Degradation of the antibacterial agents triclosan and chlorophene using hydrodechlorination by Al-based alloys

Article abstract of DOI:10.1007/s00706-018-2230-y

Abstract: Triclosan and chlorophene are chlorinated phenols used as antimicrobial agents. Both compounds are ordinarily detected in aquatic environments. The aim of this study is to prove the reactivity of three different metallic alloys used as common re

Full text of DOI:10.1007/s00706-018-2230-y

Monatshefte für Chemie - Chemical Monthly
https://doi.org/10.1007/s00706-018-2230-y(0123456789(). -, vo Vl
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ORIGINAL PAPER
Degradation of the antibacterial agents triclosan and chlorophene
using hydrodechlorination by Al-based alloys
1
1
1
•
•
´
´
´ ˇ
Jan Perko Barbora Kamenicka Tomas Weidlich
Received: 19 March 2018 / Accepted: 13 May 2018
Ó Springer-Verlag GmbH Austria, part of Springer Nature 2018
Abstract
Triclosan and chlorophene are chlorinated phenols used as antimicrobial agents. Both compounds are ordinarily detected in
aquatic environments. The aim of this study is to prove the reactivity of three different metallic alloys used as common
reductants such as Raney Al–Ni (50% Al–50% Ni), Devarda’s Al–Cu–Zn alloy (45% Al–50% Cu–5% Zn), and Arnd’s Cu–
Mg alloy (60% Cu–40% Mg) for the hydrodechlorination of these agents in alkaline aqueous solution at ambient tem-
perature and investigating such parameters as type and amount of reagents. The hydrodechlorination of triclosan was found
to be completed when 5 molar equivalents of Al in the form of Raney Al–Ni alloy (0.27 g) and 20 equivalents of NaOH
(0.8 g) per 1 mmol of triclosan were used and the reaction was performed at ambient temperature and pressure during 20 h
of vigorous stirring. Chlorophene was completely dechlorinated using 2.5 equivalents of Al (0.14 g) and 10 equivalents of
NaOH (0.4 g) per 1 mmol of chlorophene under the same conditions.
Graphical abstract
H
X
O
O
Ambient
R
R
+ Al/Ni +NaOH + H2
O
+
NaAl(OH)4
+
NaCl
+ Ni
temperature
H
Cl
R = H or 2-OH-4-chlorophenyl
X = Cl or H
R = H or 2-OH-phenyl
Keywords Reductions Á Heterogeneous catalysis Á Chlorinated phenols Á Metals Á Ni
Introduction
Pollutants) to protect the environment. There should be an
encouragement towards so-called environmental friendly
alternatives, which would have preferably no harmful
impacts on Nature. Chlorinated organics are among per-
sistent organic pollutants, which bioaccumulate in the
environment, and are highly resistant against degradation,
and also enter the bodies of living organisms where they
could change the DNA structure and cause cancer [1–3].
Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol, 1)
and chlorophene (2-benzyl-4-chlorophenol, 2) are chlori-
nated phenols used as antimicrobial agents either in
household products, cosmetics, or as the basic antiseptics
in hospitals, agriculture facilities, etc. 1 is a widely used
antibacterial agent with wide range of effect. We could find
it in personal care products such as toothpastes, antibac-
terial soaps, shampoos, and cosmetics [4, 5]. The European
Organohalogens are widely spread around many different
things that we are using in our everyday lives. We are
encountering these compounds consciously or unwittingly
on almost every step. Many of them are dangerous to
human health and to living organisms (e.g. polychlorinated
biphenyls—PCBs) and their use and production has been
eliminated or restricted with different kinds of agreements
(e.g. Stockholm Convention on Persistent Organic
´ˇ
& Tomas Weidlich
tomas.weidlich@upce.cz
1
Faculty of Chemical Technology, Institute of Environmental
and Chemical Engineering, University of Pardubice,
´
Studentska 95, 53210 Pardubice, Czech Republic
123

J. Pérko et al.
Union restricted 1 in cosmetics since 2014 but it also can
be found as an antibacterial preservative in plastics such as
kitchenware, toys, and as well in textile products such as
socks, beddings, and sports clothing [6–8]. 1 has been also
detected in human breast milk and bodies of fish [9, 10], it
is commonly detected in the wastewater treatment plants
and even though its degradation efficacy is quite high, trace
concentrations go to effluents causing death of many
aquatic organisms, such as algae, daphnids, phytoplankton,
and fish [11–13]. In wastewater treatment plants or by
incinerating 1-contained clothing, 1 could be transformed
to even more toxic compounds (e.g. by photocatalysis of
surface water, through biological methylation to methyl-
triclosan [14, 15]). Use of 1 in clothing has been banned by
the European Union because of the concerns from bacterial
resistance and generation of toxic metabolites, such as 2,8-
dichlorodibenzo-p-dioxin [16].
