Download Investigating Organic Functional Groups Spring 2010

Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Cautions
HCl and NaOH are corrosive and toxic
Purpose
In this lab you will use traditional chemical tests to identify a variety of functional groups in known chemicals.
You will use those positive results to identify the functional groups present in an unknown compound.
Introduction
Chemists today are trained to use elaborate technologies and instrumentation to determine chemical structure
and makeup. However, many years ago, these technologies were not yet available, and there were very few ways
for chemists to determine the composition of any chemical. Chemists would use a series of tests to characterize
the structure and makeup of a chemical.
You will be doing some of these tests in this lab, in particular, ones that
indicate functional groups present on a molecule.
Functional groups can be defined as the parts of organic molecules that are prone to chemical reactions.
Saturated hydrocarbons (carbon chain molecules with all single bonds and the maximum number of hydrogen
atoms) are not especially susceptible to reactions, but chemicals that contain oxygen, nitrogen, halogens (Br, Cl, F,
and I) and double or triple bonds between carbon atoms can readily react in specific conditions. Alkenes, alcohols,
aldehyde, ketone, and alkyl halide compounds will be studied.
Alkenes
Alkenes are chemicals that contain a carbon-carbon double bond as the functional group. They react with the
magenta-colored chemical potassium permanganate (KMnO4) to product manganese dioxide (MnO2), which is a
brown solid. In other words, you can determine if a chemical has a double bond by adding KMnO4 and looking for
the development of the brown solid MnO2.
Example 1: Oxidation of 1-butene by KMnO4
OH
3
H2
C
H3 C
CH2 + 4 H 2O + 2 KMnO 4
C
H
H2
C
3
H 3C
H
C
CH 2 + 2 MnO2 + 2 KOH
OH
Alcohols
An alcohol is any organic compound that has a hydroxyl functional group (-OH) bonded to a carbon atom,
which is usually connected to other carbon or hydrogen atoms. Alcohols are oxidized with Jones reagent (chromic
acid (H2CrO4) and sulfuric acid (H2SO4)) to give a carbonyl (C=O) and a green chromium compound. Positive
identification of an alcohol will be evident when the addition of chromic acid results in a green solution. This
reaction is quick, working on the order of 2-3 seconds. Aldehydes also react with chromic acid to produce the
green chromium compound, but the reaction takes a bit longer, 10-12 seconds or so.
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Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Example 2: Reduction of 2-propanol (iso-propanol)
H3 C
CH3
H
C
CH3
H3 C
H 2CrO4
C
OH
+
H 2CrO3
+
H 2O
O
Ketones and Aldehydes
Ketones and aldehydes both contain the same functional group, a carbon-oxygen double bond. In a ketone,
the carbon atom is also attached to two other carbons. In an aldehyde, the carbon is bonded to another carbon
and a hydrogen. Both ketones and aldehydes react with a chemical called 2,4-dinitrophenylhydrazine (2,4-DNPH)
to form a yellow or orange solid within a few minutes.
Example 3: Reaction of propanone (a ketone) with 2,4-DNPH
NO2
H3 C
NO 2
H
N
CH3
NH2
C
C
N
+
O
CH 3
H
N
O 2N
CH3
+ H2 O
O2N
2,4-DNPH
Example 4: Reaction of propanal (an aldehyde) with 2,4-DNPH
NO2
H
NO 2
H
N
CH3
NH 2
C
O2 N
C
N
+
O
CH 3
H
N
H
+ H 2O
O 2N
2,4-DNPH
Alkyl Halides
Alkyl halides are alkanes that have a halide ion (such as chloride or bromide) bonded to carbon in the usual
place of a hydrogen atom. Halides in organic compounds can be identified by way of a Beilstein test. A copper
wire is heated under a flame to from a layer of copper(II) oxide (CuO) on the wire. Dip the coated wire in your
compound and then place under the flame. If a halide is present in the organic compound, it reacts with copper(II)
to form a copper halide, which burns green in the flame.
Example 5: Identification of methyl bromide by Beilstein test
Cu(s)
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flame
CuO(s)
H3C
Br
CuBr2
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Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Procedure
Keep the resulting test tubes from your standard tests until the end of the experiment for comparison to your
unknown compound.
