8/9/2019 Org. Chem. Manual, 2013-1.pdf
1/53
University of Baghdad College of PharmacyDepartment of Pharmaceutical Chemistry
A laboratory manual on
for second year students
Azhar M. Jaism (M. Sc. Ph. Chem.)
Duraid H. Mohammad (M. Sc. Ph. Chem.)
Oct., 2012
HO O OH
O
O
8/9/2019 Org. Chem. Manual, 2013-1.pdf
2/53
ii
Contents
Tools and glass wares .....................................................................................................iii
Qualitative analysis of organic compounds.....................................................................
Determination of solubility class ......................................................................................
Identification of alcohols .................................................................................................6
Identification of aldehydes and ketones .........................................................................
Identification of phenols ................................................................................................ 8
Identification of carboxylic acids ....................................................................................6
Identification of carboxylic acids salts ............................................................................37
Identification of alkyl and aryl halides ............................................................................39
Identification of amines .................................................................................................43
8/9/2019 Org. Chem. Manual, 2013-1.pdf
3/53
iii
Tools and Glass Wares
Below are the mostly used tools and glass wares in organic chemistry laboratory
(courses II and III):
reagent bottles glass stoppers dropper
Bunsen burner washing bottle beaker
test tubes test tube holder test tube holder
test tube rack tripod stand wire gauze
8/9/2019 Org. Chem. Manual, 2013-1.pdf
4/53
lit
P
filt
glass
us paper
tri dish
r papers
od (stirr
r)
gradu
grad
w
iv
spatula
ted cyli
ated pip
ater bath
ders
ette burett
spatul
funnel
and fun
Hood
el stand
8/9/2019 Org. Chem. Manual, 2013-1.pdf
5/53
Org. Chem. Lab.
1
Qualitative Analysis of
Organic Compounds
ualitative analysis of organic compounds helps identify andcharacterize unknown organic compounds. Many organic
compounds are usually a component of a mixture of several
compounds that might be considered as impurities. These impurities may
be side products resulted during the preparation of the organic compound
or may be decomposition products of the original pure organic compound
and this occurs during storage under unsuitable conditions. On the other
hand, some compounds may be obtained and stored pure because of their
high degree of stability. In most cases a good separation and purification
should precede qualitative analysis of organic compounds so thatidentification will be successful.
The qualitative analysis of any organic compound should follow
these steps:
1. Physical properties studying.
• State of the organic compound (solid, liquid, gas)
• Determination of the melting point or boiling point.
• Color, taste, and odor of the compound.
•
Determination of the solubility group (solubility classificationaccording to the general families).
2. Chemical properties studying.
• Effect of the compound or its solution on litmus paper.
• Determination of elements in the organic compound (nitrogen,
sulfur, or halogens).
• Detection of the organic groups, i.e. group classification to get
more specific families.
• Specific classification tests.
•
Preparation of derivatives.
Q
8/9/2019 Org. Chem. Manual, 2013-1.pdf
6/53
Org. Chem. Lab.
2
Determination of Solubility Class
olubility class determination gives an idea about the type of
the functional group present in the compound, the polarity
and molecular weight of the compound, and the nature of thecompound (acidic, basic, neutral). This is accomplished by testing the
solubility of the compound in either of the following sets of solvents:
distilled water, 5% sodium hydroxide solution, 5% sodium bicarbonate
solution, 5% hydrochloric acid solution, and cold concentrated sulfuric
acid, or distilled water and ether.
It is well known that hydrocarbons are insoluble in water becauseof their non polar nature. If an unknown compound is partially soluble in
water, then this indicates that a polar functional group is present.
Additionally, solubility in certain solvents often leads to more specific
information about the functional group. For example, benzoic acid isinsoluble in water, but is converted by 5% sodium hydroxide solution to a
salt, sodium benzoate, which is readily water soluble. In this case, then,
the solubility in 5% sodium hydroxide solution of a water insoluble
unknown is a strong indication of an acidic functional group. Predictionof the molecular weight and size may sometimes be obtained from the
result of solubility tests. For example, in many homologous series of
monofunctional compounds, the members with fewer than about five
carbon atoms are water soluble, whereas the higher homologs are
insoluble.The first step to follow is to test the solubility of the compound in
water. Generally and for solubility classification purposes, the compound
is said to be soluble in any solvent if it dissolves to the extent of about 3
% (0.1 gm/3 ml or 0.2 mL/3 mL). This is achieved by dissolving about
0.1 gm of the solid compound or 3-4 drops of the liquid compound in
gradually increasing volumes of the solvent up to 3 ml (max. allowed
volume is 3 ml) with shaking. This technique is the one that should be
followed in solubility classification to determine whether the compound
is soluble or insoluble in that solvent.When solubility in dilute acid or dilute base is being considered, the
significant observation to be made is whether it is significantly more
soluble in aqueous acid or aqueous base than in water. Such increased
solubility is the desired positive test for acidic or basic functional groups.
Below is a very useful scheme for solubility classification:
S
8/9/2019 Org. Chem. Manual, 2013-1.pdf
7/53
Org. Chem. Lab. 3
I
H2O
5% NaOH Ether
5% HCl 5% NaHCO3
96%
cold H2SO
4
insol. sol.
sol. insol.
l i t m u s u
n c h a n g e d
l i t m u
s b l u e
l i t m u
s r e d insol. sol.
insol. sol.
insol. sol.
insol. sol.
N
I I I I A2
B
I I I I A1
I I I I S 1
I I I I S 2
Discussion on solvents
Water Water is a polar solvent with a dielectric constant equals to 80. It
has the ability to form hydrogen bonding and can act either as an acid or a
base. Therefore it can dissolve:
• Salts of ammonium ion (RNH4+) or organic acids salts with
alkali metal cations (RCOO-).
• Ionic compounds.
• Polar compounds “like dissolves like”.
• Organic compounds with low molecular weight (less than 5
carbon atoms) such as alcohols, aldehydes, ketones, and
carboxylic acids.
Water is useful to determine the degree of acidity of a compound,
even if the compound is insoluble in water, using litmus paper (acidic,
basic, or neutral).
Water is the first solvent used to determine the solubility class of a
compound. If the compound is water soluble, the next step is to test its
solubility in ether.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
8/53
Org. Chem. Lab. 4
Ether Ether is a non-polar solvent having a dielectric constant of 4.3. It
cannot form hydrogen bonding (unassociated liquid). Therefore, it differsfrom water in that it cannot dissolve ionic compounds such as salts. It
dissolves most water insoluble compounds; therefore, in the
determination of solubility class, the importance of ether is for water-
soluble compounds only and no further solubility tests using theremaining solvents are to be done.
Accordingly two probabilities are there:
1. Compounds soluble in both water and ether.These compounds:
• are non-ionic.
• contain five or less carbon atoms.
• contain an active group that is polar and can form hydrogen
bonding.• contain only one strong polar group.
This division of compounds is given S 1class and includes, e.g., aldehydes,ketenes, and aliphatic acids.
2. Compounds soluble in water only (but not in ether).
These compounds:
• are ionic.
• contain two or more polar groups with no more than four
carbon atoms per each polar group.
This group is classified as S 2 class and includes ionic salts such as salts ofcarboxylic acids and amines and compounds with more than one active
group such as poly hydroxylated compounds and carbohydrates.
Note that solubility in ether is tested only for water-soluble
compounds. For water insoluble compounds use the left side of the
solubility classification scheme, i.e. test solubility in sodium hydroxide
rather than ether.
