Sulfonated starch nanoparticles: An effective, heterogeneous and bio-based catalyst for synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes

Article abstract of DOI:10.1016/j.molstruc.2017.02.095

In recent years, biodegradable polymer based nanoparticles have attracted wide attention for the synthesis of high-performance and green catalytic species. Polymeric nanoparticles used for catalytic processes must be biocompatible and biodegradable. The o

Full text of DOI:10.1016/j.molstruc.2017.02.095

Accepted Manuscript
Sulfonated starch nanoparticles: An effective, heterogeneous and bio-based catalyst
for synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes
Javad Safari, Pegah Aftabi, Majid Ahmadzadeh, Masoud Sadeghi, Zohre Zarnegar
PII:
S0022-2860(17)30254-5
10.1016/j.molstruc.2017.02.095
MOLSTR 23489
DOI:
Reference:
To appear in: Journal of Molecular Structure
Please cite this article as: Javad Safari, Pegah Aftabi, Majid Ahmadzadeh, Masoud Sadeghi, Zohre
Zarnegar, Sulfonated starch nanoparticles An effective, heterogeneous and bio-based catalyst for
synthesis of 14-aryl-14-H-dibenzo(a,j)xanthenes, Journal of Molecular Structure (2017), doi: 10.1016/
j.molstruc.2017.02.095
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ACCEPTED MANUSCRIPT
Highlights
•
Preparation of sulfonated starch nanoparticles (SO3H-SNPs) as catalyst for organic
synthesis
.
•
•
Introducing an efficient new catalyst for the synthesis of xanthenes.
Excellent yields of products and short reaction times.

ACCEPTED MANUSCRIPT
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Sulfonated starch nanoparticles: An effective, heterogeneous and bio-based
catalyst for synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes
3
Javad Safari٭, Pegah Aftabi, Majid Ahmadzadeh, Masoud Sadeghi, Zohre Zarnegar
4
5
Laboratory of Organic Compound Research, Department of Organic Chemistry, College of
Chemistry, University of Kashan, P.O. Box: 87317-51167, Kashan, I.R., Iran.
6
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8
9
Abstract
In recent years, biodegradable polymer based nanoparticles have attracted wide attention for
the synthesis of high-performance and green catalytic species. Polymeric nanoparticles used
for catalytic processes must be biocompatible and biodegradable. The objective of this study
10 is to fabricate starch nanoparticles from native starch and preparation of sulfonated starch
11 nanoparticles (HO3S-SNPs) as acidic nanocatalyst in the synthesis of 14-aryl-14-H-
12 dibenzo[a,j]xanthenes under solvent free conditions. This procedure has a lot of advantages
13 such as very easy reaction conditions, low-cost production and natural catalyst and absence of
14 any tedious workup or purification. The corresponding products have been obtained in
15 excellent yields, high purity and short reaction times.
16 Keywords: Sulfonated starch, Starch nanoparticles, Heterogeneous catalysis, 14-Aryl-14H-
17 dibenzo[a,j ]xanthenes, Solvent-free conditions.
18 1. Introduction
19 Homogeneous inorganic acids such as H2SO4 and HF are essential and efficient catalysts for
20 the production of industrial important chemicals. However, the use of these homogeneous
21 catalysts requires costly and inefficient processes for separation, recycling, and treatment of
22 the spent acids. For example, the neutralization of the H2SO4 produces sulfate wastes, and
٭Corresponding author. E-mail addresses: safari@kashanu.ac.ir; safari_jav@yahoo.com. Tel: +98 31
5591 2320; Fax: +98 31 5591 2397.

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23 thus, the liquid acids do not fulfill the general requirement of a catalyst as a reusable material
24 in chemical processes. The use of recyclable strong solid acids instead of unrecyclable
25 homogeneous catalysts is a major area of research for the development of cleaner and more
26 efficient processes [1-3].
