International Journal of Organic Chemistry, 2013, 3, 214-219
http://dx.doi.org/10.4236/ijoc.2013.33029 Published Online September 2013 (http://www.scirp.org/journal/ijoc)
Synthesis of 5-Substituted
2,9-Dimethyl-1,10-Phenanthroline Dialdehydes and
Their Schiff Bases with Sulfur-Containing Amines
Zinia Jaman1, Mohammad R. Karim1*, Tasneem A. Siddiquee1,
Aminul H. Mirza2, Mohamad A. Ali2
1Department of Chemistry, Tennessee State University, Nashville, USA
2Department of Chemistry, Faculty of Science, University Brunei Darussalam, Gadong, Brunei Darussalam
Received July 4, 2013; revised August 14, 2013; accepted August 31, 2013
Copyright © 2013 Zinia Jaman et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Eight new Schiff bases of 5-nitro and 5-bromo-substituted 1,10-phenanthro line-2,9-dicarboxaldehydes with sulfur-con-
taining amines, thiosemicarbazide, S-alkyl/aryl dithiocarbazates and 2-mercaptoaniline have been synthesized and cha-
racterized by a variety of spectroscopic methods. The condensation reactions of the dialdehydes with the amines were
carried out both in the presence and absence of conc. sulfuric acid. A significant increase in yield of the Schiff bases
was observed when the reactions were carried out in the presence of sulfuric acid.
Keywords: 5-Nitro-1,10-Phenanthroline Dialdehyde; 5-Bromo-1,10-Phenanthroline Dialdehyde; Schiff Bases;
S-Alkyl/Aryldithiocarbazates; Thiosemicarbazide
1. Introduction
Recently, nitrogen and sulfur-containing organic chelat-
ing agents such as the Schiff bases derived from 2,9-di-
methyl-1,10-phenanthroline dialdehyde and sulfur-con-
taining amines and their metal complexes have received
considerable attention because of their important roles in
synthetic and medicinal chemistry[1]. By properly de-
signing this type of compounds and studying their struc-
ture-activity relationships, potentially useful antibacterial,
antifungal and anticancer agents can also be synthesized
[2]. 2,9-Dimethyl-1,10-phenanthroline and its derivatives
from which 2,9-dimethyl-1,10-phenanthroline dialdehy-
des are prepared, are themselves important ligands for
complexation with many metal ions [3]. This property
has made them important in different areas like self-as-
sembly and catalysis. It has also played a significant role
in both analytical and preparative coordination chemistry
as well as in the preparation of many mixed-ligand com-
plexes [4].
Although a large number of Schiff bases containing
“hard” nitrogen and “soft” sulfur donor atoms have been
synthesized using S-alkyl/aryl dithiocarbazates and het-
erocyclic aldehydes and ketones, which are able to form
stable complexes with a variety of metal ions [5], less
work has been reported on Schiff bases formed by con-
densation of 1,10-phenanthroline dialdehydes with sufur-
containing amines such as S-alkyl/aryl dithioicarbazates,
thiosemi-carbazide and aminobenzenethiol.
In view of the importance of Schiff bases derived from
1,10-phenanthroline dialdehyde and sulfur-containing
amines in coordination chemistry and biology, we report
here the synthesis and characterization of eight new
Schiff bases formed by condensation of 5-nitro-1,10-phe-
nanthroline-2,9-dialdehyde and 5-bromo-1,10-phenan-
throline-2,9-dialdehyde with different types of sulfur-
containing amines.
2. General Methods and Procedures
HPLC grade solvents were used in all the reactions. The
conventional method of synthesis of the Schiff bases
involves refluxing the reaction mixture containing the
dialdehydes and amines for 1 hour followed by filtration
of the solid products using suction filtration.
In all the reactions, 2 - 3 drops of conc. sulfuric acid
were used. The solid product that had formed was
filtered off using suction filtration. All the NMR data
*Corresponding author.
C
opyright © 2013 SciRes. IJOC

Z. JAMAN ET AL. 215
were recorded on a 400 MHz Varian NMR Spectrometer.
Mass Spectra were obtained on a Varian LC-MS with
ESI.