5% NaOH & 5% NaHCO3
Water insoluble compounds must be tested first in 5% sodiumhydroxide solution which is a basic solvent. It reacts with water insoluble
compounds that are capable of donating protons such as strong and weak
acids. The stronger the acid, the weaker the base it can react with. Water
insoluble compounds that dissolve in 5% sodium hydroxide solution must
also be tested for solubility in 5% sodium bicarbonate solution.
Therefore, for water insoluble acidic compounds sodium hydroxide
solution is considered as a detecting solvent whereas sodium bicarbonate
solution is called as a sub classifying solvent since it can react with strong
acids only. That is, these two solvents give an idea about the aciditydegree of the compound. Note that testing solubility in 5% sodium
bicarbonate solution is not needed if the compound is insoluble in 5%
8/9/2019 Org. Chem. Manual, 2013-1.pdf
9/53
Org. Chem. Lab. 5
• Show by a chemical equation only how can
concentrated sulfuric acid dissolve oxygen
containing neutral compounds.
• Depending on the chemical structure discuss
your results of solubility class of the compounds
given to you.
sodium hydroxide solution, but rather, 5% hydrochloric acid solution
should be used.
Two probabilities are there:
1. Compounds soluble in both bases. This group is given class A1. This class includes strong acids that
have the ability to react with weak bases (carboxylic acids) and phenolswith electron withdrawing groups (e.g., –NO2). Protons are weakly
attached and can be given easily.
2. Compounds soluble in 5% sodium hydroxide solution only. This group is given class A2 and it includes phenols, amides, and
amino acids (weak acids).
5% HCl If the compound is insoluble in water and sodium hydroxide
solution (and, hence, insoluble in sodium bicarbonate solution too), thismeans that the compound is not an acid but, rather, is either a basiccompound or a neutral compound. 5% hydrochloric acid solution, which
can dissolve basic compounds such as amines (RNH2), is used for such a
compound. If the compound is soluble in this solvent, then it is givenclass B. This class includes primary, secondary, and tertiary amines.
Cold concentrated H2SO4 If the compound is insoluble in water, 5% sodium hydroxide solution,
and 5% hydrochloric acid solution, solubility in cold concentrated
sulfuric acid should be tested. If the compound is soluble in this acid, it
belongs to class N which includes neutral compounds such as high
molecular weight alcohols, aldehydes, ketones, esters, and ethers (more
than four carbon atoms), and unsaturated hydrocarbons. On the other
hand, compounds that are insoluble in cold concentrated sulfuric acid
belong to class I which includes inert aliphatic (saturated) hydrocarbons,
aromatic hydrocarbons, haloalkanes, and aryl halides.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
10/53
Org. Chem. Lab. 6
H3C OH
methanol
cyclohexanol(cyclic)
OH
H2C
OHH3C
ethanol
C
H3C CH3H3C
tert -butanol
CH2
benzyl alcohol(aromatic)
H2C
CHH3C
sec-butanol
CH3
OH
OH
OH
R OH
the generalformula
Identification of Alcohols
lcohols are organic compounds that may be considered as
derivatives of water in which one of the hydrogen atoms of
water molecule (H-O-H) has been replaced by an alkyl or
substituted alkyl group. Therefore, properties of alcohols may be relatedto properties of both water and hydrocarbons. The alkyl group could be
primary, secondary, or tertiary, and may be open chain or cyclic.
Accordingly, alcohols may be defined as organic compounds that contain
hydroxyl groups attached to alkyl, substituted alkyl, or cyclic alkyl group.
Physical properties
• Alcohols are colourless liquids with a special faint odour. Benzylalcohol and cyclohexanol have characteristic odours.
• Aliphatic alcohols burn with blue flame (without smoke) while
aromatic alcohols burn with yellow smoky flame.• Boiling points of alcohols are considerably high (being associated
liquids); they increase as the molecular weight (number of carbons)
increases.
• Alcohols are miscible with water except benzyl alcohol,
cyclohexanol, and sec-butanol (which is very slightly soluble in
water.
A
8/9/2019 Org. Chem. Manual, 2013-1.pdf
11/53
Org. Chem. Lab. 7
Which alcohol has solubility class S 2, what are the
structural requirements present in this alcohol thatmade it under this solubility class?
2[(NH4)2Ce(NO3)6] + RCH2OH
ceric ammonium
nitrate
RC
O
H + 2[(NH4)2Ce(NO3)5] + 2HNO3
alcohol aldehyde
Solubility classification
Alcohols are polar compounds because of the presence of the
hydroxyl group which is also responsible for their ability to form
hydrogen bonding. The degree of the polarity depends on the size
of the alkyl side chain; the polarity decreases as the size of the
alkyl side chain increases, or in another word, as the hydroxyl
group /hydrocarbon ratio of alcohols increases, their watersolubility increases and vice versa. Besides, low molecular weight
alcohols are soluble in water due to hydrogen bonding ability withwater molecules. Therefore, alcohols that are soluble in water and
ether are classified under class S 1 such as ethanol and methanol.
Alcohols that are insoluble in water are related to class N such as
benzyl alcohol, sec-butanol, and cyclohexanol.
Chemical properties
• Alcohols are neutral compounds that don’t change the colour of
litmus paper.
• All reactions of alcohols are related to its active hydroxyl group
and are of two types:
a)
removal of the hydroxyl itself as in the reaction with hydrogenhalides to form alkyl halides or in the dehydration reaction to
form a double bond.
b) removal of the proton only from the active hydroxyl as in the
formation of esters or in the reaction with active metals such as
sodium.
1. General test (Ceric ammonium nitrate reagent)
Ceric ammonium nitrate (yellow solution) is an oxidizing agent
that reacts with alcohols to give a red complex and with phenols to give a brown to greenish brown precipitate.
Each mole of the alcohol requires two moles of the reagent.
The red coloured complex is an intermediate for the oxidation ofalcohols by the Ce (IV) solution. This red colour disappears after a
reasonable time due to completing the oxidation of this intermediate and
8/9/2019 Org. Chem. Manual, 2013-1.pdf
12/53
Org. Chem. Lab. 8
(NH4)2Ce(NO3)6 + ROH
ceric ammonium
nitrate
(yellow)
(NH4)2Ce(NO3)5 + HNO3
alcohol
(red)
OR
C
OH
H
H3C
the reduction to the colourless Ce (III) solution producing the
corresponding aldehyde or ketone.
Procedure
• Water soluble (miscible) alcohols;
mix two drops of the alcohol with one drop of ceric ammoniumnitrate solution. A red complex indicates a positive test.
• Water insoluble (immiscible) alcohols;
mix two drops of the alcohol with 0.5 ml dioxane, shake well, andadd one drop of the reagent to get a positive red complex.
This test gives positive results with primary, secondary, and
tertiary alcohols (up to 10 carbons), poly hydroxylated compounds such
as carbohydrates, and hydroxylated carboxylic acids, aldehydes and
ketones.
2. Specific tests
a) Iodoform (Haloform) test
This test is specific for alcohols which have a free methyl group
and a hydrogen attached to the carbon bearing the hydroxyl group such as
ethanol and sec-butanol.
