Hβ zeolite: An efficient and reusable catalyst for ring-opening of epoxides with amines under microwave irradiation

Article abstract of DOI:10.1007/s10562-009-0237-z

A solvent-free protocol for the synthesis of β-amino alcohols (Yield, up to 94%) is demonstrated by the ring-opening reactions of meso and terminal epoxides with aromatic amines using Hβ zeolite as catalyst under microwave irradiation. The catalytic syste

Full text of DOI:10.1007/s10562-009-0237-z

Catal Lett (2010) 134:318–323
DOI 10.1007/s10562-009-0237-z
Hb zeolite: An Efficient and Reusable Catalyst for Ring-Opening
of Epoxides with Amines Under Microwave Irradiation
•
Rukhsana I. Kureshy Santosh Agrawal
•
•
Manish Kumar Noor-ul H. Khan
•
•
Sayed H. R. Abdi Hari C. Bajaj
Received: 20 August 2009 / Accepted: 24 November 2009 / Published online: 11 December 2009
Ó Springer Science+Business Media, LLC 2009
Abstract A solvent-free protocol for the synthesis of
b-amino alcohols (Yield, up to 94%) is demonstrated by
the ring-opening reactions of meso and terminal epoxides
with aromatic amines using Hb zeolite as catalyst under
microwave irradiation. The catalytic system is 80 times
faster than the reaction conducted at RT with six times
catalyst recyclability.
the nucleophilic ring-opening of epoxides that work under
mild conditions is of great importance. In this direction
various Lewis acid promoters viz., metal halides [6–9],
metal triflates [10–13], metal alkoxides [14], metal amides
and triflamide [15–17], transition metal salts [18], hexa-
fluoro-2-propanol under reflux (HFIP) [19], ionic liquid
[20], zirconium sulfophenyl phosphonate [21], sulphated
zirconia [22], silica [23], alumina/modified alumina [24,
25] and montmorillonite clay were used as catalysts at
room temperature/microwave irradiation [26] in the pres-
ence/absence of a solvent [27]. The reactions proceed
smoothly to give the b-aminoalcohol in good to excellent
yields. However, some of these methods suffer from dis-
advantages such as the use of expensive or air-sensitive
reagents, extended reaction time, tedious work-up proce-
dures, or utilization of limited range of amines. Therefore,
the introduction of new and efficient methods is still in
demand.
Keywords Hb zeolite Á Epoxides ring-opening Á
b-Amino alcohols Á Microwave irradiation Á Amones
1 Introduction
The epoxide ring opening with amine is an important area
of research because b-amino alcohols have a wide appli-
cation in the synthesis of a vast range of biologically active
natural and synthetic products [1, 2], unnatural amino acids
[3] and chiral auxiliaries [4]. The classical and widely used
strategy for the synthesis of b-amino alcohols is the direct
aminolysis of epoxides with an excess of amine at elevated
temperature. However, under these conditions less reactive
epoxides or sluggish amines react slowly, and thermally
sensitive functional groups undergo undesirable side reac-
tions [5]. Therefore, the development of new methods for
Microwave heating becomes currently popular in recent
years [28–30] largely due to the dramatic reduction in
reaction time, increased energy efficiency, higher product
yields for a wide range of synthetic transformations [23,
26–33]. As a part of our research program to develop green
chemistry for various organic transformations under sol-
vent-free conditions [34–36], we have earlier used NaY
zeolite as efficient recyclable catalyst for epoxide ring
opening reaction at RT giving moderate to high yields and
good regioselectivity in 6–10 h [34]. Herein, we are
reporting the microwave-assisted and solvent-free protocol
for the synthesis of b-amino alcohols from the reactions of
aromatic amines with various meso and terminal epoxides
using Hb zeolite as recyclable catalyst. Excellent yield of
b-amino alcohols (up to 94%) was achieved in 2.5 min (80
times faster than reaction conducted at RT) with the
advantage of catalyst recyclability.
