BP301(T) Pharmaceutical organic chemistry-II
A polynuclear aromatic hydrocarbon is a hydrocarbon made up of fused aromatic ring molecules.
These rings share one or more sides and contain delocalized electrons. Another way to consider
PAHs is molecules made by fusing two or more benzene rings.Polynuclear aromatic hydrocarbon
molecules contain only carbon and hydrogen atoms.
Polynuclear aromatic hydrocarbons are lipophilic, nonpolar molecules. They tend to persist in the
environment because PAHs are not very soluble in water. While 2- and 3-ring PAHs are somewhat
soluble in aqueous solution, the solubility decreases nearly logarithmically as molecular mass
increases. 2-, 3-, and 4-ring PAHs are sufficiently volatile to exist in the gas phases, while larger
molecules exist as solids. Pure solid PAHs may be colourless, white, pale yellow, or pale green.
PAHs are organic molecules that form from a variety of natural and environmental pollutant
reactions. Natural PAHs form from forest fires and volcanic eruptions. The compounds are numerous
in fossil fuels, such as coal and petroleum.
Man contributes PAHs by burning wood and by the incomplete combustion of fossil fuels. The
compounds occur as a natural consequence of cooking food, particularly when food is cooked at a
high temperature, grilled, or smoked. The chemicals are released in cigarette smoke and from
Polynuclear aromatic hydrocarbons are extremely important because they are associated with genetic
damage and diseases. Also, the compounds persist in the environment, leading to increased problems
over time. PAHs are toxic to aquatic life. In addition to toxicity, these compounds are often
mutagenic, carcinogenic, and teratogenic. Prenatal exposure to these chemicals is associated with
lowered IQ and childhood asthma.
People get exposed to PAHs from breathing contaminated air, eating food that contains the
compounds, and from skin contact. Unless a person works in an industrial setting with these
chemicals, exposure tends to be long-term and low-level, so there aren’t medical treatments to
address the effects. The best defence against health effects from PAH exposure is to become aware
of situations that elevate risk: breathing smoke, eating charred meat, and touching petroleum
Isolated Fused rings
Biphenyl Linear Angular
Naphthalene (C10H8) is an aromatic hydrocarbon in which two benzene rings are fused in ortho
positions. For the purposes of naming its derivatives,the positions are indicatedby figures.
7 2 C C
HC C CH
HC C CH
5 4 H H
Isolation from coal-tar:
Napthalene is the largest single component of coal-tar aboute (6-10 percent).The hydrocarbon was
first noticed as a deposit in the condensers during the distillation of naphtha fraction and hence its
name .It is obtained chifly by cooling the middle oil fraction an(160-230°),where upon naphthalene
crystallises out.The crude crystals are removed by centrifuging.
These are melted and then treated successively with concentrated sulphuric acid (to remove
phenols).Finally the naphthalene is sublimed to give the pure product.
Physical:-Naphthalene is a white solide which crystallises in shining plates., m.p.-80°,b.p.-
218°,having a strong odour.It is very volatile and sublimes radily on warming.Naphthalene is
insoluble in water, but dissolves easily in organic solvents, particularly in eather and benzene.
Chemical:-The reactions of naphthalene are essentially the same as those of benzene .It undergoes
substitution readily and forms addition products.however it is somewhat less aromatic than
benzene.Thus the double bonds in naphthalene exhibit in part the reactivity of alkenes and it forms
addition compounds more readily than does benzene.As soon as one of the ring is fully saturated by
addition of hydrogen or halogen.
Resonance structure of naphthalene:
x-ray diffraction studies show that ,unlikebenzene,all carbon –carbon bonds in naphthalene are not of
the same length.In particular the C1-C2 bond is considerably shorter (1.36A°) than the C2-X3 bond
(1.40A°).This difference can be understood if we examine the three resonance forms given
above.Notice that the C1-C2 bond is double in two structures (A and B) and single in only one (C) ;
wherw as the C2-C3 bond is single in two structures (A and B) and double in only one (C). We
would, therefore , expect the C1-C2 bond to have more double-bond character (shorter bond length ),
and the C2-C3 bond to have more single-bond character (longer bond lenghth).
