Dehalogenation of aromatic halides using metallic calcium in ethanol

Article abstract of DOI:10.1021/es010716+

The scope and limitations of the dehalogenation of aromatic halides 1 and 4a-p using metallic calcium in ethanol at room temperature were revealed. The cleavage of the carbon-chlorine bond on the aromatic ring bearing electron-donating group was difficult compared to the one bearing electron-withdrawing group. Moreover, we applied this method to the dechlorination of polychlorinated biphenyls (PCBs) in transformer oil. It was also found that the dechlorination took place easily under mild conditions. The existence of PCBs residue in the reaction at room temperature was less than 0.04% according to the GC-MS analysis. The chlorine was identified as calcium chloride.

Full text of DOI:10.1021/es010716+

Environ. Sci. Technol. 2001, 35, 4145-4148
Dehalogenation of Aromatic Halides
Using Metallic Calcium in Ethanol
YO S H I H A R U M I T O M A , ‡
S A T O K O N A G A S H I M A , ‡
FIGURE 1. The reaction of 4-chlorobiphenyl 1 with Raney Ni-Al
alloy in an alkaline aqueous solution.
C R I S T I A N S I M I O N , ‡ A L I N A M . S I M I O N , ‡
T O M O K O YA M A D A , ‡ K E I S U K E M I M U R A , ‡
K E I K O I S H I M O T O , † A N D
M A S A S H I T A S H I R O * , ‡
Tohwa Institute for Science, and Department of Industrial
Chemistry, Faculty of Engineering, Tohwa University, 1-1-1
Chikushigaoka, Minami-ku, Fukuoka, 815-8510, Japan
FIGURE 2. The reaction of aromatic halides with metallic calcium
in ethanol at room temperature.
The scope and limitations of the dehalogenation of
aromatic halides 1 and 4a-p using metallic calcium in
ethanol at room temperature were revealed. The cleavage
of the carbon-chlorine bond on the aromatic ring
bearing electron-donating group was difficult compared
to the one bearing electron-withdrawing group. Moreover,
we applied this method to the dechlorination of polychlo-
rinated biphenyls (PCBs) in transformer oil. It was also found
that the dechlorination took place easily under mild
conditions. The existence of PCBs residue in the reaction
at room temperature was less than 0.04% according to
the GC-MS analysis. The chlorine was identified as calcium
chloride.
1 with Raney Ni-Al alloy, in a diluted aqueous alkaline
solution at 90 °C was very effective for the dehalogenation
process, yielding biphenyl 2 (in 10% aqueous NaOH solution)
or cyclohexylbenzene 3 (in 0.5% aqueous KOH solution),
respectively (30) (Figure 1). Recently, we discovered that the
reaction of aromatic halides 4a,b,d-k with commercially
available metallic calcium in ethanol at room temperature
formed the corresponding dehalogenated compounds in
good yields (Figure 2). Many dehalogenation methods using
low-valent metal such as alkali metal in alcohol (31, 32), Mg
(33), and Zn/ acidic (34) or basic (35) solution, using metal
hydrides (36), or a catalyst such as Raney Ni (37) or Pd-
carbon (38) under hydrogen gas were developed up to now.
In the dehalogenation process using metallic calcium, to the
best of our knowledge, only one method, treatment of
Arochlor with metallic calcium in alcohols under a nitrogen
atmosphere, was reported by J. A. Hawari and co-workers as
a patent (39). The authors state that GC analysis indicated
disappearance of about 50% of the PCBs in the first treatment
in methanol, but there was not enough information in the
patent to estimate the scope and limitations of their method.
We wish to report here an efficient and environmental-
friendly method for dehalogenation of aromatic halides using
metallic calcium in ethanol with emphasis on PCBs in
transformer oil (where recovery of unreacted PCBs is under
0.04%).
Introduction
It is widely recognized that polychlorinated biphenyls (PCBs)
are one of mankind’s most dangerous pollutants and
widespread environmental contaminants (1, 2). In the past
decades, investigations focused especially on the removal
and destruction of PCBs. Among the methods proposed (3,
4), incineration seemed to be preferred (5). Nevertheless,
the interest in the recovery of reusable materials (e.g., PCBs
are present mostly in transformer oils) and the necessity to
treat contaminated products with low concentration of PCBs
have renewed the interest in the dechlorination methods.
