Iodination and chlorination of aromatic polycyclic hydrocarbons with iodine monochloride in aqueous sulfuric acid

Article abstract of DOI:10.1023/A:1013192314771

Polycyclic aromatic hydrocarbons when treated with iodine monochloride in water solutions of sulfuric acid afford iodo-and chloroderivatives. Biphenyl, fluorene, acenaphthene, 1-nitronaphthalene undergo iodination. Naphthalene furnishes a mixture of iodo-and chloroderivatives, prevailing the latter. Anthracene and phenanthrene provide only chlorinated products. The iodine monochloride in the sulfuric acid is a stronger iodinating agent than in acetonitrile.

Full text of DOI:10.1023/A:1013192314771

Russian Journal of Organic Chemistry, Vol. 37, No. 8, 2001, pp. 1130 1133. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 8, 2001,
pp. 1189 1192.
Original Russian Text Copyright
2001 by Chaikovskii, Filimonov.
Iodination and Chlorination of Aromatic Polycyclic
Hydrocarbons with Iodine Monochloride in Aqueous Sulfuric
*
Acid
V. K. Chaikovskii and V. D. Filimonov
Tomsk Polytechnic University, Tomsk, 634004 Russia
Received August 18, 2000
Abstract Polycyclic aromatic hydrocarbons when treated with iodine monochloride in water solutions of
sulfuric acid afford iodo- and chloroderivatives. Biphenyl, fluorene, acenaphthene, 1-nitronaphthalene
undergo iodination. Naphthalene furnishes a mixture of iodo- and chloroderivatives, prevailing the latter.
Anthracene and phenanthrene provide only chlorinated products. The iodine monochloride in the sulfuric
acid is a stronger iodinating agent than in acetonitrile.
Polycyclic hydrocarbons readily undergo electro-
philic substitution but at the same time they are the
most prone among the other aromatic compounds to
many side and undesired processes. It is specifically
true for iodination reaction. In common iodinating
systems containing oxidant these substrates form
charge-transfer complexes with iodine that prevent
iodination. In some cases the formation of these
complexes is avoided by addition of electron-donor
compounds [1, 2]. In concentrated acid solutions the
polycyclic arenes are protonated, and in reactions
with electrophiles very often occurs one-electron
transfer [3]; in both cases arise very reactive species,
ion-radicals, that further undergo undesired trans-
formations.
We report here on the results of investigations
concerning iodine monochloride reactions with poly-
cyclic aromatic hydrocarbons: fluorene Ia, biphenyl
IIa, acenaphthene IIIa, anthracene IVa, phenanthrene
Va, naphthalene VIa, 1-nitronaphthalene VIIa in
water solutions of sulfuric acid.
The use of H SO of low concentration (10
0 vol%) ensures a minimum of side reactions.
2
4
3
Preliminary experiments and results of the preceding
work [4, 5] showed that at a higher H SO concentra-
2
4
tion arenes active in the electrophilic processes pre-
dominantly entered into side reactions resulting in
considerable tarring. We found experimentally that
the fullest conversion of the original compounds into
monohalogenated products was achieved at the use of
1
.5 2 equiv. of iodine monochloride.
We showed in [4, 5] that iodine monochloride in
aqueous sulfuric acid was a sufficiently versatile
iodinating agent that iodinated both electron-rich
aromatic compounds (aniline, aromatic nitroamines,
phenol ethers, alkylbenzenes) and moderately de-
activated arenes (halobenzenes, aromatic carboxylic
acids, some nitroarenes). Therewith the activity of the
electrophilic iodine and the preparative yields of the
reaction products can be controlled by the concentra-
tion of sulfuric acid: the more active is the arene in
electrophilic substitution processes, the lower is the
acid concentration required for iodination. The
control of the acid concentration also helps to avoid
many side processes.
We established that polycyclic hydrocarbons rather
easily underwent halogenation by ICl in sulfuric acid
solutions but the pattern of their behavior was
individual (Table 1).
With fair preparative yields were obtained mono-
and diiododerivatives of compounds Ia IIIa: 2-iodo-
fluorene (Ib) and 2,7-diiodofluorene (Ic); 4-iodo-
biphenyl (IIb), 4,4 diiodobiphenyl (IIc) and 5-iodo-
acenaphthene (IIIb). Naphthalene VIa affords quite a
number of compounds, both iodinated and chlorinated,
but we did not try to isolate them since the similar
values of R suggested that chromatographic separa-
f
tion was not promising. Nitronaphthalene VIIa did
not undergo iodination in sulfuric acid of 10 50%
concentration, but as we had reported earlier [4]
1-iodo-5-nitronaphthalene had been obtained there-
from in 21% preparative yield in 90% sulfuric acid.
*
The study was carried out under financial support by the
Russian
Foundation
for
Basic
Research
(grant
no. 00-03-32812a).
1
070-4280/01/3708-1130$25.00 2001 MAIK Nauka/Interperiodica

