Download The presence of an aromatic ring or other

Chemistry 2412L
Qualitative Organic Analysis Procedure
The identification and characterization of the structures of unknown substances are an important
part of organic chemistry. Although it is often possible to establish the structure of a compound
on the basis of spectra alone (IR, NMR, etc.), the spectra typically must be supplemented with
other information about the compound: physical state and properties (melting point, boiling
point, solubility, odor, color, etc.), elemental analysis, and confirmatory tests for functional
groups.
In this experiment you will carry out several qualitative tests that will allow you to identify
functional groups in organic molecules. Each functional group has a particular set of properties
that allow it to be identified. Some of these properties can be demonstrated by observing solubility
behavior, while others can be seen in chemical reactions that are accompanied by color changes,
precipitate formation, or other visible effects. You will then apply what you have learned by
characterizing unknown organic compounds in terms of their functional group and solubility
behavior. The functional groups you will examine include amines, alcohols, carboxylic acids,
aldehydes, ketones, esters, alkyl halides, alkenes and aromatic compounds.
The purpose of this experiment is to use qualitative analysis to identify the functional group
present in one (or more) unknown compound(s), and then to use spectroscopic data to propose
the structure of the compound. Be sure to record all observations, including the unknown
number, in your laboratory notebook.
1. Physical Properties
Procedure: Observe the appearance of your unknown, including color, physical state, odor, etc. If
your unknown is a solid, determine its melting point. If the unknown is a liquid, observe its
boiling point by distillation of ~ 3.0 mL of unknown. Be sure to add a boiling stone and take care
to distill slowly so that the temperature reading is accurate.
2. Solubility Classification
The solubility of an organic compound in water, dilute acid, or dilute base can provide useful
information about the presence or absence of certain functional groups. A flowchart showing the
sequence of solubility tests along with the appropriate conclusions is shown in Figure 1.
Solubility in water: Most organic compounds are not soluble in water, except for low molecularweight amines and oxygen-containing compounds. Low molecular-weight compounds are
generally limited to those with fewer than five carbon atoms.

Carboxylic acids with fewer that five carbon atoms are soluble in water and form solutions
that give an acidic response (pH < 7) when tested with litmus paper.

Amines with fewer than five carbons are also soluble in water, and their solutions give a
basic response (pH > 7) when tested with litmus paper.

Ketones, aldehydes, and alcohols with fewer that five carbon atoms are soluble in water
and form neutral solutions (pH = 7).
Chemistry 2412L
Solubility in NaOH: Solubility in 6M NaOH is a positive identification test for acids. A carboxylic
acid that is insoluble in pure water will be soluble in base due to the formation of the sodium salt
of the acid as the acid is neutralized by the base.
Solubility in HCl or H2SO4: Solubility in acid (6M HCl or concentrated sulfuric acid) is a positive
identification test for bases. Amines that are insoluble in pure water will be soluble in acid due to
the formation of an ammonium chloride salt.
Organic Compound
water
insoluble
soluble
6M NaOH
insoluble
test with pH paper
soluble
acidic
6M HCl
insoluble
neutral
soluble
carboxylic carboxylic
acids
acids
(high MW) (low MW)
aldehydes
ketones
alcohols
(high MW)
or
alkanes
alkenes
alkyl halides
(low or high MW)
basic
amines
(high MW)
Figure 1. The Solubility Test Flowchart
amines
(low MW)
aldehydes
ketones
alcohols
(low MW)
Chemistry 2412L
Procedure: Solubility tests are done in the sequence: water, then base, and then acid. If your
compound is soluble in water, you do not need to check for solubility in the basic or acidic
solutions.
Solubility in Water: Place 1 mL of water in a small test tubes. Add 3 drops (or 50 mg of solid) of
your unknown to the test tube. Thoroughly mix the contents of the test tube. Set the tube aside for 1
minute. If two layers form, or if the mixture is cloudy, consider the organic compound insoluble in
water. If a transparent solution results, judge the sample to be soluble in water. Record your
observations. For each of the compounds that dissolved in water, test a drop of the solution on a
piece of litmus paper. Record the pH response as acidic, basic, or neutral.
Solubility in NaOH: For the compounds that were insoluble in deionized water, test their solubility in
NaOH, again using 1 mL of solution and 3 drops or a few crystals of the compound. Record your
observations.
Solubility in 6M HCl or concentrated H2SO4: Those compounds that were insoluble in pure water
and NaOH should be tested in acid following the same procedure as before. Record your
observations.
3. Tests for Specific Functional Groups
Results of your analyses of physical properties and solubility should give you some idea as to the
nature of your unknown compound. Your subsequent tests should be based on these results. For
example, if your unknown was soluble in water and exhibited neutral pH, it could be a low MW
aldehyde, ketone or alcohol. Looking at the NMR data provided by your instructor for your
unknown will help you distinguish between carbonyl and hydroxyl groups. The IR that you
collect will confirm either the carbonyl or the hydroxyl group. Using the composition values
from the elemental analysis, you can determine the empirical formula of your unknown, and
from this, the molecular formula and the degrees of unsaturation. All of these data will help you
to select appropriate tests to identify your unknown compounds.