The usual dechlorination methods of PCBs developed thus
far (such as using sodium borohydride (6-8), photochemical
dechlorination (9-13) or electroreduction (14-16)) present
several disadvantages that are the prevention of moisture,
the generation of undesired byproducts, but also the high
costs of the required materials and energy. Now, a few
selective decontamination methods are available, based on
chemical (17, 18) or biological (19) dechlorination technolo-
gies.
Experimental Section
General. Distillated water was used in all reactions. Com-
mercially available (Wako Pure Chemicals Industry, Ltd.) ethyl
alcohol was used. Granular particles of metallic calcium
(Kishida Chemical, Co. Ltd.) were directly put in the reaction
without any treatment in advance. The GC-MS analysis was
carried out on a HP 6890 series gas chromatograph (Hewlett-
Packard) equipped with a 30 m DB-1 column (i.d. ) 0.25 µm)
(J&W Scientific) and a JMS-AM II series (JEOL) which is a
quadrupole mass spectrometer. Ionization was performed
under 70 eV electron-impact (EI) conditions. The GC-17A
(Shimadzu) gas chromatograph (30 m DB-1 and FID detec-
tion) was used for routine work and for the determination
of the yield by using ethylbenzene as internal standard. Its
recorder was a C-R6A Cromatopac (Shimazdu Ltd.). The
programs of both GC were the same, as follows: the initial
temperature of the column was 60 °C, the temperature was
kept for 3 min, then the rate of temperature increase was 25
°C/ min up to 250 °C, and the temperature was kept for 20
min.
On the other hand, we have been investigating for some
time the reduction of some functions in water as a hydrogen
source. For examples, we have previously reported the
reduction and reductive coupling of imines (20, 21) or
carbonyl compounds (22-25) and the dehalogenation of
aromatic halides (26-29) using metals in an aqueous solution.
Moreover, we also found that the reaction of 4-chlorobiphenyl
* Corresponding author phone: +81-92-541-1512; fax: +81-92-
925-2737; e-mail: mitoma@tohwa-u.ac.jp.
† Department of Industrial Chemistry, Faculty of Engineering,
Tohwa University.
Typical Procedure for the Dehalogenation of Haloge-
nated Benzenes (4b-e) and the Determ ination of Products
‡ Tohwa Institute for Science, Tohwa University.
9
10.1021/es010716+ CCC: $20.00
Published on Web 09/12/2001
2001 Am erican Chem ical Society
VOL. 35, NO. 20, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 4 1 4 5

Using the GC Analyses. A mixture of dichlorobenzene (0.796
g, 5.41 mmol), metallic calcium (2.4 g, 60 mmol), and ethanol
(10 mL) was stirred at room temperature, in a round-bottom
flask. After 24 h, the reaction mixture was poured into 100
mL of 1 N hydrochloric acid. The solution was extracted
twice with ether and washed. The total volume of ether was
exactly increased up to 40 mL by adding pure ether. An
amount of 0.1 mL of the ether solution and another 0.1 mL
of a 0.01 M solution of ethylbenzene in ether were mixed; 1
µL of the resulting mixture was injected by a microsyringe.
The initial yields of products were obtained by estimating
the ratio of the area of peaks and reporting to the area of the
peak for ethylbenzene. It was found that the chlorobenzene
was formed quantitatively. The structure and the yields of
products were identified by GC-MS and GC analysis,
respectively.
TABLE 1. Reduction of Aromatic Halides Using Calcium in
Ethanola
Typical Procedure for the Dehalogenation of Haloge-
nated Benzenes Having Nitrogen Atom in Its Chain (4m
and 4p). A mixture of p-chloroaniline 4m (0.635 g, 4.98 mmol),
metallic calcium (0.80 g, 20 mmol), and ethanol (10 mL) was
stirred at room temperature. After 24 h, the solution was
extracted with 3 × 20 mL ether. Combined organic layers
were washed, dried on MgSO4, and evaporated. The residue
(0.621 g) was dried in vacuo. The crude reaction product was
analyzed by GC-MS analysis. The recovery of 4m was more
than 97%.
Typical Procedure for the Dechlorination of the 4-Chlo-
robiphenyl (1). A mixture of 4-chlorobiphenyl (1.0537 g, 5.59
mmol), metallic calcium (0.8 g, 20 mmol), and ethanol (10
mL) was stirred at room temperature. After 24 h, the reaction
mixture was added to 100 mL of 1 N hydrochloric acid. The
solution was extracted with 3 × 20 mL ether. Combined
organic layers were washed, dried on MgSO4, and evaporated.
