Chemistry
SESSION
Purification And Characterisation
of Organic Compounds - 1
SESSION OBJECTIVES
1. Introduction — necessity of purification.
2. Methods of purification of organic
compound.
(a)Crystallisation
(b) Fractional crystallisation
(c) Sublimation
(d) Distillation
(e) Fractional distillation
(f) Steam distillation
(g)Vacuum distillation
(h)Differential extraction
(i) Chromatography
SESSION OBJECTIVES
3.
Detection of elements
(Qualitative analysis)
(a)
Detection of carbon
(b)
Detection of hydrogen
(c)
Detection of nitrogen
(d)
Detection of sulphur
(e)
Detection of halogen
(f)
Detection of oxygen
PURIFICATION
•
Filtration
•
Crystallization
•
Sublimation
•
Distillation
•
Differential extraction
•
Chromatography
FILTRATION
Only one of the compounds
is soluble in the given
solvent
eg.
(i) Urea and Naphthalene
(ii) Benzoic acid and anthracene
CRYSTALLIZATION
Most common method for purification
of solid organic compounds.
Impurities and organic compound
have different solubilities in the given
solvent.
CRYSTALLIZATION
v
The organic compound should
be insoluble or sparingly soluble
in the solvent at room temperature
but readily soluble in hot conditions.
v
The impurities should be insoluble in the solvent
even in hot conditions.
v
The organic compound should not react with the
solvent.
CRYSTALLIZATION
The mixture of benzoic acid (water
soluble) and naphthalene (water
insoluble) purified by.
CRYSTALLIZATION
How will you separate mixture of
benzoic acid and napthalene ?
benzoic acid (water soluble ) and
napthalene (water insoluble)
FRACTIONAL
CRYSTALLIZATION
Difference in solubilities of organic
compounds and impurities are very
less.
eg. urea and copper sulphate.
SUBLIMATION
Used to separate volatile organic
compounds from non volatile
impurities e.g. Naphthalene,
benzoic acid, anthracene,
camphor.
ILLUSTRATIVE PROBLEM
A mixture of benzene and aniline
can be separated by
(a) alcohol
(b) NaOH
(c) HCl
(d) Hot water
SOLUTION
Amines are basic in nature. Therefore,
aniline reacts with HCl to form a salt
which dissolves in water.
Hence, aniline can be separated from
benzene by using HCl.
Hence, answer is (c).
DISTILLATION
(i) Simple distillationdifference in boiling points of
compounds is more than
40ºC. e.g.– chloroform
(b. p. 334K) and aniline
(b. p. 457K).
DISTILLATION
(ii) Fractional distillation- difference
in boiling points of compounds is less
than 40ºC. e.g. – acetone (b. p.
329K) and methyl alcohol
(b. p. 338K).
DISTILLATION
(iii) Vacuum distillation- used for
organic compounds which
decompose at or below their
boiling points.
e.g. Glycerol.
DISTILLATION
(iv) Steam distillation- used for
organic compounds which
are immiscible with water
and are steam volatile.
e.g. Aniline.
ILLUSTRATIVE PROBLEM
The most suitable method for the
separation of mixture of ortho and
para nitrophenol in the ratio of 1:1
is
(a) distillation
(b) crystallisation
(c) vapourisation
(d) colour spectrum
SOLUTION
The boiling point of o-nitrophenol is
210oC and that of p-nitrophenol is
245oC.
Therefore, vapours of o-nitrophenol will
be formed first (lower boiling point) and
collected seperately and vapours of pnitrophenol will be formed latter.
Hence, answer is (a).
DIFFERENTIAL EXTRACTION
Used to extract pure organic
compounds from their aqueous
solution by shaking with organic
solvent in which they are
highly soluble.
Eg. Benzoic acid from its
aqueous solution using
benzene.
CHROMATOGRAPHY
• Used to purify small samples.
• Based on selective adsorption
or partition between
stationary and mobile phase.
• Column Chromatographybased on adsorption, used for
bulk quantities.
• Thin layer Chromatographybased on adsorption, used for
quantitative analysis.
CHROMATOGRAPHY
• Paper Chromatography- based on
partition and used for quantitative and
qualitative analysis.
• Gas Chromatography- used to separate and
analyse volatile organic liquids.
• High performance liquids Chromatography
(HPLC)- used for qualitative and quantitative
analysis of organic compounds.
CRITERIA OF PURITY OF
ORGANIC COMPOUNDS
1. Boiling point.
2. Melting point.
3. Mixed melting point.
QUALITATIVE ANALYSIS
Detection of C, H, N, halogens
P, S, and oxygen.
DETECTION OF CARBON AND
HYDROGEN
DETECTION OF CARBON AND
HYDROGEN
Organic compound + CuO
CO2 + H2O +Cu
Carbon Water Copper
dioxide
Passed into
lime water
Ca(OH) 2
lime water
turns milky
Passed into
anhydrous
CuSO4
Copper sulphate
turns blue
Carbon (C) present
in organic compound Hydrogen (H) present
in organic compound
DETECTION OF NITROGEN

