Poly(ethylene glycol) supported metal nitrates as well-organized reagents for hunsdiecker conversion of α,β-unsaturated acids to β-nitrostyrenes under solvent and acid-free conditions

Article abstract of DOI:10.14233/ajchem.2019.21975

Poly(ethylene glycol) (PEG) supported metal nitrates such as ferric nitrate and manganese nitrate were accomplished as well-organized reagents for Hunsdiecker conversion of α,β-unsaturated acids to β-nitrostyrenes under acid-free and solvent free conditions using grindstone technique. However, in the case of unsaturated aliphatic acids, nitro alkene derivatives were obtained as products. PEG-400 was found the best among the other PEGs (PEG-200,300, 400, 600, 3000 and 6000) used in this protocol.

Full text of DOI:10.14233/ajchem.2019.21975

Asian Journal of Chemistry; Vol. 31, No. 8 (2019), 1798-1800
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.21975
Poly(ethylene glycol) Supported Metal Nitrates as Well-Organized Reagents for Hunsdiecker
Conversion of α,β-Unsaturated Acids to β-Nitrostyrenes under Solvent and Acid-Free Conditions
1
1
2
3
2,*
K. RAMESH , S. SHYLAJA , S. RAMGOPAL , A. SAMBASHIVA RAO and K.C. RAJANNA
1Department of Chemistry, Chaitanya Bharathi Institute of Technology, Gandipet, Hyderabad-500075, India
2Department of Chemistry, Osmania University, Hyderabad-500001, India
3Department of Chemistry, M.V.S.R. Engineering College, Hyderabad-501510, India
*Corresponding author: E-mail: kcrajannaou@yahoo.com
Received: 2 February 2019;
Accepted: 9 April 2019;
Published online: 28 June 2019;
AJC-19454
Poly(ethylene glycol) (PEG) supported metal nitrates such as ferric nitrate and manganese nitrate were accomplished as well-organized
reagents for Hunsdiecker conversion of α,β-unsaturated acids to β-nitrostyrenes under acid-free and solvent free conditions using grind-
stone technique. However, in the case of unsaturated aliphatic acids, nitro alkene derivatives were obtained as products. PEG-400 was
found the best among the other PEGs (PEG-200,300, 400, 600, 3000 and 6000) used in this protocol.
Keywords: PEG supported metal nitrates, β-Nitrostyrenes, α,β-Unsaturated acids, Hunsdiecker conversion.
INTRODUCTION
EXPERIMENTAL
Solvent and acid free organic synthesis captured the atten-
tion of chemistry community all over the world because of
their importance to prevent environmental pollution, improve
green reaction conditions followed by enhanced selectivity
[1-11]. Stimulated by these striking features coupled with other
green-chemistry principles we too have focused our attention
to design, improve and execute green synthetic protocols [12-
20]. In previous publication [19] we reported the synthesis of
β-nitrostyrenes and nitroalkenes respectively from α,β-
unsaturated aromatic and aliphatic acids using metal nitrates
and few drops of HNO3 by grinding all the ingredients in a
mortar with a pestle. In another publication [20], we have exp-
lored poly(ethylene glycols) (PEGs) as efficient catalysts in
these reactions under acid-free conditions. Recent literature
reports revealed that PEGs are cost-effective and user-friendly
additives/solvents to enhance and facilitate several organic
transformations [21-27]. Enthused by these results we have tried
to further improve the greenery of the reactions. In this part of
the work, we have employed PEGs (PEG-200,300, 400, 600,
3000 and 6000) as additives along with d-block metal nitrates
like Fe(III) and Mn(II) nitrates under acid-free and solvent
free conditions.
Grind-stone method of β-nitro styrene synthesis: Known
amounts of unsaturated acid (0.1 mol), PEG (0.02 mol) and Fe(III)
or Mn(II) nitrate (O.12 mol) were taken in a mortar and ground
with a pestle till the reaction mixture became homogeneous.
After completion of the reaction, as confirmed by TLC, about
2 % Na2CO3 solution was added to the reaction mixture till it
is neutralized. Reaction product was extracted by dichloro-
methane (DCM) or dichloroethane (DCE), dried with sodium
sulfate and purified by column chromatography. Binary solvent
mixture of ethyl acetate and hexane (3:7) was used as eluent
to obtain pure product.
RESULTS AND DISCUSSION
All the reactants (α,β-unsaturated acid, PEG and metal
nitrate) are taken in a clean mortar and ground with a pestle till
the reaction is completed, as ascertained by TLC. The reactions
with aromatic carboxylic acid such as cinnamic acid afforded β-
nitro styrenes, while the aliphatic carboxylic acid such as crotonic
acid afforded nitroalkenes in good yield of products with high
regioselectivity. Initially the reactions are conducted with