3. Synthesis
We have previously reported the preparation, charac-
terization and X-ray structures of different types of
Schiff bases derived from 1,10-phenanthroline [6]. Now
we report here the synthesis and characterization of eight
new Schiff bases formed by condensation of the 5-
bromo- and 5-nitro-substituted phenanthroline dialed-
hydes with amines containing thione or thiol sulfur donor
atoms in their backbones. All the compounds have been
structurally characterized by different spectroscopic me-
thods.
3.1. Synthesis of 5-Nitro-1,10-Phenanthroline-
2,9-Dicarboxaldehyde from 5-Nitro
2,9-Dimethyl-1,10-Phenanthroline
5-Nitro-2,9-dimethyl-1,10-phenanthroline (2) was syn-
thesized from 2,9-dimethyl-1,10-phenanthroline hemi-
hydrate (1) following a previously reported procedure
(Scheme 1) [7,8]. The yield of the compound was found
to be the same as reported in the literature. The crude
product was purified by chromatography using combi
flash (ethyl acetate: dichloromethane) to give the pure
compound [Y: 70%].
5-Nitro-1,10-phenanthroline-2,9-dicarboxaldehyde (3)
was synthesized from 5-nitro-2,9-dimethyl-1,10-Phenan-
throline (2) following a known procedure (Scheme 2) [9].
The yield of the compound was found to be the same as
that reported in the literature. The crude product was
recrystallized from chloroform and dried under vacuum
to give the pure compound [Y: 91%].
NN
CH
3
H
3
C
SO
3
NN
CH
3
H
3
C
Conc. HNO3
NO
2
12
Scheme 1. Synthesis of 5-Nitro-1,10-phe nanth r oline.
NN
CH
3
H
3
CNN
CH
O
OHC
NO
2
NO
2
SeO
2
23
Scheme 2. Synthesis of 5-Nitro-1,10-Phenanthroline-2,9-di-
aldehyde.
3.2. Synthesis of 5-Bromo-1,10-Phenanthroline-
2,9-Dicarboxaldehyde from 5-Bromo-2,9-
Dimethyl -1,10-Phenanthroline
The previously reported procedure [3] involving three
steps, was also used here to synthesize 5-bromo-2,9-di-
methyl-1,10-phenanthroline (6) from 2,9-dime-thyl-1,
10-phenanthroline (1) (Scheme 3).
The yield of the compound was found to be the same
as that reported in the literatures procedure. [Y: 85%].
5-Bromo-1, 10-phenanthroline-2,9-dicarboxal dehyde
(7) was synthesized from 5-bromo-2,9-dimethyl-1,10-
phenanthroline (6) following a known procedure [10]
(Scheme 4). An increase of reaction time resulted in the
increase in the yield of the dialdehyde. The crude product
was recrystallized from hot ethanol and dried under vac-
uum to give the pure compound [Y: 82%]. The reported
yield was 62%.
N
N
N
N
CH3
CH3
Br
LDA, TBDMS-Cl
THF, rt, 1 hr
Si
Si
N
N
Si
Si
Br
Br2
DCM, reflux,1 hr
Conc. HCl
Acetone, rt, 3 hr
74%
56%
85%
N
N
CH3
CH3
14
65
Scheme 3. Synthesis of 5-br omo-1,10-phenanthroline-2,9-di-
carboxaldehyde.
NN
CH
3
H
3
CNN
CH
O
OHC
B
r
B
r
SeO
2
67
Scheme 4. Sy nthesis of 5-Bromo-1, 10-P henanthroline-2,9-di-
carboxaldehyde.

Z. JAMAN ET AL. 216
3.3. Synthesis of the Schiff Bases with
Thiosemicarbazide
Thiosemicarbazide (4 equiv.) was added to a hot solution
of 5-nitro- or 5-bromo-1,10-phenanthroline-2,9-dicarbo-
xaldehyde (1 equiv) in methanol (20 mL) containing 2 -
3 drops of conc. sulfuric acid. The solution was re-
fluxed for 1 hr whereupon the reaction mixture was al-
lowed to cool down to room temperature. The product
that had formed was filtered off, washed with methanol
and dried under vacuum. Recrystallization of the crude
product from dichloromethane afforded white crystals
(Scheme 5). Ta ble 1 shows different reaction conditions
and percent yields for the two starting materials.
