Thermal and spectral properties of alkali metal complexes of vitamin K3 analogue phthiocol

Article abstract of DOI:10.1007/s10973-015-4575-3

Hydroxynaphthoquinones, alkali, and alkali metal salts were used to synthesize several biologically important molecules. As hydroxynaphthoquinones act also as potential ligands, it is possible that alkali metal complexes may be formed as intermediates in such reactions. To ensure this, the reactions of 2-hydroxy-3-methyl-1,4-naphthoquinone (phthiocol, a vitamin K3 analogue) with sodium metal, alkali such as NaOH and KOH, and alkali metal salts such as CH₃COONa, Na₂CO₃ and K₂CO₃ were studied in the present investigation. The products were characterized by various analytical techniques, namely elemental analysis, FT-IR, ¹H NMR, UV-Vis, thermogravimetric (TG) analysis, GC-MS, and DSC studies. 100 % reduction of the ligand was observed in Phth-1 with sodium metal as reducing agent. The solution of CH₃COONa, NaOH, KOH, and K₂CO₃ in methanol facilitates the reduction of phthiocol ligand. The reduction of the ligands may be probably due to disproportionate reaction of the 'catechol' form and the fully oxidized naphthoquinone form of the ligand. The radical signatures of the ligands in complexes were detected by EPR studies and also by carbonyl frequencies in FT-IR spectra. Non-isothermal TG studies confirm the presence of adsorbed and coordinated water molecules. Residue formed after complete decomposition was observed to be 1/2 Na₂O in Phth-1 to Phth-3, K₂O in Phth-4, and 1/2 K₂O in Phth-5. Based on GC-MS and TG studies, three decomposition mechanisms are being proposed for all complexes.

Full text of DOI:10.1007/s10973-015-4575-3

J Therm Anal Calorim
DOI 10.1007/s10973-015-4575-3
Thermal and spectral properties of alkali metal complexes
of vitamin K3 analogue phthiocol
•
Laxmi Kathawate Rishikesh Patil
•
•
Ravi Yadav Sunita Salunke-Gawali
Received: 31 March 2014 / Accepted: 12 February 2015
´
´
Ó Akademiai Kiado, Budapest, Hungary 2015
Abstract Hydroxynaphthoquinones, alkali, and alkali
metal salts were used to synthesize several biologically
important molecules. As hydroxynaphthoquinones act also
as potential ligands, it is possible that alkali metal com-
plexes may be formed as intermediates in such reactions.
To ensure this, the reactions of 2-hydroxy-3-methyl-1,4-
naphthoquinone (phthiocol, a vitamin K3 analogue) with
sodium metal, alkali such as NaOH and KOH, and alkali
metal salts such as CH3COONa, Na2CO3 and K2CO3 were
studied in the present investigation. The products were
characterized by various analytical techniques, namely
elemental analysis, FT-IR, 1H NMR, UV–Vis, thermo-
gravimetric (TG) analysis, GC–MS, and DSC studies. 100
% reduction of the ligand was observed in Phth-1 with
sodium metal as reducing agent. The solution of CH3
COONa, NaOH, KOH, and K2CO3 in methanol facilitates
the reduction of phthiocol ligand. The reduction of the li-
gands may be probably due to disproportionate reaction of
the ‘catechol’ form and the fully oxidized naphthoquinone
form of the ligand. The radical signatures of the ligands in
complexes were detected by EPR studies and also by car-
bonyl frequencies in FT-IR spectra. Non-isothermal TG
studies confirm the presence of adsorbed and coordinated
water molecules. Residue formed after complete decom-
position was observed to be 1/2 Na2O in Phth-1 to Phth-3,
K2O in Phth-4, and 1/2 K2O in Phth-5. Based on GC–MS
and TG studies, three decomposition mechanisms are being
proposed for all complexes.
Keywords Vitamin K3 ꢀ Phthiocol ꢀ Hydrogen bonding ꢀ
TG studies ꢀ Vapochromic behavior ꢀ Hydroxy
naphthoquinone ꢀ Naphthosemiquinone
Introduction
2-methyl-1,4-naphthoquinone is used as a vitamin K3 in
mammals. Vitamin K3 in combination with vitamin C was
studied for the potential treatment for prostate cancer
[1–5]. Vitamin K prevents bleeding by increasing hepatic
biosynthesis of prothrombin and other coagulation factors.
It is also needed for healthy bones. Vitamin K3 is used as a
source of vitamin K in the treatment of hypoprothrom-
binemia against vitamin K deficiency. Menadione is a vi-
tamin precursor of vitamin K2, which can be converted in
the liver to active menaquinones by chemical alkylation
in vivo [6, 7]. Phytonadione (vitamin K1) and me-
naquinone (vitamin K2) occur in plants and are consumed
in the diet.
