Download The presence of an aromatic ring or other

Chemistry 2412L
Dr. Sheppard
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.
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. Be sure to add a boiling stone and take care to distill slowly so that
the temperature reading is accurate.
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 than 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 than five carbon atoms are soluble in water
and form neutral solutions (pH = 7).
Chemistry 2412L
Dr. Sheppard
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
Dr. Sheppard
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 tube. Add 3 drops (or 50 mg of solid) of your
compound (known or 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.
Beilstein Test
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 compound (known or unknown). Now, heat the wire in the
Bunsen burner flame again (in the lower outside part of the flame). The compound 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.
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
Dr. Sheppard
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 your compound (known or unknown) 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 indicates 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 your compound (known or 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 your compound (known or 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, ~1 mL of KI3 solution. Warm the solution slightly. 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, 2-butanol, and your unknown.
Chemistry 2412L
Dr. Sheppard
2,4-Dinitrophenylhydrazine Test
This reagent reacts with ketones and aldehydes, and is used to distinguish these functional
groups from other carbonyl compounds, such 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 your compound (known or unknown) in 1 mL of
ethanol. Add 1 mL of 2,4-dinitrophenylhydrazine 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 your compound (known or unknown) and 0.2 mL 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 or 0.1 g of your compound (known or 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
Chemistry 2412L
Dr. Sheppard
halide. Record your observations. Perform this test on 1-bromobutane, benzoic acid, and your
unknown.
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 your compound (known
or 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 your compound (known or 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
Dr. Sheppard
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 compound (known or unknown) 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 your compound (known or unknown) 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.