[24]) was successfully tested for the degradation of hexa-
chlorobenzene [23] or 2,4,6-trichlorophenol (2,4,6-TCP)
[24]. Also metallic alloys (especially Raney Al–Ni and
Devarda’s Al–Cu–Zn alloys) had been used in the past for
HDC of chlorinated aromatics insecticide DDT and 2,4,6-
TCP in NaBH4 solutions [25] or in various alkali hydroxide
solutions (monochloro- (MCB) and dichloro- (DCB)
biphenyls) [26], respectively. Mainly products of HDC had
been obtained by replacing chlorine with hydrogen, how-
ever, in many cases the reduction of the aromatic ring in
the molecule occurred [26]. Application of a high excess of
Al–Ni alloy and its re-use in the HDC of 2-chlorophenol
was also reported with very promising results [27, 28]. The
HDC mechanism of halogenated aromatics by metallic
alloys is not yet completely clarified—few different views
on the problematic had been reported. The direct reduction
of organically bound halogen (Carom.–X bond) could either
occur at the metal surface or there is the effect of adsorbed
hydrogen activated on nickel sponge [24, 26]. For a liter-
ature survey of the various methods see Table 1.
Chlorophene (2) application is similar to 1 and it is used
in personal care products, household products, but also in
the industry and agriculture (farming facilities) as an active
agent in disinfectants [17]. Because of its use, 2 goes to the
aquatic environment and because of its toxicity and per-
sistence it is accumulating in waters and soils [18]. It is
assumed that 2 toxicity to humans is low, but carcino-
genicity and mutagenicity of 2 to animals has been proven
[19]. Recently, it was reported that 2 displays antiandro-
genic behavior when detected in fish bile together with 1. It
showed about 50% more antiandrogenic effect compared to
other chemicals [20].
The previous studies focused on HDC were conducted
either in non-aqueous solutions (in organic solvent alone,
in a certain mixture of organic solvent/water, respectively)
[21, 22, 29], at non-ambient temperature or pressure
[21, 25, 26, 29, 30], and with a high excess of metals/alloys
against chlorinated organics [26–28]. Thus, our goal was to
come up with a HDC method under mild conditions, i.e.
ambient temperature and pressure without need for special
reactors or equipment (Fig. 1).
Nowadays, there is a continuous search for appropriate
methods for remediation of organic pollutants, in particular
chlorinated organics. Hydrodechlorination (HDC) is an
effective way for detoxification of chlorinated organics
under relatively mild conditions without toxic byproducts
formation. Unlike chemical oxidation where the pollutants
are usually degraded to (if possible) CO2 and H2O under
quite harsh conditions (and toxic byproducts could be
produced), this method enables to replace chlorine in the
molecule by hydrogen under relatively mild conditions and
generate more easily biodegradable compounds due to their
lower toxicity, i.e. no halogen in the molecule. Hydrogen
could be introduced to the system in many different ways,
e.g. by hydrogen gas bubbled to the solution or generated
in situ from hydrides, hydroxides, or hydrazine by a reac-
tion with metals (either by Pt or Pd on carbon, by a mixture
of metals as a fly ash or in the form of metallic alloys).
Those methods showed good results in the degradation of
various chlorinated pollutants, such as toxic polychlori-
nated dibenzo-p-dioxins (PCDDs), polychlorinated diben-
zofurans (PCDFs), and trichlorobenzenes (TCBs) [21, 22]
under relatively mild conditions.
The aim of this study is to test the applicability of
several common metallic alloys containing electropositive
metal(s) and Cu or Ni, such as Al–Ni (50% Al–50% Ni),
Devarda’s Al–Cu–Zn alloy (45% Al–50% Cu–5% Zn), and
Arnd’s Cu–Mg alloy (60% Cu–40% Mg) for HDC of 1 and
2 in alkaline aqueous solution at ambient temperature and
pressure as well as investigating such parameters as type
and amount of alloy(s), type and amount of base, etc. The
above-mentioned alloys have been tested in the past studies
for HDC of several halogenated anilines, and 2,4,6-tribro-
mophenol (2,4,6-TBP) and were suggested as good
reduction agents for halogenated phenols [31–35].
