Calcined oyster shell nanoparticles (COS NPs): a new, efficient and reusable catalyst for one-pot rapid preparation of 1,8-dioxo-octahydroxanthenes under solvent-free conditions

Article abstract of DOI:10.1007/s11164-017-3153-7

Calcined oyster shell nanoparticles (COS NPs) as a novel heterogeneous nanocatalyst were prepared and fully characterized by X-ray fluorescence analysis, Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy equip

Full text of DOI:10.1007/s11164-017-3153-7

Res Chem Intermed
DOI 10.1007/s11164-017-3153-7
Calcined oyster shell nanoparticles (COS NPs): a new,
efficient and reusable catalyst for one-pot rapid
preparation of 1,8-dioxo-octahydroxanthenes
under solvent-free conditions
Narges Mohammadian1 Batool Akhlaghinia1
•
Received: 8 June 2017 / Accepted: 19 September 2017
Ó Springer Science+Business Media B.V. 2017
Abstract Calcined oyster shell nanoparticles (COS NPs) as a novel heterogeneous
nanocatalyst were prepared and fully characterized by X-ray fluorescence analysis,
Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning elec-
tron microscopy equipped with an energy dispersive spectrometry (SEM-EDS) and
transmission electron microscopy. The composition of this catalyst was determined,
and it was clearly found that the particle size of COS NPs was about 100–120 nm.
The nano-structured solid catalyst as an efficient and eco-friendly catalyst was used
for the synthesis of 1,8-dioxo-octahydroxanthenes via the one-pot condensation
reaction of 5,5-dimethylcyclohexane-1,3-dione (dimedone) with various aldehydes
under solvent-free conditions. This new methodology is cost-effective and offers
several advantages such as high yield, excellent purity, short reaction time, high
atom economy, simple operation and a convenient workup procedure without the
use of any injurious solvents. Moreover, the catalyst can be readily reusable, and
considerable catalytic activity could be achieved after the six runs.
Keywords 1,8-Dioxo-octahydroxanthenes Á Calcined oyster shell nanoparticles
(COS NPs) Á Solvent-free synthesis Á Heterogeneous nanocatalyst Á Aldehyde Á
5,5-Dimethylcyclohexane-1,3-dione (dimedone)
Electronic supplementary material The online version of this article (doi:10.1007/s11164-017-3153-7)
contains supplementary material, which is available to authorized users.
&
Batool Akhlaghinia
akhlaghinia@um.ac.ir
1
Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad,
Mashhad 9177948974, Iran
123

N. Mohammadian, B. Akhlaghinia
Introduction
Oxygen-containing heterocyclic compounds such as xanthene and its derivatives are
extensively applied in organic synthesis, pharmaceutical chemistry and industry.
Xanthene derivatives, especially 1,8-dioxooctahydroxanthenes, as an important
class of organic compounds were found in many naturally occurring as well as
synthetic derivatives. They have aroused great interest in medicinal chemistry
because of their variety of biological and therapeutic properties such as anti-
bacterial, antioxidant, antifungal, antiviral, anti-inflammatory, anti-depressant and
anti-malarial and use in photodynamic therapy and as an antagonist for the
paralyzing action of zoxazolamine [1, 2]. Furthermore, in addition to their use as
valuable synthetic precursors for many organic compounds [3] and dyes [4], they
are being utilized in laser technologies [5, 6] and fluorescent materials for
visualization of biomolecules [7, 8]. 1,8-Dioxooctahydroxanthenes as a key
structural motif in a number of natural products [9–11] have been used as versatile
synthons because of the inherent reactivity of the inbuilt pyran ring [12]. Since these
moieties are privileged pharmacophores as well as valuable reactive intermediates,
synthesis of 1,8-dioxooctahydroxanthenes is a continuing hot topic in synthetic and
medicinal chemistry. The first method involves the condensation reaction of
resorcinol and phthalic anhydride in the presence of sulfuric acid, which was
reported by Bayer [13]. So far, many efforts have been continued for the
development of synthetic methods for 1,8-dioxooctahydroxanthenes, which contain
the condensation reactions of aldehydes and 1,3-cyclohexanediones under the
influence of several efficient catalysts.
The commonly used homogeneous catalysts such as H2SO4 [14], BiCl3 [15–17],
InCl3 [18], ZrO(OTf)2 [19], [Et3N–SO3H]Cl [20], I2 [21], L-proline [22] and
NaHSO4 [23] have not been entirely satisfactory, being associated with some
disadvantages, such as low yields, long reaction times, usage of volatile and toxic
solvents, large amounts of poisonous and corrosive reagents, strongly acidic
conditions, tedious workup procedures, high catalyst loading, lack of easy
availability of the catalyst, expensive and/or unrecyclable catalysts. To overcome
all of the drawbacks to using environmentally harmful homogeneous catalysts, solid
heterogeneous catalysts have been tested, such as nano-TiO2 [24], TiO2/SO42- [25],
PPA/SiO2 [26], PMA/SiO2 [27], HClO4–SiO2 [26], SiO2 [28], SbCl3/SiO2 [29],
FeCl3/SiO2 [30], silica sulfuric acid [31], NaHSO4–SiO2 [29] Fe3O4@SiO2-imid-
H3PMo12O40 nanoparticles [32], Dowex-50w [33], Amberlyst-15 [34],
[Hmim][TFA] [35], [bmim]HSO4 [36], nanosized MCM-41-SO3H [37] and ceric
ammonium nitrate-supported HY-zeolite [38].
