Download If the substance is soluble in dil. NaOH, add a solution of NaHCO3 to

1
Content
Page
1
Introduction
2
2
Basis for Identification
2
3
Determination of physical
properties, solubility and acidbase characters.
3
4
Infrared spectroscopic technique for
the determination of functional
groups in organic compounds.
6
5
Tests for special classes
8
6
Alcohols
11
7
Phenols
14
8
Aldehydes and ketones
18
9
Carboxylic acids
22
10
Esters
26
11
Amides
27
12
Amines
28
Page
Serial No.
1
Index
2
1. Introduction:
Qualitative organic analysis comprises the methods for identifying an organic substance.
This laboratory deals with the identification of organic compounds through their physicchemical properties and functional groups infrared characteristics.
2. Basis for identification:
The term identity as applied to chemical compounds means the assignment of a
molecular structure to a chemical substance, so it can be distinguished as a single
substance.
At this course the systematic scheme is employed for identification of unknown organic
substances. This scheme involves a series of steps by which one proves that the unknown
compound A has identical physical and chemical properties with a known compound B,
that is, a compound which has been described in the literature. These steps may be briefly
summarized:
a. The physical properties (e.g. state, odour … etc.) of the unknown are determined.
b. Tests of solubility in a few selected solvents are made to determine acid-base
character of the unknown.
c. Determination of the functional groups present in the unknown by examining its
infrared spectrum.
d. The unknown substance is then subjected to tests with a number of chemical
reagents (e.g. FeCl3) in order to detect presence or absence of functional groups,
such as the carboxyl (COOH), carbonyl (CO), hydroxyl (OH) … etc.
By means of this test and preceding step (step c) the classification of the unknown
is restricted to a single class of organic compounds.
e. All the data obtained in the above tests are coordinated and a list is made of all the
given compounds in that single class. Finally, the unknown is subjected to few
Page
2
specific compound tests, which would indicate the identity of the unknown.
3
3. Determination of Physical properties, Solubility and Acidbase Character:
The following steps may be considered as a preliminary procedure in the examination of
an unknown substance.
3.1 Physical properties:
A. State:
If the unknown substance is solid, it may be crystalline, amorphous or fine powder.
If the unknown substance is liquid, it may be mobile or viscous. To determine if the
unknown is true liquid or solution, add anhydrous copper sulphate, which turns to blue
with solutions.
B. Colour:
It may be coloured (e.g. white, brown, yellowish brown, etc.) or colourless.
C. Odour:
Many organic compounds have characteristic odours such as, bitter almond odour, micelike odour, pleasant odour, phenolic odour, vinegar odour or fishy odour and some are
odourless.
D. Ignition test:
Place 1-2 drops or a few milligrams of a solid on a crucible. Heat the vesselwith a small
flame and note general appearance of the flame.
Most aromatic compounds burn with a smoky flame. Low-molecular weight nonaromatic
compounds burn with a no smoky flame. The residue, if any, is most likely the oxide or
carbonate of some metals, usually white but sometimes coloured. Sugars and proteins
tend to carbonize and produce characteristic odours.
3.2 Solubility and Acid-base Character:
Water.
Dilute hydrochloric acid (dil. HCl).
Dilute sodium hydroxide (dil. NaOH).
Dilute sodium bicarbonate (dil. NaHCO3).
Page
1.
2.
3.
4.
3
Substances may be classified on the basis of their solubility or lack of solubility in certain
solvents into acidic, basic or neutral substances. The solvents used for classification are:
4
A compound in solid state is described as either soluble or insoluble; while in a
liquid state is described as miscible or immiscible.
a. Solubility in water:
Water is highly polar; also it may act as an acid (electron acceptor) or a base (electron
donor):
B:
+
H2O
B: H+ + OH-(As an acid)
RCOO- + H3O+(As a base)
RCOOH + H2O
In general water dissolves:
1. Salts:
a. Metallic salts of acids or bases.
b. Amine salts.
2. Low molecular weight (based on number of carbons) acids, bases and neutral
substance.
To detect any basic or acidic properties use a litmus paper (L.P.)
b. Solubility in Hydrochloric Acid (dil. HCl):
It has been mentioned earlier, the low molecular weight amines are soluble in water.
However, amines that are not soluble in water may be dissolved, provided they can be
converted into the ionic form (amine hydrochloride) while in water.
N: + dil. HCl
N+H CL-
Amine (insoluble in H2O)
Salt (soluble in H 2O)
c. Solubility in dilute Sodium Hydroxide (NaOH):
Water-insoluble acids or phenols may react with bases to form products (sodium salts)
that are soluble in water.