IODINATION AND CHLORINATION
1131
Table 1. Reaction of polycyclic aromatic compounds with iodine monochloride in water solutions of sulfuric acid
Ratio
Concn. Tempe-
H SO , rature,
mp,
(sol-
vent)
C
Publ.
mp,
C
substrate:
reagent,
mmol
Time,
h
Reaction
product
Yield,
%
Substrate
2
4
vol%
C
Fluorene
Ia)
10: 15
10
10
10
10
5
100
100
100
100
100
100
100
100
2
2
3
3
2
3
3
3
2-Iodofluorene (Ib)
32
43
23
35
49
65
37
30
125 126
(2-propanol)
211 213
126 127
[12]
213 214
[11]
113 114
[10]
204
[11]
63 65.5
[12]
103
[10]
209 210
[10]
53 53.5
[10]
(
1
0: 30
10: 15
0: 30
2,7-Diiodofluorene (Ic)
4-Iodobiphenyl (IIb)
(
2-propanol)
112 113
Biphenyl
IIa)
(
(ethanol)
202 204
1
4,4 -Diiodobiphenyl (IIc)
5-Iodoacenaphthene (IIIb)
9-Chloroanthracene (IVb)
9,10-Dichloroanthracene
(
ethanol)
59 61
Acenaphthene
IIIa)
Anthracene
IVa)
10: 20
10: 20
(
(hexane)
102 103
(ethanol)
209 210
(ethanol)
52 53
10
10
10
(
10: 40
(IVc)
Phenanthrene
Va)
10: 30
9-Chlorophenanthrene
(
(Vb)
(ethanol)
Anthracene IVa and phenanthrene Va in reaction
with iodine monochloride gave rise exclusively to
chloroderivatives. Therewith anthracene IVa depend-
ing on the reagents ratio afforded both 9-chloro (Vb)
and 9,10-dichloroanthracene (IVc). In order to direct
the process with anthracene to iodination we
attempted to effect an additional heterolysis of the
I Cl bond along a hypothetical scheme.
The halogenated reaction product (mp 42 42 C)
separated from the initial substrate Va was a mixture
of chloro-substituted phenanthrenes. The main
product, 9-chlorophenanthrene (Vb), was isolated
from the products mixture by recrystallization from
ethanol.
To estimate in more detail the effect of arene Ia,
IIIa VIa structure on the ratio of iodinated and
chlorinated products we analyzed the mixtures of
products obtained under conditions of kinetically
controlled reaction by GC-MS method. In these
experiments in contrast to preparative runs we used
equimolar ratio of ICl and arenes in question, and the
reactions were stopped at early conversion stages
Scheme.
ICl + H O
IOH + HCl
2
+
+
IOH + H
IO H
2
+
+
IO H
I
+ H O
2
2
(
save the case of phenanthrene Va) (Table 2). In the
To this end the iodine monochloride was stirred
for 4 h in 10, 50, or 90% H SO at room temperature
or at 100 C, and anthracene was charged into the
reaction mixture afterwards. However this procedure
did not afford any iodinated products.
latter case the GC-MS analysis was carried out on a
sample of halophenanthrenes obtained in the prepar-
ative synthesis at iodination of substrate Va with the
threefold excess of iodine monochloride and separated
from he original compound by chromatography.
2
4
Phenanthrene (Va) as anthracene (IVa) also under-
went only chlorination. It turned out to be the least
active among the compounds under study. We did not
succeeded to convert it fully into halogenated product
at 90 100 C in 10, 30, and 50% solutions of sulfuric
acid. Even at fourfold excess of iodine monochloride
and reaction at 90 100 C after 6 h TLC test still
revealed the presence of the original compound Va.
By the fluorene (Ia) example we established that
on raising the reaction temperature from 20 to 100 C
selectivity of iodination is reduced as expected (at
100 C was formed 4% of 2,7-diiodofluorene).
Besides it should be noted that the isomeric chloro-
fluorenes were not detected in the reaction products
obtained at room temperature but appeared in the
reaction mixture only at elevated temperature. In
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 8 2001

