Hydrodebromination of 2,4,6-tribromophenol in aqueous solution using Devarda's alloy

Article abstract of DOI:10.1007/s00706-012-0870-x

The effectiveness of application of aluminium and its alloys and mixtures with copper was studied for complete hydrodebromination of 2,4,6-tribromophenol to phenol in aqueous NaOH solution at room temperature. Dissolved metals were removed using precipita

Full text of DOI:10.1007/s00706-012-0870-x

Monatsh Chem (2013) 144:155–162
DOI 10.1007/s00706-012-0870-x
ORIGINAL PAPER
Hydrodebromination of 2,4,6-tribromophenol in aqueous solution
using Devarda’s alloy
•
Tomas Weidlich Anna Krejcova Lubomır Prokes
•
´ˇ
ˇ
´
´
ˇ
Received: 11 June 2012 / Accepted: 1 October 2012 / Published online: 13 November 2012
Ó Springer-Verlag Wien 2012
Abstract The effectiveness of application of aluminium
and its alloys and mixtures with copper was studied for
complete hydrodebromination of 2,4,6-tribromophenol to
phenol in aqueous NaOH solution at room temperature.
Dissolved metals were removed using precipitation and
subsequent filtration.
Viable elimination of 1 wastes in spent products as well as
in waste sludge may well be the most serious current
problem related to 1. It is also known that thermal degra-
dation of tetrabromobisphenol A (commonly used as a fire
retardant for epoxy resins) produces significant amounts of
brominated phenols [2].
In 1998, the Environmental Protection Agency (EPA,
USA) incorporated 1 into the list of hazardous wastes [3].
Since then, there has been increasing concern worldwide
about its potential toxicity and endocrine-disrupting
potency [4]. It is known that 1 interacts with thyroid hor-
mone-binding transport proteins [5, 6]. Additionally, 1
seems to have neurotoxic properties [4, 7, 8].
Keywords Aluminium Á Al-alloy Á Metals Á
NMR spectroscopy
Introduction
2,4,6-Tribromophenol (1) is the most widely produced
brominated phenol. The production volume of 1 has been
estimated at approximately 2,500 tons/year in Japan and
9,500 tons/year worldwide in 2001 [1].
Recently, some methodology developments have been
reported for elimination of 1. There has been great interest
in use of oxidation methods induced by photocatalysis [9,
10] and Fenton treatment [11, 12] for degradation and
mineralisation of 1. Another cost-effective approach for
treatment of halogenated organic compounds is reductive
dehalogenation using zero-valent metals (ZVMs). Espe-
cially Al, Mg, Fe and Zn are the safest and/or least toxic
ZVMs applicable as reductants [13–17].
2,4,6-Tribromophenol is mainly used as an intermediate
of flame retardants [tribromophenyl allyl ether, 1,2-
bis(2,4,6-tribromophenoxy)ethane, and as end-stop for
brominated epoxy resins made from tetrabromobisphe-
nol A] in the electronics manufacturing industry, being
applied in production lines of electronic devices such as
televisions, computers, and other household items. It is also
used as a wood-preservative biocide to prevent wood stain
and decay, substituting sodium pentachlorophenolate [1].
Aluminium was described as an effective reductant for
dehalogenation of aliphatic halogenoderivatives [13]. More
reactive forms of Al such as Rieke Al could be used for
dehalogenation of haloarenes in non-polar solvents in the
presence of anhydrous AlCl3 [18]. Increased reactivity was
observed using aluminium alloyed or coated with Ni or
other metals as hydrogenation catalysts for dehalogenation
of halogen aromatics dissolved in organic solvents or
aqueous solution, usually at elevated temperature [19–24].
