Table 1 Bulk electrolyses data of DDT catalysed by Co(II)
Yield (%)d
Solvent
and additive
Conversion
of DDT (%)
Entry
DDD
DDE
TTDB (E/Z)
DDMU
DDMS
DDNU
DDO
1a
IL, Co(II)
Only IL
DMF, Co(II)
IL, Co(II)
75
46
82
95
20
19
20
—
15
5/2
Trace
25/12
3/2
2
7
7
16
—
27
5
—
—
Trace
15
—
—
44
2a
Trace
19
16
3a,b
4a,c
a
6
Trace
At 21.5 V vs. Ag/AgCl; Ar atmosphere; initial concentrations: DDT 2.5 6 1022 M; Co(II) 5.0 6 1024 M; charge passed: 2.1 F mol21 of
DDT. 0.1 M Bu4NClO4 was used as a supporting electrolyte. Prolonged electrolysis; charge passed: 4.0 F mol21 of DDT. Products were
b
c
d
analyzed using 1H NMR, HPLC and GC-MS data.
elimination of Cl-atoms from the terminal aliphatic carbon atom
in the Co(II)–IL system. On the other hand, in the Co(II)–DMF
system, no such kind of products were produced, as shown in
entry 3 of Table 1. Furthermore, prolonged electrolysis (by passing
4.0 F mol21) converts over 95% of DDT into its dechlorinated
products, with tri-dechlorinated 1,19-(ethylidene)bis(4-chloroben-
zene) (DDO) as the major product (entry 4). In this case, no DDD
was produced, suggesting that all of the DDD had been converted
via a charge-separated activated complex in the polar IL, which
ultimately decreases the DG{ value, resulting in an increase in the
reaction rate.
The Co(II) has been recycled and reused for the dechlorination
of DDT in IL, where the conversions of DDT to its dechlorinated
products were found to be in the range of 73–82%. After the fourth
run, over 96% recovery of Co(II) was obtained without its
decomposition, as examined using UV-Vis spectroscopy and
MALDI-TOF mass spectrometry. Thus, Co(II) is proved to be a
tough catalyst for the dechlorination of DDT.
into
1,19-(2-chloroethylidene)bis(4-chlorobenzene)
(DDMS)
and/or DDO.
The Co(II)–IL system was further utilized for the dechlorination
of the relatively less reactive DDD, which yielded DDMS and
DDO as the major products (Table 2). Under the same conditions
in DMF, the dechlorination proceeded with only 16% conversion.
The DDT dechlorination reaction mediated by Co(II) proceeds
via the formation of an alkylated complex, with a cobalt–carbon
bond, as the intermediate, which was followed using UV-Vis
spectroscopy during electrolysis. When the electrolysis was carried
out at 21.5 V vs. Ag/AgCl, the charge neutral Co(I) species
converted to the corresponding photo-active complex with
absorption maxima at 356 and 470 nm, respectively; absorption
maxima at 410 and 505 nm, respectively, were recorded by
irradiation of the same solution with visible light under aerobic
condition. This photochemical behaviour is characteristic of that
for a complex with a cobalt–carbon bond.7
The present study successfully demonstrates the electrolytic
dechlorination of DDT and DDD in a Co(II)–IL system. The use
of the cheaper material, carbon felt, for the cathode and the
recyclability of the Co(II) in IL system makes the process cost-
effective and eco-friendly.
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas (460) from the Ministry of Education,
Culture, Sports, Science and Technology (MEXT) of Japan, and
an Industrial Technology Research Grant Program in 2005 from
New Energy and Industrial Technology Development
Organization (NEDO) of Japan.
Notes and references
{ After the electrolysis, the catholyte was extracted with diethyl ether (3 6
10 mL). The diethyl ether portion contains the mixture of dechlorinated
products. The other portion, containing IL and Co(II), was further dried in
vacuum and recycled for the next run.
The enhanced reactivity of the Co(II)–IL system over the Co(II)–
DMF system could be explained by the application of the Hughes–
Ingold predictions8 of solvent polarity effects on reaction rates.
The ET scale is one of the most widely applied of empirical polarity
scales.9 For [bmim][BF4] and DMF, the ET(30)-values are 52.5 and
43.2 kcal mol21, respectively,10 indicating the comparatively more
polar behaviour of IL. The reaction of electrochemically generated
Co(I) with DDT is a ‘‘Menschutkin type of reaction’’ in which two
neutral reactants, Co(I) and DDT, react to form charged products
DDD and DDE were identified using GC-MS and HPLC comparison
to authentic samples. DDMU 1,19-(2-chloroethenylidene)bis(4-chloroben-
zene) and TTDB (Z/E) 1,1,4,4-tetrakis(4-chlorophenyl)-2,3-dichloro-2-
butene were identified from spectral comparison to the reported values.11,12
DDMS was obtained as a pale yellowish solid; GC-MS: m/z: 284 [M+]; 1H
NMR (500 MHz, CDCl3): d (ppm) 4.0 (d, 2 H), 4.30 (t, 1 H), 7.3 (m, 8 H);
13C NMR (125 MHz, CDCl3): 46.64, 52.28, 128.95, 129.32, 133.16,
139.29 ppm. DDO was obtained as a colorless mass; GC-MS: m/z: 250
[M+]; 1H NMR (500 MHz, CDCl3): d (ppm) 1.6 (d, 3 H), 4.1 (q, 1 H), 7.3
(m, 8 H); 13C NMR (125 MHz, CDCl3): 22.14, 44.02, 129.00, 129.31,
129.75, 131.73 ppm. DDNU was obtained as colorless solid crystals;13 mp
83 uC; GC-MS: m/z: 248 [M+]; 1H NMR (500 MHz, CDCl3): d (ppm) 5.48
(s, 2 H), 7.31 (m, 8 H); 13C NMR (125 MHz, CDCl3): 115.5, 128.9, 129.9,
134.3, 139.9, 148.3 ppm.
Table 2 Bulk electrolyses data of DDD catalysed by Co(II)
Yield (%)c
Solvent and
additive
Conversion
of DDD (%)
Entry
DDMS
DDNU
DDO
1 H. Shimakoshi, M. Tokunaga, T. Baba and Y. Hisaeda, Chem.
Commun., 2004, 1806.
2 D. A. Pratt and W. A. van der Donk, Chem. Commun., 2006, 558.
3 H. Shimakoshi, M. Tokunaga and Y. Hisaeda, Dalton Trans., 2004,
878.
4 Y. Murakami, Y. Hisaeda and A. Kajihara, Bull. Chem. Soc. Jpn., 1983,
56, 3642.
5 G. Fellenberg, The Chemistry of Pollution, Wiley, Chichester, 2000,
p. 123.
1a
2a
3a,b
a
IL, Co(II)
Only IL
DMF, Co(II)
77
Trace
16
61
—
10
Trace
—
—
13
—
Trace
At 21.5 V vs. Ag/AgCl; Ar atmosphere; initial concentrations:
DDD 2.5
6
1022 M; Co(II) 5.0
6
1024 M; charge passed:
2.2 F mol21 of DDD. 0.1 M Bu4NClO4 was used as a supporting
b
electrolyte. Products were analyzed using 1H NMR, HPLC and
GC-MS data.
c
1654 | Chem. Commun., 2007, 1653–1655
This journal is ß The Royal Society of Chemistry 2007
Jabbar, Md. Abdul
