Solvent-free synthesis of novel phthalocyanines containing triazole derivatives under microwave irradiation

Article abstract of DOI:10.1016/j.poly.2012.12.016

An efficient microwave processing method has been developed for the synthesis of novel metal-free phthalocyanine and metallophthalocyanines containing 1,2,4-triazole-3-one derivatives under microwave irradiation in solvent-free conditions. The advantage of this new method includes excellent yield, operational simplicity, short reaction time and avoidance of the use of organic solvents. New compounds have been characterized by several spectral methods such as FT-IR, ¹H NMR, ¹³C NMR, electronic spectroscopy, mass spectra and elemental analyses. The thermal stabilities of these new phthalocyanines were determined by thermogravimetric analysis. For the purposes of comparing data, the reactions were carried out in solution media both under microwave irradiation and in the conventional method.

Full text of DOI:10.1016/j.poly.2012.12.016

Polyhedron 51 (2013) 82–89
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Solvent-free synthesis of novel phthalocyanines containing triazole derivatives
under microwave irradiation
⇑
Musa Özil , Mutlu Canpolat
Department of Chemistry, Art and Science Faculty, Recep Tayyip Erdog˘an University, 53100 Rize, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient microwave processing method has been developed for the synthesis of novel metal-free
phthalocyanine and metallophthalocyanines containing 1,2,4-triazole-3-one derivatives under micro-
wave irradiation in solvent-free conditions. The advantage of this new method includes excellent yield,
operational simplicity, short reaction time and avoidance of the use of organic solvents. New compounds
have been characterized by several spectral methods such as FT-IR, 1H NMR, 13C NMR, electronic spec-
troscopy, mass spectra and elemental analyses. The thermal stabilities of these new phthalocyanines
were determined by thermogravimetric analysis. For the purposes of comparing data, the reactions were
carried out in solution media both under microwave irradiation and in the conventional method.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 11 October 2012
Accepted 21 December 2012
Available online 28 December 2012
Keywords:
Phthalocyanine
Synthesis
Solvent-free
Triazole
Microwave
Conventional method
1. Introduction
cal applications such as non-linear optics, liquid crystals, electro-
chromic processes, gas or chemical sensors photosensitizers,
The application of microwave irradiation as a nontraditional en-
ergy source for the activation of reactions has now become a very
popular and useful technology in chemistry [1–3]. In particular,
solvent-free reaction conditions under microwave irradiation have
received a lot of attention due to their enhanced reaction rates, as
well as higher yields and purities. The combination of microwave
irradiation and solvent-free reaction conditions are regarded as
environmentally benign and easy to perform, paving the way to
the development of ‘Green Chemistry’ protocols [4].
1,2,4-Triazole compounds have been found to be useful for
applications in medicine and agriculture [5–7]. The synthesis, reac-
tions and biological properties of substituted triazole constitute a
significant part of modern heterocyclic chemistry [8]. There have
been reported applications in a wide spectrum of potential biolog-
ical properties of triazole derivatives, such as antifungal [9–11],
antitumor [12], analgesic [13], antibacterial [14,15] and cancer
therapy [16]. Besides their pharmacological significance 1,2,4-tria-
zole derivatives exhibit interesting chemical properties. The ability
of triazoles to form a bridge between metal ions makes such li-
gands very important for magnetochemical applications [17,18].
Thus, the heterocyclic system is an attractive scaffold to be utilized
for exploiting chemical diversity.
catalysts [19–23]. Apart from technological applications, phthalo-
cyanines are of interest photodynamic reagents for cancer therapy
as second generation photosensitizers [24,25].
The growing use of phthalocyanines as advanced materials dur-
ing the last decade has encouraged research on the synthesis of
new derivatives materials which differ in the central metal ion or
in the peripheral substituents. Despite this extensive interest, there
are relatively few synthetic routes to phthalocyanine derivatives,
covering mainly phthalonitrile derivatives compounds [19].
Recently, much effort has been dedicated to the microwave
assisted synthesis of metal-free and metallophthalocyanines
[26–33]. In addition, there have been several incidences reported
of the synthesis of unsubstituted, and some substituted, metall-
ophthalocyanines using microwave irradiation under solvent free
conditions [34–42]. We developed a fast and effective procedure
for the synthesis of bulky substituted metal-free phthalocyanines
and metallophthalocyanines.
2. Experimental
2.1. Materials and equipments
Phthalocyanines and their metal complexes constitute
remarkably versatile class of compounds with diverse technologi-
a
All chemicals, solvents, and reagents were of reagent grade
quality and were used as purchased from commercial sources.
Ethyl acetate ethoxycarbonyl hydrazone [43], and 4-nitrophthalo-
nitrile [44] were prepared according to the reported procedure.
FTIR spectra were recorded on PerkineElmer Spectrum 100
⇑
Corresponding author. Tel.: +90 464 223 61 26; fax: +90 464 223 40 19.
E-mail addresses: musaozil@hotmail.com, musa.ozil@erdogan.edu.tr (M. Özil).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.12.016

M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
83
Infrared Spectrometer. UV–Vis spectra were recorded on PerkinEl-
mer Lambda 35 UV–Vis spectrometer. 1H NMR and 13C NMR stud-
ies were done on Brucker 400 MHz NMR. Thermal analyses were
performed by the Instrumental SII EXSTAR 6000 TG/DTA 6300
spectrometer. Mass spectra were performed on Thermo TSQ Quan-
tum acces max for compounds 2–5 and on a Bruker Daltonic Auto-
flex III MALDI-TOF spectrometer for compounds 6a–e, 7a–e.
Microwave-assisted syntheses were carried out using monomode
CEM-Discover microwave apparatus.
134.84, 135.75, 141.43 (Ar–C), 115.32, 115.60 (C„N), 145.84
(C@N), 165.91 (ester –C@O), 151.19 (triazol –C@O). MS (ES+),
m/z: calc.: 359, found: 382 [M+Na]+.
