OXIDATION REACTION OF CYCLOHEXANOL AND CANNIZZARO
REACTION OF BENZALDEHYDE
By
Ni
Luh Gede Enik Karnila Yanti
Chemistry
Education Department, Faculty of Mathematics and Natural Sciences, Ganesha
University of Education
email:
enikkarnilayanti@yahoo.co.id
Abstract
The aims of the experiment was
to (1) undertand the oxidation-reduction reaction of organic compound (2)
identify product of the reaction. The
compound used are cyclohexanol and benzaldehyde were prepared by the laboratory
assistant as the subjects of this experiment. The mechanism and the product of
the redox reaction reaction were as the object in this experiment. The procedure was divided into two steps are cyclohexanol
oxidation reaction and oxidation-
reduction of aldehyde by Base Catalyst: Cannizzaro Reaction. The data obtain
are cyclohexanon as the result
of cyclohexanol oxidation is 4.80 mL and has boiling point of 153oC
with percent yield is 70.86%; the white
crystal of benzoic acid resulted is 3.11 gram with percent yield is 69.84%; and the benzyl alcohol resulted is 2.8 mL
and has boiling point of 205oC with percent yield is 73.87%.
Key
words: Oxidation reaction, Cyclohexanol, Cannizzaro reaction, Benzaldehyde.
INTRODUCTION
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Primary alcohol
|
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Aldehydes
|
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Carboxylic acid
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Cyclohexanol
Oxidation Reaction
Oxidations of primary alcohols produce aldehydes and if oxidized further
to give the carboxylic acid. Oxidation of the
secondary alcohol will produce ketones but the oxidation reaction cannot be performed at
a tertiary alcohol (L.G. Wade,
2010) .
Figure 01. Primary alcohol will result aldehyde and further
oxidation will result carboxylate acid
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Secondary alcohol
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Ketones
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Figure 02. Oxidation of secondary alcohol will result ketones
Primary and
secondary alcohols can be oxidized by some reagents are chromium oxides,
permanganate, nitric acid, and even household bleach (NaOCl, sodium
hypochlorite) (L.G. Wade, 2010) . Oxidation of
alcohol will much more occur in acid condition (Nurlita & Suja,
2004) .
Cyclohexanol is
secondary alcohol. Chromic acid reagent is often used as oxidizing agent of
secondary alcohol in laboratory (L.G. Wade, 2010) . The chromic acid
reagent is prepared by dissolving sodium dichromate (Na2Cr2O7)
or potassium dichromate (K2Cr2O7) in a mixture
of sulfuric acid and water. The active species resulted in the mixture is
probably chromic acid, H2CrO4, or acid chromate ion, HCrO4- (L.G. Wade,
2010) .
The reactions is as follows
The mechanism of oxidation by Chromic acid probably involves
the formation of a chromate ester.
Chromate ester is eliminated to gives ketone. Where the carbinol carbon
retains its oxygen atom but loses its hydrogen and gains the second bond to
oxygen, as shown in the following mechanism (L.G. Wade, 2010) .
Figure 3. Formation of the chromate ester
Figure 4. Elimination of the chromate ester and oxidation of
the carbinol carbon
Oxidation-Reduction
Reaction of
Aldehydes with Base Catalyst (Cannizzaro Reaction)
Cannizaro reaction is the reverse
of aldol condensation reaction
is a chemical
reaction that involves disproportionate
aldehydes without hydrogen at the position alpha induced by bases.
Reaction in an aldehydes
group is divided into two, namely aldehydes
that have alpha hydrogen and aldehydes that do not have alpha hydrogen. Alpha hydrogen is hydrogen attached to the alpha position of a carbonyl
group. For example, acetaldehyde
has alpha hydrogen, is an aldehydes that has
no alpha hydrogen is benzaldehyde.
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Acetaldehyde
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Benzaldehyde
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Alpha hydrogen has acidic properties;
it is due to resonance stabilization of the enolate
ion products. An
aldehydes with hydrogen
would undergo aldol
condensation reaction, being that has no alpha
hydrogen will undergo Cannizzaro reaction, with
the help of a strong base.
Will give the aldol condensation of a betha-hydroxy
aldehydes product. The word comes from the aldol here aldehydes
and alcohols that
are formed from the reaction
product, for the condensation reaction
is a reaction in
which two or more molecules combine into one larger molecule, with or without the loss of a
small molecule (the
water). Aldol condensation is an addition reaction where there is a small molecule released.
While an aldehydes without
the addition of alpha hydrogen cannot experience them to generate aldol products.
That is because an aldehydes without alpha
hydrogen (such as benzaldehyde
and formaldehyde) cannot form enolate ions
and thus cannot do
dimerization the aldol condensation.
If an aldehydes with no alpha
hydrogen is heated with a solution of potassium hydroxide or sodium
hydroxide concentrated, there will be a disproportionate reaction or dismutase
where half the aldehydes
is oxidized to carboxylic acids and the other
half would be reduced to an alcohol. This reaction is known as Cannizaro reaction.
