Novel and simple synthesis of brominated 1,10-phenanthrolines

Article abstract of DOI:10.1071/CH13711

A novel, simple, and reasonably efficient synthesis of 3,8-dibromo-1,10- phenanthroline, 3,6-dibromo-1,10-phenanthroline, 3,5,8-tribromo-1,10- phenanthroline, and 3,5,6,8-tetrabromo-1,10-phenanthroline is presented herein. The crucial role of a new catalyst (sulfur dichloride-SCl₂) for the bromination of 1,10-phenanthroline is reported. The bromination of 1,10-phenanthroline monohydrate in the presence of SCl₂ and pyridine yielded the brominated compounds, previously only possible through the complicated multi-step and tedious Skraup synthesis method. The application of the bromination catalyst SCl₂ as a medium-strength Lewis acid is demonstrated for the first time, and the results are compared with the behaviours of known weak (sulfur chloride-S2Cl₂) and strong (thionyl chloride-SOCl₂) bromination catalysts. A reaction mechanism was proposed. CSIRO 2014.

Full text of DOI:10.1071/CH13711

CSIRO PUBLISHING
Aust. J. Chem.
Full Paper
http://dx.doi.org/10.1071/CH13711
Novel and Simple Synthesis of Brominated
1,10-Phenanthrolines
A B
,
A
A
Drahom´ır Vy´prachticky´,
Dana Kanˇkova´, Veronika Pokorna´,
A
A
A B
,
Ivan Km´ınek, Vagif Dzhabarov, and Veˇra Cimrova´
A
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic,
Heyrovsky´ Sq. 2, 162 06 Prague 6, Czech Republic.
B
Corresponding authors. Email: vyprachticky@imc.cas.cz; cimrova@imc.cas.cz
A novel, simple, and reasonably efficient synthesis of 3,8-dibromo-1,10-phenanthroline, 3,6-dibromo-1,10-phenanthroline,
3,5,8-tribromo-1,10-phenanthroline, and 3,5,6,8-tetrabromo-1,10-phenanthroline is presented herein. The crucial role
of a new catalyst (sulfur dichloride – SCl2) for the bromination of 1,10-phenanthroline is reported. The bromination of
1,10-phenanthroline monohydrate in the presence of SCl2 and pyridine yielded the brominated compounds, previously
only possible through the complicated multi-step and tedious Skraup synthesis method. The application of the bromination
catalyst SCl2 as a medium-strength Lewis acid is demonstrated for the first time, and the results are compared with the
behaviours of known weak (sulfur chloride – S2Cl2) and strong (thionyl chloride – SOCl2) bromination catalysts. A
reaction mechanism was proposed.
Manuscript received: 3 January 2014.
Manuscript accepted: 9 February 2014.
Published online: 27 March 2014.
Introduction
yield). They suggested that an HCl salt activates the phenan-
throline ring for substitution. Saitoh et al.[11] reported that the
bromination of 1 in 1-chlorobutane (reflux) in the presence of
sulfur chloride (S2Cl2) and pyridine gave the desired product 3
in 34 % yield (Scheme 2). The Saitoh method gradually became
a widely used synthetic procedure for the preparation of
3,8-dibromo-1,10-phenanthroline.[12–15] Although both meth-
ods provide facile routes to the preparation of 3, little is known
about the bromination mechanism. The authors generally used 3
as a monomer for the synthesis of conjugated polymers or as an
important ligand in transition metal complexes, but no detailed
studies on the bromination reaction have been conducted. The
yields were given mostly for the crude material prior to purifi-
cation, and the reaction mixtures were not analysed. Thomas[16]
1,10-Phenanthroline (1) is an important ligand in the chemistry of
both transition and lanthanide metals, as these complexes often
show attractive chemical and physical properties.[1–4] Simple
bromination of 1,10-phenanthroline is difficult and non-
selective, which is typical of p-deficient aromatic compounds.[5]
