Synthesis of N-benzylated cobalt phthalocyaninetetrasulfonamide and its application in oxidative desulfurization catalysis

Article abstract of DOI:10.1080/00958972.2019.1683549

The FeCl₂/K₂CO₃ catalyst system was used successfully for the synthesis of oil soluble N-benzylated cobalt phthalocyaninetetrasulfonamide by the reaction of benzyl alcohol on water-soluble cobalt phthalocyaninetetrasulfonamide via heating at 135 °C for 20 h under N₂. The new oil-soluble peripherally N-benzylated phthalocyanine was characterized by elemental analysis, FT-IR, UV–vis, TG and mass spectrometry. The catalytic activity of this new cobalt complex for oxidation of dibenzothiophene (DBT) was evaluated in n-dodecane (a middle distillate model compound) using H₂O₂ as an oxidant. The acetonitrile was taken as an extracting solvent for further extracting DBT sulfoxide and sulfone. The novel peripherally substituted cobalt(II) complex showed better oxidative desulfurization catalytic activity than cobalt phthalocyanine and cobalt phthalocyaninetetrasulfonamide. DBT oxidation kinetics were evaluated by lumped n^th- and first-order kinetic models. The maximum removal of the DBT was found to be 85% at the optimized dose and experimental conditions.

Full text of DOI:10.1080/00958972.2019.1683549

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis of N-benzylated cobalt
phthalocyaninetetrasulfonamide and its
application in oxidative desulfurization catalysis
Deependra Tripathi, Himani Negi, Raj K. Singh, Udai P. Singh & Vimal C.
Srivastava
To cite this article: Deependra Tripathi, Himani Negi, Raj K. Singh, Udai P. Singh & Vimal
C. Srivastava (2019) Synthesis of N-benzylated cobalt phthalocyaninetetrasulfonamide and
its application in oxidative desulfurization catalysis, Journal of Coordination Chemistry, 72:17,
2982-2996, DOI: 10.1080/00958972.2019.1683549
To link to this article: https://doi.org/10.1080/00958972.2019.1683549
Published online: 01 Nov 2019.
Submit your article to this journal
Article views: 23
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
019, VOL. 72, NO. 17, 2982–2996
2
https://doi.org/10.1080/00958972.2019.1683549
Synthesis of N-benzylated cobalt
phthalocyaninetetrasulfonamide and its application in
oxidative desulfurization catalysis
a,b
b
b
a
Deependra Tripathci , Himani Negi , Raj K. Singh , Udai P. Singh and
Vimal C. Srivastava
a
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India;
Analytical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun, Uttarakhand, India;
b
c
Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India
ABSTRACT
ARTICLE HISTORY
The FeCl
2
/K
2
CO
3
catalyst system was used successfully for the synthe-
Received 19 May 2019
Accepted 19 September 2019
sis of oil soluble N-benzylated cobalt phthalocyaninetetrasulfonamide
by the reaction of benzyl alcohol on water-soluble cobalt phthalocya-
ꢀ
KEYWORDS
Cobalt complex;
N-benzylation;
phthalocyanine; oxidation
desulfurization;
dibenzothiophene; oxidation
kinetics
ninetetrasulfonamide via heating at 135 C for 20 h under N
2
. The
new oil-soluble peripherally N-benzylated phthalocyanine was charac-
terized by elemental analysis, FT-IR, UV–vis, TG and mass spectrom-
etry. The catalytic activity of this new cobalt complex for oxidation of
dibenzothiophene (DBT) was evaluated in n-dodecane (a middle distil-
2 2
late model compound) using H O as an oxidant. The acetonitrile
was taken as an extracting solvent for further extracting DBT sulfoxide
and sulfone. The novel peripherally substituted cobalt(II) complex
showed better oxidative desulfurization catalytic activity than cobalt
phthalocyanine and cobalt phthalocyaninetetrasulfonamide. DBT oxi-
th
dation kinetics were evaluated by lumped n - and first-order kinetic
models. The maximum removal of the DBT was found to be 85% at
the optimized dose and experimental conditions.
CONTACT Udai P. Singh
Roorkee, Uttarakhand 247667, India
ß 2019 Informa UK Limited, trading as Taylor & Francis Group
udaipfcy@Iitr.ac.in
Department of Chemistry, Indian Institute of Technology Roorkee,

