lecture 1 dr ali el-agamey chem-323: polynuclear aromatic hydrocarbon chem-323: polynuclear aromatic...
TRANSCRIPT
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LECTURE 1
Dr Ali El-Agamey
CHEM-323:
Polynuclear Aromatic Hydrocarbon
CHEM-323:
Polynuclear Aromatic Hydrocarbon
DAMIETTA UNIVERSITY
1
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Understand the principles of biphenyl nomenclature and the different methods used in its synthesis.
Understand the various methods involved in the synthesis of the different isolated polynuclear aromatic compounds.
Appreciate the effect of phenyl group on the stability of various intermediates.
Appreciate the steric effect of phenyl and benzyl groups.
Understand the role of phenyl and benzyl groups in electrophilic substitution reactions.
LEARNING OUTCOMES
LECTURES 1-2
LEARNING OUTCOMES
LECTURES 1-2
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Lecture 1-2: -Nomeclature, synthesis and reactions of biphenyl.
-Synthesis and reactions of diphenylmethane, triphenylmethane, triphenylmethyl chloride, triphenylmethanol, trans-stilbene and benzoin.
-Nomenclature of fused systems.
Lecture 3-6: -Aromatic character of fused systems.
-Structure elucidation of naphthalene
-Reactions of naphthalene.
Lecture 7-11: - Synthesis of naphthalene.
- Synthesis and reactions of anthracene and phenanthrene.
Lecture 12: -General revision for the whole course.
Reading
RT Morrison and RN Boyd, Organic Chemistry, Allyn and Bacon, Inc., 1987.
Mundy, BP et al, Name reactions and reagents in organic synthesis, Wiley, 2005
H Meislich et al, Organic Chemistry, McGraw-Hill Book Company, 1980.
IL Finar, Organic Chemistry, Volume 1 (1985) and Volume 2 (1977).
Reading
RT Morrison and RN Boyd, Organic Chemistry, Allyn and Bacon, Inc., 1987.
Mundy, BP et al, Name reactions and reagents in organic synthesis, Wiley, 2005
H Meislich et al, Organic Chemistry, McGraw-Hill Book Company, 1980.
IL Finar, Organic Chemistry, Volume 1 (1985) and Volume 2 (1977). 3
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Isolated ringsIsolated rings
(1) Biphenyl(1) Biphenyl
NomenclatureNomenclature
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Polynuclear Aromatic HydrocarbonsPolynuclear Aromatic Hydrocarbons
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Homework: Give name for the following compounds
Homework: Give name for the following compounds
Br Br
(H3C)2N N(CH3)2
Cl
ClCO2H
(a)(b)
(c)
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(1) Biphenyl(1) Biphenyl
SynthesisSynthesis
(a) Fittig’s reaction
(c) Gomberg reaction
(b) Gattermann reaction
More examples 6
2 PhBr + 2 Na + 2 NaBrPh–Ph
+ 2 N22 PhN2+Cl– Cu
HeatPh–Ph
+ N2NaOH+ Ar–H + NaCl + H2OArN2
+Cl– Ar–Ar
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(d) Ullmann coupling reaction
(e) Benzidine rearrangement
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+ CuI22 Ar–ICuHeat
Ar–Ar
More examples
Ph–NH–NH–Ph
Hydrazobenzene
PhNO2
Zn/NaOH
H+
Benzidine
NH2H2N
(i) NaNO2/HCl
(ii) H3PO2
Biphenyl
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(1) Biphenyl(1) Biphenyl
ReactionsReactions
Although –NO2 is m-directing group, p-O2NC6H4 is p-directing!!
According to the charge distribution approach, a p-nitro group would have been expected to direct to the m-position in the other ring.
N
O
O
N
O
O
N
O
O8
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(1) Biphenyl(1) Biphenyl
ReactionsReactions
However, the stabilities of the carbocation intermediates generatedfollowing o- and p-substitutions are greater than that generated from m-substitution due to the greater dispersal of charge in the formersubstitutions. Therefore, o-and p-substitutions are preferred.