The overall reaction is:
The alcohol is oxidized to the corresponding aldehyde or ketone by
the action of the produced oxidizing agent 'sodium hypoiodite', whichalso causes the aldehyde or ketone to be tri-iodinated on the terminal
methyl group producing iodoform as a yellow precipitate.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
13/53
Org. Chem. Lab. 9
ZnCl2 + HCl ZnCl3- + H+
+ HClC
R
R
R
OH
ZnCl2
+ H2OC
R
R
R
Cl
tertiary alcoholtertiary alkyl halide
insoluble in water
Procedure
(Note: read the procedure carefully and completely before starting)
Dissolve about 3 drops of the alcohol in about 2 mL of distilled
water (or 2 mL of dioxane for water insoluble compounds), add about 1
ml of 10% sodium hydroxide solution, then add iodine solution drop wise
with shaking until either a yellow iodoform precipitate is formed, inwhich case the test is positive and is completed, or the dark colour of the
iodine solution is present. In the latter case allow the solution to stand for
3 minutes during which period check for the appearance of the yellow
precipitate at the bottom of the test tube. If there is no precipitate, warm
the solution in water bath (60 ˚C) for about 3 minutes with shaking from
time to time and check for the yellow precipitate. During warming, if the
colour of iodine disappears, add few additional drops of iodine solution
with shaking until either the yellow precipitate is formed or the dark
iodine colour persists, and then complete warming. Then get rid of the
excess iodine by the addition of 10% sodium hydroxide solution drop
wise with shaking to obtain the yellow precipitate. If the precipitate is not
formed, allow the solution to stand for 10 minutes to get the positive
result. Finally if no precipitate is formed after the 10 minutes- standing
period, dilute the solution with an equal volume of distilled water to
obtain the iodoform precipitate. It is important to proceed through all
these steps so that only at the final step you can say that the test is
negative.
Both ethanol and sec-butanol give positive iodoform test and they
can be differentiated only by testing their solubility in water; sec-butanolis less soluble in water than ethanol.
b) Lucas test
This test often provides classification informations on alcohols and
is used to distinguish between the different types of alcohols (primary,
secondary, or tertiary). It depends on the formation of alkyl chloride as a
second liquid phase.
Lucas reagent is prepared from anhydrous zinc chloride andconcentrated hydrochloric acid. Zinc chloride is added to increase the
ionization of hydrochloric acid.
Benzyl alcohol shows the fastest positive result. Tertiary alcohols
are faster in the formation of conjugated halides than secondary alcohols.
Primary alcohols and methanol don’t react and don’t form two layers.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
14/53
Org. Chem. Lab. 10
Procedure
Mix 2-4 drops of the alcohol with few drops of Lucas reagent andobserve the results:
• benzyl alcohol gives immediate result as shown by the appearanceof two phases.
•
tertiary alcohols give two phases that separate within 2-3 minutes.• secondary alcohols give two phases that separate after 15-20
minutes (giving a cloudy solution).
• in primary alcohols one layer appears.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
15/53
Org. Chem. Lab. 11
C O
C
O
HR
C
O
HH3C
CH
O
CH
O
OH
C
O
CH3H3CC
CH3
O
CCH3
O
CH2
C
O
formaldehyde acetaldehyde benzaldehyde
salicylaldehydeacetone acetophenon
benzyl methyl ketone benzophenone
Identification of Aldehydes and Ketones
ldehydes are compounds of the general formula RCHO;
ketones are compounds of the general formula R Ŕ CO. The
groups R and Ŕ may be aliphatic or aromatic, and in one
aldehyde, formaldehyde, R is hydrogen.
Both aldehydes and ketones contain the carbonyl group, ,
and are often referred to collectively as carbonyl compounds. It is thiscarbonyl group that largely determines the chief chemical and physical
properties of aldehydes and ketones.
Aldehydes and ketones differ from alcohols in having two less
hydrogen atoms. Removal of these two hydrogens from a primary alcohol
as a result of oxidation yields an aldehyde; where as their removal from a
secondary alcohol gives a ketone. The relation between these carbonyl
A
8/9/2019 Org. Chem. Manual, 2013-1.pdf
16/53
Org. Chem. Lab. 12
compounds and alcohols is, therefore, oxidation-reduction relation.
Tertiary alcohols can’t undergo this reaction.
Physical properties
• All aldehydes and ketones are liquids except formaldehyde, which
is gas (boiling point -21˚C), and benzophenone, which is solid(melting point 48˚C). Formaldehyde is handled either as an
aqueous solution ( formalin, an aqueous solution of 40%
formaldehyde and 15% methanol.) or as one of its solid polymers:
paraformaldehyde, (CH2O)n, or trioxane, (CH2O)3.
• Low molecular weight aldehydes and ketones (less than 5 carbons)
are appreciably soluble in water, although they do not have the
ability to form hydrogen bonds (unlike alcohols), aromatic ones are
insoluble in water, and all of them are soluble in organic solvents.
• They are colorless except benzaldehyde, which has a pale yellowcolour (due to oxidation) with a characteristic odour.
• The boiling points of aldehydes and ketones are lower than those of
the alcohols from which they are derived; isopropyl alcohol boils at
82.5˚C while its oxidation product, acetone, boils at 56˚C, ethanol
boils at 78˚C while its oxidation product, acetaldehyde, boils at
21˚C.
• Aliphatic aldehydes and ketones burn with a blue flame (without
smoke) while aromatic ones burn with a yellow smoky flame.
Solubility classification
Aldehydes and ketones that are soluble in water are soluble in ether
too and are classified under class S 1(e.g., formaldehyde and
acetone).Aldehydes and ketones that are insoluble in water are
classified under class N such as benzaldehyde and benzophenone.
Chemical properties
• All reactions of aldehydes and ketones are related to the carbonyl
group (the active group).
• Aldehydes contain a hydrogen atom attached to its carbonyl while
ketones don’t. This difference in the chemical structure affects their
chemical properties in two ways:
a) aldehydes are easily oxidized to the corresponding acids and
have reducing properties while ketones are not oxidized under
similar conditions and do not show reducing properties.
b) aldehydes are usually more reactive than ketones towards
nucleophilic addition, the characteristic reaction of carbonyl
group.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
17/53
8/9/2019 Org. Chem. Manual, 2013-1.pdf
18/53
Org. Chem. Lab. 14
The oxidation process requires an alkaline medium; thereforesodium hydroxide solution is used, and in order to overcome the
formation of the brown silver oxide precipitate (Ag2O), ammonium
hydroxide is used to serve as a complexing agent for this precipitatemaking it a water soluble complex. Note that since the medium isalkaline, salts of the produced carboxylic acid are formed rather than the
acid itself.
Procedure
• Preparation of Tollen’s reagent
To 3mL of silver nitrate solution add 2-3 drops of 10% sodiumhydroxide solution, and then add drop wise very dilute ammonia
solution with continuous shaking until all the brown precipitate of
silver oxide is dissolved. This reagent should be freshly prepared
prior before use.
• Add 2-3 drops of the compound to 2-3 mL of Tollen’s reagent, a
silver mirror will be formed. If no reaction occurs, warm the testtube in water bath for few minutes (note that excessive heating will
cause the appearance of a false positive test by decomposition of
the reagent).
The formed silver mirror can be washed using dilute nitric acid. Ifthe test tube is not very clean, silver metal forms merely as a granular
gray or black precipitate. False-negative tests are common with water
insoluble aldehydes. A negative result indicates that the compound is aketone.
b) Reduction of Fehling's reagent This test, like Tollen’s test, is used to distinguish aldehydes from
ketones. Only aldehydes can reduce Fehling’s reagent (a deep blue
solution) to give a red cuprous oxide precipitate.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
19/53
Org. Chem. Lab. 15
Procedure
• Preparation of Fehling's reagent
Fehling’s reagent is prepared by mixing exactly equal volumes of
Fehling’s A and Fehling’s B solution in a 1:1 ratio immediately before use (usually 1 mL of each).Fehling’s A solution is an
aqueous solution of copper sulfate pentahydrate (CuSO4.5H2O)
with few drops of concentrated sulfuric acid whereas Fehling’s B
solution is an aqueous solution of potassium sodium tartrate(C4H4KNaO6,4H2O) and sodium hydroxide.
• Add 5 drops of the compound to 1 mL of Fehling’s solution, andthen heat in water bath for 5 minutes (with shaking for water
insoluble compounds).