Generally, aromatic compounds functionalised with electron-
withdrawing imine nitrogen (C¼N–) are p-deficient in nature,
and their electrophilic substitution with halogens (Br2) usually
requires harsh reaction conditions.[6] The bromo derivatives of 1
(such as 3- or 4-bromo; 3,5-, 3,6-, 3,8-, 4,7-, and 5,6-dibromo;
3,5,6-tribromo; and 3,5,6,8-tetrabromo) can be obtained
through the Skraup synthesis route.[7,8] However, this multi-step
procedure generates low yields, requires the use of carcinogens,
such as 3,3-diacetoxy-2-bromoprop-1-ene (i.e. bromoacrolein
diacetate), and produces toxic arsenic waste. An example of this
reaction for the synthesis of 3,6-dibromo-1,10-phenanthroline is
shown in Scheme 1. To our knowledge, this literature study[7] is
the only report that describes the double Skraup synthesis of
brominated 1,10-phenanthrolines; however, the products are
only characterised by elemental analysis and melting point
assessments. The preparation of p-conjugated polymers
containing 1, such as poly(1,10-phenanthroline-3,8-diyl) and
its co-polymers,[9] requires the synthesis of 3,8-dibromo-
1,10-phenanthroline as a monomer or co-monomer for coupling
polymerisation processes. For this reason, a direct and relatively
simple electrophilic bromination of 1 was investigated and
developed. Tzalis and co-workers[10] reported that the bromina-
tion of 1,10-phenanthroline monohydrochloride monohydrate in
nitrobenzene at 1408C gave 3-bromo-1,10-phenanthroline
(2, 33 % yield) and 3,8-dibromo-1,10-phenanthroline (3, 17%
COOCH3
Br
Br
H3COOC
Br
Br
ϩ
CH2
H3AsO4/H2SO4
NH2
N
3,3-diacetoxy-2-bromoprop-1-ene
bromoacrolein diacetate(BAD)
NO2
NO2
Fe
CH3COOH
Br
Br
Br
Br
H3AsO4/H2SO4
Glycerol
N
N
NH2
8-Amino-3,6-dibromoquinoline
N
3,6-Dibromo-1,10-phenanthroline
Scheme 1. Skraup synthesis route of 3,6-dibromo-1,10-phenanthroline.
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

B
D. Vy´prachticky´ et al.
compared these methods and provided a critical and detailed
discussion in which he suggested a bromination mechanism.In
this study, the reaction mixtures were separated by flash chro-
matography, and all the reaction products were purified and
characterised. Along with 3, the major by-product 2 and starting
material 1 were isolated from the reaction mixture. The yields of
other minor by-products were negligible. As concluded, both the
Tzalis and Saitoh methods are only convenient for the synthesis
of bromo derivatives 2 and 3.
or
N
N
N
N
1
. HCl . H2O
Tzalis method
Br2, 140ЊC
Saitoh method
Br2, S2Cl2
pyridine
PhNO2
Replacing sulfur chloride (S2Cl2) with sulfur dichloride
(SCl2) and using 1,10-phenanthroline monohydrate instead of
1 allowed for a much more efficient bromination of 1. With
these modifications, we were able to synthesise 3,8-dibromo-1,
10-phenanthroline(3), 3,6-dibromo-1,10-phenanthroline(4), 3,5,
8-tribromo-1,10-phenanthroline (5), and 3,5,6,8-tetrabromo-1,
10-phenanthroline (6) in reasonable yields (Scheme 3, Table 1).
However, 3-bromo-1,10-phenanthroline (2) was only isolated as
a minor product. In this paper, we report a novel electrophilic
aromatic substitution of 1,10-phenanthroline monohydrate,
yielding highly brominated derivatives of 1. This represents a
significant simplification of the Skraup synthesis method[7] for
the formation of compounds 3, 4, 5, and 6.
Br
Br
Br
ϩ
N
N
N
N
2
3
Scheme 2. Bromination of 1,10-phenanthroline monohydrochloride
monohydrate (Tzalis method[10]) and 1,10-phenanthroline (1) (Saitoh
method[11]), yielding 3-bromo-1,10-phenanthroline (2) and 3,8-dibromo-1,
10-phenanthroline (3).