27 Recently, the utilization of polymer bound catalysts is well recognized because of their ease
28 of workup, simple and clean separation of products and catalysts from the reaction mixture. In
29 this context, cellulose and starch are good candidates as natural, renewable, biocompatible,
30 and biodegradable polymers [4-6]. As an ideal support material for catalysts, starch has
31 unique properties including availability, safety, non-toxicity, and inexpensive and
32 compatibility with many other materials. Owing to these properties, starch has been used as a
33 bio-based support for a wide range of catalytic species. This catalyst gained much attention
34 due to the low-cost production, easy preparation process, high effectiveness, greener and
35 suitable for chemical transformations [4-8]. The polar hydroxyl groups in starch provide
36 active sites for numerous attractive chemical modifications [3]. One such modification is
37 sulfonation which leads to the formation of starch-SO3H. Starch-SO3H has been utilized as
38 solid acid catalyst in organic reactions [4, 5]. Therefore, the modification of starch is rapidly
39 developed along with its growing applications. Starch-based nanoparticles have received a
40 great deal of attention because of their nano-size, large surface area, biodegradable, and good
41 biocompatibility. These characteristics favour the employment of starch nanoparticles in a
42 wide range of various industrial applications especially food products, biomedical fields
43 especially drug carriers, composites filler, water treatment agent, fat replacer and catalytic
44 processes [9-13]. Moreover, starch nanoparticles have raised much attention, as sustainable
45 development policies tend to expand with the decreasing reserve of fossil fuel and the
46 growing concern for the environment [10]. These bio-based nanoparticles have received a
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47 tremendous level of attention as a promising natural material in waste water treatment due to
48 their unique biological and adsorptive properties [11, 12].
49 In recent times, xanthenes and benzoxanthenes have attracted attention of medicinal chemists
50 as well as organic chemists due to their wide range of biological and pharmacological
51 activities such as antibacterial and anti-inflammatory activities [14], photodynamic therapy
52 and as antagonism for the paralyzing action of zoxazolamine [15]. Moreover, these valuable
53 compounds have found wide usage such as fluorescent dyes [16], in laser technologies [17]
54 and as pH-sensitive fluorescent materials for visualization of biomolecules [18]. Due to the
55 high medicinal and biological importance of xanthenes, several methods have been reported
56 for the synthesis of these heterocycles, which include trapping of benzynes by phenols,
57 cyclodehydrations, condensation between aromatic 2-hydroxyl aldehydes and 2-tetralone and
58 intramolecular phenyl carbonyl coupling reactions of benzaldehyde and acetophenone
59 derivatives. Also, 14-aryl-14H-di benzo[a.j]xanthenes and related products have been
60 prepared by the reaction of 2-naphthol with formamide, 2-naphthol-1-methanol and carbon
61 monoxide [19]. On the other hand, a number of methods have been developed for the
62 synthesis of 14-H-dibenzo[a,j]xanthene by condensation of 2-naphthol and aldehydes in the
63 presence of strontium sulfamic acid [20], Amberlyst-15 [21], K5CoW12O40.3H2O [22], FeCl3
64 [23], WO3/ZrOb [24], PS/AlClb [25], Alum [26], In(OTF)3 [27]. Therefore, a significant
65 attention has been focused on designing environmentally benign catalysts and synthetic
66 strategies for the preparation of xanthenes derivatives. The green processes in modern
67 chemical synthesis involve the use of biodegradable, cost-effective and efficient catalysts,
68 non-toxic system such as water, supercritical fluids and the reactions under solvent-free
69 conditions. Advantages of solvent-free reactions include cost savings, energy consumption,
70 atom economy, or improved atom utilization reduced decreased reaction times, and a
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71 considerable reduction in reactor size and simplicity in processing, which are beneficial to the
72 industry as well as to the environment [28].
73 In the present work, we report a simple and efficient procedure for one-pot synthesis of 14-
74 aryl-14-H-dibenzo[a,j]xanthenes using sulfonated starch nanoparticles (HO3S-SNPs) as an
75 effective, neutral and heterogeneous acidic catalyst under solvent-free conditions (Scheme 1).
R
H
R
O
(1)
HO3S-SNPs
Solvent-free, 110 °C
OH
O
HO
(2)
(2)
(3)
76
77
Scheme 1. Synthesis of 14-aryl-14H-dibenzo[a,i]xanthenes using HO3S-SNPs as catalyst.
78 2. Experimental
79 Chemical substances were purchased from Merck or Aldrich. Melting points were determined
80 on an Electrothermal 9100 apparatus using open-glass capillary and are uncorrected. FT-IR
1
81 spectra were recorded as KBr pellets on a Shimadzu FT-IR-8400S spectrometer. H NMR
82 (400 MHz) spectra were obtained using a Bruker DRX-400 AVANCE spectrometer.
83 Analytical thin-layer chromatography (TLC) was accomplished on 0.2 mmprecoated plates of
84 silica gel 60 F-254 (Merck) or neutral alumina oxide gel 60F 254 (Merck). Themorphological
85 characteristics of chitosan derivatives were observed by a scanning electron microscope
86 (SEM, LEO 1544VP) operating at an accelerating voltage of 20 kV under high vacuum.
87 Nanostructures were characterized using a Holland Philips Xpert X-ray diffraction (XRD)
88 diffractometer (CuK, radiation, λ= 0.154056 nm), at a scanning speed of 2°/min from 10° to
89 100° (2θ).
