Polyethylene glycols (PEGs) were found to be efficient media for decarboxylative nitration of
Cerium (IV) ammonium nitrate (CAN) is one of the most important reagents used for organic synthesis [
Being good Michael acceptors,
Cinnamic acid, ceric ammonium nitrate (CAN), and polyethylene glycols were obtained from SD Fine Chemicals or Loba. Substituted cinnamic acids were prepared by Perkins reaction as cited in the literature [
In a typical solid state synthesis, cinnamic acid (0.01 mol), PEG (0.02 mmol), and CAN (0.012 mmol) are placed in a clean two-necked R. B. flask containing acetonitrile (MeCN) and stirred for certain time. Progress of the reaction is periodically monitored by thin layer chromatography (TLC). After completion, the reaction mixture is treated with 2% sodium carbonate solution, followed by the addition of “dichloromethane” (DCM) or “dichloroethane” (DCE). The organic layer was separated, dried over Na2SO4 and evaporated under vacuum, and purified with column chromatography using ethyl acetate : hexane (3 : 7) as eluent to get pure product. The products were characterized by IR, 1H-NMR, mass spectra, and physical data with authentic samples and found to agree well with earlier reports (Table
Binding constants of
S. N | PEG | Benesi-Hildebrand equation |
|
|
|
---|---|---|---|---|---|
dm3/mol | dm3/mol/cm | (kJ/mol) | |||
1 | PEG-200 |
|
743 | 19.23 | 16.7 |
2 | PEG-300 |
|
611 | 18.18 | 16.2 |
3 | PEG-400 |
|
1420 | 14.08 | 18.3 |
Activation parameters of cinnamic acid in different PEG media. Units of
Type of PEG | PEG |
|
Equation |
|
|
|
|
---|---|---|---|---|---|---|---|
% (V/V) | 300 K | kJ/mol | J/K/mol | ||||
0.5 | 0.01 |
|
0.999 | 110 | 84.2 | 85.9 | |
1.0 | 0.02 |
|
0.999 | 76.3 | 83.3 | −23.2 | |
PEG-200 | 2.0 | 0.03 |
|
0.995 | 70.0 | 95.5 | −41.7 |
3.0 | 0.04 |
|
0.998 | 91.8 | 81.8 | −32.6 | |
4.0 | 0.08 |
|
0.999 | 58.6 | 55.6 | −72.3 | |
5.0 | 0.1 |
|
0.995 | 67.5 | 39.7 | 39.5 | |
| |||||||
0.5 | 0.01 |
|
0.997 | 189 | 87.6 | 338 | |
1.0 | 0.03 |
|
0.996 | 38.7 | 82.3 | −145 | |
PEG-300 | 2.0 | 0.04 |
|
0.999 | 44.8 | 81.8 | −123 |
3.0 | 0.05 |
|
0.998 | 22.4 | 81.0 | −195 | |
4.0 | 0.06 |
|
0.999 | 72.7 | 80.5 | −20.0 | |
5.0 | 0.08 |
|
0.999 | 64.5 | 80.0 | −51.3 | |
| |||||||
0.5 | 0.02 |
|
0.999 | 58.0 | 83.3 | −84.0 | |
1.0 | 0.03 |
|
0.997 | 50.8 | 82.5 | −105 | |
PEG-400 | 2.0 | 0.04 |
|
0.999 | 76.7 | 81.5 | −16.0 |
3.0 | 0.06 |
|
0.999 | 72.5 | 38.0 | −80.5 | |
4.0 | 0.07 |
|
0.999 | 58.7 | 80.1 | −69.7 | |
5.0 | 0.1 |
|
0.999 | 64.0 | 79.3 | −51.0 | |
| |||||||
0.5 | 0.02 |
|
0.998 | 45.0 | 83.0 | −126 | |
1.0 | 0.03 |
|
0.999 | 38.6 | 82.2 | −145 | |
PEG-600 | 2.0 | 0.04 |
|
0.999 | 26.0 | 81.4 | −184 |
3.0 | 0.05 |
|
0.999 | 46.2 | 81.0 | −115 | |
4.0 | 0.07 |
|
0.998 | 30.1 | 80.0 | −166 | |
5.0 | 0.1 |
|
0.999 | 35.3 | 80.0 | −148 |
Thermostat was adjusted to desired reaction temperature. Flask containing known amount of ceric ammonium nitrate (CAN) in acetonitrile solvent and another flask containing the substrate (
Spectrophotometric studies were performed in order to throw light on CAN binding with PEG (polyethylene glycol). UV-Visible spectrum of CAN in MeCN indicated a band at 459 nm. It underwent a hypsochromic shift (blue shift) of about 17 to 18 nm (band-shifted from 441 to 442 nm) in presence of PEG (Figure
UV-Visible spectra of CAN in presence and absence of PEG in MeCN medium.