A common drawback of methods using metal reagents
and/or catalysts lies in contamination of the reaction
medium with the respective metals. Heavy metals (nickel,
copper etc.) are considered to be toxic [25]; therefore, if
ˇ
´
T. Weidlich (&) Á A. Krejcova
Faculty of Chemical Technology, Institute of Environmental
and Chemical Engineering, University of Pardubice,
Pardubice, Czech Republic
e-mail: tomas.weidlich@upce.cz
ˇ
L. Prokes
Department of Chemistry, Faculty of Science,
Masaryk University, Brno, Czech Republic
123

156
T. Weidlich et al.
they are used, it is necessary to secure—as efficiently as
possible—their removal from wastewater streams leaving
the reduction process. Nevertheless, there are many appli-
cable methods useful for minimisation of metal content in
the aqueous solution, e.g. coagulation and hydroxide- or
sulphide-induced precipitation [26, 27].
(270 mg mmol-1 of 1) at 25 °C, most of Al added was
dissolved in the reaction mixture. However, the HDB
reaction was found to be very slow, with only partial de-
halogenation of 1 taking place; 2,6-dibromophenol (2) and
2,4-dibromophenol (3) were the products detected in the
reaction mixture (Table 1, run 1). Using Duralumin alloy,
1 was debrominated to give a mixture of 2 (15.1 %) and
2-bromophenol (4, 75.6 mol %) together with phenol (6) as
the minor product (run 2).
Devarda’s alloy (Dev. alloy) is a well-known reducing
agent for nitrite and nitrate analysis [28]. However, to the
best of our knowledge only one paper describes Dev. alloy
as a dehalogenation agent [29] (Dev. alloy was used as a
reducing agent for determination of nitrogen and halogens
in organic substances at temperatures of 600–650 °C).
The objective of this study is to investigate the feasi-
bility of zero-valent aluminium and its alloys or mixtures
with copper for hydrodebromination (HDB) of recalcitrant
1 dissolved in alkaline aqueous solution at ambient tem-
perature. The by-product distribution and total mass
balance in reduction of 1 are investigated, and the HDB
rates by Al-based alloys and amended Al are also deter-
mined in this study. Removal of metals from the reaction
mixture using precipitation and subsequent filtration of
insoluble metal hydroxides was tested.
When powdered Fe3Al alloy was used, only 0.8 % of 3
was found in the reaction mixture, together with 99.2 % of
unreacted 1 (run 3). Brass was found to be a completely
ineffective HDB agent for 1 (run 4). However, with Dev.
alloy, 1 was debrominated quantitatively to give 6 (run 5).
When using Zn powder, 1 was debrominated quantita-
tively to give a mixture of 2, 3, and 4 (run 6). It was observed
that Zn powder turns white during the reaction but never
dissolves [as Na2Zn(OH)4] in the reaction mixture, probably
due to the low concentration of NaOH solution used. In case
of application of Fe or Mg powder, most of the starting 1
remained unreacted (runs 7, 8). These results correspond
with the known fact that Fe is stable in alkaline aqueous
solution and Mg is covered with an insoluble Mg(OH)2 layer
(see low content of Mg2? dissolved in the reaction mixture;
Table 1, run 7, footnote e).
Results and discussion
The above-mentioned results indicate that application of
an Al-based alloy with high Cu content, such as Devarda’s
alloy, is highly effective for quantitative HDB of 1 to 6.
Effect of the nature of alloys and ZVMs
The behaviour of different alloys and ZVMs in the HDB
of 1 (Scheme 1) was studied using powdered Duralumin
(Al–Cu–Mg–Mn), Devarda’s alloy (Al–Cu–Zn), Fe3Al
alloys, brass (Cu–Zn) and Al, Fe, Mg and Zn powders
under alkaline conditions at room temperature in 10-fold
molar excess of ZVMs (Table 1). As described above,
application of powdered Raney Al-based alloy is highly
effective for dehalogenation of halogenated anilines in
dilute aqueous NaOH solution [33, 34]. Structural identi-
fication of the by-products 2–5 and phenol (6) as the final
product of HDB was performed by comparison with
commercially available standards.