R. I. Kureshy (&) Á S. Agrawal Á M. Kumar Á
N. H. Khan Á S. H. R. Abdi Á H. C. Bajaj
Discipline of Inorganic Materials and Catalysis,
Central Salt and Marine Chemicals Research Institute
(CSMCRI), Council of Scientific & Industrial Research (CSIR),
Bhavnagar, Gujarat 364 002, India
e-mail: rukhsana93@yahoo.co.in
123

Ring-Opening of Epoxides with Amines Under Microwave Irradiation
2 Experimental
319
125 MHz) d = 20.43, 24.33, 25.10, 31.59, 33.16, 60.69,
74.49, 114.80, 127.77, 129.84, 145.45 ppm.
2.1 Materials and Methods
2.2.1.3 1-(Phenylamino)-Butan-2-ol (Table 3, Entry
2) 1H (CDCl3, 500 MHz) d = 0.97 (t, J = 7.5, 3H), 1.50–
1.56 (m, 2H), 2.72 (brs, 1H), 2.92–3.01 (m, 1H), 3.20–3.23
(m, 1H), 3.35–3.50 (m, 1H), 3.68–3.37 (m, 1H), 6.61–6.73
(m, 3H), 7.15–7.18 (m, 2H) ppm. 13C (CDCl3, 125 MHz)
d = 10.66, 27.99, 49.88, 71.66, 113.36, 117.89, 129.41,
148.36 ppm.
Zeolites, NaY, Nab, Hb (M/S. Zeocat, Uetikon, Switzer-
land), cyclohexene oxide, cyclopentene oxide, cyclooc-
tene oxide, 1-propene oxide, 1-hexene oxide, 1-octene
oxide, 1-decene oxide, 1-dodecene oxide, epichlorohydrin,
styrene oxide, 1-butoxy-2,3-epoxypropane, 1-isobutoxy-2,
3-epoxypropane, 1,2-epoxy-3-phenoxy propane, glycidyl
4-chloro phenyl ether and anilines 2-Meo- , 4-Meo- , 4-Me- ,
2-Cl- , 4-Cl- , 2-NO2- and 4-NO2-anilines (Aldrich, USA)
were used as received. Sineo Mas-II Microwave synthesis
workstation was used as Microwave reactor. Microanalysis
of the products was carried out on a Perkin Elmer CHN
Analyzer 2400. 1H NMR and 13C NMR spectra were
recorded in CDCl3 (Bruker F113V 500 and 125 MHz).
2.2.1.4 1-(Phenylamino)decan-2-ol (Table 3, Entry
5) 1H (CDCl3, 500 MHz) d = 0.88 (t, J = 5.5, 3H), 1.24
(m, 12H), 1.49–1.52 (m, 2H), 2.40 (brs, 1H), 2.96–3.00 (m,
1H), 3.23–3.26 (m, 1H), 3.45–3.51 (m, 1H), 3.81–3.82
(m, 1H), 6.63–6.72 (m, 3H), 7.15–7.19 (m, 2H) ppm.
2.2.1.5 1-Chloro-3-(Phenylamino)Propan-2-ol (Table 3,
Entry 7) 1H (CDCl3, 500 MHz) d = 3.15–3.21 (m, 3H),
3.31–3.34(m,1H),3.53–3.64(m,2H),4.00(m,3H),6.62–6.76
(m, 3H), 7.17(m, 2H) ppm. 13C (CDCl3, 125 MHz) d = 47.17,
47.67, 69.86, 113.40, 118.33, 129.44, 147.78 ppm.
2.2 Typical Experimental Procedure
In a 25 ml long neck round bottom flask epoxide,
(2 mmol), amine (2 mmol), zeolites (25 mg,) were taken
and mixed. The reaction was carried out under microwave
irradiation for 3 min at 70 °C, 900 W. The progress of the
reaction was checked on TLC using hexane/ethyl acetate
(8/2) as mobile phase until the epoxide was fully con-
sumed. The reaction mixture was then treated with 10 ml
of diethyl ether and the catalyst was filtered, washed with
additional 5 ml of diethyl ether and dried at 350 °C for 3 h
before further use. The filtrate was dried over anhydrous
Na2SO4 and concentrated under vacuum. The crude prod-
uct was purified by flash column chromatography using
hexane–ethyl acetate as mobile phase (80:20). The recov-
ered catalyst was used six times for ring opening of
cyclohexene oxide with aniline with retention of activity.