Beilstein Test
Note: Please check with your instructor to determine whether halogenated unknowns are being
used for this experiment.
Halogens can be detected easily and reliably by the Beilstein test. It is the simplest method for
determining the presence of a halogen, but does not differentiate among chlorine, bromine, and
iodine. A positive Beilstein test results from the production of a volatile copper halide when an
organic halide is heated with copper oxide. The copper halide imparts a blue-green color to the
flame.
Procedure: Heat the loop end of a copper wire in a Bunsen burner flame. After cooling, dip the wire
directly into a small sample of the unknown. Now, heat the wire in the Bunsen burner flame again
(in the lower outside part of the flame). The compounds will first burn. After the burning, a green
flame will be produced if a halogen is present. Record your observations. Perform this test on
bromobenzene and your unknown.
Chemistry 2412L
Chromic Acid Test
This test is based on the reduction of chromium(IV), which is orange, to chromium(III), which is
green, when an alcohol is oxidized by the reagent. A change in color of the reagent from orange to
green represents a positive test. Primary alcohols are oxidized by the reagent to carboxylic acids;
secondary alcohols are oxidized to ketones. Tertiary alcohols are not oxidized at all by the reagent.
Hence, this reaction can be used to distinguish tertiary alcohols form primary and secondary
alcohols. Unlike some other tests for alcohols, this test can be used with all alcohols, regardless of
molecular weight and solubility. Aldehydes are also result in a positive chromic acid test.
Chemistry 2412L
H
R
C
H2CrO4
H
R
OH
C
H
H2CrO4
R
O
C
OH
O
primary alcohol
H
R
C
R
OH
H2CrO4
R
C
R
O
secondary alcohol
Procedure: Dissolve 3-4 drops of a liquid alcohol in 1 mL of acetone. Add 2 drops of chromic acid
reagent and note the result that occurs. A positive test for a primary or secondary alcohol is the
appearance of a blue-green color. Tertiary alcohols do not produce the test result, and the solution
remains orange. Record your observations. Perform this test on 1-propanol, 2-butanol, phenol,
propanal, and your unknown.
Note: you may need to heat the test tube in a 60°C water bath for a few minutes to promote the
reaction.
Ferric Chloride Test
A positive ferric chloride test indicated the presence of a phenolic hydroxyl group. A typical
positive test results in the formation of a red or violet color. Some phenols will not react to this
test due to the interfering presence of other substituents on the ring.
Procedure: Add 1 drop or a few crystals of unknown to 1 mL of freshly prepared 1% FeCl3
solution. Perform this test on phenol and your unknown.
Iodoform Test
Methyl ketones (RCOCH3) react rapidly with iodine under basic conditions to give a carboxylate
(RCO2-) and iodoform (CHI3). Iodoform is a pale yellow solid, and its appearance indicates a
positive test.
Procedure: Dissolve 1 drop or 20 mg of the unknown in 0.5 mL of water (or 0.5 mL of methanol
if the compound is not soluble in water. Add 0.5 mL of 10% aqueous NaOH. Add dropwise, with
shaking, a solution of KI3 until a dark color persists. Warm the solution slightly. If the color
fades, add more KI3. Add a drop or two of NaOH to remove excess iodine, then dilute the
mixture with water. Iodoform, if present, will separate. Perform this test on 2-octanone, 2butanol, and your unknown.
Chemistry 2412L
2,4-Dinitrophenylhydrazine Test
This reagent reacts with ketones and aldehydes, and is used to distinguish these functional
groups from other carbonyl compounds, sucsh as esters, which do not react. The formation of a
red or orange precipitate constitutes a positive text. Since the reagent contains sulfuric acid,
amines may give a heavy precipitate of the amine sulfate, which appears yellow in the solution
and can be mistaken for a positive test.
Procedure: Prepare a solution of 4 drops of unknown in 1 mL of ethanol. Add 1 mL of 2,4dinitrophenylhydrazine reagent. Mix thoroughly and allow to stand. If no precipitate appears
within 5 minutes, heat the solution in a hot water bath for 5 minutes and then allow it to cool to
room temperature. Perform the test on propanal, 2-octanone, butyl amine, and your unknown.
Hinsberg Test
Primary and secondary amines react with benzenesulfonyl chloride in the presence of sodium
hydroxide to give solid benzenesulfonamides.
RNH2 + C6H5SO2Cl
RNHSO2C6H5
A positive test is indicated by the formation of a solid. The benzenesulfonamide from a primary
amine is often soluble, but can be precipitated upon the addition of acid. Those from secondary
amines are typically insoluble in water. Tertiary amines do not react.
