Oxidation of cyclohexane to adipic acid using Fe-porphyrin as a biomimetic catalyst

Article abstract of DOI:10.1021/op049974s

A one-pot oxidation from cyclohexane to adipic acid has been developed, catalyzed by Fe-porphyrin in the presence of molecular oxygen without any additives. When the reaction temperature is 140°C, oxygen pressure is 2.5 MPa, concentration of catalyst is 1.33 × 10^-5 mol %, and reaction time is 8 h, the yield of adipic acid reaches 21.4%. A turnover number of about 24582 is thus far the highest one among those reported for the direct oxidation from cyclohexane to adipic acid.

Full text of DOI:10.1021/op049974s

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Organic Process Research & Development 2004, 8, 418−420
Communications to the Editor
Oxidation of Cyclohexane to Adipic Acid Using Fe-Porphyrin as a Biomimetic
Catalyst
Ying Yuan,† Hongbing Ji,‡ Yixia Chen,† Yong Han,† Xufeng Song,† Yuanbin She,*,† and Rugang Zhong†
Institute of Green Chemistry, Beijing UniVersity of Technology, Beijing 100022, P.R. China,
and School of Chemical Engineering, South China UniVersity of Technology, Guangzhou 510640, P.R. China
Abstract:
oxidant as it only produces water as a byproduct in an
environmentally friendly oxidation of cyclohexane.5,6 Mo-
lecular oxygen is another alternative oxidant; severe reaction
conditions such as high pressure and temperature are often
necessary for activation of the C-H bond.7-12 As to these
processes oxidized by either hydrogen peroxide or molecular
oxygen, much research has focused on the process either
from cyclohexane to KA oils7-9,13 or from KA oils to the
corresponding adipic acid.5,9,14,15 Cyclohexene as a feedstock
has also been well investigated.16 Thomas and co-workers
reported a hydrogenation method to yield adipic acid from
nuconic acid.17,18 Few reports have been documented for one-
pot oxidation directly from cyclohexane to adipic acid, which
is a promising and economic process for producing adipic
acid. Iwahama and co-workers19 reported that a radical cata-
lyst, i.e., N-hydroxyphthalimide, combined with Mn(acac)2
and Co(OAc)2 attained a direct conversion of cyclohexane
into adipic acid in the presence of molecular oxygen. Yet,
an expensive radical catalyst and two cocatalysts together
with acetic acid solvent were necessary, making this process
A one-pot oxidation from cyclohexane to adipic acid has been
developed, catalyzed by Fe-porphyrin in the presence of
molecular oxygen without any additives. When the reaction
temperature is 140 °C, oxygen pressure is 2.5 MPa, concentra-
tion of catalyst is 1.33 × 10-5 mol %, and reaction time is 8 h,
the yield of adipic acid reaches 21.4%. A turnover number of
about 24582 is thus far the highest one among those reported
for the direct oxidation from cyclohexane to adipic acid.
Introduction
Adipic acid has been found to be the most vital dicar-
boxylic acid industrially, widely used in the manufacture of
polyamide nylon 66, urethane foams, acidulant in baking
powder, plastics, and lubricant additives, as well as in the
production of intermediates for pharmaceuticals, insecticides,
and bactericides.1 Most of adipic acid on the market has
originated from cyclohexane,2 which undergoes oxidation at
423-433 K and 0.9 MPa of air with a homogeneous cobalt
catalyst or metaboric acid, forming the cyclohexanone and
cyclohexanol intermediates (KA oils), which are subse-
quently oxidized into adipic acid with nitric acid as an
oxidant. Succinic and glutaric acids are usually obtained as
byproducts. Use of nitric acid is still preferred because it is
inexpensive; however, use of a catalytic process scheme will
be beneficial from the environmental standpoint. The above-
mentioned two-step process poses environmental constraints,
since nitric acid is a corrosive oxidizing agent (which yields
NOx effluents requiring end-of-pipe treatments), and suffers
from high cost, owing to a two-step operation, corrosion,
stoichiometric conversion of nitric acid, and the necessity
for pollution treatment.