Vitamin K is an essential nutrient often associated with
the clotting cascade and has been the focus of considerable
research in recent years, demonstrating an anticancer po-
tential [6, 7]. Vitamin K is usually identified as a critical
factor in blood coagulation; recent research has found that
vitamin K is also a cofactor in bone metabolism [6].
Naphthoquinones and their substituents have been widely
studied for their application in biological functions.
Therefore, when the naphthoquinone ring is substituted by
an appropriate alkyl chain, these compounds tend to exhibit
anticancer and antitumor activity [7]. They also do present
an antihemorrhagic activity, depending on the molecular
Electronic supplementary material The online version of this
article (doi:10.1007/s10973-015-4575-3) contains supplementary
material, which is available to authorized users.
L. Kathawate ꢀ R. Patil ꢀ R. Yadav ꢀ S. Salunke-Gawali (&)
Department of Chemistry, Savitribai Phule Pune University,
Pune 411007, India
e-mail: sunitas@chem.unipune.ac.in
123

L. Kathawate et al.
Physical measurements
structure. There are many synthetic forms of vitamin K,
such as vitamin K3, vitamin K4, and vitamin K5, which are
used in several areas including the pet food industry (vi-
tamin K3) and to inhibit fungal growth (vitamin K5).
Menadione (vitamin K3) is a synthetic derivative of the
naturally occurring vitamins K1 and K2.
Elemental analysis was performed on Thermo Finnigan EA
1112 Flash series elemental analyzer. FT-IR spectra of
phthiocol ligand and complexes Phth-1 to Phth-5 were
recorded between 4000 and 400 cm-1 as KBr pellets on
SHIMADZU FT 8400 spectrometer. The concentration of
Na? and K? ions in Phth-1 to Phth-5 were determined on
SYSTRONICS flame photometer 128. AR-grade NaCl and
KCl were used as standards for flame photometry analysis.
UV–Vis spectra of all compounds were recorded on SHI-
MADZU UV 1650 in methanol between 200 and 800 nm.
The X-band EPR spectrum of all complexes was recorded
at room temperature (298 K) and liquid nitrogen tem-
perature(133 K) with VARIAN, E112 EPR SPECTRO-
METER with microwave frequency 9.5 GHz with
sensitivity of 5 9 1010 spins and modulation of frequencies
from 100 to 15 Hz at SAIF-IIT Powai, Mumbai, India.
DSC curves were recorded on TA waters model Q2000
instrument. Tzero aluminum pan was used as sample
holder in DSC studies. Gas chromatograph–mass spec-
trums (GC–MS) were recorded on Shimadzu, GC–MS-
QP5050. Liquid chromatograph–mass spectrums (LC–MS)
were recorded on Shimadzu, LCMS-2010EV, with ESI
source for ionization.
Thermal and spectral properties of naphthoquinone and
their metal complexes were studied by several workers
[8–10]. The decomposition of naphthoquinone ligands with
loss of water molecules over the temperature range and solid
phase transformation, melting, etc., can be detected by
thermal studies. The activation energy of naphthoquinone
ligands varies in metal complexes, as these ligands coordi-
nate to metal ions in various oxidation states [11, 12]. Hy-
droxynaphthoquinones are redox active ligands. Scheme 1
shows the three different oxidation states of phthiocol.
KOH, NaOH, and alkali metal salts such as Na2CO3,
K2CO3 and CH3COONa are used to synthesize hy-
droxynaphthoquinone derivatives. Intrinsic radicals are
observed in polycrystalline powder form of these deriva-
tives. To find the origin of EPR signals in the hydroxy
naphthoquinones, the reaction of 2-hydroxy-3-methyl-1,4-
naphthoquinone (phthiocol; phth) was studied with ‘Na’
metal, alkali NaOH and KOH, and alkali metal salts
CH3COONa and K2CO3 in the present investigation. The
abbreviations of the complexes are as follows: the syn-
thesis with sodium metal (Phth-1), CH3COONa (Phth-2),
NaOH (Phth-3), KOH (Phth-4), and K2CO3 (Phth-5).
Thermal and spectral properties of all the compounds have
been studied, and decomposition mechanisms were pro-
posed based on GC–MS and thermogravimetric studies.
TG analyses have been performed on laboratory-con-
structed instrument. The details of each component are
given below.
Balance
An electrical single-pan analytical balance, K-14 Super (K.
Roy and Co., India), of 100 g capacity with an accuracy
of 0.1 mg is used and was mounted on a vibration-free,
horizontal platform.
Experimental
All the chemicals used in synthesis were of analytical
grade. Menadione (2-methyl-1,4-naphthoquinone) was re-
crystallized from methanol prior to synthesis. Sodium
metal was obtained from SD Fine chemicals. Milli-Q water
was used for the experimental work of flame photometry.
Anhydrous methanol was purified using the procedure re-
ported in the literature [13].