Aldehydes change the color of Fehling’s solution from blue to green,orange precipitate, and then red precipitate or copper mirror. Ketones
don’t change the color of this reagent. On the other hand, this test does
not give a sharp result with aromatic aldehydes.
3. Special tests for aldehydes and ketones containing a terminal
methyl group
These compounds include acetaldehyde, acetone, acetophenone, and benzyl methyl ketone. All of them have a methyl group attached to the
carbonyl group:
a) Iodoform (Haloform) test
Follow the same procedure of iodoform test mentioned earlier
(identification of alcohols).
8/9/2019 Org. Chem. Manual, 2013-1.pdf
20/53
Org. Chem. Lab. 16
OH
C
O
HH
OH
+ 2
resorcinol formaldehyde
HO
OH
OH
OH
OH
HO
OH
conc. H2SO4
- H2O
polymer
CH
O
benzaldehyde
CH
O
benzaldehyde
+
NaOH
heat
OH
benzyl alcohol
CONa
O
sodium benzoate
+
b) Sodium nitroprusside test To few drops of the compound add 1 mL of sodium nitroprusside
(Na2[Fe(CN)5 NO].2H2O) solution and excess of 30% sodium hydroxide
solution, a red color complex is a positive test.
4. Polymerization reaction
To 0.5 mL of formaldehyde or salicylaldehyde add 0.2 gm of
resorcinol and drop-by-drop concentrated sulfuric acid to get a red or
reddish violet color, or a white ring that changes to a reddish violet ring.
5. Cannizzaro reaction
Benzaldehyde, salicylaldehyde, and formaldehyde can undergo
Cannizzaro reaction because they do not have an alpha hydrogen atom.
In this type of reactions the aldehyde undergoes a self oxidation-
reduction in the presence of a strong basic medium to yield a mixture ofthe corresponding alcohol and the salt of the corresponding carboxylicacid (or the acid itself). Therefore, one molecule of the aldehyde serves as
the oxidizing agent while the other serves as the reducing agent.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
21/53
Org. Chem. Lab. 17
What is paraformaldehyde and from what aldehyde is
it from? Write down its molecular formula.
Procedure
To few drops of benzaldehyde (or the other aldehydes) add 0.5 mLof 30% sodium hydroxide solution and heat gently on a water bath with
shaking for five minutes. A precipitate of sodium benzoate is produced.
Dissolve this precipitate by adding few drops of distilled water, and then
add drops of concentrated hydrochloric acid to liberate benzoic acid as awhite precipitate.
As mentioned earlier formaldehyde can undergo this reaction
; however, this reaction can't be relied on for testing formaldehyde since
the acid produced, formic acid, is liquid that can't be observed separately
as compared to the solid benzoic acid resulted from benzaldehyde.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
22/53
Org. Chem. Lab. 18
phenol
OH
hydroquinone(quinol, hydroquinol)
OH
OH
resorcinol
OH
OH
OH
CH3
OH
CH3
m-cresolo-cresol
OH
CH3
p-cresol
HO
β -naphthol
OH
α -naphthol
'Phenols' is the term used to call all the members of this
class of organic compounds. The simplest member is
called phenol . Try to find out from where the term
'phenol' was derived.
Identification of Phenols
henols are organic compounds with a hydroxyl group
attached directly to benzene or substituted benzene. They
have the general formula Ar-OH. Examples of them include
phenol (also known as carbolic acid), hydroquinone, resorcinol, o-cresol,m-cresol, p-cresol, β -naphthol, and α-naphthol.
P
8/9/2019 Org. Chem. Manual, 2013-1.pdf
23/53
8/9/2019 Org. Chem. Manual, 2013-1.pdf
24/53
Org. Chem. Lab. 20
2. Substitution at the aromatic ring; e.g., bromination and nitration
reactions:
• reaction with bromine water.
• reaction with dilute nitric acid.
Chemical reactions
1. Reaction with ferric chloride
Phenols react with ferric chloride to give coloured compounds due to
the presence of the enol group. Actually this reaction is considered as a
test for any compound with enol group.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
25/53
Org. Chem. Lab. 21
Procedure
To a very dilute aqueous solution of the phenol (30-50 mg in 1-2 mLwater) or to a few crystals of the solid phenol (50-100 mg) dissolved in
water add 1 drop of ferric chloride solution and observe the resulting
colour:
Hydroquinone undergoes oxidation in the presence of ferric chloride
resulting in a deep green solution (crystals may separate) and, on further
addition of ferric chloride solution, a yellow solution of p-benzoquinone
is produced:
compound colour
phenol, m-cresol,
resorcinolviolet or blue
o- and p-cresol greenish blue
hydroquinone deep green
α- and β -naphthol no special colour
8/9/2019 Org. Chem. Manual, 2013-1.pdf
26/53
Org. Chem. Lab. 22
OH
OH
resorcinol
+ 2
C
O
C
O
O
phthalic anhydride
HO O OH
O
O
fluorescein
(pale red with green fluorescence
in alkaline medium)
+ 2H2O
2. Reaction with bromine water
This reaction is an example of substitution reaction at the phenyl
ring (mentioned earlier).
Procedure
To a concentrated aqueous solution of the phenol or to the phenolitself, add bromine water gradually. At first the bromine is decolourized
and then, on adding an excess, a white or yellowish-white precipitate of a
poly bromo-derivative is produced with all except hydroquinone and α-
and β -naphthol. On gradually adding bromine water to a solution of
hydroquinone, a deep red coloration is produced, followed by the
separation of deep green crystals which then dissolve giving a yellow
solution. The naphthols decolourize bromine water, but usually no
precipitate of the bromo compound can be obtained.
This test is not very satisfactory with those phenols which areinsoluble in water, owing to the difficulty of distinguishing the bromo
compound from the original phenol.
3. Phthalein test
Many phenols yield phthaleins which give special colours
(sometimes with fluorescence) in alkaline solutions when reacted with
phthalic anhydride and a little amount of concentrated sulphuric acid.
Phenol and resorcinol are examples.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
27/53
Org. Chem. Lab. 23
The fluorescence of resorcinol is due to the presence of an oxygen
linkage between the two phenolic nuclei (in basic medium).
Procedure
In a dry test tube put about 0.1 g of the phenol and an equal amount
of phthalic anhydride or phthalic acid, mix well, and add 1-2 drops ofconcentrated sulphuric acid. Heat gently on a direct flame for 1 minute
until the crystals of the mixture melt and fuse. Then cool the test tube and
add excess of 10% sodium hydroxide solution. Results should be as
follows:
If the resultant colour is not so clear you can dilute with water.
4. Reimer-Tiemann reaction
Treatment of phenol with chloroform and aqueous sodium hydroxidesolution introduces an aldehyde group (-CHO) into the aromatic ring at
the ortho- or para-positions:
compound colour
α-naphthol green colour
β -naphtholvery pale green with slightfluorescence
phenol red to pink
o-cresol red-violet
m-cresol blue to pink
p-cresol no change
resorcinol pale red colour with greenfluorescence
hydroquinone violet colour
8/9/2019 Org. Chem. Manual, 2013-1.pdf
28/53
Org. Chem. Lab. 24
Procedure
To about 0.2 g of the phenol add 1mL of 30% sodium hydroxidesolution and 1 mL of chloroform, heat on water bath, and observe the
colour of the aqueous layer:
5. Reduction of potassium permanganate
Phenols reduce potassium permanganate solutions and undergo
oxidation to quinones. The manganese is reduced from +7, which gives a
purple solution, to +4, which is brown. This test is highly successful with
dihydroxylated phenols than phenol itself.
