NMR study of the naphtho-1,3-dithioles formed from carbamodithioates and 2,3-dichloro-1,4-naphthoquinone

Article abstract of DOI:10.3184/030823409X12561978806846

Reaction of triethylammonium 1,2-ethanediylbis(carbamodithioate) with 2,3-dichloro-1,4-naphthoquinone in DMF furnished N,N′-ethylenebis(2- iminonaphtho[2,3-d][1,3]dithiole-4,9-dione) in 94% yield. Triethylammonium N-arylcarbamodithioates reacted with 2,3-

Full text of DOI:10.3184/030823409X12561978806846

JOURNAL OF CHEMICAL RESEARCH 2009
NOVEMBER, 689–691
RESEARCH PAPER 689
NMR study of the naphtho-1,3-dithioles formed from carbamodithioates
and 2,3-dichloro-1,4-naphthoquinone
Ashraf A. Alya*, Alan B. Brownb, Kamal M. El-Shaieba, Alaa A. Hassana and Tarek M. I. Bedaira
*aDepartment of Chemistry, Faculty of Science, El-Minia University, 61519-El-Minia, Egypt
bChemistry Department, Florida Institute of Technology, 150 W University Blvd, Melbourne, Florida 32901, USA
Reaction of triethylammonium 1,2-ethanediylbis(carbamodithioate) with 2,3-dichloro-1,4-naphthoquinone in
DMF furnished N,N'-ethylenebis(2-iminonaphtho[2,3-d][1,3]dithiole-4,9-dione) in 94% yield. Triethylammonium
N-arylcarbamodithioates reacted with 2,3-dichloro-1,4-naphthoquinone to give 2-(N-arylimino)naphtho[2,3-d][1,3]
dithiole-4,9-diones in good yields. NMR spectroscopic data of the products are discussed.
Keywords: carbamodithioates, dithioles, NMR
Sulfur heterocycles containing benzo- and naphtho-1,3-dithiole
moieties have demonstrated anti-angiogenic properties,1 and are
of interest as precursors to functionalised tetrathiofulvalenes,2,3
which in turn have a host of applications in molecular
electronics.4-6 Aly et al. have a long-term interest in reactions
of thiols and thioamides towards π-acceptors.7-10 Here we
report the reactions of the carbamodithioates 1 and 5a–e
with 2,3-dichloro-1,4-naphthoquinone (2), to give 2-imino-
1,3-naphthodithioles.
reveal any absorption related to C=S, NH and/or OH groups.
1H NMR spectra of 6a–e supported the proposed 1,3-dithiole
structures, since they did not show any NH- or OH-signals,
and the aromatic proton signals in 6a–e appeared to be
1
symmetrical. In each case, the H integrals require there be
one pendant aryl group R and one o-phenylene group. This
ratio showed that the product arose from one each of 5a–e
as appropriate and 2. All the correlations are straightforward,
and the C=N chemical shifts are 159.8 (6a), 159.0 (6b), 160.7
(6c), 157.4 (6d), and 153.3 (6e). These chemical shifts require
each carbon be a C=N not a C=S. Carbonyl signals are also
present. The other carbon resonances in the naphthoquinone
part structures support their near-symmetry, and are closely
similar in all five compounds.
In 6d and 6e, HMBC correlations were observed between
the azomethine carbon and the aliphatic protons a to nitrogen,
establishing the connection between the C=N and the benzyl
and cyclohexyl groups respectively. The NMR properties
are much more consistent with structures 6a–e than with the
alternative naphthothiazoles 7a–e.
Results and discussion
The bis(dithiocarbamate) salt 111 was synthesised by adding
carbon disulfide to a solution of ethylenediamine and
triethylamine.Onadding1equiv.of1to2equiv.of2,3-dichloro-
1,4-naphthoquinone (2) in DMF, N,N'-ethylenebis-
(2-iminonaphtho[2,3-d]-[1,3]dithiole-4,9-dione) (3) was
obtained in 6 hours in 94% yield (Scheme 1). The mass spectra
of compound 3 showed a molecular ion at m/z 520 (15%
of base peak), consistent with the formula C24H12N2O4S4,
which was confirmed by elemental analysis. The structure
assignment of 3 is supported by IR and NMR (1H, 13C) data.