Results and discussion
Effect of the alloy on the HDC of 1 in aqueous
NaOH solution
We examined the course of HDC of 1 in alkaline solution
using Cu- and Ni-based alloys, Raney Al–Ni, Devarda’s
Al–Cu–Zn, and Arnd’s Cu–Mg alloys. As mentioned
above, this method is highly effective for hydrodebromi-
nation of 2,4,6-tribromophenol in case of Al–Ni and Al–
HDC by activated zero valent metal (iron coated with
Cu [23] or Zn powder coated modified with noble metals
123

Degradation of the antibacterial agents triclosan and chlorophene…
Table 1 Reaction conditions of hydrodehalogenation in various studies
Pollutant
Number of Cl
atoms
Reductant
Ratio metal:
substrate
Temp./ Reaction
°C
Solvent Special
reactor
References
[21]
time/h
PCDBs, PCDFs
3–4
Pt/C or Pd/C ? H2
Pd/C ? N2H4
1 (Pd or Pt): 10
50
1.5–2
Aq./
org.
Org.
Yes
TCPs
3
1 (Pd): 1
RT-60
RT
0.083–3
Yesa
No
[22]
[24]
[25]
2,4,6-TCP
3
Zn(0), Zn/Pd, Zn/Pt 12–61 (Zn): 1
20–40 days Aq.
DDT and 2,4,6-
TCP
3–5
Devarda’s
alloy ? NaBH4
28–83 (Al): 1
- 100
1–4
Aq.
No
MCBs, DCBs
2-CP
1–2
1
Al–Ni/OH-
Al–Ni/F-(EDTA)
19 (Al): 1
60–0
RT
1.5–8.5
0.75–2
Aq.
Aq.
Aq./
Yesa
No
[26]
24: 1
b
[27, 28]
[29, 30]
Chlorinated
aromatics
1–3
Fly ash ? alcohol
40–170 3–13
Yes
org.
2,4,6-TBP
3
3
Devarda’s
alloy ? OH-
Al–Ni/OH-
10 (Al): 1
3.8 (Al): 1
RT
RT
2
1
Aq.
No
No
[33]
[34]
2,4,6-TBP
Aq.
aUltrasonic irradiation
bFly ash—individual metal contents in fly ash vary a lot, i.e. hard to define the ratios
Fig. 1 Chemical structures of
studied antibacterial agents
[4, 5, 17]
Cl
OH
OH
Cl
O
Cl
Cl
Triclosan (1)
Chlorophen (2)
Cu–Zn application [33, 34]. The course of HDC was
investigated by the reaction of 1 mmol of 1 in aqueous
NaOH solution (0.4 g NaOH in 100 cm3 was a part of
stock solution and various amounts of NaOH were added to
the reaction mixture just before adding the alloy) using
various amounts of alloy at ambient temperature
(20–25 °C) stirring overnight.
To the 1 mmol of 1 in aqueous solution, various
amounts of alloys and various excessive amounts of NaOH
were added to cause complete corrosion (and dissolution)
of the electropositive metal from used alloy (Table 2).
Experiments showed that HDC of 1 is taking place only in
the case of Al–Ni (Table 2, entries 6, 7). The effect of
elevated temperature on the reaction was tested in case of
Devarda’s and Arnd’s alloys by heating of the reaction
mixture at reflux for tens of minutes (30–120 min; Table 2,
entries 3 and 5). Nevertheless, none of these actions were
leading to any products of HDC whatsoever using both Cu-
based alloys. One of the reasons for the failure in the case
of Devarda’s and Arnd’s alloys could be the higher
stability of the Caryl–Cl bond compared with the Caryl–Br
bond [33].
Effect of Al–Ni alloy amount on the HDC of 1
In preliminary experiments, a high excess of reduction
agent over 1 was used. Amounts of alloy were gradually
lowered and amounts of NaOH were adjusted to optimize
the process. The results can be seen in Table 3. It was
found that optimal conditions for complete HDC were with
using at least 0.22 g of Al–Ni alloy (i.e. 4 mmol of Al) and
0.8 g NaOH (20 mmol), see Table 3, entry 7. These ratios
(substrate:metal:base) are far lower than reported [24–28].