cinnamic acid, metal nitrate and different PEGs are to select the
best PEG. The observed results are presented in Table-1.
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Vol. 31, No. 8 (2019)
PEG Supported Metal Nitrates for Hunsdiecker Conversion of α,β-Unsaturated Acids to β-Nitrostyrenes 1799
TABLE-1
effective than other PEGs. It is evident that due to the grinding
of reactants in a mortar with a pestle, mechanical energy is
converted to heat energy, which could be utilized for activation
of molecules. Since the grinding is done under solvent free
conditions, bulk and speedy activation of molecules can be
expected. Majority of such activated molecules might undergo
chemical change and afford products in good to excellent
yields. Basically poly(ethylene glycol) is an alcohol which is
capable of binding with transition metal nitrates such as Fe(III)
nitrate and Mn(II) nitrate to form to give [M(NO3)x-1(PEG)], a
ternary complex containing PEG in the metal coordination spheres.
The complex thus formed is as an effective catalyst to trigger
the nitration reaction through the generation of active nitronium
ion as shown in Scheme-I.
Effect of structure on reactivity: The results (Table-2)
revealed that the reaction is sensitive to the structural variation
of cinnamic acid, when the nitro decarboxylation reaction is
conducted with cinnamic acids in presence of PEG-400 and
metal nitrates reaction rates accelerated with the introduction
of electron donating groups and retarded with electron with-
drawing groups.
EFFECT OF ADDITIVE PEG ON METAL NITRATE MEDIATED
NITRO DECARBOXYLATION OF CINNAMIC ACID
UNDER SOLVENT FREE CONDITIONS
Fe(NO3)3
Mn(NO3)2
Entry
Time (min)
Yield (%)
Time (min)
Yield (%)
PEG-200
PEG-300
PEG-400
PEG-600
PEG-3000
PEG-6000
45
60
30
30
60
35
90
86
88
86
76
88
45
60
30
30
60
30
88
83
87
85
80
87
The products were characterized by 1H NMR, mass spectra
and physical data with authentic samples and found to agree
well with earlier reports [25,27].
β-Nitro styrene: Mass: (m/z) 149; 1H NMR: δ 6.4 (d 1H,
β-CH), δ 7.3-7.65 (m 5H, Ar-H) δ 7.8 (d 1H, α-CH).
1
1-Nitro propene: Mass: (m/z) 87; H NMR: δ 2.12 (d
3H, CH3), δ 7.0 (d 1H, α-CH), δ 7.15 (m 1H, β-CH).
Effect of PEG and metal nitrate on the reactivity: The
results (Table-1) show that the reactions afford very good to
excellent yields within 1 h when the reactants are ground in
a mortar with a pestle, in presence of laboratory desk top
d-block metal nitrates such as ferric nitrate and manganese
nitrate. Further, the reactions underwent smoothly with all the
poly(ethylene glycols) (molecular weights ranging from PEG-
200 to PEG-6000). However, among the different PEGs used
in the present study, PEG-400 has been found to be much more
Conclusion
In summary, we have accomplished poly(ethylene glycol)
supported Fe(III) nitrate and Mn(III) nitrate as efficient reagents
for the synthesis of β-nitro styrenes from α,β-unsaturated
carboxylic acids under solvent-free and mineral acid-free
conditions using cost-effective grind-stone technology. The
K
HNO3
[H-(OCH2-CH2)n-O-M(NO3)x-1] +
[PEG-Metal nitrate]
+
[M(NO3)x]
H-(OCH2-CH2)n-OH
(PEG)
(Metal nitrate)
H2O
(H2NO3)+
+
NO2
2HNO3
NO3
R-CH=CH-COOH
+
[PEG-Metal nitrate]
H+
O
C H = CH
R
O
M(NO3)x-1
+
NO2
CO2
H-(OCH2-CH2)n-O
fast
fast
[H-(OCH2-CH2)n-O-M(NO3)x-1
]
RCH=CHNO2
MNO3
H+
–
[H-(OCH2-CH2)n-O-M(NO3)x-1
]
+
+ NO3
+ PEG
where R = Alkyl (or) Aryl group; MNO3 = Metal nitrate
Scheme-I: Plausuble mechanism of nitrodecarboxylation of unsaturated acid

1800 Ramesh et al.
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NITRO DECARBOXYLATION OF CINNAMIC ACIDS IN
PRESENCE OF PEG-400 AND METAL NITRATES
UNDER SOLVENT FREE CONDITIONS
Fe(NO3)3
Mn(NO3)2
Entry
Cinnamic acid
4-Chloro cinnamic acid
4-Methoxy cinnamic acid
4-Methyl cinnamic acid
4-Nitro cinnamic acid
4-Hydroxy cinnamic acid
Acrylic acid
Time
(min)
30
60
30
30
60
30
30
60
30
60
Yield
(%)
Time
Yield
(%)
(min)
30
60
30
30
60
30
30
60
30
60
30
88
86
88
86
76
92
80
78
76
82
86
87
83
87
85
80
88
78
78
80
70
78
Crotonic acid
3-Phenyl crotonic acid
2-Chloro cinnamic acid
2-Methyl cinnamic acid
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nitrates, PEGs and unsaturated acids.
CONFLICT OF INTEREST
https://doi.org/10.1016/j.tetlet.2007.04.026.
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P.K. Saiprakash, Green. Sustain. Chem., 1, 132 (2011);
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The authors declare that there is no conflict of interests
regarding the publication of this article.
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