90 2.1. Synthesis of starch nanoparticles
91 0.35 g of maleic acid was firstly dissolved in 100 mL of distillated water, then 1 g of starch
92 was added to the this solution the resulted mixture was stirred for 3 h. Then, hydrochloric acid
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93 and sodium hydroxide solution (0.1 M) was dropped slowly into the mixture solution until the
94 pH value was titrated to 4.0 with vigorous mechanical stirring and under continuous Ar
95 atmosphere bubbling for 8 h. Afterwards, 0.054 g of potassium persulfate was added to the
96 mixture and stirred for 2 h at 70 °C under Ar atmosphere. The mixture was cooled in ice-bath
97 and the formed nanoparticles were dried by dry ice.
98 2.2. Synthesis of sulfonated starch nanoparticles:
99 HO3S-SNPs were prepared according to reported procedure in the literature [4]. A 500 mL
100 suction flask was equipped with a pressure equalizing dropping funnel containing
101 chlorosulfonic acid and gas inlet tube for conducting HCl gas over adsorbing the solution
102 water. A flask was charged with starch nanoparticles (500 g) and dispersed in dry CHCl3 (20
103 mL). Subsequently, chlorosulfonic acid (1.00 g, 9 mmol) was added drop-wise manner to a
104 cooled (ice-bath) solution of starch over a 2 h period, which HCl gas evolved from the
105 reaction vessel immediately. After the addition was completed the mixture was filtered and
106 washed with methanol (30 mL) and dried at room temperature to obtain HO3S-SNPs (5.06 g)
107 as cream powder. The number of H+ sites of starch-SO3H was determined by acid–base
°
108 titration and found to be 1.50 meq/g of modified starch at 25 C. The sulfur content of the
109 samples was determined 1.45 mmol/g by conventional elemental analysis.
110 2.3. General method for the synthesis of benzoxanthenes
111 In a glass tube a mixture of aldehyde (1.0 mmol), 2-naphthol (2.0 mmol) and HO3S-SNPs
112 (0.08 g) were stirred at 110 °C in an oil bath for the appropriate time, as indicated by TLC for
113 a complete reaction. Ethyl acetate (10 mL) was added and the reaction mixture filtered to
114 separate the catalyst. Pure products were afforded by evaporation of the solvent, followed by
115 recrystallization from ethanol. All the products were characterized by comparison of IR and
116 NMR spectral data with the values of authentic samples.
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117 14-(Phenyl)14H-dibenzo[a,j]xanthenes (3a): pale yellow solid; IR (KBr) υmax (cm−1): 3071
118 (aromatic C–H), 2923 (aliphatic C-H), 1624 (C=C), 1249 (C-O); 1H NMR (CDCl3, 400 MHz)
119 δ (ppm): 6.5 (s, 1H), 6.98-7.01 (t, 1H J=7.2 Hz), 7.13 (s, 1H), 7.15-7.17 (d, 1H J=8 Hz), 7.39
120 (s, 1H), 7.41-7.43 (d, 1H, J=7.2 Hz), 7.48-7.60 (m, 6H), 7.79-7.84 (m, 4H), 8.39- 8.41 (2H, d,
121 J=8 Hz); 13C NMR (CDCl3, 100 MHz) δ (ppm): 148.8, 145.0, 131.5, 131.1, 128.8, 128.5,
122 128.2 126.8, 126.5, 126.4, 124.2, 122.7, 118.0, 117.4, 38.1.
123 14-(3-Nitrophenyl)14H-dibenzo[a,j]xanthenes (3b): yellow solid; IR (KBr) υmax (cm−1): 3074
124 (aromatic C–H), 2923 (aliphatic C-H), 1625 (C=C), 1559 (NO2), 1346 (NO2), 1249 (C–O);
125 1H NMR (CDCl3, 400 MHz) δ (ppm): δ= 6.61 (1H, s), 7.29-7.31 (1H, d, J=7.2 Hz), 7.44-7.46
126 (2H, d, J=7.2 Hz), 7.51-7.53 (2H, d, J=8.4 Hz), 7.62 (2H, t, J=8.4 Hz), 7.83-7.85 (6H, m),
127 8.30-8.32 (2H, d, J=7.6 Hz), 8.42 (1H, s); 13C NMR (CDCl3, 100 MHz) δ (ppm): 37.3, 116.3,
128 116.8, 117.4, 121.1, 122.3, 125.4, 126.9, 128.2, 129.1, 134.7, 136.3, 137.1, 138.2, 146.5,
129 147.9, 158.3.