The driving force for Cannizaro reaction is
the formation of resonance stabilized
carboxylate ion.
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Benzoat ion
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Resonance of benzoat
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Resonance of benzoate ions
that causes the reaction is skewed to the right (products). Broadly speaking Cannizaro reaction to benzaldehyde
is as follows:
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Benzaldehyde
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Benzoat ion
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Benzyl alcohol
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Figure 5. The reaction
mechanism (addition reaction at carbonyl group)
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(1)
(2)
Simplify, the Cannizzaro mechanism can be
define as following reaction:
Cannizaro reaction is initiated by
OH- attack on the carbonyl carbon, followed by a handover
hydride. At first a benzaldehyde attacked
by OH- to form a
strong base anion (1). Since the anion
is not stable, then
there was movement of a pair of
free electrons to form double bonds (carboxyl structures)
are more stable, resulting in H atom (proton) move to the carbonyl C
atom of the
benzaldehyde another and formed an intermediate structure (2).
Anion can transfer hydride ion to the carbonyl
carbon atom in
the molecule other aldehydes.
After that proton transfer occurs to
produce the carboxyl anion
and alcohol.
METHOD
Equipments and Materials
Experiment was
done at organic chemistry laboratory Ganesha University of Education. This
experiment need time approximately 12 hours to finish all steps. To conduct the
experiment need some equipments and materials. The equipments were used are
Erlenmeyer flask 100 mL, Erlenmeyer flask 250 mL, thermometer, spatula, stirrer
rod, distillation equipment, electrical balance, beaker glass 100 mL, beaker
glass 500 mL, magnetic stirrer, heater, graduated cylinder 10 mL, graduated
cylinder 50 mL, funnel, Buncher funnel, separatory funnel, ring, clamp, statif,
volumetric pipette 5 mL and ball filler.
The materials
used in this experiment namely, 0.03 mole of K2Cr2O7,
7 mL of concentrated H2SO4, 0.065 mole of cyclohexanol,
500 mL of distilled water, 0.2 gram of H2C2O4
, 100 Ml of ether, 7 gram of KOH, 7,5 gram of benzaldehyde , dilute HCl (at
sufficiently), 5 mL of saturated Na-bisulphite, 5 ml of Na2CO3,
CuSO4 (at sufficiently) and filter paper (at sufficiently).
Cyclohexanol
Oxidation
8.82
gram of K2Cr2O7 was dissolved in 40 mL of aquades in Erlenmeyer 100 mL and it was added by 7 mL of concentrated sulfuric
acid carefully. This orange-red solution was cooled down at room temperature.
As much as 0.065 mole of cyclohexanol was mixed with 25 mL of aquades in
Erlenmeyer 250 mL. Then, dichromate solution was added into mixture of
cyclohexanol and it was shaken. The temperature was kept at 550 C by
cooling in the ice water. When the temperature was constant, the flask was
moved from the ice water and it was added by 0.2 gram of oxalic acid to reduce
the excess of dichromate. After that, this mixture was moved into round flask
150 mL and it was added by 35 mL of aquades, and then it was extracted 3 times
by using ether (3x 25 mL). The ether layer was collect, it washed by aquades
and Na-bicarbonate, then it was separated and the ether layer was dried by
anhydrous substance. Then, it was filtered and entered into 50 mL of flask and
it was distilled. The result was record.
Oxidation-
Reduction of Aldehyde by Base Catalyst: Cannizzaro Reaction
Seven gram of KOH was dissolved with
7.5 mL of water in Erlenmeyer flask 100 mL and it was cooled down in ice bath.
Then, it was added by 7.5 mL of benzaldehyde, closed and shaken until it was
formed viscous emulsion. The mixture was stirred along 1 hour. Then, it was
added by 25 mL of aquades and moved into separatory funnel. The mixture then
was extracted by using 5 mL of ether, shaken and let it until it was formed two
layers. The extract of ether was separated. The residue was extracted again
with 5 mL of ether , then the first and second extract of ether layer were
mixed. On the other hand, water layer was moved into beaker glass and acidified
by using dilute HCl while the solution was cooled down in ice bath and stirrer.
The precipitate of benzoic acid was filtered by Buchner funnel, washed by
aquades and recrystallized with hot water. On the other hand, ether layer
extract was added by 5 mL of saturated Na-bisulphite , then the product was
filtered. The ether layer was washed by 5 mL of Na2CO3
10% and 5 mL of aquades in separatory funnel. The water layer was discharged.
The ether layer was dried by anhydrous substance and it was distilled.
RESULT AND DISCUSSION
Result
Oxidation of
cyclohexanol produces colorless cyclohexanon which has boiling point of 153oC
and the volume is 4.8 mL.
Cannizzaro
reaction of benzaldehyde produces benzoic acid and benzyl alcohol. Benzoic acid
resulted is white crystal with m.p. of 121oC. The crystal obtained
is 3.11 grams. Benzyl alcohol resulted is colorless solution with b.p. of 205oC.