The recycling of oyster shell waste has become an issue of concern. To date, a
portion of oyster shell waste has been recycled for use as spat and as a substitute for
limestone in fertilizers and chicken feed. Oyster shell can be utilized as a solid
catalyst because the main phase in oyster shells is calcite, which is transformed to
quicklime (COS NPs) upon calcination at high temperature. Waste egg [39], oyster
[40], shrimp [41], mullusk [42], cockle shells [43], waste mud crab [44] and fish
scales [45] have been used as resources for obtaining CaO-based catalysts. Oyster
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
shell can act as a bifunctional catalyst. Existence of the conjugate anion (oxygen)
displays a strong basic property [46], and the metal cation, due to its small
electronegativity, exhibited very weak Lewis acidity. In recent years, ground oyster
shells have been successfully reused as various construction materials, as promising
adsorbents of metal ions in sewage [47–50] and as a catalyst for synthesis of 1,2,3-
triazoles. The use of COS NPs as a catalyst is appropriate because of the low cost,
low solubility, non-toxicity, high alkalinity, reusability, environmental compatibil-
ity, availability and also ease of handling [42, 51].
As a part of our research on the development of environmentally friendly
methods for the synthesis of organic compounds using reusable catalysts [52–73] in
the present study, preparation of COS NPs has been implemented and reported for
the first time as a novel and efficient catalyst for successful synthesis of 1,8-dioxo-
octahydroxanthenes (Scheme 1).
Experimental
General
All chemical reagents and solvents were purchased from Merck and Sigma-Aldrich
chemical companies and were used as received without further purification. The
purity determinations of the products were accomplished by TLC on silica gel
polygram STL G/UV 254 plates. The melting points of products were determined
with an Electrothermal Type 9100 melting point apparatus. The FTIR spectra were
provided on pressed KBr pellets using an AVATAR 370 FT-IR spectrometer
(Therma Nicolet spectrometer, USA) at room temperature in the range between
4000 and 400 cm-1 with a resolution of 4 cm-1. The NMR spectra were obtained in
Brucker Avance 300 MHz instruments in DMSO-d6. Mass spectra were recorded
with a CH7A Varianmat Bremem instrument at 70-eV electron impact ionization in
m/z (rel %). The chemical compositions of the COS NPs were specified with X-ray
fluorescence spectroscopy (XRF) using a BRUKER axs-S4 EXPLORER spectrom-
eter. The crystal structure of the catalyst was analyzed by XRD using a D8
ADVANCE-Bruker diffractometer operated at 40 kV and 30 mA utilizing Cu Ka
˚
radiation (k = 0.154 A). SEM images were recorded using a Leo 1450 VP (LEO,
Germany) scanning electron microscope operating at an acceleration voltage of
20 kV. Elemental compositions were determined with a Leo 1450 VP scanning
electron microscope equipped with an SC7620 energy-dispersive spectrometer
(SEM–EDS) presenting a 133-eV resolution at 20 kV. Transmission electron
Crushed
900 oC, 6 h
COS NPs
Oyster shells
Scheme 1 Preparation of COS NPs
123

N. Mohammadian, B. Akhlaghinia
microscopy (TEM) was performed with a 120-kV Zeiss Leo 912 AB (Germany)
with an accelerating voltage of 120-kV imaging with 80–500,0009 magnification
and equipped with a high-resolution CCD camera. All yields refer to isolated
products after purification by recrysralization.
Preparation of COS NPs
The oyster shells were soaked in distilled water at room temperature for 4 h, washed
several times with H2O/EtOH to remove impurities and then dried for 12 h at
100 °C. The oyster shell samples were later crushed and milled to obtain fine
powder. Subsequently, COS NPs were generated from calcination of waste oyster
shells at high temperature (900 °C for 6 h).
Typical procedure for synthesis of 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-
hexahydro-1H-xanthene-1,8(2H)-dione in the presence of COS NPs
A mixture of benzaldehyde (1 mmol, 0.106 g) and 5,5-dimethylcyclohexane-1,3-
dione (dimedone) (2 mmol, 0.289 g) in the presence of 0.025 g of COS NPs was
stirred at 90 °C. The progress of the reaction was monitored by TLC. After
completion of the reaction, the reaction mixture was cooled to room temperature.
Then, hot EtOH (3 ml) was poured into the reaction flask, and the catalyst was
removed by filtration. Finally, the crude 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-
hexahydro-1H-xanthene-1,8(2H)-dione was recrystallized from EtOH obtaining
0.343 g of white color crystals (98% yield).