Furnace
Nichrome wire resistance furnace using a quartz tube with
32 mm (internal diameter) 9 250 mm (length) was con-
structed with good thermal insulation of approximately
3 cm above the windings. This assembly was then set into a
Scheme 1 Various redox forms
of 2-oxido-3-methyl-1,4-
–
O
O
O
–
O
8
5
–
1
–
naphthoquinone. I oxidized
naphthoquinone form (NQ-); II
naphthosemiquinone form
(NSQ-.), and III catechol form
(CAT)
O
O
1e–
1e–
1e–
1e–
7
2
6
3
CH3
CH3
CH3
4
–
O
O
O
II
III
I
123

Thermal and spectral properties
cement pipe of approximately 250 mm (height) and 70 mm
(internal diameter). The inner space between the furnace
and this cement pipe was filled up using slurry of plaster of
paris, silica, and asbestos wool.
water afforded a yellow precipitate, which was recrystallized
from methanol containing a few drops of concentrated H2SO4.
The crude product was purified by column chromatography
using 5 % methanol in toluene.
Thermocouple
Synthesis of Phth-1
The tip of the chromel–alumel thermocouple (24 gauze
wires) was kept in the vicinity of the sample, and terminals
were connected to a direct temperature measuring py-
rometer with range 0–1200 °C ( 5 °C).
1 mmol of phthiocol (0.188 g) was dissolved in 15 mL an-
hydrous methanol. Na metal 1 mmol (0.230 g) was dis-
solved in 10 mL of anhydrous methanol. The two solutions
were mixed under N2 atmosphere with constant stirring for
20 min at 4 °C. Precipitated product was filtered and washed
with diethyl ether and dried under vacuum.
Temperature regulator
The terminals of the furnace were connected to a tem-
perature regulator (Argo Transformers Co. Ltd., India, 15
Amp capacities).
Synthesis of Phth-2 and Phth-5
1 mmol of phthiocol (0.188 g) was dissolved in 15 mL
anhydrous methanol. Alkali and alkali metal salts, viz
1 mmol CH3COONa for Phth-2 (0.820 g), NaOH (0.400 g)
for Phth-3, KOH (0.560 g) for Phth-4, K2CO3 (0.690 g) for
Phth-5 each was dissolved in 10 mL of anhydrous metha-
nol. The ligand and metal solutions were mixed with
constant stirring over a period 20 min at room temperature
(26 °C). Precipitated products were filtered and washed
with diethyl ether and dried under vacuum.
Standardizations of thermobalance
The instrument was standardized by carrying out dynamic
TG of standard sample such as CaC2O4.H2O and
CuSO4.5H2O. The dynamic and non-isothermal TG ex-
periments in air were perforated on this thermobalance.
Sample size
50–70 mg
Particle Size
Rate of heating
200–250 mesh (55–70 l)
3–5 °C/min
Results and discussion
Temperature range
of study
30–900 °C
The synthesis of Phth-1 was carried out under N2 atmo-
sphere, and the temperature was kept constant at 4 °C,
while the synthesis of all other complexes (Phth-2 to Phth-
5) was carried out at room temperature (26 °C). The mole
ratio of phthiocol to either ‘Na’, or alkali, or alkali metal
salts was kept constant as 1:1 in synthesis of complexes.
The products obtained are as hydrated complexes [11, 12].
Phth-1 is expected to form as anion radical complex or
neutral radical complex of Na? as the reduction is directly
done by ‘Na’ metal (Table 1).
Thermocouple
Chromel–alumel
Sample container
Cylindrical quartz glass cup 6 mm (diameter),
20 mm (height)
Atmosphere
Static air
Synthesis
Concentration of alkali metal ions in all complexes, viz
Na? and K? (wherever necessary) was determined by flame
photometry (Table 2). The cation-to-anion ratio was found to
be 1:1 in all complexes, while in Phth-4, it was observed as
2:1. The metal–ligand ratio in Phth-4 was confirmed after
repetitive synthesis and characterization by elemental ana-
lysis (Supplementary material). The presence of additional
K? ion in Phth-4 may be probably due to coordination of
ligand in monoanionic naphthosemiquinone radical form
(form II in Scheme 1). The increase in concentration of Po-
tassium ions in Phth-4 was also confirmed by flame photo-
metric analysis. Weak triplet signal was observed *g = 4 in
EPR of Phth-4, which confirms the coordination of phthiocol
ligand in naphthosemiquinone form (form II in Scheme 1).
