Ruthenium sulfophthalocyanine catalyst for the oxidation of chlorinated olefins with hydrogen peroxide

Article abstract of DOI:10.1016/S0022-328X(99)00606-3

In aqueous solution and at room temperature, various α-chloro-alkenes are effectively dechlorinated by hydrogen peroxide oxidation using a water-soluble ruthenium(II)-tetrasulfophthalocyanine catalyst, RuPcS. The molecular structure of RuPcS has been elucidated by ESI-mass spectroscopy. In the reaction conditions, and specifically in acidic media, the complex rapidly gives rise to a novel species, most likely catalytically active, whose nature is investigated.

Full text of DOI:10.1016/S0022-328X(99)00606-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 416–420
Ruthenium sulfophthalocyanine catalyst for the oxidation of
chlorinated olefins with hydrogen peroxide
a,
b
a
a
Mario Bressan *, Nicola Celli , Nicola d’Alessandro , Lolita Liberatore ,
c
a
Antonino Morvillo , Lucia Tonucci
a
Uni6ersity of Chieti ‘G. d’Annunzio’, Department of Science, 6iale Pindaro 42, I-65127 Pescara, Italy
Mario Negri Sud, ‘G. Paone’ En6ironmental Health Center, 6ia Nazionale, I-66033 Santa Maria Imbaro, Italy
Uni6ersity of Padua, Department of Inorganic Chemistry and C.N.R. Center, 6ia Marzolo 1, I-35100 Padua, Italy
b
c
Received 16 July 1999; accepted 7 October 1999
Dedicated to Professor Fausto Calderazzo.
Abstract
In aqueous solution and at room temperature, various a-chloro-alkenes are effectively dechlorinated by hydrogen peroxide
oxidation using a water-soluble ruthenium(II)-tetrasulfophthalocyanine catalyst, RuPcS. The molecular structure of RuPcS has
been elucidated by ESI-mass spectroscopy. In the reaction conditions, and specifically in acidic media, the complex rapidly gives
rise to a novel species, most likely catalytically active, whose nature is investigated. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Aqueous organometallic catalysis; Chlorinated organics; Hydrogen peroxide; Ruthenium phthalocyanine; Oxidation
1
. Introduction
been more recently achieved by using the water-soluble,
strongly complexed ruthenium(II) derivative RuPcS
(where PcS is sodium 2,3-tetrasulfophthalocyaninate,
Fig. 1) to effect the oxidation of various chlorophenols
in the presence of hydrogen peroxide [6]. In this paper
we present further results on the catalytic oxidation of
a-chloroalkenes, together with details concerning the
characterization of RuPcS and its transformations in
the presence of hydrogen peroxide.
Water-soluble metal complexes are close models to
the ubiquitous mono-oxygenase or peroxidase enzymes,
of principal importance on a global scale for the degra-
dation of xenobiotics in biological systems [1], and
could become a gentle alternative method of oxidation
of recalcitrant contaminants dissolved in water [2].
Iron- or manganese-sulfophenylporphyrin [3] and –sul-
fophthalocyanine [4] have been successfully used for the
dechlorination of chlorophenols in aqueous acetonitrile
in the presence of hydrogen peroxide. We previously
reported that dimethylsulfoxide-‘solvated’ rutheniu-
m(II) ions are able to catalyze the extensive degradation
of a variety of halogenated organics, both aromatic and
olefinic, in aqueous media and in conjunction with
mono-persulfate [5]. A substantial improvement has
*
Corresponding author. Tel.: +39-085-453-7548; fax: +39-085-
4
0
53-7545.
E-mail address: bressan@sci.unich.it (M. Bressan)
Fig. 1. RuPcS.
022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00606-3

M. Bressan et al. / Journal of Organometallic Chemistry 593–594 (2000) 416–420
417
2
. Experimental
A Sciex API 365 triple-quadrupole mass spectrometer
was used to obtain ESI-mass spectra. Instrument con-
trol and data acquisition were performed with a Macin-
tosh System 7600/132 using MASSCHROM 1.0 software.
