Transcript SATL-POC - Systematic Approach to Teaching

SATL-POC
2009
SYSTEMIC FUNCTIONAL GROUP
TRANSFORMATION
I- In Benzene-Nitrobenzene-Aniline- and Benzenediazonium salt Cycle
Chemical and Spectroscopic Identification
Chemicals and Hazards
Conc. nitric acid
Is a potent oxidizer, it reacts very fast with the
skin, causing burns. Avoid skin contact.
Conc. sulfuric acid
Is corrosive. It may cause burns. Do not remove
the sulfuric acid bottle from hood.
Conc.hydrochloric acid
Is very corrosive and is slightly toxic. Do not
remove the bottle from hood.
Benzene
Is flammable, breathing it can cause drowsiness
and unconsciousness.
Nitrobenzene
Toxic, do not breath its vapor.
Ethanol
Is flammable.
Aniline
It is toxic material, and a cancer suspect agent.
Sodium hydroxide
Is very caustic. Avoid skin contact.
Sodium nitrite
Is a toxic oxidizer
Benzenediazonium
chloride
Avoid skin contact with diazonium salts. Some
diazonium salts are explosive when dry. Always
use in solution.
Chemical Identification
a) Benzene to Nitrobenzene
• Add benzene (1 ml) to a mixture of conc. HNO3 (5 ml) and conc.
H2SO4 (5 ml), and shake for 2 min.
• Pour into cold water whereby nitrobenzene separates as a yellow oil.
Spot test for the NO2 group
• One drop of benzene solution of the sample, and one drop of
(5%) diphenylamine in benzene are introduced into a small tube.
The tube is dipped in boiling water-bath, the solvent is then
evaporated.
• Observation: A melt remains in the tube which is more or less
yellow in color.
.The structure of the compound formed is
Ph
Ar
N O
O
NH Ph
Ph
b) Nitrobenzene to Aniline
• To the nitrobenzene obtained from step (a), (5 ml) of conc. Hydrochloric
acid and small pieces of granulated tin are added.
• The solution is heated just to start the reaction, and then allowed to stand
for some time. When the reaction ceases, filter the product and test for the
amino group in the filtrate.
NO2
Conc. HNO3/H2SO4

(a)
(d) 
(b) Sn / HCl

NH2
N2Cl
(c)

Spot test for the amino group (NH2)
 This test depends on the condensation of the primary amino group with the
colorless 2,4-dinitrochlorobenzene to yield yellow condensation product.
H
O
O2N
Cl
+
H2N-R
N
N
R
O
NO2
NO2
H
O
N
N
R
O
NO2
(Yellow)
Amines containing –SO3H or –COOH groups do not react.
 Procedure: A drop of the ether test solution is treated on a spot plate with
a drop of (1%) ether solution of 2,4-dinitrochlorobenzene. Then ether has
been evaporated.
 Observation: A residual yellow or brown color or ring appears.
c) Aniline to Benzenediazonium chloride
• Aniline oil obtained from step (b) is dissolved in conc. HCl, diluted
with small amount of water (1 ml).
• The solution is cooled well and then adds few drops of sodium nitrite
solution.
NO2
Conc. HNO3/H2SO4

(a)
(d) 
(b) Sn / HCl

NH2
N2Cl
NaNO2 / HCl
(c)

Test for the diazonium salt
 A small part of the diazonium salt solution is added to a cold
solution of β-naphthol in sodium hydroxide.
Observation: Scarlet red dye indicates the presence of the
diazonium salt.
HO
HO
N2Cl
+
N
N
Scarlet red
d) Conversion of Benzenediazonium
Chloride to Benzene (Recycling)
• Add the diazonium salt obtained from step (c) to a solution of
sodium stannite (prepared from stannous chloride by adding sodium
hydroxide drop wise till a white ppt is formed and then redissolves in
alkali).
•Heat the contents of the test tube gently; detect the odor of benzene
NO2
(Starting material).
Conc. HNO3/H2SO4

(a)
Sod. (Recycling)
Stannite (d)

(b) Sn / HCl

NH2
N2Cl
NaNO2 / HCl
(c)