Synthesis of 2-hydroxy-3-methyl-1,4-naphthoquinone
(phthiocol)
The preparation followed a minor modification of the pub-
lished procedure [14]. Menadione (1.0 g; 5.8 mmol) was dis-
solved in 10 mL methanol and chilled in an ice bath. A solution
of 0.2 g of anhydrous Na2CO3 and 1 mL of 30 % H2O2 in
5 mL of water was then added, and the reaction mixture was
maintained at 0 °C. Addition of 100 mL of chilled water led to
the precipitation of 2-methyl-1,4-naphthoquinoneoxide as
colorless crystals, which were collected by filtration and dried
in air. The solid obtained was treated with 5 mL concentrated
H2SO4 andallowedtostandfor10 min.Theadditionof20 mL
123

L. Kathawate et al.
Table 1 Elemental analysis and UV–Vis spectroscopy data for Phth-1 to Phth-5
Comp
Color
UV–Vis bands/nm
Yield/%
Composition
Elemental analysis found/Calc. %
M. wt/g
C %
H %
Phth
Yellow
Red
287, 330, 388, 479
286, 329, 481
296, 329, 483
292, 329, 483
295, 324, 479
293, 331, 483
84
83
52
82
73
75
C11H8O3
188.00
210.16
228.16
228.16
310.41
358.51
–
–
Phth-1
Phth-2
Phth-3
Phth-4
Phth-5
C
C
C
C
C
11H7O3Na
11H9O4Na
11H9O4Na
11H12O5.5K2
11H13O6K3
62.51/62.86
57.27/57.90
53.85/53.66
42.82/42.56
36.53/36.85
04.48/03.35
04.31/03.09
04.36/04.50
03.86/03.89
02.53/03.36
Red
Red
Red
Red
Table 2 Observed Na? value in ppm by flame photometry for Phth-1 to Phth-5
S. No.
Expected Na?, K?
Phth-1
Phth-2
Phth-3
Phth-4
Phth-5
1
2
3
4
5
100
80
60
40
20
100.66
82.61
62.35
40.80
26.00
100.41
80.31
60.00
40.12
20.09
100.95
80.00
64.00
40.04
23.83
101.68
88.01
71.96
53.40
26.50
99.41
81.26
60.70
41.67
22.00
FT-IR studies
band was observed as an overlap of mOH and mC–H vibra-
tions in complexes Phth-3, Phth-4, and Phth-5, as the na-
ture of this band was very broad between *3700 and
2500 cm-1. This may be due to the presence of hydrogen-
bonded water molecules in the coordination sphere or the
hydrated water molecules in these complexes. A sharp
band observed at *1660 cm-1 (Fig. 1; Table 3) in free
phthiocol ligand, which was assigned to mC=O stretching
vibrations; this vibrations were observed at 1662 and
1655 cm-1 in CCl4 [15]. The peak position of mC=O band
shifts *20 cm-1 toward higher frequencies in Phth-1 to
Phth-4 (Table 3), suggestive of metal to ligand
(M ? L) charge transfer.
The mOH stretching vibrations in solid state of free ph-
thiocol ligand (Fig. 1) were observed at *3371 cm-1
,
whereas it was observed at 3471 cm-1 in CCl4 [15]. This
100
80
60
Phth
Phth-1
Phth-2
Phth-4
Phth-5
Phth-3
40
The signatures of naphthosemiquinone coordination of
the phthiocol ligand in all complexes can be evaluated by
FT-IR spectroscopy. Mac et al. [16] studied quenching of
triplet state of menadione (2-methyl-1,4-naphthoquinone;
MeNQ) by amines. A triplet state of MeNQ (Scheme 2)
was formed by flash photolysis, which shows FT-IR band
at 1503 cm-1, and was assigned to menadione radical an-
ion (MeNQ-.). This band was shifted to 1513 cm-1 by
addition of LiClO4 salt; lithium ion does not bind to me-
nadione; however, it gets associated with MNQ-. radical
anion and thus the vibrational frequencies shifted from
1503 to 1513 cm-1. The band at 1536 cm-1 was assigned
to ketyl radical (MeNQH.) (Scheme 2). In FT-IR spectra of
3500
3000
2500
Wavenumber/cm–1
80
60
40
20
0
Phth
Phth-1
Phth-2
Phth-4
Phth-5
Phth-3
Phth-1 to Phth-5,
a
sharp band was observed
at *1521 2 cm-1 (NSQ-.); this band may be assigned
to NSQ-. radical anion (Scheme 1) or to the coordinated
mC=O vibrations of phthiocol ligand. Association of neigh-
boring radical anions would generate a triplet state in solid
1700
1600
1500
1400
1300
1200
Wavenumber/cm–1
Fig. 1 FT-IR spectra of phthiocol and Phth-1 to Phth-5
123

Thermal and spectral properties
Table 3 Important FT-IR frequencies of phthiocol ligand and Phth-1 to Phth-5 complexes
Phthiocol
Phth-1
Phth-2
Phth-3
Phth-4
Phth-5
1660(s)
1591(s)
1392(s)
1276(s)
1211(s)
833(s)
1672(s), 1641(s)
1595(s), 1545(sh), 1519(s)
1390(s)
1678(s)
1668(s)
1670(s)
1589(s), 1521(s)
1392(s)
1280(s)
1230(s)
844(sh)
734(s)
1653(sh)
1593(br), 1550(br)
1386(sh)
1276(br)
1233(sh)
848(s)
1575(br), 1519(sh)
1383(s)
1585(s), 1523(s)
1390(s)
1280(s)
1265(br)
1219(sh)
835(s)
1280(s)
1222(sh)
1230(sh)
846(s)
835(sh)
727(s)
727(s)
707(s)
731(s)
734(s)
684(s),
634(sh)
617(s)
651(s)
621(s)
682(s),
671(s)
621(s)
s sharp, sh shoulder, br broad
Scheme 2 Molecular structures
of a 2-methyl-1,4-
naphthoquinone; MeNQ,
b MNQ-., and c MeNQH
(a)
(b)
(c)
O
O
OH
CH3
CH3
CH3
O
O
O
state. Radical signatures in all complexes were supported
by EPR spectroscopy.