Procedure
Add 0.1 g or 0.2 mL (3-4 drops) of the compound to 2 mL of water
or ethanol. Add 2% aqueous potassium permanganate solution drop by
drop with shaking until the purple colour of the permanganate persists. If
the permanganate color is not changed in 0.5-1 minutes, allow the
mixture to stand for 5 minutes with occasional vigorous shaking. The
compound colour
phenol yellow or no colour
resorcinolred colour with weak
fluorescence
α-naphthol dark green
β -naphthol
deep blue that turns to
green
o-cresol deep orange
m-cresol pale orange
p-cresol yellow
hydroquinone deep brown
8/9/2019 Org. Chem. Manual, 2013-1.pdf
29/53
8/9/2019 Org. Chem. Manual, 2013-1.pdf
30/53
Org. Chem. Lab. 26
C
O
OH
carboxyl group
C
O
H OH C
O
H3C OH
formic acid acetic acid
COOH
COOH
oxalic acid
CH2COOH
CH2COOH
succinic acid
COOH
CH
HO CH3
lactic acid
CHCOOH
CHCOOH
HO
HO
tartaric acid
CH2COOH
CCOOHHO
CH2COOH
citric acid
COOH
benzoic acid
COOH
OH
salicylic acid
Identification of Carboxylic Acids
arboxylic acids are organic compounds that have a carboxyl
group attached to an alkyl group(RCOOH) or to an aryl
group (ArCOOH). The 'R' may be a hydrogen and the result
is formic acid. They may be mono carboxylated, multi carboxylated,substituted (e. g., hydroxyl groups), or they may be aromatic
Physical properties
• Only formic acid, acetic acid, and lactic acid are liquids at roomtemperature. The others are solids.
• Low molecular weight carboxylic acids are soluble in water and,
therefore, lie under class S 1. Water insoluble acids dissolve in both
sodium hydroxide solution and sodium bicarbonate solution, being
classified under class A1. When they react with sodium
bicarbonate, they evolve carbon dioxide gas. This is considered as
a good simple indication of them.
C
8/9/2019 Org. Chem. Manual, 2013-1.pdf
31/53
Org. Chem. Lab. 27
C
O
OH
R C
O
HO
R
Give an example of a carboxylic acid with α-
halogenation (name and chemical structure).
Which parameter will you look for to compare
its acidity with other acids?
Give the general formula of esters, amides, and
acid chlorides.
• Their boiling points are generally high due to the association
through hydrogen bonds: two molecules of the carboxylic acid are
held together by two hydrogen bonds rather than one.
• Aromatic carboxylic acids burn with a yellow smoky flamewhereas aliphatic ones burn with a blue flame without smoke.
Chemical properties
The acidic properties of carboxylic acids are attributed to the proton
of the carboxyl group. Mono carboxylic acids are weak acids except
formic acid, which is the strongest. The tendency of the alkyl group to
release electrons weakens the acid; thus formic acid is the strongest. On
the other hand presence of electron withdrawing groups (such as
halogens) especially on the alpha carbon increases the acidity.
Reactions of carboxylic acids are related to:
• the proton as in salt formation reactions.
• removal of the hydroxyl group as in conversion to derivatives such
as esters, amides, or acid chlorides.
• substitution either in the alpha position of aliphatic acids or in the
meta position of aromatic ones.
Chemical reactions
1. General test (Ferric chloride test)
The acid solution should be made neutral before performing the test
with ferric chloride solution. This is achieved by adding very diluteammonia solution drop by drop with shaking to a solution of about 0.5 g
of the solid acid or 2 drops of the liquid acid in 1 mL water until the
medium becomes basic as indicated by changing the colour of litmus paper to blue or changing the colour of phenolphthalein indicator from
colorless to pink, in which case the characteristic odour of ammonia is
predominant. At this stage the solution is slightly basic. To make the
8/9/2019 Org. Chem. Manual, 2013-1.pdf
32/53
Org. Chem. Lab. 28
solution neutral the excess ammonia should be removed by gently heating
the test tube in a water bath with shaking from time to time until both the
odour of ammonia and the pink colour disappears. (In case of oxalic,
tartaric, citric and lactic acids keep a portion of their neutral solution for
use in calcium chloride test). Cool the solution and then add few drops of
ferric chloride solution to get different colours (solutions or precipitates)
as follows:
The steps of this test are:
When the solution is basic (excess ammonia):
Therefore elimination of the excess ammonia is important since the
brown orange precipitate of ferric hydroxide formed by this excessinterferes with the colour of the ferric salt of the acid resulting in a false
result.
acid result
formic and acetic red solution
succinic and benzoic light brown precipitate
salicylic violet solution
oxalic, tartaric, citric, and
lacticno special change
8/9/2019 Org. Chem. Manual, 2013-1.pdf
33/53
Org. Chem. Lab. 29
If the solution is still acidic (little ammonia is added), colourless
complexes are formed between the acid and ferric ions, a false negative
result.
As mentioned in the above table formic acid and acetic acid form a
red coloured solution in this test:
Succinic acid and benzoic acid give a light brown precipitate:
To distinguish between these two acids add few drops of dilute
sulphuric acid to this light brown precipitate with shaking thereby
liberating the free carboxylic acid back. If the liberated acid is water
soluble then it is succinic acid which is aliphatic. On the other hand
benzoic acid is liberated as a white precipitate because it is insoluble in
water since it is aromatic.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
34/53
Org. Chem. Lab. 30
Salicylic acid gives a violet colour:
2. Special tests for formic acid
Since formic acid has a hydrogen attached to the carbonyl group
(HC=O) it can reduce certain compounds while being oxidized:
a) Reduction of mercuric chloride
Formic acid reduces mercuric chloride to mercurous chloride in the
form of white precipitate and, in the presence of excess acid,
mercurous chloride is reduced to mercury element as a gray precipitate.
To few drops of the acid add few drops of mercuric chloride
solution, and then heat to get a white precipitate. Add excess of the
acid with heating to get the gray precipitate of elemental mercury.
b) Tollen's test
Refer to the experiment of identification of aldehydes and ketones
for preparation of Tollen's reagent and procedure of this test.
c) Alkaline potassium permanganate test
Formic acid reacts with potassium permanganate solution, a strong
oxidizing agent, in alkaline medium causing decolourization of this
violet reagent.Mix 2–3 drops of the acid with 5 mL of sodium bicarbonate
solution, and then add 1% potassium permanganate solution drop by
8/9/2019 Org. Chem. Manual, 2013-1.pdf
35/53
Org. Chem. Lab. 31
CH3COOC2H5 + H2Oconc. H2SO4
ethyl acetate(ester)
CH3COOH +C2H5OH
drop and observe the disappearance of the original violet colour of
the reagent which will be followed by the appearance of a brown
precipitate of manganese dioxide.
3. Special test for acetic acid (ester formation)
Acetic acid, on contrary to formic acid, neither can be oxidized
by, nor can reduce any of the reagents applied to formic acid. Instead,
it undergoes ester formation reaction:
Mix 1 mL of acetic acid with 2 mL of ethanol in a test tube and add
to this mixture 2–3 drops of concentrated sulphuric acid. Heat the
test tube in a water bath for 10 minutes, and then pour the mixture
into another test tube containing 5 mL sodium bicarbonate solution;
the characteristic fruity odour of ethyl acetate can be smelt, which
indicates the formation of this ester.