Calibration was carried out using polypropylene glycol
and the resolution was set in the range 0.6–0.9 amu.
Analyses were performed by direct infusion of aqueous
solution of the sample containing ammonium formate
50 mM (or formic acid 1%, ammonia 50 mM or NaOH
50 mM), which was delivered by a model 11 syringe
2.1. Preparation of RuPcS
RuPcS was prepared by template synthesis starting
from RuCl ·3H O, sodium 4-sulfophthalate and urea,
3
2
following the early general procedures for the synthesis
of metal-sulfophthalocyanines [7]. The deep-green com-
pound was isolated in the solid by salting out the
aqueous reaction mixtures with concentrated NaCl.
−
1
pump at the flow rate of 5 ml min . The infusion
pump was connected to a Sciex ion-spray interface
through a 1 m fused silica capillary (0.75 mm i.d.). Q1
scan mass spectra were acquired with a mass range
200–2000 amu using a step size of 0.1 amu and a dwell
time of 0.250 ms. The nebulizer gas (air) and the
1
5
The NꢀRuPcS derivative was similarly prepared,
1
5
starting from commercially available Nꢀurea (]99%
isotopic purity, Isotec). Anal. Found: C, 35.41; H, 1.64;
N, 10.64; S, 11.85%. Anal. Calc. for RuPcS·3H O,
RuC H N O S Na : C, 35.72; H, 1.68; N, 10.41; S,
1
2
3
2
18
8
15
4
4
−
1
1.92%. Electronic spectra (400–1500 nm, in water):
curtain gas (N ) flows were set at 1.8 l and 2.4 l min
,
2
6
30 nm (m , 25 000). Magnetic susceptibility, 20°C.
respectively. The ionization voltage was set at +4600
V, and the orifice and ring potentials were set at +75
and +280 V, respectively. In product ion scan experi-
ments, spectra were acquired with a mass range of
30–1200 amu using a step size of 0.1 amu and a dwell
time of 0.500 ms. The collision-activated dissociation
M
−
6
g= −0.25×10
in 4:1 water–D O solutions (20 mM), no detectable
shift of the indicator compound (tert-butyl alcohol) was
measured, following Evans method [8].
emu (solid state, Gouy’s method);
2
The catalytic reactions were typically carried out at
2
0°C in a 5 ml vial, by stirring magnetically 2 ml of an
(CAD) gas pressure (N ) was maintained at 2.84×
2
−
3
aqueous solution containing the catalyst (RuPcS, 0.2
10
torr.
mM) and the oxidant (H O , 2 N), to which 50 ml of the
2
2
chlorinated substrate were added, either as neat, to give
a saturated aqueous solution, or, alternatively, dis-
solved in 2 ml of an organic solvent (hexane, chloro-
form), to perform the reactions in a double phase
system. Chloride ions were analyzed spectrophotometri-
cally by the mercury thiocyanate method. Carbon diox-
ide and carbon monoxide analyses were made by
passing a moderate flow of nitrogen through the reac-
tion mixtures, previously acidified with H SO 1 N,
3. Results
To our knowledge RuPcS is the first water-soluble
phthalocyanine derivative of ruthenium so far reported,
whereas variously substituted ruthenium-phthalocya-
nines are known, both with Ru(II) and Ru(III) [10].