(2,2’)-2’-(5-Nitro-1,10-Phenanthroline-2,9-diyl) bis
(methan-1-yl-1-ylidene)bis-(hydrazinecar-bodithioate)
(8): IR: ν (cm−1): 3250 (NH2), 3154 (C-H), 1589 (C=N),
1522 (N=O), 1115 (C=S). 1H-NMR (DMSO-d6, ppm): δH
= 12.05 (s, 1NH), 12.03 (s, 1NH), 9.0 (s, 1H), 8.86 (s,
2H), 8.86 (d, J = 7.44,1H), 8.76 (d, J = 8.56,1H), 8.57 (d,
J = 7.44. 1H,), 8.48 (d, J = 8.56, 1H), 7.60 (s, br, 2NH2).
13C-NMR (DMSO-d6, ppm): δC = 178.61, 178.58, 156.80,
154.60, 146.35, 144.90, 143.78, 141.60, 141.42, 138.63,
132.39, 125.88, 125.70, 121.02, 120.97, 120.49. LC-MS
(m/z): 428 (M+H+), 427 (M+), 426 (M-H+), 411
(M+H+-NH3), 399 (M+2H+-N2H2), 391(M+H+-2NH2),
383 (M+ 2H+-NO2), 336 (M+2H+-CS2-NH3), 254
(M+4H+-N5C3S2H7).
(2,2’)-2’-(5-Bromo-1,10-Phenanthroline-2,9-diyl)bis
(methan-1-yl-1-ylidene) bis-(hydrazinecar-bodithioate)
(9): IR: ν (cm−1): 3300 (NH2), 3160 (C-H), 2951(CH
aromatic), 1568 (C=N), 1092 (C=S). 1H-NMR (DMSO-
d6, ppm): δH = 12.02 (s, 1NH), 12.00 (s, 1NH), 8.84 (d, J
= 8.68,1H), 8.76 (d, J = 8.48, 1H), 8.60 (d, J = 8.76,1H),
8.54 (s, 1H),8.52 (s, 2H), 8.45 (d, J = 9.24,1H), 7.56 (s,
Scheme 5. Synthesis of Schiff Bases w i th thiosemic arbazide.
Table 1. Reaction conditions and percent yields for the syn-
thesis of the schiff bases.
Yield %
Condition Solvent Time
X = NO2 X = Br
With H2SO4 OH
3
CH 1 hr 89 81
Without
H2SO4 OH
3
CH 1 hr 60 57
br, 2NH2). 13C-NMR (DMSO-d6, ppm): δC = 178.54(2),
154.36, 154.02, 144.94, 143.73, 141.66, 141.43, 136.35,
135.73, 130.19, 128.99, 127.28, 121.02, 120.74, 120.11.
LC-MS (m/z): 463/461 (M+2H+), 461/459 (M+), 446/444
(M+2H+-NH3), 429/427 (M+2H+-2NH3), 413/414
(M+-S-NH2), 399 (M+-NH2CSH), 385/ 383(M+3H+-Br).
349/350 (M+-CS2-2NH3), 337/335 (M+-2C2S2H2-2NH3),
281/279 (M+4H+-2CS2-2NH2).
3.4. Synthesis of the Schiff Bases with
S-Methyldithiocarbazate (SMDTC):
SMDTC was prepared following the procedure of Taraf-
der, et al. [11].
SMDTC (3 equiv.) was added to a hot solution of
5-substituted (NO2, Br) 1,10-phenanthroline-2,9-dicar-
boxaldehyde (l equiv.) in 20 mL methanol containing 2 -
3 drops of conc. sulfuric acid. The solution was refluxed
for 1 hr and then allowed to cool to room temperature.
The solid product that had formed was filtered off,
washed with methanol and dried under vacuum. The
crude product was recrystallized from dimethyl sulfoxide
to obtain white crystals (Scheme 6). Yields are shown in
Table 2 for various reaction conditions.
