AcidbaseExtraction

The purpose of this laboratory assignment was two-fold, first, we were to
demonstrate the extraction of acids and bases, finally, determining what unknowns were
present. Second, we were to extract caffeine from tea. These two assignment will be
documented in two separate entities.

Introduction: Acid/base extraction involves carrying out simple acid/base reactions in
order to separate strong organic acids, weak organic acids neutral organic compounds
and basic organic substances. The procedure for this laboratory assignment are on the
following pages.

3) Separation of Carboxylic Acid, a Phenol and a Neutral Substance

The purpose of this acid/base extraction is to separate a mixture of equal parts of
benzoic acid(strong acid) and 2-naphthanol(weak base) and
1,4-dimethoxybenzene(neutral) by extracting from tert-butylmethyl ether(very
volatile).The goal of this experiment was to identify the three components in the mixture
and to determine the percent recovery of each from the mixture.

4) Separation of a Neutral and Basic Substance

A mixture of equal parts of a neutral substance containing either naphthalene or
benzoin and a basic substance containing either 4-chloroaniline or ethyl 4-aminobenzoate
were to be separated by extraction from an ether solution. Once the separation took
place, and crystallization was carried out, it became possible to determine what
components were in the unknown mixture, by means of a melting point determination.



Results


Procedure Observations Inference

Dissolve 3.05g Phenol Mixture was a golden-
Neutral acid in 30ml brown/yellow color
t-butyl methyl ether in
Erlenmeyer flask and transfer
mixture to 125ml separatory
funnel using little ether to
complete the transfer

Add 10 ml of water Organic layer=mixture
aqueous layer=water(clear)

Add 10 ml saturated aqueous Sodium bicarbonate NaHCO3 dissolves in
solution sodium bicarbonate water.
to funnel and mix cautiously
with stopper on

Vent liberated carbon Carbon dioxide gas
dioxide and shake the mixture was released three times
thoroughly with frequent venting
of the funnel

Allow layers to separate Layer = H2O +NaHCO3
completely and draw off
lower layer into 50ml Erlenmeyer
flask 1

Add 10ml of 1.5 aqueous NaOH Flask 2 = H2O + NaHCO3
(5ml of 3M and 5ml H2O) to
separatory funnel, shake mixture,
allow layers to separate and draw
off lower layer into a 25ml
Erlenmeyer flask 2. Add additional
5ml of water to funnel, shake as before

Add 15 ml NaCl to funnel. Shake Bottom layer is white and NaCl was added to
the mixture and allow layers to separate gooey. wash the ether
and draw off lower layer, which is layer and to remove
discarded organic substances
NaOH and NaHCO3
Pour ether layer into 50ml
Erlenmeyer flask from the top
of the separatory funnel
(not allowing any water
droplets to be transferred)
Flask 3

Add anhydrous NaSO4
to ether extract until it no
longer clumps together
and set it aside

Acidify contents of flask 2 Litmus went from Acidification was now
by dropwise addition of blue to pink. Flask complete
concentrated HCl while 2 = creamy color
testing with litmus paper
and cool in ice

Acidify contents of flask 1 Litmus went from Acidification was now
by adding HCl dropwise blue to pink. Flask complete
while testing with litmus 2 = white solution
paper and cool in ice

Decant ether from flask
3 into a tared flask

Boil ether with boiling chips

Do a vacuum filtration and Solution turns to a Crystallization is now
recrystallize ether by dissolving it solid. complete
in 5ml, taking out boiling chips,
adding drops of Ligroin until the
solution was cloudy and cool it
in ice

Isolate crystals from flask 2 by Crystals = creamy-white Dried crystals are now
vacuum filtration and wash with powder ready for melting point
a small amount of ice water determination
and recrystallize it from boiling
water

Repeat the above for flask 1 Crystals = white powder

Flasks number 4 and 5 were done by the following diagram.



Results:

As a result of this acid/base experiment, the following results were obtained:




Flask 1: 31.113g
-30.223g
.890g


Flask 2: 36.812g
-36.002g
.810g


Flask 3: 90.789g
-90.114g
.065g


% yield = experimental weight x 100%
theoretical weight


Flask 1: .890g x 100% = 89%
1.00g


Flask 2: .810g x 100% = 81%
1.00g


Flask 3: .675g x 100% = 67.5%
1.00g



When taking the melting points of the unknowns, flasks 4 and 5, I came to the
conclusion that the samples contained, benzoin, melting point of 136-137Degrees(C) and
4-chloroaniline, melting point of 67-80 degrees(C), respectively.

