Study of dehalogenation of halogenoanilines using Raney Al-Ni alloy in aqueous medium at room temperature

Article abstract of DOI:10.1007/s00706-010-0362-9

Dehalogenation of halogenated anilines by action of powdered aluminium-nickel alloy in aqueous alkaline solution at room temperature has been studied. The reaction course was monitored by means of¹H nuclear magnetic resonance (NMR) spectroscopy. The rates of dehalogenation of 4-bromo-, 4-chloro-, 4-fluoro-and 3-chloroaniline were compared under conditions of minimum necessary excess of Al-Ni alloy as reducing agent in edetane buffer medium at pH 10.9. The dehalogenation rates of halogenated anilines decreased in the following order: 3-chloroaniline > 4-bromoaniline ≥ 4-chloroaniline >4-fluoroaniline. On the basis of the results obtained in buffers, the dehalogenation method of aqueous solutions of halogenoanilines was verified using NaOH as the base. Springer-Verlag 2010.

Full text of DOI:10.1007/s00706-010-0362-9

Monatsh Chem (2010) 141:1015–1020
DOI 10.1007/s00706-010-0362-9
ORIGINAL PAPER
Study of dehalogenation of halogenoanilines using Raney Al–Ni
alloy in aqueous medium at room temperature
Tom a´ sˇ Weidlich
•
Anna Krej cˇ ov a´ Lubom ´ı r Proke sˇ
•
Received: 26 October 2009 / Accepted: 22 June 2010 / Published online: 5 August 2010
Ó Springer-Verlag 2010
Abstract Dehalogenation of halogenated anilines by
action of powdered aluminium–nickel alloy in aqueous
alkaline solution at room temperature has been studied.
Monuron [4-chloroaniline (1b) as intermediate], are com-
mon water pollutants. Compounds 1 are toxic, and their
water solubility depends on the type, position and number of
the halogen substituents on the aromatic ring. In addition, 1
are much less biodegradable than aniline, which increases
their environmental impact [1, 2]. In recent years, transition-
metal-promoted reductive dehalogenation using various
metals has been recognized as an innovative approach for
degradation of 1 [3–12]. However, many of the proposed
methods suffered from some limitations, and development of
new and efficient dehalogenation procedures continues to be
of current interest.
1
The reaction course was monitored by means of H nuclear
magnetic resonance (NMR) spectroscopy. The rates of
dehalogenation of 4-bromo-, 4-chloro-, 4-fluoro- and 3-
chloroaniline were compared under conditions of minimum
necessary excess of Al–Ni alloy as reducing agent in
edetane buffer medium at pH 10.9. The dehalogenation
rates of halogenated anilines decreased in the following
order: 3-chloroaniline [ 4-bromoaniline C 4-chloroani-
line [ 4-fluoroaniline. On the basis of the results obtained
in buffers, the dehalogenation method of aqueous solutions
of halogenoanilines was verified using NaOH as the base.
A few reduction methods have been developed for
hydrodehalogenation of 1 in the presence of noble-metal
catalysts [3–7]. The hydrodehalogenation method, how-
ever, requires expensive apparatus for elevated-pressure
operations. For this reason, application of dehalogenation
based on cheap metals with high reduction potential is a
successful alternative for particular degradation of halo-
genated anilines [8–10]. Reductive dehalogenation with
Al–Ni alloy in KOH solutions was used for degradation of
various halogenated compounds [11]. The degradation
products were generally those obtained by replacing the
halogen substituent with hydrogen, although concomitant
reduction of other groups was also observed [11]. An
example of reductive degradation of halogenated biphenyls
by action of Al–Ni alloy in aqueous NaOH solution at
temperature of 90 °C showed that these vigorous condi-
tions brought about not only dehalogenation but also
hydrogenation of the aromatic system [12].
Keywords Reductions Á AOX removal Á
NMR spectroscopy Á Metals Á ICP-OES
Introduction
Halogenoanilines (1), being important intermediates in the
production of a very wide range of synthetic organic chem-
icals including for example phenylurea herbicides, such as
Metobromuron [4-bromoaniline (1a) as intermediate] or
T. Weidlich (&) Á A. Krej cˇ ov a´
Faculty of Chemical Technology, Institute of Environmental
and Chemical Engineering, University of Pardubice,
Studentska 573, 532 10 Pardubice, Czech Republic
e-mail: tomas.weidlich@upce.cz
The mechanism of dehalogenation of halogenoaromatics
using metallic alloys is not totally clarified [12]; sometimes
direct reduction at metal surface is mentioned [13], or
sometimes action of adsorbed hydrogen activated on nickel
sponge is proposed [12].
