Catalytic synthesis of 2-methyl-1,4-naphthoquinone (vitamin K3) over silica-supported aminomethyl phosphine-Ru(II), Pd(II), and Co(II) complexes

Article abstract of DOI:10.1080/10426500903061533

Ru(II), Pd(II), and Co(II) complexes of the free ditertiary aminomethylphosphine ligand, N,N-bis(diphenylphosphinomethyl) aminopropyltriethoxysilane [(EtO)3Si(CH2)3 N(CH2PPh2)2] (DIPAPTES), and its SiO2-DIPAPES have been synthesized under a nitrogen atmosphere using Schlenk techniques. All the complexes were used as catalysts for the oxidation of 2-methyl naphthalene (2MN) to give 2-methyl-1,4-naphthoquinone (vitamin K3, menadione, 2MNQ) in the presence of hydrogen peroxide as a clean and cheap oxidant. The catalytic synthesis of vitamin K3 was investigated using both homogeneous catalysis with free complexes and heterogeneous catalysis with silica-supported complexes. [(DIPAPTES)PdCl2] and its silica-supported form showed the best catalytic activity for the selective oxidation of 2-methyl naphthalene to 2-methyl-1,4-naphtoquinone compared to the other metal complexes. 2MNQ yield reached 52.26% with the 2MN conversion of 90.52% using complex [(DIPAPTES)PdCl2] and 58.59% with the 2MN conversion of 99.56% using the silica supported [SiO2(DIPAPES)PdCl2] complex for 1 h. Recycling was investigated for the silica-supported Pd(II) complex and compared with the classical production of vitamin K3. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500903061533

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Catalytic Synthesis of 2-Methyl-1,4-
Naphthoquinone (Vitamin K3) Over Silica-
Supported Aminomethyl Phosphine-
Ru(II), Pd(II), and Co(II) Complexes
a
b
c
Serhan Uruş , Mustafa Keleş & Osman Serindağ
a University-Industry-Public, Research-Development and Application
Center, Sütçü İmam University, Kahramanmaraş, Turkey
b Department of Chemistry, Faculty of Science and Letters,
Osmaniye Korkut Ata University, Osmaniye, Turkey
c Department of Chemistry, Faculty of Science and Letters,
University of Çukurova, Adana, Turkey
Version of record first published: 02 Jul 2010.
To cite this article: Serhan Uruş , Mustafa Keleş & Osman Serindağ (2010): Catalytic Synthesis of 2-
Methyl-1,4-Naphthoquinone (Vitamin K3) Over Silica-Supported Aminomethyl Phosphine-Ru(II), Pd(II),
and Co(II) Complexes, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:7, 1416-1424
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Phosphorus, Sulfur, and Silicon, 185:1416–1424, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903061533
CATALYTIC SYNTHESIS OF
2-METHYL-1,4-NAPHTHOQUINONE (VITAMIN K3) OVER
SILICA-SUPPORTED AMINOMETHYL PHOSPHINE-Ru(II),
Pd(II), AND Co(II) COMPLEXES
Serhan Urus¸,1 Mustafa Keles¸,2 and Osman Serindag˘3
1University-Industry-Public, Research-Development and Application Center,
˙
Su¨tc¸u¨ Imam University, Kahramanmaras¸, Turkey
2Department of Chemistry, Faculty of Science and Letters, Osmaniye Korkut Ata
University, Osmaniye, Turkey
3Department of Chemistry, Faculty of Science and Letters, University of C¸ ukurova,
Adana, Turkey
Ru(II), Pd(II), and Co(II) complexes of the free ditertiary aminomethylphosphine
ligand, N,N-bis(diphenylphosphinomethyl)aminopropyltriethoxysilane [(EtO)3Si(CH2)3
N(CH2PPh2)2] (DIPAPTES), and its SiO2-DIPAPES have been synthesized under a
nitrogen atmosphere using Schlenk techniques. All the complexes were used as catalysts
for the oxidation of 2-methyl naphthalene (2MN) to give 2-methyl-1,4-naphthoquinone
(vitamin K3, menadione, 2MNQ) in the presence of hydrogen peroxide as a clean and cheap
oxidant. The catalytic synthesis of vitamin K3 was investigated using both homogeneous
catalysis with free complexes and heterogeneous catalysis with silica-supported complexes.
[(DIPAPTES)PdCl2] and its silica-supported form showed the best catalytic activity for the
selective oxidation of 2-methyl naphthalene to 2-methyl-1,4-naphtoquinone compared to the
other metal complexes. 2MNQ yield reached 52.26% with the 2MN conversion of 90.52% us-
ing complex [(DIPAPTES)PdCl2] and 58.59% with the 2MN conversion of 99.56% using the
silica supported [SiO2(DIPAPES)PdCl2] complex for 1 h. Recycling was investigated for the
silica-supported Pd(II) complex and compared with the classical production of vitamin K3.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Catalyst design; menadione; oxidation; phosphines; quinones; vitamin K3
INTRODUCTION
Functionalized phosphine transition metal complexes have been used as catalysts
to generate highly enantioselective products in many asymmetric organic processes.1–5
Chiral nitrogenous phosphine ligands and their transition metal complexes have become
Received 17 March 2009; accepted 22 May 2009.
We would like to thank to Mr. Nafiz Usta, Mr. Latif C¸ ayhan, and Mrs. Serap Go¨kmen of Oxyvit Kimya
San.Tic.A.S¸. for their all support. The authors also thank C¸ ukurova University for financial support (Project No:
FEF2007D007).
Address correspondence to Osman Serindag˘, Department of Chemistry, Faculty of Science and Letters,
University of C¸ ukurova, Adana, Turkey. E-mail: osmanser@cu.edu.tr
1416

