QUALITATIVE ORGANIC ANALYSIS
SIM-ORG PROGRAM HELP SECTION
Dr. Scott Frees
Ramapo College of New Jersey
Mahwah, NJ 07430
CONTENTS:
Introduction
Strategy for Identifying and Unknown
Solubility Classification
Functional Group Classification Tests
Derivative Formation and Use
Final Identification of an Unknown Substance
This simulation program includes:
12 organic chemistry functional groups
24 classification tests
21 derivative tests
500 unknowns
GENERAL INTRODUCTION TO QUALITATIVE ORGANIC ANALYSIS
There are two methods for identifying the structure of an unknown organic
compound. The first and older method is to run classification tests to identify the
functional group of the compound following by the production of one or more derivative
compounds to confirm the exact nature of the unknown. The second method is to
determine the spectral properties of the unknown using mainly infrared and proton
magnetic resonance spectroscopy. The first method will be covered in this simulation
program. This program has 12 different functional group classes and 500 different
unknowns. It is planned that the second method will be covered in a later revision of this
program.
The general method to determine the identity of an unknown substance by
classical methods is to gather some introductory information about the compound. Note
the odor, color, and melting or boiling point of the material. Then find its solubility
characteristics by doing a solubility classification as described below. From the
information obtained from the solubility classification run appropriate functional group
tests to identify the group to which the unknown belongs. Then the unknown is
converted into one or more different solids called derivatives. Consulting tables of
derivative melting points one can then identify the exact identity of the unknown
compound.
In order to intelligently conduct the functional group classification tests a
solubility classification is usually done first to narrow down the possible functional group
possibilities.
A problem may arise when an unknown substance has two or more functional
groups in the molecule. This may lead to confusion when interpreting the functional
group and could lead one to the wrong table of derivatives. Such unknowns are more
difficult to identify. There are a few such compounds in this simulation program.
STRATEGY FOR IDENTIFYING AN UNKNOWN
The following steps should be taken to identify an unknown compound:
1. Perform a solubility classification test to determine the possible functional group
classes to which the unknown may belong.
2. Narrow the choices of possible functional groups to one group by performing
appropriate functional group tests.
3. Make one or more derivatives to finally determine the exact identity of the
unknown.
The above approach should lead to a successful identification of an unknown about 80 %
of the time. In other cases, the unknown may pose difficulties that would require
imagination and careful analysis of the data to be successful in its identification.
SOLUBILITY TEST ANALYSIS: Obtain the solubility class for the assigned
unknown. Shown below is a list of possible functional groups for each solubility class.
This classification method is not exact and may need further thought and imagination in
certain cases. These solubility classes and their consequences can be summarized below:
S1
These are very polar compounds which consist of salts of carboxylic acids or
amines. It is also possible the compound is of low molecular weight and has many polar
functional groups such as a carbohydrate.
S2
These compounds are low molecular weight (generally less than 5 carbons) with a
polar functional group such as carboxylic acid, amine, alcohol, aldehyde, or ketone.
A1
Higher molecular weight carboxylic acids fall into this class.
A2
Phenols show this kind of solubility.
B1
Primary, secondary and tertiary amines fall into this class. However, if there are
two or more phenyl groups on the nitrogen, the amine will probably not be basic enough
to form the salt and will, then, be insoluble.
N1
These are higher molecular weight compounds (generally more than 9 carbons)
containing an oxygen atom.
N2
These are medium size molecules (generally containing from 5 to 9 carbons)
containing an oxygen atom.
IN
These are neutral compounds. Alkyl halides and alkanes fall into this class.
FUNCTIONAL GROUP ANALYSIS: Below are listed 24 chemical tests that
could be used to help identify an unknown. The tests are listed in numerical/alphabetical
order.