Effect of used base
The effect of different bases on the HDB of 1 using
Devarda’s alloy in aqueous solutions was investigated
(Table 2). It is noteworthy that the use of Dev. alloy in
NaOH, KOH, and NH4OH led to a reducing agent strong
enough for complete debromination of 1 (Table 2,
runs 7–9). In the case of using Na3PO4 or Na2CO3, a
mixture of 2, 3, 4, and 6 was obtained. The dissolution of
Al from Al–Ni was found to be slow with sodium car-
bonate or sodium acetate used as the bases (runs 3–5).
HDB was found to be slow with Na3PO4. With
CH3COONa and with Na2CO3, HDB hardly occurred at all
After overnight stirring of 1 (1 mmol) dissolved in
1.6 wt % aqueous NaOH solution with Al powder
Scheme 1
OH
OH
Br
Br
+ Al + NaOH + H2O
Z
X
metal
r.t.
+ NaAl(OH)4 + NaBr
Br
Y
1
2
: X = Z = Br, Y = H
metal = Cu, Fe, Zn
3: X = Y= Br, Z = H
4: X = Br, Y= Z = H
5: X = Z = H, Y = Br
123

Hydrodebromination of 2,4,6-tribromophenol in aqueous solution using Devarda’s alloy
157
Table 1 Effect of used ZVMs and alloys
Run
NaOH/eq.
Reductant
(eq. of Al)
Compound ratio/mol %a
1
2
3
4
6
1
2
60
60
60
60
60
60
60
60
60
60
Al powder (20)
Duraluminb (20)
81
0
14
15
0
5
0
1
0
0
0
0
9
76
3
Fe3Al (20)
Cu–Zn alloyc (30 of Zn)
99
0
0
4
100
0
0
0
0
5
Dev. alloy (20)
0
0
100
0
6
Zn powder (30 of Zn)
Mg powder (30 of Mg)
Fe powder (30 of Fe)
Dev. alloy (8) ? Al powder (20)
Dev. alloy (4) ? Al powder (20)
0
63
0
20
0
17
1e
7
99d
100
0
0
8
0
0
0
0
9
5
0
56 (6e)
60 (13e)
33
8
10
1
14
4
1 (0.33 g, 1 mmol) in 150 cm3 water, room temperature, reaction time 16 h, agitation 500 rpm
a
1H NMR ratio
b
Duralumin is AA2024, which contains 4.4 % copper, 1.5 % magnesium, 0.6 % manganese, and 93.5 % aluminium by weight
Contains 70 wt % Cu and 30 wt % Zn
Filtered reaction mixture contains 0.053 mg dm-3 of dissolved Mg
c
d
e
Formation of 4-bromophenol 5
Table 2 Hydrodebromination of 1 using Dev. alloy, effect of used base
Exp.
No.
Base/eq.
Compound ratio/mol %b
Content of dissolved Al/mg dm-3
1
2
3
4
5
6
1
2
3
4
5
6
NaOH (30)
0
0
0
0
0
0
8
5
0
0
0
0
0
0
0
0
0
0
0
0
100
100
100
0
2,616 (703.4 Zn; 0.4 Cu)
2,671 (282 Zn; 0.5 Cu)
722 (188 Zn; 493.9 Cu)
240 (0.1 Zn; 0.05 Cu)
2,142 (134 Zn; 18 Cu)
2 (45 Zn 0.77 Cu)
KOH (30)
NH4OH (30)
Na2CO3 (50)
Na3PO4 (30)
CH3COONa (50)
80
0
12
2
73
0
12
1
8
99
0
0
1 (0.33 g, 1 mmol) in 100 cm3 aqueous solution of mentioned base and 25 eq. Al in the form of Devarda’s alloy, room temperature, reaction time
16 h, agitation 500 rpm
a
1H NMR ratio
(runs 4 and 6). The basicity of 1 M aqueous CH3COONa
solution is too low for effective dissolution of Al under the
used reaction conditions. It appears crucial in the debro-
mination protocol to have an alkali metal (sodium or
potassium) or ammonium hydroxide as a base. These alkali
metal hydroxides are thought to play a dual role: they cause
deprotonation of 1 and enable dissolution of 1 in aqueous
solution and influence the reducing ability of the Dev.
alloys.
