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Experiment 4: Extraction

Part A: Separation of Acidic, Basic and Neutral Substances

Part B: Isolation & Analysis

Reading: Mohrig, Hammond & SchatzCh. 11 pgs 113-132Ch. 12 pgs 132-141Ch. 20 pgs 277-310

Carey Ch. 13 pgs 574-581

watch the technique video on the course website!

Extraction Pulling a compound (or compounds) out of one phase into another

solid/liquid ! making a cup of tea

liquid/liquid ! most common in lab

liquids must be immiscible

Used for the isolation, purification, and/or separation of compounds - isolation of potential therapeutics from natural sources

- remove water soluble impurities from an organic reaction mixture

typically inorganic saltsmeans of preliminary purification (wash)

- separate two organic compounds bearing different functional groups

This technique is based on solubility differences

Terminology

- extract:pulling out what you want

- wash: removing what you don't want

both are effectively the same process

Organic compound in a separatory funnel with two immiscible liquids

- two layers

- typically an organic solvent & water

- relative solvent densities will determine

which layer is which (e.g. top or bottom)

Layers are mixed by inverting funnel gently;will separate on standing

Compound (x) will distribute (partition) itselfbetween the layers (phases)

- equilibrium based on rel. solubility of x in each layer

- organic layer will contain neutral organic compounds

- aqueous layer will contain organic & inorganic salts

Drain lower layer out the bottom;Pour upper layer out the top

Extraction: How Does it Work

less denselayer

more denselayer

xx

x xx

xx

x

separatory funnel

Organic vs. Aqueous Layer: Top or Bottom?

Densities of Some Common Extraction Solvents

solvent density

hexanes 0.672

diethyl ether 0.713

benzene 0.879

water 1.000

saturated NaCl (aq) 1.198

dichloromethane 1.335

chloroform 1.498

!

less dense(top layer)

more dense

(bottom layer)

"

If don't know densities add a few drops of water to the separatoryfunnel - water will join the aqueous layer!

Consider the solvent density vs. water

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Distribution Coefficient (K)

Ratio of concentrations of a compound [X] in the layers is known the distribution coefficient (K)

K =[X] in organic solvent

[X] in water!

solubility of X in organic solvent

solubility of X in water

If know solubility's, can calculate K

If for compound X: solubility in water is 5g/100 mL"solubility in an organic solvent is 35 g/100 mL

K= = = 735g/100mLB

5g/100mLA

0.35

0.05

K gives us information about extraction efficiency

Extraction

What if extraction efficiency is poor??- increase number of extraction steps

more efficient to carry out multiple small extractions than 1 large one

even if K ! 4

so 3 x 5mL extraction better than 1 x 15mL extraction!!

- saturate the aqueous layer with NaCl ("salting out")

shift the equilibrium (change K)

Extraction Efficiency:

- For an efficient extraction (water! organic solvent), K ! 4

- If K < 1, will be difficult to extract the compound from water

How can we use extraction to separate two (or more) organic compounds? - modify solubility?

General Principles

Extract With

water

H2O

acidHCl

weak baseNaHCO3

strong baseNaOH

Na2CO3

Removes

polar, low MW compounds

inorganic acids & basespolar organics with

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Drying Agents

Used to remove final traces of water from organic solutions

Typically anhydrous, inorganic salts! readily hydrate

Typical drying agents include:

Procedure

- add a small amount of solid drying agent to the organic solution

- swirl; drying agent should be free flowing (not clumped); avoid excess

- let stand (swirl occasionally) for 5-15 minutes

- filter or decant solution away from drying agent

Drying Agent

calcium chloride CaCl2

calcium sulfate CaSO4magnesium sulfate MgSO4

potassium carbonate K2CO3sodium sulfate Na2SO4

Capacity

high

low

high

medium

high

Speed

medium

fast

fast

medium

slow

Applications

hydrocarbons

generally useful

not for very acidsensitive cmpds

not for acidic cmpds

generally useful

Next Week (October 3 - 7)

A. Separation of a 3-Component Mixture by Extraction

strong organic acid - benzoic acid (carboxylic acid)

organic base - 4-chloroanaline (amine)

neutral substance - 1,4-dimethoxybenzene (ether)

B. Isolation & Analysis

recover compounds by neutralization/filtration or evaporation

evaluate success of separation by TLC & melting point

confirm identity of separated components by IR

Experiment 4: Extraction

DUE: Distillation Lab Report (exp 3)

