Synthesis of 1,3-dioxanes catalyzed by TsOH-SiO2 under solvent-free conditions

Article abstract of DOI:10.1080/00397910802045618

Silica-supported p-toluene sulfonic acid is found to be an excellent catalyst for the Prins reaction to produce 1,3-dioxanes in good yields from olefins and aliphatic aldehydes in dichloromethane at room temperature and solventless microwave irradiation within a short reaction time. Copyright Taylor & Francis Group, LLC.

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Synthesis of 1,3-Dioxanes
Catalyzed by TsOH-SiO2 Under
Solvent-Free Conditions
Kalyan Jyoti Borah a , Mridula Phukan a & Ruli Borah
a
a Chemical Sciences Department, Tezpur University,
Napaam, Assam, India
Version of record first published: 09 Sep 2008.
To cite this article: Kalyan Jyoti Borah , Mridula Phukan & Ruli Borah (2008):
Synthesis of 1,3-Dioxanes Catalyzed by TsOH-SiO2 Under Solvent-Free Conditions,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 38:18, 3082-3087
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Synthetic Communications1, 38: 3082–3087, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802045618
Synthesis of 1,3-Dioxanes Catalyzed by
TsOH-SiO2 Under Solvent-Free Conditions
Kalyan Jyoti Borah, Mridula Phukan, and Ruli Borah
Chemical Sciences Department, Tezpur University, Napaam, Assam, India
Abstract: Silica-supported p-toluene sulfonic acid is found to be an excellent
catalyst for the Prins reaction to produce 1,3-dioxanes in good yields from olefins
and aliphatic aldehydes in dichloromethane at room temperature and solventless
microwave irradiation within a short reaction time.
Keywords: Microwave, p-toluene sulfonic acid, prins reaction, solventless
INTRODUCTION
The acid-catalyzed condensation of olefins with carbonyl compounds is
an important reaction for carbon–carbon bond formation,[1] which is well
known as the Prins reaction (Scheme 1). This reaction is one of the
efficient methods for the synthesis of 1,3-dioxanes in the presence of con-
ventional Lewis or Brønsted acids using volatile organic solvents.
Reports on a large number of synthetic methods[1–3] involve high-
temperature reaction conditions, prolonged reaction times (6–20 h), use
of a stoichiometric amount of catalyst, environmental pollution from
organic solvents, and complicated product purification. In recent years,
the use of solid catalysts such as resin,[4] zeolite,[5] and K10 clay[2] have
gained importance in the Prins[6] reaction because of their environmental
compatibility, greater selectivity, experimental simplicity, low cost, and
simple purification of the products. Chandrasekhar and Reddy[7] first
reported the microwave-assisted Prins synthesis of 1,3-dioxane using
TaCl2-SiO2 as catalyst under solvent-free conditions. Generally, most
Received January 16, 2008.
Address correspondence to Ruli Borah, Senior Lecture, Department of Chemi-
cal Sciences, Tezpur University, Napaam, Tezpur-784028 Assam, India. E-mail:
ruli@tezu.ernet.in
3082

Synthesis of 1,3-Dioxanes
3083
Scheme 1. Microwave-assisted solvent-free Prins reaction.
of the conventional methods[8] include the use of paraformaldehyde as a
formaldehyde source. The direct use of formalin solution is highly desir-
able because it reduces the use of toxic and volatile organic solvents such
as acetonitrile, toluene, and dioxane to dissolve solid paraformaldehyde.
Only a few[3] reports are available in literature regarding using formalin
as a starting compound.
In this context, new methods and environmentally friendly con-
ditions for the synthesis of 1,3-dioxane are still demand for their use of
solventless conditions, greater selectivity, shorter reaction times, and sim-
ple workup procedure.
RESULTS AND DISCUSSION
For comparative study, we investigated TsOH=TsOH-SiO2-catalyzed
Prins reaction of paraformaldehyde (Tables 1 and 2) and various alkenes
under both solvent and solvent-free conditions. These studies revealed
that the Prins reactions of paraformaldehyde and substituted styrene
selectively produced 1,3-dioxane in the presence of TsOH-SiO2 as catalyst
within 5 min (Table 2, entries 2, 5, 8, and 10) with microwave irradiation
(180 W) as compared to reaction in dichloromethane (Table 1, entries 2,
6, 8, and 10). In addition, p-toluene sulfonic acid–catalyzed Prins reac-
tion of formalin and styrene derivatives (Table 2, entries 6, 9, and 11)
showed excellent results under microwave irradiation. Interestingly, Du
and Tian[3] reported that no 1,3-dioxane product was found for TsOH-
catalyzed Prins reaction of formalin and styrene under reflux for 20 h.
Similarly, in this case also, no reaction was observed for the Prins reac-
tion of formalin and styrene in dichloromethane after 24 h (Table 1,
entries 3 and 4), with stirring at room temperature using TsOH=TsOH-
SiO2 as catalysts. The results in Table 1 indicate that in contrast to the
conventional methods,[2,3,9] TsOH=TsOH-SiO2-catalyzed Prins reaction
of different olefins and paraformaldehyde took less reaction time