Water insoluble
ArO-Na+ + H2O
Water soluble
4
Ar-OH + dil. NaOH
RCOO-Na+ + H2O
Page
RCOOH + dil. NaOH
5
d. Solubility in Dilute Sodium Bicarbonate (NaHCO3):
Both NaOH and NaHCO3 are used to detect acidic, water-insoluble substances. The use
of bicarbonate solution only serves to distinguish strong acids (carboxylic acids) from
weak acids (phenols).
RCOOH + NaHCO3
RCOO- Na+ + CO2
+ H2O
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5
If the substance is soluble in dil. NaOH, add a solution of NaHCO3 to an aqueous
suspension of the unknown. Effervescence and evolution of CO2 indicate presence of a
carboxylic acid. If there is no observable effect, the substance is probably a phenol.
6
4. Infrared Spectroscopic technique for the determination of
functional groups in Organic Compounds:
4.1 Introduction:
Spectroscopy is the study of interaction of light with atoms and molecules. The usual
range of an infrared spectrum is between 2.5-16µm (1µm = 10-4 cm). The most common
method of expressing infrared spectra is to use wave number (1/π) units ranging from
4000-625 cm-1.
Functional groups (e.g. OH, C=0, -NH2 etc.) have vibrational frequencies within welldefined regions of this range. This makes the infrared spectrum the simplest, most rapid
and often most reliable means for assigning compound to its class.
4.2 Examination of Infrared (IR) Spectra:
It is convenient to classify IR spectrum into two regions:
1. The functional group region; which is above 1500 cm-1.
2. The finger print region; which is below 1500cm-1.
Most characteristic and diagnostic stretching vibrations occur above 1500 cm-1
(functional group region). These characteristic vibrations are summarized as the
following:
1. Alkanes
C-H
Stretch just to the right of 3000 cm-1 (2890-2880cm-1).
2. Alkenes
=C–H
Stretch just to the left of 3000 cm -1 (3050 cm-1).
3. Aromatic ring
=C–H
Stretch just to the left of 3000 cm-1 as in alkenes.
-C = C -
Ring stretch at 1600-1475 cm-1.
Stretch as a sharp peak at 3650-3600cm-1,
H-bonded of O-H is abroad band at 3500-3200cm-1.
Page
0-H
6
4. Alcohols and phenols:
7
5. Aldehydes:
C=O
Stretch at 1740-1725cm-1.
C-H
Stretch weak band at 2850-2750 cm-1.
6. Ketones:
C=O
Stretch at 1725-1700 cm-1.
7. Carboxylic acids:
O-H
Stretch very broad (strongly H-bond) at 3400-2400 cm-1.
C=O
Stretch broad at 1730-1700 cm-1.
8. Esters:
C=O
Stretch at about 1750-1735cm-1.
9. Amides
C=O
Stretch at 1670-1640 cm-1.
N-H
Stretch at 3500-3100 cm-1 (10 amides have 2 bands (NH2) inthis region).
N-H
Bending around 1640-1550 cm-1.
10. Amines:
N-H
Stretch 3500-3100 cm-1 (10 amine 2 bands, 20 amine 1 band,30 amine
Bend in 10 amine broad band 1960-1940 cm-1, 20 aminenear 1500cm-1.
N-H
Out-of-plane bending near 800 cm-1.
Page
N-H
7
no band).
8
5. Tests for special classes:
-
Up to this point, the compound has been examined to establish the solubility
behavior, and the apparent acidity, basicity or neutrality. In addition, the IR
spectrum has been examined to assign the unknown to its chemical class.
-
The specific classes of organic compounds (e.g. alcohols, phenols, carboxylic
acids etc.) are generally recognized by the detection of the main functional group
that is present in the molecule. For example, detection of the carbonyl group
indicates an aldehyde or ketone, detection of the hydroxyl group indicates either
alcohol or phenol.
The following general chemical tests are used as test for special classes:
5.1 Test with neutral ferric chloride solution (FeCl3):
It is very useful test for identification purposes and is most commonly used as a test
for:
a. Phenols:
Add a few drops of neutral FeCl3 solution to a dil. Solution or suspension of phenol
in water. Violet to dark green colour is given by many phenols.
b. Carboxylic acids:
The free acid (effervescence with sodium carbonate) must be neutralized as follows:
Place about 0.1 g of the free acid in a test tube and add a slight excess of ammonia
solution. Shake the tube and boil until the ammonia odour is completely
disappeared, then cool.
R-COOH + NH4OH
R-COO-+NH4 + H2O
To the cooled solution, add a few drops of neutralized ferric chloride solution,
compare the colour produced with that obtained from pure water with few drops of
ferric chloride solution (blank test):
- Red colouration for formate or acetate.
- Yellow colouration for lactate, citrate, tartarate or oxalate.
- Buff. or pale yellow precipitates for benzoate or phthalate.
c. Amines:
To a solution of amine in dil. HCl add 2-3 drops of ferric chloride solution with
occasional shaking; a green colouration will develop.
