purification-of-organic-compounds.ppt class 11 science chemistry

Purification of organic compounds

2. Purification of Organic
Compounds
•These techniques include:
1.Filtration
2.Centrifugation
3.Crystallization
4.Solvent extraction
5.Distillation

3. Purification of Organic
Compounds
•These techniques include:
5.Fractional distillation
6.Sublimation
7.Chromatography
8.Steam distillation
9. Sublimation

4. By Using Filtration

5. Filtration
•To separate an insoluble solidfrom a liquid
particularly when the solid is suspended
throughout the liquid
•The solid/liquid mixture is called a suspension

6. Filtration
The laboratory set-up of filtration

7. Filtration
•There are many small holesin the filter paper
allow very small particles of solventand
dissolved solutesto pass through as filtrate
•Larger insoluble particlesare retained on the
filter paper as residue

8. By Using Centrifugation

9. Centrifugation
•When there is only a small amount of
suspension, or when much faster
separationis required
Centrifugationis often used
instead of filtration

10. Centrifugation
•The liquid containing
undissolved solids is put
in a centrifuge tube
•The tubes are then put
into the tube holders in a
centrifuge
A centrifuge

11. Centrifugation
•The holders and tubes are spun around at a
very high rateand are thrown outwards
•The denser solidis collected as a lumpat
the bottom of the tube with the clear liquid
above

12. By Using Crystalisation

13. Crystallization
•Crystalsare solids that have
a definite regular shape
smooth flat facesand straight edges
•Crystallizationis the process of forming
crystals

14. 1. Crystallization by Cooling a Hot Concentrated
Solution
•To obtain crystalsfrom an unsaturated
aqueous solution
the solution is gently heatedto make it
more concentrated
•After, the solution is allowed to coolat
room conditions

15. 1. Crystallization by Cooling a Hot Concentrated
Solution
•The solubilitiesof most solids increase
with temperature
•When a hot concentratedsolution is
cooled
the solution cannot holdall of the
dissolved solutes
•The “excess”solute separates out as
crystals

16. 1. Crystallization by Cooling a Hot Concentrated
Solution
Crystallization by cooling a hot concentrated solution

17. 2. Crystallization by Evaporating a Cold Solution
at Room Temperature
•As the solventin a solution evaporates,
the remaining solution becomes
more and more concentrated
eventually the solution becomes
saturated
further evaporation causes
crystallization to occur

18. 2. Crystallization by Evaporating a Cold Solution
at Room Temperature
•If a solution is allowed to stand at room
temperature,
evaporationwill be slow
•It may take days or even weeksfor crystals
to form

19. 2. Crystallization by Evaporating a Cold Solution
at Room Temperature
Crystallization by slow evaporation of a solution (preferably
saturated) at room temperature

20. By Using Solvent
Extraction

21. Solvent Extraction
•Involves extracting a componentfrom a
mixture with a suitable solvent
•Wateris the solvent used to extract salts
from a mixture containing salts and sand
•Non-aqueous solvents(e.g. 1,1,1-
trichloroethaneand diethyl ether) can be
used to extract organic products

22. Solvent Extraction
•Often involves the use of a separating
funnel
•When an aqueous solution containing
the organic productis shaken with
diethyl etherin a separating funnel,
the organic product dissolvesinto
the ether layer

23. Solvent Extraction
The organic product in an aqueous solution can be extracted by solvent
extraction using diethyl ether

24. Solvent Extraction
•The ether layercan be run off from the
separating funnel and saved
•Another fresh portion of etheris shaken
with the aqueous solution to extract any
organic products remaining
•Repeated extractionwill extract most of
the organic product into the several
portions of ether

25. Solvent Extraction
•Conducting the extraction with several
small portions of etheris more efficient
than extracting in a single batch with the
whole volume of ether
•These several ether portions are
combinedand dried
the ether is distilled off
leaving behind the organic product

26. By Using Distillation

27. Distillation
•A method used to separate a solvent
from a solution containing non-volatile
solutes
•When a solution is boiled,
only the solventvaporizes
the hot vapour formed condensesto
liquid again on a cold surface
•The liquid collected is the distillate

28. Distillation
The laboratory set-up of distillation

29. Distillation
•Before the solution is heated,
several pieces of anti-bumping
granulesare added into the flask
prevent vigorous movementof the
liquid called bumpingto occur during
heating
make boiling smooth

30. Distillation
•If bumpingoccurs during distillation,
some solution (not yet vaporized)
may spurt outinto the collecting
vessel

31. By Using Fractional
Distillation

32. Fractional Distillation
•A method used to separate a mixture of
two or more miscible liquids

33. Fractional Distillation
The laboratory set-up of
fractional distillation

34. Fractional Distillation
•A fractionating columnis attached vertically
between the flask and the condenser
a column packed with glass beads
provide a large surface areafor the
repeated condensation and vaporization
of the mixture to occur