1. Introduction to qualitative tests
2. 2,4-dinitrophenylhydrazine (for aldehydes and ketones)
3. Acetyl chloride (for acidic hydrogen compounds such as alcohols)
4. Basic hydrolysis (for amides, esters and nitriles)
5. Beilstein test (for halogenated compounds)
6. Benedict test (for aldehydes and reducing sugars)
7. Bromine in carbon tetrachloride (for alkenes and alkynes)
8. Ceric nitrate (for alcohols and phenols)
9. Chromic acid (for aldehydes, primary and secondary alcohols)
10. Combustion test (for flammable or combustible compounds)
11. Ferric chloride (for phenols)
12. Ferric hydroxamate (for esters, acid chlorides and acid anhydrides)
13. Ferrous hydroxide (for nitro compounds)
14. Hinsberg test (to distinguish primary, secondary and tertiary amines)
15. Hydroxylamine hydrochloride (for aldehydes and ketones)
16. Iodoform test (for methyl carbonyl compounds)
17. Lucas test (to distinguish primary, secondary and tertiary alcohols of six
carbons or less)
18. Nitrous acid (to distinguish primary, secondary and tertiary amines)
19. pH in ethanol/water (to distinguish low molecular weight acidic or basic
compounds)
20. Potassium permanganate (for compounds that can be oxidized)
21. Silver nitrate in ethanol (for Sn1 reactions of alkyl halides)
22. Sodium fusion (for compounds containing halogen, nitrogen or sulfur)
23. Sodium iodide in acetone (for Sn2 reactions of alkyl chlorides or bromides)
24. Solubility classification (for general classification or organic compounds)
25. Tollens test (for aldehydes and reducing sugars)
Below are listed the 12 functional group classes that appear in this program. After each
functional group name are hints about tests that could be used to help narrow the
unknown possibilities. The groups are listed in numerical/alphabetical order.
1. Acid – Solubility class S2 or A1; pH test; combustion test
2. Acid chloride – Solubility class S2 or A1; pH test; Beilstein test; ferric
hydroxamate; sodium fusion; combustion test
3. Acid anhydride – Solubility class S2 or A1; pH test; ferric hydroxamate;
combustion test
4. Alcohol – Solubility class S2, N1 or N2; acetyl chloride; ceric nitrate; chromic
acid; Lucas test; potassium permanganate; combustion test
5. Aldehyde – Solubility class S2, N1 or N2; 2,4-dinitrophenylhydrazine;
Benedict test; chromic acid; hydroxylamine hydrochloride; potassium
permanganate; Tollens test; combustion test
6. Amide – Solubility class N1 or N2; basic hydrolysis; sodium fusion;
combustion test
7. Amine (primary and secondary) – Solubility class B1, N1 or N2; Hinsberg
test; nitrous acid; sodium fusion; combustion test
8. Amine (tertiary) – Solubility class B1, N1 or N2; Hinsberg test; nitrous acid;
sodium fusion; combustion test
9. Ester – Solubility class N1 or N2; basic hydrolysis; ferric hydroxamate;
combustion test
10. Ketone – Solubility class S2, N1 or N2; 2,4-dinitrophenylhydrazine;
hydroxylamine hydrochloride; iodoform test; combustion test
11. Nitrile – Solubility class N1 or N2; basic hydrolysis; sodium fusion; solubility
test
12. Phenol – Solubility class A2; acetyl chloride; ceric nitrate; ferric chloride;
combustion test
DERIVATIVE USAGE: Below are listed 21 derivatives that could be prepared
from various unknowns to help in a final determination of the unknown. The derivatives
are listed in numerical/alphabetical order.