To see the HDC of 1 (1 mmol) profile in time, the
experiments were conducted (Fig. 2) using 0.27 g of Al–Ni
alloy (i.e. 5 mmol of Al) and 0.8 g NaOH (20 mmol). As it
can be seen in Fig. 2, after 480 min there was about 90% of
totally dechlorinated 2-phenoxyphenol 1c and there were
only traces of
1
in the reaction mixture. After
123

J. Pérko et al.
Table 2 Reactivity of 1 with alloys in aqueous NaOH solution
Entry Added
alloy
Quantity of added
alloy/g
Content of reductant in added alloy/ Added NaOH/
mmol
Reflux time/
min
Content of unreacted
1/%
mmol
1
2
3
4
5
6
7
Devarda’s 0.96
Al–Cu–Zn 1.92
Al (16)
Al (32)
Al (10)
Mg (10)
Mg (9)
Al (20)
Al (10)
20
20
25
35
55
35
35
–
–
100
100
100
100
100
0
0.6
120
–
Arnd’s
Cu–Mg
Raney
Al–Ni
0.55
0.53
1.08
0.56
60
–
–
0
1 (1 mmol, 0.29 g) dissolved in 100 cm3 of 100 mmol dm-3 aqueous NaOH, alloy and NaOH were added (heated) and stirred at 350 rpm
overnight without heating
Table 3 HDC of 1 using Al–Ni
alloy
Entry
mmol of Al (quantity of Al–Ni/g)
NaOH/mmol
GC–MS ratio/%
1
1a
1b
1c
1
20 (1.08)
35
35
20
20
20
35
20
30
20
30
30
30
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
100
100
100
100
100
100
100
74
2
10 (0.54)
3
10 (0.54)
0
4
7.5 (0.4)
0
5
5 (0.27)
0
6
5 (0.27)
0
7
4 (0.22)
0
8
3 (0.16)
7.7
20.3
0
8.9
9.4
9
3 (0.16)
11
0
17.7
51
10
11
12
5 (0.27)
3 (0.16 g of Al foil)a
3 (0.16 g of Al foil)b
0
0
0
100
0
99
1
100
0
0
1 (1 mmol, 0.29 g) in 100 cm3 of 100 mmol dm-3 aqueous NaOH, stirred at 350 rpm overnight at ambient
temperature
aDecanted Ni slurry produced in entry 10 was used together with Al foil
bDecanted Ni slurry produced in entry 11 was used together with Al foil
approximately 24 h, 1c was the only product present in the
reaction mixture.
worth mentioning that this kind of excess was used for a
molecule which contains only one chlorine atom, whereas
in case of 1 there are three chlorine atoms in the molecule.
An economic aspect of the reaction and possible mul-
tiple re-using of the alloy used in high excess is an
important part in considering the practical application of
the alloy for HDC [27, 28]. However, the experiments on
recyclability of the Al–Ni alloy were conducted with co-
action of Al foil as possible source of Al reductant with
unsatisfactory results (Scheme 1 and Table 3, entries
10–12).
The time consumption observed goes against the results
of other scientists who were able to reduce the reaction
times to several minutes or several hours; however, those
experiments were conducted either at increased tempera-
ture or using way higher substrate:metal:base ratios
[21, 22, 24–30]. Surprisingly, in case of Choi and Kim [24]
the reaction times are in days though the metal is in high
excess against the substrate—HDC of 2,4,6-TCP by zinc or
zinc bimetals (Zn/Pt, Zn/Pd, Zn/Ni, Zn/Cu). The results are
not satisfactory, after 20 days the total degradation was
achieved only with Zn/Pd. Yang et al. [27, 28] reports HDC
of 2-chlorophenol (2-CP) by Al–Ni alloy at ambient tem-
perature and pressure in times around 45–120 min. How-
ever, the excess of reducing metal was 24:1 (Al: 2-CP). It is
HDC of 1 in aqueous solution: effect of base
The effect of different bases on the HDC of 1 using Al–Ni
alloy in aqueous solutions was investigated (Tables 4, 5). A
123

Degradation of the antibacterial agents triclosan and chlorophene…
of oxidized Al3? from the Al–Ni alloy surface into the
alkaline aqueous solution, which is accompanied by failure
of HDC, see Table 5.