3,3,6,6-Tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione [24]
(Table 3, 3a)
White solid; yield (0.343 g, 98%); mp 198–200 °C (Lit.,
199–201 °C); FT-IR (KBr): mmax/cm-1 3084.20 (alkenyl CH str.), 3026.55
(aromatic CH str.), 2955.61 (aliphatic CH str.), 1662.93 (C=O str.), 1560.19
(alkenyl C=C str.), 1492.54 (aromatic C=C str.), 1271.62–1043.68 (C–O–C str.); 1H
NMR (300 MHz, DMSO-d6, ppm) d: 7.26–6.89 (m, 5 H), 4.93 (s, 1 H, CH-9), 2.42
(s, 4 H, 2 H-2, 2 H-7), 2.03 (s, 4 H, 2 H-4, 2 H-5), 0.92 (s, 6 H, equatorial 2CH3),
0.89 (s, 6 H, axial 2CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: C-1, C-8 (C=O);
195.75, C-11, C-13; 163.39, C-10; 144.99, C-30, C-50; 127.43, C-20, C-60; 127.09,
C-40; 126.87, C-10, C-12; 115.30, C-2, C-7; 50.47, C-9; 47.44, C-4, C-5; 32.35, C-3,
C-6; 31.65, C-14, C-16 (equatorial); 30.81, C-15, C-17 (axial); 29.63; MS (EI): m/z
(%) 350 (10) [M?], 347 (100) [M?–3H], 270 (100) [M?–C6H8], 78 (62) [M?–
C17H20O3], 29 (100) [M?– C21H21O3].
3,3,6,6-tetramethyl-9-(p-tolyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione [24]
(Table 3, 3b)
White solid; yield (0.346 g, 95%); mp 214–216 °C (Lit.,
216–218 °C); IR (KBr): mmax/cm-1 3051.99 (alkenyl CH str.), 3019.30 (aromatic
CH str.), 2954.96 (aliphatic CH str.), 1689.05 (C=O str.), 1563.99 (alkenyl C=C
str.), 1507.38 (aromatic C=C str.), 1271.88–1042.50 (C–O–C str.); 1H NMR
(300 MHz, DMSO-d6, ppm) d: 6.94 (d, J = 8.4 Hz, 2 H, H-20, H-60), 6.90 (d,
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
J = 8.4 Hz, 2 H, H-30, H-50), 4.92 (s, 1 H, CH-9), 2.21 (s, 3 H, CH3), 2.15 (s, 4 H, 2
H-2, 2 H-7), 2.10 (s, 4 H, 2 H-4, 2 H-5), 1.02 (s, 6 H, equatorial 2 CH3), 0.96 (s, 6 H,
axial 2 CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: C-1, C-8 (C=O); 195.88,
C-11, C-13; 165.83, C-10; 141.49, C-30, C-50; 132.96, C-20, C-60; 128.29, C-40;
127.36, C-10, C-12; 115.49, C-2, C-7; 50.30, C-9; 47.44, C-4, C-5; 31.65, C-3, C-6;
30.44, C-14, C-16 (equatorial); 29.47, C-15, C-17 (axial); 28.05, CH3; 20.98; MS
(EI): m/z (%) 364 (5) [M?] 362 (20) [M?– 2H], 271 (28) [M?– C7H9], 240 (88)
[M?– C10H12O], 225 (100) [M?– C10H11O2], 170 (75) [M?– C12H18O2], 91 (65)
[M?– C17H21O3], 83 (80) [M?–C19H21O3], 41 (85) [M?– C22H27O2].
9-(4-methoxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [24] (Table 3, 3c) White solid; yield (0.353 g, 93%); mp 242–244 °C (Lit.,
243–245 °C); MS (EI): m/z (%) 380 (2) [M?], 281 (8) [M?– C6H11O], 255 (100)
[M?–C7H10O2], 241 (75) [M?–C8H11O2], 225 (90) [M?–C8H11O3], 173 (70) [M?–
C13H19O2], 145 (75) [M?– C14H19O3], 83 (80) [M?–C19H22O3], 41 (70) [M?–
C22H27O3].
9-(4-hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [24] (Table 3, 3d) White solid; yield (0.347 g, 95%); mp 252–254 °C (from
EtOH) (Lit., 252–254 °C); MS (EI): m/z (%) 366 (8) [M?], 363 (100) [M?– 3H],
270 (98) [M?–C6H8O], 241 (98) [M?–C8H15O], 83 (95) [M?– C18H19O3], 41 (30)
[M?–C20H21O4].
9-(2-hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [25] (Table 3, 3e). White solid; yield (0.311 g, 85%); mp 204–206 °C (Lit.,
205–206 °C); MS (EI): m/z (%) 366 (2) [M?], 280 (15) [M?– C5H10O], 226 (10)
[M?–C8H12O2], 122 (100) [M?–C15H16O3], 93 (25) [M?– C17H21O3], 76 (30)
[M?–C17H22O4], 39 (70) [M?– C20H23O4].
9-(4-(dimethylamino)phenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-
1,8(2H)-dione [26] (Table 3, 3f)
White solid; yield (0.377 g, 96%); mp
222–224 °C (Lit., 222–225 °C); MS (EI): m/z (%) 393 (15) [M?], 284 (48) [M?–
C7H11O], 271 (50) [M?–C8H12N], 224 (55) [M?–C11H21O], 133 (75) [M?–
C16H20O3], 98 (70) [M?–C19H21NO2], 82 (100) [M?–C20H25NO2], 43 (60) [M?–
C22H24NO3].