The vis–NIR spectra (400–1500 nm) of RuPcS in
water only show the diagnostic Q band at 630 nm,
arising from the p“p* transition within the heteroaro-
matic ring; the spectra are insensitive to the acidity of
the media in the 1–13 pH range. The complex is
attributed a monomeric structure on the basis of the
ESI-mass spectra (positive patterns: in all examined
cases no results were obtained with negative patterns),
which exhibit six complex signals of various intensities,
each showing the isotopic pattern of ruthenium diag-
nostic for a monomeric form and spaced by 22 amu
2
4
which was captured first by aqueous Ba(OH) 0.1 M
2
and finally by a dichloromethane solution of the violet
RuCl(DPP) ]PF complex (10 mM). Aliquots from the
2
6
filtered Ba(OH) solution were back-titrated with HCl
2
0
.1 N for CO , whereas the dichloromethane solutions
2
were spectrophotometrically analyzed for the formation
of the colorless mono-carbonyl adduct (w at 1930
CO
−
1
cm ) [9].
Organic analyses were performed on a HP 6890 GLC
instrument equipped with a flame ionization detector
(AWNa−AW ), corresponding to the RuPcS molecu-
H
(
FID), using a 30 m HP-5 capillary columns (0.32 mm
lar ion in the form of the penta-protonated tetra-sul-
fonic acid and the tetra-protonated mono-, the
tri-protonated di-, the di-protonated tri-, the mono-pro-
tonated tetra- and the penta-sodium sulfonate ions,
i.d.; 0.25 film thick) with the injection port thermostat-
ted at 250°C (carrier gas: He) on aliquots withdrawn
with a microsyringe from the aqueous reaction mixtures
either as such or diluted 1:10 with acetone. The reaction
mixtures were also treated by standard procedures with
a 10:1 excess 2-methyl-1-butanol to analyze the possibly
formed dicarboxylic acids as their isobutyl-esters. NMR
spectra were measured on a Bruker Avance 300 MHz,
IR spectra on a Bio-Rad FTS-7 PC and vis–NIR
spectra on a Cary instrument.
15
respectively (Fig. 2). Mass spectra of the N-enriched
RuPcS compound again show the diagnostic six signals
only shifted to higher molecular weight by 8 amu. No
14
evidence for NꢀRuPcS is detected, thus indicating a
isotopic enrichment close to 100%. The compound is
diamagnetic both in the solid state and in aqueous
6
solution (see Section 2), as expected for a d metal ion

418
M. Bressan et al. / Journal of Organometallic Chemistry 593–594 (2000) 416–420
The apical positions are nevertheless available for
further coordination, as demonstrated by the slow addi-
tion of carbon monoxide to RuPcS in aqueous solution
(
ca. 5 mM). After 7 days stirring under pCO=50 atm a
solid material could be isolated after evaporation in
vacuo. The IR spectra exhibit a strong absorption at
−
1
1
960 cm , attributable to the wCO of the monocar-
bonyl adduct, together with a very weak band at 2064
−
1
cm , which, on the basis of its higher energy, could be
tentatively attributed to small amounts of the corre-
sponding trans-dicarbonyl adduct. However, mass spec-
tra (ESI, positive pattern) of the carbonylated solid,
redissolved in water, only show the diagnostic pattern
of the parent RuPcS compound, while no peaks at
+
28 amu, corresponding to the mono-carbonylated
adduct, are detected. Early loss of CO is likely to occur
in the mass spectra measurement conditions.
RuPcS (0.2 mM) promotes the oxidation of a series
a-chloro-alkenes, i.e. 2-chloro-2-butene, cis- and trans-
1
,2-dichloroethylene and trichloroethylene, in the
aqueous–organic double-phase and in the presence of
excess hydrogen peroxide (Table 1). The aqueous phase
becomes slightly acidic, with a measured pH value of
1
ca. 5. Monitoring the reactions by GC–MS and H-
Fig. 2. (a) ESI-mass spectra (positive patterns) of RuPcS in aqueous
NMR indicates slow oxidation of the substrates (5–50
turnovers within 8 h) with formation of aqueous chlo-
ride ions and various organic products, which were
found both in the aqueous and in the organic phase and
whose nature depends upon a combination of oxidation
and hydrolysis reactions. Oxidation of tetra-
chloroethylene also takes place, but the reaction is
+
HCOONH 50 mM. (b) Fine structure of the RuPcSH ion peak at
4
5
m/z=635.