4. Special test for succinic acid (Fluorescence test)
In a dry test tube mix equal quantities of succinic acid and
resorcinol with 2 drops of concentrated sulphuric acid. Heat the
mixture on direct flame for 1 minute until the mixture melts. Cool and
add excess of 10% sodium hydroxide solution to get a red colour with
green fluorescence. If the colour is not so clear dilute with water.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
36/53
Org. Chem. Lab. 32
5. Special tests for tartaric acid
a) Reaction with concentrated sulphuric acid
When a mixture of about 0.5 g of tartaric acid and 1 mL of
concentrated sulphuric acid is heated gently on a flame with shaking
heavy charring takes place and carbon monoxide, carbon dioxide,
sulphur dioxide gases are evolved.
b) Reaction with calcium chloride solution
To about 1 mL of the cold neutral solution of the tartaric acid (seethe general test) add few drops of calcium chloride solution; a white
precipitate of calcium tartrate is formed. This precipitate dissolves indilute hydrochloric acid but not in dilute acetic acid.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
37/53
Org. Chem. Lab. 33
c) Reaction with Fenton's reagent
Dissolve about 0.5 g of tartaric acid in 1 mL of water and then add 1
drop of ferrous sulphate solution followed by 2 drops of hydrogen
peroxide solution. Then add excess of 10% sodium hydroxide
solution until an intense violet colour is observed.
In this reaction the components of Fenton's reagent (hydrogen peroxide and iron) undergo an oxidation-reduction reaction that
results in the generation of ferric ions which form ferric salt of
dihydroxyfumaric acid that is responsible for the violet colour.
6.
Special tests for oxalic acid
a) Reaction with potassium permanganate solution
Oxalic acid reacts with acidic potassium permanganate solutioncausing decolourization of this reagent. It doesn't react with this
reagent under alkaline medium.
Dissolve 0.5 gm of the acid in 2–3 mL of distilled water and add 2–3
mL of dilute sulfuric acid. Heat gently (water bath), and then add potassium permanganate solution drop by drop and observe the
disappearance of the violet color of the reagent.
b) Reaction with calcium chloride solution
For procedure follow the same steps mentioned above for tartaric
acid. The same results are obtained.
c)
Reaction with concentrated sulphuric acidFor procedure follow the same steps mentioned above for tartaricacid. The same gases are bubbled out with a little darkening.
d) Reaction with Fenton's reagent
For procedure follow the same steps mentioned above for tartaric
acid. Oxalic acid gives negative result with this reagent.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
38/53
Org. Chem. Lab. 34
7. Special tests for lactic acid
a) Iodoform test
Lactic acid can undergo iodoform formation reaction since it
contains a free methyl group and a hydrogen attached to the carbon
bearing the hydroxyl group:
For procedure follow the same steps mentioned in the identificationof alcohols experiment.
b) Reaction with concentrated sulphuric acid
For procedure follow the same steps mentioned above for tartaric
acid. The same gases are bubbled out with a considerable blackening
but without a marked charring.
c) Reaction with calcium chloride solution
For procedure follow the same steps mentioned above for tartaric
acid. Lactic acid gives negative result.
d) Reaction with Fenton's reagent
For procedure follow the same steps mentioned above for tartaricacid. Lactic acid gives negative result with this reagent.
8. Special tests for citric acid
a) Reaction with concentrated sulphuric acid
For procedure follow the same steps mentioned above for tartaric
acid. The same gases are bubbled out and the mixture turns toyellow but does not char. Acetone dicarboxylic acid is also formed,
and its presence is tested by heating the mixture for 1 minute, cool,
add a few milliliters of water and make alkaline with 30% sodium
hydroxide solution. Add a few milliliters of sodium nitroprusside
solution and observe the intense red colouration of the medium.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
39/53
Org. Chem. Lab. 35
b) Reaction with calcium chloride solution
For procedure follow the same steps mentioned above for tartaric
acid. Citric acid gives the same results.
c) Reaction with Fenton's reagent
For procedure follow the same steps mentioned above for tartaric
acid. Citric acid gives negative result with this reagent.
9. Special test for salicylic acid (ester formation)
In addition to the characteristic violet colour obtained with ferric
chloride, salicylic acid can also be detected by ester formation test. In this
test methyl salicylate ester separates out as an organic phase having a
characteristic odour.
Follow the same procedure and conditions used for esterification of
acetic acid but use methanol instead of ethanol. Not that methanol is toxic
internally so never withdraw it by mouth to avoid accidental ingestion.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
40/53
Org. Chem. Lab. 36
Methyl salicylate, also known as wintergreen oil , is used widely in pharmaceutical topical
preparations, give its main use with the name of a popular topical preparation.
Both ethyl acetate and methyl salicylate separate as an organic phase during ester
formation test, how can you detect the organic layer practically and theoretically? Fill the following table:
acid
tests results with description
FeCl3 test H2SO4 test CaCl2 test Fenton's test
citric
oxalic
tartaric
lactic
8/9/2019 Org. Chem. Manual, 2013-1.pdf
41/53
Org. Chem. Lab. 37
Can you skip the neutralization step in the reaction
between carboxylic acid salts and ferric chloride
solution? Explain.
Identification of Carboxylic Acids Salts
arboxylic acids salts are organic compounds with the
general formula (RCOOM) where (RCOO-) refers to the
carboxylic acid part and (M+)
is the alkali part which, in this
experiment, may be either a metal cation (Na+
or K +
) or ammonium(NH4
+). These salts are colourless or white crystalline solids and are
soluble in cold or hot water.
Identification of the carboxylic acid part (anionic part)
The carboxylic acid part can be identified by the usual steps for
identification of carboxylic acids starting with ferric chloride test and,
according to the result observed; the proper special test should be
performed then to conclude the carboxylate name (formate, lactate,
salicylate, etc.).
Identification of the alkali part (cationic part)
•
Identification of sodium or potassium cations Place about 0.1 g of the salt on the edge of a metal spatula and start
heating it gently on a flame with gradual increase in the heat strength.Sodium and potassium salts leave a residual amount of solid on the
spatula in addition to the carbon coming from decomposition of the
organic part. This residual solid may be sodium carbonate or potassium
carbonate and can be detected, after cooling, by the addition of few dropsof dilute hydrochloric acid solution which results in a strong
effervescence within the residual solid due to liberation of carbon dioxide
gas:
During ignition observe the colour of the flame. Sodium salts burn with a
golden yellow flame whereas potassium salts burn with a purple flame.
C
8/9/2019 Org. Chem. Manual, 2013-1.pdf
42/53
Org. Chem. Lab. 38
What is the proper technique for smelling chemicals?
• Identification of ammonium cation Repeat the ignition procedure mentioned above and note that
ammonium salts don't leave any residual solid except the carbon coming
from decomposition of the organic part. After cooling, addition of few
drops of dilute hydrochloric acid does not result in any effervescence.
Ammonium cation can be detected as follows. Place few crystals of
the salt in a test tube and add 0.5 mL of 10% sodium hydroxide solution.At this stage free ammonia is liberated and can be smelt easily:
Place a small filter paper over the top of the tube and fold it down around
the tube. Add 2 drops of 10% copper sulphate solution on the filter paper
covering the mouth of the test tube. Heat the test tube mildly on a flame
to boil the mixture. The liberated ammonia will react with the copper ions present on the filter paper resulting in a blue colour.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
43/53
Org. Chem. Lab. 39
CH3X
metheyl halide
C2H5 X
ethyl halide
Cl
benzyl chloride chlorobenzene
CHCl3 CCl4
chloroform carbon tetrachloride
CH2Cl
Identification of Alkyl and Aryl Halides
Physical properties
All alkyl halides and chlorobenzene are colourless liquids when pure except iodoform, CHI3, which is a yellow crystalline solid with a
characteristic odour. Methyl iodide, ethyl iodide and bromide,chloroform, and carbon tetrachloride have sweetish odours. Benzyl
chloride has a sharp irritating odour and is lachrymatory. Chlorobenzene
possesses aromatic odour.