HDB was found to be completed even when 10 equiv-
alents of Al in the form of Dev. alloy (600 mg mmol-1 of
1) and 18 equivalents of NaOH (720 mg mmol-1 of 1)
were used and the reaction was performed at room tem-
perature during 16 h of vigorous stirring (Table 3). Higher
excess of NaOH causes faster decomposition of Dev. alloy;
in this case equimolar quantity of 5 and 6 was found in the
resulting reaction mixture (entry 8). When the amount of
Dev. alloy was reduced (e.g. to 8 eq.), 19.4 mol % of 5
remained in the reaction mixture even after 16 h. Similarly,
when the molar ratio of NaOH to Dev. alloy was decreased
to 1:1, the HDB became sluggish and some 5 remained in
the reaction mixture (entries 9–11). Without addition of
Dev. alloy no reaction of 1 was observed in the NaOH
solution (entry 12). It was verified that HDB of 3 using
Effect of the amount of used alloy and NaOH
The effect of the amount of reactants (Dev. alloy and
NaOH) for quantitative HDB was determined in a series of
experiments (Table 3).
123

158
T. Weidlich et al.
Table 3 Hydrodebromination of 1 using Dev. alloy
Entry NaOH/eq. Dev. alloy eq. of Al (weight of Dev. alloy) Compound ratio/mol %a
Content of dissolved metals/mg dm-3
1
2
3
4
5
6
1
400
55
45
45
100
18
20
30
10
18
5
40 (9.6 g)
50 (15 g)
40 (9.6 g)
25 (7.5 g)
30 (9 g)
10 (3 g)
13.5 (1.2 g)
10 (3 g)
10 (3 g)
8 (2.4 g)
5 (1.5 g)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0
3
0
0
0
0
0
0
5
100
100
100
100
100
100
95
4,437 Al ? 0.1 Cu ? 1.1 Zn
4,864 Al ? 2.1 Cu ? 21.5 Zn
4,449 Al ? 1.0 Cu ? 26.6 Zn
4,769 Al ? 0.6 Cu ? 20.2 Zn
n.d.
2
3
4
5
6
7b
n.d.
3,758 Al ? 3.7 Cu ? 5.1 Zn
2,891 Al ? 1.3 Cu ? 15.3 Zn
563.7 Al ? 0.1 Cu ? 1.7 Zn
2,189 Al ? 1.6 Zn ? 0.1 Cu
217.4 Al ? \0.1 Cu ? 0.1 Zn
n.d.
8
50
47
19
57
0
50
9
53
10
11
12
13c
81
31
20
100
0
0
7.5
3.33 (1 g)
62
35
n.d.
1 (5 mmol, 1.65 g) in 200 cm3 water, room temperature, reaction time 16 h, agitation 500 rpm
a
1H NMR ratio
b
1 (1.5 mmol) in 200 cm3 water, room temperature, reaction time 16 h, agitation 500 rpm
c
HDB of 3
Devarda’s alloy (200 mg mmol-1 of 3) led to a mixture of
5, 6, and only traces of 4 (Table 3, entry 13). This means
100
90
that HDB of ortho-bromine in 3 is preferred under the used
conditions.
80
The reaction profile under conditions when using
25 mM of 1 solution in 1.6 wt % aqueous NaOH (16 eq.)
and Dev. alloy (650 mg mmol-1, 4 eq. of Al) at room
temperature is illustrated in Fig. 1. HDB was completed
after 2 h at room temperature under these conditions.