9-(4-chlorophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [24] (Table 3, 3g) White solid; yield (0.376 g, 98%); mp 228–230 °C (Lit.,
229–231 °C); IR (KBr): mmax/cm-1 2956.23 (aliphatic CH str.), 1620.44 (C=O str.),
1580.64 (alkenyl C=C str.), 1517.84 (aromatic C=C str.), 1227.39–1146.56 (C–O–C
str.); 1H NMR (300 MHz, DMSO-d6, ppm) d: 7.19 (d, J = 8.4 Hz, 2 H, H-20, H-60),
6.99 (d, J = 8.1 Hz, 2 H, H-30, H-50), 4.67 (s, 1 H, CH-9), 2.51 (s, 4 H, 2 H-2, 2
H-7), 1.93 (s, 4 H, 2 H-4, 2 H-5), 1.00 (s, 6 H, equatorial 2 CH3), 0.98 (s, 6 H, axial
2 CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: C-1, C-8 (C=O); 195.75, C-11,
C-13; 167.35, C-10; 144.10, C-40; 131.50, C-20, C-60; 129.26, C-30, C-50; 128.94,
123

N. Mohammadian, B. Akhlaghinia
C-10, C-12; 115.07, C-2, C-7; 49.51, C-9; 47.50, C-4, C-5; 32.48, C-3, C-6; 31.65,
C-14, C-16 (equatorial); 30.52, C-15, C-17 (axial); 29.16; MS (EI): m/z (%) 385 (5)
[M??1], 384 (18) [M?], 380 (90) [M?–4H], 269 (90) [M?–C6H11O2], 258 (45)
[M?–C7H12O2], 82 (90) [M?–C18H19ClO2], 41 (65) [M?–C21H24ClO2], 28 (100)
[M?–C22H25ClO2].
9-(2-chlorophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [24] (Table 3, 3h) White solid; yield (0.364 g, 95%); mp 221–223 °C (Lit.,
223–235 °C); IR (KBr): mmax/cm-1 3064.25 (alkenyl and aromatic CH str.), 2954.70
(aliphatic CH str.), 1719.86 (C=O str.), 1565.04 (alkenyl C=C str.), 1507.38
(aromatic C=C str.), 1268.87–1038.95 (C–O–C str.); MS (EI): m/z (%) 384 (2)
[M?], 270 (18) [M?– C6H10O2], 138 (68) [M?– C15H15ClO] 82 (70) [M?–
C18H19ClO2], 41 (70) [M?– C21H24ClO2], 30 (100) [M?– C22H23ClO2].
9-(3-bromophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [25] (Table 3, 3i) White solid; yield (0.420 g, 98%); mp 202–204 °C (Lit.,
1
203–204 °C); H NMR (300 MHz, DMSO-d6, ppm) d: 7.59–7.15 (m, 4 H, ArH),
4.51 (s, 1 H, CH-9), 2.11 (s, 4 H, 2 H-2, 2 H-7), 2.03 (s, 4 H, 2 H-4, 2 H-5), 1.04 (s,
6 H, equatorial 2 CH3), 1.02 (s, 6 H, axial 2 CH3); 13C NMR (75 MHz, DMSO-d6,
ppm) d: C-1, C-8 (C=O); 195.65, C-11, C-13; 169.33, C-10; 148.54, C-20; 132.47,
C-50; 129.79, C-40; 129.43, C-60, 128.58, C-30; 127.23, C-10, C-12; 114.76, C-2,
C-7; 50.35, C-9; 47.36, C-4, C-5; 31.68, C-3, C-6; 30.83, C-14, C-16 (equatorial);
29.54, C-15, C-17 (axial); 27.94; MS (EI): m/z (%) 429 (30) [M?], 307 (28) [M?–
C8H11O], 302 (100) [M?–C7H10O2], 225 (100) [M?–C7H10BrO2], 83 (100) [M?–
C18H18BrO2], 41 (100) [M?– C21H24BrO2].
9-(4-fluorophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [29] (Table 3, 3j) White solid; yield (0.361 g, 98%); mp 224–226 °C (Lit.,
226–227 °C); IR (KBr): mmax/cm-1 3080.12 (alkenyl and aromatic CH str.), 2956.57
(aliphatic CH str.), 1660.95 (C=O str.), 1623.74 (alkenyl C=C str.), 1509.68
1
(aromatic C=C str.), 1224.89–1143.95 (C–O–C str.); H NMR (300 MHz, DMSO-
d6, ppm) d: 7.22–7.02 (m, 4 H, ArH), 4.53 (s, 1 H, CH-9), 2.51 (s, 4 H, 2 H-2, 2
H-7), 2.12 (s, 4 H, 2 H-4, 2 H-5), 1.04 (s, 6 H, equatorial 2 CH3), 0.91 (s, 6 H, axial
2 CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: C-1, C-8 (C=O); 196.55, C-11,
C-13; 163.43, C-40; 159.45, C-10; 140.92, C-20, C-60; 130.33, C-30, C-50; 115.18,
C-10, C-12; 114.90, C-2, C-7; 50.44, C-9; 40.81, C-4, C-5; 32.34, C-3, C-6; 31.11,
C-14, C-16 (equatorial); 29.09, C-15, C-17 (axial); 26.95; MS (EI): m/z (%) 368
(30) [M?], 364 (100) [M?– 4H], 270 (90) [M?–C6H7F], 160 (65) [M?–C13H20O2],
82 (40) [M?–C18H19FO2], 55 (28) [M?–C19H18FO3].