In the previous equations,
Benesi-Hildebrand plot of PEG-300 interaction with CAN.
General form of the rate law for a nitrodecarboxylation (nitro-Hunsdiecker reaction) reaction could be represented by considering the following general scheme:
Reactions were conducted under two different conditions. Under pseudo first order conditions
Pseudo first order plot of cinnamic acid (ln(
Pseudo first order plot of acrylic acid (ln(
Pseudo first order plot of nitrocinnamic acid (ln(
The reaction is also conducted under second order conditions with equal concentrations of [CAN]0 = [CAN]0. Kinetic plots of [1/(
Second order kinetic plot of cinnamic acid (
Second order kinetic plot of acrylic acid (
Second order kinetic plot of nitrocinnamic acid (
In the present study, kinetic data have been collected at three to four different temperatures within the range of 300–315 K. Activation parameters such as
Eyring’s plot of cinnamic acid (ln(
Eyring’s plot of acrylic acid (ln(
In order to gain an insight into the mechanistic aspects of CAN-CA reaction in MeCN medium, the knowledge of distribution of CAN species in HNO3 medium could be useful. In HNO3 Ce(IV) mainly exists as
Progress of the reaction has been studied in the presence of a set of polyoxyethylene compounds (PEGs) with varied molecular weights ranging from 200 to 600 units, and it was found that the reaction is enhanced remarkably in all PEGs. Reaction times were reduced from 24 hrs to few hours. The catalytic activity was found to be in the increasing order PEG-300 > PEG-400 > PEG-600 > PEG-200. Further, it is also interesting to note that the absorbance of solvated Ce(IV) species is increased when PEG is added to [CAN] solution. This observation may indicate that solvated [CAN] species could bind with PEG to form
The plots of
Considering the total concentration of
This rate-law resembles Michaelis-Menten type rate law that is used for enzyme kinetics. Interestingly the plots of rate constant
The enthalpy
Activation parameters of crotonic acid in different PEG media. Units of
Type of PEG | PEG |
|
Equation |
|
|
|
|
---|---|---|---|---|---|---|---|
% (V/V) | 300 K | kJ/mol | J/K/mol | ||||
0.5 | 0.01 |
|
0.999 | 82.4 | 85.1 | −9.0 | |
1.0 | 0.02 |
|
0.999 | 56.0 | 83.3 | −91.0 | |
PEG-200 | 2.0 | 0.03 |
|
0.999 | 42.1 | 82.3 | −134 |
3.0 | 0.04 |
|
0.999 | 50.0 | 81.5 | 105 | |
4.0 | 0.05 |
|
0.999 | 64.0 | 81.2 | −57.3 | |
5.0 | 0.06 |
|
0.999 | 59.0 | 81.0 | −73.5 | |
| |||||||
0.5 | 0.01 |
|
0.999 | 81.4 | 85.0 | −12.0 | |
1.0 | 0.02 |
|
0.999 | 67.0 | 83.2 | −54.2 | |