SYNTHESIS OF VITAMIN K3
1417
increasingly important due to their improved catalytic activity.4 Catalytically efficient
chelated palladium phosphine complexes have also been developed for organic synthesis.1,5
Due to the fact that phosphines play an efficient role for the transportation of oxygen
to substrate via a transition metal center, scientists have focused on the synthesis of novel
phosphine–metal complexes and investigation of their oxidative catalytic properties.5
There are several advantages of heterogeneous catalysts compared to homogeneous
catalysts, such as reusage in catalytic systems, catalytic selectivity, oxidation efficiency,
reaction time, and economy.
Members of the vitamin K group, which are naphthoquinones derivatives, are effective
for blood coagulation. Vitamin K3 is a synthetic member of the vitamin K group. However,
vitamin K3 is more active than other vitamin K derivatives for blood coagulation.6 The
human body synthesizes vitamin K in its intestine by microorganisms, but some animals
must get vitamin K from nutrients. Vitamin K3 has five commercial products used for premix
in food: menadione sodium bisulfite (MSB), menadione sodium bisulfite stabilized (MSB
stab.), menadione sodium bisulfite complex (MSBC), menadione dimethyl pyrimidinol
bisulfite (MPB), and menadione nicotinamide bisulfite (MNB). MSB that is soluble in
water is the sulfonated form of menadione.6,7
In the classical production process, vitamin K3 is produced via a stoichiometric oxi-
dation reaction of 2-methyl naphthalene by CrO3 in sulfuric acid with the yield of 30–60%.
At the end of this reaction, 18,000 g of waste including chromium that is environmentally
hazardous with low selective oxidation efficiency is obtained to yield 1,000 g of product.
From an environmental point of view, the treatment of chromium containing waste is quite
difficult.8,9
Vitamin K3 can be cleanly synthesized in high yield using hydrogen peroxide as
clean oxidant in acetic acid via transportation of oxygen in the presence of a catalyst6–11
(Scheme 1).
CH3COOH + H2O2 ꢀ CH3COOOH + H2O
COOH
CH 2OH
CHO
+
+
O
O
O
O
CH 3
CH 3
CH 3
+
2− methylnaphthalene
6-Methyl-1,4-Naphthoquinone
2-methyl-1,4-Naphthoquinone
O
O
O
CH 3
CH 3
CH 3
CleavageProducts
O
O
RadicalCouplingProduct
Scheme 1 Multiple pathways in the oxidation of 2-methyl naphthalene.6