100
90
80
70
60
50
40
30
20
10
0
1
HDC of 2 in aqueous solution: effect of alloy
1a
1b
1c
Experiments with degradation of 2 by Raney Al–Ni,
Devarda’s Al–Cu–Zn, and Arnd’s Cu–Mg alloys were
conducted in the same manner as was above with 1 using
NaOH as the base (Table 6). Experiments showed that
HDC completely failed in case of Devarda’s and Arnd’s
alloys. Only the Raney Al–Ni alloy was proved as effective
agent (Scheme 2).
0
60
120
180
240 460 480
1440 1445
Reaction time / min
Effect of amount of Al–Ni alloy on HDC of 2
in aqueous NaOH solution
Fig. 2 Time course of HDC of by Al–Ni/NaOH. Reaction
1
conditions: room temperature (20 °C) and ambient pressure, stirred
at 350 rpm; 1 mmol (0.29 g) of 1 and 0.8 g NaOH (20 mmol)
dissolved in H2O (100 cm3) ? 0.27 g Al–Ni (5 mmol of Al). (filled
square) 1, (9) dichloro isomers 1a, (filled circle) monochloro isomers
1b, (filled triangle) 2-phenoxyphenol 1c
At first, the optimal amount of Al–Ni alloy was examined
generating the product of total HDC, then the optimal
amount of NaOH was tested. The obtained results are
illustrated in Table 7. Total HDC was found to be com-
pleted when 2.5 equivalents of Al in the form of Al–Ni
alloy (i.e. 0.14 g, 2.5 mmol of Al) against 2 and 10
equivalents of NaOH (i.e. 0.4 g, 10 mmol) against Al were
used and the reaction was performed at ambient tempera-
ture for approximately 21 h, see Table 7, entry 13. Using a
high excess of the Al–Ni alloy against 2, substituted
cyclohexanol 2b is produced and subsequent hydrogena-
tion of 2a occured. A time course of the HDC of 2 is shown
in Fig. 3—the lowest amount of alloy (0.14 g of Al–Ni, i.e.
2.5 mmol of Al as mentioned few lines earlier) was used
when the reaction was completed. However, the reactions
did not result in 100% of 2a, still around 5% in average
was present in the reaction mixture. This could be the
experimental error, which is included in the standard
deviation of this value. However, about 75% of dechlori-
nated product present in the reaction mixture after 240 min
is a good result under mild conditions. The results show
that the metal:base:substrate ratios are very low in contrast
to similar studies [24–30]. The ratios are close to those
stock solution of 1 was prepared by dissolving an appro-
priate amount of 1 and an appropriate amount of base in
distilled water. An important fact to mention is that in some
cases (Table 4, entries 3–7, 14–18, Table 5) the basicity of
the bases (or alkaline salts) was not sufficient to deproto-
nate and dissolve 1 (pKA of 1 is 7.9 [36]). Thus a low
quantity of stronger base, such as NaOH had to be used to
prepare the aqueous stock solution. Amounts of base/salt
needed for the complete HDC varied a lot, e.g. in case of
Na3PO4 the quantity present in the stock solution was
sufficient to provide as much as 96% of totally dechlori-
nated product 1c (Table 4, entry 8).
In most cases, a high excess of added salts tested as
bases negatively influenced the HDC of 1, see Table 4.
This fact corresponds with observations published earlier
[31, 33]. For effective HDC using Al–Ni alloy formation of
soluble Al3? salts (NaAl(OH)4) is crucial. Most of the
tested salts used instead of NaOH retards oxidation of Al
added as Al–Ni alloy and/or prevent subsequent dissolution
Scheme 1
Cl
OH
X
OH
O
O
Ambient
2 NaAl(OH)
+
+
+ 2 Al/Ni+
Cl
+3 H O
2
3 NaCl
5 NaOH
4
temperature
+ Ni0
Cl
X
X
1a: X = 2 Cl, 1 H
1b: X = 1 Cl, 2 H
1c: X = 3 H
1
123

