Solvent-Free Henry and Michael Reactions with Nitroalkanes Promoted by Potassium Carbonate as a Versatile Heterogeneous Catalyst

Article abstract of DOI:10.1155/2017/6267036

The use of a simple weak inorganic base such as potassium carbonate facilitated the formation of carbon-carbon bonds through both the Henry and the Michael reactions with nitrocompounds. The application of this catalyst under environmentally friendly solventless heterogeneous conditions gave satisfactory to good yields of β-nitroalcohols, involving aliphatic and aromatic starting materials, as well as high to excellent yields in the formation of Michael adducts using several different Michael acceptors and nitroalkanes.

Full text of DOI:10.1155/2017/6267036

Hindawi
Journal of Chemistry
Volume 2017, Article ID 6267036, 9 pages
https://doi.org/10.1155/2017/6267036
Research Article
Solvent-Free Henry and Michael Reactions with
Nitroalkanes Promoted by Potassium Carbonate as a Versatile
Heterogeneous Catalyst
Giovanna Bosica1 and Kurt Polidano2
1Department of Chemistry, University of Malta, Msida MSD 2080, Malta
2Cardiff University, Main Building, Park Pl, Cardiff CF10 3AT, UK
Correspondence should be addressed to Giovanna Bosica; giovanna.bosica@um.edu.mt
Received 30 January 2017; Revised 13 April 2017; Accepted 21 May 2017; Published 15 June 2017
Academic Editor: Stojan Stavber
Copyright © 2017 Giovanna Bosica and Kurt Polidano. is is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
e use of a simple weak inorganic base such as potassium carbonate facilitated the formation of carbon-carbon bonds through
both the Henry and the Michael reactions with nitrocompounds. e application of this catalyst under environmentally friendly
solventless heterogeneous conditions gave satisfactory to good yields of ꢀ-nitroalcohols, involving aliphatic and aromatic starting
materials, as well as high to excellent yields in the formation of Michael adducts using several different Michael acceptors and
nitroalkanes.
1. Introduction
formation of secondary products in these reactions. In the
case of the nitroaldol reaction, the main side product is the
formation of the nitroalkene through a further condensation
reaction of the nitroalcohol. In some cases the use of certain
catalysts resulted in the production of a conjugated enone
through an aldol condensation side reaction, whereas some
highly activated catalysts which were applied to the Michael
addition were too reactive as reactions which resulted in the
formation of the double addition products [4–6].
Herein, as a continuation of ongoing study on the
development of environmentally friendly methodologies [11–
13], our main interest in relation to this context was to
identify a simple alternative and cheap heterogeneous solid
catalyst useful for both the Henry and the Michael reactions,
in accordance with moderate reaction conditions and the
concept of Green Chemistry [14] to produce, respectively, ꢀ-
nitroalcohols (Scheme 1) and polyfunctionalised nitroderiva-
tives (Schemes 2 and 3) [15–17]. On this purpose potassium
carbonate [18, 19] was identified as a suitable catalyst and
produced average to good results for the nitroaldol reaction
(Table 3) and good to excellent results for the Michael
addition (Table 4). To the best of our knowledge, potassium
carbonate was previously reported to catalyse only a few
e formation of a carbon-carbon bond can be carried out
using various starting materials together with a vast amount
of homogeneous or heterogeneous catalysts. Two impor-
tant reactions which involve the synthesis of compounds
through carbon-carbon bond formation include the Henry
and the Michael reactions with nitroalkanes [1–3]. Under
basic conditions nitroalkanes are able to deprotonate to form
an intermediate compound known as the nitronate anion [4].
e nitronate anion can then react with aldehydes through
the Henry reaction to yield ꢀ-nitroalcohols [5]. In the case
of the Michael addition, the carbanion would react with
Michael acceptors or ꢁ,ꢀ-unsaturated compounds to yield
polyfunctionalised nitroderivatives [6].
In recent years the nitroaldol and the Michael reactions
were carried out using extensive catalysts, some of which
containing complex structures. Various methodologies have
been employed; however, in some cases, disadvantages of
having such complex structures included applying either
very low or substantially high temperatures to obtain the
respective products at great yields [7–10]. A major drawback
of some catalysts is that they resulted in the increased