Spectroscopic Characterization
 IR-Spectra
1- Nitro Group: (NO2):
• The vibrational behaviour of the nitro group also supports the structure.
The presence of nitro group in a compound is characterized by the presence
of two strong bands in its infrared spectrum which arise from the
symmetrical and asymmetrical modes which occur in the region:
(i) 1620-1535 cm-1
(ii) 1375-1275 cm-1
• Aromatic compounds show two bands:
(i) 1570-1500 cm-1
(ii) 1370-1300 cm-1
e.g. Nitrobenzene:
2- Primary amino group: (NH2)
• Primary amines show two sharp bands; these can be recognized by absorption
due to N-H str. in the region 3500-3300 cm-1. The position of absorption depends
upon the degree of hydrogen bonding.
• The dilute solution of primary amines in an inert solvent gives two sharp
bands due to symmetric and asymmetric stretching vibrations between 35003300 cm-1.
H
H
N
N
H
H
Asymmetric st. vibration
(High frequency)
e.g. p-Toluidine
H
H
Symmetric st. vibration
(Low frequency)
ASSESSMENT
QI: Analyze the following systemic diagram to chemical equations:
NO2
Conc. HNO3/H2SO4
(a)
Sod.
(d) Stannite
(b) Sn / HCl
NH2
N2Cl
NaNO2 / HCl
(c)
QII: How can you differentiate between the following pairs of
compounds: (Via spot tests)
1. Benzene and nitrobenzene.
2. Benzene and aniline.
QIII: How can you differentiate between the following
compounds by I.R. spectra:
Nitrobenzene and Aniline
QIV: What are the main objectives for using the systemic cycle (In
QI) for chemical investigation of (benzene, aniline,
nitrobenzene and diazonium salt).
II) In Benzonitrile-Benzamide- and Benzoic
Acid Cycle
1) Chemical and Spectroscopic Identification
CN
(c)
(a)


CONH2
COOH
(b)

Chemicals and Hazards
Benzonitrile
It is flammable and toxic.
Hydrogen peroxide
It is oxidizer. Avoid skin contact.
Ammonium hydroxide It is corrosive lachrymator. Dispense
this chemical in the fume hood.
Sodium hydroxide
It is very caustic, avoid skin contact.
Chemical Identification
a) Benzonitrile to Benzamide
In a small test tube, place (0.2 ml) of the nitrile, (1 ml) of ethanol and (1 ml)
of (1N) sodium hydroxide. To this mixture add dropwise (1 ml) of (12%)
hydrogen peroxide. Maintain the solution at (50-60ºC) in a water-bath for 30
min. Dilute the reaction mixture with cold water and collect the solid amide.
CN
(c)
NaNO2 / H2O2

(a)

COOH
CONH2
(b)

Identification of benzamide:
Effect of sodium hydroxide:
A small amount of the solid is heated in a test tube with sodium hydroxide solution.
Observation: Evolution of ammonia which is detected by its odor indicates
the presence of amide group.
b) Benzamide to Benzoic acid
Mix (1g) of the amide from step (a) with (10 ml; 10%) sodium
hydroxide. Boil the mixture for 10 minutes, cool well and then adds
conc. hydrochloric acid whereby benzoic acid is separated. Wash
with little water and determine its m.p.
CN
(c)
NaNO2 / H2O2

(a)

COOH
i) NaOH, ii) HCl
(b)

CONH2
Identification of the acid:
1- Acidity test: To a small amount of the acid add sodium bicarbonate
solution.
Observation: Effervescence and evolution of CO2 indicates the
presence of the acid.
2- FeCl3 test: To a suspension of the acid in water, add ammonium
hydroxide solution till just alkaline. Boil the solution
till the excess of ammonia has been expelled i.e. no
odor of ammonia is detected, add FeCl3 solution.
Observation: A buff precipitate indicates benzoic acid.
c) Benzonitrile to Benzoic acid
 Boil (1 ml) of benzonitrile with (10 ml) of 10% sodium hydroxide
till all the oil drops disappear. Cool well and then adds conc.
hydrochloric acid whereby benzoic acid is separated.
 Confirm the formation of benzoic acid as described above.
CN
NaOH
NaNO2 / H2O2

(a)
(c)

COOH
i) NaOH, ii) HCl
(b)

