Essay/Term paper: Acid base extraction

Essay, term paper, research paper:  Chemistry

Acid Base Extraction


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.