1418
S. URUS¸ ET AL.
In this study, transition metal complexes of aminomethylphosphine and its silica-
supported form have been synthesized in order to investigate their catalytic activities in
vitamin K3 synthesis reaction.
RESULTS AND DISCUSSION
Catalyst Preparation
The Pd(II) complexes of aminomethylphosphine ligands [(EtO)3Si(CH2)3N(CH2
PPh2)2] (L1), and its silica supported form (L2), were synthesized according to the lit-
erature.12–17 L1 and L2 complexes of Ru(II) were synthesized as reported earlier.17 The
Co(II) complexes of L1, L2 are novel (Scheme 2).
Scheme 2 Synthesis of Ru(II), Pd(II), and Co(II) complexes of free aminomethylphosphine ligand (L1) and its
silica-supported form (L2).
The reaction of the complexes of Ru(II), Pd(II), and Co(II) with L1 and L2 gave
red, pale yellow, and blue solids, respectively. Pd(II) and Co(II) complexes have four
coordination, and Ru(II) complex has six coordination. The complexes are soluble in
dichloromethane, ethanol, dimethyl sulfoxide, and glacial acetic acid.
All the complexes were synthesized by reacting ligand L1 and L2 with metal com-
pounds in toluene and ethyl alcohol by refluxing for 2–12 h. All products were purified by
washing with toluene and acetone, respectively.
The P-aryl bands in ligands were assigned to about 1078 cm−1 and 3032 cm−1 in the
FT-IR spectra. The phosphonyl band and the P-aryl bands of the metal complexes shift to

SYNTHESIS OF VITAMIN K3
1419
1096 cm−1 and 3051 cm−1 for complex 3, 1088 cm−1 and 3145 cm−1 for complex 4, 1083
cm−1 and 3053 cm−1 for complex 5, 1099 cm−1 and 3344 cm−1 for complex 6, 1093 cm−1
and 3344 cm−1 for complex 7, and 1096 cm−1 and 3459 cm−1 for complex 8, respectively.
Assignment of these results showed that P-aryl wave numbers of the metal complexes
shifted to higher values comparing with uncoordinated ligand. The shifted spectra of the
ligand incorporated into all the complexes show that the ligand coordinated to metal ions.15
The proton signals of the phenyl ring in the phosphine ligand and their metal com-
1
plexes in H NMR spectra were observed as multiplet at around 7.20–7.46 ppm. The
multiple peaks of P-CH2-N and NCH2CH2 protons of phosphine and their complexes were
present at around 2.41–2.52 ppm, which is in agreement with reported studies.15,16 The 1H
NMR spectra showed no remarkable differences between the uncoordinated ligands and
their metal complexes. The NCH2 resonances of the complexes are only slightly shifted to
low field compared to the free ligands, indicating that the N atom is not coordinated, as
also reported in the literature.13–15
31P NMR spectra of all the metal phosphine complexes showed more shielded signals
compared with the uncoordinated aminomethylphosphine ligand. The coordination shift
values of the complexes (ꢀ), as varied depending on the metal centers and the chemical
structures of the ligands, showed that the ligands were bound to metal centers via a P–P
bidentate to give chelated complexes rather than M–N interaction (Table I).13–17 Elemental
analysis results of the catalysts show that the L:Ru(II) ratio is 2:1, and the L:Pd (II) and
L:Co (II) ratios are both 1:1.
Catalytic Activity
Homogeneous and heterogeneous catalyst experiments were carried out using similiar
processes. In the catalytic process, 2MN and catalyst dissolved in glacial acetic acid were
pumped into the reactor, oxidation reaction was started when hydrogen peroxide and
sulfuric acid solution was control pumped onto the substrate mixture. The temperature was
controlled with a water circulator, and the reaction mixture was stirred vigorously. The
oxidation reaction temperature was held between 60 10◦C, since it was very difficult to
control at a constant temperature.
The results of the blank reactions indicated that the 2MNQ yield 3.7% with 30.5%
2MN conversion, 5.3% with 40.2% 2MN conversion, and 15.9% with 68.7% 2MN con-
version analyzed at 30 min, 60 Min, and 90 min. Furthermore, when 5, 10, and 15 mL
hydrogen peroxide volumes were used in different experiments and studied for 60-min
reaction time, 2MNQ yield and 2MN conversions were 3.1% and 22.4%, 5.4% and 40.9%,
10.8% and 69.6%, respectively.
Table I Coordination shift values of the complexes (ꢀ) (δL1: –28.18 ppm, δL2: –27.00 ppm)
31P NMR
(ppm)
31P-NMR
(ppm)
ꢀ (δcomplex- δfree ligand)
Ligands
L1
Complexes
(ppm)
–28.18
3
4
5
6
7
8
27.11
7.60
29.58
26.24
9.90
55.29
35.88
57.76
53.24
36.90
59.90
L2
–27.00
32.90