L. Prokesˇ
Department of Chemistry, Faculty of Science, Masaryk
University, Kotlarska 2, 611 37 Brno, Czech Republic
123

1
016
T. Weidlich et al.
A common drawback of the methods using metal
1a and 1b as substrates. The pH value of the reaction
solution was adjusted by means of aqueous buffers. In
preliminary experiments, a large excess of Al–Ni alloy was
adopted: the molar ratio of Al (in the form of Al–Ni) to 1a
was 10:1. After the reaction, the filtered reaction mixtures
reagents and/or catalysts lies in contamination of the
reaction medium with the respective metals. However,
there are many applicable methods useful for minimization
of metal content in the aqueous solution, e.g., coagulation,
hydroxide or sulphide precipitation, etc. [14–16].
were extracted with CDCl , and the extracts were analyzed
3
1
by means of H NMR spectroscopy [17, 18]. The reaction
The aim of the present study is to show the applicability
of aluminium–nickel alloy to dehalogenation of haloge-
nated anilines in aqueous buffers at room temperature and
to investigate parameters such as the quantity of Al–Ni
is selective, i.e. only dehalogenation takes place, aniline (2)
being the only product detected. This was confirmed using
aniline as the external standard.
1
alloy and the reaction time. H NMR spectroscopy was
The obtained experimental results indicate sensitivity of
the dehalogenation reaction to pH of the medium as well as
to the buffer composition adopted (Table 1, entries 1–11).
It was found that the dehalogenation reactions of 1a
carried out in buffers with pH \10 never led to complete
conversion, not even after 72 h of reaction at room tem-
perature and with application of considerable excess of
Al–Ni alloy (molar ratio Al:Ni:1a = 10:4.6:1). These
results correspond with the known fact that solubility of
used as a simple and rapid method for quantitative analysis
1
of the reaction mixtures. H NMR spectroscopy enables
rapid analysis of molar ratios of the reaction mixture. It is
known that the experimental precision and accuracy of
1
quantitative H NMR are on the order of 0.5%, which
rivals results obtained via modern chromatographic tech-
niques [17, 18].
Al(OH) is very low between pH 4 and pH 9.5 [19]. In
3
Results and discussion
addition, the experiments carried out showed that quan-
titative dehalogenation of 1a was not achieved even in the
NaHCO /Na CO buffer of pH 10.3, in contrast to the
Dehalogenation of 1 in buffered aqueous solutions
3
2
3
ethylenediamine tetraacetic acid (EDTA) buffer, in which,
ceteris paribus, the dehalogenation was always quantita-
tive. However, addition of trisodium ethylenediamine
The course of the dehalogenation reaction using Al–Ni
alloy was investigated using 0.01 M aqueous solutions of
3
3
Table 1 Dehalogenation of 1 mmol XAN dissolved in 100 cm distilled water mixed with 100 cm buffer solution after addition of the given
amount of Al–Ni alloy: 25 °C, 500 rpm, 24 h
Entry
4-Halogenoaniline
Type of buffer used
measured pH)
Amount of Al–Ni alloy
(mg) (mmol of Al)
Conversion to
aniline (%)
(
1
2
4-BAN
4-BAN
4-BAN
4-BAN
4-BAN
4-BAN
4-BAN
4-BAN
NaHSO
None (8.3)
BO /NaH
4
/H
2
SO
4
(1.1)
540 (10)
540 (10)
540 (10)
540 (10)
540 (10)
540 (10)
540 (10)
540 (10)
16.7
2
a
3
H
3
3
2
BO
3
(9.2)
2.4
64
4
NaOH/glycine (9.7)
Na HPO /Na PO (11.3–10.6)
NaH BO /NaHBO (12.5)
(10.3)
b
5
2
4
3
4
100
100
6
2
3
3
c
c
7
NaHCO
NaHCO
3
/Na
/Na
2
CO
CO
3
29.3
d
8
3
2
3
100
?
