Extraction - Techniques in Organic Chemistry

Extraction is a very important skill to separate substances from a phase to another phase. In a laboratory, the technique of extraction of an organic compound from one liquid phase by another liquid phase is called liquid-liquid extraction.

Huge of devices for separating the phase in liquid-liquid extraction have been invented. The most commonly used device is separatory funnel. 

 A separatory funnel stand on a iron-ring rack

 Separatory funnel is composed of a valve and a funnel with a stop. When we are going to separate the phases inside the device, we should first take off the stop from the separatory funnel to leave a vent so that liquid could flow through the valve fluently or the would "stock" a the valve.

 Remember to take out the stop before opening the valve

 Distribution Coefficients

There are different solubilities of a substance by dissolving in different solvents. So we utilize this property to separate substances from a liquid to a liquid. Hence, we are supposed to know how many substance would be extract from a liquid so scientists use a formula to quantify these property.

 We call the symbol K as the distribution coefficient or partition coefficient. The bigger is the value of K meaning the substance is prefer to dissolve in solvent2, vice versa.

 Extraction Solvent

 Choosing a good extraction could promote the yield of the final compound. There are many things should be considered while choosing a good solvent such as density, boiling point, polarity, miscibility...etc. There are some common extractions in this table:

Common extraction solvents
Solvent	Boiling Point	Solubility in water (g/100mL)	Hazard	Density (g/mL)	Fire hazard
Diethyl ether	35	6	Inhalation, fire	0.71	++++
Pentane	36	0.04	Inhalation, fire	0.62	++++
Petroleum ether	40~60	Low	Inhalation, fire	0.64	++++
Dicholomethane	40	2	LD50c, 1.6 mL/kg	1.32	+
Hexane	69	0.02	Inhalation, fire	0.66	++++
Ethyl acetate	77	9	Inhalation, fire	0.90	++

 Data sheet from Technique in Organic Chemistry /third edition/ Jerry R. Mohring; 

Christina Noring Hammond; Prul F. Schatz.

Chemically Active Extraction

 Sometimes, we have to separate two or more organic substances from organic layer, but, at this moment, these two compounds are very soluble in organic solvent, such as diethyl ether, but high polarity solvents.

To solve this problem, we are going to change the property of one substance inside the solution. For example, there are benzoic acid and 2-naphthol dissolved in diethyl ether. We can let benzoic acid dissolve into aqueous layer by adding some NaHCO_{3(aq) but 2-naphthol would not react with} NaHCO_3(aq) so that 2-naphthol would stay in the organic layer. And then we can separate benzoic acid and 2-naphthol by solvent extraction. In the end, we should only add some hydrochloric acid to acidify the solution isolated then we can get the compound we want.

Procedure

Measure the Concentration of Solution:

1. Take 1.100g adipic acid in to a 100ml flask.

2. Add 100.0mL water into the flask.

3. Heat the solution until all adipic acid are dissolved.

4. Take the flask in room temperature to cool it down.

5. Translate 30.0mL solution of adipic acid to a new flask.

6. Add some drops of phenolphthalein solution (~0.2mL) into the solution.

7. Titrate the solution by 0.200M NaOH_(aq) and figure out the concentration of adipic acid solution as a standard value.

Single Extraction

1. Take 30.0mL solution of adipic acid into a separatory funnel.

2. Pour 30.0mL diethyl ether to extract adipic acid from the solution.

3. Separate aqueous layer and organic layer.

4. Titrate the aqueous layer by 0.200M NaOH_(aq) , figure out the concentrate of adipic acid in aqueous and calculate the distribution efficiency between diethyl ether and water for adipic acid.

Multiple Extractions

1. Take 30.0mL solution of adipic acid into a separatory funnel.

2. Pour 10.0mL diethyl ether to extract adipic acid from the solution.

3. Separate aqueous layer and organic layer.

4. Double doing step 2.~3.

5. Accumulate all of the three aqueous layer.

6. Titrate the aqueous layer by 0.200M NaOH_(aq) , figure out the concentrate of adipic acid in aqueous and calculate the distribution efficiency between diethyl ether and water for adipic acid.

Chemical Extraction:

1.      Take 1.00g benzoic acid and 1.00g 2-naphthol into a 50mL flask.

2.      Add 30.0mL diethyl ether in the flask to dissolve all the substance inside.

3.      Translate the solution into a 100mL separatory funnel.

4.      Pour 30.0mL 10%(wt.) NaHCO_3(aq) in to the separatory funnel to react with benzoic acid.

5.      Separate the aqueous layer into a flask and leave the organic layer in the separatory funnel.

6.      Repeat step 3.~4.

7.      Accumulate all aqueous layer together and label it as AQ1.

8.      Pour 30.0mL 10%(wt.) NaOH_(aq) into th organic layer to react with 2-naphthol.

 Aqueous layer turned into purple because 2-naphthlate

 dissolved into water and form a new conjugation

9.      Extract the aqueous from the solution and label it as AQ2.

10.  Add some hydrochloric acid (15M) into AQ1 and AQ2 to acidify two solutions to get about pH 1.0

The upper test paper indicated pH 1.0 , and the lower test paper is pH 3.0

11.  Put two solution in to ice bath to crystallize the compounds out.

12.  Use a vacuum filtration apparatus to separate products from solutions.

13.  Air dry, and figure out the yields of the process.

 

Experimental Record

Measure the Concentration of Solution
Weight of NaOH (g)	2.000
Volume of water added (mL)	250.0
Molarity of NaOH solution (M)	0.200
Weight of adipic acid (g)	1.100
Volume of water added in to adipic acid (mL)	100.0
Volume of NaOH used to titrate 30mL adipic acid solution (mL)	22.60

Single Extraction
Volume of NaOH used to titrate 30mL adipic acid solution (mL)	16.00

Multiple Extractions
Volume of NaOH used to titrate 30mL adipic acid solution (mL)	15.70

Chemical Extraction
Weight of benzoic acid (g)	1.120
Weight of 2-naphthol (g)	0.830

Analytics

Measure the Concentration of Solution
Exact molarity of adipic acid solution(M)	0.076
Exact moles of adipic acid in the 30mL solution (mole)	2.26 x 10-3
Exact mass of adipic acid in the 30mL solution (g)	0.330

Single Extraction
Weight of adipic acid in aqueous layer (g)	0.234
Weght of adipic acid in organic layer (g)	0.096
Extraction rate (%)	29.1
Kd (Cether/ Cwater)	0.410

Multiple Extractions
Weight of adipic acid in aqueous layer (g)	0.294
Weght of adipic acid in organic layer (g)	0.036
Extraction rate (%)	32.7
Kd (Cether/ Cwater)	0.122

Chemical Extraction
Name	Yield (g)	M.P.	Yield Rate
Benzoic acid	1.120	118.0~120.0	112.0%
2-naphthol	0.830	117.0~119.0	83.0%