2.2.4. 4-(4-Benzohydrazide)-5-methyl-3,4-dihydro-2H-1,2,4-triazole-
3-one (3)
Compound 2 (1.165 g, 0.005 mol) and NH2NH2.H2O (4.9 mL,
0.1 mol) were dissolved in dry EtOH (10 mL) and irradiated by a
microwave at 55 °C, 300 W for 10 min. The process of the reaction
was checked with TLC. Product was subsequently recrystallized
two times from EtOH. Then product was filtered off and dried un-
der vacuum. Yield: 0.85 g (73%), m.p.: 236–238 °C. Anal. Calc. for
2.2. Synthesis
2.2.1. 4-Amino-methylbenzoate (1)
C
10H11N5O2: C, 51.50; H, 4.75; N, 30.03. Found: C, 51.52; H, 4.73;
0.7 g (5.2 mmol) of 4-aminobenzoic acid was dissolved in anhy-
drous MeOH (15 mL), added 4.82 g (41.1 mmol) of thionyl chloride
dropwise under N2 while stirring at 0 °C. After mixture was stirred
at room temperature at 30 min the mixture was irradiated in
microwave at 65 °C, 300 W, for 10 min. The process of the reaction
was checked with TLC. After the reaction was completed 40 mL of
saturated K2CO3(aq) was added and then extracted with EtOAc
(3 ꢀ 15 mL). Solvent was removed and recrystallized from H2O.
Yield: 2.31 g (98%), m.p.: 111–113 °C.
N, 30.02%. FT-IR
m
max/cmꢁ1: 3285 (NH2), 3206 (N–H), 3128 (triazole
N–H), 3019 (Ar–H), 2876 (Aliph. C–H), 1727 (triazole C@O), 1660
(ester C@O), 1621 (C@N). 1H NMR (DMSO-d6) (d: ppm): 2.15 (3H,
s, –CH3), 4.55 (2H, s, –NH2), 7.51 (d-like, AA0 part of AA0XX0 system,
3JHH = 8.44, 2H, Ar–H), 7.94 (d-like, XX0 part of AA0XX0 system,
3JHH = 8.44, 2H, Ar–H), 9.90 (1H, s, NH(ester) ,
) 11.67 (1H, s,
NH(triazole)). 13C NMR (DMSO-d6) (d: ppm): 12.90 (–CH3), 127.20,
128.42, 133.48, 135.76 (Ar–C), 144.03 (C@N), 165.48 (ester C@O),
154.51 (triazole C@O). MS (ES+), m/z: calc.: 233, found: 234 [M+1]+.
2.2.2. 4-(4-Methylbenzoate)-5-methyl-3,4-dihydro-2H-1,2,4-triazol-
3-one (2)
2.2.5. 2-(3,4-Dicyanophenyl)-4-(4-benzohydrazide)-5-methyl-3,4-
dihydro-2H-1,2,4-triazole-3-one (5)
A mixture of ethyl acetate ethoxycarbonyl hydrazone (0.870 g,
0.005 mol) and 4-amino-methylbenzoate (1) (0.755 g, 0.005 mol)
in solvent-free condition was irradiated in microwave at 130 °C,
300 W, for 5 min. After the mixture had cooled to room tempera-
ture, the process of the reaction was checked with TLC. The product
was subsequently recrystallized two times from EtOH. The product
was then filtered off and dried under vacuum. Yield: 0.89 g (76%),
m.p.: 230–232 °C. Anal. Calc. for C11H11N3O3: C, 56.65; H, 4.75; N,
2.2.5.1. Method A. Compound 3 (1.16 g, 0.005 mol) and 4-nitropht-
halonitrile (0.87 g, 0.005 mol) were dissolved in dry DMF (10 mL).
The mixture was irradiated by microwave at 60 °C, 300 W for
10 min. While the mixture was being irradiated, finely ground
anhydrous K2CO3 (0.83 g, 0.006 mol) was added in four portions
every 2 min. The process of the reaction was checked with TLC.
The mixture obtained was then poured into 100 mL icewater. The
precipitate was filtered off and washed with HCl (50 mL, 5%) and
then washed with water until the filtrate became neutral, and
dried. The product was subsequently recrystallized two times from
EtOH. Yield: 0.57 g (32%), m.p.: 195–197 °C.
18.02. Found: C, 56.63; H, 4.78; N, 18.00%. FT-IR m
max/cmꢁ1: 3181
(N–H), 3070 (Ar–H), 2964 (Aliph. C–H), 1718 (triazole –C@O),
1692 (ester –C@O), 1594 (C@N), 1286 (C–O). 1H NMR (DMSO-d6)
(d: ppm): 2.12 (3H, s, –CH3), 3.89 (3H, s, –OCH3), 7.59 (d-like, AA0
part of AA0XX0 system, 3JHH = 8.40, 2H, Ar–H), 8.10 (d-like, XX0 part
2.2.5.2. Method B. Compound 4 (1.80 g, 0.005 mol) and NH2NH2.H2-
O (4.9 mL, 0.1 mol) were dissolved in dry DMF (3 mL) and irradi-
ated by a microwave at 60 °C, 300 W for 5 min. The process of
the reaction was checked with TLC. The reaction mixture was
poured into an ice-water bath and HCl solution was added to elim-
inate the base trace. The solid material that formed was filtered off
and washed with water until the filtrate became neutral. Then
product was subsequently recrystallized two times from EtOAc.
Yield: 1.76 g (98%), m.p.: 195–197 °C. Anal. Calc. for C18H13N7O2:
C, 60.16; H, 3.65; N, 27.29. Found: C, 60.18; H, 3.62; N, 27.28%.
3
of AA0XX0 system, JHH = 8.40, 2H, Ar–H), 11.75 (1H, s, –NH). 13C
NMR (DMSO-d6) (d: ppm): 12.96 (–CH3), 52.84 (–OCH3), 127.41,
129.60, 130.62, 130.67 (Ar–C), 143.88 (C@N), 154.34 (triazol –
C@O), 166.00 (ester –C@O). MS (ES+), m/z: calc.: 233, found: 234
[M+1]+.
2.2.3. 2-(3,4-Dicyanophenyl)-4-(4-methylbenzoate)-5-methyl-3,4-
dihydro-2H-1,2,4-triazole-3-one (4)
Compound 2 (0.58 g, 0.0025 mol) and 4-nitrophthalonitrile
(0.43 g, 0.0025 mol) were dissolved in dry DMF (10 mL). The mix-
ture was irradiated by microwave at 60 °C, 300 W for 10 min.
While the mixture was being irradiated, finely ground anhydrous
K2CO3 (0.41 g, 0.003 mol) was added in four portions every
2 min. The process of the reaction was checked with TLC. The mix-
ture obtained was then poured into 100 mL icewater. The precipi-
tate was filtered off and washed with HCl (50 mL, 5%) and then
washed with water until the filtrate became neutral, and dried.