3
10 mmol Na EDTA (10.1)
9
4-BAN
4-BAN
4-CAN
4-BAN
4-BAN
3-CAN
4-CAN
EDTA (10.9)
EDTA (9.3)
EDTA (9.3)
EDTA (10.9)
EDTA (10.9)
EDTA (10.9)
EDTA (10.9)
270 (5)
100
69.3
73.3
100
56
1
1
1
1
1
1
a
0
1
2
3
4
5
270 (5)
270 (5)
135 (2.5)
67.5 (1.25)
135 (2.5)
135 (2.5)
100
100
The aqueous filtrate of the reaction mixture contained 528 lg (19.56 lmol) Al [by inductively coupled plasma optical emission spectroscopy
ICP-OES)]
(
b
c
d
A significant change of pH value during the dehalogenation reaction was observed
The filtrate of the reaction mixture contained 7.04 mg (0.26 mmol) Al and 0.049 mg (0.835 lmol) Ni
The filtrate of the reaction mixture contained 73 mg (2.7 mmol) Al and 8.58 mg (0.146 mmol) Ni
1
23

Study of dehalogenation of halogenoanilines using Raney Al–Ni alloy
1017
1
00
100
90
80
70
60
50
40
30
9
0
0
0
0
0
0
0
0
0
3-CAN
8
7
6
5
4
3
2
1
4-BAN
4
4
-CAN
-FAN
2
1
0
0
0
0
0
100
200
300
400
500
0
20
40
60
80
100
120
140
160
180
-
3
Reaction time / min
Dissolved Al / mg dm
Fig. 2 Comparison of reactivity of 1 with Al–Ni; reaction conditions:
3
Fig. 1 Dehalogenation of 4-CAN by Al–Ni alloy [270 mg Al–Ni per
5
3
0 cm 0.01 M 1b and 50 cm edetane buffer solution (pH 10.9)]
3
25 °C, 500 rpm; 0.01 M aqueous solution 1 (100 cm ) ? edetane
buffer (pH 10.9, 100 cm ) ? 135 mg Al–Ni
3
tetraacetate (Na EDTA) to the NaHCO /Na CO buffer
3
3
2
3
require 8 h under the same conditions. The experiments
also revealed lower reactivity of 4-fluoroaniline (1d): its
conversion to 2 reached only ca. 70% under comparable
conditions.
resulted in 100% dehalogenation conversion of 1a
Table 1, entries 7, 8). The same result was also achieved
(
in the cases using trisodium citrate (Na citrate) instead of
3
Na EDTA as the additive to the NaHCO /Na CO buffer.
3
3
3
2
This fact could be explained by dissolution of slightly
water-soluble sodium dihydroxy aluminium carbonate,
NaAl(OH) CO , in the presence of a complexing agent
Dehalogenation in dilute NaOH solution
2
3
such as EDTA or citrate [20].
Furthermore, we examined the course of dehalogenation of
1a–d in alkaline medium where the reaction mixture did
not contain a high concentration of salts. The experiments
performed with 0.01 M aqueous solution of 1 alkalized
with NaOH resulted in dehalogenation of 1 even without
any chelating agent added. Dehalogenation of 1 was found
to be finished after 17 h when 2.5 eq. Al (in the form of
Al–Ni) and 12.5 eq. NaOH were used and the reaction was
performed at room temperature under stirring (Table 2,
entries 3, 4, 7, 8).
It seems likely that, in the media of some buffers
3
?
without a chelating agent, poorly soluble Al compounds
are deposited on the surface of Al–Ni alloy, whereby the
course of dehalogenation is markedly affected (Table 1,
entries 3–4, 7).
For these reasons, we studied the dehalogenation of 1
in edetane buffer with pH 10.9 (Table 1, entries 9, 12–15)
in detail. In Fig. 1 the decrease of 1b versus increase of
dissolved Al in the reaction solution is shown.
It is clear that dissolution of ca. 16–17 mg Al caused
complete dehalogenation of 63.78 mg (0.5 mmol) 1b. This
Only this approach ensured that the poorly water-soluble
aluminium hydroxide (which precipitates on the active
surface of the Al–Ni alloy) was transformed into water-
3
?
quantity of dissolved Al is much lower than the quantity of
Al added in the form of Al–Ni alloy (Fig. 1). We observed
soluble Na[Al(OH) ]. When the amount of Al–Ni or NaOH
4
that, in case of application of EDTA buffer (pH 10.9), only
3
2 wt% Al [0.42–0.45 g/dm by inductively coupled plasma
was reduced, dehalogenation conversion never reached
100% (Table 2, entries 2, 5). It was also proved that even
1d was completely defluorinated when using 2.5 eq. Al–Ni
and 12.5 eq. NaOH under the same reaction conditions.