5
6
6a
4a
7
4
8
3
10a 10b
. H2O
N
N
1
9
10
2
Results and Discussion
Bromination of 1,10-Phenanthroline
SCl2
pyridine
Br2
For the synthesis of the tri- or tetra-bromo derivatives of 1,10-
phenanthroline (5 and 6), we used excess amounts of sulfur
dichloride (4ꢀ), pyridine (4ꢀ), and bromine (4.8ꢀ), as shown in
Exp. I (Table 1). The reaction mixture was worked up with
aqueous sodium hydroxide, passed through a short silica gel
column, crystallised, and finally subjected to gradient column
chromatography (CC), gradually eluting with chloroform and
chloroform containing 5 % v/v acetone. The actual yields after
CC for the major products 5 and 6 were 1.80 g (19 %) and 1.28 g
(11 %), respectively. The minor products 1–4 were isolated in
low yields. A greater excess amount of sulfur dichloride
(8ꢀ, Exp. II, Table 1) resulted in decreased yields for deriva-
tives 5 and 6. In reactions where the dibromoderivatives of 1,10-
phenanthroline (3 and 4) were the desired products, we
decreased the excess amount of bromine (2.4ꢀ) used in the
reaction mixture (Exp. III, Table 1). Likewise, the raw material
was treated with aqueous sodium hydroxide, passed through a
short silica gel column, crystallised, and finally subjected to
double gradient CC, first eluting with chloroform then
Br
Br
N
N
N
N
N
2
1
Br
ϩ
ϩ
Br
Br
Br
N
N
N
3
4
Br
Br
Br
Br
Br
Br
N
N
N
N
5
6
Scheme 3. Bromination of 1,10-phenanthroline monohydrate to products
1–6 in the presence of sulfur dichloride (SCl2) and the numbering scheme
used for NMR signal assignment.
Table 1. Experimental data for the bromination of 1,10-phenanthroline monohydrate (4.50 g, 22.7 mmol) in 1-chlorobutane
(200 mL) under reflux (105 1108C) over 12 h
]
Exp. # SCl2
S2Cl2 Pyridine
Br2
YieldA
[g]
Yield of product isolated by column chromatographyB [%]
YieldC
[%]
[mmol] [mmol] [mmol] [mmol]
6
5
4
3
2
1
I
90
180
90
5
–
–
90
90
90
40
73
73
110
110
55
4.65
2.61
3.73
3.05
7.59
7.14
11
7
19
10
10
4
3
1
2
1
77
79
82
75
70
76
II
1
9
1
17
3
2
1
2
1
III
IV
V
–
–
–
70
–
20
2
2
1
–
74
74
72
–
2
14
13
40
63
32
6
VID
–
72
–
3
3
ACrude yield of the mixture of products used for column chromatography.
BThe yields shown in I–V correspond to those of starting material 1,10-phenanthroline monohydrate; yields of ,1 % were neglected.
CRecovered yield after column chromatography.
DExperimental data shown in VI were taken from [16] for comparison.

Synthesis of Brominated 1,10-Phenanthrolines
C
Ϫ
Ϫ
Ϫ
Cl
Cl
Cl
ϩ
N
N
ϩ
ϩ
N
N
N
N
SOCl
S2Cl
SCl
7
8
9
ϩ
H
H
Cl
NC5H5
Br2
ϪSCl2
Br2
Ϫ
etc.
2
Cl
N
N
N
N
N
SCl
SCl
8a
8b
Scheme 4. Proposed 1,10-phenanthrolin-1-ium salt-type intermediates 7, 8, and 9 formed from reaction between 1
and S2Cl2, SCl2, and SOCl2, respectively. Compound 8 is in equilibrium with intermediates 8a and 8b, and its
bromination leads to 2.
with chloroform containing 5 % v/v acetone. Consequently,
derivatives 4, 2, and 1 were first separated, while fractions con-
taining 3 and 5 underwent further CC, eluting with chloroform
then with chloroform containing 2 % v/v acetone. The difficult
separation of 3 and 5 is expected. It has been reported[16] that
these compounds cannot be purified by re-crystallisation
because of the formation of a crystal mixture of 3 and 5 in a 3 : 1
molar ratio. They must be further purified by CC, which is
challenging because of their similar RF values. Derivatives 3, 4,
and 5 were obtained in yields of 1.32 g (17 %), 0.68 g (9 %), and
0.95 g (10 %), respectively. The minor products 1 and 2 were
isolated in low yields (Table 1). Lower amounts of sulfur
dichloride and pyridine in the reaction mixture (Exp. IV) pro-
moted the formation of 4 as the major product. This compound
was obtained in a yield of 1.56 g (20 %), whereas by-products 1–
3 and 5 were obtained in low yields. To compare the results of
the experiments using sulfur dichloride (SCl2) with those using
sulfur chloride (S2Cl2), Exp. V was performed, in which 1,10-
phenanthroline monohydrate was reacted with sulfur chloride.
Previously reported data[16] for the bromination of 1,10-phe-
nanthroline using S2Cl2 are shown (Exp. VI, Table 1) for
comparison. A short comment should be made about the des-
ignation of the isolated material 1 in experiments I–V (Table 1,
Scheme 3). In this discussion, we describe this compound as
‘product or by-product’ to emphasise that 1,10-phenanthroline
monohydrate is used as starting material. Experimental work
proved that during bromination and isolation, the starting
material loses a water molecule. As expected, in the case of
experiment VI, isolated 1 is recovered as a starting material.
