This document discusses various methods for purifying organic compounds, including crystallization, sublimation, distillation, chromatography, differential extraction, and qualitative analysis. Crystallization involves dissolving an impure compound in a solvent and obtaining pure crystals upon cooling. Sublimation separates volatile solids that change directly from solid to gas without passing through liquid state. Distillation techniques like simple distillation, fractional distillation, and steam distillation separate mixtures based on differences in boiling points. Chromatography separates compounds using differences in adsorption between a stationary and mobile phase. Differential extraction uses differences in solubility to separate compounds between organic and aqueous layers. Qualitative analysis identifies compounds through preliminary tests and determining

1. METHODS OF PURIFICATION OF
ORGANIC COMPOUNDS
PRESENTED BY :
Dr. Seema S. Pattanshetti
Assistant Professor of Chemistry
S.Nijalingappa Sugar Institute,
College of B.Sc. (Sugar Science & Technology), Belagavi
1

2. CONTENT
 Introduction
 Purification Methods
 Summary
 Questions
2

3. INTRODUCTION
Organic compounds are isolated either from
natural sources or from reactions mixtures. These
compounds are rarely pure and are usually
contaminated with small amounts of other similar
compounds, which are found to exist together or
formed during the reaction. In order to
characterize them, it is important to purify them.
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4. PROCESSES FOR PURIFICATION
1. Crystallization
2. Sublimation
3. Distillation
4. Chromatography
5. Differential Extraction
6. Qualitative Analysis
7. Criteria of purity (Melting point & boiling point)
4

5.  Method of purifications of solids
1. CRYSTALLIZATION
Aim
To separate a solid compound in pure and geometrical form.
Principle
A saturated solution of the impure substance in a suitable solvent is made at a
temperature higher than the room temperature. On cooling this solution, the
substance reappears in the form of well shaped crystals.
Process
Purification by crystallization involves the following steps:
 Choice of solvent
 Preparation of solution
 Filtration of the solution
 Separating the crystals
 Drying of crystals
Example
Crystallisation of Phthalic acid
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6. FRACTIONAL CRYSTALLISATION
 It is a method of refining the substances based on differences in
solubility. It fractionates Via differences in crystallization
(forming crystals).
 i.e. When there is a mixture of solids differing in their solubility
in the solvent each component of the mixture can be separated in
pure form by fractional crystallisation. From the mixture
dissolved in the solvent, during cooling less soluble component
crystallizes first, leaving behind other component which is more
soluble in solvent. Thus one by one different compounds are
isolated. Further individual compounds are purified by
recrystallisation.
 Ex: Austenite crystals in steel, Glauber’s salt, a crystal form of
sodium sulphate
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7. Fractional crystallization
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8. 8

9. 2. SUBLIMATION
Aim
To separate volatile solids, which pass directly into vapour
state on heating from a non-volatile solid.
Principle
A mixture of solid substances, such as camphor, benzoic acid,
ammonium chloride, iodine etc., containing non-volatile
substances, when heated, change directly into vapour without
passing through the liquid state.
Process
9

10. Fig :-Sublimation
Substance Mp Substance Mp
1,4-dichlorobenzene 55 Benzoic acid 122
Naphthalene 82 Salicylic acid 159
1-Naphthol 96 Camphor 177
Acetanilide 114 Caffeine 235
10

11. 3. DISTILLATION
Aim
To separate a solution of a solid in a liquid and for separating a solution of two
liquids whose boiling points are different.
Principle
Distillation involves the conversion of a liquid into its vapors upon heating and
then cooling the vapors back into the liquid. Depending on the difference in
boiling points of liquids.
Types of distillation
 Simple Distillation
 Fractional Distillation
 Distillation Under Reduced Pressure or Vacuum Distillation
 Steam Distillation
11

12. SIMPLE DISTILLATION
Principle
It is used for separating liquids having boiling points
differing by 10-20 degrees. The liquid having the lower
boiling point distills over first, and the other liquid
component is left behind. In this process, vaporization
and condensation occur side by side.
Example
Simple distillation of a Cyclohexane- Toluene mixtures
12

13. Simple distillation 13

14. FRACTIONAL DISTILLATION
Principle
It is used for separating two liquids in any mixture, which
have boiling points within a narrow range of temperatures.
In such cases, simple distillation does not give complete
separation and a modified version called fractional
distillation is employed.
Example
Fractional Distillation of a Cyclohexane- Toluene
mixtures
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15. FRACTIONAL DISTILLATION
 Process: The mixture of liquids taken in distillation
flask fitted with thermometer & condenser is heated.
The liquid having lower B.P. Boils first & it vapours
are condensed& collected till there is no rise in temp.
When boiling of more volatile liquid stops , another
liquid starts boiling at its B.P. & can be collected in
the pure form separately.
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16. Fractional distillation
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17. DISTILLATION UNDER REDUCED
PRESSURE OR VACUUM DISTILLATION
Principle
The lowering of pressure on the surface of a liquid lowers
its boiling point. As a result of this, a liquid can be boiled
and distilled, without any decomposition, at temperature
much below its normal boiling point.
Process
17