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8
5.2 Test with 3,5-Dinitrobenzoyl chloride for alcohols or phenols:
To about 0.5 g of 3,5-Dinitrobenzoyl chloride in dry test tube add 2 ml of alcohol or
about 0.5 g of phenol in dil. NaOH, then warm the mixture until a clear solution is
obtained. Cool and scratch, a white or yellowish crystalline solid will separate.
9
O
O
-
-
+
N
N
O
O
-
+
R OH
O
N
O
+
+
heat
O
-HCl
+
O
Cl
O
N
O
-
R
O
An Ester
5.3 Test with 2,4-dinitrophenylhydrazine for aldehydes and ketones:
- To about 0.5 ml of aliphatic aldehyde or ketone, add about 2 ml of 2,4dinitrophenylhydrazine (reagent A; in water). A yellow precipitate is produced in
the cold.
- To about 0.5 ml of aromatic aldehyde or ketone in methanol add about 2 ml of
2,4-dinitrophenylhydrazine (reagent B; in methanol). An orange precipitate is
obtained.
O
-
+
N
O
R
1
-
+
+
N
N
O
R
O
O
O
-
-H 2O
+
O
+
N
O
O
NH
NH
NH2
N
-
R
R
1
2,4-dinitrophenylhydrazone
5.4 Test with hydroxylamine hydrochloride (R-NH2OH.HCL for carboxylic esters):
Add about 0.2 g of hydroxylamine hydrochloride to about 0.5 ml (g) of ester, then
add about 5 ml of dil. Sodium hydroxide, gently boil for 2 min, cool and acidify with
dil. Hydrochloric acid, then add a few drops of ferric chloride solution. A violet to
deep red-brown colour is produced immediately.
R-COOR’ + NH2-OH.HCL
NaOH
R’-OH + RCONH OH + NaCl
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9
5.5 Test with 30% sodium hydroxide for ammonium salts and amides:
To about 0.1 g of unknown in a test tube, add 3ml of 30% sodium hydroxide solution
and then note any reaction on cold.
10
Boil gently for few minutes and then note any further reaction:
-
Ammonia odour on cold may indicate the presence of ammonium salt.
Ammonia odour on hot may indicate the presence of amides or imides.
Fishy odour and oily droplets may indicate presence of amine salt.
R-COO-+NH4+NaOH
R-COO-Na+
+ NH3
+ H2O
heat
R-CONH2+
R-COO-Na+ + NH3
NaOH
5.6 Test with nitrous acid for aromatic amines (Diazonium salt test):
Mix about 0.5ml of aromatic amine with about 1ml of concentrate HCL. Dilute with
3ml of water (to dissolve any ppt) and cool in ice.Then add few drops of sodium
nitrite solution.
+
HN
NH2
N
Cl
O
Na N
O
-
+
H2O
10
+
Page
HCl
+
11
6 Major Classes of Organic Compounds:
6.1Alcohols (R-OH):
1. Physical Properties:
a. State: liquids.
b. Colour: all are colorless.
c. Odour: they have faint odours except glycerol which is odourless.
d. Solubility test:
They are completely miscible with water except benzyl alcohol.
e.
Ignition test:
All alcohols are flammable with no smoky flame except benzyl alcohol which
burns with smoky flame.
2. Infrared Spectra:
- (-OH stretching) broad peak at 3500-3200 cm-1.
- Aliphatic C-H stretching just below 3000cm-1.
- Aromatic C-H stretching just above 3000cm-1.
3. A special test for hydroxyl (-OH) group:
a. 3,5-Dinitrobenzoyl Chloride:
To about 0.5g of 3,5-Dinitrobenzoyl Chloride in dry test tube add 2ml of alcohol.
Then warm the mixture until a clear solution is obtained. Cool and scratch, a white
or yellowish crystalline solid will separate.
-
+
N
O
O
+
-
heat
-HCl
O
+
O
Cl
O
O
N
O
-
R
11
N
R OH
O
N
O
+
+
Page
O
O
-
12
4. A special Compound Tests:
a. Special test for glycerol:
1. Borax Test:
Ta an aqueous solution of borax adds 2 drops of phenolphthalein.A pink colour is
formed. On adding glycerol the colour will fade.
Na2B4O7 + H2O
2NaOH + 4H3BO3
HO
HO
O
HO
OH
B OH
+
HO
Glycerol
B
O
HO
Boric acid
OH
Glyceroborate (strong acid)
b. Special Tests for Ethanol (Alcohol):
1. Iodoform Test:
To 0.5ml of alcohol add 1ml of 10%NAOH, I2 solution is then added drop wise
until persistent yellow colour is given, warm in a water-bath a yellow precipitate
is formed.