1. Introduction to derivative use
2. 1-naphthylurethane (for alcohols and phenols)
3. 2,4-dinitrophenylhydrazone (for aldehydes and ketones)
4. 3,5-dinitrobenzoate (for alcohols)
5. Acetamide (for primary and secondary amines)
6. Acid from hydrolysis (for acid chlorides, anhydrides, esters, amides and
nitriles)
7. Amide (for carboxylic acids, acid chlorides and anhydrides)
8. Anilide (for carboxylic acids, acid chlorides and anhydrides)
9. Benzamide ( for primary and secondary amines)
10. Benzenesulfonyl chloride (for primary and secondary amines)
11. Bromo derivative (for phenols)
12. Methiodide (for tertiary amines)
13. Neutralization equivalent (for acids, esters, amides and nitriles)
14. Oxime (for aldehydes and ketones)
15. Phenylhydrazone (for aldehydes and ketones)
16. Phenylurethan (for alcohols)
17. Picrate (for tertiary amines)
18. p-Nitrobenzyl ester (for carboxylic acids)
19. p-Nitrophenylhydrazone (for aldehydes and ketones)
20. p-Toluenesulfonamide (for primary and secondary amines)
21. p-Toluidide (for primary and secondary amines)
22. Semicarbazone (for aldehydes and ketones)
SOLUBILITY CLASSIFICATION
The solubility of an organic compound in various solvents can give valuable
information about the unknown. The general rule of “like dissolves like” or “polar
compounds dissolve more readily in polar solvents” is useful. Also, organic acids (such
as carboxylic acids and phenols) react with bases to form water soluble salts and organic
bases (such as amines) react with acids to form water soluble salts. It should be noted
that the polarity of an organic compound is increased by the kind and number of polar
functional groups in the molecule and that the polarity decreases as the size of the non
polar aliphatic group (define aliphatic group in a hyperlink) in the molecule increases.
With this background, one begins the solubility classification by adding 3 drops
or 3 mg of the unknown to 3 ml of water and shaking the mixture. If the unknown
dissolves, it is a polar compound and in placed in solubility group S1. An unknown in
class S1 is then tested as above using ether as the solvent. If it dissolved in both water
and ether it is then placed in class S2. For unknowns that do not fall into either class S1
or S2, the unknown’s solubility in 5% sodium bicarbonate is determined. If it is soluble,
the unknown is placed in class A1. If it is not soluble, the solubility in 5% sodium
hydroxide is studied. If it is soluble at this point, the unknown belongs in class A2. If an
unknown is insoluble to this point it is next tested for solubility in 5% hydrochloric acid.
Compounds soluble in 5% hydrochloric acid are placed in solubility class B1. For
compounds insoluble to this point the next solvent to try is concentrated sulfuric acid.
Unknowns soluble in only this acid are placed in solubility class N1. A further
distinction can be made for compounds soluble in concentrated sulfuric acid by testing
their solubility in 85% phosphoric acid. Such compounds that are soluble in 85%
phosphoric acid are placed in class N2. Finally, for compounds insoluble to this point are
placed in class IN.
These solubility classes and their consequences can be summarized below:
S1
These are very polar compounds which consist of salts of carboxylic acids or
amines. It is also possible the compound is of low molecular weight and has many polar
functional groups such as a carbohydrate.
S2
These compounds are low molecular weight (generally less than 5 carbons) with a
polar functional group such as carboxylic acid, amine, alcohol, aldehyde, or ketone.
A1
Higher molecular weight carboxylic acids fall into this class.
A2
Phenols show this kind of solubility.
B1
Primary, secondary and tertiary amines fall into this class. However, if there are
two or more phenyl groups on the nitrogen, the amine will probably not be basic enough
to form the salt and will, then, be insoluble.
N1
These are higher molecular weight compounds (generally more than 9 carbons)
containing an oxygen atom.
N2
These are medium size molecules (generally containing from 5 to 9 carbons)
containing an oxygen atom.
IN
These are neutral compounds. Alkyl halides and alkanes fall into this class.
The results of a solubility classification should not be strictly interpreted as there
are many overlaps. Use the results of this classification only as a focus into which
classification tests should be done first.
FUNCTIONAL GROUP CLASSIFICATION TESTS
INTRODUCTION TO QUALITATIVE TESTS - The first test that should be
done is a solubility test to determine the class or classes to which the unknown belongs.