The resonance energy of naphthalene is about 61 kcal/mole.This value is less than twice the amount
of a single benzene ring (36 kcal/mole).As a result, naphthalene is somewhat less aromatic (more
reactive) than benzene.
8 1 8 1 8 1
7 2 2
7 2 7
6 3 6 3
5 4 5 5 4
Preparation of Napthalene:
i) From 3-Benzoyl propanoic acid:
When 3-benzoyl propanoicacid is heated with sulphuric acid, α napthol is formed, which on
distillation with zinc dust forms naphthalene.
3-Benzoyl propanoic acid
4-Phenyl butanoic Acid
ii) From 4-phenyl-1-butene:
When 4-phenyl 1 butene is passed over red hot calcium oxide naphthalene is formed.
CH 2CH 2CH=CH 2
4 Phenyl 1 Butene Napthalene
iii) Haworth synthesis:
It involves five steps.
Step I: Formation of 3-benzoyl propanoic acid by the treatment of benzene with succinic anhydride.
Benzene Succinic Anhydride 3 Benzoyl Propanoic Acid
Step II: 3 benzoyl propanoic acid is treated with amalgamated zinc to produce 4-phenyl butanoic
3 Benzoyl Propanoic Acid 4 Phenyl Butanoic Acid
Step III: 4- phenyl butanoic acid is heated with conc. Sulphuric acid to form Tetralone (ring closer
4-Phenyl Butanoic Acid
Step IV: Tetralone is again heated with amalgamated zinc and HCl to give tetraline.
Step V: Tetraline is heated with palladium to yield naphthalene.
Reactions of Naphthalene:
Naphthalene is more reactive than benzene. It undergoes several reactions like oxidation, reduction,
addition, nitration, halogenations, acylation etc.
i.Oxidation of Naphthalene:
Kmno4/Acidic medium COOH
O3, Zn/H2O CHO
ii.Reduction of Naphthalene:
Addition of bromine or chlorine to naphthalene gives naphthalene dibromide or naphthalene
dichloride. Further addition of bromine or chlorine results in formation of naphthalene tetra bromide
or naphthalene tetra chloride.
Naphthalene Br Br
1,4- Dibromo naphthalene 1,2,3,4-Tetrabromo naphthalene
cl Fe HCL
iv)Electrophilic substitution reactions:
Naphthalene ,like benzene, undergoes electrophilic substitution reactions.substitution occurs
primarilyatC1(α-position). This can be understood if we examine the intermediate
carboniumion.Tworesonsnce forms can be written for the intermediate carbonium ion obtained from
the attack at C-1(without involving the other ring), whereas only such form is possible for
substitution at C-2.E+in the following equations represents an electrophile.
Attack at C-1
H E H
Naphthalene 1-Substitution product
Attack at C-2
1 + H
+E + E -H +
Less stable 2-substitution product
Consequently the former intermediate is more stable and the product with a substituent at C-1
predominates. Substitution at C-2 (ß-position) occurs only when the reactions are carried at higher
temperatures or when bulkier solvents are used.
Naphthalene nitrates with a mixture of nitric acid and sulphuric acid at low temperature to form
mainly the α-nitronaphthalene.
Type equation here.
iii. Halogeantion reaction:
Naphthalene in presence of iron catalyst reacts with halogen to form α-substituted naphthalene.
cl Fe HCL
Sulphonation of Napthalene at low temperature (80oC) produces naphthalene-1-sulfonic acid
while at higher temperature (120oC) it produces naphthalene -2-sulfonic acid.
80 C 120 C
Napthalene 1 Sulfonic Acid Napthalene Napthalene 2 Sulfonic Acid
Friedel craft alkylation at low temperature is carried out for naphthalene, which reacting with
iodomethane to produce 1-methyl naphthalene as major product and 2-methyl naphthalene as minor
Naphthalene 1-methyl naphthalene(major) 2-methyl naphthalene (minor)
vi. Friedel-craft acylation:
Naphthalene undergoes Friedel-crafts reaction with acetyl chloride to form the α or β products
depending on the conditions.