Figure 3 illustrates the dissolution rate of Al from the
different quantities of Al–Ni alloy in the presence of
3
optical emission spectroscopy (ICP-OES)] added in the
3
Al–Ni alloy (2.7 g/dm ) was dissolved even after 17 h. In
the next step, we subsequently performed tests to find the
optimum 1:Al–Ni ratio sufficient for quantitative dehalo-
genation in the EDTA buffer with pH 10.9 (Table 1,
entries 9, 12–15). At molar ratio of Al:Ni:1 = 2.5:1.15:1,
we compared the dehalogenation rates of 1a–d (Fig. 2).
The results illustrate the reactivity differences between
the individual 1. Whereas 3-chloroaniline (1c) is quanti-
tatively dehalogenated after 5 h of reaction, 1a and 1b
3
100 cm 1 wt% NaOH solution. It is clear that complete
dissolution of Al from Al–Ni alloy is accomplished after
ca. 16 h (Fig. 3). This fact explains the complete defluo-
rination of 2 mmol 1d using 270 mg Al–Ni (5 mmol Al).
The nickel contents measured in the filtrates of reaction
3
mixtures were 0.025 ± 0.005 mg/dm Ni.
123

1
018
T. Weidlich et al.
Table 2 Dehalogenation of 1 in
aqueous NaOH solution
(
Entry
Aqueous solution
of XAN (mmol XAN)
Quantity of NaOH (g)
(mmol NaOH)
Quantity of Al–Ni
(mg) (mmol Al)
Conversion to
aniline (%)
3
200 cm ), reaction conditions:
1
7 h stirring at 500 rpm, 25 °C
a
1
0.01 M 4-BAN (2)
0.01 M 4-BAN (2)
0.01 M 4-BAN (2)
0.01 M 3-CAN (2)
0.04 M 3-CAN (8)
0.04 M 3-CAN (8)
0.01 M 4-CAN (2)
0.01 M 4-FAN (2)
2 g (50)
0.6 (15)
1 (25)
270 (10)
270 (5)
270 (5)
270 (5)
810 (15)
810 (15)
270 (5)
270 (5)
0
42
2
3
4
5
6
7
8
100
100
71
1 (25)
1.2 (30)
2.4 (60)
1 (25)
100
100
100
a
Application of Al powder
instead of the Al–Ni alloy
1 (25)
hydrazine, which is commonly used for transfer hydroge-
nation [22], leads to 1b conversion only 6.7% higher than
that achieved with the same amount of Al–Ni alloy without
additional reducing agent (Table 3, entries 2, 5).
3
2
2
1
1
00
50
00
50
00
Application of gaseous H as reducing agent [23] in the
2
2
70 mg Al/Ni
270mg Al/Ni
presence of Raney nickel from spent Al–Ni alloy caused
55 44 00 mm gg AA /l l/ NN ii
only low dechlorination conversion of 1b (Table 3, entry
7). In addition, it was reported earlier [24] that the debro-
mination rate of 4-bromoacetanilide is more than two times
lower compared with the dechlorination rate of 4-chloro-
acetanilide, using Raney nickel and gaseous H as reducing
2
50
agent. It is clear from our study that the dehalogenation rate
of 1a and 1b is practically the same using Al–Ni alloy in
EDTA buffer with pH 10.9. Although the dechlorination
reaction mechanism is not totally clarified yet, from the
above-mentioned informations it can be proposed that Al
plays the active role during the dehalogenation. This means
that, in basic aqueous solution, activated aluminium metal
of the Raney Al–Ni alloy directly reduces halogenoaniline
and, in addition, the hydrogen produced during dissolution
of Al and activated on highly porous nickel metal on the
catalyst’s surface takes part in the dehalogenation reaction.
From the findings presented it is presumed that the de-
halogenation process can be expressed by the summary
equation given in Scheme 1.
0
0
200
400
600
800
1000
Reaction time / min
Fig. 3 Content of dissolved Al in 1 wt% aqueous NaOH solution
during the reaction of Al–Ni alloy at room temperature
Spent nickel catalyst was isolated by filtration from the
reaction mixture and could be recovered using for example
a hydrometallurgical process such as leaching with H SO4
2
[
21].
If the described method is combined with subsequent
neutralization and filtration of precipitated hydroxides, then
there occurs no significant contamination of water at the
outlet from the process of dehalogenation with metal ions
3
content of Al less than 0.05 mg/dm and Ni less than
(
3
.01 mg/dm .