O2N NO2O2N NO2
p–substitution
O2N
NO2
O2N
NO2
m–substitution9
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(2) Diphenylmethane(2) Diphenylmethane
Synthesis and reactionsSynthesis and reactions
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(3) Triphenylmethane (Tritane)(3) Triphenylmethane (Tritane)
Synthesis and reactionsSynthesis and reactions
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Homework: write the product of the following reaction
Homework: write the product of the following reaction
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H+
NN
CH3
CH3
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LECTURE 2
Dr Ali El-Agamey
CHEM-323:
Polynuclear Aromatic Hydrocarbon
CHEM-323:
Polynuclear Aromatic Hydrocarbon
DAMIETTA UNIVERSITY
12
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(3) Triphenylmethyl chloride (Trityl chloride)
(3) Triphenylmethyl chloride (Trityl chloride)
Ag2 Ph3CCl
C6H6, no air2 Ph3C Dimer
(White solid)Yellow colour
Ph3C–CPh3
was believed to be
Hexaphenylethane
Actually
H
Ph3C
Real dimer product
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(4) Triphenylmethanol
(Triphenylcarbinol)
(4) Triphenylmethanol
(Triphenylcarbinol)
Synthesis and reactionsSynthesis and reactions
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(5) trans-Stilbene
(trans-1,2-Diphenylethene)
(5) trans-Stilbene
(trans-1,2-Diphenylethene)
Synthesis and reactionsSynthesis and reactions
(6) Benzoin(6) Benzoin
Synthesis and reactionsSynthesis and reactions
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Homework: Complete the following equation
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Homework: Write the mechanism of the following reaction
CHO
OMe
KCN ???
S
(1) KOH
O
O(2) HCl
S
HO CO2H
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Naphthalene, anthracene and phenanthrene are obtained from coal tar, naphthalene being the most abundant (5%) of all constituents of coal tar.
Uses: moth balls, which contain naphthalene, are used as insect repellants (naphthalene is very volatile).
Many synthetic dyes contain naphthalene moiety.
Naphthalene
Fused rings
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How many isomers for monosubstitution of naphthalene (C8H7X)?
Nomenclature of naphthalene, anthracene and phenanthrene
Fused rings
How many isomers for monosubstitution of anthracene (C14H9X)?
How many isomers for monosubstitution of phenanthrene (C14H9X)?
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How many isomers for disubstitution of naphthalene (C8H6X2)?
How many isomers for disubstitution of naphthalene (C8H6XY)?
Homework
How many isomers for disubstitution of anthracene (C14H8X2)?
How many isomers for disubstitution of phenanthrene (C14H8X2)?
In each case write the name of each isomer?
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Nomenclature of naphthalene, anthracene and phenanthrene
CH3
(a)
Br
(b)
ClI
(c)
(a) (b) (c)
NO2
O2N
SO3H
H2N
OH
NO2
NO2
SO3H
NO2
(a) (b) (c)
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Homework: Give names for the following compounds
(d)
CO2HCl
(a)
NO2
NO2(b)
(c)
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LECTURE 3
Dr Ali El-Agamey
CHEM-323:
Polynuclear Aromatic Hydrocarbon
CHEM-323:
Polynuclear Aromatic Hydrocarbon
DAMIETTA UNIVERSITY
21
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Undergo electrophilic substitution reactions.
Like benzene, they are unusually stable as indicated from their low heats of hydrogenation and combustion.
Aromatic character of naphthalene, anthracene and phenanthrene
Naphthalene, anthracene and phenanthrene are classified as aromatic because of their properties, which resemble those of benzene.