Alkyl and aryl halides (R X, Ar X) have boiling points higherthan the parent hydrocarbon because of the heavier molecular weight.
Accordingly, for a given compound, iodides have the higher boiling point
than bromides and chlorides.
In spite of their polarity alkyl halides are insoluble in water due totheir inability to form hydrogen bonds. They are soluble in most organic
solvents.
Iodo-, bromo-, and polychloro- compounds are denser than water.
Chemical reactions
1. Reaction with alcoholic silver nitrate.
Alcoholic silver nitrate reagent is useful in classifying halogen
compounds. Many halogen containing compounds react with silvernitrate to give an insoluble silver halide (AgX), and the rate of this
reaction indicates the degree of reactivity of the halogen atom in thecompound. Besides, the identity of the halogen can sometimes be
determined from the colour of the silver halide produced; silver chloride
is white (turns to purple on exposure to light), silver bromide is pale
yellow, and silver iodide is yellow. These should, of course, be consistentwith results from elemental analysis (sodium fusion for detection of
halogens).
8/9/2019 Org. Chem. Manual, 2013-1.pdf
44/53
Org. Chem. Lab. 40
RX + AgNO3C2H5OH
AgX + RONO2
R XAg+
R X Ag
δ+
δ+
δ−
AgX + R +
R + NO3
-
R ONO2
R 3CCl RI C C
H
R CH2X
H
C C
H
R H
CH2X
H2C
Br
CH2Br
ArX C C
H
R H
X
C C
H
R X
H
HCCl3 CCl4
It is obvious that this reaction follows S N1 mechanism. Generally thereactivity of alkyl halides towards this reagent is:
R 3CX > R 2CHX > RCH2X
Procedure
Add one drop or a couple of crystals of the unknown to 2 mL of2% ethanolic silver nitrate solution. If no immediate reaction is observed,
stand for 5 minutes at room temperature and observe the result. If no
reaction takes place, warm the mixture in water bath for 30 seconds andobserve any change. If there is any precipitate (AgX) add several drops of
1 M nitric acid solution to it; silver halides are insoluble in this acid.
tert - chlorides, methyl and ethyl iodides, allylic chlorides, and ethyl
bromides give fast result at room temperature:
pri- and sec- chlorides, benzyl chloride, and 1-chloro-2,4-
dinitrobenzene give result only on warming:
Chlorobenzene, chloroform, iodoform, carbon tetrachloride, and
vinylic chlorides don't give any positive result even on heating:
Cyclohexyl halides exhibit a decreased reactivity when comparedwith the corresponding open-chain secondary halides. Cyclohexyl
chloride is inactive, and cyclohexyl bromide is less reactive than 2-
8/9/2019 Org. Chem. Manual, 2013-1.pdf
45/53
Org. Chem. Lab. 41
RCl + NaIacetone
RI + NaCl
RBr + NaI RI + NaBracetone
R XI-
I C X
δ−
δ−
I R
bromohexane, although it will give a precipitate with' alcoholic silver
nitrate.
2. Sodium iodide in acetone test.
This test, complementing the alcoholic silver nitrate test, is used to
classify aliphatic chlorides and bromides as primary, secondary, ortertiary. This test depends on the fact that sodium chloride and sodium
bromide are only very slightly soluble in acetone.
The mechanism follows direct displacement (S N2) process;therefore, the order of reactivity of simple halides is:
primary> secondary> tertiary
With sodium iodide, primary bromides give a precipitate of sodium
bromide within 3 min at 25°C, whereas the chlorides give no precipitate
and must be heated to 50°C in order to effect a reaction. Secondary andtertiary bromides react at 50°C, but the tertiary chlorides fail to react
within the time specified. Tertiary chlorides will react if the test solutionsare allowed to stand for a day or two.
These results are consistent with the following S N2 process:
Procedure
To 1 mL of the sodium iodide-acetone reagent in a test tube addtwo drops of the compound. If the compound is a solid, dissolve about 0.1
g in the smallest possible volume of acetone, and add the solution to the
reagent. Shake the test tube, and allow the solution to stand at room
temperature for 3 min. Note whether a precipitate is formed and also
whether the solution turns reddish brown, because of the liberation of free
iodine. If no change occurs at room temperature, place the test tube in
water bath at 50°C.Excessive heating causes loss of acetone and
precipitation of sodium iodide, which can lead to false-positive results. At
the end of 6 min, cool to room temperature and note whether a reactionhas occurred. Occasionally, a precipitate forms immediately after
combination of the reagents; this represents a positive test only if the
8/9/2019 Org. Chem. Manual, 2013-1.pdf
46/53
Org. Chem. Lab. 42
precipitate remains after the mixture is shaken and allowed to stand for 3
minutes.
3. Differentiation between alkyl and aryl halides
(Formaldehyde- sulfuric acid test)
With this test aryl halides (chlorobenzene) produce pink, red, or
bluish red colour whereas alkyl halides produce yellow, amber, or browncolour.
Procedure
This reagent is prepared at the time of use by adding 1 drop of
formaldehyde to a test tube containing 1 mL concentrated sulfuric acid. In
another test tube add 1 drop of the compound to be tested to 1 mL of
hexane. From this solution take 1-2 drops and add them to 1 mL of the
reagent. Shake well and observe the colour.
4. Special tests for chloroform
a) Riemer- Tiemann reaction
For procedure and chemical equations refer to "Identification of
Phenols" experiment. Resorcinol results in a red colour with slight
fluorescence in the aqueous layer while α- or β - naphthol results in a deep blue aqueous layer fading to green.
b) Reduction of Fehling's reagent
For preparation of Fehling's reagent and chemical equations refer
to "Identification of Aldehydes and Ketones" experiment. Boil 1 mL ofchloroform gently (water bath) with 3 mL of Fehling's reagent with
constant shaking for 3- 4 minutes. Reduction occurs and reddish cuprous
oxide slightly separates.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
47/53
Org. Chem. Lab. 43
H3C N H
H
N
CH3
H
H N CH3
H
H
Identification of Amines
mines are basic organic compounds that are considered as
derivatives of ammonia. They are classified as primary,
secondary, or tertiary according to the number of groupsattached to the nitrogen atom: RNH2, R 2 NH, or R 3 N respectively where R
is any alkyl or aryl group.
Physical properties
Like ammonia, amines are polar compounds and all of them canform intermolecular hydrogen bonds except tertiary amines.
They have lower boiling points than alcohols or carboxylic acids of
the same molecular weight but higher boiling points than non polar
A
8/9/2019 Org. Chem. Manual, 2013-1.pdf
48/53
Org. Chem. Lab. 44
compounds. Methylamine is gas while o-phenylenediamine and p,p-
diaminodiphenylmethane are solids. The others are liquids.
All amines are capable of forming hydrogen bonds with water, thus
those with six carbon atoms or less are quite soluble in water. They are
soluble in organic solvents as ether, alcohol and benzene.
All of them have fish like odour except the methylamines and
ethylamines which smell just like ammonia.Aromatic amines are colourless when pure, but they are easily
oxidized by air becoming coloured. They are generally very toxic and can be absorbed through the skin.
Chemical reactions
All classes of amines (primary, secondary, and tertiary) have an
unshared pair of electrons on the nitrogen atom, just like ammonia. That
is why they are similar to ammonia in their chemical behavior (mainly basicity and neocleophilicity).