Table 1
Oxidation of chlorinated organics by hydrogen peroxide catalyzed by
RuPcS a
Oxidation b Products
1
Substrate
much slower. As evidenced by the H-NMR spectra,
2
-chloro-2-butene gives rise to the early formation of a
2
-Chloro-2-butene 50
3-Chloro-2-butanone, acetic acid,
chloride, 3-hydroxy-2-butanone
13:12:8:1 molar ratio)
Chloride, formic acid
(1:1 molar ratio)
number of transient intermediates, which are rapidly
transformed into 3-chloro-2-butanone, which is the ex-
pected product of ketonization (ca. 65% of substrate
oxidation), 2-hydroxybutanone, which arises upon
epoxidation followed by hydrolysis and dehydrochlori-
nation (ca. 5%) and acetic acid, the final product of the
oxidative cleavage of the substrate. No evidence of
butanedione, a possible further oxidation product of
3-hydroxy-2-butanone, was obtained (Fig. 3). Chloride
ions were also found, in agreement with the measured
amounts of dechlorinated products. In the same reac-
tion conditions 1,2-dichloroethylene (cis and trans iso-
mers) gave only the products from the oxidative
cleavage, i.e. formic acid and chloride ions in equimolar
amounts, with no evidence of carbon monoxide. Also,
trichloroethylene only undergoes oxidative cleavage,
with formation of formic acid and chloride ions in a ca.
(
1,2-cis-
5
8
Dichloroethylene
Trichloroethylene
Chloride, formic acid
c
(
3:1 molar ratio)
a
2
ml of aqueous H O , 2 N, containing the RuPcS catalyst, 0.2
2 2
mM (non buffered solutions, pH ca. 5) and 2 ml of hexane or CDCl3,
to which 50 ml of the substrates are added; 20°C.
b
Turnovers at 8 h.
Smaller amounts of carbon dioxide are also detected.
c
in an octahedral geometry (since square-planar struc-
tures give rise to paramagnetic species, it is likely that
two water molecules are coordinated in apical posi-
tions, even if no evidence has been obtained from mass
spectra). However, H-NMR spectra of RuPcS (ca. 10
mM in D O) exhibit only a broad and unresolved signal
in the 8 ppm region of benzene protons of the phthalo-
cyanine ring, most likely due to the strong intermolecu-
lar interactions (stacking) commonly found in
phthalocyanine complexes.
1
3
:1 molar ratio, even if only ill-measurable amounts of
2
carbon dioxide are detected, which is the other product
from the oxidative cleavage of trichloroethylene. Again,
no carbon monoxide is evolved.
Oxidations are almost completely inhibited in alka-
line media, despite the expected larger reactivity of

M. Bressan et al. / Journal of Organometallic Chemistry 593–594 (2000) 416–420
419
Fig. 3. Proposed pathway for the oxidation of 2-chloro-2-butene by H O and RuPcS catalyst; (i) oxidation, (ii) dehydrochlorination and/or
2
2
hydrolysis.
hydrogen peroxide. In these conditions (pH]13) the
green RuPcS complex, or its hydroxo- and/or oxo-
bridged derivatives, is the overwhelmingly dominant
species, as indicated by the persistence (and intensity) of
the 630 nm band. In acidic media (pH55), where the
catalytic processes take place satisfactorily, RuPcS un-
dergoes an irreversible transformation in the presence
of hydrogen peroxide, with the fast formation (30 min)
of yellow solutions, whose electronic spectra show the
complete disappearance of the distinctive 630 nm band
and no other absorption up to 1500 nm (which repre-
sents the upper wavelength detectable for aqueous hy-
drogen peroxide solutions). UV spectra of an organic
phase added to the aqueous reaction mixtures do not
exhibit the two distinctive absorptions of ruthenium
tetroxide, at 310 and 385 nm, thus indicating that no
release of free metal occurs during the transformation,
and indeed upon simple demetallation, a fairly uncom-
mon event for phthalocyanine complexes, with no dis-
appearance of the p“p* band expected [11]. However,
no mass spectral data could be obtained for the yellow
compound, most likely a polymeric species, present in
these solutions. Accordingly, evaporation under vac-
uum results in aqueous irreducible concentrates, from
which only intractable waxy solids were obtained after
drastic treatments with refluxing methyl orthoformate.
