Download Experiment # 8: Characterization Tests for the Oxygen

Experiment # 8: Characterization Tests for the Oxygen-Containing Compounds
Capati, Gabrielle Ann Margaret V.
March 2013
Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
España, Manila
Abstract
There are several organic families and one of them is called Oxygen-Containing since these compounds
contains a bond with the element Oxygen; some examples are Alcohols, Ethers, Aldehydes, Ketones and Carboxylic
Acids. The experiment dealt with differentiating the different types of Oxygen-Bearing organic compounds through the
use of different reagents and techniques. This was conducted to classify the samples from being a primary alcohol, a
secondary alcohol, a tertiary alcohol, aldehyde or a ketone. Nine different chemicals were prepared for each test. In
the Dichromate Test, Formaldehyde, 1O Butyl and 2O Butyl ended with a green-blue solution which satisfied this test
while no compounds produced a orange presipitate for the DNPH Test. For Tollen’s Test, Formaldehyde was the only
test sample which exhibited the expected result of silver mirror deposits. On the other hand, for Iodoform, 3 O Butyl,
Acetone, Benzoic Acid and Acetamide yielded a yellow solution that gave a positive result. In the Fehling’s Test, all
test solutions formed a blue colored solution except for Formaldehyde while it was only 2 O Butyl and Phenol who
produced emulsions that satisfied the Lucas test.
I.
Introduction
One important part of experimental organic chemistry is to be able to analyze and
identify an organic compound from its functional groups. There are several steps in order to
acquire this and there is no definite process. But there are systematic ways in different
experimental organic chemistry books. “Analysis of Oxygen Bearing Organic Compounds” is an
experiment in which a variety of tests are available to identify a compound’s property whether it
is a Primary, Secondary, Tertiary Alcohol, Aldehyde or a Ketone. All these tests exploit
differences in the type and degree of reactivity of each of the functional groups.
This experiment focused on distinguishing the several kinds of functional groups from
each other. Standard compounds were used to identify the characteristics of each group
present. Its general objective is to be able to observe and analyze the physical result of each
test and to be able to relate it to the functional groups.
II.
Review of Related Literature
There are several organic families and one of them is called Oxygen-Containing since
these compounds contains a bond with the element Oxygen; some examples are Alcohols,
Ethers, Aldehydes, Ketones and Carboxylic Acids. In analyzing the oxygen bearing organic
compounds, there are several tests that may be performed to distinguish among the different
classes of alcohols, aldehydes, and ketones. All these tests exploit differences in the type and
degree of reactivity of each of the functional groups. The tests that are included to come up with
such results are interconnected with one another like that of the Dichromate test, followed by
the Tollen’s test to yield an aldehyde if positive for mirror coating. The second set of procedure
would again start with The Dichromate test, followed by the Tollen’s test and finally the Lucas
test to yield either primary alcohol if it became turbid or secondary alcohols as it’s result if it did
not turn turbid. The last set of interconnected tests were that of again, the Dichromate test,
Followed by the DNPH that would determine if the unknown sample is a Ketone, positive forred-
orange precipitate, or a tertiary alcohol, negative for red-orange precipitate (Analysis of Oxygen
Bearing Compunds, 2010).
The Dichromate Test is a test used to distinguish between primary, secondary and
tertiary alcohol by the use of K2Cr2O7. Primary alcohol is oxidized to aldehydes and carboxylic
acid, while Secondary alcohol is oxidized to ketones, and dichromate cannot oxidize Tertiary
alcohol. Dichromate ions (Cr2O72-) are orange, and on reduction Cr3+ ions formed are green
(Zhang & Xu, 2005)
The DNPH Test a testing used to know the functional group of Aldehyde and Ketones.
DNPH stands for 2,4 Dinitrophenylhydrazine test and it is expected that for a positive result it
must form a yellow, orange, or orange-red precipitate (The 2,4 Dinitrophenylhydrazine Test, No
Date).