70
60
50
40
30
20
10
0
phenol
2-bromophenol
2,4-dibromophenol
2,6-dibromophenol
2,4,6-tribromophenol
4-bromophenol
Effect of Cu recycling
To evaluate the long-term activity of Cu obtained in the
finely powdered form from the used alloys, Cu slurry was
used in HDB reactions of 1 in multiple cycles. Each
subsequent HDB cycle was performed in the same reac-
tion bottle with the remaining metal slurry. At the end of
each cycle, the reaction mixture was decanted and the
bottle with the remaining metal slurry was refilled with a
fresh 1 and NaOH solution at 24-h intervals. As can be
seen from Table 4, freshly prepared Cu slurry could not
be applicable as a catalyst for exhaustive HDB of 1 to
phenol using Al powder as a reductant (10 mmol of Al
for 1 mmol of 1).
0
20
40
60
80
100
120
Reaction time/min
Fig. 1 Illustration of the reaction profile of 1 debromination [25 mM
solution in 1.8 wt % aq. NaOH (18 eq.) using Devarda’s alloy (10 eq.
of Al)]
Reaction mechanism
Three mechanisms were proposed for the hydrodehalogen-
ation (HDH) of halogenated aromatics using ZVMs and metal-
coated ZVMs [16, 23, 35]. One is direct reduction at the metal
surface, another is hydrogenation at the hydrogenation catalyst
surface and the third is adsorption of halogenated aromatic
compound at metal surface followed by hydrogenation at the
noble metal/electropositive metal surface [16, 23, 35].
In the first and second recycling step, 1 was converted to
a mixture of 2–5 and 6 as a minor product. In the additional
three recycling steps, HDB of 1 hardly occurred at all and
around 10 % of unreacted 1 remained in the reaction
mixture together with 2, 3, 4 and 5, practically no phenol
was formed.
123

Hydrodebromination of 2,4,6-tribromophenol in aqueous solution using Devarda’s alloy
159
Table 4 Effect of recycled Dev. alloy and Cu(NO3)2 on HDB of 1 using Al as reductant
Run
NaOH /eq.
Source of Cu and A /eq.
Compound ratio/mol %a
Dissolved
Al/mg dm-3
1
2
3
4
5
6
1b,c
2b
3b
4b
5b
6b
7b
8b
9d
18
18
18
60
60
60
60
60
60
60
60
180
Dev. alloy (10)
0
0
0
0
0
0
4
100
0
1,892
827
Spent Dev. alloy from run 1
Spent Dev. alloy from run 2 ? Al (6)
Spent Dev. alloy from run 3 ? Al (6)
Spent Dev. alloy from run 4 ? Al (6)
Spent Dev. alloy from run 5 ? Al (6)
Spent Dev. alloy from run 6 ? Al (6)
Al (6)
46
10
38
46
43
48
16
38
54
0
22
4
28
66
27
8
0
16
6
0
0
0
0
0
0
0
0
4
3,974
3,949
3,774
3,680
3,609
3,709
n.d.
0
29
30
29
32
9
0
16
15
8
0
13
12
1
0
0
74
0
0
Cu(NO3)2 (10) ? Al (50)
42
18
0
20
28
0
0
10d
11d
12d
a 1
Cu(NO3)2 (10) ? Zn (50)
0
0
n.d.
Cu(NO3)2 (10) ? Mg (50)
Cu(NO3)2 (10) ? Mg (50)
100
100
0
n.d.
0
0
0
0
n.d.
H NMR ratio
1 (0.825 g, 2.5 mmol) in 100 cm3 water, room temperature, reaction time 16 h, agitation 500 rpm
b
c
d
Reaction time 3 h
1 (1 mmol, 0.33 g) in 100 cm3 water, room temperature, reaction time 16 h, agitation 500 rpm
According to our experiments, Duralumin (Al–Cu–Mg–
Scheme 2 shows that the HDB of 1 by Al-based alloy
occurs stepwise, with the three bromine atoms on the
molecule 1 being sequentially substituted by hydrogen to
form the final phenol.
Mn alloy with low content of Cu) and Al powder are much
more effective HDB agents for 1 than brass (Cu–Zn alloy)
(Table 3). The poor performance of Al alone is a conse-
quence of the rapid formation of soluble NaAl(OH)4 salt
and effervescence of hydrogen gas. In the case of Dev.
alloy with high Al and Cu content and only a negligible
amount of Zn, the HDB of 1 works well.