methanol for all complexes as well as in free phthiocol
ligand. Two bands in UV region were centered
at *327 nm for free phthiocol and these bands were as-
signed to p?p* transition of quinonoid and benzenoid
rings, respectively [17–19]. There was hypsochromic shift
observed due to band at *329 nm in Phth-1 to Phth-5. A
single broad band was observed in all complexes as well as
in free phthiocol ligand in visible region. This band is as-
signed with charge transfer transition.
Paranaphthoquinone (p-NQ) vibration (1276 cm-1) of
free phthiocol ligand was shifted (*5 cm-1) toward higher
frequencies in Phth-1 and Phth-3 to Phth-5. mC–O vibrations
of free phthiocol ligand (1211 cm-1) was shifted to
1225 5 cm-1 higher frequencies in all complexes, and
d
to lower frequencies in all complexes.
CH3 vibration (1178 cm-1) was shifted *1130 10 cm-1
1H NMR spectra
TG studies of Phth-1 to Phth-5
There were six resonance peaks expected for free phthiocol
ligand and five peaks for alkali metal complexes Phth-1 to
Phth-5, a singlet due to –OH and –CH3, doublet due to
C(5)H and C(8)H, and triplets due to C(6)H and C(7)H
(Scheme 1). Phth-1 to Phth-5 show upfield shift in proton
resonance of C(5) to C(8) protons as well as in d C(3)–CH3
as compared to phthiocol free ligand. A sharp singlet of
C(2)OH in phthiocol free ligand at d = *10.9 was absent
in all complexes (Table 4).
The curve of free phthiocol ligand and all alkali metal
complexes: Phth-1 to Phth-5 are shown in Fig. 3, and
thermodynamic data are represented in Table 5.
The mass losses in all complexes start from *30
to *100 °C in TG studies, which accounts for loss of
adsorbed water molecules [11, 12, 20]. The nature of TG
curves varies in all complexes (Fig. 3).
The complexes Phth-1, Phth-3, and Phth-4 showed a
pyrolytic decomposition involving four steps, whereas
Phth-2 showed three steps and Phth-5 showed five steps in
their pyrolytic decomposition. Step I in all complexes led
to the loss of adsorbed water molecules, as this loss was
observed at a temperature below 100 °C.
Electronic spectral studies
UV–Vis spectra of free phthiocol ligand and Phth-1 to
Phth-5 were recorded between 275 and 800 nm in metha-
nol (Fig. 2). There were mainly three bands observed in
The step III and step IV in Phth-1 and Phth-4 led to
decomposition of phthiocol anion, whereas in Phth-2 and
123

L. Kathawate et al.
Table 4 Chemical shift d/ppm in phthiocol and Phth-1 to Phth-5
Comp. name
d C(5)H(d)/J(Hz)
d C(6)H(t)/J(Hz)
d C(7)H(t)/J(Hz)
d C(8)H(d)/J(Hz)
d C(3)H(s)/J(Hz)
d C(2)OH(s)/J(Hz)
Phthiocol
Phth-1
Phth-2
Phth-3
Phth-4
Phth-5
7.969/6.3
7.833/7.5
7.842/7.8
7.701/7.5
7.699/7.2
7.854/7.2
7.821/6.1
7.593/7.3
7.760/7.6
7.442/7.5
7.581/7.3
7.764/7.3
7.778/6.3
7.695/7.2
7.584/7.5
7.587/7.2
7.439/7.3
7.589/7.3
7.989/5.4
7.886/7.2
7.915/7.5
7.817/7.5
7.817/7.2
7.921/8.4
1.956
1.845
1.965
1.766
1.764
1.967
10.900
–
–
–
–
–
3
2
1
0
0
20
Phthiocol
Phth-1
Phth-2
Phth-3
Phth
Phth-1
Phth-2
Phth-3
Phth-4
Phth-5
40
60
80
300
400
500
600
100
Wavelength/nm
0
200
400
600
800
1000
Temperature/oC
Fig. 2 UV–Vis spectra of phthiocol and Phth-1 to Phth-5; methanol
concentration used was 1 9 10-4
M
0
20
Phth-3, phthiocol anion decomposed in step II to step IV.