The product was subsequently recrystallized two times from EtOH.
Yield: 0.79 g (89%), m.p.: 224–226 °C. Anal. Calc. for C19H13N5O3: C,
63.51; H, 3.65; N, 19.49. Found: C, 63.53; H, 3.63; N, 19.51%. FT-IR
FT-IR
m
max/cmꢁ1: 3310 (NH2), 3269 (N–H), 3096 (Ar–H), 2924
(Aliph. C–H), 2231 (CN), 1723 (triazole C@O), 1671 (ester C@O),
1597 (C@N). 1H NMR (DMSO-d6) (d: ppm): 2.15 (3H, s, –CH3),
4.55 (2H, s, –NH2), 7.64 (d-like, AA0 part of AA0XX0 system,
3JHH = 8.20, 2H, Ar–H), 8.00 (d-like, XX0 part of AA0XX0 system,
3JHH = 8.20, 2H, Ar–H), 8.24 (1H, d, J = 8.74, Ar–CH), 8.42 (1H, d,
J = 8.74, Ar–CH), 8.53 (1H, s, Ar–CH), 9.90 (1H, s, NH(ester)), 11.67
(1H, s, NH(triazole)). 13C NMR (DMSO-d6) (d: ppm): 12.84 (–CH3),
110.13, 121.68, 121.80, 127.76, 128.66, 134.57, 136.01, 141.52
(Ar–C), 116.05, 116.44 (C„N), 147.13 (C@N), 151.34 (triazole
C@O), 165.35 (ester C@O). MS (ES+), m/z: calc.: 359, found: 359.9
[M+1]+.
m
max/cmꢁ1: 3107 (Ar–H), 2958 (Aliph. C–H), 2227 (CN), 1716 (tria-
zol –C@O), 1701 (ester –C@O), 1593 (C@N), 1282 (C–O). 1H NMR
(CDCI3) (d: ppm): 2.30 (3H, s, –CH3), 3.97 (3H, s, –OCH3), 7.45 (d-
like, AA0 part of AA0XX0 system, 3JHH = 8.40, 2H, Ar–H), 8.23 (d-like,
2.2.6. General procedures for metal-free phthalocyanine derivatives
(6a,7a)
2.2.6.1. Method I. A mixture of compound 4 (0.09 g, 0.25 mmol) or
compound 5 (0.09 g, 0.25 mmol) and two drops of DBU in dry
n-pentanol (5 mL) was heated under reflux under N2 for 20 h.
The solvent was evaporated to 1/10 of the initial volume and the
3
XX0 part of AA0XX0 system, JHH = 8.40, 2H, Ar–H), 7.94 (1H, d,
J = 8.40, Ar–CH), 8.49 (1H, dd, J = 8.40, J = 8.80, Ar–CH), 8.55 (1H,
d, J = 8.80, Ar–CH). 13C NMR (CDCI3) (d: ppm): 13.04 (–CH3),
52.83 (–OCH3), 111.31, 117.22, 121.49, 122.29, 126.93, 131.54,

84
M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
reaction mixture was precipitated by adding MeOH at room tem-
perature. The product was separated by filtration as a green solid.
The precipitate was washed successively with cold H2O, MeOH and
EtOH to remove the starting materials unaffected by the reaction
and dried in vacuo. The green product was washed with hot EtOH,
EtOAc, acetone, (C2H5)2O and CHCl3. All of synthesized metal-free
phthalocyanines were soluble in DMF and DMSO.
and two drops of DBU in 2-(dimethylamino)ethanol (2 mL) was
irradiated by microwave at 160 °C, 300 W, for 5 min. Above purifi-
cation method was also applied to this method.
2.2.7.3. Method III. A mixture of compound 4 (0.09 g, 0.25 mmol) or
compound 5 (0.09 g, 0.25 mmol), anhydrous metal salts [NiCl2
(8.17 mg, 0.0625 mmol), Zn(CH3COO)2 (11.50 mg, 0.0625 mmol),
CoCl2 (8.17 mg, 0.0625 mmol), CuCl2 (8.47 mg, 0.0625 mmol) and
two drops of DBU in solvent-free condition was irradiated by
microwave at 160 °C, 300 W, for 5 min. Above purification method
was also applied to this method.
2.2.6.2. Method II. A mixture of compound 4 (0.09 g, 0.25 mmol) or
compound 5 (0.09 g, 0.25 mmol) and two drops of DBU in 2-
(dimethylamino)ethanol (2 mL) was irradiated by microwave at
160 °C, 300 W, for 5 min. After cooling to room temperature, the
reaction mixture was treated with H2O to precipitate the product
which was filtered off. Above purification method was also applied
to this method.
2.2.7.3.1.Cobalt(II) phthalocyanine (6b). M.p.> 300 °C. Anal. Calc.
for C76H52CoN20O12: C, 61.01; H, 3.50; N, 18.72. Found: C, 61.24; H,
3.63; N, 18.63%. FT-IR
1715 (–C@O), 1596 (C@N), 1277 (C–O). UV–Vis (DMF): kmax, nm
m
max/cmꢁ1: 3071 (Ar–H), 2946 (Aliph. C–H),
(log e): 684 (4.29), 625 (3.74), 294 (4.02). MALDI-TOF mass m/z
2.2.6.3. Method III. A mixture of compound 4 (0.09 g, 0.25 mmol) or
compound 5 (0.09 g, 0.25 mmol) and two drops of DBU in solvent-
free condition was irradiated by microwave at 160 °C, 300 W, for
5 min. After cooling to room temperature, the reaction mixture
was treated with water to precipitate the product which was fil-
tered off. Above purification method was also applied to this
method.
calc.:1495.34, found: 1495.35 [M]+, 1496.32 [M+1]+.