3,3,6,6-tetramethyl-9-(4-nitrophenyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [24] (Table 3, 3k) White solid; yield (0.387 g, 98%); mp 224–226 °C (Lit.,
224–226 °C); MS (EI): m/z (%) 395 (5) [M?], 254 (50) [M?– C6H8NO3], 224 (42)
[M?–C8H13NO3], 160 (32) [M?–C14H19O3], 139 (50) [M?–C15H14NO3], 83 (90)
[M?–C18H18NO4], 28 (95) [M?– C21H21NO5].
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Calcined oyster shell nanoparticles (COS NPs): A new,…
4-(3,3,6,6-tetramethyl-1,8-dioxo-2,3,4,5,6,7,8,9-octahydro-1H-xanthen-9-yl)ben-
zonitrile [24] (Table 3, 3l) White solid; yield (0.367 g, 98%); mp 219–221 °C
(Lit., 220–222 °C); IR (KBr): mmax/cm-1 2956.68 (aliphatic CH str.), 2226.29 (CN
str.), 1695.23 (C=O str.), 1558.74 (alkenyl C=C str.), 1494.45 (aromatic C=C str.),
1
1271.45–1042.74 (C–O–C str.); H NMR (300 MHz, DMSO-d6, ppm) d: 7.62 (d,
J = 8.1 Hz, 2 H, H-20 H-60), 7.16 (d, J = 7.8 Hz, 2 H, H-30, H-50), 5.08 (s, 1 H, CH-
9), 2.14 (s, 8 H, 2 H-2, 2 H-7, 2 H-4, 2 H-5), 0.99 (s, 12 H, 4 CH3); 13C NMR
(75 MHz, DMSO-d6, ppm) d: C-1, C-8 (C=O); 195.52, C-11, C-13; 164.22, C-10;
152.34, C-30, C-50; 131.71, C-20, C-60; 128.39, CN; 119.96, C-10, C-12; 114.55,
C-40; 107.15, C-2, C-7; 50.43, C-9; 47.43, C-4, C-5; 31.66, C-3, C-6; 29.12, C-14,
C-16, C-15, C-17 (equatorial, axial); 28.45; MS (EI): m/z (%) 375 (5) [M?], 372
(35) [M?– 3H], 250 (65) [M?–C8H13O], 126 (75) [M?–C15H22O3], 83 (100) [M?–
C19H18NO2], 41 (100) [M?– C22H24NO2].
3,3,6,6-tetramethyl-9-(thiophen-2-yl)-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [29] (Table 3, 3m) White solid; yield (0.303 g, 85%); mp 163–165 °C
(from EtOH) (Lit., 164–165 °C); MS (EI): m/z (%) 356 (2) [M?], 353 (100) [M?–
3H], 270 (90) [M?– C4H6S], 245 (75) [M?–C5H4OS], 233 (90) [M?–C6H4OS], 121
(50) [M?–C14H19O3], 110 (65) [M?–C15H19O3], 82 (90) [M?– C17H22O3], 43 (70)
[M?–C18H17O3S].
3,3,6,6-tetramethyl-9-(pyridin-4-yl)-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-
dione [74] (Table 3, 3n) White solid; yield (0.315 g, 90%); mp 211–213 °C
(Lit., 212–214 °C); 1H NMR (300 MHz, DMSO-d6, ppm) d: 8.30 (d, J = 5.4 Hz, 2
H, H-20, H-60), 6.96 (d, J = 4.8 Hz, 2 H, H-30, H-50), 4.43 (s, 1 H, CH-9), 2.16 (s, 4
H, 2 H-2, 2 H-7), 2.10 (s, 4 H, 2 H-4, 2 H-5), 1.07 (s, 6 H, equatorial 2 CH3), 1.05 (s,
6 H, axial 2 CH3); 13C NMR (75 MHz, DMSO-d6, ppm) d: C-1, C-8 (C=O); 195.61,
C-11, C-13; 169.30, C-10; 154.98, C-30, C-50; 149.76, C-20, C-60; 123.13, C-10,
C-12; 114.14, C-2, C-7; 50.30, C-9; 47.30, C-4, C-5; 31.66, C-3, C-6; 30.89, C-14,
C-16 (equatorial); 29.55, C-15, C-17 (axial); 28.13; MS (EI): m/z (%) 351 (10)
[M?], 349 (95) [M?– 2H], 271 (100) [M?–C4H6N], 215 (48) [M?–C8H8O2], 160
(38) [M?–C12H18NO], 83 (50) [M?–C17H18NO2], 55 (35) [M?–C18H18NO3].
Results and discussion
Characterization of the catalyst
The chemical composition of the COS NPs was confirmed by X-ray fluorescence
spectroscopy (XRF). Based on the data in Table 1, the principal composition of the
COS NPs is CaO.
The oyster shell and COS NPs were characterized using FT-IR spectroscopy, as
shown in Fig. 1. The observed absorption bands for aragonite phases (calcium
2-
carbonate) in the oyster shell structure are due to the planar CO3 ion (Fig. 1a).