Scheme 2 shows the possible pathways proposed for
debromination of 1 by Dev. alloy. The pathway is proposed
according to the products identified in the reaction system.
The first step of the proposed pathway is the formation of 2
and 3 after removal of either an ortho or para bromine
atom. Based on the nearly even distribution of the products
2 and 3 in the reaction system, the chances for substitution
of bromine at ortho and para positions in 1 are likely equal,
with the para-bromine being slightly preferred to be
transformed. 4 is formed by the next step of HDB of 2. 3 is
further debrominated to form the major daughter product 5
via preferred elimination of the ortho-bromine and minor 4
via substitution of the para-bromine. 4 and 5 are further
debrominated to form 6.
Regarding the above-mentioned information, the effect
of the Cu dose added to the reaction mixture in the form
of Dev. alloy was studied by investigating the HDB of 1
using a combination of Dev. alloy and Al powder. The
amount of alloy was gradually diminished and 10 eq. of
Al metal and 20 eq. of NaOH as 0.8 wt % aq. solution
were used (Table 1, runs 9, 10). It was found that HDB
was never completed under these conditions. Similarly,
when using co-action of Cu slurry from spent Dev. alloy
and Al powder, HDB was found to be incomplete in all
cases.
These facts indicate that mainly the content of Al and
Cu coupled together in an alloy enables effective dehalo-
genation of 1. Similarly, as we demonstrated (Table 4,
entries 9–12), the alloying of Al with Cu significantly
enhanced the conversion of 1 to dibromophenols 2 and 3
and bromophenols 4, 5 (compared with Al powder). Con-
sulting the reported bimetallic HDH mechanism [16, 23,
36, 37], HDB on Devarda’s alloy is proposed as direct
reduction at the Al–Cu surface of Dev. alloy. At the
metallic Al–Cu surface, the electrons provided by Al could
attack 1 to form less brominated phenols.
Treatment of aqueous filtrate
As we have demonstrated, if the above-mentioned HDB is
combined with separation of copper slurry (Cu is stable in
the alkaline reaction mixture) by decantation, subsequent
filtration at pH value 9.2 0.25 (separation of zinc
hydroxide), additional neutralisation of the obtained filtrate
to pH 6.7 0.25 and a second filtration step [separation of
Al(OH)3], then no significant contamination of the aqueous
filtrate with metals occurs (content of Al less than
0.05 mg dm-3, Zn less than 0.07 mg dm-3 and Cu less
123

160
T. Weidlich et al.
Scheme 2
OH
OH
Br
Br
Br
Br
+ Al-M
- Br-
OH
+ Al-M
OH
- Br-
Br
Br
- Br-
+ Al-M + OH-
2
+ Al-M
4
-Br-
OH
OH
- Br-
+ Al-M
- Br-
Br
1
+ Al-M
- Br-
6
Br
5
Br
3
than 0.01 mg dm-3). Alternatively, dissolved or dispersed
metals could be removed using a precipitation agent such
as TMT-15 (commercially available 15 wt % aqueous
solution of 1,3,5-trimercapto-s-triazine trisodium salt)
which enables better removal of metals (less than
0.01 mg dm-3 of Al, Cu and Zn).
Hydrodebromination of 1
The reaction was carried out in a 250-cm3 round-bottomed
flask equipped with a magnetic stirrer. The reaction
mixture was prepared by dissolution of an appropriate
amount of 1 in aqueous NaOH solution (100 or 150 cm3),
and possible additive was added (Tables 1–4). Powdered
reduction agent (quantities mentioned in Tables 1–4) was
added in one portion to the reaction mixture under stirring,
and the flask outlet was fitted to a glass tube filled with
granulated charcoal. The reaction mixture was stirred at
500 rpm at temperature of 25 °C for 16 h and filtered. A
25-cm3 aliquot of the filtrate was acidified to pH 2
using 16 wt % H2SO4 and extracted with three portions
The formed powdered copper can simply be collected by
filtration and recovered by a hydrometallurgical process.