I I
+
Na OH
OH
+
H3C
Na
Na
O
I
+ HI
+
H3C
I
Na
+ H2O
I
O
Ethanol
I
H3C
+
O
I
I
O
I
O
I
Na
I
+
Na
OH
O
+
I
I
3 Na OH
+
I
3Na O
I
O
Iodoform
2. Ethylacetate Test: (Esterification)
Heat gently 1ml of ethanol with 0.5ml acetic acid and a few drops of
concentrated H2SO4 for about 1minute. Cool, pour into a few ml of water or
Na2CO3. Note the fruity odour of ethyl acetate.
O
+
H3C
O
H3C
OH
O
H3C
CH3
Page
12
OH
13
c. Special Test for Methanol:
1. Methylsalicylate Test: (Esterification)
Heat gentle 1ml of Methanol with 0.5g of salicylic acid and few drops of
concentrated H2SO4 for 1minute. Cool, pour into a few ml of water or Na2CO3.
Note the odour of methyl salicylate (oil of winter green).
CH3
O
O
OH
OH
OH
+
Salicylic acid
O
H3C
OH
Methanol
conc. H2SO 4
+
H2O
Methylsalicylate
d. Special Test for Benzyl Alcohol:
1. Action of Concentrated H2SO4:
To 0.5ml of the benzyl alcohol, add 0.5ml of concentrated H2SO4 and shake the
mixture. Heat is evolved and a white gelatinous precipitate separates.
OH
conc. H 2SO 4
OH
13
-H 2O
Page
2
14
6.2 Phenols (Ar-OH):
1. Physical Properties:
a. State: All phenols are solid except m-cresol which is liquid.
b. Colour: Slightly coloured, due to atmospheric oxidation.
c. Odour: Phenolic Odour.
d. Flammability: Flammable with smoky flame.
e. Solubility:
1. The parents of both monohydric and dihydric phenols are the only H2O
soluble phenols e.g., phenols, catechol, resorcinol and hydroquinone with
acidic solution.
2. All phenols are soluble in NAOH (Acidic Compounds).
3. Phenols are more acidic than H2O and alcohol but less acidic than
carboxylic acids and so unable to liberate CO2 from Na2CO3 solution.
2. Infrared Spectra:
- (O-H) stretching gives a broad peak at 3500-3200 cm-1.
- Aromatic C-H stretching gives peak just above 3000 cm-1.
3. Special Tests for Phenolic Hydroxyl Group:
a. 3,5-Dinitrobenzoyl Chloride:
To about 0.5g of 3,5-Dinitrobenzoyl Chloride in dry test tube add about 0.5g
of phenol derivative in dilute NAOH, and then warm the mixture until a
clear solution is obtained. Cool and scratch, a white or yellowish crystalline
solid will separate.
O
O
-
-
+
N
N
O
R OH
O
N
O
+
+
O
+
-
heat
-HCl
O
+
O
Cl
O
O
N
O
-
R
Page
14
b. Bromine-water:
To the aqueous solution of phenol derivative in presence of alcohol as a
solubilizer, add an excess of bromine water. Some phenol give a white to
yellowish-white ppt. Catechol gives red colour. Hydroquinone gives red
colour then deep green then separation of crystals.
15
OH
OH
Br
Br
EtOH
+
Br
Br
H2O
Br
c. Ferric Chloride Test (FeCl3):
Dissolve 0.1g of phenol derivative (unknown sample) in 3ml water then add
2 drops of Ferric Chloride.
o Phenol, m-cresol, resorcinol give violet-blue colour.
o Catechol gives a green colour with rapid darkening.
o Hydroquinone, gives a green colour, immediately disappear with
crystal separation, solution changes to yellow.
d. Azodye Formation:
-In a first test tube add 5 drops of aniline and 1ml concentrated HCL. Add
3ml of H2O and shake to dissolve any hydrochloride which may separate.
then cool in ice. (Aniline HCl)
-In a second test tube the phenol derivative (unknown sample) is added to
dilute NaOH. Then cool to 0-5c.(phenolic solution)
- add 1ml sodium nitrite(20% NaNO2) solution to aniline HCL. It will form
the Diazonium salt.
- add the formed Diazonium salt to the phenolic solution to obtain azo-dye
(orange-scarlet to dark red precipitates are obtained according to the phenol
used).
- Phenol and m-cresol give orange precipitate.
- Resorcinol gives red to orange precipitate.
NH2
+
N Cl
-
N
NaNO 2 + HCl
at CO -35c
Diazonium Salt
H2C
-
+
ONa
+
N Cl
-
N
N
N
+
H2C
OH
Page
15
Benzene-azo-phenol
16
e. Phthalein Reaction:
To equal amounts (0.2g) of the phenol derivative (unknown sample) and
phthalic anhydride or phthalic acid contained in a dry test tube, add 2 drops of
concentrated H2SO4 and fuse by gentle heating for one minute. Cool, and then
pour into a beaker containing 10%NaOH to obtain a characteristic colour,
easily disappears upon acidification by HCL and repeat upon alkalinization by
NaOH.