Comparison between experiments I–IV and V–VI shows that
the bromination of 1,10-phenanthroline monohydrate using
sulfur dichloride is more efficient than bromination involving
sulfur chloride. The actual yields of compounds 3–6 varied
between 10 and 20 % after CC (calculated on the basis of the
starting material 1 monohydrate). From this perspective, the
procedure involving SCl2 as the catalyst can be recommended
for the syntheses of compounds 4 and 5. For the synthesis of 3,
the aforementioned procedure[6–11] whereby S2Cl2 is used as the
catalyst is more convenient, whereas the procedure using SOCl2
as a strong Lewis acid[14] (see below) is the most convenient for
the preparation of 6. All synthesised compounds, 2–6, were
obtained with good purity (see 1H, 13C NMR, and Fourier
transform infrared (FTIR) data in the Supplementary Material)
and were fully characterised (yield, melting point, elemental
1
analysis, H and 13C NMR, and FTIR). Heteronuclear (C, H)
shift correlated 2D NMR spectra (HETCOR) enabled us to
distinguish between the aromatic carbons substituted with
hydrogen atoms and non-substituted carbon atoms (those that
were either brominated or only connected to carbon atoms). This
tool proved to be very helpful throughout this study.
Proposed Reaction Mechanism
The development of the synthesis procedure was the main
objective of this work, instead of mechanistic studies. Nev-
ertheless, we propose a reaction mechanism based on the
published approaches and previous knowledge. Garcia
et al.[17] reported the bromination of pyridine and quinoline in
the presence of S2Cl2 or SOCl2. They proposed the formation
of a protonated pyridinium salt-type reaction intermedi-
ate, which exists as an equilibrium mixture of the 1,4-
dihydropyridine derivative and the pyridine addition product.
Similarly, 1,10-phenanthrolin-1-ium salt-type intermediates
7, 8, or 9 may be expected when 1 reacts with sulfur chloride,
sulfur dichloride, or thionyl chloride, respectively (Scheme 4).
For compound 8, we propose that an equilibrium between 1,4-
dihydrophenanthroline (8a) and its addition product with
pyridine (8b) exists. In our experiments (Table 1), it was
established that SCl2 must be added before the addition of
pyridine (see the Experimental section) to avoid reduction in
the yield and efficiency of the bromination reaction. These
results support the importance of the 8a28b equilibrium
mentioned in Scheme 4 and the literature.[17] Thomas[16] used
molecular modelling with the RHF-STO-3G method, as well
as some synthetic approaches to explain the bromination
of 1,10-phenanthroline to produce 2 and 3. Calculations
suggested that in singly protonated 1,10-phenanthrolin-1-ium
(10), the electron density is concentrated on the non-
protonated ring; thus, bromination to 8-bromo-1,10-
phenanthrolin-1-ium (11) is more likely than the formation of
3-bromo-1,10-phenanthrolin-1-ium (12). Electrophilic aro-
matic substitutions are directed towards regions of high
electron density in an aromatic substrate. Synthetic investi-
gation of the bromination of 1N-methyl-1,10-phenanthroline
supported the calculated results. The higher calculated sta-
bility of 11 compared with that of 12 and fast proton shuttling
between N1 and N10 were also considered in the reported