Besides the two, Tollen’s Test is also a very useful in determining the functional group of
a test solution. It is positive with the presence of Aldehyde. This test is also known as the “Silver
Mirror” test, for it will exhibit this result after the reaction. It is used in organic chemistry to test
for the presence of aldehydes. In this reaction, an aldehyde is oxidized to a carboxylic acid while
the Ag1+ is reduced to silver metal, which deposits as a thin film on the inner surface of the
glass (Shakhashiri, 1992).
On the otherhand, Iodoform test is used to identify methyl ketones. The reagent used is
a mixture of iodine (I2) and Potassium Iodide (KI). Only methyl ketones (not other types of
ketones) can undergo the iodoform reaction because only methyl ketones have three H atoms
on the a carbon which are necessary to form the iodoform product. Acetaldehyde has an Rmethyl group which behaves the same as methyl ketones. Alcohols that upon oxidation form
methyl ketones will also undergo this reaction (Iodoform Test, No Date).
Second to the last test is Lucas test, which is for the identification of 2O alcohol and 3O
alcohol with an expected result of the formation of emulsion. The reagent used is an aqueous
solution of strong acid (HCl) and zinc chloride. The reaction that occurs in the Lucas test is an
SN1 nucleophilic substitution. Only alcohols that can generate stable carbocation intermediates
will undergo the reaction. The acid catalyst activates the OH group of the alcohol by protonating
the oxygen atom. The C-OH2+ bond breaks to generate the carbocation, which in turn reacts
with the chloride ion (nucleophile) to generate an alkyl halide product (Lucas Test, No Date).
Last is the Fehling’s Test, by which the presence of aldehydes is detected by reduction
of the deep blue solution of copper(II) to a red precipitate of insoluble copper oxide. The positive
test is indicated by a green suspension and a red precipitate (Fehling’s Test, No Date).
III. Methodology
A. Chemicals, Reagents and Apparatus
The chemicals used in the optical method of analysis such as 10% K2Cr2O7, 5% NaClO
and anhydrous ZnCl2 were provided and the concentrations were made available by the
laboratory facilitators. The laboratory apparatuses that were used were found inside the
laboratory including the test tubes for the test solutions and water baths for heating.
B. Dichromate Test
Using a test tube that contains 3 drops of the test solution, 2 drops of 10% K2Cr2O7 and
5 drops of 6M H2SO4 were placed. Any color change was observed.
C. DNPH Test
With another test tube that has 2 drops of the test solution, 1mL of 95% ethanol, and 20
drops of DNPH was placed. The color of the precipitate that forms was noted. When precipitate
did not appear even after 15 minutes, it was heated in a water bath for another 15 minutes.
D. Tollen’s Test
To 5 drops of the test solution in a test tube, 2 mL of the Tollen’s reagent was added.
After 5 minutes, the observations were recorded. When there was no visible change observed, it
was heated in a water bath for 5 minutes.
E. Iodoform Test
A test tube that contains 5 drops of the test solution, 20 drops of 10% KI was added.
Another 20 drops of 5% NaClO was slowly added then it was heated in a water bath. Any
change in its appearance and odor was observed.
F. Fehling’s Test
To 5 drops of the test solution, a mixture of 10 drops of Fehling’s A and 10 drops of
Fehling’s B was combined. It was placed in a hot water bath until changes were observed.
G. Lucas Test
With another test tube that has 5 drops of the test solution, 15 drops of the concentrated
HCl and a pinch of anhydrous ZnCl2 were added. The mixture was shaken until an insoluble
layer or emulsion was formed and the time factor was also noted. When no change was
observed, the solution was placed in a water bath until a formation of turbidity was seen.
IV. Results and Discussion
A. Determination of Functional Groups
The first test was the Dichromate Test, which allows the the test samples to react
with Dichromate. A positive result is the formation of a green-blue solution which means
that it contained the functional groups of Aldehyde and 1O and 2O Alcohol.