2.2.1.6 1-Butoxy-3-(Phenylamino)-Propane-2-ol (Table 3,
Entry 8) 1H (CDCl3, 500 MHz) d = 0.93 (t, J = 7.5 Hz,
3H), 1.36–1.40 (m, 2H), 1.55–1.60 (m, 2H), 2.62 (brs, 1H),
3.12–3.16 (m, 1H), 3.16–3.31 (m, 2H), 3.44–3.55 (m, 4H),
4.01–4.02 (m, 1H), 6.63–6.71 (m, 3H), 7.15–7.19 (m, 2H)
ppm. 13C (CDCl3, 125 MHz) d = 13.93, 19.32, 31.71, 46.79,
71.45, 72.92, 113.19, 117.76, 129.28, 129.39, 148.31 ppm.
2.2.1.7 1-Isobutoxy-3-(Phenylamino)Propan-2-ol
(Table 3, Entry 9) 1H (CDCl3, 500 MHz) d = 0.92 (d,
J = 6 Hz, 6H), 1.88 (m, 1H), 2.66 (brs, 1H), 3.12–3.16 (m,
2H), 3.22–3.31 (m, 2H), 3.44–3.48 (m, 2H), 3.51–3.53 (m,
1H), 4.00(m, 1H), 6.63–6.71 (m, 3H), 7.15–7.18 (m, 2H)
ppm. 13C (CDCl3, 125 MHz) d = 19.36, 28.04, 46.85,
69.08, 73.16, 113.20, 117.75, 129.29, 148.32 ppm.
2.2.1 The Spectral Data for Some of the Selected
Compounds
2.2.1.1 2-(Phenylamino)-Cyclopentanol (Table 2, Entry
1) 1H (CDCl3, 500 MHz) d = 1.33–1.40 (m, 1H), 1.57–
1.81 (m, 3H), 1.91–1.97 (m, 1H), 2.20–2.27 (m, 1H), 2.80
(brs, 1H), 3.55–3.57 (m, 1H), 3.99–4.01 (m, 1H), 6.63–6.71
(m, 3H), 7.14–7.17 (m, 2H) ppm. 13C (CDCl3, 125 MHz)
d = 21.01, 31.15, 32.79, 62.11, 76.88, 78.17, 113.46,
117.60, 129.33, 147.80 ppm.
2.2.1.8 1-Phenoxy-3-(Phenylamino)Propan-2-ol (Table 3,
Entry 10) 1H (CDCl3, 500 MHz) d = 2.96 (brs, 1H),
3.27–3.31 (m, 1H), 3.42–3.45 (m, 1H), 4.01–4.08 (m, 3H),
4.24–4.27 (m, 1H), 6.69–6.79 (m, 3H), 6.94–7.02 (m, 3H),
7.22–7.34(m, 4H) ppm. 13C (CDCl3, 125 MHz) d = 46.69,
68.83, 70.07, 113.37, 114.60, 118.11, 121.37, 129.40,
129.65, 148.10, 158.44 ppm.
2.2.1.2 2-(4-Methoxyphenylamino)Cyclohexanol (Table 2,
Entry 5) 1H (CDCl3, 500 MHz) d = 0.99–1.01 (m, 1H),
1.26–1.38 (m, 4H), 1.68–1.76 (m, 2H), 2.08–2.10 (m, 2H),
2.23 (s, 3H), 2.88 (brs, 1H), 3.03–3.07 (m, 1H), 3.28–3.33
(m, 1H), 6.62 (m, 2H), 6.99 (m, 2H) ppm. 13C (CDCl3,
3 Results and Discussion
Initially, the solvent-free ring opening reaction of cyclo-
hexene oxide as representative substrate was carried out
123