35. Fractional Distillation
•The temperature of the escaping vapour
is measured using a thermometer
•When the temperature reading becomes
steady,
the vapour with the lowest boiling
point firstly comes outfrom the top of
the column

36. Fractional Distillation
•When all of that liquid has distilled off,
the temperature reading risesand
becomes steady later on
another liquid with a higher boiling
pointdistils out
•Fractions with different boiling pointscan
be collected separately

37. By Using Sublimation

38. Sublimation
•Sublimation is the direct change of
a solid to vapouron heating, or
a vapour to solidon cooling
withoutgoing through the liquid
state

39. Sublimation
•A mixture of two compounds is heated in an
evaporating dish
•One compound changes from solid to
vapour directly
The vapour changes back to solidon a
cold surface
•The other compound is not affected by
heatingand remainsin the evaporating dish

40. Sublimation
A mixture of two compounds can be separated by
sublimation

41. 3. DISTILLATION
Aim
Toseparateasolutionofasolidinaliquidandforseparatingasolutionoftwo
liquidswhoseboilingpointsaredifferent.
Principle
Distillationinvolvestheconversionofaliquidintoitsvaporsuponheatingand
thencoolingthevaporsbackintotheliquid.Dependingonthedifferencein
boilingpointsofliquids.
Typesofdistillation
Simple Distillation
Fractional Distillation
Distillation Under Reduced Pressure or Vacuum Distillation
Steam Distillation
41

42. SIMPLE DISTILLATION
Principle
Itisusedforseparatingliquidshavingboilingpoints
differingby10-20degrees.Theliquidhavingthelower
boilingpointdistillsoverfirst,andtheotherliquid
componentisleftbehind.Inthisprocess,vaporization
andcondensationoccursidebyside.
Process
Example
Simple distillation of a Cyclohexane-Toluene mixtures
42

43. Video of How Simple
Distillation Works ?
http://www.youtube.com/watch?v=T4eIc
_v-SrI
43

44. FRACTIONAL DISTILLATION
Principle
Itisusedforseparatingtwoliquidsinanymixture,which
haveboilingpointswithinanarrowrangeoftemperatures.
Insuchcases,simpledistillationdoesnotgivecomplete
separationandamodifiedversioncalledfractional
distillationisemployed.
Process
Example
Fractional Distillation of a Cyclohexane-Toluene
mixtures
44

45. Video of How Fractional
Distillation Works ?
http://www.youtube.com/watch?v=Z6Oy
NB8V7Hc&list=UUunr-
10Cibvv4CKUBeI_Hkw
45

46. STEAM DISTILLATION
Principle
Thistechniqueisusedforseparating/purifyingliquids,
whichareimmisciblewithwater,volatileinsteam,&have
highvaporpressureattheboilingtemperatureofwater.
Process
Example
Isolation of Citral
46

47. Video of How Steam
Distillation Works ?
http://www.youtube.com/watch?v=7g4e3dh
tgjI
47

48. By Using
Chromatography

49. Chromatography
•An effective method of separating a
complex mixture of substances
•Paper chromatographyis a common
type of chromatography

50. Chromatography
•A solution of the mixture is dropped at
one end of the filter paper

51. Chromatography
•The thin film of wateradhered onto the surface
of the filter paperforms the stationary phase
•The solvent is called the mobile phaseor eluent

52. Chromatography
•When the solvent moves acrossthe sample spot
of the mixture,
partition of the componentsbetween the
stationary phase and the mobile phase occurs

53. Chromatography
•As the various components are being
adsorbed or partitionedat different rates,
they move upwards at different rates
•The ratio of the distance travelled by the
substance to the distance travelled by the
solvent
known as the R
fvalue
a characteristicof the substance

54. k= C
s
C
m
K is the partition coefficients of the
components of a mixture between two
immiscible phases -stationary phase
and mobile phase
C
s
is the concentration of the substance in
the stationary phase (Adsorbent)
C
m
is the mobile phase ( Eulent)

55. By Using Sublimation

56. 2. SUBLIMATION
Aim
Toseparatevolatilesolids,whichpassdirectlyintovapour
stateonheatingfromanon-volatilesolid.
Principle
Amixtureofsolidsubstances,suchascamphor,benzoicacid,
ammoniumchloride,iodineetc.,containingnon-volatile
substances,whenheated,changedirectlyintovapourwithout
passingthroughtheliquidstate.
Process

57. Fig :-Sublimation
Substance Mp Substance Mp
1,4-dichlorobenzene 55 Benzoic acid 122
Naphthalene 82 Salicylic acid159
1-Naphthol 96 Camphor 177
Acetanilide 114 Caffeine 235