0
Experimental
In the presence of aluminium powder alone, dehalo-
genation of 1a or 1b did not occur (Tables 2, 3). However,
when aluminium or zinc dust was employed in the presence
of a low quantity of Al–Ni alloy, different results were
obtained. Application of Zn dust in the presence of a small
amount of Al–Ni alloy leads to dehalogenation with 59%
conversion (for comparison: the same amount of Al–Ni
alloy without additional reducing agent leads to dehalo-
genation of 42.2% 1b) (Table 3, entries 2–4).
The experiments were carried out using an electromagnetic
stirrer equipped with a StarFish attachment (Radleys Dis-
covery Technologies, UK), which enables parallel
performance of reactions under the same reaction condi-
tions, with temperature control by means of a contact
thermometer. All operations were carried out in air at
25 °C. Distilled water was used for preparation of aqueous
solutions. Each of the experiments described was repeated
at least twice. Compounds 1a–d and 2, Al–Ni alloy (50%
Al ? 50% Ni, Raney type, powder), the chemicals used for
Under the same reaction conditions and with the use of
Al dust, the dehalogenation reaction conversion reaches
1
00%. Replacement of Al as the hydrogen source by
preparation of buffers, and CDCl were purchased from
3
1
23

Study of dehalogenation of halogenoanilines using Raney Al–Ni alloy
1019
Table 3 Dechlorination of 1b
Entry
Reducing agent
Quantity of NaOH
g) (mmol NaOH)
Conversion of
4-CAN (%)
with various alloys and metals
after 17 h of vigorous stirring at
room temperature
(
1
2
3
270 mg Al (10 mmol of Al)
110 mg Al–Ni (2 mmol Al)
2 (50)
2 (50)
2 (50)
0
42.2
100
110 mg Al–Ni (2 mmol Al)
? 135 mg Al (5 mmol)
3
NaOH dissolved in 20 cm
water was added dropwise to
4
5
6
110 mg Al–Ni (2 mmol Al)
2 (50)
2 (50)
59
3
00 cm 0.01 M aqueous
?
330 mg Zn powder (5 mmol)
110 mg Al–Ni (2 mmol Al)
100 mmol N
270 mg Al–Ni (5 mmol Al)
2
solution of 1b within 1 h
48.9
a
?
2 4
H
Raney Ni obtained by
decantation after
1 (25)
100
11
dehalogenation procedure
(
a
7
Raney Ni ? H
2
(balloon)
No base was used
entry 6)
Scheme 1
NH2
NH2
Ni
+ 2 Na[Al(OH) ] + 3 NaX
4
3
+ 2 Al + 3 H O + 5 NaOH
2
3
X
1
1
a X = 4-Br
c X = 3-Cl
1b X = 4-Cl
1d X = 4-F
commercial suppliers (Sigma-Aldrich or Across) at purity
of at least 97% and used without further purification.
Table 4 Working conditions for inductively coupled plasma optical
emission spectrometry (ICP-OES) analysis
1
H NMR spectra of all products were recorded using a
Parameter
Value
Bruker AMX 360 spectrometer at 25 °C at 360.14 MHz.
Chemical shifts are given in parts per million (ppm) on the
delta scale (d). The reaction mixture was analysed by
Power
1,100 W
Observation height
Working gas
Plasma gas
6.5 mm
3
Argon 99.999%
3
0.6 dm /min
3
11 dm /min
3
0.65 dm /min
3
1.5 cm /min
extraction of 20 cm decanted reaction mixture with
3
3
1
9 1 cm and 2 9 0.5 cm CDCl , and the joined CDCl
3 3
1
Auxiliary gas
Nebulizer gas
Pump speed
extracts were analysed by means of H NMR spectroscopy.
Besides that, residues of Al–Ni alloy separated by decan-
tation were also extracted with CDCl , and the extracts
3
Photomultiplier voltage
k nickel
600 V
were analysed in the same way, but no difference between
the compositions of these two extracts was observed. Gas
chromatography–mass spectrometry (GC–MS) analyses
were performed using a GC–MS Shimadzu GCMS QP
231.604 nm
167.081 nm
Fixed
k aluminium
Background correction
Replicates
2
010 instrument equipped with a DB-XLB capillary col-
5
umn (30 m 9 0.25 mm, 0.25 lm) operating at ionization
energy of 70 eV [25].