320
R. I. Kureshy et al.
Table 1 Data for ring opening of cyclohexene oxide with aniline as a
model substrate under microwave irradiationa
Table 2 Ring opening of cyclohexene oxide with various amines in
the presence of Hb zeolite under MW irradiationa
Yield (%)b
Entry
1
Epoxide
Amine
Product
Catalyst (25mg)
O
+
M.W. (3min)
NH2
89
HO
NH
O
NH2
HO
NH
NH2
2
88
Entry Zeolite Temp. (°C) MW (W) Time (min) Yield (%)b
O
1
2
3
4
5
6
7
8
9
10
a
Hb
Hb
Hb
Hb
Hb
NaY
Nab
Hb
Hb
–
60
70
80
70
70
70
70
RT
70
70
900
900
900
500
700
900
900
900
900
900
3
82
91
92
69
81
80
52
85
87
ND
HO
HO
HO
NH
NH
NH
3
NH2
NH2
3
4
91
83
3
3
3
OMe
3
3
MeO
240c
90d
3
NH2
5
6
7
8
9
93
94
80
89
HO
HO
HO
HO
HO
NH
NH
NH
NH
NH
OMe
O
OMe
NH2
Cyclohexene oxide (0.20 ml, 2 mmol), aniline (0.19 ml, 2 mmol),
zeolite (25 mg) under MW
b
Isolated yield
Me
c
Reaction was carried out at RT
Me
d
Reaction was carried out at 70 °C oil bath heating
NH2
Cl
with aniline as the representative nucleophile under micro-
wave (MW) irradiation by varying the temperature from 60
to 80 °C and microwave output from (500 to 900 W) using
Hb, zeolites as catalysts (entries 1–5). Results as shown in
Table 1 reveal that the 70 °C temperature and 900 W output
of MW irradiation was the optimum reaction condition
(entry 2). Under this optimum condition Nab and NaY
zeolites were also used as catalyst for the same reaction
(Entries 6, 7). The results obtained have indicated that
among the three zeolites tested, the Hb zeolite gave the best
catalytic activity in terms of product yields (entry 2) within
3 min. When the same reaction was carried out at room
temperature 85% isolated yield of the product was achieved
in 4 h (entry 8) while at 70 °C, 87% isolated yield was
obtained in 1.5 h. (entry 9). Furthermore, conducting the
same reaction in the absence of Hb zeolite under MW there
was no product formation (entry 10), signifying that the
catalyst is necessary for the reaction to proceed.
Cl
NH2
Cl
Cl
NH2
No product
formation
NO2
O2N
NH2
NO2
10
No product
formation
HO
NH
NO2
a
Cyclohexene oxide (0.20 ml, 2 mmol), amine (0.19 ml, 2 mmol),
Hb zeolite (25 mg) at 70 °C, 900 W, 3 min MW irradiation
b
Isolated yield
anilines (Table 2; entries 5, 6, 8) with electron donating
groups yielded more product than ortho substituted anilines
(Table 2, entries 4, 7). However, in the case of anilines
having electron withdrawing nitro group on ortho or para
position the ring opening reaction with cyclohexene oxide
does not commence (entries 9, 10).The structure of
b-amino alcohols was determined on the basis of proton
Under the optimized reaction condition (as per Table 1
entry 2), cyclopentene oxide and cyclooctene oxide were
allowed to react with aniline as nucleophile that produced
amino alcohols in 89 and 88% yield, respectively (Table 2,
entries 1, 2). In order to evaluate the effect of electronic
and steric influence of the nucleophile, cyclohexene oxide
was used as representative substrate for the ring opening
reaction with various substituted anilines viz., 2-Meo-,
4-Meo-, 4-Me-, 2-Cl-, 4-Cl-, 2-NO2- and 4-NO2-anilines.