3084
K. J. Borah, M. Phukan, and R. Borah
Table 1. Prins reaction in dichloromethane catalyzed by TsOH-SiO2
Solid support
(silica gel)
Entry Alkene
Aldehyde
Time
Yield (%)a,b
1
2
3
4
5
6
7
8
9
10
11
12
13
Styrene
Styrene
Styrene
Styrene
a-Methyl styrene
a-Methyl styrene
p-Chloro-styrene
p-Chloro-styrene
p-Methoxy styrene
p-Methoxy styrene
1-Octene
HCHO
HCHO
Formalin
Formalin
HCHO
HCHO
HCHO
HCHO
HCHO
HCHO
Formalin
HCHO
HCHO
—
1g
—
1g
—
1g
—
1g
—
1 g
—
1g
—
1 h
75
82
30 min
24 h
24 h
90 min
30 min
3 h
No reaction
No reaction
70
85
85
89
78
86
2 h
90 min
70 min
20 h
90 min
2 h
No reaction
1-Octene
1-Octene
67
62
aAll products were characterized by 1H NMR, MS, and CHN analysis and also
by their comparison with literature[2,4,8,9] data.
bIsolated yields.
(30 min–3 h) in dichloromethane at room temperature. All other alde-
hydes, such as pentanal and octanal, were similarly transformed to the
corresponding 1,3-dioxanes (Table 2, entries 14, 15, and 16) after
irradiation with styrene in microwaves for 2–3 min. Furthermore,
the TsOH-SiO2-catalyzed Prins reaction yielded more product (Table 1,
entries 2, 6, 8, and 10) as compared to TsOH-catalyzed reaction
(Table 1, entries 1, 5, 7, and 9) in dichloromethane within a short period.
Again, microwave irradiation decreases the selectivity of TsOH-catalyzed
Prins reaction for the formation of 1,3-dioxane (Table 2, entry 1) deriva-
tives. It was found that the alkyl-substituted olefins afforded the corre-
sponding 1,3-dioxanes in low yields (Table 1, entries 12, 13, and Table
2, entry 12) as compared to styrene derivatives.
EXPERIMENTAL
General
All chemicals are commercially available and were used without
further purification. The products were characterized by 1H NMR,
MS, and CHN analysis and also by comparison with literature[2,4,8,9]
data.