JOURNAL OF COORDINATION CHEMISTRY
2983
1. Introduction
Due to environmental and health concerns, regulatory agencies and federal bodies
have introduced stringent fuel specifications. This has increased the demand for desul-
furization technologies that can limit the sulfur content to less than 10 ppm in the fin-
ished liquid fuels. Sulfur has negative effect on the air quality and human health.
From the initial crude pretreatment to crude distillations and finally in every secondary
petroleum refining process, sulfur is treated as egregious substance. Apart from foul
odor, its high corrosiveness to the reactor internals (column surface, plates, distribu-
tors, packing supports, etc.) increases the maintenance cost of refinery operations. In
addition, catalytic poisoning behavior increases the operation cost and damages the
exhaust devices [1].
In order to achieve deep desulfurization of fuels, many efforts have been made for
enhancing the desulfurization potential of conventional processes. Hydrodesulfurization
(HDS) has limited prospects in achieving deep desulfurization due to its incapability in effi-
ciently removing sterically hindered sulfur of the organic sulfur-containing species like
dibenzothiophene (DBT) and its derivatives. Apart from this, the high H cost and require-
2
ment of high temperature and pressure conditions have made research in other desulfur-
ization technologies like adsorption, oxidation, extraction and bio-desulfurization highly
interesting [2, 3]. Oxidative desulfurization (ODS) has gained the attention of many
researchers to achieve the deep desulfurization due to less energy requirements, ease of
operation and efficiency to work on the refractory sulfur species like DBT [4]. In the ODS,
the organo-sulfur compounds are oxidized to corresponding polar sulfoxides and sulfones
which can then be extracted in a polar immiscible organic solvent or removed by adsorp-
tion. Although ODS can be done by employing an oxidant only, e.g. hydrogen peroxide,
ozone, organic hydroperoxides and molecular oxygen, many other methods are in use to
increase the efficiency of oxidation using catalysts [5, 6], photocatalyst [7] and electro-
chemical oxidation [8]. For catalytic ODS, simple metal salts [9–11], metal complexes
[12–17], polymer encored metal complexes [18, 19], and polyoxometalates [20, 21] have
been examined. Some macrocyclic metal complexes were also found to possess good
catalytic activity in ODS, e.g. iron porphyrin and metal phthalocyanines [22, 23].
Phthalocyanine (Pc) is a symmetrical 18p-electron aromatic macrocycle, closely
related to naturally occurring porphyrins. Like porphyrins, the Pc macrocycle can make
complexes with metal ions, and metal phthalocyanines have attracted interest due to
their similarity in structure with the active site of the metalloenzymes [24, 25]. Apart
from their well-explored catalytic applications, several other uses have been explored
as dyes, pigments, solar cells, light emitting diodes, laser cancer therapy, etc. [26].
Several peripherally and non-peripherally substituted phthalocyanines have been pre-
pared recently because these substituents modulate their chemical, physical and cata-
lytic properties and their solubility [27]. Metal phthalocyanines with peripherally
substituted sulphonamides [28–30] are important merox catalysts for sweetening of
various petroleum products and have improved catalytic and solubility characteristics
as compared to phthalocyanines.
Efforts were also made to utilize these peripherally substituted phthalocyanine sul-
phonamides as oxidation catalysts [31]. To utilize this water-soluble tetra sulphona-
mide phthalocyanine complex as an ODS catalyst and also to enhance its catalytic

2
984
D. TRIPATHI ET AL.
activity by modulating the solubility characteristics, this manuscript presents a process
for synthesizing an oil-soluble peripherally substituted phthalocyanine sulphonamide,
i.e. N-alkylated cobalt phthalocyaninetetrasulfonamide by direct reaction of benzyl
alcohol with water-soluble cobalt phthalocyanine tetrasulfonamide.
N-alkylation of sulfonamide using alcohol as alkylating reagent has some advantages. First,
alcohol is readily available and second there is no generation of harmful byproducts as with
conventional methods using alky halide or aldehyde [8, 32]. Along with alcohol as alkylating
reagent, homogeneous or heterogeneous transition metal complexes catalyze this reaction
via hydrogen transfer methods [33, 34]. The cupric acetate/K CO system has been reported
2
3
to provide an excellent yield of secondary amines [35]. FeCl /K CO efficiently catalyzed cou-
2
2
3
pling between p-toluene sulphonamide and benzylic alcohol also [36]. However, the reaction
has not reported on the Pc macrocycle. In this work, N-benzylated cobalt phthalocyanine tet-
rasulfonamide was synthesized by benzyl alcohol reaction on cobalt tetrasulfonamide using
FeCl /K CO as catalyst. The complex was further evaluated as an ODS catalyst for DBT in
2
2
3
model fuel by H O . Comparison of catalytic activity has been made with the cobalt phthalo-
2
2
cyanine and cobalt phthalocyaninetetrasulfonamide.
2. Materials and methods
2.1. Chemicals and materials
4
-Sulfophthalic acid, CoCl ꢁ6H O, nitrobenzene, benzyl alcohol and cobalt(II) phthalo-
2
2
cyanine were purchased from Sigma-Aldrich, Bangalore, India. Ammonium molybdate,
cobalt(II) acetate tetrahydrate, FeCl , DBT, n-dodecane, ethanol and acetonitrile were
2
purchased from Merck Millipore (formerly E-Merck, Darmstadt, Germany). Thionyl chlor-
ide was obtained from Acros Organics, Mumbai, India. Other chemicals like ammonium
chloride, urea, methanol, pyridine, sodium hydroxide, K CO and acetone were of the
2
3
highest available grade and used without purification.
2.2. Synthesis of cobalt tetrasulfophthalocyanine 1
Cobalt tetrasulfophthalocyanine 1 was prepared by the previously described proced-
ure [37].
2.3. Synthesis of cobalt tetrachlorosulfophthalocyanine 2
Cobalt tetrachlorosulfophthalocyanine 2 was prepared as previously described proced-
ure [37].
2.4. Synthesis of cobalt phthalocyaninetetrasulphonamide 3
In preparation of cobalt phthalocyaninetetrasulphonamide [37], total wet cake of 5.0 g
cobalt tetrachlorosulfophthalocyanine 2 was homogeneously dispersed in 100mL
ꢀ
methanol/ice water (10%). The reaction mixture was stirred at 5–8 C and ammonia
gas was passed until the mixture was alkaline (pH 8–9). Pyridine (5 mL) was then
added and the mixture stirred at room temperature for 20 min. This was followed by