J. Pérko et al.
Table 4 Effect of base on the HDC of 1 using Al–Ni alloy
Entry
mmol of Al (quantity of Al–Ni/g)
Used base/mmol
NaOHa/mmol
GC–MS ratio/%
1
1a
1b
1c
1
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
5 (0.27)
5 (0.27)
2.5 (0.14)
10 (0.54)
5 (0.27)
5 (0.27)
10 (0.54)
5 (0.27)
5 (0.27)
10 (0.54)
5 (0.27)
10 (0.54)
5 (0.27)
5 (0.27)
KOH (2)
–
–
1
1
1
1
1
–
–
–
–
–
–
1
1
5
5
5
0
0
0
0
100
100
2
NaOH (10)
0
0
3
NaF (10)
28.8
1.8
12.4
81.4
47.6
0
45.8
3.3
11.5
0.8
8.5
2.1
5.6
4
13.9
94.1
55.5
7
4
NaF (35)
5
NaF (35)
23.6
9.5
6
NaF (85)
7
NaF (35)
34
12.8
96
8
Na3PO4 (10)
Na3PO4 (11)
Na3PO4 (15)
Na2CO3 (10)
Na2CO3 (10)
Na2CO3 (35)
CH3COONa (10)
CH3COONa (35)
CH3COONH4 (10)
CH3COONH4 (10)
CH3COONH4 (35)
0
9
9.2
10.4
68
23.5
25.4
24.2
24.7
24.9
28.9
18.5
24.5
29.8
0
13.8
16.2
5.7
4.6
4.3
8.3
5.5
21.4
13.6
0
53.5
48
10
11
12
13
14
15
16
17
18
2.1
2.7
0.5
8.8
3.0
50
68
70.3
54
73
4.1
11.2
100
45.4
0
To 1 (1 mmol, 0.29 g) dissolved in 100 cm3 of aqueous solution of mentioned base (or salt) Al–Ni alloy was added and stirred at 350 rpm
overnight at ambient temperature
aGiven amount of NaOH is in 100 cm3 of solution with which was made the experiment. NaOH was added to secure total dissolution of 1
Table 5 Effect of dissolved Al on the HDC of 1 using Al–Ni alloy
Entry
mmol of Al (quantity of Al–Ni/g)
Used base/mmol
Conversion to 1c/%
Dissolved Al/mg dm-3
1
2
3
4
5
6
7
8
9
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
10 (0.54)
NaOH (10)
100
100
100
100
100
96
1559
835.1
832.3
916.9
1257
568.6
255.2
141.7
4.283
NaF (4)
NaF (20)
Na3PO4 (1)
Na3PO4 (5)
CH3COONa (4)
CH3COONa (20)
CH3COONH4 (4)
CH3COONH4 (8)
93
74
5
1 (1 mmol, 0.29 g) dissolved in 100 cm3 aqueous solution of 100 mmol dm-3 NaOH, appropriate quantity of base (salt) and of Al–Ni alloy was
added, reaction mixture at room temperature stirred at 350 rpm overnight
appropriate amount of 2 (10 mmol dm-3) and an appro-
priate amount of base (100 mmol dm-3) in distilled water.
Apart from the above-mentioned way of dissolving (adding
small portion of NaOH) the studied compound, in this case,
to achieve dissolving all of 2, the stock solution was heated
at around 70 °C. Although in cases of Na2CO3 and NaF
only heating was not sufficient and a small portion of
NaOH (one pellet, ca 0.2 g) was added to the stock solu-
tion. The lowest effective amount of Al–Ni alloy for the
complete HDC of 2 was 0.27 g (5 mmol of Al) or 0.14 g
´
reported by Tundo and Rodrıguez [21, 22]; however, they
did not achieve those results under mild conditions as
aqueous solution at ambient temperature and pressure, see
Table 1.