HO
HO
OH
H H
O
Fuse/H 2SO 4
O
-H 2O
O
HO
O
O
Phenol phthaein (Colourless)
HCl
NaOH
O
+ -
Na O
-
O Na+
O
4. Special Compound Tests:
a. Phenol:
Page
FeCl3: Violet colour.
Bromine water: White ppt.
Phthalein reaction: Pink colour in NaOH.
Azodye: Orange ppt.
16
OH
17
b. M-Cresol:
OH
CH3
FeCl3: Violet colour.
Bromine water: White ppt.
Phthalein reaction: Bluish purple.
Azodye: Orange ppt.
c. Resorcinol:
OH
OH
FeCl3: Violet colour.
Bromine water: Yellow ppt.
Phthalein reaction: Green fluorescence.
Azodye: Red to Orange ppt.
d. Catechol:
OH
OH
FeCl3: Green colour.
Bromine water: Red colour.
Phthalein reaction: Blue colour.
e. Hydroquinone:
OH
Page
17
OH
FeCl3: Green with separation of green crystals.
Bromine water: Deep red with green crystals.
Phthalein reaction: purple.
18
O
O
R
6.3Aldehydes (
R
H ) and
Ketones (
1
R
):
1. Physical Properties:
a. State and Colour:
- All aldehydes are colourless liquids except formaldehyde which is a gas and only
its aqueous solution is considered.
- Acetone and acetophenone are also colourless liquids.
b. Odour:
- Aqueous solution of formaldehyde gas has pungent odour.
- Benzaldehyde has bitter almond oil odour.
- Acetaldehyde, acetone and acetophenone have characteristic odour.
c. Flammability:
- Aliphatic aldehydes and ketones are flammable with blue no smoky flame.
- Aromatic aldehydes and ketones are flammable with smoky flame.
d. Solubility:
- Aliphatic aldehydes and ketones are miscible with water with no effect on litmus
paper.
- Aromatic aldehydes and ketones are immiscible with water but they are miscible
with concentrate H2SO4.
2. Infrared Spectra:
- Ketones:
C=O Stretch at 1725-1700 cm-1.
- Aldehydes: C=O Stretch at 1740-1725 cm-1.
C-H Stretch at 2850-2750 cm-1.
3. Special Tests for Carbonyl Group of Aldehyde and Ketones:
a. 2,4-Dinitrophenylhydrazine:
- To about 0.5ml of aliphatic aldehyde or ketone, add about 2ml of 2,4dinitrophenylhydrazine… A yellow precipitate is produced in the cold.
- To about 0.5ml of aromatic aldehyde or ketone, add about 2ml of 2,4dinitrophenylhydrazine… An orange precipitate is obtained.
+
N
O
R
1
-
+
+
N
N
O
R
O
O
O
+
-
-H 2O
O
+
N
O
O
NH
NH
NH2
N
-
R
R
1
18
-
Page
O
19
b. Schiff’s Reagent:
Add 1ml of Schiff’s reagent to equal volume of the aldehyde or ketone on
shaking a magenta red colour develops.
These two tests confirm the presence of carbonyl group (aldehyde and ketones).
4. Differentiation between aldehydes and ketones:
a. Reduction of ammonia AgNO3 (Tollen’s test):
Place about 5ml of AgNO3 solution in a clean test tube and 2 drops of dilute
NaOH solution. Add dilute ammonia solution drop wise until the precipitated
Ag2O is redissolved. Then add 3 drops of aldehyde. A silver mirror is formed,
(a grey precipitate is obtained).
AgNO3 + NaOH
Ag2O + 2NaNO3 + H2O
Grey ppt
Ag2O + NH4OH
Ag (NH3)2+
Silver ammonia ion (Colourless)
R-CHO + 2Ag (NH3)2+
2Ag + RCOONH4 + 3NH2 + H20
Silver metal (mirror)
N.B.: With aromatic aldehydes (being water insoluble). It is advisable to
warm the mixture gently on a water bath, shaking the tube vigorously from
time to time to break up the oily globules of the aromatic aldehydes.
(This test is positive only with aldehydes, while ketones give no mirror)
b. Fehling’s Solution:
To 1ml of the aldehyde add about 1ml of 10% Na2CO3 solution. Then add few
drops of Fehling’s solution (A+B) and then boil in a water-path. The solution
usually turns green and on standing a fine yellow or red precipitate of cuprous
oxide slowly separates.
Aliphatic aldehydes reduce Fehling’s solution rapidly while aromatic
aldehydes (e.g. Benzaldehyde) very slowly.
This test is positive with aldehydes only while ketones give negative tests.