(i) Experimental point of view
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Resonance Energy
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Resonance energy of A = 61 kcal mol-1
Resonance energy of B = 84 kcal mol-1
Resonance energy of C = 92 kcal mol-1
Resonance energy of benzene = 36 kcal mol-1
Aromatic character of naphthalene, anthracene and phenanthrene
(A) (B) (C)
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Flat (sp2-hybidized); cyclic
-cloud above and below the plane due to ???
HÜckel`s rule ???
Aromatic character of naphthalene, anthracene and phenanthrene
(ii) Theoretical point of view: they have the structure required for aromatic compounds
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Resonance structures and bond lengths of naphthalene, anthracene and phenanthrene
There are n+1 principal resonance structures for polynuclear aromatic hydrocarbon containing n benzene rings fused together in a linear manner.
Bond length
Double bond character
The different carbon-carbon bond lengths reveal the decreased aromaticity of fused polynuclear aromatic hydrocarbons.
Phenanthrene is an angular polynuclear aromatic hydrocarbon.
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Fused ringsFused rings
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Naphthalene, anthracene and phenanthrene are obtained from coal tar.
Naphthalene being the most abundent (5%) of all constituentsof coal tar.
(a) Uses
In moth balls as insect repellants.
Many synthetic dyes contain naphthalene moiety.
(1) Naphthalene(C10H8)
(b) Structure Elucidation
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Reactivity of naphthalene as compared to benzeneReactivity of naphthalene as compared to benzene
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In naphthalene, two fused rings share a pair of –electrons, therefore the aromaticity and the resonance energy per ring is less than that of benzene itself.
Resonance energy of naphthalene = 61 kcal mol-1
Resonance energy per ring = 30.5 kcal mol-1
Resonance energy of benzene = 36 kcal mol-1
Stability of the compound increases
Stability of the compound increasesAs R.E. increasesAs R.E. increases
Resistance to destroy aromatic
character increases
Resistance to destroy aromatic
character increases
Reactivity
decreases
Reactivity
decreases
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Reactivity of naphthalene as compared to benzeneReactivity of naphthalene as compared to benzene
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What happened when aromatic character of one ring of naphthalene is destroyed?
Therefore, naphthalene undergoes oxidation or reduction more readily than benzene but only to the stage where a substituted benzene is formed; further oxidation or reduction requires more vigorous conditions.
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(1) Oxidation
Reactions of naphthaleneReactions of naphthalene
O
CO2H
CO2H
O
O
O
O
O2, V2O5 CrO3
AcOH
HNO3
1,4-Naphthoquinone
O
O
CH3CH3 CrO3
AcOH
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(1) Oxidation
Reactions of naphthaleneReactions of naphthalene
Oxidation by V2O5 is important industrial process (naphthalene is available from coal tar).
Vitamins K1 and K2 are derivatives of 1,4-naphthoquinone.
Because of this tendency to form quinones, it is not always feasible to prepare naphthalenecarboxylic acids by oxidation of methyl side chains.
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(2) Reduction
Reactions of naphthaleneReactions of naphthalene
Na, C5H11OH H2, Pt or Ni
Na, C2H5OH
H2, Pt or Ni
Tetralin Decalin
1,4-Dihydronaphthalene
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(3) Electrophilic susbstitution reactions
Reactions of naphthaleneReactions of naphthalene
1-Substitution versus 2-substitution
Number of resonance structures Aromatic sextet is retained (benzene has large R. E.)
Fries rule: The most stable arrangement of a polynuclear compound is that form which has the maximum number of rings in the benzenoid condition.
Carbocation and T.S. resulting from attack at the 1-position are much more stable than those resulting from attack at the 2-position . Therefore, 1-susbstitution will be preferred.
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(i) Nitration
Reactions of naphthaleneReactions of naphthalene
NO2
HNO3, H2SO4 Red.
NH2
NaNO2, HCl
N2 Cl
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LECTURE 4
Dr Ali El-Agamey
CHEM-323:
Polynuclear Aromatic Hydrocarbon
CHEM-323:
Polynuclear Aromatic Hydrocarbon
DAMIETTA UNIVERSITY
35
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Reactions of naphthalene: Nitration; Halogenation; Chloromethylation; Friedel-Crafts reactions (alkylation and acylation).