HDC of 2 in aqueous solution: effect of base
The effect of different bases on the HDC of 2 using Al–Ni
alloy in aqueous solutions was investigated (Table 8). A
stock solution of 2 was prepared by dissolving an
123

Degradation of the antibacterial agents triclosan and chlorophene…
Table 6 Effect of used alloy on
the HDC of 2
Entry Used alloy
Quantity of alloy/g Reductant/mmol NaOH/mmol Content of unreacted 2/%
1
2
3
4
5
6
Devarda’s
Al–Cu–Zn
Arnd’s
0.9
Al (15)
Al (20)
Mg (1.7)
Mg (17.7)
Al (15)
Al (5)
35
35
100
100
100
100
0
1.2
0.11
1.07
20
Cu–Mg
100
35
Raney Al–Ni 0.81
0.27
20
0
2 (1 mmol, 0.22 g) was dissolved in 100 cm3 of 100 mmol dm-3 aqueous NaOH solution, additional base
and tested alloy was added at ambient temperature and the reaction suspension was stirred at 350 rpm
overnight
Scheme 2
OH
OH
HO
Ambient
temperature
- NaAl(OH)4
- NaCl
+ Al/Ni + NaOH + H2O
+
2
Cl
2a
2b
Table 7 HDC of 2 using Al–Ni
alloy
Entry
mmol of Al (quantity of Al–Ni/g)
NaOH/mmol
GC–MS ratio/%
2
2a
2b
1
30 (1.62)
20 (1.08)
15 (0.80)
10 (0.54)
5 (0.27)
20
0
80.5
86.7
92.7
97.4
100
100
100
100
100
100
100
100
100
75.4
55
19.5
13.3
7.3
2.6
0
2
20
0
3
20
0
4
20
0
5
10
0
6
5 (0.27)
15
0
0
7
5 (0.27)
17.5
20
0
0
8
5 (0.27)
0
0
9
2.5 (0.14)
2.5 (0.14)
2.5 (0.14)
2.5 (0.14)
2.5 (0.14)
1.3 (0.07)
1.3 (0.07)
17.5
20
0
0
10
11
12
13
14
15
0
0
15
0
0
12.5
10
0
0
0
0
35
24.6
45
0
15
0
To 2 (1 mmol, 0.22 g) dissolved in 100 cm3 of aq. NaOH solution Al–Ni was added and stirred at 350 rpm
overnight at room temperature
(2.5 mmol of Al) mainly these amounts had been weighed
to the reactions, only the amounts of base differed. Effec-
tive amounts of bases needed for the total HDC varied a
lot, for example in case of Na3PO4 only the quantity pre-
sent in the stock solution (10 mmol in 100 cm3 of solution
with which was made experiment) was sufficient to provide
as much as 100% of totally dechlorinated product,
however, with a higher amount of Al–Ni alloy, which was
probably the main reason for the complete HDC of 2 (see
Table 8, entries 7–9). From Table 8, entries 16–23 can be
seen that with higher amounts of base/salt the HDC per-
centage increases, but at certain point the HDC percentage
starts to decrease. This phenomenon is in agreement with
the fact that excess of base/salt prevents the dissolution of
123

J. Pérko et al.
Al from Al–Ni alloy. The reaction mechanism is very
complex but from the information we obtained from pub-
lications reporting on the same topic [27, 28, 31] we
assume the main steps are as follows: first, the dissolution
of the passivated Al (Al2O3 layer on the surface of Al–Ni
alloy) is taking place; subsequently, hydrogen is generated
by a reaction of Al with water; hydrogen is reacting in
assistance by Ni catalyst (probably on Ni surface) with the
organic substrate to promote HDC and give products (in
case of 2 it is 2a; in case 1 it is 1a, 1b, 1c;). The basic
aqueous solution also helps to secure total dissolution of 1
and 2. As can be seen in Table 5 the higher amounts of
dissolved Al in the reaction mixture were analyzed by the
higher conversion to products of total HDC. Also the
possibility of direct reduction of the substrate by Al–Ni
alloy might be taken into account, yet it is a hypothesis
which needs to be secured by more information obtained
from data as well as from the literature.
100
90
80
70
60
50
40
30
20
10
0
2
2a
0
60
120
180
240 1440 1445
Reaction time / min
Fig. 3 Time course of HDC of
2
by Al–Ni/NaOH. Reaction
conditions: room temperature (20 °C) and ambient pressure, stirring
at 350 rpm; 1 mmol (0.22 g) of 2, 0.14 g Al–Ni (2.5 mmol Al), 0.8 g
NaOH (20 mmol)
Table 8 Effect of base on the
HDC of 2 using Al–Ni alloy
Entry
mmol of Al (quantity of Al–Ni/g)
Used base/mmol
NaOHa/mmol
GC–MS ratio/%
2
2a
2b
1
10 (0.54)
10 (0.54)
5 (0.27)
NaOH (10)
NaF (10)
–
1
1
1
1
1
–
–
–
–
–
–
–
–
–
1
1
1
1
1
1
1
1
0
83.6
92.8
63.8
96.3
84.9
96.7
99.5
100
100
100
100
100
98