D
D. Vy´prachticky´ et al.
presence of S2Cl2 led to products 2 and 3 only. On the other
hand, the monobrominated product 2 can be obtained from
bromination in the presence of S2Cl2. These results suggest that
the formation of a 1,10-phenanthrolin-1-ium salt-type inter-
mediate (10) is important for efficient bromination. It seems that
SCl2 is a stronger Lewis acid than S2Cl2 (cf. the structures of 7
and 8 in Scheme 4). Perhaps the equilibrium reaction 2SCl2 2
S2Cl2 þ Cl2 is responsible for the higher activity of sulfur
dichloride compared with that of sulfur chloride. The strongest
Lewis acid is likely SOCl2, which promotes the formation of the
salt-type intermediate 9 in the first step and affords the fully
brominated compound 6 as the only product.[18] In conclusion,
the bromination efficiencies of the selected catalysts (Lewis
acids) may be ranked as follows: S2Cl2 , SCl2 , SOCl2. Sulfur
chloride (S2Cl2) is convenient for the preparation of compounds
2 and 3, sulfur dichloride (SCl2) is useful for the preparation of
compounds 3–6, and thionyl chloride (SOCl2) may be used for
the preparation of compound 6 only. The identification and
ϩ
N
N
N
N
ϩ
H
10
10
H
Br2
Br2
Br
OH
Br
ϩ
N
N
N
ϩ
N
Ϫ
OHϪ
11
H
12
H
2
Br2
Br2
Br
Br
Br
Br
Br
Br Br
Br
ϩ
ϩ
N
N
ϩ
N
N
ϩ
N
N
N
N
H
H
OHϪ
OHϪ
H
H
Ϫ
OHϪ
OH
Br2
Br2
1
purities of all materials were determined by H and 13C NMR
4
4
3
Br
Br
3
and FTIR (see Supplementary Material). These spectral data
conveniently complement the lack of such information in the
literature. Brominated 1,10-phenanthrolines can serve as func-
tional ligands for both transition and lanthanide metals, as
monomer units for polymers or macromolecular networks,
and/or as compounds in organic syntheses.
Br
Br
Br
Br
ϩ
N
N
N
N
ϩ
Ϫ
OHϪ
OH
H
H
Br2
5
Br2
Br
N
Br
Br
N
Br
Experimental
General
Br
Br
The starting material 1,10-phenanthroline monohydrate (mp
102–1038C) was purchased from TCI. The 1,10-phenanthroline
(mp 116–1178C) and other chemicals were purchased from
Sigma–Aldrich or LachNer (Czech Republic), and were used
directly without purification. Silica gel 60 (0.063–0.200 mm,
Merck) was used for column chromatography (column diame-
ter: 3–4 cm; column length: 60 cm). TLC was performed on
Silica gel 60 F254 aluminium sheets (Merck), and the RF values
have the usual meaning (i.e. RF ¼ distance travelled by sub-
Br
Br
ϩ
ϩ
N
N
OHϪ
Ϫ
OH
H
H
6
Scheme 5. General mechanism for 1,10-phenanthroline bromination,[16]
resulting in products 2–6, considering the following: (i) the bromination is
much more probable on the non-protonated ring (solid arrows) than on
the protonated ring (dashed arrows); and (ii) proton shuttling between N1
and N10.
stance/distance travelled by solvent front). H and 13C NMR
1
spectra were measured in CDCl3 on an upgraded Bruker
Advance DPX-300 spectrometer at 300.13 (1H) and 75.45 (13C)
MHz using hexamethyldisiloxane as internal standard. Hetero-
nuclear (C, H) shift correlated 2D spectra (HETCOR) were
measured in CDCl3 using the same equipment. FTIR spectra
were measured on a Perkin–Elmer Paragon 1000 PC Fourier
transform infrared spectrometer by means of diamond attenu-
ated total reflectance (ATR).
mechanism. In spite of the fact that such a mechanism does
not explain the rate of bromination or the distribution of
products, we believed that it is a reasonable explanation for
the bromination reaction in the presence of SCl2 yielding
bromo derivatives 2–6.
The reaction mechanism shown in Scheme 5 assumes the
formation of a 1,10-phenanthrolin-1-ium salt-type intermediate
in the first step and proton shuttling between N1 and N10 in
the second step. Both literature approaches[16,17] are comple-
mentary and served as a draft of the proposed mechanism shown
in Scheme 5.
Procedure Involving Sulfur Dichloride
(SCl2, Exp. I–IV, Table 1)
1,10-Phenanthroline monohydrate (4.50 g, 22.7 mmol) was
dissolved in 1-chlorobutane (160 mL) under argon. Then, sulfur
dichloride (Table 1) and pyridine (Table 1) were added
over 10 min. Finally, a solution of bromine (Table 1) in
1-chlorobutane (40 mL) was added dropwise, and the reaction
mixture was refluxed (1108C) for 12 h. After cooling, the
reaction flask was placed in a refrigerator overnight resulting in
the precipitation of a yellow solid. An aqueous solution of 10 %
NaOH (200 mL) and chloroform (200 mL) were added to the
solid, and the mixture was stirred vigorously. The organic phase
was separated and passed through a short silica gel column
(,10–15 cm) before drying over Na2SO4.