From the results of the solubility tests, some idea of the type of organic compound should
be evident. If the solubility test results put the unknown substance in the ‘Neutral’
section, it is recommended that the classification tests be done in this order: aldehydes,
ketones, alcohols, esters, amides, nitriles, ethers, alkenes and alkynes. Select a test from
the list of tests that would help confirm the presence or absence of the suspected
functional group class. Do as many tests that may be necessary to absolutely confirm the
functional group to which the unknown belongs. Be careful to interpret correctly the test
results for those unknowns that may contain two or more functional groups. At that
point, proceed to the preparation of derivatives to identity the exact identity of the
unknown.
2,4-DINITROPHENYLHYDRAZINE TEST (for aldehydes and ketones) - This test will
be positive for an aldehyde or ketone as indicated by the formation of a yellow, orange or
red precipitate which is called a 2,4-dinitrophenylhydrazone. This precipitate can also be
used as a derivative for the unknown if its melting point is determined (see below for
derivative use). The color of the precipitate can help further identify the extent of
conjugation for the carbonyl group. Highly conjugated aromatic aldehydes or ketones
generally give red solids whereas non conjugated carbonyl compounds give yellow
products.
ACETYL CHLORIDE (for acidic hydrogen compounds) - This test will help identify
carboxylic acids, phenols and alcohols. A positive test will be noted by the evolution of
heat which may be hard to detect. So, this test may give false positive or negative tests
depending on the expertise of the person doing the test. In some cases, a solid (usually
white) may form. If this happens, the solid, if isolated and its melting point is
determined, could be used as a derivative for the unknown. If water is present in the
unknown, the test will probably give a false positive test as acetyl chloride reacts
vigorously with water.
BASIC HYDROLYSIS (for amides, esters and nitriles) - Amides and esters can be
hydrolyzed by heating in a sodium hydroxide solution. This reaction pH gives the acid as
a water soluble carboxylate salt. Acidifying this solution with concentrated hydrochloric
acid would result in a precipitate if the carboxylic acid is water insoluble. If this
precipitate is formed, it should be filtered and used as a derivative for the unknown.
BEILSTEIN TEST (for halogenated compounds) - Placing a small amount of an organic
compound on the end of a copper wire and heating it in the open flame of a Bunsen
burner results in a transient green color in the flame if the compound contains a halogen
atom. If the unknown is volatile, it may evaporate before it burns resulting in a negative
test.
BENEDICT TEST (for aldehydes and sugars) – When easily oxidized organic compound
(such as aldehydes and reducing sugars) is heated in Benedict’s solution (which is a blue
solution containing a complexed copper (II) ion) a brick red precipitate of cuprous oxide
forms. If the unknown is not soluble in the reagent a negative test may be observed due
to the lack of a reaction.
BROMINE IN CARBON TETRACHLORIDE (for alkenes and alkynes) – When a
solution bromine in carbon tetrachloride is added dropwise to an unknown compound, the
brownish color of elemental bromine disappears as the bromine adds to the unsaturated
organic compound.
CERIC NITRATE (for alcohols and phenols) – Alcohol with 10 carbons or less will give
a red color with ceric nitrate solution whereas phenols will give a green-brown to brown
precipitate. Easily oxidized compounds may destroy the ceric nitrate solution before the
test may be observed.
CHROMIC ACID (for aldehydes, primary and secondary alcohols) – Easily oxidized
compounds convert the red chromium (VI) ion to a green chromium (III) precipitate.
COMBUSTION (for flammable or combustible organic compounds) – When a few
milligrams of an organic liquid or solid are placed directly into a Bunsen burner flame
they often burn. Note that highly halogenated organic compounds may not burn. Very
volatile compounds may evaporate before burning or burn very rapidly. The manner in
which a compound burns can give some information about its nature. Highly oxygenated
compounds burn with a blue flame, aliphatic compounds give a yellow flame and
aromatic compounds give a sooty flame.