The IR spectrum did not show any absorption from C=S, NH,
or OH groups, but did show C=O absorption at 1665 cm-1.
The NMR spectra of 6e (Table 1) exemplify those of the
whole series. The 1H NMR spectrum contains one CHN
proton at dH = 2.91, and four aromatic protons. This ratio
showed that the product arose from one each of 5e and 2.
Neither 6e nor the alternative benzothiazole product 7e has
a σ plane, so either should theoretically give 15 13C lines (the
cyclohexyl ring has local symmetry). Fourteen lines were
observed, so one pair of nonequivalent carbons is co-resonant.
1
The H NMR spectrum likewise did not show NH nor OH
resonances. The aliphatic CH2-protons appeared as a broad
singlet at dH 2.80. The aromatic protons appeared as two 4H
multiplets at dH = 7.56–7.68 and 7.80-7.92. Salient 13C NMR
signals correspond to C=O at dC = 176.7, C=N at dC = 161.0,
CO–C–S at dC = 139.6, and aliphatic CH2 at dC 54.0.
1
The aromatic H pattern resembles an AA'XX' pattern and is
so analysed; 13 this analysis yields values for all the coupling
constants in the system (JAA', JAX, JAX', and JXX').13 Since
the two sides of the o-phenylene ring are nonequivalent,
the pattern is technically an ABXY, with A and B being
The carbamodithioates 5a–e prepared from 4a-e12 reacted
with compound 2, to give 2-iminonaphtho[2,3-d][1,3]
dithiole-4,9-diones 6a–e (Scheme 2). The IR spectrum did not
O
Cl
2
Et3HN
Cl
NH2
NH2
S
Et3N, ether
O
+
CS2
H
NH
S
2
NHEt3
S
N
24 h, 0 °C
DMF, r.t., 6 h
S
O
1
O
S
S
N
N
S
S
3 (94%)
O
O
Scheme 1 Synthesis of N,N'-ethylenebis(2-iminonaphtho[2,3-d][1,3]dithiole-4,9-dione).
* Correspondent. E-mail: ashrafaly63@yahoo.com
PAPER: JC090753

690 JOURNAL OF CHEMICAL RESEARCH 2009
O
O
S
S
RN
R
Et3N, ether
NH
6a-e
R
NH2
4a-e
2, DMF
+
CS2
72 h, 0 oC
Et3NH
S
S
r.t., 6-8 h
O
5a-e
S
S
N
Yield of 6 (%)
Yield of 5 (%)
R
4-7
R
O
C6H5-
95
96
80
87
90
82
85
76
82
70
a
b
c
p-CH3-C6H4-
p-Cl-C6H4-
C6H5-CH2-
C6H11-
7a e
-
d
e
Scheme 2 Reactions of carbamodithioates 5a-e with 2: synthesis of naphtho-1,3-dithioles 6a-e
9a
9
8a
O
O
8
1
S
O
O
S
S
S
S
7
2
N
N
S
S
1'
6
S
3
N
N
2'
4a
5
3a
4'
3'
4
9
8
7e
6e
Fig. 1
co-resonant, and X and Y also co-resonant. The 1H–1H
coupling constants require that dH 8.12 be H-6,7 and dH 7.76
be H-5,8. These protons give HMQC correlation to carbons
at dC 127.11 (C-6,7; co-resonant) and dC 134.21, 134.16
(C-5,8). The assignments are supported by the observation of
HMBC correlation between C-6,7 and H-6,7 together with
the absence of HMBC correlation between C-5,8 and H-5,8.