130 14-(4-Nitrophenyl)14H-dibenzo[a,j]xanthenes (3c): pale yellow solid; IR (KBr) υmax (cm-1):
131 3041 (aromatic C–H), 1622 (C=C), 1583, 1548 (NO2), 1348 (NO2), 1242 (C–O), 800-850; 1H
132 NMR (CDCl3, 400 MHz) δ (ppm): 6.61 (1H, s), 7.43–7.45 (2H, t, J=8.0 Hz), 7.51–7.53 (2H,
133 d, J=8.1 Hz), 7.59–7.61(2H, t, J=8.0 Hz), 7.68–7.70 (2H, d, J=8.1 Hz), 7.84–7.87 (4H, m),
13
134 8.00–8.02 (2H, d, J=8.0 Hz), 8.28–8-30 (2H, d, J=8.0 Hz); C NMR (CDCl3, 100 MHz) δ
135 (ppm): 36.9, 115.9, 116.2, 117.1, 120.2, 122.5, 124.8, 126.1, 128.1, 129.7, 132.6, 134.1,
136 135.9, 148.3, 159.1.
137 14-(2-Flouro)14H-dibenzo[a,j]xanthenes (3d): cream solid; IR (KBr) υmax (cm−1): 3090
1
138 (aromatic C–H), 2923 (aliphatic C-H), 1623 (C-C), 1458 (C=C), 1243 (C–O), 1100-1250; H
139 NMR (CDCl3, 400 MHz) δ (ppm): 6.79 (1H, s), 6.81–6.83 (1H, d, J=6.8 Hz), 6.96-7.04 (2H,
140 m), 7.20–7.24 (3H,m), 7.41–7.62 (4H, m), 7.79–7.84 (4H, m), 8.40-8.42 (2H, d, J=8.8 Hz);
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141 13C NMR (CDCl3, 100 MHz) δ (ppm): 30.2, 115.1, 115.2, 116.7, 117.9, 122.3, 124.4, 125.1,
142 127.1, 128.2, 128.6, 129.1, 130.9, 131.1, 131.5, 132.4.
143 14-(2-Chlorophenyl)14H-dibenzo[a,j]xanthenes (3e): white solid; IR (KBr) υmax (cm−1): 3056
1
144 (aromatic C–H), 2924 2992 (aliphatic C-H), 1247 (C-O); H NMR (CDCl3, 400 MHz) δ
145 (ppm): 6.80 (1H, s,) 6.89–6.96 (2H, m), 7.25–7.26 (1H, d, J=8.4 Hz), 7.38–7.46 (3H, m),
146 7.49-7.51 (2H, d, J=8.8 Hz), 7.61-7.65 (2H, t, J=7.6 Hz), 7.79–7.84 (4H, m), 8.76-8.76 (2H,
13
147 d, J=8.4 Hz); C NMR (CDCl3, 100 MHz) δ (ppm): 36.4, 117.9, 123.3, 124.6, 125.5, 127.8,
148 128.6, 129.4, 129.5, 131, 132.5, 132.6, 134.5, 141.3, 147.5, 149.8, 152.
149 14-(4-Chlorophenyl)14H-dibenzo[a,j]xanthenes (3f): yellow solid; IR (KBr) υmax (cm−1):
1
150 3050 (aromatic C–H), 2922 (aliphatic C-H), 1625 (C-C), 1244 (C-O); H NMR (CDCl3, 400
151 MHz) δ (ppm): 6.48 (1H, s), 7.10–7.12 (2H, d, J=7.2 Hz), 7.42–7.50 (6H, m), 7.58–7.61 (2H,
13
152 t, J=7.2 Hz), 7.80–7.86 (4H, m), 8.32–8.34 (2H, d, J=8 Hz); C NMR (CDCl3, 100 MHz) δ
153 (ppm): 37.39, 116.74, 118.02, 122.42, 124.38, 126.93, 128.65, 128.92, 129.10, 129.50,
154 131.05, 131.25, 132.08, 143.47, 148.68.
155 14-(2,4-Dichlorophenyl)14H-dibenzo[a.j]xanthenes (3g): pale yellow solid; IR (KBr) υmax
1
156 (cm−1): 3061 (aromatic C–H), 2923 (alyphatic C-H), 1624 (C-C), 1247 (C-O); H NMR
157 (CDCl3, 400 MHz) δ (ppm): 6.75 (1H, s), 6.89-6.91 (1H, t, J=6.4 Hz), 7.27-7.31 (2H, m),
158 7.42-7.49 (4H, m), 7.60-7.64 (2H, t, J=8.4 Hz), 7,79-7.84 (4H, t), 8.64-8.66 (2H, d, J=8 Hz);
159 13C NMR (CDCl3, 100 MHz) δ (ppm): 36.6, 117.3, 117.5, 118.4, 123.3, 126.7, 127.5, 128.4,
160 130.8, 133.5, 135, 141.5, 150.9.