1
132
CHAIKOVSKII, FILIMONOV
Table 2. Composition of reaction products of polycyclic arenes Ia, IIIa VIa with iodine monochloride in 10% sulfuric
acid
Substrate
temperature, V[6]
C)
E ,
Content
of the main
substance, %
1
/2
Reaction
product
(
Mass spectrum, m/z (I , %)
rel
+
Fluorene
1.25 Fluorene
2-Iodofluorene
59
41
166 [M] (100), 139 (7), 115 (4), 82 (14), 69 (6), 63 (3)
+
(Ia) (20)
292 [M] (66), 165 (100), 139 (3.5), 127 (3), 115 (3),
8
2 (15), 63 (4)
+
Fluorene
Ia) (100)
1.25 Fluorene
2-Iodofluorene
34.5
59.5
166 [M] (100), 139 (7), 115 (4), 82 (14), 69 (6), 63 (3)
292 [M] (66), 165 (100), 139 (3.5), 127 (3), 115 (3),
+
(
8
2 (15), 63 (4)
+
2
,7-Diiodofluorene
3.9
418 [M] (100), 291 (68), 209 (11), 163 (77), 145 (20),
27 (7), 98 (4), 82 (27), 63 (6), 32 (4)
1
+
2
-Chlorofluorene
1.1
10.8
13.1
69.9
200 [M] (27), 166 (100), 163 (17), 139 (3), 82 (14)
+
Naphthalene
VIa) (100)
1.34 Naphthalene
1-Iodonaphthalene
128 [M] (100), 102 (7), 74 (2), 64 (3), 51 (3)
+
(
254 [M] (100), 127 (88), 101 (5), 77 (5), 63 (3), 51 (3)
+
1
-Chloronaphthalene
166 [M] (33), 162 (100), 127 (31), 126 (14), 81 (8),
6
3 (9), 50 (3)
+
2
-Chloronaphthalene
5.1
1.1
162 [M] (100), 127 (31), 126 (14), 81 (8), 63 (9), 50 (3)
200 [M] (70), 196 (100), 161 (20), 160 (7), 126 (24),
+
Isomeric
dichloronaphthalenes
Acenaphthene 1.11 Acenaphthene
IIIa) (100) 3-Iodoacenaphthene
122 (9), 99 (14), 74 (8), 63 (7)
+
60.6
6.9
31.3
1.1
21
153 [M] (100), 126 (4), 76 (22), 63 (6)
+
(
280 [M] (100), 152 (71), 126 (8), 78 (10), 63 (6)
+
5
5
-Iodoacenaphthene
-Chloroacenaphthene
280 [M] (100), 152 (71), 126 (8), 76 (9), 63 (6)
+
188 [M] (56), 153 (100), 94 (6), 76 (20), 44 (9)
+
Anthracene
IVa) (100)
0.84 Anthracene
9-Chloroanthracene
178 [M] (100), 152 (10), 88 (10), 76 (7)
+
(
63
212 [M] (100), 176 (33), 151 (9), 121 (4), 106 (9),
9
3 (9), 88 (24), 75 (9)
+
9
,10-Dichloro-
16
246 [M] (100), 211 (7), 176 (38), 123 (17), 105 (9),
anthracene
1.23 9-Chlorophenanthrene
87 (12), 75 (4)
212 [M] (100), 176 (38), 151 (7), 106 (10), 93 (8),
+
Phenanthrene
Va) (100)
95.3
4.7
(
88 (25), 75 (10)
+
Isomeric
246 [M] (100), 210 (7), 176 (35), 123 (14), 105 (9),
dichlorophenanthrenes
88 (14), 74 (4)
general the chlorinated products either were absent
or were obtained in minor amounts ( 1%) with
fluorene (Ia) and acenaphthene (IIIa). With naphthal-
ene (VIa) arise more chlorinated than iodinated
products, and anthracene (IVa) and phenanthrene
sulfuric acid indicating that iodination is more
selective. In this medium are iodinated fluorene Ia,
biphenyl (IIa) (E1/2 < 1.48 V), acenaphthene (IIIa),
naphthalene (VIa) that have E1/2 values considerably
lower than 1.58 V, and 1-nitronaphthalene (VIIa)
which is inert in acetonitrile [4]. Besides, ace-
naphthene (IIIa) possessing lower value of E1/2 than
polycycles Va and VIa provides considerably less of
chlorination product (Table 2). Thus the value of half-
wave potential 1.58 V assumed in [3] as criterion of
iodination possibility of polycyclic hydrocarbons with
iodine monochloride cannot be considered as general-
ly valid. Our results are not in disagreement with the
mechanism of iodination and chlorination of poly-
cyclic hydrocarbons by ICl suggested in [3]: It is
presumed that aromatic cation-radicals arise which
(Va) afford no iododerivatives (Table 2).
It is known [3] that in reaction with iodine mono-
chloride in acetonitrile some polycyclic hydrocarbons
characterized by half-wave oxidation potential
E1/2 < 1.58 V afford exclusively chloroderivatives,
and 1-nitronaphthalene does not react with ICl in
acetonitrile. Our results show that iodinating ability
of ICl in the sulfuric acid is notably higher than in
acetonitrile. Also the fraction of iodinated products as
compared to that of chloroderivatives is also higher in
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 8 2001