1. Testing for alkenes: Set up two test tubes in the test tube rack. In tube one, put in 4 drops of hexane. In
tube two, put in 4 drops of pentene. Add 2 mL of ethanol to each tube. Add two drops of the
permanganate solution, stopper, and shake (be careful you know which tube is which!) Record the results
on the data sheet.
2. Testing for alcohols: Set up two new test tubes in the test tube rack. In tube one, put in 1 drop of hexane,
and in tube two put in one drop of ethanol. Add 1 mL of acetone to each tube followed by 1 drop of the
chromic acid reagent. Gently swirl the tubes. Record the results on the data sheet.
3. Testing for ketones: Set up two test tubes in the test tube rack. In tube one, put in 2 drops of hexane, and
in tube two, put in 2 drops of acetone. Add 2 mL of ethanol to each tube followed by 3 mL of the 2,4-DNPH
reagent. Stopper and shake well. Let the solution stand for up to 15 minutes. You can go onto the next
test in this time. Record the results on the data sheet.
4. Testing for aldehydes: You will be using two tests for aldehydes, the chromic acid test as well as the 2,4DNPH test. Because you already know what the negative tests for these look like, you will only be doing
the positive tests. Set up two test tubes in the test tube rack. In tube 1, put in 1 drop of hexanal, 1 mL of
acetone, and 1 drop of chromic acid. Swirl the tube. In tube 2, put in 2 drops of hexanal, 2 mL of ethanol,
and 3 mL of the 2,4-DNPH reagent. Stopper and shake the tube. Wait up to 15 minutes for a reaction in
tube 2. Compare the tests to the positive and negative tests in 2 and 3 above. Record the results on the
data sheet.
5. Testing for alkyl halides: Take a small length of copper wire and brush it clean using the sand paper. Hold
it over a flame for about 30 seconds. Take it out of the fire and let it cool down. Dip the wire in hexane and
hold over the flame. Repeat the procedure using methylene chloride. Record the results on the data
sheet.
6. Testing your unknown: Obtain your unknown and perform the tests described in steps 1-5. Make careful
observations and record your results on the data sheet. Compare to the results to those for the known
chemicals to determine the functional groups present in your compound.
Waste Disposal
Collect all chemicals in the appropriate waste container.
Clean-Up
Wash all glassware with soap then rinse 3 times with tap water, and once with deionized water.
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Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Data Sheet 1
Name: _______________________________
Alkyl Halide Test
Aldehyde Tests
Ketone Test
Alcohol Test
Alkene Test
Test
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Sample
Lab Partner: ______________________________
Observations
Hexane
(control)
Propene
Hexane
(control)
Ethanol
Hexane
(control)
Acetone
Reaction with
Chromic acid
Reaction with
2,4-DNPH
Hexane
(control)
Methylene
Chloride
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Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Data Sheet 2
Unknown Number: _______________________________________
Observations
Alkyl Halide
Test
Aldehyde Test
Ketone Test
Alcohol Test
Alkene Test
Test
Positive
(+) or
Negative
(-)?
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Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Post-lab Assignment
Name: ______________________________
1. Which functional groups are present in your unknown chemical? Explain your reasoning using the results
of the tests performed on your unknown.
2. Using what you have learned in this lab, is there a way to identify a chemical that has an alcohol and an
aldehyde functional group on it? If yes, which tests would you use and why?
3. Propose a way to identify a compound with both an aldehyde and a ketone functional group. Explain your
answer.
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Austin Peay State University Department of Chemistry
Chem 1041
Investigating Organic Functional Groups
Pre-lab Assignment
Name: _________________________________
1. Draw the Lewis-dot structures of the compounds listed below that you will be using in this lab. Circle and
name the functional group.
a) Hexane
d) Ethanol
b) Acetone
e) Hexanal
c) Propene
f)
Methylene chloride
2. Name and circle the functional groups shown in the compounds below. Which test would you use for the
following chemicals?
CH3
a) b) H3 C
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C
C
H
H2
C
CH3
CH3
H
CH
C CH3
O
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