(3) Schuchardt, U.; Cardoso, D.; Sercheli, R.; Pereira, R.; de Cruz, R. S.;
Guerreiro, M. C.; Mandelli, D.; Spinace´, E. V.; Pires, E. L. Appl. Catal., A
2001, 211, 1-17.
(4) Thomas, J. M.; Raja, R.; Sankar, G.; Bell, R. G. Acc. Chem. Res. 2001, 34,
191-200.
(5) Usui, Y.; Sato, K. Green Chem. 2003, 5, 373-375.
(6) Raja, R.; Lee, S. O.; Sanchez-Sanchez, M.; Sankar, G.; Harris, K. D. M.;
Johnson, B. F. G.; Thomas, J. M. Top. Catal. 2002, 20, 85-88.
(7) Guo, C.-C.; Chu, M.-F.; Liu, Q.; Liu, Y.; Guo, D.-C.; Liu, X.-Q. Appl.
Catal., A 2003, 246, 303-309.
(8) Guo, C.-C.; Huang, G.; Zhang, X.-B.; Guo, D.-C. Appl. Catal., A 2003,
247, 261-267.
(9) Chavan, S. A.; Srinivas, D.; Ratnasamy, P. J. Catal. 2002, 212, 39-45.
(10) Pigamo, A.; Besson, M.; Blanc, B.; Gallezot, P.; Blackburn, A.; Kozynchen-
ko, O.; Tennison, S.; Crezee, E.; Kapteijn, F. Carbon 2002, 40, 1267-
1278.
(11) Raja, R.; Thomas, J. M. J. Mol. Catal. A: Chem. 2002, 181, 3-14.
(12) Dugal, M.; Sankar, G.; Raja, R.; Thomas, J. M. Angew. Chem., Int. Ed.
2000, 39, 2310-2313.
(13) d’Alessandro, N.; Liberatore, L.; Tonucci, L.; Morvillo, A.; Bressan, M.
New J. Chem. 2001, 25, 1319-1324.
(14) Crezee, E.; Barendregt, A.; Kapteijn, F.; Moulijn, J. A. Catal. Today 2001,
69, 283-290.
Using green oxidants such as hydrogen peroxide or
molecular oxygen is gathering increasing interest towards
cyclohexane oxidation.3,4 Hydrogen peroxide is a preferred
(15) Besson, M.; Blackburn, A.; Gallezot, P.; Kozynchenko, O.; Pigamo, A.;
Tennison, S. Top. Catal. 2000, 13, 253-257.
(16) Sato, K.; Aoki, M.; Noyori, R. Science 1998, 281, 1646-1647.
(17) Thomas, J. M.; Raja, R.; Johnson, B. F. G.; Hermans, S.; Jones, M. D.;
Khimyak, T. Ind. Eng. Chem. Res. 2003, 42, 1563-1570.
(18) Thomas, J. M.; Raja, R.; Johnson, B. F. G.; O’Connell, T. J.; Sankar, G.;
Khimyak, T. Chem. Commun. 2003, 1126-1127.
* Corresponding author. E-mail: sheyb@bjut.edu.cn. Telephone: +86-10-
86667823. Fax: +86-10-67391065.
† Beijing University of Technology.
‡ South China University of Technology.
(1) Davis, D. D.; Kemp, D. R. In Kirk-Othmer Encyclopedia of Chemical
Technology, 4th ed.; Kroscwitz, J. I., Howe-Grant, M., Eds.; Wiley: New
York, 1991; Vol. 1, pp 466-493.
(19) Iwahama, T.; Syojyo, K.; Sakaguchi, S.; Ishii, Y. Org. Process Res. DeV.
1998, 2, 255-260.
(2) Saji, P. V.; Ratnasamy, C.; Gopinathan, S. U.S. Patent 6,392,093, B1, 2002.