Conclusion
We achieved the bromination of 1,10-phenanthroline mono-
hydrate in the presence of SCl2 yielding products 3–6,
depending on the reaction conditions (Table 1). The results were
compared with those of bromination reactions in the presence of
S2Cl2. Compound 3 is obtained through bromination in the
presence of SCl2 or S2Cl2 (Table 1), whereas the preparation of
the highly brominated materials 4–6 are only possible in the
presence of SCl2. The bromination of 1,10-phenanthroline in the

Synthesis of Brominated 1,10-Phenanthrolines
E
13C
13C
155 150 145 140 135 130 125
[ppm]
[ppm]
8.0
160 155 150 145 140 135 130 125
[ppm]
[ppm]
8.0
8.2
8.4
8.6
8.8
8.2
8.4
8.6
8.8
9.0
9.2
9.4
9.0
9.2
9.4
9.6
9.8
Fig. 1. 2D HETCOR 13C spectrum versus 1H NMR spectrum of 3,5,8-
tribromo-1,10-phenanthroline 5.
Fig. 2. 2D HETCOR 13C spectrum versus 1H NMR spectrum of 3,5,6,8-
tetrabromo-1,10-phenanthroline 6.
3,5,8-Tribromo-1,10-phenanthroline 5 and 3,5,6,8-
Tetrabromo-1,10-phenanthroline 6
respectively. Their analyses and spectra are discussed below.
The HETCOR spectrum (CDCl3) of 6 is shown in Fig. 2.
Sulfur dichloride (9.26 g, 90 mmol), pyridine (7.11 g, 90 mmol),
and bromine (17.6 g, 110 mmol) were mixed accordingly
(Exp. I, Table 1). Na2SO4 was removed by filtration, the solvent
was evaporated, and a solid was crystallised (charcoal) from 1,2-
dichloroethane/chloroform (4 : 1) to afford a yellow crystalline
solid (yield: 4.65 g). The crude material was subjected to gra-
dient chromatography eluting with CHCl3 then CHCl3 con-
taining 5 % v/v acetone. The corresponding fractions were
combined and characterised as compounds 5 and 6 (major
products) and compounds 1–4 (minor products) (Table 1, Exp. I)
as follows:
3,6-Dibromo-1,10-phenanthroline 4
Sulfur dichloride (0.51 g, 5 mmol), pyridine (3.16 g, 40 mmol),
and bromine (11.2 g, 70 mmol) were mixed accordingly
(Exp. IV, Table 1). Na2SO4 was removed by filtration, the
solvent was evaporated, and the residue was dissolved in 1,1,2-
trichloroethylene. The raw product was crystallised by addition
of petrolether (yield: 3.05 g). The crude material was purified by
gradient chromatography eluting with CH2Cl2 then CH2Cl2
containing 10 % v/v acetone. The corresponding fractions were
combined and characterised as compound 4 (major product) and
compounds 1–3 and 5 (minor products) (Table 1, Exp. IV):
3,5,8-Tribromo-1,10-phenanthroline 5
Yield: 1.80 g (19 %), mp 290–2918C (lit. 2908C[16]).
n
max(ATR)/cmꢁ1 3039, 2920, 1581, 1480, 1412, 1272, 1204,
3,6-Dibromo-1,10-phenanthroline 4
Yield: 1.56 g (20 %), mp 248–2498C (lit. 247–2488C[7]).
1104, 1034, 937, 914, 891, 805, 732, 622, 560, 530.
dH (300.1 MHz, CDCl3) 9.13–9.18 (broad peak, 2H, H2þH9),
8.77 (d, J 2.1, 1H, H4), 8.27 (d, J 2.1, 1H, H7), 8.03 (s, 1H, H6).
dC (75 MHz, CDCl3) 120.9 (C3þC8), 121.6 (C5), 129.2 (C4a),
129.8 (C6a), 129.9 (C6), 136.7 (C7), 137.9 (C4), 143.8 (C10a),
144.7 (C10b), 152.2 (C2), 152.5 (C9) all aromatic. Anal. Calc.
for C12H5N2Br3 (416.9): C 34.57, H 1.21, N 6.72, Br 57.50.