1. Ramini and Simon tests (Sodium nitroprusside tests).
(conventional Ramini and Simon tests)
In Ramini test the amine reacts with acetone and the product
interacts with sodium nitroprusside (Na2[Fe(NO)(CN)5].2H2O) that is
dissolved in 50 % aqueous methanolic solution to produce a colouredcomplex. In Simon test acetone is replaced by 2.5 M acetaldehyde
solution. These two tests distinguish between primary and secondary
aliphatic amines.To distinguish between aromatic amines (primary, secondary and
tertiary) the modified Ramini and Simon tests are applied. These tests
use the same reagents and procedure of the conventional tests but the
modifications are the replacement of the methanolic solution of sodium
nitroprusside by a solution of sodium nitroprusside in dimethylsulfoxide
(modified sodium nitroprusside reagent) and the use of a saturatedaqueous solution of zinc chloride instead of water.
Procedure
• Ramini test
To 1 mL of methanolic sodium nitroprusside solution add 1 mL of
distilled water, 5 drops of acetone, and about 30 mg of the amine. In most
cases the characteristic colour appears in a few seconds, although in somecases 2 minutes may be necessary.
• Simon test Follow the above procedure exactly but use 5 drops of 2.5 M
acetaldehyde solution instead of acetone. Up to 2 minutes may be neededfor the colour to develop.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
49/53
Org. Chem. Lab. 45
• Modified Ramini test To 1 mL of the modified sodium nitroprusside reagent add 1 mL of
saturated aqueous zinc chloride solution, 5 drops of acetone, and about 30
mg of the amine. Primary and secondary aromatic amines produce
orange-red to red-brown colours within a period of few seconds to 5
minutes. Tertiary aromatic amines give a colour that changes from
orange-red to green over a period of about 5 minutes.
• Modified Simon test Follow the above procedure exactly but use 5 drops of 2.5 M
acetaldehyde solution instead of acetone. Primary aromatic amines give
an orange-red to red-brown colour within 5 minutes; secondary aromatic
amines give a colour changing from red to purple within 5 minutes;tertiary aromatic amines give a colour that changes from orange-red to
green over a period of about 5 minutes.
Examples are outlined in the following table:
Amine Ramini test Simon testModified
Ramini test
Modified
Simon test
tert -butylamine deep red red-brown
dicyclohexylamine deep redviolet with
precipitate
diethylamine red-brown deep blue
anilineturbid orange,
changes to
henna colour
brown
o-phenylenediamineturbid red
brown
turbid henna
colour
p,p-diaminodiphenylmethanelight brown
precipitate
light brown
precipitate
N,N-dimethylaniline
brown
changes to
green
brown changes
to green (rapid
change)
diphenylamineorange- red to
red brownpale orange
8/9/2019 Org. Chem. Manual, 2013-1.pdf
50/53
Org. Chem. Lab. 46
R 2NH + HONO
2° amine nitrous
acid
N -nitrosoamine
(yellow oil or solid)
N
R
R
N O + H2O
R 3N + H+
3° aliphatic
amine
R 3NH+
soluble
2. Nitrous acid test.
The reaction of amines with nitrous acid (HNO2) is another test
that classifies the amine not only as primary, secondary, or tertiary, but
also as aliphatic or aromatic.
Primary aromatic and aliphatic amines react with nitrous acid to
form an intermediate diazonium salt. The aliphatic diazonium saltsdecompose spontaneously by rapid loss of nitrogen, particularly when the
original amino group is attached to a secondary or tertiary carbon, while
most aromatic diazonium salts are stable at 0°C but lose nitrogen slowly
on warming to room temperature.
Secondary amines undergo a reaction with nitrous acid to form N-
nitrosoamines, which are usually yellow oils or solids. These are
carcinogenic compounds; therefore, students are advised not to perform
nitrous acid test for secondary amines.
Tertiary aliphatic amines do not react with nitrous acid, but they
form a soluble salt.
Tertiary aromatic amines react with nitrous acid to form the orange-
coloured hydrochloride salt of the C-nitrosoamine. Treating the solution
with base liberates the blue or green C-nitrosoamine.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
51/53
Org. Chem. Lab. 47
NaNO2 + HCl HONO + NaCl
sodium nitrite nitrous acid
NR 2 + HONO + HCl
3° aromatic
amine
NHR 2C l + H2ONO
hydrochloride salt of C -nitrosoamine
(orange)
NaOH
NR 2 + NaCl + H2ONO
C -nitrosoamine
(green)
Procedure
Nitrous acid is prepared instantaneously by the reaction of sodium
nitrite and hydrochloric acid:
In a test tube dissolve 0.5 mL or 0.5 g of the amine in a mixture of
1.5 mL of concentrated hydrochloric acid and 2.5 mL of water, and cool
the solution to 0°C in a beaker of ice. In another test tube dissolve 0.5 g
of sodium nitrite in 2.5 mL of water, and add this solution drop wise, withshaking to the cold solution of the amine hydrochloride. Move 2 mL of
the final solution to another test tube, warm gently, and examine for
evolution of gas.
Results
• The observation of rapid bubbling or foaming as the aqueous
sodium nitrite solution is added at 0°C indicates the presence of a
primary aliphatic amine.
• The evolution of gas (bubbling) upon warming to room
temperature indicates that the amine is a primary aromatic amine,and the solution should be subjected to the coupling reaction (test
3).
• If a pale yellow oil (heavier than water) or low-melting solid,
which is the N-nitrosoamine, is formed with no evolution of gas,
the original amine is a secondary amine.
• If a dark-orange solution or an orange crystalline solid is formed,
which is the hydrochloride salt of the C -nitrosoamine, the amine is
tertiary aromatic. Treating 2 mL of this solution with few drops of
10 % sodium hydroxide or sodium carbonate solution produces the bright-green or -blue nitrosoamine base.
8/9/2019 Org. Chem. Manual, 2013-1.pdf
52/53
Org. Chem. Lab. 48
ArN2Cl +
ONa
diazonium salt
of primary
aromatic aminessodium-2-naphthol
+ NaOH
ONa
NN Ar
azo dye
(red- orange)
+ NaCl + H2O
R 2N H + C S2 + NH4OH + H2OCR 2N SNH2
S
carbon disulf ide
dialkyldithiocarbamate
NiCl2
CR 2N S
S
2Ni
• If only solubilization of the amine is obtained with no other results,
the amine is tertiary aliphatic.
3. Coupling reaction (a test for primary aromatic amines).
Procedure
Dissolve 0.1 g of 2-naphthol in a mixture of 2 mL of 10 % sodiumhydroxide solution and 5 mL distilled water. Add 2 mL of the cold
diazonium solution and observe the result. The formation of a red- orange
dye (red precipitate in case of phenol) with evolution of gas only upon
warming indicates that the compound is a primary aromatic amine.
4. Carbon disulfide reagent test (for secondary aliphatic amines).
8/9/2019 Org. Chem. Manual, 2013-1.pdf
53/53
Org. Chem. Lab. 49
Procedure
In a test tube dissolve 50 mg (1-2 drops) of the amine in 5 mLdistilled water (or 1-2 drops of concentrated hydrochloric acid if
necessary). In another test tube mix o.5- 1 mL of concentrated ammonia
solution with 1 mL of nickel chloride in carbon disulfide reagent
(NiCl2/CS2). Add 0.5- 1 mL from the first test tube to the second one. Adefinite precipitation indicates that the unknown is a secondary amine. A
slight turbidity is an indication of a trace of a secondary amine as animpurity.
5. Lignin test (for primary and secondary aromatic amines).
This test depends on the action of lignin in the newsprint paper.
Procedure
Dissolve 10- 20 mg of the amine in a few drops of ethanol andmoisten a small area of newsprint paper with this solution. Place 2 dropsof 6 N hydrochloric acid on the moistened spot. The immediate
development of a yellow or an orange colour is a positive test for a primary or secondary aromatic amine.