Synthesis of 1,3-Dioxanes
3085
Table 2. Microwave-assisted Prins reaction catalyzed by TsOH-SiO2
Solid
support
Microwave
Time
Entry Alkene
Aldehyde power (W) (silica gel) (min) Yield (%)a,b
1
Styrene
HCHO
180
—
5
More
products
85
90
No reaction
90
2
3
4
5
Styrene
Styrene
Styrene
a-Methyl
styrene
HCHO
Formalin
Formalin
HCHO
180
180
180
180
1 g
—
1 g
1 g
5
2
2
4
6
7
a-Methyl
styrene
a-Methyl
styrene
p-Chloro-
styrene
p-Chloro-
styrene
p-Methoxy
styrene
p-Methoxy Formalin
styrene
Formalin
Formalin
HCHO
180
180
180
180
180
180
—
1 g
1 g
—
2
4
5
3
4
2
85
No reaction
8
95
96
94
92
9
Formalin
HCHO
10
11
1 g
—
12.
13
14
15
1-Octene
1-Octene
Styrene
a-Methyl
styrene
HCHO
Formalin
Pentanal
Pentanal
300
300
180
180
1 g
—
1 g
1 g
5
5
1
2
70
No reaction
76
72
16
Styrene
Hexanal
300
1 g
7
52
aAll products were characterized by 1H NMR, MS, and CHN analysis and also
[2,4,8,9]
by their comparison with literature
bIsolated yields.
data.
Typical Procedures for the Preparation of 1,3-Dioxanes
Microwave Method
A mixture of styrene (3 mmol), paraformaldehyde (3 mmol), and p-toluene
sulfonic acid (0.5 mmol) was mixed thoroughly with activated silica gel
(1g, 60–120 mesh, dried overnight at 100ꢀC) at room temperature for
15 min. The mixture was irradiated in a microwave oven (180 W) for
5 min. After completion of the reaction as indicated by thin-layer chromato-
graphy (TLC), the reaction mixture was cooled to room temperature. The

3086
K. J. Borah, M. Phukan, and R. Borah
resulting product was directly charged onto a small silica-gel column and
eluted with a mixture of ethyl acetate–n-hexane (1:9) to find pure 1,3-diox-
ane (85%).
Conventional Method
A mixture of styrene (3 mmol), paraformaldehyde (3 mmol), and
p-toluene sulfonic acid (0.5 mmol) was stirred in dichloromethane
(5 ml) at room temperature for 1 h. After completion of the reaction
as indicated by TLC, the reaction mixture was diluted with water and
extracted with ether (2 ꢁ 10 ml). The combined organic layers were dried
over anhydrous sodium sulfate and distilled under reduced pressure in a
rotary evaporator. The crude reaction mixture was further purified by
column chromatography using ethyl acetate–n-hexane (1:9) as eluent
to find pure product 1,3-dioxane (75%).
Spectral Data of Selected Products
4-Phenyl-1,3-dioxane (entry 1, Table 1):
1H NMR (400 MHz, CdCl3) d 1.68–1.75 (1H, m), 2.04–2.17 (1H, m),
3.83–3.93 (1H, m), 4.17–4.23 (1H, m), 4.65 (1H, d, J ¼ 11.2 Hz), 4.90
(1H, d, J ¼ 6.4Hz), 5.20 (1H, d, J ¼ 6.4 Hz), 7.23–7.30 (5H, m); EIMS
m=z 164 (Mþ), 118, 105 (100), 77. Found: C, 73; H, 7.61%. Calcd. for
C10H12O2: C, 73.15; H, 7.37%. 13C NMR d 33.9, 66.9, 78.7, 94.2,
125.7, 127.9, 128.5, 141.5.
4-methyl-4-phenyl-1,3-dioxane (entry 6, Table 1):
1H NMR (400 MHz, CdCl3) d1.45(3H, s) 2.9–2.18 (1H, m), 2.25–2.32
(1H, m), 3.65–3.74 (1H, m), 3.90–3.96 (1H, m), 4.73 (1H, d, J ¼ 6.4
Hz), 4.91 (1H, d, J ¼ 6.4Hz), 7.23–7.31 (5H, m); EIMS; m=z 178
(Mþ), 163, 132, 117, 105 (100), 91, 77, 51. Found: C, 74.21; H, 7.98%.
Calcd. for C11H14O2: C, 74.13; H, 7.92%. 13C NMR d 32.1, 34.9, 63.6,
75.7, 89.1, 125.7, 1
CONCLUSIONS
This article describes an efficient method for the synthesis of 1,3-dioxane
with microwaves without using any organic solvent (using paraformalde-
hyde as and formalin as starting compound) in good yields.

Synthesis of 1,3-Dioxanes
3087
ACKNOWLEDGMENTS
The authors are thankful to the Council of Scientific and Industrial
Research, New Delhi, India, for awarding a research grant (No.
01(2067)=06=EMR-II) to R. B.
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