These would be correlations between one of the two carbons
and the other hydrogen, e.g. between C-6 and H-7: two bonds
in the C/H-6,7 pair but four bonds in the C/H-5,8 pair. HMBC
correlations are much more commonly observed over two
bonds than over four. The non-protonated carbons at dC =
132.1, 132.0 give HMBC correlation with C-5,8 and H-6,7;
these carbons are assigned as C-4a,8a. The almost co-resonant
carbons at dC 176.2, 175.8 and dC 143.6, 143.3 give no
HMBC correlations; they are assigned as C-4,9 and C-3a,9a
respectively. The downfield sp3 carbon at dC 69.5 is assigned
as C-1'; the attached H at dH 2.91 gives HMBC correlation
with the remaining sp2 carbon at dC 153.3, which is assigned
as the C=N. In the alternative naphthothiazole structure 7e,
H-1' would be three bonds from C-3a, hence might give
HMBC correlation with this carbon; that this correlation is
Table 1 NMR spectroscopic data of compound 6e
1H NMR (CDCl3)
COSY
Assignment
8.12 (ABXY, JAX = 7.6, JAB = 7.1, JAY = 1.4; 2H)
7.76 (ABXY, JAX = 7.6, JAY = 1.4, JXY = 0.0; 2H)
2.91 (tt, J = 9.8, 3.8; 1H)
1.82 (m; 4H)
7.76
H-6,7
H-5,8
H-1'
H-2',3'
H-4'
H-2'
H-3',4'
8.12
1.82, 1.46
2.91, 1.67, 1.46, 1.29
1.82, 1.29
2.91, 1.87, 1.46, 1.29
1.82, 1.67, 1.46, 1.29
1.67 (m; 1H)
1.46 (m; 2H)
1.29 (m; 3H)
13C NMR (CDCl3)
HMQC
7.76
HMBC
Assignment
176.2, 175.8
153.3
C-4,9
C=N
2.91
143.6, 143.3
134.21, 134.16
132.1, 132.0
127.1
C-3a,9a
C-5,8
C-4a,8a
C-6,7
C-1'
8.12
8.12, 7.76
8.128.12, 7.76
2.911.82
1.82, 1.462.91, 1.29
1.671.29
1.82, 1.291.82, 1.46
69.5
32.2
C-2'
25.44
C-4'
24.50
C-3'
PAPER: JC090753

JOURNAL OF CHEMICAL RESEARCH 2009 691
(C-3'), 127.2 (C-6,7), 125.9 (C-4'), 119.5 (C-2'). IR (KBr): nmax
3105–3008 (w, Ar-CH), 1665 (s, CO), 1610 (s, C=N), 1590 (s, C=C)
cm-1. lmax (CH3CN, lg e, nm): 400 (4.0). MS (EI): m/z (%) = 323
[M+] (93), 220 (20), 188 (34), 160 (22), 135 (100), 104 (37), 76 (38).
C17H9NO2S2 (323.39): Calcd C, 63.14; H, 2.81; N, 4.33; S, 19.83.
Found: C, 63.00; H, 2.75; N, 4.20; S, 20.00%.
2-(p-Tolylimino)naphtho[2,3-d][1,3]dithiole-4,9-dione (6b): Red
crystals (0.29 g, 85%), m.p. 184°C (ethanol). 1H NMR (CDCl3) 8.11
(m, 2H; H-6,7), 7.76 (m, 2H; H-5,8), 7.22 (d, J = 8.1, 2H; H-3'), 6.93
(d, J = 8.2, 1H; H-2'), 2.37 (s, 3H; CH3). 13C NMR (CDCl3) 176.2,
175.8 (C-4,9), 159.0 (C=N), 148.3 (C-4'), 143.4, 143.2 (C-3a,9a),
135.7 (C-1'), 134.30, 134.26 (C-5,8), 132.1, 132.0 (C-4a,8a), 130.4
absent does not exclude structure 7e, but is more supportive
of 6e (Scheme 2). Further evidence for structure 6e comes
from comparison of experimental and calculated (ChemNmR:
increment method) 13C chemical shifts to those of model
compounds. First, the experimental azomethine dC for 6e
(153.3) is much closer to the calculated C=N values for itself
(162.6) and compound 8 (dC 162.8), than to the C=S values
for 914 (exp. 189.0, calcd 193.9; Fig. 1). Second, the carbon
resonances on the side positions of the benzene ring differ
by several ppm in 9;14 in 8 and in 6e, these chemical shifts
are calculated to coincide, and in the experimental spectrum
of 6e, they are within 0.08 ppm. Correlations in compounds
6a–d are equally straightforward. Therefore, compounds
6a–e are assigned as naphtho-1,3-dithioles (Scheme 2).