161 14-(4-Methyl)14H-dibenzo[a,j]xanthenes (3h): pale yellow solid, IR (KBr) υmax (cm−1): 3061
162 (aromatic C–H), 2923 (aliphatic C-H), 1624 (C-C), 1247 (C-O); 1H NMR (CDCl3, 400 MHz)
163 δ (ppm): 2.13 (3H, s), 6.46 (1H,s), 6.95-6.97 (2H,d, J=7.6 Hz), 7.39-743 (4H, m), 7.47-7.50
164 (2H, d, J=8.8 Hz), 7.56-7.60 (2H, t, J=8Hz), 7.78-7.84 (4H, m), 8.39-8.41 (2H, d, J=8.4 Hz);
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165 13C NMR (CDCl3, 100 MHz) δ (ppm): 20.95, 37.67, 117.48, 118.04, 122.76, 124.25, 126.79,
166 128.15, 128.81, 128.82, 129.22, 131.11, 131.49, 135.93, 142.18, 148.
167 14-(2-Methoxy)14H-dibenzo[a,j]xanthenes (3i): cream solid, IR (KBr) υmax (cm−1): 3051
168 aromatic C–H), 2921 (aliphatic C-H), 1622 (C=C), 1247 (C-O); 1H NMR (CDCl3, 400 MHz)
169 δ (ppm): 3.62 (s, 3H, OCH3), 6.46 (s, 1H, ArH), 6.67-6.69 (2H, d, J=8.4 Hz), 7.40-7.44 (4H,
170 m), 7.47-7.49 (2H, d, J=8.8 Hz), 7.57-7.60 (2H, t, J=7.6 Hz), 7.78-7.84 (4H, m), 8.38-8.40
171 (2H, d, J=8.4 Hz).; 13C NMR (CDCl3, 100 MHz) δ (ppm): 44.11, 55.17, 114.78, 118.59,
172 119.21, 122.54, 125.23, 127.77, 129.65, 129.72, 130.01, 132.16, 132.76, 137.45, 149.04, 158.
173 14-(4-Methoxy)14H-dibenzo[a,j]xanthenes (3j): pink solid; IR (KBr) υmax (cm−1): 3050
174 (aromatic C–H), 2922 (aliphatic C-H), 1593 (C=C), 1247 (C-O); 1H NMR (CDCl3, 400 MHz)
175 δ (ppm): 3.62 (3H, s), 6.45 (1H, s), 6.67-6.69 (2H, d, J=8.8 Hz), 7.40-7.49 (6H, m), 7.57-7.60
176 (2H, t, J=7.2 Hz), 7.78-7.80 (2H, d, J=8.8 Hz), 7.82-7.84 (2H, d, J=8.Hz), 8.38-8.40 (2H, d,
177 J=8.4 Hz); 13C NMR (CDCl3, 100 MHz) δ (ppm): 37.11, 55.05, 113.85, 117.54, 118.02,
178 122.70, 124.23, 126.77, 128.74, 128.82, 129.17, 131.08, 131.43, 137.39, 148.68, 157.21.
179 14-(3-Hydroxyphenyl)14H-dibenzo[a,j]xanthenes (3k): Pale Pink solid; IR (KBr) υmax (cm−1):
180 3070 (OH), 1595 (C=C), 1246 (C-O); 1H NMR (CDCl3,400 MHz) δ (ppm): 3.45 (s, 3H), 6.45
181 (s, 1H), 6.33 (d, 1H, J=8.2 Hz), 7.08 (t, 2H, J=8.4 Hz), 7.21 (d, 1H, J=7.5 Hz), 7.33 (t, 2H,
182 J=7.2 Hz), 7.52 (d, 2H, J=9.0 Hz), 7.58 (t, 2H, J=7.6 Hz), 7.72–7.80 (m, 4H), 8.40 (d, 2H,
183 J=8.7 Hz); 13C NMR (CDCl3, 100 MHz) δ (ppm): 37.22, 116.05, 118.02,118.75, 123.66,
184 125.02, 126.45, 130.30, 130.56, 131.03, 131.76, 132.11, 138.54, 149.45, 154.43.
