bottom layer, what does that indicate about the aqueous layer?

the bottom layer is the aqueous layer

In this extraction lab, what are we converting the compounds to?

from neutral species to ionic forms

What does the ionic form then do?

change its solubility and allow it to be extracted into the aqueous/polar layer

What do the non-ionized compounds do?

remain dissolved in the nonpolar solvent layer

What can p-toluic acid be deprotonated by?

either hydroxide or bicarbonate

What can p-tert-butylphenol be deprotonated by?

only hydroxide

Why can't acetanilide be deprotonated by common bases?

the pKa of acetanilide is too high

What is the setup for extraction?

place separatory funnel in the support ring stand and glass stopper on top of funnel

What are the percentages of the mixture used in this lab?

38.5% p-toluic acid, 23% acetanilide, 38.5% p-tert-butylphenol

What is the first step of this extraction lab?

mix the weighed mixture with tert-butyl-methyl-ether (TBME) in E. flask until dissolved

What do you add to the separatory funnel for extraction?

the mixture with TBME and extraction liquid

What should you do to prevent the glass stopper from getting stuck?

apply grease

What are the appropriate steps to vent and mix the separatory funnel?

hold stopper in place with one hand while gently mixing, vent the funnel and point towards back of fume hood, close the stop cock and repeat

Why is it important to vent the separatory funnel often?

to prevent pressure from building up

When should you stop mixing and venting and place the separatory funnel back into the supporting ring?

when no more gases are produced through venting

What is the next step after you have finished mixing and venting the separatory funnel?

allow layers to separate, remove the glass stopper, and drain the bottom layer into an E. flask

When draining your extraction solution, what should you watch out for?

not letting the top layer drain through

If you need to remove the top layer, what is the appropriate way to do so?

pour out through the top of the separatory funnel to prevent cross-contamination

What does the addition of sodium bicarbonate (NaHCO3) in step 2 of the flow chart do?

deprotonate the stronger acid (p-toluic) and travel to aqueous layer due to increase in polarity

In step 3 of the flow chart, what is used to separate the remaining compounds out of the ether layer?

strong base to deprotonate the weaker acid

What is done in step 5 of the flow chart?

heat sample to drive out any remaining dissolved ether in aqueous layer

If there is any dissolved ether left, what could it affect?

solubility in the alcohol; however, it does not affect solubility in acid

While heating your sample, what temperature should you NOT exceed?

60C

What should be done before adding hydrochloric acid (HCl)?

after heating, cool sample to room temperature and place in an ice-bath

What would happen if you added HCl to a warm compound?

compound will oil out instead of crystallizing

In step 6 of the flow chart, what do you dry the TMBE layer with?

sodium sulfate (Na2SO4) and then later filter it out

After drying the TMBE layer, what is done to remove any of the remaining ether left in the solution?

use round-bottom flask and rotovap

What are the hazards of acetanilide used in this lab?

toxic and irritant

What are the hazards of tert-Butyl methyl ether used in this lab?

flammable and irritant

What are the hazards of sodium hydroxide used in this lab?

toxic and corrosive

What are the hazards of hydrochloric acid used in this lab?

corrosive and irritant

What are the hazards of HCl and sodium bicarbonate (NaHCO3) together?

foaming

What are the hazards of anhydrous sodium sulfate used in this lab?

irritating and hydroscopic

Following the rotovap and drying process, what else needs to be done the next week of lab?

record mass and melting point of each compound, TLC of 3 compounds, and 3 vials