Synthesis of 14-aryl- and alkyl-14H-dibenzo[a,j]xanthenes catalyzed by silica-supported ferric hydrogensulfate

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Synthesis of 14-Aryl- and Alkyl-14H-
dibenzo[a,j]xanthenes Catalyzed by
Silica-supported Ferric Hydrogensulfate
Hossein Eshghi a , Mehdi Bakavoli a & Hassanali Moradi a
a Department of Chemistry, School of Sciences, Ferdowsi University
of Mashhad, Mashhad, Iran
Version of record first published: 09 Jun 2011.
To cite this article: Hossein Eshghi, Mehdi Bakavoli & Hassanali Moradi (2011): Synthesis of 14-Aryl-
and Alkyl-14H-dibenzo[a,j]xanthenes Catalyzed by Silica-supported Ferric Hydrogensulfate, Organic
Preparations and Procedures International: The New Journal for Organic Synthesis, 43:3, 302-307
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Organic Preparations and Procedures International, 43:302–307, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2011.582003
Synthesis of 14-Aryl- and
Alkyl-14H-dibenzo[a,j]xanthenes Catalyzed by
Silica-supported Ferric Hydrogensulfate
Hossein Eshghi, Mehdi Bakavoli, and Hassanali Moradi
Department of Chemistry, School of Sciences, Ferdowsi University
of Mashhad, Mashhad, Iran
Xanthenes, especially benzoxanthenes are of interest as functional materials in many dis-
ciplines due to their useful spectroscopic properties.1–3 They are used as dyes4 in laser
technologies,5 in fluorescent materials for visualization of biomolecules,6 as intracellular
pH indicators,7 as photostable dyes, polymerizable light emitting dyes,8,9 and white organic
light emitting dyes.10 Natural xanthene dyes may also be extracted from soil and plants
such as Indigofera longeracemosa.11 Recently, various methods have been reported for the
synthesis of benzoxanthenes, including the reaction of 2-naphthol with aldehydes in the
presence of a catalyst, such as amberlyst-15,12 sulfamic acid,13 I2,14,15 AcOH–H2SO4,16
heteropoly acids (HPAs),17–19 task-specific ionic liquids,20 phosphoric acid10 and HClO4-
SiO2.21 However, some of these methods suffer from one or more disadvantages such as low
yields, long reaction times, special apparatus, excess reagents, and the use of toxic catalyst.
Thus, the development of an improved procedure for the synthesis of dibenzoxanthene
derivatives would be highly desirable.
Solvent-free organic reactions have been used as useful technique during the past
decade in organic synthesis.22,23 These protocols often lead to shorter reaction times, easier
work-up, higher yields, compliance with green chemistry requirements and may enhance the
regio- and stereoselectivity of reactions.22,23 Recently, ferric hydrogensulfate has emerged
as a promising solid acid catalyst for acid catalyzed reactions.24–30 As a continuation
of our study in catalytic ability of the ferric hydrogensulfate,25–29 this work reports an
efficient, mild and convenient method for the synthesis of some novel 14-substituted-14H-
dibenzo[a,j]xanthenes in the presence of silica-supported ferric hydrogensulfate (SFH)
Fe(HSO4)3/SiO2 (10 mol%) as a new catalyst (Scheme 1).
In order to determine the most appropriate reaction conditions and evaluate the catalytic
efficiency of silica-supported ferric hydrogensulfate, initially a model study was carried out
on condensation reaction of 4-nitrobenzalehyde and 2-naphthol. The results were compared
with unsupported ferric hydrogensulfate catalyst.25 Fe(HSO4)3/SiO2 proved to be the best
Submitted November 1, 2010.
Address correspondence to Hossein Eshghi Department of Chemistry, School of Sciences,
Ferdowsi University of Mashhad, Mashhad 91775-1436, Iran. E-mail: heshghi@.um.ac.ir
302