185 14-(4-Hydroxyphenyl)14H-dibenzo[a,j]xanthenes (3l): Pink solid; IR (KBr) υmax (cm−1): 3405
186 (OH), 1590 (C=C), 1245 (C-O); 1H NMR (CDCl3,400 MHz) δ (ppm): 5.01 (s, 1H, OH), 6.42
13
187 (s, 1H, CH), 6.55–8.36 (m,16H, Ar); C NMR (CDCl3, 100 MHz) δ (ppm): 37.45, 115.85,
188 117.85,118.50, 123.20, 124.62, 127.23, 129.30, 129.56, 130.00, 131.58,131.61, 138.02,
189 149.18, 154.32.
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190 3. Results and discussion
191 Sulfonic acid-based solid catalysts have used in organic reactions due to their unique
192 properties, such as high reactivity, availability, selectivity, eco-friendly reaction conditions,
193 and ability to promote a wide range of chemical reactions. Since the sulfonation of D-glucose
194 was first reported as a carbohydrate acid catalyst by Hara et al., [29] much efforts have been
195 devoted to developing various types of solid acid catalysts from bio-based polymers, such as
196 sucrose, starch, cellulose and bagasse [30-33] This class of biocompatible and biodegradable
197 catalysts have shown much better performance than commercially available solid acid
198 catalysts, such as Nafion NR50, zeolites and Amerlyst-15 [34]. Furthermore, nanoscale
199 polymers have been attracting more research interest in catalytic systems because of their
200 unique physical and chemical properties, such as nano size, high surface-to-volume ratio and
201 stiffness and improved dispersibility. The polymeric nanoparticles offer a number of distinct
202 advantages over bulk polymers. They have been used in different types of chemical reactions
203 as a suitable support for different catalytic species [35]. In the first of research, starch was
204 modified to starch nanoparticles by a nanoprecipitation process. Next, HO3S-SNPs were
205 prepared by the reaction of chlorosulfonic acid with starch nanoparticles and the by-product,
206 HCl gas, was easily removed from the reaction vessel (Scheme 2).
OSO3H
OSO3H
HO3SO
HO3SO
HO3SO
HO
OH
OH
OH
HO
HO
OSO3H
Strach
Nps
CHCl3
0 °C
Strach
Nps
HCl
+
+ ClSO3H
OSO3H
OSO3H
HO3SO
HO3SO
OH
HO
HO
OH
207
208
Scheme 2: Preparation steps for fabricating HO3S-SNPs.
209 The morphology and structure of starch nanoparticles were investigated by FT-IR, XRD,
210 TEM and SEM. The FT-IR spectrum of starch nanoparticles are shown in Fig. 1. The O-H
211 stretching and the C-H stretching vibration gave strong signals at 3431 and 2924 cm−1,
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212 respectively. Meanwhile, the band at 1630 cm−1 was ascribed to O-H bending vibration.
213 Besides, several discernible absorbencies at 1154 and 1023 cm−1 were assigned to the C-O
214 bond stretching vibrations of glucose units [36].
215
216
Fig. 1: FT-IR of starch nanoparticles.
217 Fig. 2 (a) and (b) display XRD result of native starch and starch nanoparticles, respectively.
218 The sharp diffraction peaks at 5.8◦, 17.4◦, 22.3◦, and 24.2◦ were presented in spectrogram of
219 unmodified starch, which indicated that starch exhibited a typical B-type X-ray pattern. The
220 spectrogram of starch nanoparticles showed a broad peak, suggesting that it was the
221 amorphous nature. Fu et al. also reported the similar XRD results for starch nanoparticles
222 [36].
(b)
(a)
223
224
Fig. 2. XRD patterns of (a) starch and (b) starch nanoparticles.
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225 Fig. 3 presents the XRD-diffraction patterns of the HO3S-SNPs. The same broad peak was
226 observed in XRD pattern of HO3S-SNPs, indicating retention of the amorphous nature of the
227 starch nanoparticles during the sulfonation process.
228
229
Fig. 3. XRD pattern of HO3S-SNPs.
230 Fig. 4 (a) and (b) showed SEM and TEM micrographs of starch nanoparticles, respectively.
231 SEM in Fig. 4(a) shows the surface morphology of the starch nanoparticles. TEM image in
232 Fig. 4(b) indicates that the particles are nearly spherical and they have a range diameter of 50-
233 80 nm. SEM image for HO3S-SNPs in Fig. 4(c), shows significant difference between starch
234 nanoparticles and sulfonated starch. After sulfonation of the starch nanoparticles, the
235 aggregates were foliated with rougher surfaces.
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(a)
(b)
236
(c)
237
238
Fig. 4. (a) SEM and (b) TEM image of starch nanoparticles and (c) SEM of HO3S-SNPs.