JOURNAL OF COORDINATION CHEMISTRY
2985
addition of 6 mL of 10% sodium hydroxide solution followed by stirring the reaction
ꢀ
mixture for 40 min at room temperature. The contents were then heated to 80 C and
held for 1 h. Thereafter sample was cooled to room temperature and poured over a
mixture of ice and concentrated hydrochloric acid keeping the pH acidic (2–3). The
precipitated cobalt phthalocyaninetetrasulphonamide was filtered, washed thoroughly
with cold water and dried in a vacuum oven to yield 4.4 g of the product. The blue
cobalt phthalocyaninetetrasulphonamide 3 was obtained in 95.8% yield (4.4 g). IR (KBr
ꢂ1
cm ): 3400, 3188, 1770, 1719, 1608, 1518, 1466, 1397, 1324, 1158, 921, 747. Anal.
Calcd for C H N O S Co, calcd: C, 43.29%; H, 2.27%; N, 18.93%. Found: C, 43.85; H,
3
2 20 12 8 4
2.05; N, 19.10. UV–vis: kmax 663.0, 331.0.
2.5. Synthesis of N-benzylated cobalt phthalocyaninetetrasulfonamide 4
Cobalt phthalocyaninetetrasulphonamide (171 mg, 0.25 mmol), benzyl alcohol (540
mg, 5.0 mmol), 5 mol. % FeCl (10 mg) catalyst and 20 mol. % K CO (69 mg) were
2
2
3
added to the reaction tube, respectively. Thereafter, the reaction was carried out by
ꢀ
using a round bottom flask (RB) under nitrogen at 135 C for 20 h, and then cooled to
room temperature. Acetone (20 mL) was added to dissolve the reaction mixture and
filtered through celite. Acetone and benzyl alcohol were removed under vacuum and
blue solid was obtained. The blue N-benzylated cobalt phthalocyaninetetrasulphona-
ꢂ1
mide 4 was obtained in 98% yield (3.7 g). IR (KBr cm ): 3403, 1659, 1583, 1519, 1466,
1
3
395, 1325, 1194, 920, 747. Anal. Calcd for C H N O S Co, Calcd: C, 57.73%; H,
60 44 12 8 4
.55%; N, 13.47%. Found: C, 58.21; H, 3.83; N 13.54. UV–vis: kmax 664.0, 332.0.
2.6. Characterization
Elemental analysis was performed on a Perkin Elmer Series II CHNS/O 2400 analyzer.
Fourier transform infrared spectra (FT-IR) were recorded on a Thermo-Nicolet 8700
–1
Research spectrophotometer with a 4 cm resolution using potassium bromide.
Spectra in the UV–vis region were recorded with a Varian Cary 50 UV–Vis spectropho-
tometer using 1 cm path length cuvettes at room temperature. Thermogravimetric
analyses (TGA) of samples were carried out using a Perkin Elmer EXSTAR TG/DTA 6300
ꢀ
in aluminum pans. Analysis was carried out from 30 to 900 C under nitrogen (200 mL
–1
ꢀ
min ) with heating rate 10 C/min. Mass spectra were measured on a MALDI TOF MS
AB Sciex, MALDI TOF/TOF 5800) using DHB (2,5-dihydroxybenzoic acid) as MALDI
matrix and analysis was performed in þ ve ion mode.
(
2.7. Catalytic desulfurization
N-benzylated cobalt phthalocyaninetetrasulfonamide 4 was evaluated as ODS catalyst
on a heterocyclic model sulphur compound, i.e. DBT taken in n-dodecane (a model
compound for fuel). H O was taken as an oxidant in different concentrations while
2
2
different amounts of acetonitrile were taken as an extractant for the formed sulfoxide
and sulfone. The batch oxidation experiments were performed at 1 atm pressure in a
glass reactor equipped with a stirrer. The cobalt complex amount was optimized by