Flask 4: 90.912g
-89.174g
1.738g

% yield = 1.738g x 100% = 90.4%
1.922g


Flask 5: 87.833g
-86.064g
1.769g


% yield = 1.769g x 100% = 87.3%
2.027g



Conclusion:

After each procedure was complete, it became apparent that flask number 4 and
flask number 5 contained benzoin and 4-chloroaniline, respectively. The melting point
range that was experimentally determined for each was 136-137 for benzoin and 67-70
for 4-chloroaniline. As you can see, this experiment was not error-free, as my percentage
yield was not 100%. This is expected for any experiment; for there is no way that, under
the conditions, this experiment can be free of error. This error could have occurred for
many reasons. The most prevalent reason, I feel that maybe not all of the substance was
transferred from the flask to the vacuum, giving a slight error. Also, some residue could
have also been left in the vacuum funnel when transferring the crystal substances.


Questions

2) It is necessary because nothing would come out of the stopcock- the reason for this is
because of pressure. Leaving the stopper on, would decrease the pressure pushing down
on the liquid and the pressure pushing upward would prevail, allowing nothing to escape.

3) I would not expect p-nitrophenol (pka = 7.15) to dissolve NaHCO3(pka = 6.4) because
having a weak acid and a weak base, the reaction would favor the products, not the
reactants, hence, the reaction would not proceed forward. I would expect
2,5-dinitrophenol(pka = 5.15) to dissolve in NaHCO3 the reaction would proceed
forward.

5) a) 1g benzoic acid x 1mol = .00699 mol benzoic acid
143g benzoic acid

b) 1ml 10% solution NaHCO3 x 1g_ x 1mol = .00116 mol NaHCO3
4ml 96g NaHCO3
.00699 moles of benzoic acid



Introduction:

The purpose of the second part of this laboratory assignment was to extract
caffeine from tea using dichloromethane and then to confirm the identity of it by
preparing a derivative of the extracted caffeine which has a sharp melting point, unlike
caffeine itself. Once the extraction was complete, we were to test for melting point and
get a HPLC reading for our derivative.

Discussion:

Tea leaves contain acidic, colored compounds as well as a small amount of
undecomposed chlorophyll, which is soluble in dichloromethane. Caffeine can be easily
extracted from tea. This procedure can be done using conventional methods. Simply
pouring hot water on the tea bags and steeping the bags for about 5-7 minutes would
extract most of the caffeine that the tea contains. Pure caffeine itself is a white, bitter,
odorless crystalline solid, therefore, it is obvious that more than just caffeine is in the
liquid tea solution since tea is a brown color. Because of this, dichloromethane is used to
dissolve the caffeine that is in the tea, which leaves the other constituents in the aqueous
layer. Using a separatory funnel, it becomes possible to extract the dissolved caffeine
from the aqueous layer and the extraction is now ready for further procedure.



Results


Procedure Observation Inference

To a 250ml beaker
containing 7 tea bags,
add 100ml of boiling
water.

Allow the mixture to stand Brown aqueous solution
for 5-7 minutes while steeping containing caffeine and
the tea from the bags other impurities.

Decant the mixture into
another flask

Cool solution to near Dichloromethane =
room temperature and water soluble, clear,
extract twice with 15ml heavier that water.
portions of dichloromethane
using a gentle rocking motion
and venting.

Drain off dichloromethane Dichloromethane Evaporation of the
layer on first extraction; organic layer found solvent leaves crude
include emulsion layer on on the bottom of the caffeine, which on
the second extraction. funnel where the sublimation, yields
caffeine is dissolved. a relatively pure
Chlorine = top, aqueous product.
solution.

Drain extraction 1 and 2
back into the funnel

Dry combined dichloromethane The solvent layer is
solutions and any emulsion yellow.
layer with sodium sulfate

Wash the drying agent Residue of greenish
with further portions of white crystalline weighs
solvent and steam bath 50mg(solid)
the solvent

To 5mg of the Salicylic acid is water
sublimed caffeine in water soluble.
beaker, add 7.5mg of
salicylic acid and .5 ml
of dichloromethane.

Heat mixture to a boil Petroleum ether is a poor
and add a few drops solvent for the product.
petroleum ether until
the mixture turns cloudy.

Insulate beaker and allow
it to cool slowly to room
temperature and then cool
in an ice bath

Remove the solvent with Needle-like crystals are Caffeine salicylate is
a Pasteur pipette while the isolated(white color) formed.
beaker is in the ice bath
then vacuum filter.


Caffeine beaker: 51.61g
-51.56g
.05g = 50mg


% yield = .05g x 100% = 20%
.25g


Caffeine salicylate: 17.198g
-17.036g
.062g

% yield = .062g x 100% = 25%
.25g


Conclusion


According to the HPLC graph that follows, my product was very pure. The actual
melting point of caffeine salicylate is 137 degree(C), my product was found to have a
melting point of 138 degrees (C). As before, of course this experiment was not done
completely error-free, the error is due almost entirely on human error.