1420
S. URUS¸ ET AL.
Phosphine–M complexes (M: Pd, Pt) are known as oxidative catalysts in the presence
of peroxides. In the first step of the catalytic process, 2MN is oxidized to 2-methyl-1-
naphthol and then to 2-methyl-1,4-naphthalenediol. The first step is the rate-determining
step because it is slow (Scheme S1, available online in the Supplemental Materials)5,18,19
and needs to be controlled using a suitable catalyst and oxidant amount in order to increase
the 2MNQ selectivity.
Oxidation times were monitored with an interval of 30 min for all complexes. An
aliquot of the reaction mixture was taken from the reactor at 30 min, 60 Min, and 90 min and
extracted with the appropriate amount of acetone. According to the possible mechanism of
the oxidation of 2-methyl naphthalene, when the reaction time is increased over 1 h, further
oxidation can form and some other oxidized organic compounds can arise. Based on the
experimental results, 1 h reaction time has been found to be adequate for the oxidation of
2-methyl naphthalene (Figure 1).
120
110
100
90
120
110
100
90
80
80
70
70
60
60
50
50
40
40
0,25
0,75
1,25
1,75
0,25
0,75
1,25
1,75
Reaction time (h)
Reaction time (h)
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
60
60
50
40
30
20
10
0
50
40
30
20
10
0
0,25
0,75
1,25
1,75
0,25
0,75
1,25
1,75
Reaction Time (h)
Reaction Time (h)
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
7
6
5
4
3
2
1
0
20
18
16
14
12
10
8
6
4
2
0
0,25
0,75
1,25
1,75
0,25
0,75
1,25
1,75
Reaction Time (h)
Reaction Time (h)
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
Complex 8
Figure 1 Influence of the reaction time on the oxidation of 2-methyl naphthalene. Temperature: 60 10◦C,
H2O2 = 10 mL, 2-methyl naphthalene = 3,15 g.

SYNTHESIS OF VITAMIN K3
1421
120,00
100,00
80,00
60,00
40,00
20,00
120
100
80
60
40
20
0
0,00
0,25
0,50
1,00
0,05
70,25
20,50
0,10
90,42
52,26
3,83
0,20
68,23
21,56
0,05
91,35
52,41
2,93
99,67
55,14
3,92
% Conversion
99,45
% Conversion
% 2MNQ
% 2MNQ
54,15
% 6MNQ
3,92
% 6MNQ
Catalyst Amount (g)
Catalyst Amount (g)
(4)
(7)
Figure 2 Influence of the amount of the catalysts 4 and 7 on the oxidation of 2-methyl naphthalene. Temperature:
60 10◦C, H2O2 = 10 mL, 2-methyl naphthalene = 3.15 g.
The oxidation of 2-methyl naphthalene was also studied by changing the amount of
the catalyst 4 from 0.05 g to 0.20 g and solid supported catalyst complex 7 from 0.25 g
to 1.0 g in each reaction, respectively. Because of the very fast oxidation of naphthol
derivatives to 2-methyl-1,4-naphthoquinone and 6-methyl-1,4-naphthoquinone (isomer),
and also to other organic compounds, 2-methyl-1,4-naphthoquinone selectivity reached its
maximum value using 0.1 g of catalyst for complex 4 and 0.5 g for complex 7, respectively.9
The amount of 2-methyl-1,4-naphthoquinone increases together with a slight increase
in amount of isomer (6-methyl-1,4-naphthoquinone) with increased amount of catalyst
(Figure 2).
γ = k [cat][H2O2] formula can be simplified if the catalyst amount is a constant;
reaction rate is first-order with equation γ = k’[H2O2]. According to the equation, hydrogen
peroxide concentration directly affects the reaction.20–22 In Figure 3, conversion of 2-methyl
naphthalene and 2-methyl-1,4-naphthoquinone vs. three different volumes of hydrogen
peroxide are displayed using metal complexes 4 and 7 in the oxidation reaction. The
increase in the concentration of hydrogen peroxide increased 2MNQ selectivity and 2MN
conversion. H2O2 amount certainly depends on participation of the catalyst, because, in
the oxidation mechanism, H2O2 is activated by formation of metal-peroxo pre-complexes,
which are a prerequisite for oxygenation activity.9
Although complex 5 and its silica-supported form complex 8 showed medium ox-
idative catalytic activity, complex 3 and complex 6 did not exhibit any catalytic effect.
Complex 4, which is a free complex, has been found as the best catalyst for the selective
oxidation of 2-methyl naphthalene to 2-methyl-1,4-naphthoquinone in comparison with
the other complexes. The selective catalytic activity of the silica-supported forms of these
complexes were similar to free forms of them (Table S1, Supplemental Materials). Due