2
Journal of Chemistry
O
+
２2
．
HO
２2
H
R
O
−
／
＋2＃／3
+
．
O
+
２1
−
２1
／
R
H
1
2
3
Scheme 1: e Henry (nitroaldol) reaction.
−
／
O
+
O
（3＃
O
．
．
＋2＃／3
（2＃
＃（3
+
+
O
O
−
＃（3
（3＃
／
O
4
5
6
Scheme 2: Michael addition model reaction using methyl acrylate and nitroethane with K CO .
2
3
−
／
O
+
２2
２1
．
EWG
＋2＃／3 (30 mol%)
+
+
．
（2＃
２1
−
EWG
／
O
２2
1
7
8
Scheme 3: Michael reactions using 30 mol% K CO .
2
3
examples of Michael addition reactions, although never
under neat conditions but with the required assistance of
solvents [20, 21], ultrasounds activation, and ionic liquids
[22], or with the use of a limited number of substrates as
starting materials [23] or else not involving nitroalkanes but
different nucleophiles [24–26].
nitroalkanes and different aldehydes and ꢁ,ꢀ-unsaturated
compounds, respectively.
As reported in Table 3, aliphatic aldehydes gave the
best results in the least amount of reaction time while
aromatic aldehydes with electron withdrawing substituents
gave better yields than those containing electron donating
groups. Parasubstituted aromatics were the most difficult
substrates to react and when utilising 4-nitrobenzaldehyde a
small amount of CH Cl was required as the starting material
2. Results and Discussion
2
2
was solid. In general average to good yields were obtained
with this catalyst as the reaction itself is reversible [2] and thus
it is difficult for it to reach completion. e major role played
by the catalyst was that reactions only afforded in a selective
way the nitroaldol product and no traces of any condensation
side product were present.
In both reactions, the first part of the study consisted of
the optimization screening through the investigation of some
Henry (Table 1) and Michael reactions (Table 2) using potas-
sium carbonate as the catalyst together with the variation
of both physical and chemical conditions and without any
solvent.
e Michael reaction was first investigated by performing
a variety of trials using nitroethane (5) and methyl acrylate
(4) as model reaction (Scheme 2).
Following these preliminary investigations, the Henry
reaction gave good results when undergone at temperatures
of 60∘C, increasing the reaction rate substantially and using
10 molar% of catalyst (entry 5, Table 1). On the other hand,
high temperatures were detrimental to the Michael additions
as a second by-product was afforded, this most probably
being the double Michael adduct. In order to decrease the
formation of the bis-addition, the reaction temperature was
kept at room temperature to promote increased formation
of the desired monoaddition and together with the use of
30 molar% of catalyst the best result was obtained (entry
5, Table 2). ese selected conditions were then employed
in other Henry and Michael reactions in order to verify a
more general applicability of the preliminary protocol, using
e previous conditions were then applied to Michael
reactions using different nitroalkanes and diversely func-
tionalised Michael acceptors (Scheme 3) and the catalyst
performed even better providing good to excellent product
yields (Table 4). Only when using nitromethane were very
low yields recorded, since the formation of the bis-addition
side product was revealed due to the fact that it is a small and
unhindered molecule, while using a secondary nitroalkane
the temperature was increased to 60∘C as there is no possible
formation of the bis-adduct. Also the results obtained from
these trials indicated that 30 mol% of catalyst gave good
yields at room temperature when using methyl acrylate
as the Michael acceptor. However, reaction temperatures
were increased to 60∘C and 90∘C when using cyclic and
sterically hindered Michael acceptors like cyclic enones and
trans-methyl crotonate in order to increase the speed of
the reaction, whereas reactions which involved the use of