FERRIC CHLORIDE (for phenols) – Some (but not all) phenols give a color when ferric
chloride solution is added. This test is not a definitive one and the results should be
carefully evaluated.
FERRIC HYDROXAMATE (for esters, acid chloride and anhydrides) – Esters of
carboxylic acids give a magenta color with this reagent. Acid chloride and anhydrides
give a magenta or burgundy color with the test reagent.
FERROUS HYDROXIDE (for nitro compounds) – Most compounds that contain a nitro
group will give a brown to red-brown precipitate of ferric hydroxide by oxidation of
ferrous hydroxide.
HINSBERG TEST (to distinguish primary, secondary and tertiary amines) –
Benzenesulfonyl chloride can be used to distinguish primary, secondary and tertiary
amines. The amine functional group must be confirmed before this test can be performed
as the test will give very confusing results with any other functional group. Primary
amines give a solid benzenesulfonamide product that is soluble in 5% sodium hydroxide.
Secondary amines give a solid benzenesulfonamide product that is insoluble in 5%
sodium hydroxide. Tertiary amines do not react with benzenesulfonyl chloride.
HYDROXYLAMINE HYDROCHLORIDE (for aldehydes and ketones) – Aldehydes
and most ketones give a red color when added to a solution of hydroxylamine
hydrochloride in ethanol-water that has a universal indicator added.
IODOFORM TEST (for methyl carbonyl compounds) – This test is mainly used to
identify methyl ketones. The iodoform regent iodinates the methyl group which they
cleaves in the basic solution
One should confirm the presence of a carbonyl group in the unknown before this test is
done as misleading results could occur with other compounds. For example,
acetaldehyde and alcohols that have a methyl group bonded to the C-OH group can also
give a positive test since such an alcohol can be oxidized to a methyl ketone by the
iodoform reagent.
LUCAS TEST (to distinguish primary, secondary and tertiary alcohols of six carbons or
less) – A solution of zinc chloride in aqueous hydrochloric acid can be used to distinguish
primary, secondary and tertiary alcohols. The unknown compound must be soluble in the
reagent in order for the test to be valid. When a tertiary alcohol is added dropwise to the
reagent, an immediate second layer or a liquid alkyl chloride is formed. Secondary
alcohols form a second layer of the insoluble alkyl chloride in three to 5 minutes.
Primary alcohols are unreactive with the Lucas reagent.
NITROUS ACID (to distinguish primary, secondary and tertiary amines) – Primary
aromatic amines give nitrogen gas evolution with the nitrous acid reagent. Other
aromatic amines can undergo coupling reactions to form colored products.
pH IN ETHANOL (to distinguish low molecular weight acidic or basic compounds) –
The pH of compounds that are soluble in water or aqueous alcohol can be measured. If
the pH is in the acid range the compound can be a carboxylic acid, acid chloride or
anhydride. If the pH is in the basic range, the compound may be an amine. Organic salts
may hydrolyze in water which can lead to acidic or basic solutions.
POTASSIUM PERMANGANATE ( for compounds that can be oxidized) – Organic
compounds that can be readily oxidized will convert the purple of the permanganate ion
to a brown precipitate of manganese dioxide. Such organic compounds include:
aldehydes, reducing sugars, primary or secondary alcohols and some alkenes and alkynes.
SILVER NITRATE IN ETHANOL (for alkyl halides that can undergo Sn1 reactions) –
Tertiary alkyl halides will give a white to yellow silver halide precipitate with this
reagent. Some secondary halides will react more slowly. Aryl and vinyl halides do not
react.
SODIUM FUSION (for compounds that contain halogen, nitrogen or sulfur) – When an
organic compound is placed in molten elemental sodium the molecules are violently
destroyed. Any halogen, nitrogen or sulfur in the original molecule are converted to ionic
materials which are then identified. The halide is identified by precipitation with silver
ions. The sulfide ion is identified by precipitation with lead ions. The cyanide ion
formed the nitrogen in the molecule is converted into Prussian blue by ferrous sulfate.
