Catalytic and noncatalytic ammonolysis of chloropentafluorobenzene

Article abstract of DOI:10.1023/A:1012492726911

Ammonolysis of chloropentafluorobenzene both in the presence and in the absence of copper(I) salt results mainly in replacement of the para-and ortho-fluorine atoms with respect to chlorine rather than replacement of the chlorine atom. Ammonolysis of 4-chloro-2,3,5,6-tetrafluoroaniline and 2-chloro-3,4,5,6-tetrafluoroaniline in the absence of copper(I) salt yields exclusively the corresponding fluorine substitution products, whereas in the presence of copper(I) salt the chlorine atom is replaced. Successive ammonolysis of chloropentafluorobenzene in the presence of copper catalyst along these two paths was put into the basis of a new method for preparation of 2,3,5,6-tetrafluoro-1,4-phenylenediamine. * This study was financially supported by the Russian Foundation for Basic Research (project no. 99-03-33111), by the Ministry of Science and Technology of the Russian Federation (project no 9.3.01), and by the Ministry of Education of the Russian Federation (project no. 015.05.01.13).

Full text of DOI:10.1023/A:1012492726911

Russian Journal of Organic Chemistry, Vol. 37, No. 3, 2001, pp. 404 409. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 3, 2001,
pp. 429 434.
Original Russian Text Copyright
2001 by Selivanova, Pokrovskii, Shteingarts.
Catalytic and Noncatalytic
Ammonolysis of Chloropentafluorobenzene*
G. A. Selivanova, L. M. Pokrovskii, and V. D. Shteingarts
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
Novosibirsk State University, Novosibirsk, Russia
Received July 10, 2000
Abstract Ammonolysis of chloropentafluorobenzene both in the presence and in the absence of copper(I)
salt results mainly in replacement of the para- and ortho-fluorine atoms with respect to chlorine rather than
replacement of the chlorine atom. Ammonolysis of 4-chloro-2,3,5,6-tetrafluoroaniline and 2-chloro-3,4,5,6-
tetrafluoroaniline in the absence of copper(I) salt yields exclusively the corresponding fluorine substitution
products, whereas in the presence of copper(I) salt the chlorine atom is replaced. Successive ammonolysis of
chloropentafluorobenzene in the presence of copper catalyst along these two paths was put into the basis of
a new method for preparation of 2,3,5,6-tetrafluoro-1,4-phenylenediamine.
Polyfluorinated aromatic amines and diamines are
often obtained by reactions of polyfluoroarenes with
ammonia and amines. Numerous examples were re-
ported on nucleophilic replacement of fluorine in
polyfluoroarenes by amino group by the action of
ammonia in water or aqueous ethanol [1 7]. It was
found that in compounds containing both fluorine and
other halogen atoms fluorine atoms are more reactive
than chlorine [6] and bromine [1]. The ammonolysis
of chloro- and bromopentafluorobenzene yields
mainly the corresponding 4-halotetrafluoroanilines.
Likewise, reactions of chloropentafluorobenzene (I)
with hydrazine hydrate [6, 8], dimethylamine [9], and
piperidine [10, 11], as well as reaction of bromopenta-
fluorobenzene with hydrazine hydrate [9], gave with
high yield products of fluorine replacement preferen-
tially in the para-position relative to chlorine or
bromine. We have found no examples of the reverse
lability order of fluorine and heavier halogens in
such reactions in the absence of a catalyst. However,
reactions of chlorofluorobenzenes with aqueous
ammonia in the presence of copper compounds [12]
lead to the corresponding fluoroanilines as a result
____________
of replacement of the chlorine atom. Until recently,
the possibility for catalytic replacement by amino
group of a non-fluorine halogen atom in polyfluoro-
aromatic compounds was questionable. Nevertheless,
this problem is very important from the viewpoint
of extending the scope of utilization of such accessible
compounds as chloropolyfluorobenzenes [13]. The
goal of the present work was to study ammonolysis of
chloropentafluorobenzene (I) in the absence of a catal-
yst and in the presence of copper(I) salt. We also tried
to elucidate the sequence of noncatalytic and catalytic
transformations of primary substitution products under
similar conditions. The reactions were carried out in
a steel high-pressure reactor; the reaction time was
48 h. The reaction mixtures were analyzed by GLC
and 19F NMR spectroscopy. The results are sum-
marized in Table 1.
The reaction of chloropentafluorobenzene (I) with
30% aqueous ammonia at 120 C yields mainly
4-chloro-2,3,5,6-tetrafluoroaniline (II) and 2-chloro-
3,4,5,6-tetrafluoroaniline (III) at a ratio of
3:1
(run. no. 1, Scheme 1). These results coincide with
published data on the ammonolysis of compound I in
aqueous ethanol [6] and are consistent with those
reported for reactions of I with other amines [9, 11].
The reaction mixture also contained small amounts
(3 10%) of 3-chloro-2,4,5,6-tetrafluoroaniline (IV)
and 4-chloro-2,5,6-trifluoro-1,3-phenylenediamine (V)
*
This study was financially supported by the Russian Founda-
tion for Basic Research (project no. 99-03-33111), by the
Ministry of Science and Technology of the Russian Federa-
tion (project no 9.3.01), and by the Ministry of Education of
the Russian Federation (project no. 015.05.01.13).
1070-4280/01/3703-0404$25.00 2001 MAIK Nauka/Interperiodica