(2,2’)-Dimethyl 2,2’-(5-Nitro-1,10-Phenanthro-line-
2,9-diyl)bis(methan-1-yl-1-ylidene)-bis(hydr-azinecar
bodithioate)(10):
IR: ν (cm−1): 3200 (N-H), 2980, 2914 (CH aromatic
and aliphatic), 1580 (C=N), 1527(N=O), 1099 (C=S).
1H-NMR (DMSO-d6, ppm): δH = 13.78 (s, 1NH), 13.77
(s, 1NH), 9.02(s, 1H), 8.94(d, J = 8.64,1H), 8.78 (d, J =
7.96, 1H), 8.52 (s,2H), 8.35(d, J = 9.00,1H), 8.32(d, J =
8.36, 1H), 2.61 (s, 6H, CH3). 13C-NMR (DMSO-d6, ppm):
δC = 200.13(2), 155.57, 153.53, 146.45, 145.43(2),
Scheme 6. Synthesis of the hiff Bases with S-methyldi-
able 2. Reaction conditions and percent yields for the syn-
Yield %
Sc
thiocarbazate (SMDTC).
T
thesis of the schiff bases.
Condition Solvent Time
X = N NO2 O2 X =
With H2SO4 OH
3
CH 1 hr 55 54
Without
H2SO4 3OHCH 1 hr 35 46

Z. JAMAN ET AL. 217
145145.0.35, 13.26, , 1.16,
12120.38, 162). LC-MS (M+): 492
is(methan-1-yl-1-ylidene)-bis(hydr-azinecar
bo
7 (C=N), 1056(C=S). H-NMR
(D
e Schiff Bases with
S-Benzyldithiocarbazate (SBDTC)
scribed by
Aud ed to a hot
ethan-1-yl-1-ylidene)-bis(hydrazinecarbodit
hi
2PhCH2SCS), 279 (M+2H-2PhCH2SCSNH).
.27(2),
.01, 1
5, 139
.95(
3 126.39
m/z,
26
(M+3H+), 491 (M+2H+), 490 (M+H+), 489(M+), 474(M+-
CH3), 459(M+-2CH3), 443 (M+-NO2), 397 (M+2H+-
2CH3S), 384 (M+H+-CH3SCSNH), 308 (M+H+-
2CH3SCS), 307 (M+-2CH3SCS), 303 (M+-2CH3SH-
C2H2S2).
(2,2’)-Dimethyl 2,2’-(5-Bromo-1,10-Phenanthro-line-
2,9-diyl)b
dithioate)(11):
IR: ν (cm−1): 3240 (N-H), 3160, 2915 (CH aromatic
and aliphatic), 1561
MSO-d6, ppm): δH = 13.79 (s, 1NH), 13.76 (s, 1NH),
8.74 (d, J = 8.60, 1H), 8.61 (s, 1H), 8.57 (s, 2H), 8.56 (d,
J = 8.56,1H), 8.39 (d, J = 8.84,1H),, 8.29 (d, J = 8.40,1H),
2.61 (s, 3H, CH3), 2.60 (s, 3H, CH3). 13C-NMR
(DMSO-d6, ppm): δC = 199.89, 199.77, 153.30, 153.07,
145.87, 145.46, 144.34, 136.72, 136.68, 130.73, 130.72,
129.37, 127.93, 120.70, 120.31, 119.91, 16.93(2).
LC-MS (m/z, M+): 525/523 (M+H+), 524/522 (M+),
477/475 (M+-CH3S), 450/448 (M+2H+-CS2), 443/441
(M+-Br), 429/427 (M+-2CH3S), 366(M+H+-Br-CS2), 338
(M+-Br-CH3S-2N2).
3.5. Synthesis of th
SBDTC was prepared using a procedure de
rieth et al. [12]. SBDTC (3 equiv) was add
solution of 5-substituted (NO2, Br) 1,10-phenanthroline-
2,9-dicarboxaldehyde (1 equiv.) in 20 mL methanol fol-
lowed by the addition of two drops of acetic acid. The
reaction mixture was refluxed for 1 h, then left to cool to
room temperature. The product that had formed was fil-
tered off, washed with methanol and dried in vacuum.