The % mass loss of phthiocol anion in Phth-1 to Phth-5
varied as it was almost 85:15 in Phth-1 and Phth-2, 56:44 in
Phth-4, and 44:56 in Phth-3 and Phth-5. Thus, decompo-
sition mechanism varied in all complexes. The respective
metal oxide, viz ‘ Na2O or ‘ K2O was formed after
complete pyrolytic decomposition of Phth-1 to Phth-3,
Phth-5, and K2O for Phth-4.
Phthiocol
Phth-4
Phth-5
40
60
80
The decomposition temperatures in all complexes were
found to be on the higher side as compared to that of the free
phthiocol ligand; thus, all the complexes were thermody-
namically more stable as compared to the free phthiocol
ligand. As an organic moiety, there was 100 % loss in mass
observed in the curve of free phthiocol ligand.
100
0
200
400
600
800
1000
Temperature/oC
Fig. 3 TG curves of Phth-1 to Phth-5
DSC studies
material). DSC curve of Phth-4 showed four endothermic
peaks in temperature range *100–163 °C (Fig. 4b).
DSC curves were recorded in the temperature range of
30–300 °C. There was a single endothermic peak observed
due to melting point of free phthiocol ligand at *173 °C in
DSC curve (Fig. 4a). There were two (Phth-2 and Phth-5)
and three (Phth-3) endothermic peaks observed in the tem-
perature range *100–270 °C (figures in Supplementary
GC–MS studies of phthiocol and Phth-1 to Phth-5
Similar fragmentation pattern was observed in GC–MS
spectra for all complexes. The representative GC–MS
123

Thermal and spectral properties
Table 5 Thermogravimetric data for Phth-1 to Phth-5
Sr. No.
Mol. formula,
Mol. wt./g
Step no.
Temp. range/°C
Mass loss/%
Probable composition
of group lost
Residue/%
Phth-1
PhthNa.H2O*, 228.17
I
035–039
135–145
275–610
780–820
05.02/05.92**
02.67/01.97
65.98/66.75
07.54/11.78
0.75 H2O:
0.25 H2O:
0.85 Phth:
0.15 Phth:
PhthNa.0.25H2O
PhthNa
II
III
IV
PhthNa0.15
(Na2O)0.5
18.79/13.58
PhthNa.
Phth-2
Phth-3
PhthNa.H2O, 228.17
PhthNa.H2O, 228.17
I
094–099
315–524
655–800
07.05/07.89
63.53/66.76
11.77/11.77
H2O:
II
III
0.85 Phth:
0.15 Phth:
PhthNa0.15
(Na2O)0.5
17.65/13.58
PhthNa.
I
027–032
086–112
131–790
807–850
06.06/07.89
09.51/11.77
23.43/22.78
42.42/43.98
H2O:
II
0.15 Phth:
0.29 Phth:
0.56 Phth:
PhthNa0.85
PhthNa0.56
(Na2O)0.5
18.58/13.58
PhthK2.H2O
PhthK2
III
IV
Phth-4
Phth-5
PhthK2.2H2O, 301.40
I
037–112
148–202
236–415
447–892
08.27/05.97
14.85/05.97
11.18/15.34
31.31/41.47
H2O:
II
H2O:
III
IV
0.27 Phth:
0.73 Phth:
Phth0.73K2
(K2O)
34.39/31.25
PhthK.2H2O
PhthK.H2O
PhthK
PhthK.2.5H2O, 271.31
I
027–029
076–110
172–201
239–520
600–750
03.16/03.31
06.22/06.63
06.36/06.63
26.19/29.08
38.71/37.00
0.5 H2O:
H2O:
II
III
IV
V
H2O:
0.44 Phth:
0.56 Phth:
PhthK0.56
(K2O)0.5
19.36/17.35
* Phth Phthiocol ligand [2-oxido-3-methyl-1,4-naphthoquinone]
** Figures indicate calculated mass loss
Table 6 Value of gyromagnetic ratio ‘g’ Phth-1 to Phth-5
radical mechanism in all complexes. The decomposition
mechanisms were proposed for free phthiocol ligand and
complexes, Phth-1 to Phth-5. Fragmentation peaks were
Sr. No.
giso (298 K)
giso (133 K)
giso(133 K) in Methanol
.
correspond to loss of CO and –O–C. = CH- groups.