19
R-COONa +Cu2O + 4H+
Red ppt
Page
R-CHO + 2Cu++ + Na2CO3 + H2O
20
5. Special Chemical Tests:
a. Special chemical test for Formaldehyde: (HCHO):
To 0.5 g of formaldehyde solution adds 2 g salicylic acid and 0.5 ml of
concentrated H2SO4 on the wall of the test tube. A crimson red colour is
produced.
b. Special chemical test for Acetaldehyde: (CH3CHO):
i.
To 1 ml of acetaldehyde add few mls of 30% NaOH. A yellow resin
which turns to red on warming is produced.
ii.
Iodoform Reaction: To 0.5 ml acetaldehyde add 1 ml of 10%KI
solution then add sodium hypochlorite drop wise until persistent
yellow colour is obtained, warm gently in a water bath. A yellow ppt is
formed.
iii.
Nitroprusside Reaction: Add 1 ml sodium Nitroprusside solution to 0.5
ml aldehyde then add dil. NaOH in excess. A red colour is produced.
c. Special chemical test for Benzaldehyde (C6H5CHO):
i.
Bisulphite addition:
Shake 1 ml of Benzaldehyde with about 0.5 ml of saturated sodium
Bisulphate(NaHSO3) solution. The mixture becomes warm, and the white
product separates (rapidly on cooling).
Na O
OH
O
S
O
O
+
Na S
H
HO
OH
O
Benzaldehyde Sodium metabisulphite
O
Iodoform Test:
To 2 ml of acetone (or Acetophenone) add 5 ml of NaOH (10%) then add
iodine solution with shaking till a yellow colour persist. place in waterbath at 600C for 3-5 minutes. A pale yellow ppt is formed.
Page
i.
20
CH3)/Acetophenone
d. Special chemical test for Acetone (H3C
(C6H5COCH3):
Special tests for Acetone and Acetophenone are the same because they have
the same group R-C-CH3but the main differences are that Acetone is aliphatic
and water miscible, while Acetophenone is aromatic and water immiscible
(miscible with concentrated H2SO4).
21
O
H3C
R
I
+
3I I
+ 4 Na OH
O
I
I
+
-
O Na+
+ 3 H2O
R
ii. Nitroprusside reaction:
Add I ml of sodium Nitroprusside solution to 0.5 ml of acetone (or
Acetophenone). Add dil. NaOH solution in excess. A red colour is
produced.
O
O
CH3
-
alkali
-OH
R
CH2
R
+ H2O
O
CH3
R
+
[Fe(CN) 5NOCH 2COR] --
[Fe(CN) 5NO] --
Nitroprusside ion
m-Dinitrobenzene test:
To 1 ml of acetone (or Acetophenone) add about 0.1 g of finely
powdered m-dinitrobenzene and then add excess of dil. NaOH. A
violet colour is produced but slowly fades.
O
+
O
-
O
N
+
O
N
O
NaOH
+
+
O
R
-
H
N
O
-
+
O
N
O
O
-
Violet coloured compound
21
CH3
R
-
Page
iii.
Red
22
Carboxylic Acids (R-COOH):
1. Physical properties:
a. Colour and state:
All are colourless crystalline solids except formic, acetic and the syrupy lactic
acids.
b. Odour:
- Formic acid has a pungent odour.
- Acetic acid has a vinegar odour.
- Lactic acid has a milk-souring odour.
- Cinnamic acid has a characteristic pleasant odour.
c. Flammability:
- Some of the smoky flammable aromatic acids include benzoic, salicylic, tartaric
and lactic acids.
- α-Hydroxy carboxylic acids produce a burnt-sugar odour, e.g. citric, tartaric and
lactic acids.
- Tartaric acid is identified by its swelling, while citric acid is differentiated by its
yellow stain-darkening-charring upon continuous heating.
- Salicylic acid produces phenolic odour and benzoic gives suffocating odour.
d. Solubility:
- All are NaOH and Na2CO3 soluble, but only aliphatic ones are H2O soluble.
- Dicarboxylic acids (e.g. phthalic) are more H2O-soluble than monocarboxylic
ones due to higher degree of hydrogen bonding.
2. Infrared Spectra:
a. OH stretch at 3400-2400 cm-1, very broad.
b. (-C=O) stretch at 1730-1700 cm-1.
3. Tests for carboxyl (COOH) Group:
a. Na2CO3 Test:
Add 2 ml of dil. Sodium bicarbonate (Na2CO3) to 0.5 g of carboxylic acid
derivatives then note the effervescence and evolution of CO2.
RCOOH + Na2CO3
RCOO- Na+ + CO2
+ H2O
b. FeCl3 Test:
The free acid must be neutralized at first as follow:
Place about 0.1 g of the acid in a boiling tube and add a slight excess of ammonia
solution, add a piece of unglazed porcelain and boil until the odour of ammonia is
completely disappeared and then cool. To the neutral solution of the acid add a
few drops of ferric chloride solution, and note the results.