Lab Reports are due at thebeginningof your regular lab session

Exp 4 Notebook: Research Plan MUST be a flowchartuse the entire page for the flowchart; experimental

section will follow on a new page

Extraction Overview

1. Your mixture contains the following components (dissolve in ether)

2. Separation of the 4-chloroaniline (an amine) is achieved by extractingthe mixture with acid

Ar-NH2+HCl! Ar-NH3+ Cl -

3. The benzoic acid (a carboxylic acid) is separated upon extraction with base

Ar-CO2H +NaOH! Ar-CO2- Na+

4. The 1,4-dimethoxybenzene will remain in the organic layer

Extraction Technique: The Basic Setup

separatory funnel set in a ring(be sure it is the right size)

stopper & stopcock should fit avoid leaks

stopcock should beclosed!

collection flask below "just in case"

add solution slowly avoid spills - use a funnel

solution must be cool avoid large pressure build up

funnel (optional)

metal ring

ring stand

empty flaskor beaker

stopcock should beclosed!!!

stopper

note that the tip of thefunnel is below the

rim of the flask!

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Extraction Technique: Separationadd appropriate aqueous reagent to the solution

stopper the funnel and invert hold on to the stopper!

vent carefully release pressure; vent gases

point funnel away from yourself & othersrepeat several times DON'T SHAKE! avoid emulsions

set funnel back into ring

allow layers to separate be sure you know which layer is which!

remove stopper so funnel will drain!

drain lower layer through stopcockkeep tip of funnel below rim of container

pour upper layer out through top avoid contamination

hold stoppersecurely!

CAUTION!escaping gases

Experimental Details

Separation

1. Obtain approximately 1.5g compound mixture (1:1:1 ratio by weight)- record accurate weight (does not need to be 1.50g!)

2. Dissolve in ether! transfer resulting solution to the separatory funnel- use a little extra solvent to complete transfer

3. Add HCl to the separatory funnel; stopper and invert separatory funnel to mix-be sure you know which layer is which!-vent frequently to prevent pressure build-up

4. Separate layers- wait for separation to occur, then drain lower layer

!aqueous layer - will contain amine salt(flask #1)-organic layer remains - will contain benzoic acid & 1,4-dimethoxybenzene

5. Repeat steps 3-4- to ensure complete extraction of the amine from the organic layer- REMEMBER:multiple extractions using smaller amounts of reagent

are more efficient than a single extraction with the same reagent volume!


6. Add NaOH to separatory funnel; stopper and invert sep funnel to mix- mix thoroughly -- deprotonation of benzoic acid is a bit slow

7. Separate layers as before- wait for separation to occur, then drain lower layer

!aqueous layer - will contain carboxylic acid salt(flask #2)- organic layer remains - will contain 1,4-dimethoxybenzene

8. Repeat steps 6 & 7- to ensure complete extraction of the carboxylic acid from the organic layer

9. Wash organic layer with saturated NaCl (aq)- preliminary drying- drain lower layer out through bottom (set aside to discard later)

- pour top layer out through top of sep funnel(flask #3)

!will contain 1,4-dimethoxybenzene


Isolation of Components

Flask 3: organics; dry over anhydrous Na2SO4swirl to mix; should be some free-flowing solid

- more is not better

- let sit for 5-10 min (keep busy while you wait!)decant liquid into tared roundbottom flaskconcentrate using the rotary evaporator - no sand baths! Fire Hazard! -HINT: place flask with organics in back of hood and do

something else while you wait for the rotavap!

Flask 1: acidic extracts; make basic with concentrated NaOH (check pH)

Ar-NH3+ Cl -+NaOH! Ar-NH2 ($)

cool & collect crystals

Flask 2: basic extracts; make acidic with concentrated HCl (check pH)

Ar-CO2- Na++HCl! Ar-CO2H ($)

cool & collect crystals

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Finishing Up

1. dry samples-samples#1 & 2 will be very wet; first press between two pieces of filter

paper, then dry under vacuum (be sure side arm test tube isclean!!)

2. weigh samples (& calculate % recovery)- how much of each compound can you expect to recover?

3. determine melting point of each compound

4. evaluate success of separation by TLC- spot initial 1:1:1 mixture, plus 3 isolated components- developing solvent is chloroform (use in the hood!)- how can you tell if separation was successful?

5. Get IR spectra from your TA-use to confirm identity of each component

Some Pointers: Label your flasks!

- one Erlenmeyer/beaker looks pretty much like the next

NEVER throw anything away until you're absolutely sure you don't need it- you can always dispose of it later- once discarded, it's tough to get it back!