2-
There are four vibrational modes in the free CO3
ion [75]: the symmetric
123

N. Mohammadian, B. Akhlaghinia
Table 1 Chemical composition of COS NPs
Constituent
Percentage
CaO
SrO
Fe2O3
0.204
SiO2
SO3
Moister
12.439
86.522
0.245
0.102
0.489
Fig. 1 FT-IR spectra of (a) oyster shells; (b) COS NPs; (c) sixth reused COS NPs
stretching vibration of the carbonate ion at about 1080 cm-1 (t1); the out-of-plane
bending absorption at about 856 cm-1 (t2); the asymmetric stretching vibrations at
about 1130–1720 cm-1 (t3); the split in-plane bending vibration at about 717 cm-1
(t4). The strong band detected at 1760 cm-1 can also be attributed to the C=O group
of the carbonated ion. The FT-IR spectrum of COS NPs was shown as Fig. 1b. As
can be seen, the absorption bands at 1332–1620 show the existence of CaO phase in
the structure.
Also, XRD analysis was applied to detect the crystallinity of the COS NPs and
the sixth recovered COS NPs. As presented in Fig. 2, the characteristic peaks at 2h,
30.5°, 38.1°, 52.6°, 63.2°, 66.9° and 79.1°, corresponded to the (1 1 1), (2 0 0), (2 2
0), (3 1 1), (2 2 2) and (4 0 0) crystallographic faces, which are in agreement with
the standard data of CaO (JCPDS 04-007-9734) [76]. The XRD results also
demonstrate the presence of cubic phase CaO. These indicated diffraction peaks
clearly pointed to a cubic structure for the catalyst and the sixth recovered one. The
average crystallite size of CaO NPs, calculated using the Debye-Scherrer equation
d = Kk/b cosh, is about 100 nm.
To figure out the morphology and nanostructure of COS NPs, scanning electron
microscope imaging combined with associated EDS and transmission electron
microscope imaging was performed. The SEM images of COS NPs are depicted in
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
Fig. 2 The XRD patterns of (a) COS NPs; (b) 6th recovered COS NPs
Fig. 3a. As is obvious, the SEM images of COS NPs were illustrated with a
spherical morphology. According to the TEM images in Fig. 3b, the average
diameters of the COS NPs were estimated to be 120 nm. As seen from the pictures,
the morphology of COS NPs is spherical.
The existence of Ca, O and C as the main components of the COS NPs was
demonstrated using the energy-dispersive spectrum (EDS), which is in good
agreement with the XRF results (Fig. 4).
Catalytic synthesis of 1,8-dioxo-octahydroxanthene derivatives
After successful preparation and full characterization of the nanocatalyst, the
catalytic efficiency of COS NPs was evaluated in the synthesis of 1,8-dioxo-
octahydroxanthene derivatives via a three-component condensation reaction of
aromatic aldehydes and two equivalents of dimedone (Scheme 2).
In a series of experiments, the promotion effect of COS NPs in the preparation of
1,8-dioxo-octahydroxanthene derivatives was studied by the reaction of benzalde-
hyde with two equivalents of dimedone under different reaction conditions. The
effects of the molar ratio of the reaction components, amount of catalyst, solvent
and temperature were investigated in a typical experiment (Table 2).
No significant formation of 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-
1H-xanthene-1,8(2H)-dione was observed when the blank experiment was carried
out in the absence of COS NPs and solvent even after a long period of time
(Table 2, entry 1). Interestingly, performing the same reaction in the presence of
finely powdered oyster shells and bulk CaO as catalysts at 90 °C results in 15% and
25% yields of product, respectively, after 18 h (Table 2, entries 2, 3). Due to the
longer reaction time in the presence of oyster shells and bulk CaO (as the main
component of COS NPs), the model reaction was conducted in the presence of COS
123

N. Mohammadian, B. Akhlaghinia
Fig. 3 a SEM images of COS NPs; b TEM images of COS NPs
NPs (Table 2, entry 4). Surprisingly, a significant improvement was observed in the
yield and reaction rate (the yield was dramatically increased to 98% after 30 min).
To ascertain the optimum conditions with respect to the reaction temperature, the
model reaction was performed at different temperatures. No improvement in the
yield and reaction rate was observed by increasing the reaction temperature
(Table 2, entries 5, 6). Performing the model reaction at lower temperature (80 °C)
increased the duration of the reaction (Table 2, entry 7). To evaluate the most
appropriate catalyst loading, the model reaction was carried out using different
amounts of COS NPs under solvent-free conditions (Table 2, entries 8, 9). It was
found that the best results in terms of yield, as well as reaction time, were obtained
using 0.025 g of catalyst. Moreover, the effect of reaction media on the reaction rate
as well as on the yield of product was investigated. The results showed that among
the tested solvents, such as H2O, EtOH and the solvent-free system, the best result
was obtained (excellent yield) after 30 min in solvent-free conditions (Table 2,
entries 10, 11). To improve the yield of the desired product, the reaction is
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
Fig. 4 EDS spectrum of COS NPs
Scheme 2 Preparational of 1,8-dioxo-octahydroxanthene derivatives in the presence of COS NPs
performed using an additional quantity of dimedone (Table 2, entry 12). According
the result obtained in Table 2, increasing the amount of dimedone does not improve
the reaction rate or product yield. In continuing of our study, by considering the
main component of the COS NPs (see the XRF results in Table 1), we decided to
probe the catalytic reactivity of the principal composition of the COS NPs. Toward
this point, analytical-pure CaO was also used as catalyst in the model reaction. As is
depicted in Table 2, analytical-pure CaO under optimized reaction conditions
catalyzed the condensation reaction as well as COS NPs (Table 2, entry 13). The
obtained result validated the efficiency of CaO (as the main component of COS
NPs) for catalyzing this transformation, and no impurity elements/phase in oyster
shells promoted the catalytic activity of COS NPs.