- Coloured solutions or ppt are obtained only from neutralized acids or their salts
using neutral FeCl3 Solution.
- N.B.: Any excess NH4OH must be avoided because on addition of FeCl3, a brown
ppt of Fe(OH)3 will be formed.
Page
22
-
23
R-COOH + NH4OH
i.
ii.
iii.
iv.
v.
R-COO-+NH4 + H2O
Formate and acetate:
Red colour
Boiling
reddish brown
Benzoate and phthalate:
Buff. Ppt
+ H2SO4
white ppt (free acid)
Salicylate:
Brown-red colour
one drop
violet colour
HCl
α – Hydroxy acids:
Yellow colour (blank must be done)
Oxalate:
Very faint yellow colour (blank also done)
4. Special Compound Tests:
a. Formic acid (HCOOH):
It is identified by its reducing property as follow:
ii. KMnO4:
Acidic decolourization by dil. H2SO4:
- Add a few ml of dil. H2SO4 to a solution of formic acid, add dil. Solution of
KMnO4 drop by drop and note decolourization which is hastened by warming.
Alkaline decolourization by 10% Na2CO3:
- To 2-3 drops of formic acid, add 5 ml 10% Na2CO3 solution. Then add 1 %
aqueous solution of KMnO4 drop wise, immediate decolourization takes place in
the cold with the simultaneous precipitation of manganese dioxide MnO2.
iii. Tollen’s:
- It reduces ammonium AgNO3 into Ag-mirror or grey metallic silver oxide on
boiling.
- Place about 5 ml of AgNO3 solution in a clean test tube and 2 drops of dilute
NaOH solution. Add dilute ammonia solution drop wise until the precipitated
Ag2O is redissolved. Then add 3 drops of formic acid. A silver mirror is formed,
(a grey precipitate is obtained).
23
HgCl2:
- It reduces HgCl2 into HCl-insoluble white ppt of Hg2Cl2 or grey ppt of Hg.
- Add HgCl2 solution to formic acid and warm. A white ppt of mercurous chloride
Hg2Cl2 (insoluble in dil. HCl) is produced.
- Sometimes the reduction proceeds as far as metallic mercury, which appears as a
grey ppt.
Page
i.
24
b. Acetic acid (CH3COOH):
i. Ethyl acetate ester (bad apple-like odour)
ii. No reducing property (unlike formic).
c. Lactic acid [CH3-CH(OH)COOH]:
i. Iodoform test: yellow ppt on the cold.
- To 0.5 ml of alcohol add 1 ml of 10% NAOH, I2 solution is then added drop wise
until persistent yellow colour is obtained, warm in a water-bath, a yellow
precipitate is formed.
ii. Concentrated H2SO4 Test: (Brisk eff.)
d. Tartaric acid:
i. Fenton’s Test:
To a tartaric acid solution add 1 drop fresh FeSO4 solution, 1 drop H2O2
solution then excess of NaOH solution to obtain intense violet colour.
HO
O
OH
H
HO
OH
H
O
OH
H
+ FeSO 4/H2O 2
O
OH
3+
2 Fe
O
excess NaOH
HO
O
Tartaric acid
-
3
Dihydroxyfumaric-Ferric salt (violet)
ii. Tollen’s Ag-mirror only from neutralized acid.
iii. Concentrated H2SO4 Heavy charring.
e. Citric acid:
HO
O
O
OH
OH
24
To a concentrated solution of citric acid add 1 ml dil. H2SO4 and 1 ml HgSO4
solution then boil, and add 1 ml of KMnO4 solution. A white ppt will be obtained
with decolourization of KMnO4.
Page
-
O
25
f. Oxalic acid:
O
OH
O
OH
i.
CaCl2:
To a neutralized acid solution, add CaCl2 solution to obtain white ppt of
calcium oxalate, insoluble in acetic acid but soluble in HCl.
ii.
KMnO4:
Only acid but not alkaline reduction.
g. Salicylic acid:
O
OH
OH
i.
Methyl salicylate ester (oil of winter green odour).
ii.
Phthalein Test:
Its phenolic group gives bright red colour by Phthalein test (coupling
with phthalic anhydride).
h. Benzoic acid(C6H5-COOH) :
Identified by cancellation (note that neutral benzoic acid gives buff ppt with
neutral FeCl3 solution).
i. Phthalic acid:
i.
Phthalein Test: (Coupling with phenol) bright red colour.
25
Fluorescein test:
Fuse carefully together in a dry test tube for about 1 minute a few crystals
of resorcinol and an equal quantity of phthalic acid, moistened with 2
drops of concentrated H2SO4. Cool, dissolve in water and add NaOH
solution in excess. A red solution is produced which exhibits an intense
green fluorescence.