18. DISTILLATION UNDER REDUCED
PRESSURE
18

19. DISTILLATION UNDER REDUCED
PRESSURE
19

20. DISTILLATION UNDER REDUCED
PRESSURE
 PROCESS
 Some liquids decompose during heating
even before the boiling point. For such
liquids distillation under reduced
pressure is used.
 When external pressure is reduced the
liquid boils at a lower temp. Than its
boiling point.
20

21. DISTILLATION UNDER REDUCED
PRESSURE
 Distillation appartus involves an
assembly to reduce external pressure
using suction pump.As shown in fig.
 Ex: Recovery of glycerol is at 298oc.
But it can be made to boil at 180oC by
decreasing external pressure to 12mm
of Hg.
Sugar industry cane juice is concentrated
by ds process.(Vaccum distillation).
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22. STEAM DISTILLATION
Principle
This technique is used for separating/purifying liquids, which are immiscible with water,
volatile in steam, & have high vapor pressure at the boiling temperature of water.
Example
Isolation of Citral , Compounds like Aniline(B.P.1840c ), Phenol (B.P. 1820C)
 Process :
1. The organic mixture together with some water is placed in an round bottom (RB) flask (2) (from
figure). Which is connected in left side to the steam generating R.B. flask (1) and right side to the
water condenser.
2. Heat the mixture to avoid the condensation of steam init .
22

23. STEAM DISTILLATION
 Some liquids have boiling points such higher than the water but boils at
lower temp. When steam is passed. These liquids are usually insoluble or
soluble in water. This type of liquids are called steam volatile liquids.
 In this, liquid is heated on wire gauge during which steam is passed
through the liquid. Liquid vapourises & comes out along with water
vapour sthen mixture is condensed. Those which are non volatile are left
in the flask.
 Organic liquids is separated by extraction using solvents like ether by
separating funnel.
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24. STEAM DISTILLATION
24

25. STEAM DISTILLATION
contd..2
1. The water in the flask is heated and then a current of steam is passed into the
mixture.
2. In flask no (2) the outlet connected from R.B. flask (1) should be dipped thoroughly
in the liquid mixture to disperse water steam coming from R.B. flask (1).
3. The vapour of the compound along with the steam leaves the flask from the outlet
and gets condensed in the water condenser.
4. It is then collected in a conical flask containing ice to solidify the liquid.
5. Further from normal distillation process, we can get separated pure organic liquids.
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26. Applications:
 From this method aniline can be
purified.
 From plant extracts also we can purify
like lemon grass oil, eucalyptus oil etc.
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27. 4.CHROMATOGRAPHY
Aim
To identify, purify and/or separate constituents of a mixture
that are present in very small amounts. It is modern technique
used for the separation & identification of organic
compounds.
Chromos (Greek) – colour.
Principle
The principle behind this technique is the differential
adsorption of the various components of a mixture between
two different phases that are as follows:
 Fixed or stationary phase
 Mobile or Moving phase
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28. COMMONLY EMPLOYED
CHROMATOGRAPHIC TECHNIQUES
 Column Chromatography
 Paper Chromatography
 Ascending and Descending Paper
Chromatography
 Radial Paper Chromatography
 Thin Layer Chromatography
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29. COLUMN CHROMATOGRAPHY
This is the simplest chromatography based on the
differential adsorption of the constituents of a mixture.
A suitable adsorbent like alumina (Al2O3), taken in the
form of a slurry in petroleum ether, constitutes the
stationary phase.
Column chromatography 29

30. THIN LAYER CHROMATOGRAPHY
Principle
In this chromatography, the stationary phase is a thin
layer of an adsorbent (generally alumina) coated on
Flat glass strip. The solvent (mobile phase) moves up
the layer due to the capillary action and thus causes
the separation of constituents of the mixture.
The constituents are identified by measuring their
RF values.
Example
Separation of vitamins by thin layer chromatography 30

31. Thin layer Chromatography
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32. Paper Chromatography
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33. Paper chromatography
 Paper chromatography is an analytical method used to separate
coloured chemicals or substances.
 Chromatography is a method of separating mixtures by using
a moving solvent on filter paper. ... The solvent flows along
the paper through the spots and on, carrying the substances
from the spot. Each of these will, if the solvent mixture has
been well chosen, move at a different rate from the others.
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34. Paper Chromatography
 In paper chromatography, substances are
distributed between a stationary phase and a
mobile phase. The stationary phase is the water
trapped between the cellulose fibers of
the paper. The mobile phase is a developing
solution that travels up the stationary phase,
carrying the samples with it.
 EX: dyes which make up a particular ink. ... Samples of
each ink are spotted on to a pencil line drawn on a sheet
of chromatography paper.
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35. 5. DIFFERENTIAL(Solvent) EXTRACTION
Principle
To extract a compound that is present in very small amounts
in an aqueous solution with the help of an organic liquid in
which that compound is highly soluble.
Process
Differential extraction
Example :-Extraction of Caffeine from Tea , 35