2.2.7.3.2. Nickel(II) phthalocyanine (6c). M.p. >300 °C. Anal. Calc.
for C76H52NiN20O12: C, 61.02; H, 3.50; N, 18.72. Found: C, 60.88; H,
3.41; N, 19.02%. FT-IR m
max/cmꢁ1: 3111 (Ar–H), 2948 (Aliph. C–H),
1715 (–C@O), 1596 (C@N), 1280 (C–O). 1H NMR (DMSO-d6) (d:
ppm): 2.28 (12H, s, –CH3), 3.66 (12H, s, –OCH3), 6.52 (8H, d, Ar–
H), 7.44–8.06 (8H, m, Ar–H), 8.22 (8H, d, Ar–H), 8.53 (4H, s, Ar–
2.2.6.3.1. 2(3),9(10),16(17),23(24)-Tetrakis[5-methyl-4-(4-meth-
ylbenzoate)-3-oxo-3,4-dihydro-2H-1,2,4-triazol-2-yl]phthalocyanine
(6a). M.p. >300 °C. Anal. Calc. for C76H54N20O12: C, 63.42; H, 3.78;
H). UV–Vis (DMF): kmax, nm (log e): 660 (4.21), 609 (4.08), 288
(3.85). MALDI-TOF mass m/z calc.: 1494.34, found: 1494.36 [M]+,
1495.34 [M+1]+.
N, 19.46. Found: C, 63.31; H, 3.86; N, 19.27. FT-IR
m
max/cmꢁ1: 3234
2.2.7.3.3.Copper(II) phthalocyanine (6d). M.p.> 300 °C. Anal. Calc.
for C76H52CuN20O12: C, 60.82; H, 3.49; N, 18.66. Found: C, 60.62; H,
(Pc-NH), 3073 (Ar–H), 2987 (Aliph. C–H), 1707 (–C@O), 1597
(C@N), 1252 (C–O). 1H NMR (DMSO-d6) (d: ppm): ꢁ1.29 (2H, s,
NH(metal-free)), 2.30 (12H, s, –CH3), 3.68 (12H, s, –OCH3), 6.55 (8H,
d, Ar–H), 7.50–8.02 (8H, m, Ar–H), 8.15 (8H, d, Ar–H), 8.46 (4H, s,
3.61; N, 18.82%. FT-IR
1711 (–C@O), 1592 (C@N), 1270 (C–O). UV–Vis (DMF): kmax, nm
m
max/cmꢁ1: 3107 (Ar–H), 2952 (Aliph. C–H),
(log e): 685 (4.23), 633 (4.19), 334 (4.05). MALDI-TOF mass m/z
Ar–H). UV–Vis (DMF): kmax, nm (log
e): 701 (4.32), 631 (4.20),
calc.:1499.34, found: 1499.34 [M]+, 1500.35 [M+1]+.
325 (3.54). MALDI-TOF mass m/z calc.: 1438.42, found: 1438.43
2.2.7.3.4. Zinc(II) phthalocyanine (6e). M.p. >300 °C. Anal. Calc.
for C76H52ZnN20O12: C, 60.74; H, 3.50; N, 18.64. Found: C, 61.03;
[M]+, 1439.42 [M+1]+.
2.2.6.3.2.
2(3),9(10),16(17),23(24)-Tetrakis[5-methyl-4-(4-ben-
H, 3.61; N, 18.32%. FT-IR m
max/cmꢁ1: 3080 (Ar–H), 2949 (Aliph.
zohydrazide)-3-oxo-3,4-dihydro-2H-1,2,4-triazol-2-yl]phthalocya-
nine (7a). M.p. >300 °C. Anal. Calc. for C72H54N28O8: C, 60.08; H,
C–H), 1715 (–C@O), 1599 (C@N), 1278 (C–O). 1H NMR (DMSO-d6)
(d: ppm): 2.32 (12H, s, –CH3), 3.62 (12H, s, –OCH3), 6.63 (8H, d,
Ar–H), 7.12–7.81 (8H, m, Ar–H), 8.03 (8H, d, Ar–H), 8.47 (4H, s,
3.78; N, 27.25. Found: C, 60.22; H, 3.53; N, 27.38%. FT-IR mmax
/
cmꢁ1: 3338 (NH2), 3201 (NH), 3069 (Ar–H), 2927 (Aliph. C–H),
1709 (–C@O), 1600 (C@N). 1H NMR (DMSO-d6) (d: ppm): ꢁ1.53
(2H, s, NH(metal-free)), 2.22 (12H, s, ꢁCH3), 5.65 (8H, s, ꢁNH2), 6.73
(8H, d, Ar–H), 7.32–7.97 (8H, m, Ar–H), 8.29 (8H, d, Ar–H), 8.52
(4H, s, Ar–H), 9.78 (4H, s, NH(ester)). UV–Vis (DMF): kmax, nm (log
Ar–H). UV–Vis (DMF): kmax, nm (log e): 686 (4.26), 630 (3.73),
290 (4.02). MALDI-TOF mass m/z calc.: 1500.34, found: 1500.37
[M]+, 1501.36 [M+1]+.
2.2.7.3.5.Cobalt(II) phthalocyanine (7b). M.p. >300 °C. Anal. Calc.
for C72H52CoN28O8: C, 57.79; H, 3.50; N, 26.21. Found: C, 57.48; H,
e
): 703 (4.31), 627 (4.30), 287 (3.80). MALDI-TOF mass m/z
3.72; N, 26.38%. FT-IR
(Ar–H), 2928 (Aliph. C–H), 1708 (–C@O), 1598 (C@N). UV–Vis
m
max/cmꢁ1: 3235 (NH2), 3099 (NH), 3055
calc.:1438.47, found: 1438.49 [M]+, 1439.48 [M+1]+.
(DMF): kmax, nm (log e): 681 (4.30), 623 (3.88), 262 (4.12). MAL-
2.2.7. General procedures for metallophthalocyanine derivatives (6b–
6e and 7b–7e)
DI-TOF mass m/z calc.: 1495.39, found: 1495.41 [M]+, 1496.42
[M+1]+.
2.2.7.1. Method I. A mixture of compound 4 (0.09 g, 0.25 mmol) or
compound 5 (0.09 g, 0.25 mmol), anhydrous metal salts [NiCl2
(8.17 mg, 0.0625 mmol), Zn(CH3COO)2 (11.50 mg, 0.0625 mmol),
CoCl2 (8.17 mg, 0.0625 mmol), CuCl2 (8.47 mg, 0.0625 mmol)]
and two drops of DBU in dry n-pentanol (5 mL) was heated under
reflux under N2 for 20 h. After cooling to the room temperature, the
reaction mixture was precipitated by the addition of MeOH and
green product was filtered off. It was washed successively with
cold H2O, MeOH and EtOH to remove the starting materials unaf-
fected by the reaction and dried in vacuo. The green product was
washed with hot EtOH, EtOAc, acetone, (C2H5)2O and CHCl3. All
of synthesized metallophthalocyanines were soluble in DMF and
DMSO.