Synthesis of 14-Aryl- and Alkyl-14H-dibenzo[a,j]xanthenes
303
R1
R1
R1
R2
Fe(HSO4)3/SiO2
R2CHO
+
Solvent free, 90oC
O
OH
2
3
1
a) R1= H, R2 = Ph;
b) R1= H, R2 = 4-MeC6H4;
e) R1= H, R2 = 4-BrC6H4;
h) R1= H, R2 = n-Pentyl;
c) R1= H, R2 = 4-MeOCH4;
f) R1= H, R2 = 4-NO2C6H4;
i) R1= H, R2 = Et;
d) R1= H, R2 = 4-ClC6H4;
g) R1= H, R2 = 3-NO2C6H4;
j) R1= OMe, R2 = Ph;
k) R1= OMe, R2 = 4-MeC6H4; l) R1= OMe, R2 = 4-MeOC6H4;
m) R1= OMe, R2 = 4-ClC6H4; n) R1= OMe, R2 = 4-NO2C6H4; o) R1= OMe, R2 = 3-NO2C6H4
Scheme 1
and most efficient catalyst with the same loading (10 mol%), and gave exclusively 3f in
96% yield in shorter reaction time under solvent-free conditions.
After optimizing the conditions, we next examined the scope of this procedure to other
substrates using 2-naphthol and 7-methoxy-2-naphthol with different aromatic and aliphatic
aldehydes. The results are summarized in Table 1. Aromatic aldehydes carrying different
functional groups were subjected to the reaction and in all cases the desired product were
obtained in high yields. The presence of an electron-donating group (methoxy) on the
Table 1
Preparations of 14-Aryl- or Alkyl-14H-dibenzo[a,j]xanthenes in the presence of
Fe(HSO4)3/SiO2 Catalyst.
Entry
Product
Time (h)
Yield (%)
mp◦C
Lit. mp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
0.75
1.0
2.5
0.6
0.75
0.6
1.3
2.4
2
0.4
0.6
1.0
0.3
0.25
0.8
91
95
95
94
95
96
94
82
89
96
95
91
97
97
94
183–184
239–240
205–206
289–290
297–300
310–312
210–212
98–99
151–152
208–209
183–184
197–198
212–213
246–247
240–241
18318
238–24018
203–20518
289–29019
297–29821
311–31219
210–21119
98–9926
150–15119
—
—
—
—
—
—

304
Eshghi et al.
2-naphthol ring increased the reaction rate (Entries 10–15), in comparison to the unsubsti-
tuted 2-naphthol.
The nature of the functional group on the aromatic ring of the aldehyde exerted a strong
influence on the reaction time. A decrease of the time was observed with aldehydes bearing
electron-withdrawing groups at the p-position (Table 1, Entries 6 and 14), in comparison
to benzaldehyde while electron-donating groups (Table 1, Entries 2 and 3) increased the
reaction time. Similar findings were reported only with HPAs procedures.17–19 In all of the
reactions, TLC monitoring showed that the starting materials completely disappeared in
the first 30 min.
The work-up procedure is very simple and includes extracting the reaction mixture
with ethyl acetate and filtration of mixture to separate the heterogeneous catalyst. The
filtrate was concentrated to give crude product which then was crystallized from ethanol to
give pure 14-aryl- or alkyl-14H-dibenzo[a,j]xanthene 3a-o in excellent yields. The absence
of OH absorptions in the 1H-NMR and IR spectra confirms the structure of our products. In
all the 1H-NMR spectra (CDCl3, 25◦C), the characteristic peak of 14-H xanthene appeared
at δ 5.5–7.0 region as a singlet.
One of the special features of silica-supported ferric hydrogensulfate (10 mol%) is its
insolubility in organic solvents which makes its recovery very convenient. Next we inves-
tigated the reusability and recycling of catalyst from the reaction of p-chlorobenzaldehyde
(1 mmol), 2-naphthol (2 mmol) and silica-supported ferric hydrogensulfate (SFH). When
the reaction was complete, the catalyst was separated and reactivated by washing with
ethanol and drying in an oven. Then we compared the mass of the recovered catalyst.
It could be re-used in subsequent reactions without significant decrease in amount (mass
measuring after drying showed 2–3% decrease) and activity (1–2% decrease) even after five
runs. The applicability of the present method to a large scale process was examined with
250 mmol of p-chlorobenzaldehyde and 500 mmol of 2-naphthol which gave 3d in 85%
yield.
The spectral properties of these compounds suggest that they could be interesting
organic fluorophores which in the presence of special substituent groups, absorb or emit
the light exclusively. Factors such as the excitation wavelength, the solvent system, the pH,
and concentrations are important in the emission efficacy.
Experimental Section
Chemicals were either prepared in our laboratories or purchased from Merck, Fluka and
Aldrich Chemical companies. The progress of the reactions was monitored by thin-layer-
chromatography (TLC) using silica gel SILG/UV 254 plates (Merck). The products were
characterized by comparison of their physical data with those of known samples or by
their spectral data. Melting points were recorded on an Electrothermal type 9100 melting
point apparatus and are uncorrected. IR spectra were obtained on a Shimadzu–IR 470
1
spectrophotometer. The H NMR (100 MHz) spectra were determined on a Bruker AC
100 spectrometer. Chemical shifts are reported in δ ppm downfield from TMS as internal
standard; coupling constants J are given in Hz. Elemental analyses (C, H, N, S) were
determined using the Thermo Finnigan Flash EA microanalyzer and the results were
in good agreement ( 0.3%) with the calculated values. Silica gel 60 (230–400 mesh)