CATALYTIC AND NONCATALYTIC AMMONOLYSIS
405
Scheme 1.
which is the product of further transformations of
amines II and III.
amino group in the substrate (if primary products of
ammonolysis of I undergo reductive dechlorination)
or the use of aqueous ammonia instead of water; both
these call for additional investigation.
When the reaction was performed with aqueous
ammonia of a lower concentration (22.5%, run no. 3)
at 180 C, the major products were diamine V and
2-chloro-4,5,6-trifluoro-1,3-phenylenediamine (VIII)
at a ratio of 14:1. Previously unknown compounds
V and VI were isolated by recrystallization, anf their
structure was confirmed by the 19F NMR and high-
In an attempt to obtain compound V as the major
product we performed the reaction at higher tempera-
ture (200 C, run no. 2). In this case the major products
were 2,5,6-trifluoro-1,3-phenylenediamine (VI) and
2,3,5,6-tetrafluoroaniline (VII), whereas the fraction
of compound V in the mixture was as poor as 5%.
The formation of diamine VI and amine VII may be
regarded as analogous to some extent to the formation
of pentafluorobenzene in the reduction of chloropenta-
fluorobenzene (I) with copper in water at 300 C [14].
A question arises so as to whether replacement of
fluorine in the initial substrate is followed by reduc-
tive dechlorination or the primary product is penta-
fluorobenzene which then undergoes ammonolysis. It
should be emphasized that in our case the hydro-
dechlorination occurs under considerably milder con-
ditions than those reported in [14]; presumably, the
reactor material plays the role of reducing agent. The
reason for the above difference may be the presence of
resolution mass spectra (see Experimental). The 19F
chemical shifts of compounds V and VI (Table 2)
differ by no more than 1 2 ppm from those calculated
by the additivity scheme using substituent increments
from [15]; the corresponding differences for the other
isomers containing three nonequivalent fluorine atoms
are 4 8 ppm. The coupling constants given in Table 2
are also consistent with the proposed structures. The
1
signal at
6 ppm in the H NMR spectrum of VI
is split due to coupling with fluorine atoms through
Scheme 2.
X = Cl, Br.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 3 2001

