KAl(SO4)2.12H2O as an eco-friendly and reusable catalyst for the synthesis of amides by the Ritter reaction

Article abstract of DOI:10.3184/174751912X13418518739562

KAl(SO₄)₂.12H₂O (Alum) is an eco-friendly, inexpensive, readily available and reusable and was applied as catalyst to the synthesis of N-alkyl amides from nitriles and alcohols by the Ritter reaction. This solvent-free procedure is very simple with excellent yields and easy work-up.

Full text of DOI:10.3184/174751912X13418518739562

JOURNAL OF CHEMICAL RESEARCH 2012
SEPTEMBER, 539–540
RESEARCH PAPER 539
KAl(SO ) .12H O as an eco-friendly and reusable catalyst for the synthesis
4
2
2
of amides by the Ritter reaction
a
a
b
Bahareh Sadeghi *, Ebrahim Farahzadi and Alireza Hassanabadi
a
Department of Chemistry, Yazd Branch, Islamic Azad University, PO Box 89195-155, Yazd, Iran
bDepartment of Chemistry, Zahedan Branch, Islamic Azad University, PO Box 98135-978, Zahedan, Iran
KAl(SO ) .12H O (Alum) is an eco-friendly, inexpensive, readily available and reusable and was applied as catalyst to
4
2
2
the synthesis of N-alkyl amides from nitriles and alcohols by the Ritter reaction. This solvent-free procedure is very
simple with excellent yields and easy work-up.
Keywords: KAl(SO ) .12H O, alum, Ritter reaction, N-alkyl amides, nitriles, alcohols, solvent-free conditions
4
2
2
The Ritter reaction is as an important methodology for amide
synthesis by reaction of a nitrile with an alcohol. The reaction
the solvent evaporated and the residue (catalyst) was washed
1
with CHCl and reused. Apparently, treatment with CHCl3
3
is especially useful for the preparation of bulky amides from
removes tars more efficiently from the catalyst surface
(Table 1, entries 14 and 15). This catalyst was reusable,
although a gradual decline in activity was observed.
The scope and universality of this protocol was demon-
strated by subjecting a broad range of secondary and primary
benzylic alcohols, ethanol and allyl alcohol and tertiary
aliphatic alcohol, to the reaction with acetonitrile, benzylic and
aromatic nitriles in the presence of alum (Table 2).
In most cases, the reactions proceeded cleanly and the
desired amides were obtained in excellent yields. Ritter reac-
tion of simple allyl alcohol and secondary alcohols with nitriles
in the presence of alum afforded the corresponding amides
in good yields. No Ritter reaction took place with ethanol as
primary alcohols. The efficiency of the present procedure was
examined with 60 mmol of tert-butyl alcohol and acetonitrile
which gave N-tertiary butyl acetamides in 85% yield.
tertiary alcohols and various nitriles. The product N-tert-butyl
2
,3
amides are pharmaceutically important and also serve as
precursors of the corresponding amines. The method has also
been used for the syntheses of amides utilising catalysts such
4
5
6
7
as Ca(HSO ) , P O /SiO , Bi(OTf) , H PW O , heteropoly
4
2
2
5
2
3
9
3
12 40
8
10
acids, phosphomolybdic acid/SiO , Nafion NR 50 and MFI
2
11
zeolites. However, in some cases, the reuse of the catalysts is