2.2.7.3.6. Nickel(II) phthalocyanine (7c). M.p. >300 °C. Anal. Calc.
for C72H52NiN28O8: C, 57.80; H, 3.50; N, 26.21. Found: C, 57.33; H,
3.63; N, 26.02%. FT-IR m
max/cmꢁ1: 3336 (NH2), 3205 (NH), 3067
(Ar–H), 2928 (Aliph. C–H), 1707 (–C@O), 1597 (C@N). 1H NMR
(DMSO-d6) (d: ppm): 2.17 (12H, s, –CH3), 5.79 (8H, s, –NH2), 6.65
(8H, d, Ar–H), 7.24–7.81 (8H, m, Ar–H), 8.16 (8H, d, Ar–H), 8.72
(4H, s, Ar–H), 9.63 (4H, s, NH(ester)). UV–Vis (DMF): kmax, nm (log
e
): 685 (4.29), 632 (4.00), 253 (3.80). MALDI-TOF mass m/z calc.:
1494.39, found: 1494.39 [M]+, 1495.37 [M+1]+.
2.2.7.3.7.Copper(II) phthalocyanine (7d). M.p. >300 °C. Anal. Calc.
for C72H52CuN28O8: C, 57.62; H, 3.49; N, 26.13. Found: C, 57.48; H,
3.53; N, 25.82%. FT-IR
(Ar–H), 2926 (Aliph. C–H), 1705 (–C@O), 1597 (C@N). UV–Vis
m
max/cmꢁ1: 3346 (NH2), 3213 (NH), 3062
(DMF): kmax, nm (log e): 696 (4.30), 628 (4.26), 287 (4.07). MAL-
2.2.7.2. Method II. A mixture of compound 4 (0.09 g, 0.25 mmol) or
compound 5 (0.09 g, 0.25 mmol), anhydrous metal salts [NiCl2
(8.17 mg, 0.0625 mmol), Zn(CH3COO)2 (11.50 mg, 0.0625 mmol),
CoCl2 (8.17 mg, 0.0625 mmol), CuCl2 (8.47 mg, 0.0625 mmol)]
DI-TOF mass m/z calc.: 1499.38, found: 1499.42 [M]+, 1500.39
[M+1]+.
2.2.7.3.8. Zinc(II) phthalocyanine (7e). M.p. >300 °C. Anal. Calc.
for C72H52ZnN28O8: C, 57.54; H, 3.49; N, 26.10. Found: C, 57.72;

M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
85
H, 3.66; N, 25.93%. FT-IR
m
max/cmꢁ1: 3315 (NH2), 3222 (NH), 3059
sharp –C„N stretching vibration band at 2227 cmꢁ1 in the FT-IR
spectrum. In the 1H NMR spectrum of compound 4 in deuterated
chloroform, the signal belonging to –NH proton for the compound
2 disappeared after the formation of compounds 4. The new aro-
matic protons were observed at 7.49–8.55 ppm. In the 13C NMR
spectrum of 4, the characteristic signals were observed at 115.3
and 115.6 related to dicyano carbon atoms. In the mass spectrum
of compound 4, the presence of characteristic molecular ion peak
at m/z: 382 [M+Na]+ confirmed the proposed structure. 2-(3,4-
Dicyanophenyl)-4-(4-benzohydrazide)-5-methyl-3,4-dihydro-2H-
1,2,4-triazol-3-one (5) was synthesized by the reaction of com-
pound 3 with 4-nitro phthalonitrile in the presence of finely
ground anhydrous K2CO3 as a base at 60 °C in DMF for 5 min (hold
time) at 300 W maximum power. With this method, the yield of
product was much lower (32%). A possible reason for the lower
yield of compound 5 is intermolecular H bonding. Therefore, we
decided to obtain compound 5 from the reaction of compound 4
with hydrazine hydrate at 60 °C in DMF for 5 min (hold time) at
300 W maximum power. We obtained compound 5 with excellent
yield (98%) using this method. The characteristic vibration corre-
sponding to –C„N was observed at 2231 cmꢁ1 for compound 5.
The 1H NMR spectra of the substituted phthalonitrile compound
showed signals with ranging from 8.24 to 8.53 ppm belonging to
aromatic protons. The 13C NMR spectra of compound 5 indicated
the presence of nitrile carbon atoms at 116.0 and 116.4 ppm. In
the mass spectra of compound 5, the molecular ion peak was ob-
served at 359.9 [M+H]+ (Scheme 1).
The metal-free phthalocyanines (6a,7a) were synthesized with
microwave irradiation in both solvent-free and solution media
(dimethylaminoethanol) of the corresponding dicyano compounds
4 and 5 at 160 °C for 5 min. For comparison data we synthesized
compounds 6a and 7a in n-pentanol in the presence of a strong or-
ganic base such as DBU at reflux temperature for 24 h. The metall-
ophthalocyanines ( 6b–6e, 7b–7e) were obtained from dicyano
derivatives 4, 5 and corresponding anhydrous metal salts CoCl2,
NiCl2, CuCl2, and Zn(CH3COO)2, respectively, by microwave irradi-
ation in both solvent-free and solution media (dimethylaminoeth-
anol) at 160 °C for 3 min and 5 min, respectively. For comparison
data we synthesized compounds 6b–6e and 7b–7e in n-pentanol
in the presence of a strong organic base such as DBU at reflux tem-
perature for 24 h. After conversion into phthalocyanine derivatives,
the characteristic –C„N stretch for substituted phthalonitrile
derivatives disappeared in the IR spectra, which is indicative of
phthalocyanine formation. The 1H NMR spectra of phthalocyanines
demonstrated almost identical chemical shifts. In addition, the ring
cavity protons for 6a and 7a were observed as weak peaks at ꢁ1.27
and ꢁ1.56 ppm as anticipated. The MALDI-TOF-MS spectra of
phthalocyanines exhibited low fragmentation in reflectron mode.
The molecular ion peaks of all phthalocyanines confirmed the pro-
posed structures. Elemental analyses of the novel compounds
showed good agreement with the calculated values (Scheme 2).