For the dissolution of spent Cu from Devarda’s alloy, some
strong acid with oxidising properties (typically HNO3) is
necessary [38]. Cu(NO3)2 was obtained by this method.
Nevertheless, this procedure is accompanied by production
of noxious NOx fumes.
of CDCl3 (1 9 0.5 and 2 9 0.5 cm3). The H NMR and
1
However, in the case of using in situ-generated Cu
particles from aqueous Cu(NO3)2 by the action of Al or Zn
powder (cementation process), the HDB of 1 was never
completed. The activity of ZVMs with addition of
Cu(NO3)2 for HDB of 1 is summarised in Table 4. None-
theless, copper salts are in great demand in the metallurgy
and chemical industry (for preparation of hydrogenation
catalysts), where experience with recycling of copper
wastes has been gathered.
GC–MS spectra of this CDCl3 extract indicate conversion
of 1 to 6 [30, 31].
The above-mentioned aqueous filtrate of the reaction
mixture (solution 1) after HDB using Al–Cu–Zn typically
contains more than 2,000 mg dm-3 Al, more than
10 mg dm-3 Zn and more than 1 mg dm-3 Cu, according
to ICP-OES analysis. Solution 1 was maintained at pH
9–9.3 using 24 wt % aqueous solution of H2SO4, and the
insoluble part was filtered off; the obtained filtrate was
acidified at pH 6.7–7.0 using a 24 wt % aqueous solution
of H2SO4 and filtered. The filtrate contained less than
0.1 mg dm-3 of Al, less than 0.07 mg dm-3 of Zn and less
than 0.01 mg dm-3 of Cu.
Experimental
Al (powder, 200 mesh), Zn (powder, -100 mesh), Mg
(powder, -325 mesh), Cu–Zn (70 % Cu ? 30 % Zn,
powder, -60 mesh), Devarda’s alloy (45 % Al ? 50 %
Cu ? 5 % Zn, -100 mesh), Fe3Al (powder, -270 mesh),
2,4,6-tribromophenol, 2,6- and 2,4-dibromophenol, 2- and
4-bromophenol, precipitation agent TMT-15 (15 wt %
aqueous solution of 1,3,5-trimercapto-s-triazine trisodium
salt) and all organic solvents and inorganic salts used were
purchased from commercial suppliers (Sigma-Aldrich,
Alfa Aesar, Degussa, Germany) with purity of at least
98 % and used without further purification. All operations
were carried out in air at 25 °C. Distilled water was used
for preparation of aqueous solutions.
Alternatively, dissolved or dispersed metals could be
removed using a precipitation agent such as TMT-15
(20 cm3 of 15 wt % aqueous solution of 1,3,5-trimercapto-
s-triazine trisodium salt per 1 dm3 of solution 1, pH
adjustment of the reaction mixture to pH 9.5 0.5 and
after 30 min stirring interval the subsequent acidification of
the mixture to pH 6.5–7), which enables better removal of
metals (less than 0.01 mg dm-3 of Cu, Zn, less than
0.1 mg dm-3 of Al).
GC–MS analyses were performed on a GC–MS Shima-
dzu GCMS QP 2010 instrument equipped with the DB-
XLB capillary column (30 m 9 0.25 mm, 0.25 lm),
123

Hydrodebromination of 2,4,6-tribromophenol in aqueous solution using Devarda’s alloy
161
operating at ionisation energy of 70 eV [32]. The 1H NMR
spectroscopy of the CDCl3 extract from the reaction
mixture was used for rapid determination of the HDB
reaction. The 1H and 13C NMR spectra were recorded on a
Bruker DRX 500 spectrometer.
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The experiments were carried out in a batch system using
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Acknowledgments This work was sponsored by the Technology
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