406
SELIVANOVA et al.
Table 1. Conditions and results of noncatalytic and catalytic ammonolysis of halogenated arenes I III, XI, and XIII
(48 h, 30% aqueous ammonia)
Run
Substrate Reagent, Substrate CuX Tempera-
Yield,
g
Product (fraction, mol %, GLC)
no. (amount, g)
ml
molar ratio
ture,
C
1
2
3
4
I (25)
I (11)
I (10)
I (3)
180
180
100a
60
120
21.4
5.5
8.6
2.0
II (70), III (22), IV (5), V (3)
V (5), VI (71), VII (23)
200
180
120
II (4), III (0.1), IV (1), V (83), VIII (6)
1: 1 (CuCl)
1: 1 (CuBr)
1: 1 (CuCl)
II (9.6), III (7.9), IV (2.2), V (4.4), VI (1.3),
VII (8.8), VIII (1.2), IX (51.9), X (10.4)
5
I (3)
60
120
2.0
II (0.2), III (3), IV (0.2), V (5.3), VI (2.1),
VII (8.7), VIII (1.3), IX (55.8), X (17.8)
6
7
8
XI (3)
XI (1)
II/IIIb
60
60
60
120
120
120
2.5
0.7
2.0
XI (89), IX (1.5), XII (9.5)
XI (77.5), IX (3), XII (19.5)
1: 1 (CuCl)
II (0.2), III (2.4), IV (0.2), V (3.5), VI (3.8),
VII (12.6), VIII (1.9), IX (55.5), X (15)
9
XIII (1)c
XIII (1)c
60
60
120
125
0.5
1.0
XIII (7), XV (39), XVI (19)
10
1: 1 (CuCl)
VII (39), XIII (1.2), XV (15), XVI (13)
a
b
c
Aqueous ammonia (22.5%).
A mixture containing 63% of II, 20% of III, and 10% of V (GLC).
A mixture containing 74% of XIII and 11% of chloro-2,3,4,5-tetrafluorobenzene (XIV) (GLC).
the same constants as are the corresponding fluorine
signals in the 19F NMR spectrum (Table 2).
The known methods are characterized by approxi-
mately 3 times lower yield, and some procedures
include a number of steps described in [2, 3, 16, 17].
Taking into account possible extensions of the
developed approach to synthesis of polyfluorinated
p-phenylenediamines, it was important to study the
mechanism of ammonolysis of chloropentafluoroben-
zene (I) in the presence of copper(I) salts. The above
results do not allow us to choose between two paths
shown in Scheme 3, which differ by the order of
replacement of fluorine and chlorine.
Our results indicate that the ammonolysis of I in
the absence of copper(I) salt involves exclusively
replacement of fluorine. By contrast, the reaction of
I with aqueous ammonia in the presence of copper(I)
chloride or bromide (runs nos. 4 and 5; Scheme 2)
afforded tetrafluoro-p- and -o-phenylenediamines
IX and X as the major products together with amines
II IV and VII and diamines V, VI, and VIII. The
results were the same regardless of whether copper(I)
chloride or bromide was used.
However, we believe that path b can be ruled out
for the following reasons. First, even traces of amine
XI were not detected among the products, although
the conditions for catalytic ammonolysis of compound
I (run no. 7) were milder than those reported in [2, 3]
for complete transformation of XI into 2,4,5,6-tetra-
fluoro-1,3-phenylenediamine (XII) and diamine IX
in the absence of copper salt. Second, in the latter
case the major product was diamine XII ( 90%)
with a small impurity of isomer IX. The presence of
copper ions could both accelerate the ammonolysis of
I and change the reaction direction toward formation
of diamine IX. However, by special experiment (run
no. 6) we showed that the reaction direction does not
change. On the other hand, path a is well consistent
with the results of catalytic ammonolysis of a mixture
The catalytic ammonolysis of compound I provides
a new method for preparation of diamine IX. This
procedure is superior to the known methods utilizing
hexafluorobenzene as starting compound [13] (which
can be regarded as equivalent to I in accessibility).
Scheme 3.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 3 2001