3
1
The H NMR spectroscopy was sufficient for this study,
Al and Ni, both containing 1 g/dm (SCP, Baie D’Urf e´ ,
Canada), were used. Limits of detection (three times
standard deviation in place of background correction) were
because the concentrations of the target compounds were
high enough. In addition, the reaction systems were free of
by-products. In addition, the complete dehalogenations of 1
were verified using the GC–MS method and AOX analysis.
Elemental analysis of aluminium and nickel in filtered
samples of reaction mixtures was carried out with a
sequential, radially viewed inductively coupled plasma
3
3
5
lg/dm for Ni and 30 lg/dm for Al.
AOX (adsorbable organically bound halogens) analyses
were performed according to European ISO 9562 standard.
The stock solutions of halogenated anilines were pre-
pared at room temperature by dissolving the corresponding
amount of halogenoaniline in distilled water using over-
night stirring.
(
(
ICP) atomic emission spectrometer INTEGRA XL 2
GBC, Dandenong Australia), equipped with a ceramic V-
groove nebulizer and a glass cyclonic spray chamber (both
Glass Expansion, Australia). Working conditions are
Preparation of buffer solutions
summarised in Table 4. For instrumental calibration (Al
3
00–50–10–5–1 mg/dm and Ni 1–0.5–0.1–0.05–0.01 mg/
Buffer solutions were prepared by mixing equal volumes of
the following aqueous solutions (measured pH): NaOH/
1
3
dm ), commercially available stock standard solutions of
123

1
020
T. Weidlich et al.
glycine buffer solution (pH 9.7): 1 M NaOH ? 1 M
glycine; EDTA buffer solution (pH 10.9): 1.7 M
NaOH ? 1 M ethylenediamine tetraacetic acid trisodium
Acknowledgments We are grateful to the Grant Agency of the
Czech Republic (203/07/P248) and Ministry of Education, Youth and
Sports of the Czech Republic MSM 0021627502 for financial support.
salt dihydrate (Na EDTA); solution of EDTA buffer (pH
3
9
.3): 1.5 M NaOH and 1 M Na EDTA; Na CO /NaHCO
3 2 3 3
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[
and the powder of Al–Ni alloy (0.135 g, 2.5 mmol of Al)
was added. The reaction mixture was stirred at 500 rpm at
6
1:208
17. Maniara G, Rajamoorthi K, Rajan S, Stockton GW (1998) Anal
Chem 70:4921
18. R ´ı os SM, Barqu ´ı n CM, Nudelman CN (2009) Environ Chem Lett.
doi:10.1007/s10311-009-0210-5
1
2
2
2
5 °C for 17 hours, filtered, and the filtrates were extracted
3
with three portions of CDCl3 (1 9 1 cm
and
3
9 0.5 cm ). H NMR and GC–MS spectra of this CDCl
1
2
3
9. Anderson E, Hansson H (2005) http://www.chemeng.lth.se/
exjobb/011.pdf
0. Gannelin CR, Triggle DJ (1997) Dictionary of pharmacological
agents 1-2. Chapman and Hall, London, p 663
1. Lee JY, Rao SV, Kumar BN, Kang DJ, Reddy BR (2010) J
Hazard Mater 176:1122
extract indicated the conversion of 1 to aniline (identified
using 2 as internal standard) [26, 27].
According to AOX analysis, the starting 0.01 M aque-
3
ous solution of 4-CAN contained 350–360 mg Cl/dm of
AOX. Obtained filtrates from the dehalogenation procedure
3
using Al–Ni/NaOH contained less than 1 mg Cl/dm of
22. Batcho AD, Leimgruber W (1990) Org Synth Coll Vol 7:34
2
3. Aureggi V, Franckevicius V, Kitching MO, Ley SV, Longbottom
DA, Oelke AJ, Sedelmeier G (2008) Org Synth 85:72
4. de Koning AJ (1975) Org Prep Proc Int 7:31
5. Agueera A, Almansa E, Tejedor A, Fenrandez-Alba AR, Malato
S, Maldonado MI (2000) Environ Sci Technol 34:1563
6. Uray G, Wolfbeis OS (1981) Monatsh Chem 112:627
AOX.
2
2
These filtrates were adjusted to pH 7 using 20 wt%
aqueous solution of HCl, and the insoluble part was filtered
3
off. The filtrate contained less than 0.05 mg/dm of Al and
2
3
less than 0.01 mg/dm of Ni.
27. Jazwinski J (2005) J Mol Struct 750:7
1
23