239 To investigate the feasibility of the synthetic methodology for the synthesis of
240 benzoxanthenes, initial experiments were performed by using 2-naphthol and benzaldehyde as
241 reactants at 110 °C under solvent-free conditions. Initially, the Starch-SO3H was studied for its
242 activity in the model reaction. The results showed that 0.08 g of catalyst was optimal for this
243 reaction (Table 1, Entry 4). In a blank experiment no desired product was observed under
244 similar reaction conditions in the absence of acidic catalyst (Table 1, Entry 1). In the next
245 stage for getting the best conditions, we carried out a model study with the same reagent
246 system at 90°C, 100°C, 110°C and 120°C temperatures, (Table 1, Entries, 4 and 8-11).
247 Increasing the temperature enhances the reaction rate substantially with respective 70%, 85%,
248 92% and 80% yield. According to the results, we obtained the best results at 110 °C, and
249 therefore all the reactions were performed at this temperature for the synthesis of 14-aryl-14-
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250 H-dibenzo[a,j]xanthenes. The reaction time was still long and needs to be improved and for
251 this reason, HO3S-SNPs were used in this organic reaction. It was observed that SO3H-SNP is
252 better than the Starch-SO3H tested in this study in terms of reaction yield (92%) and reaction
253 time (45 min) (Table 1, entry 13). Some solvents such as EtOH, MeOH, CH3CN, H2O and
254 CH2Cl2, did not show improvement in the yield of product (Table 1, Entries 14-18).
255 Table 1. Results of screening the conditions.
Temp (∘C)
Entry
Catalyst
Catalyst(g)
Solvent
Time
(min)
Yield
(%)
1
2
-
-
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
EtOH
110
110
240
240
240
105
180
210
105
105
105
180
180
240
45
-
Starch
0.08
0.08
0.08
0.05
0.01
0.1
-
3
Starch NPs
Starch-SO3H
Starch-SO3H
Starch-SO3H
Starch-SO3H
Starch-SO3H
Starch-SO3H
Starch-SO3H
Starch-SO3H
Starch-SO3H
HO3S-SNPs
HO3S-SNPs
HO3S-SNPs
HO3S-SNPs
HO3S-SNPs
HO3S-SNPs
110
-
4
110
90
75
70
84
81
80
85
70
-
5
110
6
110
7
110
8
0.15
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
110
9
120
10
11
12
13
14
15
16
17
18
100
90
r.t.
110
92
65
58
70
35
40
Reflux
Reflux
Reflux
Reflux
Reflux
120
120
120
120
120
MeOH
CH3CN
CH2Cl2
H2O
256 Under the optimized reaction conditions, a series of aldehydes with 2-naphthol were explored
257 in the presence of HO3S-SNPs. The results were summarized in Table 2. The procedure was
258 highly effective for the preparation of 14-aryl-14-H-dibenzo[a,j]xanthenes. As expected, the
259 aromatic aldehyde substrates containing electron donor groups (such as OMe and OH),
260 showed weaker results than the cases containing electron withdrawing groups (such as NO2,
261 Cl).
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14
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262 Table2. Synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes using HO3S-SNPs.
Entry
R
Product
SO3H-SNPs
M.p (ºC)
(Reported)
Ref
Time(min)
Yield(%)a
(Found)
183-185
208-210
310-312
209-210
213-215
287
1
2
C6H5
3a
3b
3c
3d
3e
3f
45
40
30
40
45
35
30
70
80
70
70
70
92
181-183
211-212
310-312
211-212
214-215
287-289
254-255
227-230
263-265
202–204
240-241
138-140
37
38
38
38
39
37
40
41
41
42
42
42
3-NO2C6H4
4-NO2C6H4
2-FC6H4
95
3
97
4
95
5
2-ClC6H4
92
6
4-ClC6H4
95
7
2,4-ClC6H4
4-CH3C6H4
2-OCH3C6H4
4-OCH3C6H4
3-OHC6H4
4-OHC6H4
3g
3h
3i
95
252-253
226
8
95
9
91
263-265
203-204
241-242
139-140
10
11
12
3j
94
3k
3l
90
92
263 a Isolated yields
264 The formation of benzoxanthenes from aldehyde derivatives and 2-naphthol in the presence of
265 HO3S-SNPs as catalyst can be explained by a tentative mechanism is presented in Scheme 3.
266 HO3S-SNP is supposed as a Lewis acid catalyst to facilitate the activation of the aldehyde.
267 The acidic SO3H groups distributed on the surface of starch nanoparticles in high
268 concentrations activate the carbonyl group of the aldehyde. Then, one molecule of 2-naphthol
269 condense with an activated aldehyde (I) to provide intermediate (II), which can be regarded as
270 a fast Knoevenagel addition. In the next step, the active methylene of the second molecule of
271 2-naphthol react with intermediate (II) via conjugate Michael addition to produce the
272 intermediate (III), which undergoes intramolecular cyclodehydration to furnish the desired 14-
273 aryl-14-H-dibenzo[a,j]xanthenes (V) [42, 43].