The solution obtained is 2.8 mL.
Discussion
Oxidation Reaction of Cyclohexanol
In
theoretical, the oxidation reaction of cyclohexanol that is secondary alcohol
produces a ketone namely cyclohexanon. The chromic
acid reagent is often used for laboratory oxidations of secondary alcohol
which is prepared by dissolving sodium dichromate (Na2Cr2O7)
in sulfuric acid as the following equation:
The oxidation
mechanism by chromic acid involves the formation of a chromate ester. Chromate ester is eliminated to gives ketone.
Where the carbinol carbon retains its oxygen atom but loses its hydrogen and
gains the second bond to oxygen, as shown in the following mechanism:
Formation of chromate ester
For
the experiment, it was obtained 4.8 mL of colorless cyclohexanone that has
boiling point of 153oC.
Oxidation reaction of cyclohexanol become
cyclohexanone can be seen as the following reaction:
C6H11OH + Cr2O72-
→ C6H11O + Cr3+ + H2O
Based
on the reaction above, in theoretical mole of cyclohexanone resulted = mole of
cyclohexanol used which is 0.065 mole.
Theoretical
mass of cyclohexanone = mole cyclohexanone x Mr
= 0.065 mol x
99 gr/mole
= 6.435 gam
While,
based on the experiment, volume of cyclohexanone (r= 0,95 g/mL) resulted = 4.8 mL.
So,
the mass of cyclohexanone = volume of cyclohexanone x r
= 4.8 mL x 0,95 g/mL
= 4.56 gram
From
the calculation above, it can be obtained the percentage of yield as the
following way:
% yield =
=
=
70.86 %
Cannizzaro Reaction of
Benzaldehyde
Redox
reaction of benzaldehyde by using basic catalyst involves several mechanisms
which can be drawn as follows:
Based
on the experiment, it produced benzoic acid and benzyl alcohol. 3.11 gram of white
crystal of benzoic acid obtained is with melting point of 121oC.
While, colorless benzyl alcohol obtained is 2.8 mL with boiling point of 205oC.
Theoretically, the mass of benzoic
acid obtained must be 4,453 gram and the volume of benzyl alcohol obtained must
be 3,79 mL according to the following equation:
Mass of
benzaldehyde = V benzaldehyde x ρ
= 7,5 mL x 1,04 gr/mL
= 7,8 gram
= 0,073 mole
While benzaldehyde is reacted to
form benzoic acid and benzyl alcohol with ratio 1:1. Therefore, the theoretical
mass of benzoic acid and benzyl alcohol obtained can be calculated as follow:
Mole benzoic
acid = mole of benzyl alcohol = ½ mole benzaldehyde = 0,0355 mole
M of benzoic
acid = mole x Mr
=0,0365 mole x
122 gr/mole
= 4,453 gram
M of benzyl
alcohol = mole x Mr
=0,0365 mole x 108
gr/mole
= 3,942 gram
V of benzyl
alcohol = Mass / ρ
= 3,942 gram/ 1,04 gr/mL
= 3,79 mL
From the experiment, mass of
benzoic acid obtained is 3,11 gram. While, the mass of benzyl alcohol obtained
can be calculated as follow:
M of benzyl
alcohol = V benzyl alcohol x ρ
=2,8 mL x 1,04 gr/mL
= 2,912 gram
Then, the percent
yield of benzoic acid and benzyl alcohol from experiment can be calculated as
follow:
CONCLUSION
Based on the
experiment it can be concluded that oxidation reaction of cycohexanol result
cyclohexanon, colorless cyclohexanone obtained is 4.8
mL that has boiling point of 153oC. the percent yield is 70.86 %. Cannizzaro
reaction of benzaldehyde result benzoic
acid and benzyl alcohol, the white crystal of benzoic acid resulted is
3.11 gram with percent yield is 69.84% ; and the benzyl alcohol resulted is 2,8
mL and has boiling point 205oC with percent purity 73.87%.
ACKNOWLEDGMENT
Firstly, writer is grateful to the God,
for the unlimited knowledge was created. Then, thanks for lecture Mr. I Nyoman
Tika, M.Si who teach Organic Experiment subject. Thank for the laboratory
assistant, Mr. Lasia who guides the writer in conducting experiment and give
information how to work safely. Also thanks, the lecture assistant, Mrs. Dewi
who guides the writer in conducting experiment. Moreover, the last for all
members of VA class who give great motivation to the writer.
REFERENCES
L.G.
Wade, J. (2010). Organic Chemistry. Upper Saddle River: Pearson
Eduation, Inc.
Muderawan, I
Wayan dan I Wayan Suja. 2008. Praktikum
Kimia Organik. Singaraja :Universitas Pendidikan Ganesha
Nurlita,Frieda dan I Wayan Suja.2004.Buku Ajar
Praktikum Kimia Organik.Singaraja : IKIP Negeri Singaraja
Solomon, Graham and Craig Fryhle. 2000.Organic Chemistry, Seventh Edition. USA
: John Wiley&Sons.Inc
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