2
986
D. TRIPATHI ET AL.
taking 0.05 mmol DBT in 100 mL n-dodecane, 0.5 mmol H O and 100 mL of aceto-
2
2
nitrile. After the catalyst optimization, sulfur mass proportion to oxidant was optimized
taking 0.05 mmol DBT and varying the H O2 ratio as 1:5, 1:10, 1:15 and 1:20.
2
Thereafter, the extractant amount was optimized by varying its ratio to n-dodecane as
ꢀ
1
:1, 1:2, 2:1 and 2.5:1. Effects of temperature (30, 40, 50 and 60 C) and reaction time
(15, 30, 60, 90 and 120 min) were studied at the optimized catalyst amount, oxidant
proportion and extractant amount. Comparative catalytic activity was evaluated at the
optimized conditions taking the cobalt phthalocyanine and cobalt phthalocyaninete-
trasulfonamide 3 in the same amount. DBT oxidation efficiency was estimated by ana-
lyzing n-dodecane layer using XRF (X-ray fluorescence) analysis with a Lab-X3500,
Oxford Instruments, UK, and also by estimating the DBT oxides in the extractant layer
by measuring the amount of evaporated content and analyzing the oxide ratio with a
Perkin-Elmer gas chromatograph-sulfur chemiluminescence detector (GC-SCD).
3. Results and discussion
3.1. Synthesis and characterization
The synthetic procedure is shown as Scheme 1. N-benzylated cobalt phthalocyaninete-
trasulfonamide was prepared from cobalt phthalocyaninetetrasulfonic acid by a multi-
step reaction sequence. First, cobalt phthalocyaninetetrasulfonic acid 1 was obtained
from 4-sulfophthalic acid, ammonium chloride, urea and CoCl reaction. Refluxing of
2
the mixture containing 1 with thionyl chloride readily gave cobalttetrachlorosulfoph-
thalocyanine 2 in almost quantitative yield. Amination using NH of 2 gave the cobalt
3
phthalocyaninetetrasulfonamide 3.
Elemental analyses, FT-IR, color, yield and other physical properties of 1, 2 and 3
were very similar to previous work [37]. The FeCl /K CO catalyst system was used for
2
2
3
N-alkylation of cobalt phthalocyaninetetrasulfonamide 4 with benzyl alcohol [36].
Literature reports that 1.0 mmol p-toluene sulphonamide needs 5 mmol benzyl alco-
hol and 5 mol. % of catalyst FeCl with 20 mol. % base, i.e. K CO for reaction under
2
2
3
inert atmosphere for 20 h to achieve 100% conversion. Therefore, the same ratio of
the reactant was taken for conversion of the cobalt phthalocyaninetetrasulfonamide to
N-benzylated derivative. Finally, dark blue crystalline powder of N-benzylated cobalt
phthalocyaninetetrasulphonamide 4 was obtained in 98% yield (3.7 g) and was charac-
terized by elemental analysis, FT-IR, TG, UV–vis spectroscopy and mass spectrometry.
Elemental analysis gives evidence in support of synthesis of 4. For
C H N O S Co, calculated values of various elements are: C, 57.73%; H, 3.55%; N,
6
0 44 12 8 4
1
3.47%, in good agreement with the found values as: C, 58.21; H, 3.83; N 13.54. The
synthesis of 4 was also confirmed by the FT-IR spectra (Figure 1). In the FT-IR spectrum
ꢂ1
of 3 (Figure 1(a)), the absorption bands at 3188 and 3400 cm were characteristic of
ꢂ1
the primary NH stretch while the band at 1608 cm was due to primary NH bending
ꢂ1
vibration. Peaks at 1770 and 1719 cm were also present due to the C¼O stretch
from anhydride impurities. C¼C stretches due to the aromatic nuclei from the phthalo-
ꢂ1
cyanine ring were present at 1608, 1518 and 1466 cm . Sulphonamide S ¼ O
ꢂ1
stretches are present at 1397, 1324 and 1158 cm . The S-N group is present at 921
ꢂ1
ꢂ1
cm and C-H def (aromatic) out of plane stretch at 747 cm . The FT-IR spectrum of

JOURNAL OF COORDINATION CHEMISTRY
2987
Scheme 1. Synthesis of 4.
(Figure 1(b)) was in accord with the structure shown in Scheme 1. Comparison of
4
the FT-IR spectra of 3 and 4 prove successful N-benzylation in the products, e.g. the
presence of the secondary NH group was indicated by an intense stretch at 3403
ꢂ1
cm and the observed characteristic vibrations of the secondary NH def at 1659 and
ꢂ1
1
583 cm
confirmed the N-benzylation. The aromatic C¼C stretching peaks were
ꢂ1
observed at 1583, 1519 and 1466 cm while the S ¼ O stretch from sulphonamide is
ꢂ1
at 1395, 1325 and 1194 cm along with the S-N band at 920 and aromatic C-H def

2
988
D. TRIPATHI ET AL.
Figure 1. FT-IR spectra of (a) 3 and (b) 4.
ꢂ1
(
out of plane) at 747 cm . No impurities due to anhydride are observed in 4, reveal-
ing the high purity of the sample after N-benzylation.
Compound 4 was also confirmed by observing difference in the thermal stability
curves. Figure 2 presents the recorded TG curves of weight loss of 3 and 4 with their
thermal stabilities 3 > 4 in nitrogen. The initial weight loss of 4 was due to water loss.
Major weight loss occurs due to decomposition of side chains of cobalt phthalocyanine
ꢀ
at 300 C; the second major weight loss is due to decomposition of the phthalocyanine
ꢀ
ꢀ
rings (starting at 650 C). Final residual weight at 800 C was lower for 4 (25%) than 3
43%) which was due to the higher content of decomposed benzylic side chains in 4,
(
and this phenomenon indirectly confirmed the successful N-benzylation.
Because of insolubility of 4 in aqueous solution, both cobalt phthalocyanines were
dissolved in DMSO and their electronic spectra were evaluated as shown in Figure 3.
Both showed electronic spectra with two strong absorption regions. In the B band
region, 3 and 4 showed peaks at 331 and 332 nm, respectively, with two shoulders at
255 and 300 nm. Both 3 and 4 showed intense Q band absorptions at 663 and 664
nm, respectively, together with a shoulder at 600 nm. Although the position of the
absorption bands did not change because of no significant reduction in electronic
density of the phthalocyanine, the intensity of both the B and Q band was enhanced
for the N-benzylated cobaltphthalocyaninetetrasulfonamide due to the increased solu-
bility of 4 in DMSO.
Mass spectrometry is a powerful method for confirming the structure of the pro-
posed N-benzylated phthalocyanines structure. The MALDI-TOF-MS spectrum of N-
benzylated cobaltphthalocyaninetetrasulfonamide 4 (Figure 4) shows different peaks