The remarkable results obtained with the above reaction conditions encouraged
us to show the generality and scope of this new protocol. A variety of aromatic
aldehydes with different substituents were condensed with two equivalents of
dimedone in the presence of COS NPs under optimized reaction conditions. The
results are shown in Table 3. From the results, we found that both categories of
aromatic aldehydes bearing either electron-withdrawing or electron-donating
123

N. Mohammadian, B. Akhlaghinia
Table 2 Optimization of various reaction parameters for the synthesis of 3,3,6,6-tetramethyl-9-phenyl-
3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione in the presence of COS NPs
Entry Molar ratio Catalyst
1a:2a
Amount of
catalyst (g)
Solvent Temperature Time
(°C)
Isolated
yield (%)
(min)
1
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2.5
1:2
–
–
–
90
18 (h)
18 (h)
18 (h)
30
Trace
15
25
98
98
98
90
98
95
10
90
98
90
2a
3b
4
Oyster shells 0.03
–
90
CaO
0.03
–
90
COS NPs
COS NPs
COS NPs
COS NPs
COS NPs
COS NPs
COS NPs
COS NPs
COS NPs
0.03
–
90
5
0.03
–
110
100
80
30
6
0.03
–
30
7
0.03
–
50
8
0.025
0.02
–
90
30
9
–
90
35
10
11
12
13
0.025
0.025
0.025
0.025
H2O
EtOH
–
Reflux
Reflux
90
10
1 (h)
30
Analytical-
pure CaO
–
90
35
aThe reaction was performed in the presence of finely powdered oyster shell
bThe reaction was performed in the presence of bulk CaO
cBold values refer to optimized conditions
substituents underwent an electrophilic substitution reaction with dimedone and
uniformly afforded good yields of the corresponding products in high yields within
20–35 min under solvent-free conditions. The nature and electronic properties of
substituents on the aromatic ring had no obvious effect on the yield or reaction time.
The high yield was also obtained in the case of the heterocyclic aldehydes (Table 3,
entries 13–14).
In this study, completion of the reaction was established by the disappearance of
5,5-dimethylcyclohexane-1,3-dione (dimedone) and formation of the desired
product on TLC, followed by the appearance of C=O and C=C stretching
frequencies at 1719–1620 cm-1 and 1623–1558 cm-1, respectively, in the Fourier
transform infrared (FT-IR) spectra. Primary elucidation of the structures of all
isolated products (after purification by crystallization) was done by comparison of
their melting points and mass spectra with the authentic samples. In all of the cases,
the molecular ions were evident in the mass spectra as well as some useful
fragmentation information for each compound, which can be beneficial for
depicting the desired products. The selected products were further characterized
1
1
by H NMR, 13CNMR and FT-IR spectroscopy. In H NMR spectra of 1,8-dioxo-
octahydroxanthenes, the C-9 proton at the bridge between the two dimedone rings
appears in the region 5.08–4.51 ppm. The C-4 and C-5 protons (two methylene
groups) and C-2 and C-7 protons give rise to two resonating signals in the region of
2.14–1.93 ppm and 2.51–2.11 ppm, respectively. Two sets of methyl groups (in
axial and equatorial positions) appeared as two singlet peaks around 1.02–0.89 ppm
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
Table 3 Synthesis of different structurally 1,8-dioxo-octahydroxanthenes in the presence of COS NPs
under solvent-free conditions
Entry
Aldehydes
Product
Time
(min)
Isolated
yield (%)
1
2
PhCHO
30
98
95
4-CH3C6H4CHO
30
3
4-CH3OC6H4CHO
30
93
4
5
4-HOC6H4CHO
2-HOC6H4CHO
35
35
95
85
6
7
4-(CH3)2NC6H4CHO
30
20
96
98
4-ClC6H4CHO
123

N. Mohammadian, B. Akhlaghinia
Table 3 continued
Entry
Aldehydes
Product
Time
(min)
Isolated
yield (%)
8
2-ClC6H4CHO
25
20
20
25
95
98
98
98
9
3-BrC6H4CHO
4-FC6HCHO 4
10
11
4-O2NC6H4CHO
4-CNC6H4CHO
12
13
14
20
25
20
98
85
90
2-Thiophene-
carbaldehyde
4-Pyridine-carbaldehyde
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
Scheme 3 Proposed reaction mechanism for the synthesis of 1,8-dioxo-octahydroxanthenes in the
presence of COS NPs
and 1.04–0.92 ppm, respectively. In the 13C NMR spectra, signals around
195.8–195.5, 169.3–163.3 and 115.4–114.5 ppm were assigned to the quaternary
carbon atoms at the (C-1 and C-8), (C-11 and C-13) and (C-10 and C-12) positions,
respectively (the equivalent carbon atoms of two dimedone rings give rise to one
signal). The resonating peaks of C-9 (carbon at the bridge between the two
dimedone rings), (C-2 and C-7), (C-4 and C-5) and (C-3 and C-6) were observed in
the expected region around 47.5–47.3, 50.4–49.5, 32.4–31.6 and 31.6–29.1 ppm. In
the experimental section, the characteristic spectral data for the synthesized 1,8-
dioxo-octahydroxanthenes have been discussed, which were in good corroboration
with the literature [77] and proposed structures.