CATALYTIC AND NONCATALYTIC AMMONOLYSIS
407
Table 2. 1H and 19F NMR spectra ( and F, ppm, J, Hz) of polyfluorinated aromatic amines (acetone-d6, 20%)
Comp.
no.
19F NMR spectruma
1H NMR spectrum
V
2-F, 5.2 [5.0],
5-F, 16.3 [17.0],
JF, F-ortho = 22,
JF, F-para = 8
6-F, 8.2 [ 6.0],
JF, F-ortho = 22,
JF, F-meta = 1.5
4.92 (2H, NH2), 4.77 (2H, NH2)
J
J
F, F-para = 8,
F, F-meta = 1.5
VI
2-F, 3.2 [3.9],
5-F, 17.5 [19.7],
JF, F-ortho = 22,
JF, F-para = 11,
JF, H-ortho = 12.5
6-F, 9.3 [ 14.3],
JF, F-ortho = 22,
JF, F-meta = 3,
JF, H-meta = 8
5.99 (Harom, JF, H-ortho = 12.5,
JF, H-meta = 8), 4.78 (2H, NH2),
4.56 (2H, NH2)
J
J
J
F, F-para = 11,
F, F-meta = 3,
F, H-meta = 8
XVb
XVIb
3-F, 18.7 [17.5],
4-F, 12.6 [13.7],
JF, F-ortho = 21,
JF, F-meta = 4,
JF, H-ortho = 11
6-F, 28.1 [25.2],
JF, F-para = 11,
JF, F-meta = 4,
JF, H-ortho = 11
6.80 (Harom, JF, H-ortho = 11,
JF, H-meta = 7), 4.78 (2H, NH2)
J
J
J
F, F-ortho = 21,
F, F-para = 11,
F, H-meta = 7
2-F, 21.4 [20.4],
4-F, 8.8 [8.5],
JF, F-ortho = 22,
JF, F-meta = 7,
5-F, 20.4 [22.0],
JF, F-ortho = 22,
JF, F-para = 11,
6.66 (Harom, JF, H-ortho = 12.5,
JF, H-meta = 8), 4.85 (2H, NH2)
J
J
J
F, F-para = 11,
F, F-meta = 7,
F, H-meta
8
JF, H-meta
8
JF, H-ortho
12
a
The values in brackets were calculated by the additivity scheme using the increments from [15].
The 19F chemical shifts of amine XI [20] were used as increment for the amino group.
b
of anilines II and III ( 3:1) (run no. 8), which was
obtained by the reaction of I with ammonia in the
absence of copper. The major products were amine
VII and diamines IX and X, the ratio of the two latter
being almost the same as in the products of catalytic
ammonolysis of compound I.
Presumably, the relative rates of noncatalytic sub-
stitution of fluorine and catalytic substitution of
chlorine depend on the presence of amino group in the
substrate. In the ammonolysis of compound I both
in the presence and in the absence of copper(I) salt
replacement of fluorine in the para- and ortho-posi-
tions with respect to chlorine prevails over replace-
ment of chlorine. The main direction of noncatalytic
ammonolysis of amines II and III is also replacement
of fluorine which occurs in the meta-position with
respect to the amino group, as in the case of penta-
fluoroaniline [2, 3]. By contrast, in the catalytic
process substitution of the chlorine atom in II and III
becomes the main reaction pathway. Probably, the
presence of amino group favors catalytic replacement
of chlorine in the para-position, which successfully
competes with noncatalytic substitution of fluorine in
the other positions. This assumption is supported by
the results of ammonolysis of chloro-2,3,5,6-tetra-
fluorobenzene (XIII): the noncatalytic reaction, like
with compound I, results in exclusive replacement of
fluorine and formation (according to the 19F NMR and
GC MS data) of isomeric chlorotrifluoroanilines XV
and XVI (run no. 9), while the catalytic process
(unlike the reaction with amines II and III) affords
amine VII and a comparable amount of the fluorine
Scheme 4.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 3 2001