multiplets at 7.9 ppm (six peaks) corresponding to the
X proton (positions 1 of the phthalocyanine ring; posi-
tions 2 are occupied by the sulfonate moieties) and at
8.1 ppm corresponding to the AB portion of the spec-
trum (protons in positions 3 and 4), thus pointing to
the integrity of the benzene ring substituted at positions
2, 5 and 6, as in the starting phthalocyanine complex.
In H O–D O (4:1) mixtures and at pH ca. 1, three
2
2
signals of equal intensity also appear at 7.0 ppm,
separated by 51 Hz, attributable to hydrogen atoms
1
4
1
coupled to one nitrogen atom ( N). The H-NMR
15
spectra of the corresponding NꢀRuPcS derivative
nicely confirm the attribution, with the same signal
appearing at 7.0 ppm as a doublet separated by 74 Hz
(Fig. 4). The values of both J( Hꢀ N) and J( Hꢀ N)
coupling constants are distinctive of protons directly
bound to nitrogen ( J), whereas the measured
J( Hꢀ N)/J( Hꢀ N) ratio is in full agreement with the
expected value of −1.4027 [12]). In increasingly D O
1
14
1
15
1
1
15
1
14
2
enriched media the signals at 7.0 ppm progressively
loose intensity because of extensive replacement of the
nitrogen-bonded protons by deuterium. At higher pH
values the signals disappear suddenly, indicating fast
15
exchange with water protons. The N-NMR spectra
15
(DEPT-45 experiments) of the N enriched compound
in pure water show a neat quintuplet at −360 ppm,
1
1
15
1
Definite changes in the H-NMR spectra accompany
with the same J( Hꢀ N) observed in the H-NMR
spectra, clearly attributable to the ammonium ion. The
intensity ratio between benzene and ammonium pro-
tons is close to 3:1 in aqueous media and this leads one
to conclude that ammonium arises upon cleavage of
one of the nitrogen atoms of the phthalocyanine ring,
most likely from the meso-position. Oxidative cleavage
of amines to ammonia is known to be catalyzed by the
copper-containing enzymes amine oxidases and has
been recently reported to occur also in the presence of
a synthetic copper complex mimicking the above en-
zyme [13]. Nevertheless, the observed reaction is rather
unexpected and deserves further investigation.
the dramatic change in the visible spectra, described
above. The yellow solutions are still diamagnetic, there-
fore indicating either persistence of ruthenium in the
same oxidation state (+2), or, alternatively its oxida-
2
tion to diamagnetic species, such as a ruthenium(VI) (d
ion) in a tetragonally distorted geometry with apical
ligand(s), for which a spin-paired electronic configura-
tion is expected. However, and unlike the starting
RuPcS complex, the yellow acidic solutions exhibit
well-resolved signals in the 8 ppm region (aromatic
protons), a clear indication that stacking has been
extensively removed. An ABX pattern is observed, with

420
M. Bressan et al. / Journal of Organometallic Chemistry 593–594 (2000) 416–420
cations of the phthalocyanine ligand must have oc-
curred, akin, for instance, to those reported for the
celebrated oxidative degradation of heme to biliverdin
and recently observed also in relevant iron-porphyrin
model compounds [15].
Acknowledgements
The authors thank A. Ravazzolo, C.N.R., Padova,
for technical assistance, and M.U.R.S.T., Cofin98 fund-
ing, for financial support.
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Fig. 4. H-NMR spectra of RuPcS (10 mM) in aqueous H O (0.2 M)
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1
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