Phth-1
Phth-2
Phth-3
Phth-4
Phth-5
2.0552
4.2519
1.9713
2.0140
4.2799
–
4.2519
Broad signal
2.0072
Broad signal
–*
–
EPR studies
Broad signal
2.0078
–
EPR spectra of the radical anion of vitamin K3 have been
studied in various solvents [21–31]. Hyperfine coupling
constants of protons of methyl group of vitamin K3 are
solvent dependent [25, 31]. In general, the spin density
distribution in quinone chemistry is influenced by solvents
via quinonoid oxygens and the total spin density remains
unchanged in the quinonoid ring. NaOH, KOH, and KF in
solvents (0.1 NaOH, methanol/water, ethanol/water, etha-
nol (abs), methanol, DMSO, THF) were also used to gen-
erate the anionic radicals of menadione (MNQ-.). The
* Not recorded
spectrum of free phthiocol ligand was shown in Fig. 5.
Three decomposition pathways are proposed based on
fragmentation patterns observed in GC–MS of phthiocol
complexes and are shown in Scheme 3. Molecular mass
formed after decomposition was compared with the %
mass loss in TG studies. Decomposition occurred via
123

L. Kathawate et al.
gyromagnetic ratio ‘g’ observed in the presence of above
salts in various solvent is 2.00045 0.00002. It is also
known that hydroquinone reacts with potassium fluoride
(KF) in methanolic solutions producing the dipotassium
salt. A disproportionate reaction of the dinegative anion
and the neutral substance would produce radical anions.
MNQ2ꢁ þ MNQ ꢀ 2MNQꢁꢀ
The powder spectra of menadione with ‘KF’ salt show
potassium (I = 3/2) hyperfine with hyperfine coupling
constant of 0.0166 mT. A salt of menadione cation radical
will be formed as shown in the following reaction,
5
(a)
0
–5
Phthiocol
MNQꢁꢀ þ Kþ ꢀ MNQKꢀ
MNQKꢀ þ Kþ ꢀ MNQKþ2 ꢀ
–10
–15
This salt shows EPR spectrum of axial symmetry.
In this investigation 1:1 M ratio of phthiocol with
sodium, alkali and alkali metal salts were used to synthe-
size Phth-1 to Phth-5 complexes. With this proportion, only
the hydroxyl group was deprotonated, and if the radicals
are formed by this mechanism, they will be neutral
radicals.
–20
173.19°C
–25
30
80
130
180
230
280
Temperature/oC
2
0
(b)
Phth-4
2Phthꢁ þ 2Phth ꢀ 2Phthꢁꢀ
2 Phthꢁꢀ þ 2 Kþ= 2Naþ ꢀ 2PhthꢀK = 2PhthꢀNa
A single line was observed at room temperature
at *g = 2.0552 (at 298 K in Fig. 6, Table 6), whereas
weak signal is observed at *g = 4 in polycrystalline
powder or methanol solution (at 133 K in Fig. 7), X-band
EPR spectra of Phth-1. It is reported that naphthoquinones
could form polymeric structures through hydrogen bonding
[30]. The radical spins of the neighboring molecules could
interact with each other to form triplet state in Phth-1 as
evidenced at 133 K. The weak signals observed for Phth-1
and Phth-4 (Supplementary information) at g = *4 are
indicative of ion pairs formation of the molecules and tri-
plet state.
92.95/°C
141.88/°C
–4
–6
163.54/°C
109.73/°C
130
30
80
180
230
280
Temperature/oC
Fig. 4 DSC (Heating) curves of a phthiocol and b Phth-4
100
90
80
70
60
50
40
30
20
10
44
188
Phthiocol
131
77
105
160
39
63
115
89
143
169
201
222226
243
30
40
50
60
70
80
90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240
m/z
Fig. 5 GC–MS spectra of phthiocol ligand
123

Thermal and spectral properties
M(H2O)n
O
O
M = Na, K, H (Phthiocol), n = Phth-1, Phth-2 and Phth-3 = 1,
Phth-4 = 2, Phth-5 = 2.5
O
Calc. = 187 g
Found:
GCMS; Phth, Phth-1, Phth-2, Phth-3, Phth-4, Phth-5 = 188 g
CH3
–H2O
Adsorbed and coordinated H2O molecules
(CO)
C
O
O
C
C(CH )
3
Calc. = 28 g
(CO)
Calc.= 83 g
Found:
Found:
TG; Phth-1 = 28 g (step IV),
Phth-2 = 28 g (step III),
Phth-3 = 28 g (step II)
GC-MS; Phth, Phth-1 to Phth-5 = 89 g,
TG; Phth-4 = 82 (step IV)
Phth-5 = 82 (step IV)
O
O
.