The residue (0.840 g) was dried in vacuo. The crude reaction
product was analyzed by GC-MS analysis. It was found that
the ratio of products 2, 12, and 13 was 35%, 40%, and 15%,
respectively.
a
Substrate: 5 m m ol, calcium : 20 m m ol, reaction tem perature: room
b
tem perature, reaction tim e: 24 h. Ratios and structures were deter-
m ined by the GC-MS analyses. The yield of the products was
Typical Procedure for the Dehalogenation of Polychlo-
robiphenyls (PCBs) in Transform er Oil. Transformer oil
containing a mixture of PCBs (1.0271 g), metallic calcium
(0.8 g, 20 mmol), and ethanol (10 mL) were stirred at room
temperature. After 24 h, the reaction mixture was added to
100 mL of 1 N hydrochloric acid. The solution was extracted
with 3 × 20 mL ether. Combined organic layers were washed,
dried on MgSO4, and evaporated. The residue (1.007 g) was
dried in vacuo. The crude reaction product was analyzed by
GC-MS analysis. The results were summarized in Table 2.
Measurem ent of the Concentration of PCBs by the GC-
MS Analysis. In the measurement of PCBs, the conditions
of the GC-MS analysis of chlorinated biphenyls were the
follwing: the GC-MS analysis was carried out on a HP 6890
series gas chromatogragh (Hewlett-Packard) equipped with
a 60 m DB-5 (i.d. ) 0.25 mm, 0.25 µm film thickness) (J&W
Scientific) and JMS-700 series (JEOL). The program of GC
was as follows: the initial temperature of the column was
105 °C, the temperature was kept for 3 min, then the rate of
the temperature increase was 20 °C/ min up to 210 °C, and
the temperature was kept for 15 min. The temperature of the
column was then increased by 1.5 °C/ min up to 243 °C and
then by 40 °C/ min up to 280 °C, where it was maintained for
10 min. The injection was performed by a splitless mode.
The carrier gas was He and its column flow was 2.0 mL/ min.
The temperature of the injection port, interface, and ion
source were 295, 295, and 200 °C, respectively. The ionization
energy and current were 45 eV and 600 µA. The resolution
was 10 000. Monitor ion was as follows: 188.0393, 190.0363
(monosubstituted chlorinated biphenyls), 222.0003, 223.9974
(disubstituted chlorinated biphenyls), 255.9613, 257.9584
(trisubstituted chlorinated biphenyls), 289.9224, 291.9194
(tetrasubstituted chlorinated biphenyls), 301.9627 (M+),
c
determ ined by the GC analyses using ethylbenzene as
standard. The am ount of calcium was 60 m m ol.
a internal
d
303.9597 (M+ + 2) (13C of biphenyl in tetrasubstituted
chlorinated biphenyls).
Identification of the Chlorine Ion. In the titration of
chlorine ion, a large excess of pure water was added to the
reaction mixture in order to quench the metallic calcium
without the use of hydrochloric acid. Then, the solvent was
removed in vacuo. The obtained solid was used in Mohr’s
titration.
Results and Discussion
Dehalogenation of Arom atic Halides. Although several other
alcohols (such as methanol, iso- or n-propanol) were tested
as solvents in this process, ethanol was by far the most
efficient for the dehalogenation. Results of the dehalogenative
process in the metallic calcium-ethanol system are resumed
in Table 1. Entries 1-3 showed that if debromination and
deiodination of the corresponding halogenated benzene is
easy to realize, the dechlorination process is difficult, even
when increasing the quantity of metallic calcium up to 60
mmol. On the other hand, dichlorobenzene isomers 4d and
4e reacted with 60 mmol of calcium yielding quantitatively
4c (entries 4 and 5). The reactions of 4-iodochlorobenzene
4f and 4-bromochlorobenzene 4g also produced 4c in
quantitative yield (entries 6 and 7). In the same manner,
bromoalkylbenzene 4h suffered debromination (in this case
with increased quantity of metallic calcium), while p-
chlorotoluene 4i was completely recovered (entries 8-10).
In contrast with alkylbenzenes, in alkenylchlorobenzenes
9
4 1 4 6 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 20, 2001

TABLE 2. Treatment of PCBs in Transformer Oil with Calcium
and Ethanol at Room Temperature
FIGURE 4. The reaction of 4-chlorobiphenyl 1 with metallic calcium
in ethanol at room temperature.