Found: C 34.71, H 1.12, N 6.66, Br 57.83. The HETCOR
spectrum (CDCl3) of 5 is shown in Fig. 1.
n
max(ATR)/cmꢁ1 3027, 1589, 1577, 1492, 1411, 1382, 1204,
1097, 1031, 911, 894, 799, 733, 554, 473. dH (300.1 MHz,
CDCl3) 9.19–9.15 (m, 2H, H2þH9), 8.60 (dd, J 8.1, 1.7, 1H,
H4), 8.25 (d, J 2.4, 1H, H7), 7.99 (s, 1H, H5), 7.72 (dd, J 8.4, 4.5,
1H, H8). dC (75 MHz, CDCl3) 120.6 (C3), 122.4 (C6), 124.1
(C8), 128.1 (C4a), 128.6 (C5), 129.8 (C6a), 136.1 (C7), 136.5
(C4), 144.1 (C10a), 146.6 (C10b), 151.4 (C2), 151.7 (C9) all
aromatic. Anal. Calc. for C12H6N2Br2 (338.0): C 42.64, H 1.79,
N 8.29, Br 47.28. Found: C 42.75, H 1.73, N 8.41, Br 47.51.
The minor products 1, 2, 3, and 5 were obtained in yields of
0.04 g (1 %), 0.10 g (2 %), 0.22 g (3 %), and 0.37 g (4 %),
respectively. Their analyses and spectra are discussed below
(1–3) or above (5). The HETCOR spectrum (CDCl3) of 4 is
shown in Fig. 3.
3,5,6,8-Tetrabromo-1,10-phenanthroline 6
Yield: 1.28 g (11 %), mp 354–3558C (lit. 356–3578C[7], lit.
355–3568C[18]). nmax(ATR)/cmꢁ1 3022, 1577, 1472, 1405,
1266, 1103, 959, 915, 887, 825, 730, 595, 566, 537. dH
(300.1 MHz, CDCl3) 9.17 (s, 2H, H2þH9), 8.89 (d, J 2.4,
2H, H4þH7). dC (75 MHz, CDCl3) 122.1 (C3þC8), 125.3
(C5þC6), 129.8 (C4aþC6a), 139.1 (C4þC7), 143.8 (C10aþ
C10b), 152.6 (C2þC9) all aromatic. Anal. Calc. for C12H4N2Br4
(495.8): C 29.07, H 0.81, N 5.65, Br 64.46. Found: C 29.14,
H 0.73, N 5.64, Br 64.51.
3,8-Dibromo-1,10-phenanthroline 3
Sulfur dichloride (9.26 g, 90 mmol), pyridine (7.11 g, 90 mmol),
and bromine (8.80 g, 55 mmol) were mixed accordingly
(Exp. III, Table 1). Na2SO4 was removedbyfiltration, the solvent
was evaporated, and a solid crystallised (charcoal) from 1,1,2-
trichloroethylene giving a yellow crystalline solid (yield: 3.73g).
The minor products 1, 2, 3, and 4 were obtained in yields
of 0.06 g (1 %), 0.12 g (2 %), 0.07 g (1 %), and 0.24 g (3 %),

F
D. Vy´prachticky´ et al.
C12H6N2Br2 (338.0): C 42.64, H 1.79, N 8.29, Br 47.28. Found:
C 42.67, H 1.54, N 8.23, Br 47.07.
13C
The side-products 1, 2, 4, and 5 were obtained in yields of
0.03 g (1 %), 0.08 g (1 %), 0.68 g (9 %), and 0.95 g (10 %),
respectively. Their analyses and spectra are discussed below
(1 and 2) or above (4 and 5). The HETCOR spectrum (CDCl3) of
3 is shown in Fig. 4.
155 150 145 140 135 130 125
[ppm]
[ppm]
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
9.2
9.4
Procedure Involving Sulfur Chloride (S2Cl2, Exp. V, Table 1)
1,10-Phenanthroline monohydrate (4.50 g, 22.7 mmol) was
dissolved in 1-chlorobutane (160 mL) under argon; and sulfur
chloride (74 mmol), pyridine (73 mmol), and bromine
(72 mmol) in 1-chlorobutane (40 mL) were added gradually.
The reaction mixture was refluxed (1108C) for 12 h. After
cooling, the reaction flask was placed in a refrigerator overnight,
resulting in the precipitation of a yellow solid. An aqueous
solution of 10 % NaOH (200 mL) and chloroform (200 mL)
were added to the solid, and the mixture was stirred vigorously.
The organic phase was separated and dried over Na2SO4. The
chloroform was removed under vacuum, and the yellow solid
was dried to a constant weight (yield: 7.59 g). The raw material
was chromatographed in chloroform to yield the major products
(1–3) and minor products (4 and 5).
Fig. 3. 2D HETCOR 13C spectrum versus 1H NMR spectrum of 3,6-
dibromo-1,10-phenanthroline 4.