Synthesis of 14-Aryl- and Alkyl-14H-dibenzo[a,j]xanthenes
305
Table 2
1H NMR and Combustion Analyses of 3j-o
Combustion Analyses (Found)
Other
Cmpd
1H NMR (δ)
C
H
3j
7.85–7.00 (m, 15 H), 6.35 (s,
1 H), 4.05 (s, CH3, 6 H)a
7.73–6.90 (m, 14 H), 6.20 (s,
1 H), 4. 04 (s, CH3, 6 H), 2.20
(s, CH3, 3 H)b
7.70–7.1 (m, 10 H), 7.05 (dd,
2 H, J1 = 9.2 Hz, J2 = 2 Hz),
6.65 (d, 2 H, J = 9.6 Hz), 6.10
(s, 1 H), 4.01 (s, CH3, 6 H),
3.60 (s, CH3, 3 H)b
83.23 (83.48)
83.31 (83.65)
5.30 (5.58)
5.59 (5.78)
—
—
3k
3l
80.34 (80.58)
5.39 (5.47)
—
3m
3n
3o
7.90–7.0 (m, 12 H), 7.1 (dd,
2 H, J1 = 7.4 Hz, J2 = 2.9
Hz), 6.60 (s, 1 H), 4.02 (s,
CH3, 6 H)c
8.05–7.6 (m, 10 H), 7.4 (d, 2 H,
J = 9.1 Hz), 7.05 (m, 2 H),
6.75 (s, 1 H), 4.01 (s, CH3,
6 H)d
8.5 (s, 1 H), 7.9–7.15 (m, 12 H),
7.0 (dd, 2 H, J1 = 9 Hz, J2 =
2 Hz), 6.50 (s, 1 H), 4.02 (s,
CH3, 6 H)a
76.90 (77.12)
75.15 (75.44)
75.15 (75.36)
4.67 (4.96)
4.57 (4.76)
4.57 (4.67)
7.83 (7.75)
3.02 (3.13)
3.02 (3.09)
aIn CD3CN; bIn CDCl3; cIn Acetone-d6; dIn DMSO-d6.
was purchased from Merck. Ferric hydrogensulfate was prepared according to previously
reported procedure.25
Procedure of Preparation of Fe (HSO4)3/SiO2 (10 mol%)
Ferric hydrogensulfate (3.47 g, 10 mmol) was ground in a mortar and the powder was
added to a suspension of chromatographic grade SiO2 (6.01 g, 0.1 mol) in absolute ethanol
(50 mL). The yellowish mixture was stirred for 10 h, and then concentrated to dryness; the
solid material was collected and dried at 120◦C for 2 h. The homogeneous, free flowing
and white powder catalyst (SFH) was obtained (9.45 g, 99%). Because of its tendency to
absorb moisture; it should be stored in a stoppered flask, under these conditions, its stability
and efficacy are maintained for a long period of time.

306
Eshghi et al.
General Procedure for the Synthesis of Dibenzo[a. j]xanthenes (3a-o)
A mixture of 2-naphthol (0.145 g, 1 mmol for the synthesis of 3a-i) or 7-methoxy-2-naphthol
(0.174 g, 1 mmol for the synthesis of 3j-o), aldehyde (0.5 mmol), and Fe(HSO4)3/SiO2 (10
mol%) (0.095 g, 0.1 mmol) was ground thoroughly in a mortar for 5 min. The homogeneous
mixture was then placed in a round bottom flask and heated at 90◦C in small scale reactions
without stirring for appropriate time (Table 1). For large scale reactions, a mechanical
stirrer was used. The progress of the reaction was monitored by TLC. After the completion,
the reaction mixture was extracted with ethyl acetate (20 ml) and the catalyst filtered off.
The organic layer was washed with HCl 15% (10 ml), water (3 × 10 ml), and evaporated
to afford the crude product, which was recrystallized from ethanol or acetonitrile. The
1
known products (3a-i) were characterized by IR and H-NMR spectroscopic data and
comparision their melting points with the reported values.18,19,21 The new products (3j-o)
were characterized as shown in Table 2.
Acknowledgement
We are thankful to Ferdowsi University Research Council for their financial support of this
work (Grant: P671:25-09-88).
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