Formaldehyde, 1O Butyland 2O Butyl satisfied this test, as shown in Table 1.
Table 1. Dichromate Test.
Test Solution
Dichromate Test
1O Butyl
From a clear solution to orange (immiscible) then a
blue (still immiscible) solution
2O Butyl
From a clear solution to orange (immiscible) then a
blue (still immiscible) solution
3O Butyl
From a light yellow solution to orange solution
Phenol
From a light red solution to orange solution with black precipitate
(turbid) formed
Acetone
From a light yellow solution to orange solution
Formaldehyde
From a clear solution to orange then a blue solution
Benzoic acid
From a light yellow solution to orange solution
Acetemide
From a light yellow solution to orange solution
Ethyl Acetate
From a light yellow solution to orange solution
The second test was the DNPH Test, which allows the the test samples to react
with DNPH and Ethanol. The formation of an orange precipitate means a positive result
since it containes the functional group of Aldehydes and Ketones. Table 4.2 showed that
no compound gave a positive result since the usual precipitate formed was black instead
of orange.
Table 2. DNPH Test.
Test Solution
DNPH Test
O
1 Butyl
From a clear solution to orange with a small amount of black precipitate formed
2O Butyl
From a clear solution to orange with a small amount of black precipitate formed
3O Butyl
From a clear solution to orange with a small amount of black precipitate formed
Phenol
From a clear solution to orange with a small amount of black precipitate formed
Acetone
From a clear solution to orange with orange fur-like precipite then after some
time small amounts of black precipitate formed
Formaldehyde
From a clear solution to light orange with orange fur-like precipitate
Benzoic acid From a clear solution to orange with a small amount of black precipitate formed
Acetemide
From a clear solution to orange with a small amount of black precipitate formed
Ethyl Acetate From a clear solution to orange with a small amount of black precipitate formed
The third test was through the use of AgNO3 which was expected to form silver
mirror deposits. This test is called the Tollen’s Reagent , it has the functional group of
Aldehydes. Thus in the experiment, Formaldehyde was the only test sample which
exhibited this positive result. Shown in Table 3 are the observations obtained during this
test.
Table 3. Tollen’s Test.
Test Solution
Tollen’s Test
1O Butyl
From a clear solution then small amount of white fur-like precipitate formed
2O Butyl
From a clear solution to light orange solution
O
3 Butyl
From a clear solution then small amount of white fur-like precipitate formed
Phenol
From a light red solution then black gelatinous precipitate formed
Acetone
From a clear solution then small amount of white fur-like precipitate formed
Formaldehyde
From a clear solution to gray solution with black metallic precipitate formed
Benzoic acid
From a clear solution then small amount of white fur-like precipitate formed
Acetemide
From a clear solution then small amount of white fur-like precipitate formed
Ethyl Acetate
From a clear solution then small amount of white fur-like precipitate formed
The fourth test, which is The Iodoform Test, it is expected to yield a yellow color
appearance which means that the presence of Methyl Ketones is there. Observing the
results in Table 4, 3O Butyl, Acetone, Benzoic Acid and Acetamide exhibited this positive
effect.
Table 4. Iodoform Test.
Test Solution
Iodoform Test
1O Butyl
From a clear solution to orange then back to a clear solution
2O Butyl
From a clear solution to orange then back to a clear solution
3O Butyl
From a light yellow solution to orange then back to a light yellow solution
Phenol
From a light red solution to yellow (turbid) then peach solution with a small
amount of red precipitate
Acetone
From a clear solution then small amount of yellow precipitate formed
Formaldehyde
Benzoic acid
Acetemide
Ethyl Acetate
From a clear solution to a very light yellow solution
From a clear solution to a lemon colored solution
From a clear solution to red orange then a light yellow solution
From a clear solution to a red orange solution
The fifth test was the Fehling’s test. It will determine if there’s a presence of
Aldehyde and Ketone in the solution. If a blue colored solution appears, then it made a
positive result. All test solutions formed a blue colored solution except for Formaldehyde,
as presented in Table 5.