Page
ii.
26
O
O
6.4 Esters
R
R
1
:
1. Physical properties:
a. State and colour:
All are colourless and most of them are liquids but few of them are solid at room
temperature. e.g. salol (phenylsalicylate).
b. Odour:
Characteristic odour depending on the type of ester.
c. Flammability:
Aromatic members are flammable with smoky flame e.g. salol, methylsalicylate.
d. Solubility:
Insoluble in H2O. But, soluble in concentrated H2SO4.
2. Infrared Spectra:
C=O stretch at 1735-1750 cm-1.
3. Tests for Ester Group:
a. Test with hydroxylamine hydrochloride:
Add about 0.2 g of hydroxylamine hydrochloride to about 0.5 ml (g) of ester, then
add about 5 ml of dil. Sodium hydroxide, gently boil for 2 min, cool and acidify
with dil. Hydrochloric acid, then add a few drops of ferric chloride solution. A
violet to deep red-brown colour is produced immediately.
R-COOR’ + NH2-OH.HCL
NaOH
R’-OH + RCONH OH + NaCl
b. 30% NaOH: with methylsalicylate it gives a white precipitate.
Page
26
c. FeCl3: Methyl and phenylsalicylate give violet colour due to phenolic hydroxyl
group.
27
6.5 Amides (R-CONH2):
1. Physical properties:
a. State and colour:
All amides are colourless solids except formamide which is a liquid.
b. Odour:
All amides are odourless.
c. Flammability:
Aromatic amides e.g.: salicylamide flammable with smoky flame. While urea
evolves NH3 odour, it melts then resolidifies.
d. Solubility:
Aliphatic amides are H2O-soluble e.g. urea, while aromatic amides are soluble in
NaOH but not in H2O.
2. Infrared Spectra:
C=O (stretch): 1670-1640 cm-1.
N-H (stretch): 3500-3100 cm-1. (10 amides have 2 NH2 bands in this region).
3. Tests for amide Group:
a. 30% NaOH: All amides give NH3 odour with the sodium salt of the corresponding
acids.
R-CONH2 + NaOH
R-COO-Na+ + NH3
b. Soda lime Test:(mix. of NaOH and CaO)
Mix 0.2 g of the amide with about 1 g of powdered soda lime by grinding
in a small clean mortar, note any odour on cold. Transfer the mixture into
hard-glass test tube and heat the tube very gently at first, then more
strongly and smell cautiously the odour produced. NH3 odour is
produced.
4. Special compound Tests:
a. Urea:
O
H2N
Formation of biuret and biuret reaction: place 0.2 g of urea in a dry test tube, heat
gently. Just above the melting point (m.p.)and note the production of NH3. After
1-2 min the liquid suddenly solidify with the formation of biuret.
2
O
heat
H2N
NH2
H2N
NH
NH2
+
NH3
Dissolve the solid residue in a few ml of warm 10% NaOH. Cool, add 1 drop of very
dilute CuSO4. A purple colour is obtained.
27
O
O
Page
-
NH2
28
6.6Amines (R-NH2):
10 Amine: R-NH2
20 Amine: R2NH
30 Amine: R3N
1. Physical properties:
a. Colour and state:
- 10 Aromatic amines are mainly liquids (e.g. aniline), except p-toluidine, and they
have dirty-brown colour due to air-light effect.
- 20 Aromatic amines are dirty-brown liquids (e.g. N-methylaniline).
- 30Aromatic amines are brownish liquids (e.g. N,N-dimethylaniline).
b. Odour:
Characteristic fishy odour. (Stronger in case of 30 amines).
c. Flammability:
Aromatic amines are flammable with smoky flame.
d. Solubility:
Aromatic amines are H2O-insoluble and HCl-soluble forming H2O-soluble
hydrochloride salts.
2. Infrared Spectra:
N-H Stretch 3500-3100 cm-1 (10 amine 2 bands, 20 amine 1 band, 30 amine no band).
C-N Stretch 1350-1000cm-1.
3. Tests for amino Group:
a. HNO2 Test:
- Mix 0.5 ml of aromatic amine in 1 ml of concentrated HCl, then dilute with 3 ml
H2O, cool in ice, add a few drops of NaNO2 solution.
- 10 Aromatic amine: Diazonium salt is formed and confirmed by:
1. Azo dye Test: coupling with ice-cold, phenol in excess NaOH solution gives
brilliant red or orange dye.
2. Deamination: boiling the Diazonium salt solution with alkali sodium stannite
(which is prepared by the addition of SnCl2 solution to NaOH and a few
drops of NH4OH) gives benzene odour.
3. Hydrolysis: boiling the Diazonium salt solution with H2O gives phenolic
odour.
-
Cl
N
NH2
+
+
HCl
Na N
O
-
+ H2O
Page
O
+
28
N