The cyclization of ethyl carbazete with compound 1 to the corre-
sponding compound 2 and the macrocyclization of compounds 4
and 5 to the corresponding phthalocyanines were accomplished
by heating the compounds 1, 4 and 5 to their respective melting
points by using microwave irradiation. The polarity of the system
was increased during the reaction progress from the neutral ground
state to the dipolar transition state for cyclization. Consequently, the
microwave stabilizing effects of dipole–dipole interactions with the
electric field are increased with the polarity of reactants.
(Ar–H), 2926 (Aliph. C–H), 1708 (–C@O), 1603 (C@N). 1H NMR
(DMSO-d6) (d: ppm): 2.13 (12H, s, –CH3), 5.63 (8H, s, –NH2), 6.53
(8H, d, Ar–H), 7.36–7.88 (8H, m, Ar–H), 8.15 (8H, d, Ar–H), 8.61
(4H, s, Ar–H), 9.52 (4H, s, NH). UV–Vis (DMF): kmax, nm (log e):
693 (4.38), 632 (4.15), 271 (3.81). MALDI-TOF mass m/z calc.:
1500.38, found: 1500.38 [M]+, 1501.41 [M+1]+.
3. Results and discussion
3.1. Synthesis and characterization
Microwave irradiation (MW) has been used for the rapid
synthesis of a variety of compounds and this technique, under sol-
vent-free conditions, is regarded as an environmentally acceptable
practice for a number of reasons, including the fact that the reac-
tions are quite often cleaner, faster, and higher yielding than con-
ventional synthesis. In some cases it is possible to conduct a
reaction without solvent under microwave irradiation, as we de-
scribed [45,46]. In this case, we introduced a facile preparation of
bulky substituted metal-free phthalocyanines and metallophthalo-
cyanines, under solvent free and reflux conditions, using micro-
wave irradiation.
Recently, it has been reported that in the preparation of phthal-
ocyanines using microwave irradiation, the yield of reaction was
generally found to be under 50% [26–30,47,48]. Here, we were able
to synthesize phthalocyanines and metallophthalocyanines and
found the yield of reaction to be more than 85%.
Methyl 4-aminobenzoate (1) was synthesized by 4-aminoben-
zoic acid resulting in several reaction conditions [49–51]. Then
we obtained methyl 4-aminobenzoate from 4-aminobenzoic acid
by using microwave irradiation with an excellent yield (98%)
obtained from the employment of a new method. 4-(4-Meth-
ylbenzoate)-5-methyl-3,4-dihydro-2H-1,2,4-triazol-3-one (2) was
obtained from the reaction of ethyl 2-(1-ethoxyethylidene)hydra-
zinecarboxylate with methyl 4-aminobenzoate under solvent free
condition through the use of microwave irradiation. The formation
of compound 2 was obviously verified by the appearance of –NH, –
C@Otriazol, –C@Oester, and –C–O stretching vibration bands at 3181,
1718, 1692, 1286 cmꢁ1, respectively, in the FT-IR spectrum. The 1H
NMR spectra of the compounds 2 showed signals 2.12, 3.89, 7.59
(J = 8.40), 8.10 (J = 8.40) and 11.75 ppm belonging to –CH3, –
OCH3, Ar–H and –NH, respectively. The 13C NMR spectra of the
compounds
2 showed signals 12.9, 52.8, 143.9, 154.3 and
166.0 ppm belonging to –CH3, –OCH3, –C@N, –C@Otriazol, –C@Oester
,
respectively. Furthermore, in the mass spectra, the molecular ion
peaks were observed at m/z: 234 [M+1]+ for compound 2. Com-
pound 2 was treated with hydrazine hydrate to give 4-(4-ben-
zohydrazide)-5-methyl-3,4-dihydro-2H-1,2,4-triazol-3-one
Comparison of the IR spectral data clearly indicated the formation
(3).
of compound 3 by the disappearance of the –C–O band, and the
appearance of new –NH2 and –NH bands at 3285 and 3206 cmꢁ1
.
The 1H NMR spectra of 3 showed new signal due to –NH2 and –
NH protons at 4.55 and 9.90 ppm, respectively. In the 13C NMR
spectrum of 3, the signal belonging to –OCH3 for the precursor
compound 2 disappeared after the formation of 3. In the mass
spectra, the molecular ion peaks were observed at m/z: 234
[M+1]+ for 3.
2-(3,4-Dicyanophenyl)-4-(4-methylbenzoate)-5-methyl-3,4-di-
hydro-2H-1,2,4-triazol-3-one (4) was synthesized by the reaction
of compound 2 with 4-nitro phthalonitrile in the presence of finely
ground anhydrous potassium carbonate as a base at 60 °C in DMF
for 10 min (hold time) at 300 W maximum power. The formation
of compounds 4 was obviously verified by the disappearance of
the –NH band of compound 2, the appearance of considerably
To demonstrate that reactions under microwave irradiation in
solvent-free conditions obtain the best results, the experiments
were run under solution media with both microwave irradiation
and conventional heating. The results are shown in Table 1. From
the results, we determined that the yields of product under sol-
vent-free conditions were much higher than with other methods.

86
M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
NH2
HO
O
60 oC 10 min MW
SO2CI2
CH3OH
NH2
O
O
CH3
1
H
C
3
N
O
O
130 oC 5 min MW
O
NH
H
C
3
CH
3
H
N
N
H3
C
O
N
CN
CN
O
O
CN
CN
55 oC 10 min
MW
CH3
O2
N
2
60 oC 10 min
MW
NH2NH2.H2O
H
N
N
N
N
H3
C
O
H3
C
O
N
N
O
O
HN
NH2
O
CH3
CN
4
3
60 oC 5 min MW
CN
60 oC 5 min MW
NH2NH2.H2O
O2
N
CN
CN
N
N
H3
C
O
N
HN
NH2
O
5
Scheme 1. The synthesis of initial compounds.