White crystals of the compound were obtained by re-
crystallizing the crude product from dimethylsulfoxide
(Scheme 7). Yields with and without acid are given in
Table 3.
(2,2’)-Benzyl 2,2’-(5-Nitro-1,10-Phenanthroline-2,9-
diyl)bis(m
oate)(12): IR: ν (cm−1): 3150 (N-H), 3026 (C-H aro-
matic), 2920 (C-H aliphatic), 1566 (C=N), 1605,1494
(C=C aromatic),1526 (N=O), 1094(C=S). 1H-NMR
(DMSO-d6, ppm): δH = 13.79 (s, 1NH), 13.78 (s, 1NH),
8.99(s, 1H), 8.88(d, J = 8.80,1H), 8.71 (d, J = 8.32, 1H),
8.48(s,1H), 8.47(s,1H), 8.29(d, J = 8.88,1H), 8.25(d, J =
8.44, 1H), 7.48 - 7.31(m, 10H), 4.54 (s, 4H, 2xCH2).
13C-NMR (DMSO-d6, ppm): δC = 198.25, 198.14, 155.51,
153.41, 146.41, 145.62, 139.36, 136.38, 129.32(6),
129.12(8), 128.56(2), 127.38, 126.19, 121.03, 120.39,
37.87(2). LC-MS (m/z): 642 (M+H+), 641 (M+),
597(M+H+-NO2), 479 (M+3H+-PhCH2S), 393 (M+2H+-
2PhCH2S), 356 (M+4H+-2PhCH 2-CS2-S), 303 (M+2H+-
+
N
N
CHO
CHO
N
N
MeOH/H 2SO4
NH2NH-C-S-CH2Ph
SN
H
NSCH2Ph
S
XX
S
NN
HSCH2Ph
12. X = NO2
13. X = B
3. X = NO2
7. X = B
r
r
Scheme 7. Synthesis of the Schiff Bases with S-benzyldi-
thiocarbazate (SBDTC).
Table 3. Reaction Conditions and Percent Yields for the
Synthesis of Schiff Bases.
Yield %
Condition Solvent Time
X = NO2 X = NO2
With HSO OHCH 1
2 43hr 65 96
Without
H2SO4 OH
3
CH 1 hr 60 92
(nzyl 2,rom,10-Phenanthro ne-
2,9-s(meth l-1-ylidene)-bis drazinecarb
dithioate)(13):
,
R (DMSO-d6, ppm): δH = 13.76 (s,
1N
e procedure
e (4 equiv.)
and ) 1,10-phenanthroline-2,9-di-
ic), 1579 (C=N), 1555 (C=C) 1528 (N=O).
H
2,2’)-Be
diyl)bi 2’-(5-B an-1-y o-1 li (hy
o
IR: ν (cm−1): 3180 (N-H), 3027 (=CH aromatic), 2925
(C-H aliphatic), 1566 (C=N), 1600, 1479 (C=C aromatic)
1095 (C=S). 1H-NM
H), 13.73 (s, 1NH), 8.58 (d, J = 8.24,1H), 8.51 (s, 1H),
8.49 (s, 1H) ,8.43 (s, 1H), 8.41 (d, J = 8.42, 1H), 8.24 (d,
J = 8.36,1H), 8.15 (d, J = 7.96, 1H), 7.48 - 7.27(m, 10 H),
4.54 (s, 4H). 13C-NMR (DMSO-d6, ppm): δC = 198.04(2),
153.35, 153.30, 146.28, 145.13, 143.59, 136.74, 136.46,
129.29(6), 129.08(8), 129.56(2), 128.33, 127.37, 120.70,
52.69, 52.79. LC-MS (m/z): 677/675 (M+H+), 676/674
(M+), 597/595 (M+-Br), 553/551 (M+- PhCH2S), 526/524
(M+-2CH3S-2N2), 403/401 (M+H+- 2PhCH2S-N2), 391
(M+4H+-Br-2PhCH2-N 2).
3.6. Synthesis of the Schiff Bases with
2-Mercaptoaniline
The compound was prepared using the sam
as described in 3.3, using 2-mercaptoanilin
5-substituted (NO2, Br
carboxaldehyde (1 equiv.). Table 4 shows different re-
action conditions and percent yields. Cyclized products
were obtained in both cases as shown in the equation
(Scheme 8).