418
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10.1021/op049974s CCC: $27.50 © 2004 American Chemical Society
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Scheme 1
Table 1. One-pot oxidation of cyclohexane to adipic acid
catalyzed by T(o-Cl)PPFe in the presence of molecular
oxygena
temperature pressure reaction
isolated
entry
(°C)
(MPa)
time (h) yield (%)
TON
1
2
130
140
150
160
140
140
140
140
140
140
2.5
2.5
2.5
2.5
2.0
3.0
2.5
2.5
2.5
2.5
8
8
0.4
14.1
12.7
6.2
11.0
11.6
0.2
12.7
10.0
2.0
689
24295
21883
10683
18953
19987
345
21883
17230
3446
3
8
4
8
5
8
6
8
7
6
8
9
9
10
12
10
less benign. Several heterogeneous catalytic systems10-12,20
have also been explored. However, either severe reaction
conditions such as temperature, pressure or acidic solvent
or low activities existed in the investigated reaction systems.
In the present contribution, a novel one-pot oxidation of
cyclohexane to adipic acid using molecular oxygen as an
oxidant has been developed, in which metalloporphyrins
proved to be effective catalysts in a solvent-free reaction
system with high turnover number. In addition, this oxidation
does not need any other additives including solvents. To our
knowledge, there are few reports21 using metalloporphyrins
for one-pot oxidation from cyclohexane to adipic acid; the
use of acetonitrile as a solvent, the low yield of adipic acid
of about 7%, and the need to use more than 0.1 g of
porphyrin as catalyst make the process difficult to be
industrialized.
a Reaction conditions: catalyst (1 mg); cyclohexane (0.14 mol); oxygen
atmosphere.
Results and Discussion
Catalytic Properties Influenced by Different Reaction
Conditions. One-pot oxidation of cyclohexane to adipic acid
using molecular oxygen as the only oxidant was performed
as in Scheme 1.
Figure 1. Plots of yield of adipic acid and TON versus amount
of catalyst. Reaction conditions: cyclohexane (0.14 mol), oxygen
atmosphere (2.5 MPa), 140 °C, 8 h.
oxidation peaked at a concentration of 1.33 × 10-5 mol %.
It is contrary to the common knowledge that more catalyst
can generate more product. Under the optimal operating
parameters obtained from the above, the corresponding
oxidative products and TONs are shown in Figure 1.
From Figure 1, the plot of yield of adipic acid versus
catalyst amount has a turning point when the concentration
of catalyst is 1.33 × 10-5 mol %. As to the elucidation for
this phenomenon, the reason might be the self-polymerization
of T(o-Cl)PPFe.22 The use of as many as 0.1 or 0.5 g of
porphyrin catalyst within only 5 g of solvent in the
documented patent21 might partially explain the low activity
for the above-discussed reasons.
To our best knowledge, the obtained TON (about 24582)
of this present catalyst is the highest for those catalyst
systems towards one-pot oxidation from cyclohexane to
adipic acid. For example, TONs of about 4192, 239, and
594 could be achieved for Co/Mn cluster complex,9 FeAlPO
zeolite,12 and N-hydroxyphthalimide combined with Mn(a-
cac)2 and Co(OAc)2,19 respectively.
In our endeavor for optimizing the reaction conditions
for one-pot oxidation from cyclohexane to adipic acid, the
existence of optimal values for investigated parameters
including reaction temperature, reaction pressure, and reac-
tion time have been discovered as shown in Table 1.
All parameters were revealed to have optimal values, and
the increase or decrease of investigated parameters led to a
less efficient generation of adipic acid. The optimal reaction
temperature is 140 °C (entry 2). The higher temperature
normally means faster oxidation but the occurrence of more
side reactions, which widely exist in oxidation reactions
(entries 1-3). Similar phenomena were also found while
varying reaction pressure (entries 2, 5-6) and reaction time
(entries 2, 7-10). The optimal values for reaction pressure
and reaction time are 2.5 MPa and 8 h, respectively. These
investigated rules could be attributed to the reason that further
oxidation of adipic acid forms smaller oxygenates and
complete oxidation forms carbon dioxide and water, widely
employed in wastewater treatment.