The data thus obtained revealed that the para substituted
1
coupling constant in the H NMR spectrum. For example,
1
in H NMR (500 MHz) of 2-(4-chlorophenylamino)cyclo-
hexanol two signals appeared at d 3.05 (ddd, J = 12.5 Hz,
123

Ring-Opening of Epoxides with Amines Under Microwave Irradiation
321
Table 3 Ring opening of
various epoxides with aniline in
the presence of Hb zeolitea
under microwave irradiation
H
β
Zeolite
HO
R
NH
HN
R
OH
+
O
+
(3min)
MW
R
NH2
(B)
(A)
1 R = C6H5
2 R = CH3CH2
3 R = CH3(CH2)2CH2
4 R = CH3(CH2)4CH2
5 R = CH3(CH2)6CH2
6 R = CH3(CH2)8CH2
7 R = ClCH2
8 R = CH3(CH2)3OCH2
9 R =(CH3)2CHCH2OCH2
10 R = C6H5OCH2
11 R = ClC6H4OCH2
Yield (%)b A:B d
Entry Epoxide
Product
O
1
88
74:26
HO
NH
OH
O
2
3
4
5
6
90
91
92
93
90
74:26
70:30
44:56
45:55
40:60
NH
OH
O
NH
OH
O
NH
OH
O
NH
OH
9
O
NH
9
7c
8
89
91
92
89
40:60
45:55
42:58
34:66
OH
O
Cl
Cl
NH
O
OH
O
O
NH
OH
9
O
O
O
O
O
O
NH
OH
10
a
Oxide (2 mmol), aniline
NH
(2 mmol), Hb zeolite (25 mg) at
70 °C, 900 W, MW (3 min)
irradiation
OH
O
11
93
38:62
b
O
Isolated yield
O
NH
c
One minute MW irradiation
Cl
d
Cl
Regioisomeric ratio was
determined by 1H NMR analysis
8.5 Hz, 4 Hz) and d 3.32 (ddd, J = 13.5 Hz, 9.5 Hz, 4 Hz)
for the CHNH and CHOH protons, respectively, which are
indicative of trans stereochemistry of b-amino alcohols in
agreement with earlier reports [19, 21, 37].
To asses the regioselectivity the above protocol with
various terminal epoxides viz., styrene oxide, 1-propene
oxide, 1-hexene oxide, 1-octene oxide, 1-decene oxide,
1-dodecene oxide, epichlorohydrin, 1-butoxy-2,3-
123

322
R. I. Kureshy et al.
epoxypropane, 1-isobutoxy-2,3-epoxypropane, 1,2-epoxy-
3-phenoxy propane, 1,2-epoxy-3-(4-chlorophenoxy) pro-
pane was tested for the ring opening reaction with aniline as
nucleophile and the results are shown in Table 3. Overall
excellent yields of b-amino alcohols (85–91%) were
obtained within 3 min under MW irradiation in all the cases.
However, the regioselectivity for the secondary alcohol
(product A) was highest as compared to terminal alcohol
(product B) for styrene and propene oxides (A:B::74:26). In
the case of terminal alkene oxide the regioselectivity for the
product B increases with increase in chain length. Highest
selectivity for the product B was achieved for dodecene
oxide (Table 3, entry 6) so was the case with the ring opening
of epichlorohydrin (entry 7). In the case of alkoxy oxides the
regioselectivity for the product B was higher for branched
alkoxy oxide (Table 3, entry 9) than for the respective
straight chain oxide (entry 8). On the other hand, the
formation of the product B was preferred with the substrate
1,2-epoxy-3-phenoxy propane (Table 3, entry, 10) than with
substrate 1,2-epoxy-3-(4-chlorophenoxy) propane.
4 Conclusion
In conclusion a very simple, efficient and eco-friendly
protocol for the synthesis of b-amino alcohols using easily
commercially available Hb zeolite as a catalyst under
microwave irradiation in solvent free condition has been
developed. An excellent yield of b-amino alcohol has been
achieved (94%) within 3 min. The catalytic system is 80
times faster than the reaction conducted at RT with the
added advantage of six times catalyst recyclability. Ter-
minal epoxides such as styrene oxide and propene oxide
preferably produce secondary alcohols in excess while,
long chain alkene oxides and alkoxy oxides preferentially
produce terminal alcohols in excess.
Acknowledgments SA thankful to CSIR for awarding the Senior
Research Fellowship. RIK thankful to DST and CSIR, Net Work
Project for financial assistance and also thankful to Analytical Dis-
cipline for providing instrumentation facility.
In order to evaluate the recycling capability of the cat-
alyst Hb, the ring opening of cyclohexene oxide as repre-
sentative substrate with aniline was carried out. After the
completion of the catalytic reaction, 10 ml of diethyl ether
was added to the reaction mixture and filtered. The
recovered catalyst was further washed with an additional
5 ml portion of diethyl ether and dried for 3 h at 350 °C
before reuse. The reactivity of the recovered catalyst was
retained in the subsequent six test runs under identical
reaction conditions.
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