A possible mechanism for this transformation, which is in accordance with the
literature studies [26, 78, 79], is proposed in Scheme 3. After a long reaction time, a
123

N. Mohammadian, B. Akhlaghinia
comparatively lower yield of product was observed in the absence of COS NPs,
which confirmed the catalytic activity of COS NPs in the preparation of 1,8-dioxo-
octahydroxanthenes (Table 2, entry 1). Initially, COS NPs as a basic solid catalyst
facilitated the formation of an enol form of 5,5-dimethylcyclohexane-1,3-dione
(dimedone) (activated 1,3-cyclic diketone I) [78]. In the next step, the nucleophilic
attack of I to aldehyde led to the formation of intermediate II, which upon
dehydration generated the intermediate III [78]. Subsequently, intermediate III was
then attacked by another activated 1,3-cyclic diketone (Michael addition) to give
tetraketone IV. Dehydration and aromatization of IV afforded the 1,8-dioxo-
octahydroxanthenes V [78]. In the following, COS NPs re-entered the catalytic
cycle. More investigation of the elucidation of the mechanism and scope of this
reaction is presently underway in our laboratory.
Furthermore, the probability of reusing and recycling the COS NPs for several
runs on the model reaction was also studied. The results displayed in Fig. 5 showed
that COS NPs could be reused and recycled for six runs without any significant
decrease in the catalytic activity (yields in the range of 98–88%). After completion
of the reaction, COS NPs were separated from the reaction mixture, washed with
ethanol and dried at 100 °C for 1 h, and the recycling studies were then performed
utilizing the separated catalyst in subsequent reactions (model reaction). As can be
seen in Fig. 1c, the shapes and intensities of the characteristic peaks were well
preserved, and no significant changes occurred in the structure of the nanocatalyst
after repeated cycles of the reaction. Due to catalyst pollution with reagents, a slight
reduction in the catalytic activity of recycled COS NPs was observed.
Fig. 5 Synthesis of 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione in
the presence of reused COS NPs
123

Calcined oyster shell nanoparticles (COS NPs): A new,…
Table 4 Comparison between the efficiency of COS NPs and some other catalysts for the preparation of
3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione
Entry Catalyst
Solvent Temperature
(°C)
Time
(h)
Yield
(%)
Refs.
1
2
H2SO4
H2O
–
Reflux
Room
2
84
84
[14]
[25]
2-
TiO2/SO4
24
temperature
3
4
5
PMA/SiO2
SbCl3/SiO2
CH3CN Reflux
4
95
[27]
[29]
[32]
–
120
50 min 93
Fe3O4@SiO2-imid-H3PMo12O40
nanoparticles
EtOH
Reflux
1.5
94
6
7
8
Dowex-50w
Amberlyst-15
COS NPs
–
100
3
5
87
92
[33]
[34]
CH3CN Reflux
90
–
30 min 98
Present
study
To attain deeper insight into the efficiency of COS NPs for the synthesis of 1,8-
dioxo-octahydroxanthene derivatives, an evaluation was performed by comparing
its performance with other reported methods in the literature (Table 4). These
comparison experiments were based on the model reaction. As Table 4 displays (the
data reported in the literature for the synthesis of 3,3,6,6-tetramethyl-9-phenyl-
3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione), COS NPs have improved the
synthesis of the corresponding products in different terms (not only afforded the
products in excellent yield in very short reaction times and mild conditions, but also
avoided the problems associated with the catalyst cost, difficult preparation and
handling, tedious workup, safety and pollution) surprisingly.
Conclusion
In this research, COS NPs were designed and characterized by using X-ray
fluorescence analysis (XRF), Fourier transform infrared (FT-IR) spectroscopy,
X-ray powder diffraction (XRD), scanning electron microscopy equipped with an
energy-dispersive spectrometry (SEM-EDS) and transmission electron microscopy
(TEM). Catalytic application of the new described catalyst was studied for the first
time in the synthesis of 1,8-dioxo-octahydroxanthenes via the one-pot condensation
reaction of 5,5-dimethylcyclohexane-1,3-dione (dimedone) with various aldehydes
under solvent-free conditions. As solvent-free reactions are an efficient technique
instead of using harmful organic solvents, the present method offers simplicity of
product isolation, a remarkable decrease in reaction time, increased reaction yield,
fitting the green chemistry protocol as well as reusability of the catalyst, which can
be reused for six cycles without a significant loss of activity.
123

N. Mohammadian, B. Akhlaghinia
Acknowledgements The authors gratefully acknowledge the partial support of this study by Ferdowsi
University of Mashhad Research Council (grant no. p/3/43388).
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