CH3 COCl, AlCl3 CH3 COCl, AlCl3
C 6H 5NO2 CS 2
(Polar Solvent) (Non polar solvent)
Methyl 2 Napthyl Ketone Napthalene Methyl 1 Napthyl Ketone
Derivatives of naphthalene :
OH OH SO3H
Medicinal uses of Napthalene:
1.Production of Napthols.
2.Production of Dyes.
Phenyl azo-beta-napthol red dye
3.Preparing of beta blocker drugs.
4.To synthesize synthetic dyes.
6.Veterinary medicine – dusting powder.
7.Polyethylene naphthalene to prepare plastic bottles.
8.Naphthalene sulfonic acids are used to prepare plasticizers, natural rubbers etc.
9.Naphthalene drugs to cure cough, urine infection, eye trouble etc.
Phenanthrene is apolycyclic aromatic hydrocarboncomposed of three fusedbenzenerings. In its pure
form, it is found incigarette smokeand is a knownirritant,photosensitizingskin to light. Phenanthrene
appears as a white powder having bluefluorescence.Phenanthrene is the backbone of morphine.
6 5 4 3
Resonance structure of phenanthrene:
Like anthracen ,phenanthrene is aplanar molecule. All fourteen carbone atoms are sp2
hybridized.The sp2 orbitals overlap with each other and with s orbitals of ten hydrogen atoms to C-C
and C-H σ bonds.Each carbon atom also possesses a p orbital and these are perpendicular to the
plane containing the bonds. The lateral overlap of these p orbital produces a π molecular orbital
containing ten electrons.Phenanthrenen shows aromatic properties because the resulting π molecular
orbital satisfies the Huckel`s rule (n=3 in 4n+2).
Preparation of phenanthrene:
(i) Haworth phenanthrene synthesis:
Napthalen succinic anhydride oxobutanoic acid 4-(naphthalen-1-yl)butanoic acid
Reaction of phenanthrene:
When oxidised with chromic acid in acetic acid phenanthrene yields a diketone,phenantraquinone
which upone further oxidation gives diphenic acid.
Electrophilic addition versus electrophilic substitution
Br2,,Fe Br3 HBr
The reactivity of the 9- and 10-positions toward electrophilic attack, whether reaction leads to
substitution or addition, is understandable since the initially formed carbocation is the most stable
one, in which aromatic sextets are preserved in two of the three rings.
This carbocation can then either (a) give up a proton to yield the substitution product, or (b) accept a
nucleophile to yield the addition product.
The tendency for these compounds to undergo addition is due to the comparatively small sacrifice in
resonance energy (12 kcal/ mol for anthracene, 20 kcal/ mol or less for Phenanthrene).
Derivatives of phenanthrene:
H 3C N
Medicinal uses of phenanthrene:
1.Anthraquinone is used in the manufactutre of alizarin and several other dyes.
OH O OH
3.steroid moiety contain phenanthrene nucleus.
4.sex hormones and bile acids.
5.steroid used as oral contraceptive and antiinflamatory agent.
6.Cardiac glycosides,morphine, codeine
Anthracene is present is coal-tar to the extent of 0.3 to 3.5 perecent hence its name Greek anthrac-
meaning coal.on distillation of tar , it passes over in the high boiling fractions anthracene oil.The
molecule of anthracene is made of three benzene nuclei fused in ortho positions . It is a colorless
solid polycyclic aromatic hydrocarbon.
8 9 1
5 10 4
Resonance structure of anthracene:
x-ray diffraction studies show that,like naphthalene ,all carbon bonds in anthracene are not of the
same length . in particular, the C1-C2 bond is considerably shorter(1.37A°) than the (C2-C3)bond.