2,9-Di-(benzo[d]thiazol-2-yl)-5-Nitro-1,10-Phenant-
hroline (14): IR: ν (cm−1): 3062 (CH aromatic), 1610
(C=C aromat
1-NMR (DMSO-d6,):

H = 8.89 (s,1H), 8.83 (d, J = 7.28,
1H), 8.68(d, J = 7.56, 1H), 8.61(2d, app t, J = 8.76, 2H),
8.33 - 8.23 (m, 4H), 7.64(m, 4H). 13C-NMR (DMSO-d6,
ppm): δC = 168.77, 168.60, 154.89, 154.89, 153.99,
152.07, 149.23, 147.15 145.54, 144.20, 136.36(2),
136.21, 134.30, 126.90(2), 126.72(3), 126.40, 126.33,

Z. JAMAN ET AL. 218
Scheme 8. Synthesis of Substitute d Schiff Bas es wi th 2-Mar-
captoaniline
Table 4. Reaction Conditions and Percent Yields of the
Schiff Bases.
Yield %
Condition Solvent Time
X = NO X = NO
2 2
With H2SO4 OH
3
CH 1 hr 45 30
Without
H2SO4 3OHCH 1 hr 25 25
1233.670.12 121.0LC-MS/z,
M+)M+3H 2 (M+2H), 491 (M+), 462(MH+-
O),447 (M+2H+-NO2), 391 (M+2H+-C6H4CN), 392
7 (C=C). H-NMR
(D
-bromo-2,
nthroline dialdehydes with sufur-con-
e been successfully synthesized. The
ent of Chemistry at Tennessee
g the necessary support to
so thank the Department of
[1] P. G. Sammes and G. Yahioglu, “1,10-Phenanthroline: A
Versatile LigaReviews, Vol. 23,
No. 5, 1994, pcs9942300327
.85, 12
: 494 (
, 122.8
+), 49
1.89,
+
9. (m
+
N
(M+3H+-C6H4CN), 359 (M+2H+-C6H4CNS), 283 (M+-
2C6H4CN), 254(M+3H+-2C6H4CS).
2,9-Di-(benzo[d]thiazol-2-yl)-5-Bromo-1,10-Phenan
throline (15): IR: ν (cm−1): 3053 (CH aromatic), 1602
(C=C aromatic), 1579 (C=N), 1541
MSO-d6,): 
H = 8.87 (3d,app q, J = 8.4, 3H), 8.75(s,
1H), 8.71(d, J = 7.47, 1H), 8.35 - 8.22 (m, 4H), 7.64 (m,
4H). 13C-NMR (DMSO-d6, ppm): δC = 169.07(2),
153.93(2), 149.67, 137.44(2), 136.19(2), 135.37(2),
131.13(2), 130.98, 126.83(2), 126.53, 123.68, 122.78,
120.33(2), 119.57, 116.43(2), 116.09, 114.79. LC-MS
(m/z, M+): 528/526 (M+2H+), 527/525 (M+H+), 526/524
(M+), 474/472(M+-2CN), 452/450 (M+2H+-CS2), 391
(M+H+-C6H4CNS), 279 (M+-C6H4CH2S).
4. Conclusion
Eight new Schiff bases of 5-nitro- and 59-di-
methyl-1,10-phena
taining amines hav
addition of conc. H2SO4 to the reaction mixtures has a
significant effect on the yields of the products. We tried
to do the reaction without acid because of the possibility
of forming salts by the protonation of nitrogen atoms of
the phenanthroline moiety which might cause lower
solubility of the Schiff bases. However, it was observed
that the yield increased significantly when the reaction
was carried out under mild aicidic conditions. This is due
to the fact that protonation of the carbonyl group (C=O)
enhances the nucleophilic attack by an anion. Also, reac-
tion time was reduced significantly compared to that re-
ported in the previous work, probably because of the
presence of the substituted group in the 5-position in the
phenanthroline moiety.
5. Acknowledgements
We thank the Departm
State University for providin
carry out the research. We al
Education, Title III funds for providing instrumental
support.
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