4
–6
not possible.
KAl(SO ) .12H O (Alum), a solid acid, is a versatile cata-
4
2
2
lyst that makes reaction processes more convenient, more eco-
nomic and environmentally benign. Owing to the numerous
advantages associated with this cheap and non-hazardous
catalyst, under mild conditions, we have now used it as a solid
phase acidic green catalyst in a new rapid method affording
excellent yields for the synthesis of N-alkyl amides at 100 °C.
The compounds 3a-o were characterised by melting point,
1
13
H and C NMR and IR spectroscopy and elemental analy-
Results and discussion
9
,17–20
ses.
In continuation of our investigations of the application of solid
1
2–16
Compounds 3p was new and it structure was deduced by
acids in organic synthesis
we have investigated the synthe-
elemental and spectral analysis. The mass spectrum of com-
sis of amides 3 from nitriles 1 and alcohols 2 in the presence of
1
pound 3p showed the molecular ion peak at 175. The H NMR
KAl(SO ) .12H O, which is cheap and readily available under
4
2
2
spectrum of compound 3p exhibited protons of the aromatic
heterogeneous conditions. (Scheme 1).
1
3
groups in the expected region of the spectrum. The C NMR
We report a simple and efficient protocol for the Ritter
reaction using KAl(SO ) .12H O. We first carried out some
spectrum of compound 3p showed nine signals in agreement
4
2
2
comparative experiments with a number of solid acids and the
comparative results are summarised in Table 1.
Table 1 Acid-catalysed synthesis of N-(tert-butyl) benzamide
These results clearly show the advantages of our methodol-
ogy over other protic or Lewis acid catalysed Ritter reactions.
To optimise the reaction conditions, the reaction of tert-butyl
alcohol and benzonitrile was used as a model reaction.
Reactions at different temperatures and various molar ratios of
substrates in the presence of Alum revealed that the best condi-
tions were solvent-free at 100 °C and the best molar ratio of
alcohol (mmol) : nitrile (mmol) : Alum (g) was 1:1:0.1.
The reusability of the Alum catalyst was also examined.
Entry Catalyst ((mmol))(g) Alco.
Conditions Time Yield
a
/
Nitrile
/Solvent
/h
/%
mmol
/mmol)
After each run, CHCl was added and the product was filtered,
3
1
2
3
4
5
6
7
8
9
Ca(HSO
/SiO
Bi(OTf)
PMA/SiO
40 ((0.05))
Alum (0.05)
Alum (0.1)
4
)
2
2
((1))
1/31 100 °C/CH
3
CN
2
91
P
2
O
5
(0.2)
1/1
0.8/3.9
2.9/2.6
1/3
100 °C/–
2.5 92
3
((0.16))
(2.9)
100 °C/H
80 °C/–
Reflux/H
2
O
17
85
95
99
78
96
97
85
90
63
65
78
90
87
2
6
10
2
H
3
PW12
O
2
O
1/1
100 °C/–
100 °C/–
1/1
2
Alum (0.15)
Alum (0.1)
1/1
100 °C/–
2
1/1
50 °C/–
2
1
0
1
2
3
4
5
Alum (0.1)
1/1
150 °C/–
2
1
1
1
1
1
Alum (0.1)
1/1
Reflux/DCM
Reflux/EtOH
4
Scheme 1 Preparation of amides from alcohols and nitriles
Alum (0.1)
1/1
4
4 2 2
in the presence of KAl(SO ) .12H O under heterogeneous
Alum (0.1)
1/1
Reflux/H
2
O
4
conditions.
Alum (0.1), 2nd run
Alum (0.1), 3nd run
1/1
100 °C/–
100 °C/–
2
1/1
2
a
*
Correspondent. E-mail: bsadeghia@gmail.com
Isolated yield.