Procedure: Mix 50 mg or 2 drops of unknown and 0.2 g of benzenesulfonyl chloride in 4 mL of
10% aqueous NaOH solution. Stopper the test tube and shake vigorously until the oily sulfonyl
chloride has reacted. Perform this test on butylamine, diethylamine, and your unknown.
Silver Nitrate Test
The reaction of an alkyl halide with silver nitrate in ethanol will result in the formation of a white
or yellow silver halide precipitate that is insoluble in nitric acid. This reaction quite often
proceeds slowly, and occasionally slight warming is necessary.
RX
+ AgNO3
RONO2
+ AgX(s)
It is important to check if the precipitate is soluble in dilute nitric acid. Carboxylic acids form
insoluble silver salts that precipitate, but these dissolve in nitric acid whereas the silver halides
do not.
Procedure: In a test tube, dissolve 0.5 mL of unknown in 0.5 mL of ethanol. Add 0.5 mL of alcoholic
silver nitrate solution. If no sign of a reaction is visible in 3 minutes at room temperature, warm the
mixture in hot water. To ensure that the precipitate is a silver halide and not the salt of a carboxylic
acid, add 0.5 mL of 6M HNO3 to the solution with the precipitate. Stir the mixture. If the precipitate
does not dissolve, you have a positive test for the alkyl halide. Record your observations. Perform
this test on 1-bromobutane, benzoic acid, and your unknown.
Chemistry 2412L
Lucas Test
This test for alcohols depends on the appearance of an alkyl chloride as an insoluble second layer
when an alcohol is treated with a mixture of hydrochloric acid and zinc chloride (Lucas reagent):
ROH + HCl
ZnCl2
RCl + H2O
Primary alcohols do not react at room temperature; therefore, the alcohol is seen simply to dissolve.
Secondary alcohols will react slowly, whereas tertiary, benzylic, and allylic alcohols react instantly.
Procedure: Place 2 mL of Lucas reagent in a test tube and add 3-4 drops of the unknown. Stopper the
test tube and shake vigorously. Tertiary alcohols give an immediate cloudiness in the solution as the
insoluble alkyl halide separates from the aqueous solution. After a short time, the immiscible alkyl
halide will form a separate layer. Secondary alcohols produce a cloudiness after 2-5 minutes.
Primary alcohols dissolve in the reagent to give a clear solution. Some secondary alcohols may have
to be heated slightly to encourage reaction with the reagent. Record your observations. Perform the
test on 1-butanol, 2-butanol, t-butyl alcohol and your unknown.
Note: this test often fails on alcohols with more than six carbon atoms
Bromination Test
Bromine readily adds across the carbon-carbon double bond of an alkene to produce a
dibromoalkane. A red solution of bromine in methylene chloride will quickly become colorless
as the addition reaction with the alkene takes place. The general equation describing the test is:
Br
Br2
(red)
Br
(colorless)
(colorless)
Procedure: Place 3 drops of the unknown in a test tube. Add 5 drops of Br2 in CH2Cl2 one drop at a
time. Note what happens to the red bromine solution as it is added to each tube. Record your
observations. Perform this test on cyclohexane, cyclohexene, and your unknown.
Potassium Permanganate Test
This test is positive for double and triple bonds but not for aromatic rings. It depends on the
conversion of the purple ion MnO4- to a brown precipitate of MnO2 following the oxidation of an
unsaturated compound.
Chemistry 2412L
C
C
+
MnO4(purple)
C
C
OH
OH
+
MnO2
(brown)
Other easily oxidized compounds also give a positive test with potassium permanganate solution.
These include aldehydes, some alcohols, phenols, and aromatic amines.
Procedure: Dissolve 2 drops of a liquid or 25 mg of a solid in 2 mL of water or ethanol. Slowly add
10-20 drops of the potassium permanganate solution drop-wise while shaking. In a positive test, the
purple color of the reagent is discharged, and a brown precipitate of manganese dioxide forms,
usually within 1 minute. If alcohol was the solvent, the solution should not be allowed to stand for
more than 5 minutes because oxidation of the alcohol will begin slowly. Record your observations.
Perform this test on cyclohexene, toluene, and your unknown.
Ignition Test
The presence of an aromatic ring or other centers of unsaturation will lead to the production of a
sooty yellow flame in this test. Compounds that contain little oxygen and have a high carbon-tohydrogen ratio burn at a low temperature with a yellow flame. Compounds that contain oxygen
generally burn at a higher temperature with a clean blue flame.
Procedure: Place a small amount of the compound on a spatula and place it in the flame of a Bunsen
burner. Observe whether a sooty flame is the result. Compounds giving a sooty yellow flame have a
high degree of unsaturation and may be aromatic. Perform this test on naphthalene and your
unknown.
IR
Determine the IR spectrum for your unknown.
GCMS
Follow your instructor’s directions to obtain GCMS data for your unknown.
Additional Data
Elemental analysis, 1H-NMR and 13C-NMR data can be found on your instructor’s website.