WWU -- Chemistry Experiment 11 ISOLATION OF CAFFEINE FROM TEA Reading Assignment –pp. 119 – 127 –Technique 7, pp. 595 – 613 –Green Lab people: download

WWU -- ChemistryWWU -- Chemistry

Experiment 11ISOLATION OF CAFFEINE FROM

TEA

• Reading Assignment– pp. 119 – 127– Technique 7, pp. 595 – 613– Green Lab people: download materials– Technique 16, pp. 726 - 731


Caffeine

N

N N

N

O

CH3

CH3

O

CH3


Distribution Coefficient

K =C2

C1


See page 597 for an example on how this equation is applied to extraction.


Bottom line!

You will remove more solute (caffeine) from an aqueous solution by using two 1 mL portions of methylene chloride than by using one 2 mL portionof methylene chloride! See the textbook for an example.


Separatory funnel

Remove from topbefore you start to drain!

Remember! Closestopcock beforepouring stuff in thetop of the funnel!


Which layer on the top?Which layer is on the bottom?

You need to know the density of the methylene chloride and the density of the aqueous phase to answer this question!


Green extraction of caffeine from tea

You will remove caffeine from tea using a Solid PhaseExtraction column (SPE).

Be sure to download the experiment and some of the technique materials from Charles Wandler’s web page.


Solid Phase Extraction (SPE)

Two Neoprene adapters

SPE columnfilled withC-18 silica

Filter flaskTo housevacuum


C-18 silica Silica is alkylated with long chain hydrocarbon groups, using 18carbons long. This is usually referred to as C-18 silica.

O

Si

O

O

Si

OO

O

O

Si

OO

O

Si

OO

O

Si

O OO

Si

OO

Si

OO

Si

OO

Si

O OO

Si

OO

Si

OO

Si

O OO

CH2

CH3

17Si

CH3

CH3

CH2

CH3

17Si

CH3

CH3

SiCH3)3SiCH3)3

SiCH3)3


Solid phase extraction (SPE)

• The C-18 column packing is NON-POLAR• Caffeine will move more slowly because

it is attracted to the column packing.• The more polar components such as

tannins, gallic acid and chlorophyll move more quickly down the column with the the polar water

• Once the aqueous materials have moved down the column, then you elute the caffeine with ethyl acetate.


Sublimation Behavior


Sublimation Apparatus

To house vacuum


Three examples:

1. A solid will melt if its vapor pressure is below the applied pressure when the solid is heated to its melting point.

2. A solid will sublime if its vapor pressure is higher than the applied pressure as it is heated. You will not observe melting behavior.

3. If you want to sublime a solid that has a vapor pressure of 50 mm Hg, you can do this if you reduce the pressure, under vacuum, to below this value.


MIDTERM EXAMINATION

• Friday, February 10th • 2:00 to 2:50 PM• Distillation lab (Exp 6) is due Monday

or Tuesday, depending on your section.Dr. Pavia will post answers to the questions in the post lab on his bulletin board after Tuesday so you have them for the test on Friday!


Coverage• EXP. 2 SOLUBILITY• EXP. 3 CRYSTALLIZATION• EXP. 5 CHROMATOGRAPHY• EXP. 6 SIMPLE AND FRACTIONAL

DISTILLATION AND GAS CHROMATOGRAPHY

ALSO READ:• PP. 1 - 36• 49 – 71• 80 - 93• TECHNIQUES 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 15


BRING YOUR CALCULATOR


Experiment 52PREPARATION OF A C-4 OR C-5

ACETATE ESTER

• Reading Assignment– pp. 128 – 135– pp. 470 – 475– Technique 3, pp. 529 – 534; 536– Technique 6, pp. 585 – 595– Technique 7, pp. 605 – 611– Technique 8, pp. 617 – 629– Technique 19, pp. 742 – 760– Appendix 3, pp. A14 – A32– Appendix 4, pp. A32 – A50 (probably not

required


Main Reaction

R O H CH3 C OH

OH2SO4

R O C CH3

O

H O H

+

+


* *

Ideal stopping place

ROHCH3COOHH2SO4CH3COORH2O

extract withH2O

aqueousphase

ROHCH3COOH (most)H2SO4 (most)H2O

organic phase

CH3COORH2SO4 (trace)CH3COOH (trace)H2O (trace)ROH (some)

extract withNaHCO3

aqueousphase

organic phase

CH3COORH2O (trace)ROH (some)

H2SO4CH3COOH

CH3COORH2O (trace)ROH (some)

saturatedNaCl

aqueousphase

organic phase

H2OROH

CH3COORH2O (trace)

Na2SO4

H2O

CH3COOR(crude)

CH3COOR(crude)

distillationCH3COOR(pure) There may be some ROH

left in the ester


Why the extraction with NaHCO3?

CH3

C

O

O HNa HCO3 CH3

C

O NaH2CO3

O CO2 + H2O

Partly solubleIn the ester

Ionic substancenow soluble in theaqueous phase


3 4 5 6

Minutes

-18

0

50

100

150

mVolts

4.94

3

6.39

2

s:\iln\chemistry\fall2003-summer2004\summer 2004\chem 354\lampman_kriz\c4c5esters\kjester_7;05;45 pm.run

X:Y:

5.2355 Minutes0.00600 mVolts

SR+SR-

WI:2

Preparation of Esters: Gas Chromatography

O C CH3

O

solvent

Unreactedcyclopentanol

Some Alkene mayAppear here


Preparation of Esters: Gas Chromatography

Ret. Time Width Peak Peak Result Time Offset Area Sep. 1/2 Status No. Name () (min) (min) (counts) Code (sec) Codes ---- ------------ ---------- ------- ------- ---------- ---- ----- ------ 1 4.2884 4.943 0.000 10754 BB 1.8 2 95.7116 6.392 0.000 240011 BB 1.4 ---- ------------ ========== ------- ======= ========== ---- ----- ------ Totals: 100.0000 0.000 250765 Total Identified Counts : 250765 counts

Assume that all response factors = 1.000

In some cases, you may observe extra unknown peaks. Recalculatethe percentages of your data based on the alcohol and ester peaks. Round off the percentages:

4.3 % cyclopentanol95.7% cyclopentyl acetate


We will not be using response factors for the esters Lab (assuming that they are 1.0). However, you may need to recalculate the data to give new areas if you have “extra” peaks that don’t belong.

The example data in the previous slide can be used directly without doing calculations. The usual productsinclude alkene from dehydration, unreacted alcohol and ester. Esters have the longest retention times, alkenes are lowest and unreacted alcohol is in the middle someplace!

You will also be running the infrared spectrum of yourproduct.


1)

2)

3)

O

CCH3 OH + H+

O

CCH3 OH

HO

CCH3 OH

H

fast

O

CCH3 OH

H

RO

H

O

CCH3 OH

H

OR H

rate-determining

O

CCH3 O

H

OR

H

H

O

CCH3 O

H

OR

H

H

O

CCH3

OR

HO

HH+ +

fast


Infrared spectroscopy and other material associated with the esters lab will be covered

on February 17th

Documents

WWU -- Chemistry Experiment 11 ISOLATION OF CAFFEINE FROM TEA Reading Assignment –pp. 119 – 127 –Technique 7, pp. 595 – 613 –Green Lab people: download