408
SELIVANOVA et al.
replacement products (run no. 10, Scheme 4). The
assistance by amino group to aminodechlorination at
the para- and ortho-positions in the catalytic reaction
may be explained a priori by formation of two types
of complexes between the substrate and copper(I) ion.
In terms of the classical mechanism of catalysis by
copper compounds as applied to ammonolysis of aryl
halides [12], copper(I) ion coordinates at the halogen
atom thus faciltating its elimination as halide ion.
The presence of an amino group could increase the
basicity (coordinating power) of the halogen. This
means that replacement of X = F or H by X = NH2
could raise the equilibrium concentration of type A
complex (see below). On the other hand, copper(I) ion
could also coordinate at the amino group as the most
basic center. As a result, the amino group should
became electron-acceptor para(ortho)-orienting sub-
stituent, and in the corresponding type B complex
the chlorine atom should readily be replaced.
products were identified by GC MS using a Hewlett
Packard G1081A system consisting of an HP 5890
Series II gas chromatograph and HP 5971 mass-selec-
tive detector; energy of ionizing electrons 70 eV;
oven temperature programming from 50 C (2 min) at
10 deg/min to 280 C (5 min); injector temperature
280 C; ion source temperature 173 C; HP-5 capillary
column, 30 m 0.25 mm 0.25 m; carrier gas
helium, 1 ml/min; data acquisition at 1.2 scan/s, mass
range 30 650 amu.
Commercial chloropentafluorobenzene (I), 1,4-di-
amino-2,3,5,6-tetrafluorobenzene (XI), and aqueous
ammonia were used. The latter was saturated with
gaseous ammonia to attain a concentration of 30%
(d 0.893 g/cm3). Compound XIII was a mixture with
isomeric 2,3,4,5-tetrafluorochlorobenzene (XIV) at
a ratio of 7:1; it was synthesized by reaction of I with
hydrazine hydrate according to the procedure reported
in [6] and subsequent oxidation of the hydrazo deriva-
tives [18]. The spectral parameters of previously
known compounds were in agreement with published
1
data [2, 16, 18 21]. Table 2 contains the H and 19F
NMR spectral data of newly synthesized compounds
V, VI, XV, and XVI.
Typical procedure for reaction of polyfluoro-
aromatic compounds with aqueous ammonia.
A steel rotating high-pressure reactor was charged
with polyhalogenated benzene, aqueous ammonia, and
copper halide (in the catalytic process), and the reactor
was rotated for 48 h at 120 C. The mixture was
cooled, transferred into a flask, and steam-distilled.
The distillate was extracted with diethyl ether, the
extract was dried and evaporated, and the residue was
analyzed by GLC (Table 1).
Presumably, the mechanism of catalysis involving
formation of complex B can be ruled out, for we
observed no catalytic effect of copper in the ammo-
nolysis of compound XI. Another reason is that no
fluorine replacement occurred at the ortho-position
with respect to the amino group in amine II and at
the para-position in amines III, XV, and XVI.
2,3,5,6-Tetrafluoro-1,4-phenylenediamine (IX).
The reaction mixture obtained by the above procedure
from 40 g of chloropentafluorobenzene and 720 ml of
30% aqueous ammonia was steam-distilled. A fraction
was collected until crystals appeared in the distillate.
It was extracted with diethyl ether (3 50 ml) to
obtain 4.2 g of a solid product containing (GLC) 1.8 g
of compound VII, 0.9 g of amine III, 0.4 g of
diamine IX, and 0.1 g of diamine X. From the next
portion of the distillate 16 g of a solid material was
filtered off. Extraction of the filtrate with diethyl ether
gave an additional 3.1 g of a solid product which was
combined with the major portion. According to the
GLC data, the product contained 14.4 g of diamine IX
and 1.9 g of X. By recrystallization from petroleum
ether (bp 70 100 C) we isolated 9 g (38%) of 2,3,5,6-
tetrafluoro-1,4-phenylenediamine containing 97% of
the main substance, mp 142 144 C [2].
EXPERIMENTAL
The H and 19F NMR spectra of 20% solutions in
1
acetone-d6 were recorded on Bruker WP-200 and
Bruker AM-400 spectrometers relative to HMDS and
C6F6, respectively, as internal references. The reaction
mixtures were analyzed by GLC on a Hewlett
Packard HP 5890 chromatograph equipped with
a thermal conductivity detector; injector temperature
200 C; detector temperature 240 C; oven temperature
programming from 40 C (1 min) to 240 C at a rate
of 10 deg/min; HP-5 capillary column (polymethyl-
phenylsilicone), 151000 0.53 mm, film thickness
1.5 m; carrier gas helium, 5 ml/min. The components
were quantitated by the internal normalization
technique.
The high-resolution mass spectra were obtained
on a Finnigan MAT-8200 mass spectrometer. The
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 3 2001

CATALYTIC AND NONCATALYTIC AMMONOLYSIS
409
6-Chloro-2,4,5-trifluoro-1,3-phenylenediamine
(V) was synthesized by the general procedure from
20 g ( 0.1 mol) of chloropentafluorobenzene and
200 ml of aqueous ammonia (d = 0.915 g/cm3,
2.37 mol). The mixture was treated as described
above and was subjected to steam distillation for
30 min to remove volatile components. The still
residue was cooled to 18 20 C, and the precipitate
was filtered off. We isolated 18.5 g of dark needles
containing (GLC) 86% of diamine V and 6% of di-
amine VIII. Recrystallization from petroleum ether
(bp 70 100 C) gave 11 g of diamine V (purity 91%,
yield 56%); the second recrystallization gave 5.8 g of
compound V containing 97% of the main substance
(yield 30%), mp 133.5 134.5 C. Found: M+ 196.0016.
C6H4ClF3N2. Calculated: M 196.0015.
2,4,5-Trifluoro-1,3-phenylenediamine (VI) was
obtained by the general procedure (run no. 2, Table 1).
Double recrystallization from petroleum ether (bp 70
100 C) gave 2.5 g of diamine VI containing 97% of
the main substance (yield 24%), mp 68 68.5 C.
Found: M + 162.0402. C6H5F3N2. Calculated:
M 162.0405.
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