JOURNAL OF COORDINATION CHEMISTRY
2989
Figure 2. Thermogravimetric curves of 3 and 4.
and the m/z peak assignments are given in Table 1. Although using DHB (2,5-dihy-
droxybenzoic acid) as MALDI matrix, the molecular ion peak was not observed, inter-
pretation of the fragmentation pattern shows that benzyl alcohol reacted with the
FeCl /K CO catalyst system with N-benzylation of the cobaltphthalocyaninetetrasulfo-
2
2
3
namide leading to formation of N-benzylated cobaltphthalocyaninetetrasulfonamide 4.
3.2. Oxidative desulfurization studies
Catalytic potential of 4 was evaluated for ODS of refractory ograno-sulfur compounds.
DBT can be considered as representative for such refractory compounds, and the oxi-
dation reaction shown in Scheme 2 was used to examine the comparative catalytic
activity of 4 in comparison to cobalt phthalocyanine and cobalt phthalocyaninetetra-
sulphonamide 3. Many metal salts and complexes have already been reported as cata-
lysts for this reaction since the oxidized DBT sulfoxides and sulfone species can be
easily extracted in acetonitrile [12–14, 18–20, 22, 23]. H O was oxidant while n-dodec-
2
2
ane was used as the DBT oxidation reaction medium since it is a model fuel com-
pound. Reaction optimization was done with respect to the catalyst amount, oxidant
(
H O ) to sulfur mass proportion, ratio of extractant (acetonitrile) relative to the n-
2 2
dodecane, temperature and time of reaction (Table 2).
Experiments were performed in 100 mL n-dodecane solutions containing 0.5 mmol
DBT, 5.0 mmol H O and varying molar ratios of 4 to DBT (Figure 5(a)). Acetonitrile
2
2
ꢀ
(
100 mL) was added as an extractant and reaction was performed by stirring at 40 C
for 2 h under atmospheric pressure. Best activity of DBT removal of 81% was obtained
for catalyst:DBT molar ratio of 1:10. For catalyst:DBT molar ratio of 1:15 and 1:20,
amount of catalyst and thus active sites were not high enough to cause oxidation of
DBT to DBT sulfoxide and DBT sulfone. Similarly, at higher catalyst dosage, the clog-
ging/agglomeration of catalysts may have not allowed DBT to reach the active
sites [38].

2
990
D. TRIPATHI ET AL.
Figure 3. UV–vis spectra of (a) 3 and (b) 4 in DMSO.
Figure 4. MALDI-TOF-MS spectra of 4.

JOURNAL OF COORDINATION CHEMISTRY
2991
Table 1. The major peak assignment in MALDI-TOF-MS spectra of N-benzylated cobaltphthalocya-
ninetetrasulfonamide 4.
m/z
Species
m/z
Species
NH
N
N
O
O
O
S
S
S
O
O
O
N
N
8
06.95
N
N
N
N
820.99
N
N
N
N
N
C o
N
N
N
N
O
O
N
S
S
O
O
O
HN
O
O
NH
S
S
O
N
O
N
N
HN
O
NH
O
O
O
O
S
S
S
S
O
O
N
N
N
N
N
N
N
N
N
N
N
N
C o
N
C o
N
N
N
8
47.97
885.93
O
N
O
O
O
S
S
S
S
O
O
O
HN
O
NH
CH2
NH
H2C
HN
O
NH
O
O
O
O
S
S
S
9
01.78
S
925.87
O
O
O
N
N
N
N
N
N
N
N
N
N
C o
N
N
N
N
N
N
O
O
O
O
S
S
S
S
O
O
O
HN
NH
O
H2C
CH2
HN
O
O
O
CH2
O
S
S
H2C
O
NH
HN
O
N
O
O
S
S
N
N
N
N
N
N
C o
N
N
N
N
N
1005.84
N
N
9
38.94
N
O
O
N
S
S
O
O
O
O
S
S
HN
NH
O
HN
O
NH
H2C
CH2
The H O to sulfur molar proportion was optimized by doing oxidation experi-
2
2
ments with varying H O ratio as 1:5; 1:10; 1:15 and 1:20 keeping the catalyst:DBT
2
2
molar ratio ¼ 1:10; temperature ¼ 40 ˚C; time ¼ 2 h and acetonitrile:n-dodecane