(1.42A°). this difference in bond lengths can be understood if we examine the four resonance forms
given above .Notice that the C1-C2 bond is double in three structures(A,B andC), and single in only
one (D);whereas the C2-C3 bond is single in three structures(A,B andC) and double in only one (D).
we would, therefore,expect the C1-C2 bond to have more double-bond character (shorter bond
length), and the C2-C3 bond to have more single-bond character(longer bond length).
The resonance energy of anthracene is 84 kcal/mole. This averages to 28 kcal/mole per ring,which is
substantially lower than that of benzene (36 kcal/mole).As a result, anthracene is much less aromatic
than benzene and behaves more like an unsaturated aliphatic hydrocarbon.
(A) (B) (C)
Preparation of Anthracene:
Two molecules of benzyl chloride is condensed in presence of AlCl3 to produce Anthracene.
Benzyl Chloride Anthracene
ii.By Haworth Synthesis:
Step I: Benezene on reaction with phthalic anhydride in presence of AlCl3 produces O-Benzoyl benzoic acid.
O benzoyl benzoic acid
Phthalic anhydride Benzene
Step II: O-benzoyl benzoic acid is heated with conc. H2SO4 to give 9.10-anthraquinone.
O benzoyl benzoic acid 9,10 anthraquinone
Step III: Distillation of 9,10-anthraquinone with zinc dust will produce anthracene.
Pyrolysis of O-methylbenzophenone at 450oC can produce anthracene.
iv.By Diel-Alder Reaction:
This involves the reaction of 1, 4 napthaquinone with 1, 3 butadiene. The product is oxidized with
chromium trioxide in GAA to form 9, 10 anthraquinone, which on distillation (Zn) produce
+ CH 2=CH-CH=CH 2
1,4 napthaquinone Diel alder adduct
CrO 3 Zinc
CH 3COOH Distillation
Properties of anthracene:
Anthracene is a colorless solid. It mealts at 218°C and boils at 340°C.Anthracene is insoluble in water,but
dissolves in benzene. It shows a strong blue flurescence when exposed to ultraviolet light.This fluorescent
property of anthracene is used in criminal detection work,since a small amount of finely powder anthracene
on clothing,skin,money, etc.,is not detected under oridinary light but easily noticed when exposed to
Chemical anthracene undergoes addition and electrophilic substitution reactions These reactions
preferentially occur at the C-9 and C-10 positions.This can be understood if we examine the intermediate
carbonium ions obtained from attack at C-1,C-2, and C-9(all other positions are equivalent to either 1 or 2 or
9 by symmetry).E+ in the following equations represents an electrophile
Attack at C-1
8 H H E
5 4 +
Attack at C-2
8 9 1
Attack at C-9
8 9 1
Attack at C-9 yields a carbonium ion intermediate in which two benzene rings are retained; where as
attack C-1 or C-2 yields an intermediate in which a naphthalene system is retained. The former
intermediate is more stable and its formation favoured because the resonance energy of two benzene
rings (2 * 36 =72 kcal) exceeds that of naphthalene (61kcal).
Reactions of Anthracene:
i.Electrophillic substitution reactions:
x = Cl, Br, I
Anthracene 1 Sulfonic acid
Anthracene 2 Sulfonic acid
HNO 3 / H2SO4
Non polar solvent
9 Acetyl anthracene
1 Acetyl anthracene
HO 3S SO 3H
anthracene High Temp
Anthracene 2,7 disulfonic acid
SO 3H SO 3H
Anthracene 1, 8 disulfonic acid
Anthracene undergoes Diels-Alder reaction at 9, 10 positions and form endo anthracene maleic
Maleic anhydride O
Diel Alder Adduct
Anthracene undergoes oxidation with sodium dichromate and sulfuric acid to form 9, 10
Na 2Cr 2O 7
anthracene 9.10 Anthraquinone
Anthracene on reduction with sodium and ethyl alcohol produces 9, 10 dihydroanthracene.
Na/ C 2H5OH
anthracene 9.10 Dihydroanthracene
Dimerization of anthracene in UV light produces dianthracene.