(C-3'), 127.2 (C-6,7), 119.5 (C-2'), 21.1 (CH3). IR (KBr): nmax
=
3086–3008 (w, Ar-CH), 2972–2860 (m, aliph-CH), 1660 (s, CO),
1610 (s, C=N), 1590 (s, C=C) cm-1. lmax (CH3CN, lg e, nm): 406
(4.1). MS (EI): m/z (%) = 337 [M+] (100), 322 (27), 220 (16), 188 (4),
149 (56), 117 (19), 104 (38), 91 (36), 76 (15), 65 (26). C18H11NO2S2
(337.42): Calcd C, 64.07; H, 3.29; N, 4.15; S, 19.01. Found: C,
64.00; H, 3.20; N, 4.07; S, 18.92%.
1
The o-phenylene H NMR signals of 6a-d cannot be fully
solved as AA'XX' patterns, apparently because the chemical
shifts of H-6,7 differ just enough to distort the AA' part of the
pattern; the assignments of these signals are based on their 2D
correlations and by analogy with 6e.
2-(4-Chlorophenylimino)naphtho[2,3-d][1,3]dithiole-4,9-dione
(6c). Reddish blue crystals (0.27 g, 76%), m.p. 218°C (ethanol).
1H NMR (CDCl3) 8.12 (m, 2H; H-6,7), 7.78 (m, 2H; H-5,8), 7.39 (d,
J = 8.2, 2H; H-3'), 6.97 (d, J = 8.2, 2H; H-2'). 13C NMR (CDCl3) 176.1,
175.7 (C-4,9), 160.7 (C=N), 149.1 (C-1'), 143.6, 143.1 (C-3a,9a),
134.41, 134.38 (C-5,8), 132.0, 131.9 (C-4a,8a), 131.2 (C-4'),
130.0 (C-3'), 127.2 (C-6,7), 121.1 (C-2'). IR (KBr): nmax = 3090-
3010 (w, Ar-CH), 1660 (s, CO), 1612 (s, C=N), 1580 (m, C=C) cm-1.
lmax (CH3CN, lg e, nm): 408 (3.6). MS (EI): m/z (%) = 357 [M+]
(100), 322 (16), 220 (20), 188 (20), 169 (71), 104 (32), 76 (26).
C17H8ClNO2S2 (357.84): Calcd C, 57.06; H, 2.25; Cl, 9.91; N, 3.91;
S, 17.92. Found: C, 57.22; H, 2.20; Cl, 10.08; N, 3.80; S, 17.80%.
2-(Benzylimino)naphtho[2,3-d][1,3]dithiole-4,9-dione (6d): Pale
red crystals (0.28 g, 82%), m.p. 176–178°C (ethanol). 1H NMR
(CDCl3) 8.14 (m, 2H; H-6,7), 7.77 (m, 2H; H-5,8), 7.37 (m, 4H;
H-2',3'), 7.30 (m, 1H; H-4'), 4.44 (s, 2H; CH2). 13C NMR (CDCl3)
176.3, 175.7 (C-4,9), 157.4 (C=N), 144.2, 143.1 (C-3a,9a), 137.4
(C-1'), 134.34, 134.25 (C-5,8), 132.1, 132.0 (C-4a,8a), 128.7, 127.8
Conclusion
Carbamodithioates react with 2,3-dichloro-1,4-naphthoquinone
to give naphtho-1,3-dithioles and not naphthothiazoles.
Experimental
Melting points are uncorrected. 1H NMR and 13C NMR spectra
were measured on Bruker AM-400 or AV-400 spectrometers (400.13
MHz for 1H and 100.6 MHz for 13C); chemical shifts are in ppm
from TMS (d), and coupling constants are in Hz. The AV-400 was
purchased with assistance from the National Science Foundation
(CHE 03-42251). For preparative thin layer chromatography (PLC),
glass plates (20 × 48 cm) were covered with slurry of silica gel Merck
PF254 and air-dried using the solvents listed for development. Zones
are detected by quenching of indicator fluorescence upon exposure
to 254 nm UV light. Elemental analyses were carried in Assiut
Microanalysis Centre of Assiut University. Mass spectroscopy was
performed with a Finnigan Mat 8430 spectrometer at 70 eV Institute
of Organic Chemistry, TU-Braunschweig. Germany. IR spectra were
run on a Shimadzu 470 spectrometer using KBr pellets.