Application to the Dechlorination of Polychlorinated
Biphenyls (PCBs). The next step in our investigation was to
extend the research to the dechlorination of PCBs in
transformer oil. In a previous research, we revealed that the
direct use of Raney Ni-Al alloy in a dilute alkaline solution
was effective for the dechlorination of 4-chlorobiphenyl 1 to
give the cyclohexylbenzene 3 in good yield (30). In contrast
with this result, it turned out that the reaction of 4-chloro-
biphenyl 1 with the metallic calcium-ethanol system yielded
biphenyl 2 along with the side products 12 and 13 (Figure
4). In addition, a mixture of PCBs in transformer oil such as
alkylbenzenes was used as starting material in the same
process. As previously mentioned, high concentrations of
PCBs are present in dielectric or lube-used oils (1, 2). All
PCBs present in the oil submitted to dechlorination were
reduced to hydrocarbons by the calcium-ethanol system, at
room temperature and in mild conditions (Table 2). After a
24 h treatment, at room temperature, the residue of PCBs in
the reaction mixture was less than 0.04%, according to GC-
MS analysis. The product in the dehalogenation could not
be isolated because interference with alkylbenzenes present
in the transformer oil. The formation of chlorine ion during
this process was confirmed by Mohr’s titration method.
Moreover, ethanol could be recycled as solvent for the next
PCBs dechlorination process. We also found out that small
quantities of iodine added to the reaction mixture can shorten
the reaction time down to only 5 h instead of 24 h. We believe
that this method is environmental-friendly and presents
significant economical advantage.
a
The concentration and identification were determ ined by GC-MS.
The concentration is the ratio between the weights of PCBs (in µg) and
total substances (in g). The N.D. m eans nondetection of any PCBs.
Literature Cited
(1) Nicholson, W. J.; Landrigan, P. J. Human Health Effects of
Polychlorinated Biphenyls. In Dioxins and Health; Schecter, A.,
Ed.; Plenum: New York, 1994.
(2) Zook, D. R.; Rappe, C. Environmental Sources, Distribution and
Fate of Polychlorinated Dibenzodioxins, Dibenzofurans and
Related Organochlorines. In Dioxins and Health; Schecter, A.,
Ed.; Plenum: New York, 1994.
FIGURE 3. The reaction scheme of 4-chloroacetophenone 4k.
(3) Santilli, N.; Chianese, A.; Pochetti, F.; Peluso, L. Ing. San. Ambient.
1992, gen-feb, 9.
(4) Woodyart, J. P. Environ. Prog. 1990, 9(2), 121.
(5) Lee C. C.; Huffman, G. L. Environ. Prog. 1989, 8(3), 190.
(6) Stojkovski, S.; Markovec, L. M.; Magee, R. J. J. Chem. Technol.
Biotechnol. 1991, 51, 407.
such as p-chlorostyrene 4j the dechlorination process
occurred easily, accompanied by the reduction of the side-
chain double bond (entry 11). When p-chloroacetophenone
4k was submitted to dehalogenation, almost equivalent
quantities of 4l and 9 were formed (entry 12). While
submitting 4l to dechlorination in the same conditions (entry
13), the recovery of the starting material leads to the
assumption that in the transformation of 4k the first step is
the dechlorination, and the reduction of the carbonyl group
occurs only after elimination of the halogen (Figure 3). This
process is somehow comparable with the dechlorination and
reduction of 4j. In the same time, dechlorination of 4-amino-,
4-methoxy- and 4-hydroxychlorobenzene derivatives
(4m -o) produced no transformation of the starting material.
We can therefore assume that in halogenated benzenes
bearing electron-withdrawing groups (4d-g or 4j, 4k) the
dehalogenation process is favored compared to halogenated
benzenes with electron-donating groups (4l-o and less in
4h and 7). An interesting behavior presented 4-nitrochlo-
robenzene 4p (thus, a chlorobenzene bearing an electron-
withdrawing group) which gave the azo- and azoxy-coupling
products 10 and 11, respectively, without dehalogenation
and without isolation of the possible p-chloroaniline inter-
mediate.
(7) Roth, J. A.; Dakoji, S. R.; Hughes, R. C.; Carmody, R. E. Environ.
Sci. Technol. 1994, 28, 80.
(8) Liu, Y.; Schwartz, J. Tetrahedron 1995, 51, 4471.
(9) Ishikawa, M.; Fukuzumi, S. J. Am. Chem. Soc. 1990, 112, 8864.
(10) Ishikawa, M.; Fukuzumi, S. Chem. Lett. 1990, 963.