PEG-300 | 2.0 | 0.04 |
|
0.998 | 35.2 | 81.5 | −154 |
3.0 | 0.05 |
|
0.999 | 54.6 | 79.0 | −80.0 | |
4.0 | 0.06 |
|
0.999 | 54.5 | 80.4 | −86.5 | |
5.0 | 0.08 |
|
0.999 | 78.5 | 80.0 | −5.3 | |
| |||||||
0.5 | 0.01 |
|
0.999 | 81.2 | 85.0 | −13.0 | |
1.0 | 0.02 |
|
0.999 | 65.4 | 83.3 | −57.0 | |
PEG-400 | 2.0 | 0.04 |
|
0.999 | 35.0 | 82.0 | −155 |
3.0 | 0.05 |
|
0.999 | 67.0 | 81.5 | −48.5 | |
4.0 | 0.06 |
|
0.999 | 45.0 | 80.7 | −119 | |
5.0 | 0.08 |
|
0.998 | 68.6 | 80.0 | −37.5 | |
| |||||||
0.5 | 0.01 |
|
0.998 | 80.0 | 85.0 | −16.3 | |
1.0 | 0.02 |
|
0.998 | 46.0 | 83.2 | −123 | |
PEG-600 | 2.0 | 0.03 |
|
0.999 | 44.0 | 82.3 | −128 |
3.0 | 0.04 |
|
0.998 | 45.0 | 81.2 | −120 | |
4.0 | 0.06 |
|
0.997 | 37.4 | 80.5 | −144 | |
5.0 | 0.09 |
|
0.999 | 52.0 | 80.0 | −91.8 |
Activation parameters of methoxy cinnamic acid in different PEG media. Units of
Type of PEG | PEG |
|
Equation |
|
|
|
|
---|---|---|---|---|---|---|---|
% (V/V) | 300 K | kJ/mol | J/K/mol | ||||
0.5 | 0.01 |
|
0.996 | 107 | 85.0 | 73.0 | |
1.0 | 0.02 |
|
0.998 | 115 | 84.4 | 102 | |
PEG-200 | 2.0 | 0.04 |
|
0.999 | 50.2 | 81.50 | −104 |
3.0 | 0.06 |
|
0.999 | 42.0 | 80.2 | −127 | |
4.0 | 0.08 |
|
0.999 | 32.0 | 80.0 | −158 | |
5.0 | 0.12 |
|
0.999 | 37.0 | 79.0 | −140 | |
| |||||||
0.5 | 0.01 |
|
0.997 | 86.0 | 35.3 | 110 | |
1.0 | 0.03 |
|
0.999 | 46.0 | 98.5 | −175 | |
PEG-300 | 2.0 | 0.04 |
|
0.959 | 45.0 | 82.0 | −123 |
3.0 | 0.05 |
|
0.999 | 20.2 | 78.0 | −192 | |
4.0 | 0.06 |
|
0.999 | 73.0 | 81.0 | −26.0 | |
5.0 | 0.08 |
|
0.999 | 66.2 | 80.0 | −46.0 | |
| |||||||
0.5 | 0.02 |
|
0.999 | 63.5 | 83.3 | −66.0 | |
1.0 | 0.03 |
|
0.999 | 83.2 | 77.0 | 21.3 | |
PEG-400 | 2.0 | 0.04 |
|
0.999 | 81.0 | 81.4 | −2.0 |
3.0 | 0.06 |
|
0.999 | 67.0 | 80.0 | −41.0 | |
4.0 | 0.08 |
|
0.999 | 50.0 | 80.0 | −99.0 | |
5.0 | 0.10 |
|
0.999 | 77.3 | 79.5 | −7.3 | |
| |||||||
0.5 | 0.02 |
|
0.999 | 66.0 | 83.3 | −58.0 | |
1.0 | 0.03 |
|
0.998 | 49.5 | 82.3 | −110 | |
PEG-600 | 2.0 | 0.05 |
|
0.999 | 41.0 | 81.3 | −134 |
3.0 | 0.06 |
|
0.999 | 52.0 | 80.5 | −95.0 | |
4.0 | 0.08 |
|
0.999 | 47.0 | 38.72 | −110 | |
5.0 | 0.1 |
|
0.998 | 56.0 | 80.3 | −81.0 |
Activation parameters of nitrocinnamic acid in different PEG media. Units of
Type of PEG | PEG |
|
Equation |
|
|
|
|
---|---|---|---|---|---|---|---|
% (V/V) | 300 K | kJ/mol | J/K/mol | ||||
0.5 | 0.01 |
|
0.999 | 100 | 85.0 | 50.0 | |
1.0 | 0.02 | y = −10.87 |
0.999 | 90.3 | 83.1 | 24.0 | |
PEG-200 | 2.0 | 0.04 |
|
0.999 | 39.2 | 37.05 | −141 |
3.0 | 0.06 |
|
0.999 | 46.0 | 38.04 | −116 | |