C
–
+
CH
O M
3
+
O
OR
–
+
O M
O
0.5 (M O)
+
2
CH
3
Calc. = 159 g
Found:
(phenylmethylidyne)oxonium
Calc. = 105 g
Calc. = 159 g
Found:
GC-MS; Phth, Phth-1 to Phth-5 = 160 g,
TG; Phth-1 = 159 g (step III),
Phth-2 = 159 g (step II)
Found:
GC-MS; Phth, Phth-1 to Phth-5 = 160 g,
TG; Phth-1 = 159 g (step III),
Phth-2 = 159 g (step II)
GC-MS; Phth, Phth-1 to Phth-5 = 105 g,
TG; Phth-3 = 105 g (step IV),
Phth-4 = 105 g (step III),
Phth-5 = 105 g (step V)
(CH3-C=C=O)
(CO)
(CO)
+
–
+
O
O M
–
+
O M
Calc. = 120 g
Found:
GC-MS;
Phth, Phth-1 to Phth-5 = 115 g
CH
3
0.5 (M2O)
+
Calc. = 131 g
Found:
cyclohexa-1,3-dien-5-yne
Calc.= 76 g
GC-MS; Phth, Phth-1 to Phth-5 = 131 g
Found:
(CO)
GC-MS; Phth, Phth-1 to Phth-5 = 77 g
O–M
+
CH CH
Calc. = 92 g
Found:
GC-MS;
CH
3
+ 0.5 (M2O)
+
(CH3CHO)
C
Phth, Phth-1 to Phth-5 = 89 g
0.5 (M O)
+
2
Calc. = 103 g
Found:
GC-MS; Phth, Phth-1 to Phth-5 = 105 g,
TG; Phth-3 = 105 g (step IV),
Phth-4 = 105 g (step III),
Calc. = 29 g
Found:
TG; Phth-1 = 28 g (step IV),
Phth-2 = 28 g (step III),
Phth-3 = 28 g (step II)
C
Calc.= 50 g
Found:
GC-MS; Phth, Phth-1 to Phth-5 = 50 g,
TG; Phth-3 = 54 g
Phth-5 = 105 g (step V)
+ 0.5 (M2O)
benzene cation
Calc.= 76 g
Found:
GC-MS;
Phth, Phth-1 to Phth-5 = 77 g
Scheme 3 Proposed decomposition mechanism of phthiocol and Phth-1 to Phth-5
123

L. Kathawate et al.
reduction of the phthiocol ligand in all complexes. This
reduction may be most probably due to disproportion re-
action of ‘catechol’ form (form III, Scheme 1) and the fully
oxidized naphthoquinone (NQ) form of the ligand (form I,
Scheme 1). Half field triplet signal was observed in poly-
crystalline powder EPR spectra of Phth-1, Phth-2, and
Phth-5. A triplet state may be generated by the interaction
between radical spins of the neighboring coordinated
naphthosemiquinone form phthiocol ligands. Thus, EPR
studies also revealed the polymeric nature of these
complexes.
Half field check
Field Set: 2000 G
Scan Range: 4000 G
Pyrolytic decomposition of all compounds was studied
by non-isothermal TG studies in air atmosphere. Pyrolytic
decomposition of phthiocol ligand in all complexes was
observed to involve two or more steps. Residue formed
after complete decomposition of complexes is observed to
be ‘ Na2O in Phth-1 to Phth-3, K2O in Phth-4, and ‘ K2O
Phth-5. Based on GC–MS and TG studies, three decom-
position mechanisms were proposed for all complexes.
Alkali KOH and NaOH, and alkali metal salts such as
Na2CO3, K2CO3, and CH3COONa are used to synthesize
hydroxynaphthoquinone derivatives. Intrinsic radicals are
observed in polycrystalline powder form of these deriva-
tives, for example, in synthesis of naphthoquinone oximes
[32]. The present investigation concludes that alkali metal
complexes of hydroxy naphthoquinones may form as in-
termediates of such reactions.
2200 2400 2600 2800 3000 3200 3400 3600 3800 4000
G
Fig. 6 Polycrystalline powder, X- band EPR spectra of Phth-1 at
298 K (field set: 3000 G, scan range: 2000 G, time constant: 0.63 s,
scan time: 4 min, modulation amplitude: 9 2 G, modulation fre-
quency: 100 kHz, receiver gain: 1.6 9 103 9 10, microwave power:
5 mW, temperature: 298 K, microwave frequency: 9.1 GHz)
Modulation Amplitude: × 0.63 G
Microwave Power: 10 mW
Acknowledgements LK acknowledges Department of Science and
Technology (DST) for Senior Research Fellowship, and SSG is
grateful to DST, New Delhi, India, for Young Scientist Scheme for
financial support Ref. No. (SR/FT/CS-030/2009).
400
800 1200 1600 2000 2400 2800 3200 3600 4000
G
Fig. 7 X-band EPR spectra of Phth-1 in methanol at 133 K (field set:
4000 G, scan range: 2000 G, time constant: 0.63 s, scan time: 4 min.,
modulation amplitude: 9 2 G, modulation frequency: 100 kHz,
receiver gain: 1.6 9 103 9 10, microwave power: 5 mW, tem-
perature: 133 K, microwave frequency: 9.1 GHz)
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