16.4
0
2
7.2
36.2
2.9
15.1
3.3
0
3
NaF (10)
0
4
5 (0.27)
NaF (35)
0.8
0
5
2.5 (0.14)
2.5 (0.14)
10 (0.54)
10 (0.54)
7.5 (0.4)
7.5 (0.4)
5 (0.27)
NaF (22.5)
6
NaF (35)
0
7
Na3PO4 (10)
Na3PO4 (20)
Na3PO4 (10)
Na3PO4 (17.5)
Na3PO4 (15)
Na3PO4 (35)
Na3PO4 (60)
Na3PO4 (20)
Na3PO4 (35)
Na2CO3 (10)
Na2CO3 (10)
Na2CO3 (35)
Na2CO3 (60)
Na2CO3 (110)
Na2CO3 (22.5)
Na2CO3 (35)
Na2CO3 (47.5)
0.5
0
8
0
9
0
0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
0
0
0
0
5 (0.27)
0
0
5 (0.27)
1.5
4
0.5
0
2.5 (0.14)
2.5 (0.14)
10 (0.54)
5 (0.27)
96
4
96
0
0
100
100
90
0
0
0
5 (0.27)
10
8.5
28.7
37
16
47.9
0
5 (0.27)
91.5
71.3
63
0
5 (0.27)
0
2.5 (0.14)
2.5 (0.14)
2.5 (0.14)
0
84
0
52.1
0
2 (1 mmol, 0.22 g) in 100 cm3 aqueous solution of mentioned base (salt, respectively) with Al in the form
of Al–Ni alloy, ambient temperature (20–25 °C) and pressure, stirred at 350 rpm overnight
aGiven amount of NaOH is in 100 cm3 of solution with which was made the experiment. NaOH was added
to secure total dissolution of 2
123

Degradation of the antibacterial agents triclosan and chlorophene…
in air at ambient temperature (20–25 °C). All used solu-
tions were prepared in distilled water. Stock solutions of 1
or 2 were prepared in concentrations of 10 mmol dm-3 in
aqueous solution of appropriate base (salt, respectively).
To the 10 mmol dm-3 solution of studied 1 or 2 dissolved
in 100 mmol dm-3 of base, the appropriate amount of
tested alloy (Al–Ni, Devarda’s, Arnd’s) was added. The
flask with the reaction mixture was closed with glass tube
filled with granulated charcoal and the reaction mixtures
were stirred at 350 rpm at ambient temperature (20–25 °C)
for approximately 21 h and filtered subsequently. Obtained
filtrate was acidified using 18% H2SO4 to pH around 3,
then transferred into the separation funnel and extracted
with CH2Cl2 (2 9 5 cm3) and then let evaporate in the
fume hood. After evaporation were prepared samples for
GC/MS by dissolving the solid or viscous liquid in pure
CH2Cl2.
Conclusion
Possibilities of facile hydrodechlorination of two non-
biodegradable antibacterial agents triclosan (1) and chlor-
ophene (2) in aqueous NaOH solution using three types of
metal alloys were investigated. The effect of different
conditions, such as type of alloy, type of applied base, and
their amounts on the rate of HDC was compared. We
proved that only Raney Al–Ni alloy in diluted NaOH (or
KOH) aqueous solution is an effective HDC agent for both
compounds at ambient temperature and pressure. Alkali
metal hydroxides are thought to play a dual role: they
enable dissolution of 1 and 2 in aqueous solution and
influence the reducing ability of the Raney Al–Ni alloy.
The reducing ability of the Raney Al–Ni alloy exhibited
upon addition of alkaline aqueous solutions follows the
order:
NaOH = KOH [ Na3PO4 [ NaF C Na2CO3 [
CH3COONa [ CH3COONH4.
Mass spectrometry
We demonstrated that 20 mmol of NaOH and 4 mmol
of Al in the form of Al–Ni alloy per 1 mmol of 1 cause
complete HDC of 1. In case of 2, 10 mmol of NaOH and
2.5 mmol of Al in the form of Al–Ni per 1 mmol of 2
enable quantitative HDC of 2. The application of a higher
excess of reductant in the HDC process of 2 is accompa-
nied by hydrogenation of the phenolic ring. Further
research in this matter should be done to see if produced
2-benzylcyclohexanol (2b) is easily biodegradable and if
there is an economic justification in such excess of the
alloy. In addition, we demonstrated that Devarda’s and
Arnd’s alloys are not applicable for HDC of 1 and 2.
Mass spectra were measured on a GC–MS configuration
comprised of an Agilent Technologies 6890 N gas chro-
matograph equipped with a 5973 NetworkMS detector (EI
70 eV, mass range 33–550 Da). Samples were prepared by
dissolving in pure dichloromethane.
Acknowledgements This study was supported by Technology
Agency of the Czech Republic TG02010058.
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