ACETANILIDE PURIFICATION BY RECRYSTALLIZATION Kathleen Anne Francisco, Ma.Casey Louisse Garcia, Aimee Di anne Hermoso, Frances Geraldine Ibale, Rigel Larga Group IV, 2EPharmacy, Faculty of Pharmacy, University of Santo Tomas
ABSTRACT
Recrystallization is a purification process for organic substances that are solid at room temperature. In this experiment, acetanilide was synthesized by the acetylation of aniline with acetic anhydride. Using a water bath, the crude acetanilide was dissolved in the recystallizing solvent. After the crude acetanilide was completely dissolved, it is filtered using a fluted filter paper and cooled in an ice bath until crystals were formed. The crystals were then collected and washed with distilled water. Limiting reagent, theoretical yield and percentage yield were then calculated. The limiting reagent is aniline. The theoretical yield is 2.70g and the percentage yield of the reaction is 29.63%. This is the percentage percentage of pure acetanil acetanilide ide obtained obtained from the acetylation acetylation of aniline aniline and acetic acetic anhydride.
INTRODUCTION
Organic compounds that are
Recrystallization
is
a
synthesized in the laboratory or
purification process used to remove
isolated from natural resources can
impurities from organic compounds
contain
impurity,
that are solid at room temperature
according to the Tooling University
(Wigal, C.). It is a technique that is
is
that
based on the difference in the
reduces the quality of a material.
solubilities of the desired compound
Thus,
and
an
impurities.
unwanted
a
An
substance
purification
process
is
the
impurity the
(impurities)
needed for the elimination of these
contaminating
desired
impurities.
compound, as a function of varying
temperature
(Cerritos
Community
College).
insoluble
a
solution
at
a
temperature above the compound’s
Choosing
the
appropriate
recrystallizing solvent is a significant step in the recrystallization process.
melting point. As a result, the compound is deposited as oil, not as crystals (Wigal, C.).
This will result in the production of a higher
in
percentage
aminobenzene, is a primary amine. It
product. These are some of the
has an amino group (-NH2) directly
criteria in choosing the suitable
attached to a benzene ring with a
solvent
recrystallization
chemical formula of C6H5 NH2.It is a
process: (1) the crude crystals should
colourless liquid but darkens upon
have low solubility in the chosen
exposure to light and air. It is denser
solvent at room temperature; (2) the
and
crude crystals should have high
According
solubility in the chosen solvent when
Britannica, it was first obtained in
heated to boiling; (3) The crude
1826 by the destructive distillation of
crystals should not react with the
indigo. Thus, taking its name from
solvent; (4) the solvent should boil at
the
temperature below the solid melting
Indigoferaanil ( Indigoferasuffruticos
point;
a). It is an organic based used to
(5)
the
the
solvent
of
or
the
for
yield
Aniline,phenylamine
should
slightly
soluble to
in
Encyclopedia
indigo-yielding
dyes,
drugs,
water.
plant
moderately be volatile so crystals
make
explosives,
dried readily and (6) the solvent
plastics and photographic and rubber
should be non-toxic, non-flammable,
chemicals.
and inexpensive (Dr.Pahlavan). The impurities in reverse should be dissolved in the solvent at high and low temperatures.
If the solvent’s
boiling point is higher than the compound’s
melting
point,
the
compound will oil out. Oiling out occurs
when
a
compound
is
Figure 1. Chemical Structure of Aniline
Acetic
anhydride
(CH3CO)2O, also known asAcetyl
(chemicaland21.com, retrieved July 28, 2013).
ether is a clear, colourless, mobile (free-flowing)liquid with a sharp odour similar to that of acetic acid. It hydrolyses in water to yield acetic acid. It is used in the manufacture of cellulose acetate for films and plastic
Figure 3. Chemical Structure of Acetanilide
goods. They are also used in the manufacture of industrial chemicals,
The
pharmaceuticals, perfumes, synthetic fibers
and
explosives
(Prof.
objectives
of
the
experiment are: (1) to synthesize acetanilide by the acetylation
Shakhashiri).
of
aniline; (2) purify crude acetanilide product by recrystallization and (3) calculate the percentage yield of pure acetanilide.
Figure 2. Chemical Structure of Acetic Anhydride
MATERIALS AND METHODS
Materials Acetanilide
or
N-
phenylacetamide, C6H5NH(COCH3),
The researchers made use of
varies from gray to white in color and may
chemical reagents hexane, methanol
be in the form of flakes or powder. It is
and water as the choices for selecting
denser and slightly soluble in water. It is
the
used to accelerate the reactions that produce
solvent. Pure acetanilide was also
rubbers as well as a plasticizer to increase
used.Aniline and Acetic anhydride
the pliability of various plastics. It is soluble
were the chemicals used in the
in alcohol, ether, chloroform, acetone,
synthesizing
glycerol and benzene. It is the product of the
Activated charcoal was also used as
acetylation of aniline and acetic anhydride
a decolorizing agent.
appropriate
of
recrystallization
Acetanilide.