2
992
D. TRIPATHI ET AL.
Scheme 2. Oxidation of DBT by H2O2 in the presence of 4.
Table 2. Percentage DBT oxidation and kinetics by different catalysts for DBT present in n-dodec-
ane along with H O at optimized conditions.
2
2
th
st
n
Order kinetics
1 Order kinetics
DBT removal Reaction
k
n
(1-n)
2
-1
2
Catalyst
efficiency (%)
order
((mmol/L) /min)
R
ARE (%)
k
1
(min )
R
ARE (%)
Without catalyst
Cobalt acetate
Complex 3
Cobalt phthalocyanine
Complex 4
38
51
58
73
85
6.8
7.1
5.1
3.7
3.3
1.760
13.441
1.497
0.959
1.904
0.930
0.968
0.941
0.979
3.91
4.73
7.30
7.88
0.0053
0.0118
0.0143
0.0215
0.0314
0.686 12.92
0.653 25.29
0.853 19.79
0.807 36.64
0.896 42.82
0.926 15.01
Note. ARE: average relative error.
Experimental conditions: catalyst: DBT molar ratio ¼ 1:10, DBT:H
2
O
2
molar ratio ¼ 1:15, acetonitrile:n-dodecane vol-
ume ratio ¼ 2:1, temperature ¼ 40 ꢀC, time ¼ 2.00 h.
volume ratio ¼ 1:1 (Figure 5(b)). At lower DBT:H O molar ratio (¼1:10), hydroxyl
2
2
radicals generated were not enough to oxidize the DBT. DBT:H O molar ratio of
2
2
1
:15 gave maximum 83% DBT and no further increase was observed by increas-
ing H O .
2
2
Different volume ratios of acetonitrile to the n-dodecane were tried while fixing the
catalyst:DBT molar ratio at 1:10, DBT:H O molar ratio at 1:15, temperature ¼ 40 ˚C
2
2
and reaction time ¼ 2 h; acetonitrile:n-dodecane volume ratio of 2:1 gave the best
extraction efficiency of 85% and no measurable increase was observed at higher
extractant volume ratios, e.g. 2.5:1. As per the results shown in Figure 5(c), the lower
volume of extractant (1:2) resulted in low oxidation of 56% only.
Optimization with respect to temperature and time were done as these are import-
ant parameters which affect the DBT oxidation. However, when the experiments were
performed at different reaction temperatures, it was observed that there is no effect
ꢀ
on increasing the temperature beyond 40 C (Figure 5(d)). H O is decomposed to
2
2
ꢀ
form oxygen instead of hydroxyl radicals at temperatures ꢃ 50 C [38]. This reduces
the DBT removal efficiency at higher temperatures.
ODS catalytic activity of 4 in comparison to cobalt phthalocyanine and 3 was exam-
ined. The higher activity of 4 in comparison to 3 may be explained on the basis of
increased solubility of 4 in n-dodecane due to N benzyl peripheral substituents.
Higher activity than cobalt phthalocyanine can be explained on the basis of slightly
reduced electron density around the active metal center due to the presence of elec-
tron withdrawing peripheral N-benzylated sulphonamide moieties. The active metal

JOURNAL OF COORDINATION CHEMISTRY
2993
Figure 5. Effect of various parameters on DBT oxidation efficiency in presence of 4 as catalyst. (a)
catalyst:DBT molar ratio; DBT:H O molar ratio ¼ 1:15, acetonitrile:n-dodecane volume ratio ¼ 2:1,
2
2
ꢀ
temperature ¼ 40 C, time ¼ 2.00 h. (b) DBT:H O molar ratio; catalyst:DBT molar ratio ¼ 1:10;
2
2
ꢀ
acetonitrile:n-dodecane volume ratio ¼ 2:1, temperature ¼ 40 C, time ¼ 2.00 h. (c) Acetonitrile:
n-dodecane volume ratio; catalyst:DBT molar ratio ¼ 1:10; DBT:H O molar ratio ¼ 1:15, tempera-
2
2
ꢀ
ture ¼ 40 C, time ¼ 2.00 h. (d) Temperature; catalyst:DBT molar ratio ¼ 1:10; DBT:H O molar
2
2
ratio ¼ 1:15, acetonitrile:n-dodecane volume ratio ¼ 2:1, time ¼ 2.00 h.
center is more electron deficient in 4 compared to unsubstituted cobalt phthalocyan-
ine, leading to higher catalytic efficiency.
3.3. Comparative assessment and kinetics
In order to evaluate the ODS catalytic potential of 4 in comparison to 3, cobaltphtha-
locyanine and simple cobalt acetate experiments were performed at optimized reac-
tion conditions of catalyst:DBT ratio of 1:10 (mmol), DBT:H O ratio (mmol) of 1:15,
2
2
ꢀ
acetonitrile:n-dodecane ratio of 2:1, 40 C temperature and time varying from 15 min
to 2 h (Figure 6). Under these conditions, 4 is the best catalyst followed by the
cobaltphthalocyanine and 3 showing a maximum of 85, 73 and 58% DBT oxidation,
respectively. Cobalt acetate shows very low activity of 38% DBT oxidation (Table 2).
The higher activity of 4 in comparison to 3 may be explained on the basis of
increased solubility of 4 in n-dodecane due to N benzyl peripheral substituents.