When extracting, invert funnel gently - don't shake - keeps emulsions from forming

- emulsions will take alongtime before layers separate

Vent frequently - avoid pressure build up - sep funnel could explode

During isolation, be sure solutions are acidic/basic (check with pH paper)- do NOT dip paper into solution; use a boiling stick or glass rod

- MIX THOROUGHLY after each addition of HCl or NaOH

Come prepared- easy to get confused if you're not clear on what you're doing- mustwrite a flow sheet for the pre-lab research plan

(use the entire width of the page)

Infrared Spectroscopy (IR)

Infrared region of electromagnetic spectrum": 2,500-16,000 nm#: 1.9 x 1013 - 1.2 x 1014 Hz

Photon energies associated with this region are weak-not large enough to excite electrons-can induce vibrational excitation of covalently bonded atoms & groups

Exact frequencies of vibrations determined by the strength of the bondsinvolved and the masses of the connected atoms

Wide variety of vibrational motions; commonly talk about "stretching & bending"e.g. for C-H bond

symmetricstretch

asymmetricstretch

scissoring(in plane bending)

H

H

C

H

H

C

H

H

C

Infrared Spectroscopy

Absorption in specific region in IR spectrum corresponds to specific typesof molecular vibrations:

FREQUENCY (cm-1)

4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600

Bonds to H t r ip leb o n d s

doub leb o n d s

f ingerpr in treg ion

O-H , N-H C=O C-C , C-O , C-N, et c .C!C, C!N

C!O , e t c .C- H C= CC= N Ar-H

2.5 3.0 3.5 4.0 5 6 7 8 9 10 11 12 13 14 16

(MICRONS)

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Infrared Spectroscopy

Plot light absorbsed/transmitted as a function of frequency, can determinewhat types of functional groups are present in a molecule

IR spectrum of tert-butylbenzene

SDBS Database National Institute of Advanced Industrial Science and Technology; 11/7/07

C-H stretch

Distinguishing features by IR spectroscopy (see Carey, pg 579)

Carboxylic acids- broad OH stretch (ca.3000 cm-1) - may be diffuse- C=O stretch (ca.1710 cm-1)

Amines- NH stretch (ca.3400 cm-1) - 2 bands for a NH2 group

Ethers- none of the above- will likely seeminorFG absorbances C-H stretch (ca.2850-3150 cm-1) C-O stretch (ca.1000-1250 cm-1)- minor absorbances will be present in acid & amine spectra as well

Identification of Mixture Components

Infrared Spectrum of a Carboxylic Acid

OH stretch

C=O stretch

O

OHR

Infrared Spectrum of an Amine (RNH2)

NH stretch

%

NO C=O

R-NH2

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Infrared Spectrum of an Ether

C-O stretch

%

NO C=O

%

NO NH

C-H stretch

OR

will show minor FG absorbances only

Writing the Lab Report:Exp #3 Distillation

Purpose - technique experiment: what will you learn?

- what conclusions will you reach?- a general discussion of theory/expected results is not a purpose!

Results & Discussion- Plot data for both simple & fractional distillations (include graphs)

these are essentially temp vs time plots as discussed in class

raw data (# drops vs temperature) does not belong here!

- Evaluate data! simple distillation

discuss temp vs. volume graph(equiv to temp vs. time!)

compare to theory (what do you expect to see)?

do your results agree with your expectations? explain!

what does plot tell you about composition of drops over time?

e.g. what does the temperature change indicate?

are the drops pure? does purity vary?

report % recovery and % holdup

!

!


Results & Discussion

- Evaluate data ! fractional distillation

discuss same topics as for simple distillation

- Compare the two distillation techniquescompare how well the two components separated in each case

what data can you use? bp recorded vs known bp

Temp vs. Vol plots

discuss differences in % holdup and % recovery

relates to the efficiency of the two processes

- Decide which method is better for the separation of cyclohexane & toluene

clearly explain why you made this choice (based on your results)

do your findings agree with your expectations?

again, first must decide what you expect to see

your expectations shouldn't influence interpretation of your data

!


Conclusion- a brief recap of your findings- make a general statement about distillation techniques you studied

- should be brief (2-3 sentences)

Appendix A: Calculations

- Percent Recovery

- Percent Holdup

amount of material retained by the distillation apparatus

!

!

% recovery =amount distillate recovered (mL)

amount of original solution (mL)x 100

% holdup =amount liquid left in flask(mL)

amount of original solution (mL)x 100

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