IODINATION AND CHLORINATION
1133
further undergo recombination with iodine radical and
chloride anion. It should be noted that numerous
other iodinating reagents are the most active in
sulfuric acid medium (see, e.g., [7 9]).
atives of polycyclic hydrocarbons and isolation of the
reaction products Ib, c, IIb, c, IIIb, IVb, c, Vb. The
recrystallization of the products was performed from
the solvents indicated in Table 1.
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2
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2
4
1
0 mmol of aromatic substrate Ia VIa, the mixture
9. Lulinski, P. and Skulski, L., Bull. Chem. Soc. Jpn,
was heated to 100 C, and stirred for 3 h. The reaction
mixture was poured into water and washed with
sodiumcarbonate solution. The solid products
obtained from halogenation of compounds Ia Va
2000, vol. 73, pp. 951 956.
,
10. Slovar organicheskikh soedinenii (Dictionary of
,
Organic Compounds), Khil brona, I. and Benberi, G.,
Eds., Moscow: Inostr. Lit., 1946,
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4
from tars on a short column packed with Al O , and
analyzed. The liquid halogen-containing products
11. Sintezy iodistykh organicheskikh soedinenii (Synthese
2
3
,
of Iodinated Organic Compounds), Yagupol sko-
arising in reaction with naphthalene VIa were
go, L.M., Novikova, A.N., and Merkusheva, E.B.,
Tomsk, 1976, pp. 25 27.
extracted with hexane, dried on CaCl , and purified
2
on a short column packed with Al O . Similarly were
carried out the preparative syntheses of haloderiv-
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1971, vol. 92, pp. 1021.
2
3
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 8 2001