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-
OH
starch-SO3
O
+
R
H
O
R
H
R
H
R
H
OH
OH+
I
starch-SO3H
O
-
starch-SO3
-H2O
V
R
II
H
-H2O
OH
IV
O
R
C+
-
-
starch-SO3
+
starch-SO3
H2O
R
OH+
HO
OH
III
274
275
Scheme.3: Proposed reaction mechanism.
276 To have a better understanding of the performance of our catalytic system, the effectiveness
277 of the SO3H-SNPs was also compared to that of catalysts reported previously in the synthesis
278 of 14-aryl-14-H-dibenzo[a,j]xanthenes from the reaction of 2-naphthol and various aromatic
279 aldehydes and the results are listed in Table 3. As can be seen in this table, the present catalyst
280 was found to be the most efficient catalyst among all of the catalysts in the literatures. The
281 reaction in the presence of HO3S-SNPs was indicated a lot of significant such as; simplicity of
282 the reaction, excellent yields, low reaction times, naturally safe, biodegradable, economical,
283 and eco-friendly catalyst. These advantages can be related to the highly activity due to its
284 nanoporosity and high surface area.
285 Table 3: The synthesis of 3a using different catalysts.
Entry
1
Catalyst
Time (min)
45
Yield(%)a
92
Temp (◦C)
110
Ref.
HO3S-SNPs
This research
2
3
Dowex-50 W
TCCA
160
50
84
74
100
110
22
44
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16
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4
5
Iodine
H5PW10V2O40
H2SO4/SiO2
18
60
85
92
97
96
90
91
93
50
70
40
45
50
92
80
90
90
100
125
r.t.
45
46
47
48
49
50
20
41
41
41
41
41
41
43
43
6
60
7
PFPAT
Cellulose sulfuric acid
189
120
24h
8h
8
110
85
9
SBA-15-SO3H
Sulfamic acid
AgBr
10
11
12
13
14
15
16
17
18
125
140
140
140
140
140
140
r.t
90
AgI
70
CuCl
120
140
160
40
NiO
CaO
AgI-nano
SBA-15-CO2H
MCM-41-SO3H
6h
60
r.t
286 a Isolated yields
287 The reusability of the HO3S-SNPs was tested for the model reaction. The separated catalyst
288 was used several times and loss of catalytic activity was not observed (Fig. 5).
289
290
Fig. 5. Recoverability of HO3S-SNPs.
291 Conclusions
292 In summary, the present work was the first report on using HO3S-SNPs as a novel and very
293 promising solid acid catalyst for the synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes. The
294 application of starch-SO3H as a highly efficient, inexpensive, easy work-up, and natural solid
295 acid catalyst makes the present methodology economically and eco-friendly acceptable.
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296 Moreover, solvent free, low-cost, non-toxicity, high yields of the desired benzoxanthenes and
297 short reaction times are supporting the protocol toward the green chemistry. Further
298 applications of these biopolymer catalysts are currently under investigation in our laboratory.
299 Acknowledgments
300 We gratefully acknowledge the financial support from the Research Council of the University
301 of Kashan for supporting this work by Grant No. (363022/16).
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472 Figure captions
473 Table 1. Results of screening the conditions.
474 Table2. Synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes using SO3H-SNPs.
475 Table 3: The synthesis of 3a using different catalysts.
476 Scheme 1. Synthesis of 14-aryl-14H-dibenzo[a,i]xanthenes using SO3H-SNPs as catalyst.
477 Scheme 2: Preparation steps for fabricating SO3H-SNPs.
478 Scheme.3: Proposed reaction mechanism.
479 Fig. 1: FT-IR of starch nanoparticles.
480 Fig. 2. XRD patterns of (a) starch and (b) starch nanoparticles.
481 Fig. 3. XRD pattern of SO3H-SNPs.
482 Fig. 4. (a) SEM and (b) TEM image of starch nanoparticles and (c) SEM of SO3H-SNPs.
483 Fig. 5. Recoverability of SO3H-SNPs.
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ACCEPTED MANUSCRIPT
R
R
O
H
R
H
O
O
O
O
OEt
EtO
OH
HO
O
O
CH3COONH4
Sulfonated starch
nanoparticles