3.2. Thermal behavior of phthalocyanine compounds
phthalocyanines are well known, the obtained novel phthalocya-
nines ( 6a–6e, 7a–7e) were observed not to be stable above
311 °C. The decomposition of compound 7a occurs in the 341–
629 °C range, thus indicating that this structure presents higher
The thermal behaviors of the phthalocyanines were investi-
gated by TG/DTA. Although the potential thermal stabilities of

M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
87
CN
CN
CN
CN
N
N
N
N
H3C
O
H3C
O
N
N
HN
NH2
O
O
O
Compound
6a, 7a
M
2H
Co
CH3
5
4
6b, 7b
6c, 7c
Ni
6d, 7d
6e, 7e
Cu
Zn
H
C
3
H
N
2
O
O
O
NH
CH
CH
3
3
N
N
O
N
O
N
N
N
CH
3
O
NH
2
N
N
N
N
N
N
N
N
NH
O
O
H
C
N
H
C
3
N
3
O
O
N
N
M
N
N
N
N
M
N
N
N
N
N
N
N
N
O
CH
3
O
O
CH
O
3
N
N
N
N
O
C
NH
H N
2
H
3
N
N
N
C
O
N
O
N
N
H
3
H C
3
O
NH
NH
O
O
CH
3
2
6a-6e
7a-7e
Scheme 2. Synthesis of metal-free and metallophthalocyanines.
Table 1
Compare of yields and time under microwave irradiation and conventional heating.
Comp. Yields (%)
Time (min)
Comp. Yields (%)
Time (min)
Method I Method II Method III Method I Method II Method III
Method I Method II Method III Method I Method II Method III
6a
6b
6c
6d
6e
29
32
37
31
42
78
83
86
82
88
38
45
33
30
35
1440
1440
1440
1440
1440
3
3
3
3
3
5
5
5
5
5
7a
7b
7c
7d
7e
38
45
48
39
52
80
85
87
83
91
44
32
45
51
50
1440
1440
1440
1440
1440
3
3
3
3
3
5
5
5
5
5
stability than the other metal-free and metallophthalocyanines.
The initial and main decomposition temperatures are given in
Table 2. The initial decomposition temperatures decreased in the
order of 6d > 6b > 6c > 7d > 7b > 7c > 7a > 6a > 6e > 7e.
3.3. Ground state electronic absorption spectra
Phthalocyanine compounds exhibit typical UV–Vis electronic
spectra with two significant absorption bands, one of them in the

88
M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
Table 2
631, 701 and 627, 703 nm corresponding to the Q band in the vis-
Thermal properties of the studied phthalocyanines.
ible region for compounds 6a and 7a, respectively. The UV–Vis
spectra of metallophthalocyanines 6b–6e and 7b–7e in DMF
showed intense Q absorption at about kmax = 660–686 and 681–
696 nm with a weaker absorption at 609–633 and 623–632 nm,
respectively (Figs. 1 and 2). B band absorptions of compounds
6b–6e and 7b–7e were observed at kmax = 288–334 and 253–
287 nm as expected, respectively.
Compound
M
Initial decomposition
temperature in °C
Main decomposition
temperature in °C
6a
6b
6c
6d
6e
7a
7b
7c
7d
7e
2H
Co
Ni
Cu
Zn
2H
Co
Ni
343
318
321
311
348
341
325
331
323
377
608
456
548
518
566
629
455
515
451
577
4. Conclusion
Cu
Zn
In conclusion, the synthesis of initial compounds (2,3), dinitrile
derivatives (4,5) and tetrasubstituted phthalocyanine derivatives
(6a–6e, 7a–7e) have been reported for the first time. The new com-
pounds were characterized by IR, UV–Vis, 1H NMR, 13C NMR, mass
spectroscopy and elemental analysis. For the purposes of compar-
ing data, the reactions were carried out under solvent free condi-
tion using microwave irradiation and, in solution media, with
both microwave irradiation and using conventional methods. The
present procedure described in this paper demonstrated that
microwave processing combined with solvent-free condition leads
to shorter reaction time, higher yield, a clean reaction product and
easier work-up than classical thermal processing. Consequently,
we have developed a fast and effective procedure for the synthesis
6a
6b
6c
6d
6e
2.0
1.5
1.0
0.5
0.0
of
bulky
substituted
metal-free
phthalocyanines
and
metallophthalocyanines.
References
[1] P. Lidstrom, J. Tierney, B. Wathey, J. Westman, Tetrahedron 57 (2001) 9225.
[2] C.O. Kappe, Angew. Chem., Int. Ed. 43 (2004) 6250.
[3] C.R. Strauss, R.S. Varma, Top. Curr. Chem. 266 (2006) 199.
[4] R.S. Varma, Green Chem. 1 (1999) 43.
300
400
500
600
700
800
Wavelength (nm)
[5] I. Gao, G. Hofstra, R.A. Fletcher, Can. J. Bot. 66 (1988) 1178.
[6] G. Turan-Zitouni, M. Sıvacı, S.F. Kılıç, K. Erol, Eur. J. Med. Chem. 36 (2001) 685.
[7] R.A. Fletcher, G. Hofstra, J. Plant Gowth Regul. 9 (1990) 207.
[8] M.R. Grimmett, in: A.R. Katritzky, C.W. Rees (Eds.), Comprehensive
Heterocyclic Chemistry, Pergamon Press, London, 1984.
Fig. 1. UV–Vis spectra of Pcs 6a–6e in DMF.
[9] R.S. Upanhayaya, N. Sinha, S. Jain, N. Kishore, R. Chandra, S.K. Arora, Bioorg.
Med. Chem. 12 (2004) 2225.
[10] G. Menozzi, L. Mosti, P. Fossa, C. Mısiu, C. Murcioni, P.L. Colla, Il Farmako 56
7a
7b
7c
7d
7e
2
1
0
(2001) 633.
[11] B. Kahveci, O. Bekircan, Sß.A. Karaog˘lu, Indian J. Chem. 44b (2005) 2614–2617.
[12] Y.A. Al-Soud, M.N. Al-Dweri, N.A. Al-Masoudi, Il Farmaco 59 (2004) 775.
[13] G. Turan-Zitouni, Z.A. Kaplancikli, K. Erol, F.S. Kilic, Il Farmaco 54 (1999) 218.
[14] F. Malbec, R. Milcent, P. Vicart, A.M. Bure, J. Heterocycl. Chem. 21 (1984) 1769.
[15] H. Bayrak, A. Demirbasß, N. Demirbaßs, Sß.A. Karaog˘lu, Eur. J. Med. Chem. 45
(2010) 4726.
[16] R.A. Smith, J. Barbosa, C.L. Blum, M.A. Bobko, Y.V. Caringal, R. Dally, J.S.