5
40 JOURNAL OF CHEMICAL RESEARCH 2012
4 2 2
Table 2 Preparation of amides from alcohols and nitriles in the presence of KAl(SO ) .12H O under heterogeneous conditions
Entry
R
R′
Product
Time/h
Yield/%a
M.p. /°C
Reported[ref.]
Found
17]
1
2
3
4
5
6
7
8
9
C
6
H
3
5
(CH
(CH
3
)
3
3
C
C
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
2
1.5
2
2
2.5
3
2.5
1.5
2.5
1.5
3
2
2.5
2
96
90
93
93
90
85
80
90
89
90
74
90
89
92
85
85
132–134
96–98
133–135[
CH
CH =CH
)
3
95–96[
18]
9]
[
2
C
C
6
H
5
CHCH
CH
CHCH
3
62–64
63–65
18]
19]
19]
C
C
3-NO
4-CF
4-CH
6
H
H
5
C
6
H
5
5
2
128–130
114–115
127–130
136–137
117–120
116–118
112–115
113–115
126–129
116–117
75–77
129–130[
114–116[
128–130
6
5
6
H
3
[
2
C
6
H
4
4
(CH
(CH
(CH
3
)
3
)
3
)
3
C
3
C
3
C
19]
3
C
6
H
135[
[17]
3
C
6
H
4
117–118
18]
C
C
6
H
H
5
CH
CH
2
6 5 2
C H CH
117[
[
18]
18]
18]
1
1
1
1
1
1
1
0
1
2
3
4
5
6
6
5
2
(CH
(CH
(CH
(CH
3
)
3
)
3
)
3
)
3
3
3
3
C
113–115
CH
CH
4-CH
CH
2
CN
=CH
OC
C
C
C
114–115[
[
2
125–127
117[
20]
3
6
H
4
[
18]
3
C
C
6
H
H
5
CHCH
CHCH
3
75–76
18]
C
C
6
H
H
5
CH
CH
2
6
5
3
2
3
99–101
124–126
100–101[
–
6
5
2
CH
2
=CHCH
2
a
Isolated yields of products.
References to known products.
b
with the proposed structure. The IR spectrum of compound 3p
also supported the suggested structure.
We gratefully acknowledge financial support from the Research
Council of the IslamicAzad University ofYazd and The Islamic
Azad University of Zahedan of Iran.
In summary, under solvent-free conditions, alum is a
reusable, efficient, cheap, eco-friendly, readily available and
heterogeneous catalyst for this reaction. Allylic and benzylic
alcohols as well as tertiary alcohols react efficiently in Ritter
reaction with some advantages such as selectivity, generality,
simplicity, clean reactions, easy work up, scale up and improved
yields.
Received 13 April 2012; accepted 25 June 2012
Paper 1201260 doi: 10.3184/174751912X13418518739562
Published online: 28 August 2012
References
1
2
3
4
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Experimental
Alcohols, nitriles, and other necessary compounds were purchased
from Fluka and Merck companies. IR spectra were run on a Shimadzu
IR-470 spectrometer. H and NMR spectra were obtained using a
1
13
5
6
7
8
9
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potential of 70 eV.
8
5
General procedure
A mixture of alcohol (3 mmol), nitrile (3 mmol), KAl(SO ) .12H O
1
4
2
2
J.S. Yadav, B.V. Subba Reddy, T. Pandurangam, Y. Jayasudan Reddy and
(
0.3 g) was placed in a round bottom flask. The materials were mixed
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and heated at 100 ºC for the given time (Table 2). The progress of the
reaction was followed by TLC. After the completion of the reaction,
the resulting mixture was cooled to room temperature and extracted
with EtOAc (2 × 20 mL). The organic layer was washed with 10%
NaHCO3 and water, dried with Na SO and concentrated under
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2
575.
1
3
B.F. Mirjalili, M.M. Hashemi, B. Sadeghi and H. Emtiazi, J. Chin. Chem.
Soc., 2009, 56, 386.
2
4
reduced pressure to give the products in 81–96% yields. The solid
1
1
4
5
B. Sadeghi, A. Hassanabadi and S, Bidaki, J. Chem. Res., 2011, 35, 666.
B. Sadeghi, A. Hassanabadi and E, Taghvatalab, J. Chem. Res., 2011, 35,
product was then crystallised from H O.
2
N-Allyl-2-phenylacetamide (3p): White powder; m.p. 124–126 °C.
7
07.
−1
IR (KBr) (νmax, cm ): 3330, 3055, 1635, 1493,1412, 1205, 739, 693.
16
17
18
B. Sadeghi, A. Hassanabadi and M, Kamali, J. Chem. Res., 2012, 36, 9.
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K.V. Katkar, P.S. Chaudhavi and K.G. Akamanchi, Green Chem., 2011, 13,
835.
+
1
MS (m/z, %): 175 (M , 10). H NMR (500 MHz, d -DMSO): δ 7.24–
6
7
5
.38 (5H, m, 5 CH phenyl moiety), 5.91 (1H, m), 5.17(1H, s, NH),
13
.21–5.23(2H, m), 3.87(2H, m, CH ), 3.49(2H, s, CH ), C NMR
2
2
(
125.75 MHz, d -DMSO): δ 41.2, 47.3, 117.1, 128.1, 129.6, 131.2,
19 F. Tamaddon and F. Tavakoli, J. Mol. Cat. A: Chem., 2011, 337, 52.
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2207.
6
1
7
34.2 135.9, 172.3. Anal. Calcd. for C H NO: C, 75.40; H, 7.48; N,
.99. Found: C, 75.28; H, 7.60; N, 7.82%.
11 13

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