SODIUM IODIDE IN ACETONE (for alkyl halides that can undergo Sn2 reactions) –
Primary and some secondary alkyl chlorides or bromides will give a precipitate of
sodium iodide in the reagent. Alkyl iodides will not give the precipitate. Aryl or vinyl
halides do not react.
SOLUBILITY (for general classification of organic compounds) See SOLUBILITY
CLASSIFICATION section above.
TOLLENS TEST (for aldehydes and reducing sugars) – Water soluble aldehydes and
reducing sugars give a silver mirror or black precipitate of elemental silver with the
Tollens reagent.
DERIVATIVE FORMATION AND USE
INTRODUCTION TO DERIVATIVE USE - Derivative Tests - Once the
classification tests have indicated an organic family of compounds (e.g an aldehyde), one
can see if derivatives of the unknown can be synthesized to help in its identification.
Based on the results of the classification tests, which derivative tests to use can be
determined. On selecting the relevant test, the results will be illustrated. If the derivative
test is positive, it is evidence that the correct family of compound has been chosen, and
the melting point of the derivative should be recorded on a data sheet. Order all the
derivative tests relevant to the search (e.g. for an aldehyde, obtain the melting points of
both the semicarbazone and 2,4-dinitrophenylhydrazine derivatives) and then proceed to
the final identification of the unknown substance.
1-NAPHTHYLURETHANE DERIVATIVE – (for alcohols and phenols)
2,4-DINITROPHENYLHYDRAZONE – (for aldehydes and ketones)
3,5-DINITROBENZOATE – (for alcohols)
ACETAMIDE – (for primary and secondary amines)
ACID FROM HYDROLYSIS – (for acid chloride, anhydride, ester, amides, and nitriles)
AMIDE – (for carboxylic acids, acid chlorides, and anhydrides)
ANILIDE – (for carboxylic acids, acid chlorides, and anhydrides)
BENZAMIDE – (for primary and secondary amines)
BENZENESULFONAMIDE – (for primary and secondary amines)
BROMO DERIVATIVE – (for phenols)
METHIODIDE – (for tertiary amines)
NEUTRALIZATION EQUIVALENT – (for acids, amides, esters and nitriles)
OXIME – (for aldehydes and ketones)
PHENYLHYDRAZONE – (for aldehydes and ketones)
PHENYLURETHAN – (for alcohols and amines)
PICRATE – (for tertiary amines)
p-NITROBENZYL ESTER – (for carboxylic acids)
p-NITROPHENYLHYDRAZONE - (for aldehydes and ketones)
p-TOLUENESULFONAMIDE – (for primary and secondary amines)
p-TOLUIDIDE – (for primary and secondary amines)
SEMICARBAZONE – (for aldehydes and ketones)
FINAL IDENTIFICATION OF AN UNKNOWN SUBSTANCE
Tables of organic substances can be used to identify the unknown based on the
results of the classification tests and the derivative melting point results.
TABLES OF UNKNOWNS – Once the derivative melting point data have been recorded
enter the Tables of Unknowns by selecting the suspected functional group class. Here a
list of organic compounds separated by type will appear. Select the family that the
unknown belongs to. A list of all the compounds of that type, presented in order of
increasing boiling/melting point will appear. Also listed are the melting points of any
derivatives that can be synthesized from the class of the unknown compound. By
matching the table data with the unknown compound data obtained above, one can
identify the unknown.
ANSWER TRIAL - Based on all the melting point data in the Tables of Unknowns, one
will now have an idea of what the unknown sample is. To see if you are correct, you can
enter it into the program by selecting Answer Trial. Make sure that you select the
compound correctly, exactly as it appears in the table of unknowns. If you are correct, a
congratulation message will appear. If you are wrong, first re-check your of the unknown.
If it is still incorrect, then you will need to go back into the program in order to correctly
identify the unknown sample.