Dimerization H3C CH3
Derivatives of anthracene:
O H H HO H
H O O OH
Anthraquinone Anthrone Oxanthrone Anthranol
Medicinal uses of anthracene:
1.Anthracene glycosides are oxygenated derivatives of pharmacological importance that are used as
laxatives or catharatics,antineoplasticagent,polycystic kidney.
OH O OH
2.Anti-inflamatory, antibacterial, antifungal andantiproliferative activity.
OH O OH OH O OH
3.As natural dyes.
OH O OH
Diphenylmethane is an organic compound with the formula(C6H6)2CH2 abbreviated by (CH2Ph2).The
compound consists of methane where in two hydrogen atoms are replaced by two phenyl groups.It is
a white solid.
Preparation of diphenylmethane:
Derivatives of diphenyl methane:
Medicinal uses of diphenylmethane:
1.Diphenylmethane is widely used in the synthesis of luminogens for aggregation induced emission.
2.Diphenylmethyl potassium used in the preparation of polymerization.
Triphenylmethane (C6H6)3CH is the chromogen of a large number of dyes.The common
chromophore is the p-quinoid structure and the auxochromes are OH,NH2 and NR2.
Triphenylmethane dyes are very brilliant intense colours but fade quickly in light. Therefore,they are
no longer much used on textiles. However, they are used in large quantities for coloring paper and
typewriter ribbons where pastncess to light is not so important.
Preparation of triphenylmethane :
Derivatives of triphenylmethane:
Gentian violet Aurin
CH3 CH3 Cl
CH3 Medicinal uses
Crystal violet used as preparation of detergents , fertilizers, textile dye.
Triphenymethane is used in copying papers, in hectograph and printing inks.
ArunBahl | B.S. Bahl ,Advance organic chemistry ,S. CHAND & COMPANY PVT.LTD
CAHNMANN, H. J.: Partially deactivated silica gel columns in chromatography.
Chromatographic behavior of benzo[tf]pyrene. Anal. Chem. 29, 1307 (1957).
COMMINS, B. T.: Interim Report on The Study of Techniques For Determination Of
Polycyclic Aromatic Hydrocarbons In Air. In: Analysis of carcinogenic air pollutants. Nat.
Cancer Inst. Monograph No. 9, p. 225 (1962).
G. Cornelissen, H. Rigterink, M.M.A. Ferdinandy, P.C.M. Van
NoortEnvironSciTechnol, 32 (1998), pp. 966-970
Baklanov, O. Hänninen, L.H. Slørdal, J. Kukkonen, N. Bjergene, B. FayAtmosChemPhys, 7 (
2007), pp. 855-874
S.J.M. Delgado, N. Aquilina, S. Baker, S. Harrad, C. Meddings, R.M. HarrisonAnal
Methods, 2 (2010), pp. 231-242
Jeffery A. Greathouse, Nathan W. Ockwig, Louise J. Criscenti, T. R. Guilinger, Phil Pohl and
Mark D. Allendorf. Computational screening of metal–organic frameworks for large-
molecule chemical sensing, Phys. Chem. Chem. Phys., 2010, 12, 12621
F. Perera, S. Wang, J. Vishnevetsky, B. Zhang, K.J. Cole, D. TangEnviron Health
Perspect, 119 (8) (2011), pp. 1176-1181
I.C. Lai, C.L. Lee, K.Y. Zeng, H.C. HuangSeasonal variation of atmospheric polycyclic
aromatic hydrocarbons along the Kaohsiung coastJ Environ Manage, 92 (8) (2011), pp. 2029-
Cachada, P. Pato, T. Rocha-Santos, D.S.E. Ferreira, A.C. DuarteSci Total
Environ, 430 (2012), pp. 184-192
Z. Wang, C. Yang, J.L. Parrott, R.A. Frank, Z. Yang, C.E. Brown, B.P. Hollebone, M. Landri
ault, B. Fieldhouse, Y. Liu, G. Zhang, L.M. HewittJ Hazard Mater, 271 (2014), pp. 166-177