Table 5. Fehling’s Test.
Test Solution
Fehling’sTest
1O Butyl
From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
2O Butyl
From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
3O Butyl
From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
Phenol
From a light red solution to layers of red and blue (immiscible) then a
aquamarine solution, after placing in a hot water bath no changes were
observed
Acetone
From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
Formaldehyde
From a clear solution to light blue then dark blue, after placing in a hot water
bath for 2 minutes it became a blue-ish white (turbid) with brown precipitate
formed, after 4 minutes it became a clear solution with brown precipate formed
Benzoic acid
From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
Acetemide
From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
Ethyl Acetate From a clear solution to light blue then a darker blue solution, after placing in a
hot water bath no changes were observed
Lastly, the reagent for this test was the Lucas Reagent. After the addition of the
Lucas reagent it showed that the formation of emulsion means a positive result since it
contains the functional group of Alcohols. As seen in Table 6, 2O Butyl and Phenol
satisfied this test.
Table 6. Lucas Test.
Test Solution
Lucas Test
1O Butyl
No changes have been observed
2O Butyl
From a clear solution to a white solution (turbid)
3O Butyl
From a light yellow solution to a light yellow (foggy) solution which eventually
faded away
Phenol
From a light red solution to a red (turbid) solution with a small amount of red
(immiscible) particles that settles at the surface, after settling it turns into a
white (turbid) solution
Acetone
From a clear solution to a very light yellow solution
Formaldehyde
No changes have been observed
Benzoic acid
No changes have been observed
Acetemide
Ethyl Acetate
V.
No changes have been observed
No changes have been observed
Conclusion and Recommendations
With the data gathered through the series of tests conducted, the general objective of
being able to observe and analyze the physical result of each test and to be able to relate it to
the functional groups was accomplished and thus, the experiment was a success.
For instructors and researchers, find more compounds that can be used to further add
data since this experiment isn’t expensive and doesn’t require that much time.
For students, be more cautious in the analyzation and observation stage especially
when it requires you to take note of the time. Don’t be careless in missing out any description of
the end product since that is the most important part of the experiment.
VI. References
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Topacio, K. L., Robidillo, C. J. (2012). Preliminary Test and Solubility Classification of
Organic Compounds. http://www.studymode.com/essays/Preliminary-Test-And-Solubility
-Classification-Of-900545.html
Achas, M. L., Alvarez, M. A., Bangot, K. A., Bayani, K. (2012,). Analysis of OxygenBearing Organic Compounds. http://www.studymode.com/essays/Analysis-Of-OxygenBearing-Organic-Compounds-1118013.html
Lanta, G., Llamado, C. A., Manaig, Jeron. (2012). Oxygen Bearing Compounds.
http://www.studymode.com/essays/Oxygen-Bearing-Compounds-1298312.html
Zhang, S., Xu, L. (2005) “Selective Oxidation of Benzylic Alcohols and TBDMS Ethers to
Carbonyl Compounds with CrO3-H5IO6”. In: “Synthesis”, pp. 1757-1760.
No Author. (No Date). The 2, 4 Dinitrophenylhydrazine Test. http://www.harpercollege.
edu/tm-ps/chm/100/dgodambe/thedisk/qual/dnp.htm
Shakhashiri, B. Z. In Chemical Demonstrations: A Handbook for Teachers of
Chemistry; The University of Wisconsin Press: 1992; Vol. 4, p 240-243.
No Author. (No Date). Iodoform Test. http://www.organicchem.org/oc2web/lab/exp/oxid/
iodoform.pdf
No Author. (No Date). Lucas Test. http://www.organicchem.org/oc2web/lab/exp/oxid/
lucas.pdf
No Author. (No Date). Fehling’s Test. https://dspace.ist.utl.pt/bitstream/2295/50905/1/
Testes%20de%20a%C3%A7ucares-alunos.pdf