2
994
D. TRIPATHI ET AL.
Figure 6. DBT oxidation kinetics by different catalysts for DBT present in n-dodecane along with
H O at optimized conditions. Experimental conditions: catalyst:DBT molar ratio ¼ 1:10; DBT:H O
2
2
2 2
ꢀ
molar ratio ¼ 1:15, acetonitrile:n-dodecane volume ratio ¼ 2:1, temperature ¼ 40 C; time ¼
2
.00 h.
For performing kinetic study, residual DBT content in the extract layer was noted
after various reaction times as shown in Figure 6. Maximum oxidation could be
achieved in 1 h (Figure 6) which does not increase in 2 h; 1 h gives maximum oxida-
th
st
tion of 85%. The n order and 1 -order reaction models represented by Equations (1)
th
and (2) were chosen to determine the oxidation kinetics [38, 39]. n -order kinetic
expression can be written as [40]:
C t1 ꢂnꢂC
1ꢂn
¼ ð1ꢂnÞknt
(1)
0
where, C is the residual concentration of DBT at time t (mmol/L), C is the initial con-
t
o
centration of DBT (mmol/L), n is the order of reaction and k is reaction constant for
n
th
the n order reaction. First-order kinetic expression can be written as:
Ct ¼ Co exp ðꢂk1tÞ
(2)
where, k is the first-order rate constant. A non-linear regression method was used to
1
solve Equations (1) and (2) by minimizing the average relative error as given by:
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
n
X ꢀ
1
n
00
ðCt, exp , i ꢂ Ct, cal, iÞ
Ct, exp , i
ꢀ
ꢀ
ARE ¼
(3)
i¼1
where, Cexp and Ccat are the experimental and calculated value of DBT concentrations
in mmol/L. Table 2 shows the values of n, k , kn and ARE for different catalysts.
1
Comparison of three kinetic models was carried out by plotting a graph between
experimental values and calculated values of C as shown in Figure 4. Data repre-
t
2
sented in comparison of R and ARE values in Table 2 for two models show that the
n -order kinetic model better represented the kinetic data. Order of reaction and the
th
first-order rate constant were least with 4 as catalyst indicating its efficacy over other
tested catalysts.

JOURNAL OF COORDINATION CHEMISTRY
2995
4. Conclusion
Oil-soluble N-benzylated cobalt phthalocyaninetetrasulfonamide (4) was synthesized
by reaction of benzyl alcohol on water-soluble cobalt phthalocyaninetetrasulfonamide
using the FeCl /K CO catalyst system. This N-benzylated phthalocyanine was charac-
2
2
3
terized by elemental analysis, FT-IR, UV–vis, TG and mass spectrometry. It was further
used to remove a refractory sulfur compound, DBT, via oxidative-extractive desulfuriza-
tion using H O as an oxidant and acetonitrile as an extracting solvent. Effects of vari-
2
2
ous parameters were studied and the optimized parameters were: 4:DBT molar ratio ¼
1
:10; DBT:H O molar ratio ¼ 1:15, acetonitrile:n-dodecane volume ratio ¼ 2:1, tem-
2
2
ꢀ
th
perature ¼ 40 C; time ¼ 2 h. Oxidation kinetics were best represented by the n -
order kinetic model with n ¼ 3.3 using 4 as catalyst. At the optimized conditions, max-
imum removal of the DBT was 85% by 4.
Acknowledgements
The author kindly acknowledges the Director, IIT Roorkee and Director, CSIR-IIP for his permis-
sion to carry out the doctoral research. The authors thank the analytical science division and
institute instrumentation center of the institutes for providing the analysis.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
[
[
[
1] M.F. Ali, A. Al-Malki, S. Ahmed. Fuel Process. Technol., 90, 536 (2009).
2] I.V. Babich, J.A. Moulijn. Fuel, 82, 607 (2003).
3] M. Muzic, Katica, K. Sertic-Bionda, T. Adzamic. Clean Technol. Environ. Policy, 14, 283
(
2012).
4] S. Otsuki, T. Nonaka, N. Takashima, W. Qian, A. Ishihara, T. Imai, T. Kabe. Energy Fuels, 14,
232 (2000).
[
1
[
[
[
[
[
5] V.C. Srivastava. RSC Adv., 2, 759 (2012). doi:10.1039/C1RA00309G
6] S. Kumar, V.C. Srivastava, S.M. Nanoti. Sep. Purif. Rev., 46, 319 (2017).
7] J. Zhang, D.S. Zhao, L.Y. Yang, L. Yongbo. Chem. Eng. J., 156, 528 (2010).
8] G.W. Lamb, J.M.J. Williams. Chim. Oggi, 26, 17 (2008).
9] D. Xu, W. Zhu, H. Li, J. Zhang, F. Zou, H. Shi, Y. Yan. Energy Fuels, 23, 5929 (2009).
[
10] O. Gonz ꢀa lez-Garc ꢀı a, L. Cede n~ o-Caero. Catal. Today, 148, 42 (2009).
[11] S. Murata, K. Murata, K. Kidena, M. Nomura. Energy Fuels, 18, 116 (2004).
[12] G. Silva, S. Voth, P. Szymanski, E.M. Prokopchuk. Fuel Proc. Technol., 92, 1656 (2011).
[13] A.V. Anisimov, E.V. Fedorova, A.Z. Lesnugin, V.M. Lesnugin, L.A. Aslanov, V.R. Rybakov,
A.V. Tarakanova. Catal. Today, 78, 319 (2003).
[14] W. Zhu, H. Jiang, X. Li, Y. Yan, J. Lu, J. Xia. Energy Fuels, 21, 2514 (2007).
[15] S. Kumar, V.C. Srivastava, A. Kumar, S.M. Nanoti. RSC Adv., 6, 25293 (2016).
[16] S. Erdogan, S. Koytepe, T. Seckin, Y. Onal, S. Vural, C.A. Basar. Clean Technol. Environ.
Policy, 16, 619 (2014).
[
[
17] W.N.W. Abdullah, W.A.W.A. Bakar, R. Ali, Z. Embong. Clean Techn. Environ. Policy, 17, 433
(
2015).
18] M.R. Maurya, A. Arya, A. Kumar, M.L. Kuznetsov, F. Avecilla, J.C. Pessoa. Inorg. Chem., 49,
586 (2010).
6