Johnson, M.F. Katz, N. Kennure, J. Kinger-Wood, W. Lee, T.B. Lowinger, J. Lyons,
V. Marsh, D.H. Rogers, S. Swartz, T. Walling, H. Wild, Bioorg. Med. Chem. Lett.
11 (2001) 2775.
[17] E.V. Lider, E.V. Peresypkina, K.A. Volkova, E.V. Abramova, Y.G. Shvedenkov, V.N.
Ikorskii, L.A. Sheludyakova, A.I. Smolentsev, L.G. Lavrenova, Russ. Chem. Bull.
57 (2008) 1931.
[18] O.G. Shakirova, A.V. Virovets, D.Y. Naumov, Y.G. Shvedenkov, V.N. Elokhina,
L.G. Lavrenova, Inorg. Chem. Commun. 5 (2002) 690.
[19] C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines Properties and Applications,
vols. I–IV, VCH Publisher, Weinheim, 1983–1996.
300
400
500
600
700
[20] C.G. Claessens, W.J. Blau, M. Cook, M. Hanack, R.J.M. Nolte, T. Torres, D. Wöhrle,
Wavelength (nm)
Monatsh. Chem. 132 (2001) 3.
[21] Ö. Bekarog˘lu, Appl. Organomet. Chem. 10 (1996) 605.
[22] M.J. Cook, J. Mater. Chem. 6 (1996) 677.
Fig. 2. UV–Vis spectra of Pcs 7a–7e in DMF.
[23] J.J. Simon, J. Andre, Molecular Semiconductors, Springer, Berlin, 1985.
[24] S. Müller, V. Manterava, N. Stoichkova, H. Kliesch, A. Sobki, D. Wöhrle, M.
Shopova, J. Photochem. Photobiol. B: Biol. 35 (1996) 167.
visible region at about 609–703 nm corresponding to the Q band,
ant the other in the UV region, approximately at about 253–
334 nm. The electronic absorption spectra of the metal-free
phthalocyanines (6a,7a) and metal-phthalocyanines (6b–6e,7b–
7e) in DMF are illustrated in Figs. 1 and 2.
The metal-free phthalocyanine compounds (6a,7a) showed two
absorption bands in the Q band region due to D2h symmetry of this
compound in DMF. The absorption bands were observed at 287
and 325 nm in the UV region corresponding to the B band and at
[25] I. Okura, Photosensitization of Porphyrins and Phthalocyanines, Gordon and
Breach Science Publishers, Amsterdam, 2000.
_
[26] M. Özil, E. Ag˘ar, S. Sßaßsmaz, B. Kahveci, N. Akdemir, I.E. Gümrükçüog˘lu, Dyes
Pigm. 75 (2007) 732.
[27] Z. Bıyıklıog˘lu, H. Kantekin, M. Özil, J. Organomet. Chem. 692 (2007) 2436.
[28] B. Kahveci, S. Sasßmaz, M. Özil, C. Kantar, B. Koßsar, O. Büyükgüngör, Turk. J.
Chem. 30 (2006) 681.
[29] B. Kahveci, M. Özil, C. Kantar, S. Sasßmaz, Sß. Ißsık, Y. Köysal, J. Organomet. Chem.
692 (2007) 4835.
_
[30] K. Serbest, I. Deg˘irmenciog˘lu, Y. Ünver, M. Er, C. Kantar, K. Sancak, J.
Organomet. Chem. 692 (2007) 5646.

M. Özil, M. Canpolat / Polyhedron 51 (2013) 82–89
89
[31] D.K. Modibane, T. Nyokong, Polyhedron 28 (2009) 1475.
[32] C. Kantar, N. Akdemir, E. Ag˘ar, N. Ocak, S. Sßaßsmaz, Dyes Pigm. 76 (2008) 7.
[33] T.E. Youssef, Polyhedron 29 (2010) 1176.
[42] A. Burczyk, A. Loupy, D. Bogdal, A. Petit, Tetrahedron 61 (2005) 179.
[43] M. Pesson, S. Dupin, M. Antoine, Bull. Soc. Chim. France (1962) 1364.
[44] J.G. Young, W. Onyebuagu, J. Org. Chem. 55 (1990) 2155.
[34] A. Shaabani, R.M. Moghaddam, A. Maleki, A.H. Rezayan, Dyes Pigm. 74 (2007)
279.
[45] M. Özil, E. Menteßse, B. Kahveci, Eur. J. Chem. 3 (4) (2012) 442, http://
dx.doi.org/10.5155/eurjchem.3.4.442-446.691.
[35] K.S. Jung, J.H. Kwon, J. Mater. Sci. 39 (2004) 723.
[36] K.S. Lokesh, N. Uma, B.N. Achar, Polyhedron 28 (2009) 1022.
[37] A. Shaabani, J. Chem. Res. (S) (1998) 672.
[38] D. Villemin, M. Hammadi, M. Hachemi, N. Bar, Molecules 6 (2001) 831.
[39] N. Safari, P.R. Jamaat, M. Pirouzmand, A. Shaabani, J. Porp. Phthalocyan. 8
(2004) 1209.
[46] M. Özil, Sß.A. Karaog˘lu, B. Kahveci, Synt. Comm. (2013), http://dx.doi.org/
10.1080/00397911.2011.632831.
_
[47] I. Acar, Z. Bıyıklıog˘lu, M. Durmusß, H. Kantekin, J. Organomet. Chem. 708–709
(2012) 65.
[48] A. Nas, S. Fandaklı, H. Kantekin, A. Demirbasß, M. Durmusß, Dyes Pigm. 95 (2012)
8.
[40] M. Mayukh, C.M. Sema, J.M. Roberts, D.V. McGrath, J. Org. Chem. 75 (2010)
7893.
[41] A. Shaabani, N. Safari, A. Bazgir, F. Bahadoran, N. Sharifi, P.R. Jamaat, Synth.
Commun. 33 (2003) 1717.
[49] G.A. Sheikha, R.A. Khalaf, A. Melhem, G. Albadawi, Molecules 15 (2010) 5721.
[50] G.R. Leticia, I.A. Rivero, Arkivoc xi (2008) 295–306.
[51] V.V. Rekha, M.V. Ramani, A. Ratnamala, V. Rupakalpana, G.V. Subbaraju, C.
Satyanarayana, C.S. Rao, Org. Process. Res. Dev. 13 (2009) 769.