Exp 19 - Joseph
Marcus


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Unformatted text preview: Joseph
Marcus
 Experiment
19:
Synthesis
of
Aspirin
and
Oil
of
Wintergreen
 August
16,
2009
 In
this
experiment,
two
organic
molecules
are
synthesized:
oil
of
wintergreen
and
 aspirin.
A
crude
sample
of
aspirin
is
synthesized
and
later
purified.
Its
purity
is
 tested
through
several
analytical
techniques.
The
salicylic
acid
reacts
with
acetic
 anhydride
to
make
aspirin.

 




















 
 +
 
 
 

 
 
 Eqtn.
1



Salicylic
acid

+



Acetic
anhydride




Acetylsalicylic
Acid

+
Acetic
Acid
 This
experiment
uses
two
different
reactions
involving
salicylic
acid.
The
salicylic
 acid
has
2
functional
groups:
an
alcohol
group
and
a
carboxylic
acid
group.
In
the
 first
part
of
the
experiment,
aspirin
is
synthesized
by
reacting
by
reacting
the
acetic
 acid
with
the
alcohol
group
of
the
salicylic
acid.
Instead
of
using
acetic
acid
in
the
 experiment,
acetic
anhydride
was
used
in
its
place
to
react
with
the
alcohol
group
 and
force
the
reaction
to
completion.
This
reaction
forms
aspirin
(acetylsalicylic
 acid)
and
acetic
acid.

In
the
other
reaction,
methanol
(an
alcohol)
reacts
with
the
 carboxylic
acid
group
of
salicylic
acid
to
produce
oil
of
wintergreen.
This
reaction
 does
not
go
to
completion
and
when
FeCl3
(indicator)
reacts
with
the
product,
the
 solution
turns
purple,
indicating
the
presence
of
salicylic
acid.
 Fe3+
 +
 (impurity)
 
 
 
 Eqtn.
2:

Fe3+
+

salicylic
acid(impurity)

brightly
colored
magenta
complex.
 After
synthesizing
a
sample
of
aspirin,
several
tests
are
conducted
to
determine
the
 chemical
composition
of
the
solution
and
to
create
a
purified
sample.
FeCl3
is
 reacted
with
the
crude
aspirin
to
test
for
the
presence
of
salicylic
acid.

The
solution
 was
clear,
indicating
a
miniscule
amount
of
salicylic
acid
present.
Then
some
of
the
 crude
aspirin
is
re‐crystallized
in
order
to
obtain
a
purified
sample.
Warm
ethanol
 was
added
drop‐wise
to
the
crude
sample
and
it
was
cooled
and
filtered
to
get
 purified
aspirin.
The
melting
points
of
both
the
pure
and
crude
samples
are
 measured
experimentally
as
a
means
of
determining
each
of
their
purities.
The
 melting
point
range
for
the
crude
aspirin
was
125°C
to
132°C.
The
range
for
the
 pure
sample
was
132°C
to
136°C.
These
melting
points
are
consistent
with
the
 freezing
point
depression
predictions,
which
states
that
the
range
of
freezing
point
 to
boiling
point
will
decrease
as
the
number
of
solute
molecules
decreases.
To
 conclude,
an
analysis
is
made
on
the
composition
and
purity
of
the
crude
and
 purified
aspirin
samples.

 In
the
final
parts
of
the
experiment,
the
purified
and
crude
aspirin
samples
are
 neutralized
with
0.1M
NaOH
(standardized
in
lab).
Once
the
samples
are
 neutralized,
excess
NaOH
is
added
to
hydrolyze
each
sample.
To
determined
how
 much
NaOH
is
used
in
hydrolysis,
a
back‐titration
is
done
with
HCl.
Given
that
the
 moles
of
NaOH
used
in
hydrolysis
is
equal
to
the
number
of
moles
of
aspirin
in
the
 sample,
the
mass
of
aspirin
can
be
calculated
as
a
percentage
of
the
totalmass
of
the
 sample.
The
purified
aspirin
was
87.1%
pure
and
the
crude
aspirin
was
46.6%
pure.

 The
hydrolysis
reaction
is
as
follows:
 
 ‐‐[NaOH]‐‐>
 Eqtn
3.
 
 +
 
 
 
 Hydrolysis
Reaction
(after
neutralization)
 Some
possible
sources
of
error
could
have
come
from
assuming
the
molarity
of
the
 HCl
(0.1M)
that
was
provided.
In
the
last
few
parts
of
the
experiment,
NaOH
and
HCl
 are
used
to
titrate
and
back
titrate
pure
and
impure
aspirin.
The
NaOH
is
 standardized
in
the
lab
while
the
HCl
molarity
is
assumed
to
be
0.1M.
The
 standardization
of
the
NaOH
is
another
source
of
error.
The
assumption
that
the
 KHP
was
completely
dry
was
made.
Another
source
of
error
could
have
come
from
 the
assumption
that
all
esters
in
the
reaction
were
hydrolyzed,
since
most
organic
 reactions
do
not
go
to
completion.

 ...
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This note was uploaded on 12/02/2009 for the course CHEM chem1C taught by Professor O'dea during the Spring '09 term at UCSB.

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