Sulfonation.
Naphthols and naphthylamines.
Synthesis of 1-substituted naphthalenes.
Synthesis of 2-substituted naphthalenes.
Summary of naphthalene reactions.
LEARNING OUTCOMES
LECTURE 4
LEARNING OUTCOMES
LECTURE 4
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(i) Nitration
Reactions of naphthaleneReactions of naphthalene
NO2
HNO3, H2SO4 Red.
NH2
NaNO2, HCl
N2 Cl
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(ii) Halogenation
Reactions of naphthaleneReactions of naphthalene
Br
Br2, CCl4,
No Lewis acid needed
Mg
MgBr
X
X2, FeX = Cl, Br
Introduction of NO2 and X groups opens the way to the preparation of a series of 1-substituted naphthalenes.
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(iii) Chloromethylation
Reactions of naphthaleneReactions of naphthalene
Friedel-Crafts reactions is carried out under mild conditions.
CH2O, HCl
CH2Cl
(iv) Friedel-Crafts reactions
Friedel-Crafts alkylation is of little use because (1) polyalkylation and (2) side reactions.
Alkylnaphthalenes can be prepared via acylation or ring closure.
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Reactions of naphthaleneReactions of naphthalene
NaOCl,
CH3COCl
AlCl3
COCH3
COCH3
Solvent: CS2 or
C2H2Cl4
Solvent: C6H5NO2NaOCl,
CO2H
CO2H
(iv) Friedel-Crafts reactions
Acetylation affords access to the preparation of a series of 2-substituted naphthalenes.
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Reactions of naphthaleneReactions of naphthalene
(v) Sulfonation
SO3H
SO3H
Conc H2SO4, 80 oC
Conc H2SO4, 160 oC
Conc H2SO4, 160 oC
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Reactions of naphthaleneReactions of naphthalene
(v) Sulfonation
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At low T, 1-S is formed faster than 2-S
E2 > E1
However, at high T, which speeds up a reaction, or if the reaction is left for long time, 2-S becomes the main product.
Therefore, 1-S is called kinetically controlled product
k1 > k2
Δ H2 > Δ H1 E-2 (E2 + Δ H2) >> E-1 (E1 + Δ H1) k-1 >> k-2
1-S reforms N much faster than does 2-S and hence 2-S accumulates at the expense of 1-S i.e. the equilibrium is established in favor of the formation of 2-S, which is called the thermodynamically controlled product.
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The lower stability of 1-S is attributed to the steric interaction between the sulfonic group and the hydrogen atom in the 8-position.
(v) Sulfonation
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Reactions of naphthaleneReactions of naphthalene
SO3H
SO3H
PCl5
PCl5
Cl
Cl
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Reactions of naphthaleneReactions of naphthalene
Naphthols and naphthylamines
SO3Na NaOH,Fusion
ONa dil H2SO4OH
NH2
dil H2SO4
OH
+ NH3
OH NH3, (NH4)2SO3
, PressureNH2
Bucherer reaction
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Reactions of naphthaleneReactions of naphthalene
Naphthols and naphthylamines
OH
FeCl3OHHO
Violet-blue ppt
-Binaphthol
OHFeCl3
OH
OH
Green ppt
-Binaphthol
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Synthesis of 1-substituted naphthalenesSynthesis of 1-substituted naphthalenes
NO2 NH2 N2 Cl
X MgX
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Synthesis of 2-substituted naphthalenesSynthesis of 2-substituted naphthalenes
SO3H OH NH2
N2 ClXMgX
Acetylation and sulfonation affords access to the preparation of a series of 2-substituted naphthalenes.
NH2NO2
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Summary of naphthalene reactionsSummary of naphthalene reactions