3,8-Dibromo-1,10-phenanthroline 3
13C
Yield: 1.05 g (14 %), mp 279–2808C. The elemental analysis
and spectral data were the same as those shown above, and
confirmed the structure of 3.
160 155 150 145 140 135 130 125
[ppm]
[ppm]
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
9.2
9.4
3-Bromo-1,10-phenanthroline 2
Yield: 2.35 g (40 %), mp 168–1708C (lit. 169–1708C[7], lit.
164–1678C[10], lit. 1658C[16]). nmax(ATR)/cmꢁ1 3018, 2940,
1577, 1493, 1415, 1374, 1208, 1095, 1025, 895, 865, 830,
725, 637, 508, 467. dH (300.1 MHz, CDCl3) 9.18–9.15
(m, 2H, H2þH9), 8.35 (d, J 2.4, 1H, H4), 8.21 (dd, J 8.1, 1.8,
1H, H7), 7.79 (d, J 9.0, 1H, H5), 7.66 (d, J 8.7, 1H, H6), 7.63
(dd, J 8.1, 4.4, 1H, H8). dC (75 MHz, CDCl3) 119.9 (C3),
123.4 (C8), 125.5 (C5), 128.0 (C6), 128.6 (C4a), 129.7 (C6a),
136.1 (C7), 137.5 (C4), 144.5 (C10a), 146.0 (C10b), 150.8 (C2),
151.2 (C9) all aromatic. Anal. Calc. for C12H7N2Br (259.1):
C 55.63, H 2.72, N 10.81, Br 30.84. Found: C 55.82, H 2.54,
N 10.87, Br 31.07.
Fig. 4. 2D HETCOR 13C spectrum versus 1H NMR spectrum of 3,8-
dibromo-1,10-phenanthroline 3.
1,10-Phenanthroline 1
Yield: 1.32 g (32 %), mp 114–1158C (Aldrich material
114–1178C, lit. 1038C[16], lit. 1168C[19]). nmax(ATR)/cmꢁ1
3374, 3026, 2933, 1587, 1558, 1501, 1418, 1343, 1215, 1136,
1090, 852, 733, 703, 618. dH (300.1 MHz, CDCl3) 9.18
(dd, J 4.2,1.8, 2H, H2þH9), 8.23 (dd, J 8.1, 1.5, 2H, H4þH7),
7.77 (s, 2H, H5þH6), 7.62 (dd, J 7.8, 4.3, 2H, H3þH8).
dC (75 MHz, CDCl3) 123.1 (C3þC8), 126.6 (C5þC6), 128.7
(C4aþC6a), 136.0 (C4þC7), 146.3 (C10aþC10b), 150.4
(C2þC9) all aromatic. Anal. Calc. for C12H8N2 (180.2):
C 79.98, H 4.47, N 15.54. Found: C 80.08, H 4.32, N 15.74.
The minor products 4 and 5 were obtained in yields of 0.15 g
(2 %) and 0.19 g (2 %), respectively. Their analyses were the
same as those shown above.
The raw material was chromatographed eluting with CHCl3
containing 5 % v/v acetone and compounds 4, 2, and 1 were
obtained. The fractions containing3 and 5 werechromatographed
further eluting with CHCl3 then CHCl3 containing 2 % v/v ace-
tone to obtain purified 3 and 5 (Table 1, Exp. III) as follows:
3,8-Dibromo-1,10-phenanthroline 3
Yield: 1.32 g (17 %), mp 279–2808C (lit. 221–2228C[7]
,
lit. 270–2738C[10], lit. 270–2728C[14], lit. 284–2868C[15], lit.
2708C[16]). nmax(ATR)/cmꢁ1 3025, 1585, 1477, 1412, 1374,
1207, 1101, 1034, 905, 891, 776, 720, 509. dH (300.1 MHz,
CDCl3) 9.14 (d, J 2.4, 2H, H2þH9), 8.36 (d, J 2.4, 2H, H4þH7),
7.70 (s, 2H, H5þH6). dC (75 MHz, CDCl3) 120.2 (C3þC8),
126.9 (C5þC6), 129.6 (C4aþC6a), 137.6 (C4þC7), 144.1
(C10aþC10b), 151.6 (C2þC9) all aromatic. Anal. Calc. for
Supplementary Material
1H and 13C NMR and FTIR spectra of samples 1–6 are available
on the Journal’s website.

Synthesis of Brominated 1,10-Phenanthrolines
G
Acknowledgements
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