(C-2',3'), 127.5 (C-4'), 127.2 (C-6,7), 62.6 (CH2). IR (KBr): nmax
=
3090–3000 (w, Ar-CH), 2970–2840 (m, aliph-CH), 1662 (s, CO),
1615 (m, C=N), 1595 (m, C=C), 1450 (m, CH2) cm-1. lmax (CH3CN,
lg e, nm): 392 (3.7). MS (EI): m/z (%) = 337 [M+] (58), 332 (18),
188 (26), 149 (15), 117 (19), 104 (32), 91 (100), 76 (30), 65 (22).
C18H11NO2S2 (337.42): Calcd C, 64.07; H, 3.29; N, 4.15; S, 19.01.
Found: C, 64.20; H, 3.20; N, 4.12; S, 18.89%.
Starting materials
The bis(dithiocarbamate) salt 1 was prepared according to ref. 11,
and the carbamodithioates 5a–e were prepared according to ref. 12.
2-(Cyclohexylimino)naphtho[2,3-d][1,3]dithiole-4,9-dione
(6e):
Yellow crystals (0.23 g, 70%), m.p. 170–171°C (ethanol). NMR (see
Table 1). IR (KBr): nmax = 3098-3002 (w, Ar-CH), 2990–2820 (m,
aliph-CH), 1665 (s, CO), 1610 (s, C=N), 1595 (s, C=C), 1455 (w, CH2)
cm-1. lmax (CH3CN, lg e, nm): 380 (3.5). MS (EI): m/z (%) = 329 [M+]
(100), 296 (60), 286 (54), 247 (30), 220 (31), 189 (33), 141 (36), 104
(42), 76 (28), 67 (14). C17H15NO2S2 (329.44): Calcd C, 61.98; H, 4.59;
N, 4.25; S, 19.47. Found: C, 61.78; H, 4.50; N, 4.20; S, 19.30%.
Reactions of 1 with 2
A mixture of 1 (0.414 g, 1 mmol) with 2 (0.454 g, 2 mmol) in DMF
(50 mL) was stirred at room temperature 6 h. The precipitate formed,
3, was washed with cold ethanol (50 mL) and then dissolved in
acetone (20 mL). The solution was subjected to preparative TLC
using toluene: ethyl acetate (1:1, silica gel). The zone of compound 3
was extracted and the product 3 was recrystallised.
N,N'-Ethylenebis(2-iminonaphtho[2,3-d][1,3]dithiole-4,9-dione)
(3): Greenish white colourless crystals (0.52 g, 94%), m.p. >360°C
(ethyl acetate). 1H NMR (DMSO-d6): 8.12–8.04 (m, 2H, Ar-H),
7.76–7.60 (m, 6H, Ar-H), 3.20 (s, 4H, CH2). 13C NMR (100.6 MHz,
DMSO-d6): dC = 178.7 (4C=O), 162.0 (2C=N), 140.0 (4 CO–C–S),
132.0 (4 CO–C-Ar), 130.8 (Ar-4CH), 128.0 (Ar-4CH), 50.3 (2CH2).
IR (KBr): nmax = 3100–3000 (w, Ar-CH), 2900–-2840 (m, aliph.-CH),
1665 (s, CO), 1625 (m, C=N), 1595 (m, C=C) cm-1. lmax (CH3CN, lg
e, nm): 370 (3.6). MS (EI): m/z (%) = 520 [M+] (15), 286 (14), 272
(18), 260 (100), 228 (22), 224 (20), 152 (24), 128 (34), 77 (24), 67
(22). C24H12N2O4S4 (520.62): Calcd C, 55.37; H, 2.32; N, 5.38; S,
24.64. Found: C, 55.20; H, 2.34; N, 5.30; S, 24.60.
Received 21 August 2009; accepted 21 October 2009
Paper 09/0753 doi: 10.3184/030823409X12561978806846
Published online: 17 Novmber 2009
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PAPER: JC090753