EXTRACTION

- a separation technique

Extraction

• Transferring a solute from one solvent to another

• Solvents must be immiscible – usually one is water an one is organic

• Solute (the compound being separated) must be more soluble in one solvent than in the other

• Usually uses either a separatory funnel or conical vial

Separatory Funnel

REMEMBER… - Glass to glass requires (a little) grease! - Plastic parts should NEVER be put in the oven!

All photos of separatory funnels in this presentation are from the following site: :http://orgchem.colorado.edu/hndbksupport/ext/extprocedure.html

There are many different models!

Using a Separatory Funnel...

1. Filling – Support funnel.

Stopcock must be closed. A clean beaker under funnel –

Do not over-fill!

Using a Separatory Funnel...

2.Holding

Put stopper between index and middle finger -– hold bowl of funnel with thumb and tips of remaining fingers

Using a Separatory Funnel...

3. Shaking

Make sure stopcock is closed – shake with tip pointed away from everyone – every few seconds, vent the funnel into the hood

Using a Separatory Funnel...

4.Layer Identification

Usually the more dense solvent is on the bottom – To check, add a few milliliters of distilled water and watch where it goes!

Using a Separatory Funnel...

5.Emulsions

Emulsions are collodial mixtures of the two solvents. To get rid of these, either: (a) add a few mL of sat. NaCl; (b) filter; (c) add small amount water soluble detergent; (d) apply light vacuum; or (e) change solvent.

Using a Separatory Funnel...

5.Removing one layer…

Bottom layer is removed via stopcock (1)

Top layer is poured out (“decanted”) off the top (2)

(1)

(2)

Partition CoefficientFor a solute A, the extracting solvent Sx, and the

original solvent So

Partition (K) = [A] in Sx

Coefficient ------------

[A] in So

Partition Coefficient

(gm A/molar mass A)

K = [A] in Sx Liter of Sx

---------- = -------------------

[A] in So (gm A/molar mass A)

Liter of So

Molar mass divides out …

Partition Coefficient

• When the volume of two solvents is the same (V will cancel out), K is reduced to gm A in Solvent x / gm A in Solvent o

• If K> 1 ... Solute mostly in extracting

solvent (Sx)

• Increasing Volume of Sx, increases gm A removed but not always practical

Effect of Multiple Extractions

Fn = [ Vo (KVx + Ao) ]n

Fn = fraction of original solute remaining in So after n extractions with a constant volume of Sx

K = partition coefficient

Vx = volume of extracting solvent

Vo = volume of original solvent

(see page 136-137 of text for derivation/explanation)

Effect of Multiple Extractions

Example:

1 extraction with 30 mL of ether

Fn of 1/16 or 0.0625

3 extractions with 10 mL each of ether (same total volume)

Fn of 1/216 or 0.00463

Criteria for Extracting Solvent

1. Will not irreversibly alter the solute and does not react with the other solvent.

2. Immiscible with the original solvent.

3. High K for desired material – selectively remove desired solute.

4. Readily separated from solute after removal..

What affects K?

• Relative polarities affect solubility of solute in each solvent.

• Reversible chemistry can affect

solubility (e.g. protonation/deprotonation).

Effect of pH on Solubility

HA A-

(the salt is more water soluble)

RNH2 RNH3+

Add base

Add base

Add acid

Add acid

WHY??

Extraction Experiment

Dissolve 3 g of 1:1:1 (by mass) mixture of …

(a) benzoic acid

(b) 2-napthol

(c) 1,4-dimethoxybenzene

… in 30 mL of diethyl ether

C

OH

O

OH

OCH3

OCH3

Dissolve the 3 g mixture of the above compounds in 30 mL of diethyl ether Add 15 mL of saturated NaHCO3 solution Shake. Separate layers.

Flask A(what is in Flask A?)

Cautiously acidify with HClCool in ice Isolate solid

compounds remaining in the organic layer

(what are these compounds?)

Add 10 mL of 1.5 M NaOH solutionShakeSeparate layers

SOLID FROM FLASK A

Flask B(what is in Flask B?)

Cautiously acidify with HClCool in ice Isolate solid

SOLID FROM FLASK B

Dry organiclayer withNa2SO4.

Decant ether off drying agent

Flask C(what is in Flask C?)

Evaporateoff ether

SOLID FROM FLASK C

benzoic acid 2-naphthol

1,4-dimethoxybenzene

pKa ~ 4.2

pKa ~ 9.5

pH ~ 8-9

pH ~ 12-13

To Prepare your NB…

- 10 Compounds needed in Table of Chemical & Physical Properties: benzoic acid, 2-naphthol, 1,4-dimethoxybenzene, diethyl ether, sodium bicarbonate, sodium hydroxide, sodium chloride, water, concentrated hydrochloric acid, anhydrous sodium sulfate.

- Figures needed: - Flowchart (can print and tape into NB)- Figures 2.60, 2.61, and 2.62

- The Handout (posted on Moodle with Flowchart) is your procedure for lab. This can also be printed and taped into your NB, but make sure that you’ve read and understand what you’re going to be doing in lab!!!

To Prepare your NB… (cont’d)

- There are 4 Chemical Reactions. You need to figure out how to correctly write these AS CHEMICAL STRUCTURES:

(1)Benzoic Acid + Na(HCO3) ?? + ??

(2)Sodium benzoate + HCl ?? + ??

(3)2-naphthol + NaOH ?? + ??

(4)Sodium 2-naphtholate + HCl ?? + ??

To Think About…-What is the definition of a Bronsted-Lowry Acid?

- How do you identify an “acidic hydrogen?” (Hint: Why type of atoms are they bonded to before they are pulled off by a base or “fall off” as H+ ?)

- pKa is a relative measure of acidity. Acidity increases with decreasing (more negative) pKa values.

- Comparing the pKa of a molecule with the pH of the solution that it’s dissolved/mixing in will indicate if the molecule is charged or neutral.

- Remember, that when talking about solubility, “like dissolves like.” So polar dissolves in polar, and nonpolar dissolves in nonpolar.

- What is the function of anhydrous sodium sulfate???

Complete the Experiment by..

- Submit the samples of all three solutes which you recovered by extraction (properly labeled in a vial!)

- Allow the samples to air dry in drawer (for 1 week).

- Weigh and record recovered masses of each compound next lab period. (Employ weigh-by-difference technique so pre-weigh empty vials/lid/tape!)

- Calculate exactly how much (grams) of each compound was in the original ~3 g sample.

- Then, calculate the %-recovery of each compound in Flask A, B, and C. (Remember, the ~3 g original mixture had a 1:1:1 ratio of the three compounds. Ideally, you should have retained about the same amount, b/c just separating.)

More info…

• How to test acidity of a solution using Blue Litmus Paper: http://www.youtube.com/watch?v=6DCBWK_Hg5w

• How to dry over anhydrous sodium sulfate: http://orgchem.colorado.edu/Technique/Procedures/Drying/Drying.html