4.0 | 0.07 |
|
0.999 | 42.0 | 38.40 | −128 | |
5.0 | 0.09 |
|
0.998 | 33.0 | 38.99 | −156 | |
| |||||||
0.5 | 0.01 |
|
0.999 | 81.2 | 85.0 | −13.0 | |
1.0 | 0.02 |
|
0.999 | 65.4 | 83.3 | −60.0 | |
PEG-300 | 2.0 | 0.04 |
|
0.999 | 35.5 | 37.0 | −153 |
3.0 | 0.05 |
|
0.999 | 57.0 | 81.0 | −80.0 | |
4.0 | 0.06 |
|
0.998 | 54.4 | 81.2 | −89.5 | |
5.0 | 0.08 |
|
0.999 | 75.1 | 80.0 | −16.0 | |
| |||||||
0.5 | 0.02 |
|
0.977 | 64.1 | 83.2 | −64.0 | |
1.0 | 0.03 |
|
0.999 | 44.2 | 82.0 | −126 | |
PEG-400 | 2.0 | 0.04 |
|
0.999 | 72.1 | 81.4 | −31.2 |
3.0 | 0.06 |
|
0.999 | 72.4 | 80.4 | −27.0 | |
4.0 | 0.07 |
|
0.998 | 66.0 | 80.0 | −46.0 | |
5.0 | 0.10 |
|
0.999 | 64.0 | 79.3 | −51.0 | |
| |||||||
0.5 | 0.01 |
|
0.998 | 80.1 | 85.0 | −16.2 | |
1.0 | 0.02 |
|
0.997 | 71.0 | 83.4 | −41.3 | |
PEG-600 | 2.0 | 0.04 |
|
0.999 | 34.0 | 82.0 | −159 |
3.0 | 0.06 |
|
0.999 | 39.1 | 80.5 | −138 | |
4.0 | 0.08 |
|
0.999 | 30.2 | 80.0 | −165 | |
5.0 | 0.10 |
|
0.999 | 46.5 | 79.2 | −109 |
Activation parameters of acrylic acid in different PEG media. Units of
Type of PEG | PEG |
|
Equation |
|
|
|
|
---|---|---|---|---|---|---|---|
% (V/V) | 300 K | kJ/mol | J/K/mol | ||||
0.5 | 0.01 |
|
0.999 | 98.5 | 85.0 | 45.3 | |
1.0 | 0.02 |
|
0.998 | 70.0 | 84.0 | −45.3 | |
PEG-200 | 2.0 | 0.03 |
|
0.998 | 65.3 | 82.2 | −57.0 |
3.0 | 0.04 |
|
0.997 | 68.0 | 82.0 | −47.0 | |
4.0 | 0.06 |
|
0.999 | 55.0 | 81.0 | −86.0 | |
5.0 | 0.08 |
|
0.998 | 51.0 | 80.5 | −98.2 | |
| |||||||
0.5 | 0.01 |
|
0.999 | 98.5 | 85.0 | 46.0 | |
1.0 | 0.02 |
|
0.998 | 95.0 | 83.2 | 39.3 | |
PEG-300 | 2.0 | 0.03 |
|
0.997 | 89.0 | 83.0 | 21.0 |
3.0 | 0.04 |
|
0.999 | 76.2 | 82.0 | −18.0 | |
4.0 | 0.05 |
|
0.999 | 51.0 | 81.0 | −100 | |
5.0 | 0.07 |
|
0.998 | 45.3 | 80.2 | −116 | |
| |||||||
0.5 | 0.02 |
|
0.997 | 69.2 | 83.4 | −47.4 | |
1.0 | 0.03 |
|
0.998 | 78.0 | 82.5 | −15.0 | |
PEG-400 | 2.0 | 0.04 |
|
0.999 | 81.2 | 82.0 | −1.6 |
3.0 | 0.06 |
|
0.997 | 66.0 | 81.0 | −50.0 | |
4.0 | 0.08 |
|
0.998 | 55.0 | 80.2 | −84.0 | |
5.0 | 0.10 |
|
0.999 | 71.0 | 80.0 | −28.4 | |
| |||||||
0.5 | 0.01 |
|
0.998 | 83.0 | 85.4 | −8.0 | |
1.0 | 0.02 |
|
0.997 | 55.4 | 83.3 | −93.0 | |
PEG-600 | 2.0 | 0.03 |
|
0.997 | 53.0 | 83.0 | −99.0 |
3.0 | 0.05 |
|
0.998 | 20.0 | 77.4 | −191 | |
4.0 | 0.07 |
|
0.998 | 26.0 | 80.5 | −182 | |
5.0 | 0.09 |
|
0.998 | 39.0 | 80.0 | −135 |
Being a versatile chemical reagent CAN has been applied to organic reactions in catalytic or stoichiometric amounts. Our research group has succeeded in using CAN to perform nitrodecarboxylation of