CONH2
1) Spectroscopic Characterization
 IR-Spectra
Nitrile group:
• The infrared absorption occurs in the triple bond region
between (2280-2200 cm-1). The shift in νC≡N stretching
absorption depends upon the electronic effects of atoms or
groups attached to the C≡N group.
• In aliphatic nitriles, the intensity of νC≡N stretching band is low.
CH3-C≡N
2280 cm-1
CH3-CH2-C≡N
2257 cm-1
• In aromatic nitriles, the νC≡N stretching decreases by about
20 cm-1 but band intensity increases as compared to the
saturated compounds.
e.g. I.R. spectrum of benzonitrile
Amide group:
 The νC=O absorption in amides takes place at lower wave
number. In addition to the νC=O absorption, amides can be
recognized by N-H stretching and N-H def. bands.
 Primary amides in dilute solutions show two bands (N-H str.)
near 3400 cm-1 and 3500 cm-1. These two bands arise due to
symmetrical and asymmetrical N-H stretching.
e.g. I.R. spectrum of benzamide
Signals and their absorption peaks:
Proton type
Three proton triplet
Two proton quartet
Two proton hump
δ (ppm)
8.85
7.7
2.9-4.0
Carboxylic Group:
• Carboxylic group (-COOH) is the easiest functional group to detect by infrared
spectroscopy since this group can be considered as being formed from C=O and O-H
units. The absorption of O-H stretching appears as a broad band near 3000 cm-1. The
νC=O stretching absorption in aliphatic acids occurs at 1725-1700 cm-1.
• Some of the acids viz., acetic acid, benzoic acid, exist as dimmers due to hydrogen
bonding. Formation of bridge lowers the force constants and thus, νC=O and νO-H
absorption occur at lower wave numbers. As the hydrogen bonded structure is
stabilized by resonance, the O-H stretching occurs as a broad band in the region 33002500 cm-1.
O
H O
O
H O
C
C
O H
O
C
C
O
H
O
1H-NMR-
Spectra:
The following chart represents the 1H-NMR- Spectrum of a-chloro
propionic acid as a representative of this class of compounds.
Proton type / splitting
Three protons doublet
One proton quartet
One proton singlet for –COOH (off the scale)
δ (ppm)
8.85
7.7
2.9-4.0
2) Quantitative Determination of Carboxylic Acids
• This method is generally applied for water soluble acids. e.g. succinic acid,
acetic acid, …………….,
• This method is based on the fact that a normal alkali neutralizes one
equivalent weight of the acid (N. NaOH ≡ eq.wt of the acid)
N.B. Use succinic acid for this determination.
Procedure:
1. Dissolve a small amount (2.5-3 g) of the exactly weighed carboxylic acid
in a 100 ml measuring flask.
2. Titrate (10 ml) of this solution against 0.5 N sodium hydroxide solution
using phenolphthalein as an indicator. The appearance of faint but
permanent pink color is the end point.
3. Take at least three concordant readings.
Calculations: (10 ml) of the acid = V ml x 0.5 N NaOH
(100 ml) of the acid = 10 x V ml x 0.5 N NaOH
(100 ml) of the acid = 5 x V ml x N NaOH
Or 5 x V ml x N NaOH = X g of the acid
Therefore equivalent weight of the acid = X x 1000
5V
3- Synthesis
(i) Synthesis of Benzamide from Benzonitrile
CN
CONH2
90% H2SO4
 Equation:
C6H5C
N
+
H2O
H2SO4
C6H5CONH2
 Procedure:
Add (2g; 2 ml) of benzonitrile to (20 ml) of 90% sulfuric acid in a conical
flask, a clear solution is rapidly obtained. Heat the solution in an oil-bath
at 120-130ºC for 20 minutes, and then cool the solution and pour it onto
(50g) of crushed ice. Filter the precipitated benzamide at the pump, wash it
with water, and recrystallize it once or (twice) from water. Determine its
melting point. M.p. 128-130ºC.
(ii) Synthesis of Benzoic Acid from Benzamide
C6H5CONH2 + NaOH
C6H5COONa
+
NH3
Procedure:
Place (1g) of benzamide from step (i) and (15 ml) of
(10%) sodium hydroxide solution in a 100 ml roundbottomed flask fitted with a reflux condenser, and boil the
mixture gently for (30) minutes, during which ammonia is
freely evolved. Transfer the contents of the flask to a
beaker, cool the solution in ice-water and add conc.
Hydrochloric acid until the mixture is strongly acidic.
Benzoic acid immediately precipitates. Allow the reaction
mixture to stand in the ice-water for few minutes, and then
filter off the benzoic acid at the pump, wash with cold
water, and dry. Recrystallize from hot water. Determine its
melting point. M.p. (121ºC).
(iii) Synthesis of Benzoic Acid from Benzonitrile
C6H5C
N +
H2O
C6H5COONa
+
NH3
Procedure:
Boil (5 ml; 5.1g) of benzonitrile and (75 ml) of (10%) aqueous
sodium hydroxide in a 200 ml round bottom flask under reflux until
no more oily drops of unchanged nitrile run down from the
condenser (usually about 40 minutes). Then remove the condenser
and boil the solution for a few minutes to remove free ammonia.
Cool the liquid, and add conc. hydrochloric acid cautiously until
precipitation of benzoic acid is complete. Cool the mixture again
thoroughly, filter off the benzoic acid at the pump, and wash with
cold water and finally recrystallize from hot water. Determine its
melting point. M.p. (121ºC).
ASSESSMENT
QI: Analyze the following systemic diagram to chemical equations:
CN
NaOH
(c)
(a)
NaNO2 / H2O2
CONH2
COOH
NaOH
(b)
QII: Arrange the following nitriles in the following systemic diagram
according to their νC≡N
CH3C≡N, CH3CH2C≡N, CH2=CH-CN
CN
Increases
CN
decreases
CN
Increases
QIII: Write mechanisms of the following reactions:
a)
C6H5C
N
b) C6H5CONH2
+
H2O
+
NaOH
H2SO4
C6H5CONH2
C6H5COONa
+
NH3