36. Solvent extraction
 All the org. Compounds are usually soluble in common
solvents like Ether, benzene, toluene Chloroform.
 When an org. Com. Is also soluble in water & present in
aqueous solution, it can be separated by using org. Solvent in
which the compound is more soluble compared to water.
 Ex : extraction of uranium& plutonium salt from soln. Of
HNo3
 Ex: extraction of benzene from naptha using sulfolane as
solvent.
36

37. Solvent extraction
 When a solute is added to mixture of two
immiscible liquids, the solute itself gets
distributed between two liquids in such a way
that the ratio of concentration of solute in
organic layer to con. Of solute in organic layer
to concentration of solute in aqueous layer is
constant at constant temp.
 So efficiency of extraction can be increased by
multi step extraction.
 C organic / C aqueous = K
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39. 39

40. 6. QUALITATIVE ANALYSIS
The systematic qualitative analysis of organic
compounds includes the following different stages:
 Preliminary tests and physical examinations.
 Detection of elements
 Determination of functional group or groups.
 Determination of physical constant.
 Identification of the compound by search of
literature with similar physical and chemical
properties.
 Confirmation of compounds by preparing suitable
derivative and specific chemical tests.
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41. SUMMARY
41

42. Criteria of purity:
 Melting point (MP)
 Boiling point (BP)
 Melting point (MP)
 A pure solid substance melts sharply at a definite temperature,
while an impure substance will have a lower and indefinite melting
point.
 Melting point, temperature at which the solid and liquid forms of a
pure substance can exist in equilibrium. As heat is applied to a
solid, its temperature will increase until the melting point is
reached. ... When all the solid has melted, additional heat will raise
the temperature of the liquid.
 The apparatus employed for the determination of the melting point
of a given solid substance is Thieles tube.
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43. Melting point (MP)
 A pure solid substance melts sharply at a definite temperature, while an impure
substance will have a lower and indefinite melting point.
 The apparatus employed for the determination of the melting point of a given solid
substance is Thieles tube.
 The crystals are powdered finally and filled into a capillary tube sealed at one end.
 The capillary tube should be 5-6 cm long and 1 mm in diameter.
 The substance should stand in the capillary 3-4 mm from the bottom when therolly
packed.
 The capillary tube is tied with a thermometer and placed along the side in a
paraffin liquid.
 Now Thieles tube is slowly heated when solid is converted into liquid that
temperature is noted and that temperature we will call it as melting point.
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44. Thiele’s tube
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45. Melting point apparatus
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46. Capillary tube
46

47. Boiling point (BP)
 A pure organic liquid boils at a fixed
temperature which is characteristic of that
substance (capillary tube method).
 The boiling point of a substance is the
temperature at which the vapour pressure of
a liquid equals the pressure surrounding the
liquid and the liquid changes into a vapour.
 The boiling point of a liquid varies depending upon the
surrounding environmental pressure.
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48. Boiling point
48

49. Boiling point
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50. Boiling Point
 When only a small quantity of the liquid is available its boiling point is
determined by the capillary tube method.
 A few drops of the liquid are placed in a thin walled small test tube (Na
fusion tube).
 A capillary tube sealed at one end is dropped into it.
 The glass tube containing the liquid and capillary is then tied along a side the
thermometer so that the liquid stands just near the bulb.
 The thermometer is then placed into theil’s tube containing paraffin. Theil’s
tube is heated slowly.
 When the boiling point is reached, bubbles issue in a rapid stream from the
lower end of the capillary.
 The thermometer is read when you get contagious bubbles.
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51. CONCLUSION
 Purification process is widely used in industry.
 Distillation is among most important and widely
used in industrial operation today. About 95% of
all separation process today is carried out in
industry with more than 40,000 distillation system.
 Sublimation is also use to create freeze- dried
substances. e.g. tea, soup, drug.
 Steam distillation is employed in industry for the
recovery of various essential oils from plant and
flowers.
 Better chemical stability, crystallization process is
use due it help to increase physical stability,
bioavailability and sustain release.
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52. QUESTIONS
Two marks Questions;
1. What is sublimitation?
2. Define simple distillation.
3. What is the principle for simple distillation?
4. Define chromatography.
5. What is melting point?
6. What is boiling point?
7. what type of materials can be purified by fractional distillation?
8. Define steam distillation
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53. Five Marks questions:
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1. Explain simple distillation with working principle
2. Describe sublimation method.
3. write a note on fractional distillation with neat diagram
4. Explain thin layer and paper chromatography
5. Briefly explain the steam distillation
6. Write a note on fractional crystallization
7. Write the procedure for determination of boiling point of any liquid
8. Give the procedure for determination of melting point of any solid
substances.
9. Explain column chromatography.

54. 54