(11) Tanaka, Y.; Uryu, T.; Ohashi, M.; Tsujimoto, K. J. Chem. Soc.,
Chem. Commun. 1987, 1703.
(12) Epling, G. A.; Elorio, E. Tetrahedron Lett. 1986, 27, 675.
(13) Davidson, R. S.; Goodin, J. W. Tetrahedron Lett. 1981, 22, 163.
(14) Zhang, S.; Rusling, J. F. Environ. Sci. Technol. 1995, 29, 1195.
(15) Zhang, S.; Rusling, J. F. Environ. Sci. Technol. 1993, 27, 1375.
(16) Petersen, D.; Lemmrich, M. L.; Altrogge, M.; Voss, J. Z.
Naturforsch. 1990, 45b, 1105.
(17) De Filippis, P.; Scarsella, M.; Pochetti, F. Ind. Eng. Chem. Res.
1999, 38, 380.
(18) Yak, H. K.; Wenclawiak, B. W.; Cheng, I. F.; Doyle, J. G.; Wai, M.
C. Environ. Sci. Technol. 1999, 33, 1307.
(19) Kuypers, B.; Cullen W. R.; Mohn, W. W. Environ. Sci. Technol.
1999, 33, 3579.
(20) Tsukinoki, T.; Mitoma, Y.; Nagashima, S.; Kawaji, T.; Hashimoto,
I.; Tashiro, M. Tetrahedron Lett. 1998, 39, 8873.
(21) Tsukinoki, T.; Nagashima, S.; Mitoma, Y.; Tashiro, M. Green
Chem. 2000, 2, 117.
9
VOL. 35, NO. 20, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 4 1 4 7

(22) Tsukinoki, T.; Ishimoto, K.; Tsuzuki, H.; Mataka, S.; Tashiro, M.
Bull. Chem. Soc. Jpn. 1993, 66, 3412.
(23) Tsukinoki, T.; Kawaji, T.; Hasimoto, I.; Mataka, S.; Tashiro, M.
Chem. Lett. 1997, 235.
(32) Pinder, A. R. Synthesis 1980, 425.
(33) Zagorski, M. G.; Salomon, R. G., J. Am. Chem. Soc. 1984, 106,
1750.
(34) Erickson, R. E.; Annino, R.; Scanlon, M. D.; Zon, G. J. Am. Chem.
Soc. 1969, 91, 1767.
(35) Yamanaka, H.; Oshima, R.; Teramura, K.; Ando, T. J. Org. Chem.
1972, 37, 1734.
(36) Krishnamurthy, S.; Brown, H. C. J. Org. Chem. 1980, 45, 849.
(37) Bohmer, V.; Marschollek, F.; Zetta, L. J. Org. Chem. 1987, 52,
3200.
(38) Sargent, L. J.; Ager, J. H. J. Org. Chem. 1938, 23, 1958.
(39) Hawari, J. A.; Samson, R. U.S. Patent 5 185 488, 1993.
(24) Tsukinoki, T.; Kawaji, T.; Hashimoto, I.; Etoh, T., Sahade, D. A.;
Tashiro, M. Eng. Sci. Rep., Kyushu Univ. 1997, 19, 15.
(25) Sahade, D. A.; Mataka, S.; Sawada, T.; Tsukinoki, T.; Tashiro, M.
Terahedron Lett. 1997, 38, 3745.
(26) Tashiro, M.; Fukata, G. J. Org. Chem. 1977, 42, 835.
(27) Tashiro, M.; Iwasaki, A.; Fukata, G. J. Org. Chem. 1978, 43, 196.
(28) Tashiro, M.; Tsuzuki, H.; Tsukinoki, T.; Mataka, S.; Nakayama,
K.; Yonemitsu, T. J. Labeled Comp. Radiopharm. 1990, 28, 703.
(29) Tsukinoki, T.; Kakinami, T., Iida, Y.; Ueno, M.; Ueno, Y.;
Mashimo, T.; Tsuzuki, H.; Tashiro, M. J. Chem. Soc., Chem.
Commun. 1995, 209.
Received for review March 6, 2001. Revised manuscript re-
ceived June 21, 2001. Accepted July 2, 2001.
(30) Liu G. B.; Tsukinoki T.; Kanda T.; Mitoma Y.; Tashiro M.
Tetrahedron Lett. 1998, 39, 5991.
(31) Bruck, P.; Thompson, D.; Winstein, S. Chem. Ind. 1960, 405.
ES010716+
9
4 1 4 8 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 20, 2001