Organic compound  NaOH  CaO  Smell of NH3
Soda lime
confirms the
presence of
nitrogen in
organic compound
LASSAIGNE’S EXTRACT
Lassaigne’s extract is prepared to
convert covalency of organic compound
into electrovalency by fusing with Na.
ORGANIC COMPOUND
Organic compound
Fused with sodium
(Na)
Lassaignes’s extract
(has NaCN)
sodium cyanide
Few drops of NaOH
Na4
and freshly prepared FeSO4
Fe(CN)6
Sodium ferrocyanide
Excess of HCl
and FeCl 3
(ferric chloride)
Fe
4
Fe( CN ) 6
3
Ferric ferrocyanide
prusslain blue
colouration confirms
presence of nitrogen
in organic compounds
DETECTION OF HALOGEN
Beilstein's test
Organic compound
Heated over
Copper wire
Green flame confirms the presence
of halogen/s in the organic compound
LASSAIGNE’S TEST FOR
HALOGENS

Organic compound
Fused with sodium
(has covalent bonds
with carbon and halogens)
dil. HNO3
Lassaignes extract
(has NaX
sodium halide)
and AgNO3
White ppt of
silver chloride
(AgCl) soluble in
ammonia confirms
the presence of
chlorine in
organic compound
Pale yellow ppt
of
silver bromide
(AgBr) sparingly
soluble in
ammonia
confirms the
persence of
bromine in
organic
compound
Yellow ppt of
silver iodide
(Agl)
insoluble
in ammonia
confirms the
presence of
iodine in
organic
compound
DETECTION OF PHOSPHORUS

Organic compound
With Na 2O
(sodium peroxide)
Phosphorus present in organic compound
change to phosphate (Na 3PO4)
boiled with nitric acid
(HNO3) and added
ammonium molybdate
[(NH4)2MoO4]
Yellow ppt of
ammonium
phosphomolybdate
[(NH4)3PO4.12MoO3]
confirms the presence
of phosphorus in
organic compound
DETECTION OF SULPHUR
fused with mixture of
Organic compound
Potassium nitrite (KNO3)
and sodium carbonate
Sulphur present in organic
compound changes into sulphate
Extracted with
water, filtered
and added dil. HCl
BaCl2
white ppt of
barium sulphate
(BaSO4) confirms
the presence of
sulphur in
organic compound
ILLUSTRATIVE PROBLEM
When acetic acid and lead acetate
solutions are added to sodium
extract, black percipitate is formed.
It shows that organic compound has
_____ element.
(a) chlorine
(b) oxygen
(c) phosphorus
(d) sulphur
SOLUTION
Sodium extract + CH3COOH + (CH3COO)2Pb
Black ppt
(PbS)
It shows the presence of sulphur in organic
compound.
Hence, answer is (d).
LASSAIGNE’S TEST FOR
SULPHUR

Organic compound
Lassaignes's extract
Fused with sodium
(has Na 2S
sodium shulphide)
Divide the extract in two parts
To one portion add acetic acid
(CH3COOH) and lead acetate
[Pb(CH3COO)2]
Black ppt. of lead sulphide
(PbS) confirms the presence
of sulphur in organic compound
To other portion add
freshly
prepared sodium
nitroprusside
Na 2[Fe(CN)5(NO)]
Violet colouration
of Na 4[Fe(CN)5NOS]
confirms the presence
of sulphur in organic
compound
DETECTION OF OXYGEN
Presence of oxygen in organic
compound is detected by testing for
functional group containing oxygen
eg- alcohol (–OH), aldehyde (–
CHO), ketone (RCOR), carboxylic
acid (–COOH), ester (–COOR) and
nitro (–NO2).
Thank you