Amount of Catalyst. It should be noted that the effect
via the amount of biomimetic catalyst towards cyclohexane
As to the reaction mechanism, the reaction course of
oxidation catalyzed by T(o-Cl)PPFe proceeds through a
(20) Belkhir, I.; Germain, A.; Fajula, F.; Fache, E. J. Chem. Soc., Faraday Trans.
1998, 94, 1761-1764.
(21) Ratnasamy, P.; Raja, R. EP 0784045-A1, 1997.
(22) Guo, C. C.; Liu, X. Q.; Liu, Y.; Liu, Q.; Chu, M. F.; Zhang, X. B. J. Mol.
Catal. A: Chem. 2003, 192, 289-294.
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radical pathway; T(o-Cl)PPFe(IV)dO• is regarded as active
species. The detailed mechanism from cyclohexane to adipic
acid has been further studied.
180 mg of crude product was obtained. Then, the crude
product was dissolved in CH2Cl2 and purified by column
chromatography (neutral Al2O3, CH2Cl2 as eluant), and T(o-
Cl)PPFe was obtained as a green powder (160 mg). Analysis
data are as follows: UV-vis(CH2Cl2): λmax: 416.2 nm
(Soret band), 545.8 nm (Q-band); IR: 2925 cm-1 (νC-H),
1630 cm-1 (νC-C benzene), 1312 cm-1 (νC-N pyrrole), 1008
cm-1 (νFe-N), 751 cm-1 (δC-H benzene); the above results
show that the synthetic complex was metalloporphyrin as
expected.
Cyclohexane Oxidation. A typical oxidation for cyclo-
hexane is as follows: Into a 200-mL autoclave with magnetic
stirrer and temperature-controlling device were placed 15 mL
of cyclohexane (0.14 mol) and 1 mg of T(o-Cl)PPFe (8.84
× 10-6 mol %) catalyst. After flushing several times with
O2, 2.5 MPa of O2 was charged. The reaction was performed
at 140 °C for 8 h. The oxidation products were a mixture of
solids and liquids. The solid products were separated from
the resulting mixtures by vacuum distillation, followed by
recrystallization. The obtained product gave 2.503 g of pure
adipic acid (21.4%). Identifications of the different products
were carried out with melting-point testing device and IR
and HPLC analysis. TON is defined as the ratio of moles of
product (adipic acid) to moles of central metal (iron).
Conclusions
In conclusion, a novel, solvent-free one-pot oxidation from
cyclohexane to adipic acid catalyzed by T(o-Cl)PPFe was
successfully achieved in the presence of molecular oxygen.
By far this present catalyst system, reported as a biomimetic
catalyst for oxidation from cyclohexane to adipic acid,
presents the highest turnover number of about 24582 in
similar oxidative processes and gives an efficient alternative
process for the synthesis of adipic acid.
Experimental Section
Preparation of Catalyst. meso-Tetra(o-chlorophenyl)
porphyrins (hereafter abbreviated as T(o-Cl)PP) were syn-
thesized according to the documented procedure.23 Metal
complexes of T(o-Cl)PP were synthesized using DMF as
solvent, and a typical example (meso-tetra (o-chlorophenyl)
iron porphyrin, abbreviated as T(o-Cl)PPFe) is as follows:
A three-neck round-bottomed flask equipped with a ther-
mometer, reflux condenser, and magnetic force stirrer were
charged with 20 mL of DMF, 0.27 mmol T(o-Cl)PP and
0.30 mmol FeCl2. The mixture was stirred under reflux for
2 h at 165 °C. TLC presented the complete disappearance
of the starting material. Into the obtained cooled mixture,
20 mL of deionized water and 30 mL of 10% HCl were
added, and a crystalline product formed. After overnight
deposition, followed by filtration and dryness in a vacuum,
Acknowledgment
We are grateful to the Scientific and Technical Nova’s
Star Plan Project of Beijing Manicipality (No. 953811200)
and Beijing Natural Science Foundation (No. 2002002) for
financial support of this work.
Received for review January 12, 2004.
OP049974S
(23) Lei, Y. W.; Guo, C. C.; Zeng, D. Z. Huaxue Shiji [Chem. Reagents (Beijing)]
1994, 16, 105-108 (in Chinese).
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