2
996
D. TRIPATHI ET AL.
[19] L. Wang, S. Li, H. Cai, X. Yanyan, W. Xihui, C. Yujing. Fuel, 94, 165 (2012).
[20] C. Komintarachat, W. Trakarnpruk. Ind. Eng. Chem. Res., 45, 1853 (2006).
[21] W.N.A.W.M. Mokhtar, W.A.W.A. Bakar, R. Ali, A.A.A. Kadir. Clean Technol. Environ. Policy, 17,
1487 (2015).
[
[
22] X.R. Zhou, J. Li, N.X. Wang, K. Jin, W. Ma. Fuel Process. Technol., 90, 317 (2009).
23] R. Zhao, J. Wang, D. Zhang, Y. Sun, B. Han, N. Tang, J. Zhao, K. Li. ACS Sustainable Chem.
Eng.5, 2050 (2017).
[
[
24] F.H. Moser, A.L. Thomas. The Phthalocyanine, CRC, Boca Raton (1983).
25] C.C. Leznoff, A.B.P. Lever. Phthalocyanines: Properties and Applications, VCH Publishers,
New York (1993).
[26] N.B. McKeown. Phthalocyanine Materials: Synthesis, Structure, and Function, Cambridge
University Press, Cambridge (1998).
[
[
27] F. Dumoulin, M. Durmu s¸ , V. Ahsen, T. Nyokong. Coord. Chem. Rev., 254, 2792 (2010).
28] B. Sain, S.N. Puri, G. Das, B.P. Baloni, S. Kumar, A. Kumar, V.K. Kapoor, V.K. Bhatia, T.S.R.P.
Rao, G.P. Rai. US Patent No. A1 (2002).
[29] G. Das, B. Sain, S. Kumar, M.O. Garg, G. Murali Dhar. Catal. Today, 141, 152 (2009).
[30] T.V. Rao, K.N. Rao, S.L. Jain, B. Sain. Synth. Commun., 32, 1151 (2002).
[31] T.V. Rao, P.M. Krishna, D. Paul, B.R. Nautiyal, J. Kumar, Y.K. Sharma, S.M. Nanoti, B. Sain,
M.O. Garg. Pet. Sci. Technol., 29, 626 (2011).
[
[
32] J.W. Kim, K. Yamaguchi, N. Mizuno. J. Catal., 263, 205 (2009).
33] F. Shi, M.K. Tse, S. Zhou, M.-M. Pohl, J. Radnik, S. H u€ Bner, K. J €a Hnisch, A. Br u€ Ckner, M.
Beller. J. Am. Chem. Soc., 131, 1775 (2009).
[
[
34] M.H.S.A. Hamid, P.A. Slatford, J.M.J. Williams. Adv. Synth. Catal., 349, 1555 (2007).
35] X. Cui, F. Shi, M.K. Tse, D. G o€ rdes, K. Thurow, M. Beller, Y. Deng. Adv. Synth. Catal., 351,
2949 (2009).
[36] X. Cui, F. Shi, Y. Zhang, Y. Deng. Tetrahedron Lett., 51, 2048 (2010).
[37] B.B. Agrawal, S.F. Fish, S.N. Puri, P. Gupta, G.C. Joshi, R. Krishna. Ind. J. Technol., 25, 397
(1987).
[38] S. Kumar, V.C. Srivastava, R.P. Badoni. Int. J. Chem. React. Eng., 12, 1 (2014). doi:10.1515/
ijcre-2013-0095
[
[
39] S. Singh, V.C. Srivastava, S. Gautam. Int. J. Chem. React. Eng., 14, 539 (2016).
40] S. Pandey, V.C. Srivastava. Pet. Sci. Technol., 36, 40 (2018).