1422
S. URUS¸ ET AL.
120,00
100,00
80,00
60,00
40,00
20,00
0,00
120,00
100,00
80,00
60,00
40,00
20,00
0,00
5,00
54,21
21,30
0,03
10
15
5,00
55,80
23,40
0,05
10
90,23
51
15
92,87
52,14
3,11
98,75
53,32
3,24
% Conversion
% 2MNQ
99,55
54,2
3,85
% Conversion
% 2MNQ
% 6MNQ
3,02
% 6MNQ
H2O2 (mL)
H2O2 (mL)
(4)
(7)
Figure 3 Influence of the concentration of H2O2 on the oxidation of 2-methyl naphthalene. Temperature: 60
10◦C, H2O2 = 10 mL, 2-methyl naphthalene = 3.15 g, 0.1 g complex 4 and 0.5 g complex 7.
to the fact that the complex 7 heterogeneous catalyst system has some advantages (easily
recyclable, and clean, cheap oxidant with high 2MNQ yield), it was worthwhile to inves-
tigate catalytic recycling for complex 7. Thus, three recycling oxidation experiments were
carried out using complex 7.
The results of the recycling process showed that complex 7 had almost the same
selective catalytic activity in the oxidation of 2-methyl naphthalene in first two recycle. In
the third recycle, catalytic activity slightly decreased. Despite the decrease in activity in
the last period, the average results of three catalytic recycles have indicated that selective
catalytic synthesis of vitamin K3 using silica supported Pd(II)-phosphine, complex 7, is
efficient in comparison to the classical process of synthesizing vitamin K3 (Table S2,
Supplemental Materials).
Acetic acid and sulfuric acid join in the oxidation mechanism together with the cata-
lysts by transporting oxygen to the aromatic ring. In comparison with classical production,
modern synthesis of vitamin K3 will be applicable and cheaper in the near future.
EXPERIMENTAL
All synthesis reactions were carried out under nitrogen atmosphere using the Schlenk
method. The 1H NMR and 31P NMR spectra were recorded at 25◦C in DMSO-d6 and CDCl3
using a Varian Mercury 200 MHz NMR spectrometer. Solid NMR spectra were measured
using solid NMR Bruker Superconducting FT-NMR Spectrometer Avance TN 300 MHz
WB. The infrared spectra were recorded with a Perkin Elmer Spectrum RXI/FT-IR Sys-
tem. Elemental analyses were performed using a LECO CHNS 932 instrument. During
oxidation experiments, the products were analyzed on a Varian 3800 GC-FID with Silicone
OV-17 packed column and characterized by Perkin Elmer Clarus 500 GC-MS with Elite
5-MS capillary column. Metal contents were determined by Perkin Elmer Analyst 400
Atomic Absorption. All chemicals and reagents were purchased from Merck, Riedel de