RECRYSTALLIZATION PROCESS
Methods DETERMINATION
OF
The dried crude acetanilide
THE
RECRYSTALLIZING SOLVENT
was poured with 20 mililiters of the
A corn-grain amount of pure acetanilide was placed into each of the three test tubes. The first test tube was added with one milliliter of distilled water. It was shaken and placed in a warm water bath 37-40 degrees Celsius for one to five minutes. It was then allowed to cool and observations were recorded. The procedure was repeated in the second and third test tubes but using hexane and methanol, respectively.
recrystallizing solvent. It was heated in a water bath until the entire solid (crude acetanilide) was dissolved. Activated charcoal was then added to decolorize the mixture. While the mixture was hot, it was filtered using a fluted filter paper. After filtration, it was cooled in an ice bath to allow the
formation
of
crystals.
The
crystals formed were collected and washed with distilled water. After the collection and washing of crystals, it were then dried and weighed. Theoretical and percentage
ACETANILIDE PRODUCTION
yield were computed.
Two mililiters of aniline and 20 mililiters of distilled water were mixed in an Erlenmeyer flask. Three mililiters of acetic anhydride was then slowly added to the solution. It was cooled in an ice bath to hasten crystallization.
After
which,
the
Figure 4. Folding of Fluted Filter Paper
solution was filtered using a wet paper
Using a fluted filter paper
containing the crude acetanilide was
increases the surface area inside the
dried and weighed. Observations and
funnel, thus speeds up the filtering
results were recorded.
process.
filter
paper.
The
filter
room
RESULTS AND DISCUSSION
Choosing
the
appropriate
recrystallizing solvent is a vital step in the recrystallization process. It aids
in
the
purification
of
the
product. Ideally, the recrystallizing solvent
should
dissolve
the
compound of interest at elevated
temperature
and
lower
temperatures but soluble at elevated temperatures. This fits the criteria for choosing
the
recrystallizing acetanilide water.
appropriate solvent.
will
Thus,
recrystallize
Purification
of
in
crude
acetanilide will also take place.
temperatures but insoluble at lower temperatures.
In
contrast,
the
impurities should be soluble at room temperature but insoluble during heating (Wigal, C.).
Addition
of
activated
charcoal decolorizes the solution. It adsorbs the impurities because it has a large surface area and it can remove impurities more effectively.
SOLVENT
AT ROOM
UPON
UPON
TEMPERATURE
HEATING
COOLING
Water
Insoluble
Soluble
Insoluble
Methanol
Soluble
Soluble
Soluble
Hexane
Insoluble
Insoluble
Insoluble
Table 1. Solubility of Pure Acetanilide in Different Solvents at Different Temperatures
However,
too
much
activated
charcoal used will not only adsorb the impurities but also the desired product (Pastro, etc., 1998).
Table 1 shows the solubility of pure acetanilide
in
different
solvents:
water, methanol and hexane, at different
temperatures:
temperature,
elevated
and
acetanilide
is
The
lower
temperatures. In all the temperatures, pure
Figure 5. Synthesis of Acetanilide
room
soluble
in
Weight
of
Acetanilide
hexane.
Weight
recrystallize in these solvents. For water, pure acetanilide is insoluble at
and
acetanilide were weighed.
methanol while it is insoluble in Thus, acetanilide will not
crude
of
Acetanilide
Crude
3.0g
Pure
0.8g
pure
After process,
the
recrystallization
percentage
computed. percentage
To
yield
compute
were
for
COMPUTING FOR THEORETICAL YIELD
the
yield, theoretical and
limiting reagent should be known.
The limiting reagent is the reactant
involved in the reaction that is used up first (Chang, 2008). Theoretical yield is the amount of a product
CALCULATION OF PERCENTAGE
formed when the limiting reactant is
YIELD
completely
consumed
(Zumdahl,
2012). DETERMINATION
OF
LIMITING
REAGENT
Thus, the percentage yield of the
Aniline:
reaction is 29.63%. This is the pure acetanilide mililiters
obtained of
aniline
from and
two three
mililiters of acetic anhydride.
Acetic anhydride:
REFERENCES : BOOKS
Chang, R. (2008). General Chemistry : The
Thus, the limiting reagent is aniline because it will be the first one to be used up.
ed.).
Essential Concepts (5 New
York
McGraw-Hill. Pg. 81-85
th
:
Pastro, D.J., John, C.R., & Miller, M.S.
(1998). Experiment Techniques
and
in
Organic
Chemistry. New Jersey: Prentice Hall.
ONLINE ENCYCLOPEDIA
Aniline. In Encyclopædia Britannica
online. Retrieved
from
http://global.britannica.com/E
Pg. 43-46
checke /topic/25473/aniline
Zumdahl, S. (2012). Chemistry An Atoms First
Approach.
United States of America : Brooks/Cole. Pg. 404-405 ONLINE http://www.toolingu.com/definition500150-15780-impurities.html Retrieved July 30, 2013 Cerritos Community College. Purification of Impure Acetanilide (Recrystallization). Organic Chemistry 211
Laboratory .
Retrieved from
http://web.cerritos.edu/jbrad
ury/Sit
Pages/Chem.%20211%20lab/2 1%20L b/recrystallization.pdf Retrieved on
August 3, 2013
Wigal, C. (2004). Purifying Acetanilide by
Recrystallization.
Modular Program
Laboratory in
Chemistry.
Retrieved
from
http://www.chm.uri.edu/bdeb ef/ch
292/rextallization.pdf
Retrieved
30,2013
on
July
Retrieved on
August 3, 2013