Journal of Chemistry
3
Table 1: Optimization of nitroaldol reaction using K CO .
2
3
Mol (%)
catalyst
Temperature
(∘C)
Yielda of 3
Entry
R
R
R
Time (h)
1
2
(%)
1
Ph
CH
CH
CH
CH
CH
CH
CH
H
H
H
H
H
24
24
4
24
4
10
30
10
30
10
25
25
60
25
60
35
54
48
58
68
3
3
3
3
3
2
3
4
5
3
3
CH CH CH
CH CH CH
3
2
2
3
2
2
aYield of pure isolated products.
Table 2: Optimization of Michael reaction using model reaction.
Mol %
Time
(h)
5
27b
24
7
7.5
48
6
Temperature
(∘C)
Yielda of 6
Entry
catalyst
10
(%)
1
2
3
4
5
6
7
8
25
25, 60b
25
60
25
25
50
35
47
50
58
54
60
61
10
20
10
30
30
30
30
58
55
7
aYield of pure isolated product.
bReaction was carried out at room temperature for 24 hours; temperature was increased to 60 C for 3 hours.
∘
Table 3: Henry reaction using 10 mol% K CO at 60∘C.
2
3
Entry
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
R
R
R
Time (h)
Yielda of 3 (%)
1
2
CH
CH CH CH
CH
CH
H
CH
CH
H
CH
H
H
CH
H
H
H
H
H
4
5
4.5
4.5
4
48
46
75
60
48
50
60
58
3
3
3
2
2
3
3
3
CH
Ph
CH
3
3
3
3
PhCH
n-C H
5
2
2
5
5
7
7
9
CH CH CH CH
n-C H
4.5
6.5
8
72
3.5
5
24
4
5
3
2
2
2
2
PhCH CH
n-C H
2
2
3
n-C H
p-NO C H
Ph
c-C H
n-C H
72
5
11
3
n-C H
55b
60
65
60
66b
62
2
6
4
4
H
H
H
H
Br
H
H
H
H
6
11
p-OCH C H
3
6
4
p-NO C H
2
6
4
CH
H
3
aYield of pure isolated product.
bReaction was carried out under CH Cl solvent as the starting aldehyde was solid.
2
2
acrylonitrile required lower temperatures of 0∘C to prevent
immediate polymerization of acrylonitrile from occurring,
which was evident through the formation of a thick yellow
solid.
thus shows great applicability with a variety of substrates,
containing different backbone structures, such as aliphatic
straight chain and cyclic and aromatic compounds, to
undergo both Henry and Michael reactions. Compared with
the reported methods using expensive or unavailable organic
catalysts, a common and inexpensive inorganic base (K CO )
was here employed as the base catalyst. e presented reac-
tions proceeded with complete regioselectivity providing the
nitroaldol and Michael monoaddition products, respectively,
2
3
3. Conclusions
In summary, the utilisation of potassium carbonate in neat
conditions is a very versatile and green synthetic method and

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7

8
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while tolerating many different functionalities. e common
catalyst and the ready availability of the starting materials
and the simplicity and versatility of the procedure and the
valuable products make the protocol potentially practical and
useful to synthetic chemists.
according to staring materials (Table 4). e reaction was
lef standing for the appropriate time. e catalyst was then
filtered using a small column fitted with cotton and Florisil.
e filtrate was then evaporated in vacuo and the crude
product was purified via column chromatography using a
mixture of cyclohexane and ethyl acetate affording the pure
6: IR (neat): ]max 3001, 2956, 2850, 1732, and 1556 cm−1; 1H
4. Experimental Section
NMR (250 MHz, CDCl ) ꢃ 4.74–4.59 (m, 1H), ꢃ 3.70 (s, 3H),
3
ꢃ 2.45–2.01 (m, 4H), and ꢃ 1.59–1.54 (d, 3H, J = 6.72 Hz); 13C
4.1. General Information. All commercially available chem-
icals and reagents were purchased from Aldrich and used
without further purification. IR spectra were recorded on a
Shimadzu IRAffinity-1 FTIR Spectrometer, calibrated against
a 1602 cm−1 polystyrene absorbance spectrum. Samples were
either analysed as a thin film or in a Nujol6 mull, between
sodium chloride discs. e 1 H- and 13C-NMR spectra were
recorded on Bruker AM250 NMR spectrometer fitted with a
dual probe at frequencies of 250 MHz and 62.9 MHz for 1H
and 13C NMR, respectively. An Aspect 3000 computer using
NMR (62.9 MHz, CDCl ) ꢃ 172.4, 82.4, 51.9, 30.0, 29.9, and
3
19.3.
Conflicts of Interest
e authors declare that there are no conflicts of interest
regarding the publication of this paper.
Acknowledgments
1
16 K complex points for H NMR and 64 K complex points
for 13C NMR was used for processing. Samples were dissolved
e authors thank the University of Malta and the Strategic
Educational Pathways Scholarship, Malta (European Social
Fund (ESF) under Operational Programme II, Cohesion
Policy 2007–2013, “Empowering People for More Jobs and a
Better Quality Of Life”), for financial support.
in deuterated chloroform (with TMS): 5 mg in 0.8 mL CDCl
3
for 1H NMR and between 35 mg and 50 mg in 0.8 mL
CDCl for 13C NMR. Reaction monitoring was done by
3
TLC and GC analysis. Ready-purchased silica on PET sheets
with fluorescent indicator, 254 nm, was used as stationary
phase for TLC. Gas chromatography was carried out on a
Shimadzu GC-2010 plus gas chromatograph equipped with
a flame ionisation detector and HiCap 5 GC column with
dimensions of 0.32 mm (internal diameter) × 30 m (length)
× 0.25 ꢂm (film thickness), using nitrogen as carrier gas. e
synthesised compounds are known. Supplemental material
(available online at https://doi.org/10.1155/2017/6267036) is
available from the correspondence author.
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