SYNTHESIS OF VITAMIN K3
1423
Haen, Fluka, and Sigma, and all solvents were dried using established procedures and im-
mediately distilled under nitrogen atmosphere prior to use. [(EtO)3Si(CH2)3N(CH2PPh2)2]
(L1) and its silica supported form (L2) ligands and their metal complexes [Ru(L1)2Cl2]
(3), [Pd(L1)Cl2] (4), [Ru(L2)Cl2] (6), and [Pd(L2)Cl2] (7) were synthesized according to
the literature.12–17 0.150–0.250 mm, 170–300 m2/g silica was used as solid support for
heterogeneous catalysts.
Preparation of [Co(L1)Cl2] (5)
L1 (1.3 g, 2.1 mmol) was added to a stirred solution of [CoCl2.6H2O] (0.5 g; 2 mmol)
in CH2Cl2 (10 mL). The mixture was stirred and refluxed for a further 2 h. The addition of
diethyl ether gave a blue solid, which was then filtered off and dried. Yield 1.226 g (82%). El-
emental analysis calculation for [C35H45NO3P2Cl2SiCo]: C, 56.20, H,6.10, N, 1.87; Found:
C, 56.81, H, 5.92, N, 1.80%. 1H NMR (CDCl3, 25◦C): δ 7.30 [m, 20H, 4Ph], 3.73 [m, 2H,
SiCH2], 1.36 [m, 2H, SiCH2CH2], 2.41 [br, 6H, SiCH2CH2CH2N and P CH2 N], 3.73 [m,
2H, OCH2], 1.20 [m, 3H, OCH2CH3] ppm. 31P-NMR (CDCI3, 25◦C): δ 29.58. [Co PPh2]
ppm. FT-IR (KBr, cm−1) 3054 (m, Ar H); 2984 (m, R H), 1646 (w, C C (Ph)), 1437 (s,
C C (Ph)), 1126–1083 (m, C N (ter-amine)), 722–695 (s, monosubstitute Ar H).
Preparation of [Co(L2)Cl2] (8)
L2 (2 g) was added to a stirred solution of [CoCl2.6H2O] (0.5 g, 2.1 mmol) in ethyl
alcohol (5 mL). The mixture was stirred and refluxed for a further 4 h, and a blue solid
separated, which was then filtered, washed with CH2Cl2, and dried under vacuum. Yield
2.2 g (81%). FT-IR (KBr, cm−1) 3458 (m, Ar H), 2955 (m, R H), 1651 (w, C C (Ph)),
1095 (m, C N (ter-amine)), 802 (s, monosubstitute Ar H). 31P-NMR (CDCI3, 25◦C): δ
32.90 ppm, Co: 3.8% (AAS).
Catalytic Oxidation of 2-Methyl Naphthalene by Complexes 3, 4, and 5,
and Silica-Supported Complexes 6, 7, and 8
To determine the optimum oxidation time in the experiments, 3.15 g 2-methyl naph-
thalene (0.022 mol), 40 mL glacial acetic acid, 10 mL hydrogen peroxide (30%), 0.6 mL
sulfuric acid (98%), and 0.1 g catalyst (for complexes 3, 4, and 5) and 0.5 g catalyst (for
the complexes 6, 7, and 8) were used, respectively. Additionally, various oxidant and cata-
lyst amounts were also investigated for the selective oxidation of 2-methyl naphthalene to
2-methyl-1,4-naphthoquinone using complexes 4 and 7, respectively.
The catalytic reactions were carried out in a glass reactor having a water circulator
wrapped around it to control the reaction temperature between 60–80◦C. 2-Methyl naphtha-
lene and the catalyst in glacial acetic acid was added into the reactor, and hydrogen peroxide
containing sulfuric acid was pumped into the reactor with a pump by the flow rate of 10
mL/min. While the reaction was going on, for each at 30, 60, and 90 min, 5 mL reaction
mixture was taken and extracted with acetone and injected to GC. 2-Methyl naphthalene,
2-methyl-1,4-naphthoquinone, and 6-methyl-1,4-naphthoquinone (isomer) amounts were
calculated from external calibration curves that were prepared before analysis. Catalytic
reaction yields were characterized and verified by GC-MS. All experiments were performed
in triplicate.

1424
S. URUS¸ ET AL.
CONCLUSIONS
Bidentate tertiary aminomethylphosphine complexes of Ru(II), Pd(II), and Co(II)
with N,N-bis(diphenylphosphinomethyl)aminopropyltrietoxysilane and its silica-supported
form have been synthesized using Schlenk techniques. The coordination of the ligand to
metal ions gave shielded chemical shifts in NMR spectra in comparison with the free
ligand. As a clean and more efficient production of 2-methyl-1,4-naphthoquinone, some
catalysts were tested in glacial acetic acid containing sulfuric acid, which accelerates the
oxidation reaction. Based on the experimental data, complex 4 has been found an efficient
free catalyst, whereas complex 7 is the best recyclable solid-supported catalyst compared
with other complexes in the selective oxidation of 2-methyl naphthalene to 2-methyl-
1,4-naphthoquinone. For 1 h, 2-methyl-1,4-naphthoquinone yield reached to 52.26% with
2MN conversion 90.42% using complex 4 and reached to 58.58% 2MNQ yield with
conversion of 99.56% using complex 7. According to the results of the recycling tests,
solid-supported complex 7 could be an applicable heterogeneous catalyst compared to the
classical production based on the recycling numbers, conversion, and 2MNQ selectivity.
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