Bifunctional molecular sieve catalysts for the benign ammoximation of cyclohexanone: One-step, solvent-free production of oxime and ε-caprolactam with a mixture of air and ammonia [19]

Full text of DOI:10.1021/ja011001+

J. Am. Chem. Soc. 2001, 123, 8153-8154
8153
Bifunctional Molecular Sieve Catalysts for the
Scheme 1
Benign Ammoximation of Cyclohexanone: One-Step,
Solvent-Free Production of Oxime and
E-Caprolactam with a Mixture of Air and Ammonia
Robert Raja,*,†,‡ Gopinathan Sankar, and
†
John Meurig Thomas*,
†,§
Scheme 2
DaVy Faraday Research Laboratory
The Royal Institution of Great Britain
1 Albemarle Street, London, U.K. W1S 4BS
2
Department of Chemistry, UniVersity of Cambridge
Lensfield Road, Cambridge, U.K. CB2 1EW
Department of Materials Science and Metallurgy
UniVersity of Cambridge, U.K. CB2 3QZ
ion (framework)-substituted aluminophosphate molecular sieve
catalysts for converting 1 to 2 and 3 in a one-step, solVent-free
manner, in the liquid-phase, using oxygen (as air) and ammonia.
ReceiVed April 20, 2001
ReVised Manuscript ReceiVed May 30, 2001
II III
The catalysts are: (M M )AlPO-36, M ≡ Co, Mn; they are
The conversion of cyclohexanone (1) to the oxime (2) and its
subsequent Beckmann rearrangement to ꢀ-caprolactam (3) are vital
15
structurally well-defined possessing pore apertures of 6.5 × 7.5
2
Å, and a surface area (overwhelmingly internal) of ca. 700 m
1
stepping stones in the manufacture of nylon-6 (Scheme 1). On
-1
16
g . X-ray absorption spectroscopy has established that of the
atom % of the framework Al isomorphously replaced by M
ions, approximately 50% are in the M and 50% in the M state
Figure 1). M ions, since they have protons loosely bound to an
an industrial scale, one popular procedure in converting 1 to 2 is
to employ hydroxylamine sulfate, the sulfuric acid thus liberated
being neutralized by ammonia,2 with the consequential produc-
III
4
II
III
,3
II
(
4
tion of large quantities of (low value) ammonium sulfate. The
adjacent framework oxygen atom, are the loci of Br o¨ nsted acid
traditional industrial route for effecting the Beckmann rearrange-
ment (2f3) is by use of a strong mineral acid such as oleum
Scheme 2).
Workers at Enichem Co. showed that the titanosilicate molec-
ular sieve TS-1 offered an attractive, more environmentally benign
III
active sites. The M framework ions, on the other hand, are
“
redox” active sites, capable of activating hydrocarbons and
(
17
oxygen. The pore dimensions of MAlPO-36 are just large
enough to permit ingress of any of the molecules 1, 2, or 3. In
II III
(
M M )AlPO-18, M ≡ Co, which we have also studied (see
2 2
route of production, a particular advantage being the use of H O
below) for the purposes of elucidating the nature of the catalysis,
all of the Co ions are in the Co state; and the pore diameter
is so small that only air, H and ammonia (or hydroxylamine
when formed ) may gain access to the interior surface of the
sieve.
Our designed bifunctional catalysts, M M AlPO-36, perform
as the oxidant5 in aqueous solution. Other hydrogen peroxide-
,6
III
16
7
based processes employ organic solvents such as methanol,
2
O
2
ethanol, or 2-propanol, and a stabilizer such as sodium EDTA so
as to generate 1,1′-dihydroxydicyclohexyl peroxide. Earlier,
Armor had demonstrated a direct (gas phase) route to 2 and 3
from 1 using two distinct (double-bed) catalysts consisting of a
18
8
II III
very well in consecutively converting 1 to 2 to 3 because: (i)
variety of silicas and aluminas in the range 120-250 °C.
hydroxylamine (NH
2
OH) is readily formed in situ inside the pores
In a program directed9
-11
toward developing more benign
III
from NH and O at the M active (redox) sites, (ii) the NH OH
3
2
2
reagents and catalysts for the laboratory-scale production of
desirable commodity chemicals (such as adipic acid from either
converts 1 to 2 both inside and outside the pores, and, likewise,
at the Br o¨ nsted active sites 2 is isomerized to 3 inside the pores
cyclohexane12 or n-hexane, or lactones from ketones ), we have
13
14
2 2
of the molecular sieve catalyst, and (iii) O yields NH OH more
investigated the effectiveness of two bifunctional transition-metal-
efficiently than H or TBHP at the redox active sites.
2
O
2
We now show that all the results given Table 1 are readily
interpretable, with additional structural and shape-selective nu-
ances, in terms of points (i-iii) above. Moreover a kinetic study
*
Corresponding authors.
†
Royal Institution of Great Britain.
Department of Chemistry.
‡
§
Department of Materials Science.
2
(see Supporting Information) shows that NH OH is initially
(
1) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis: The Applications
and Chemistry of Catalysis by Soluble Transition Metal Complexes, 2nd ed.;
formed at a rapid rate but is then converted to 2 in the presence
of cyclohexanone. Furthermore, experiments carried out in the
absence of cyclohexanone proved unequivocally the formation
Wiley-Interscience: New York, 1992.
(2) Ullmann’s Encyclopedia of Industrial Chemistry; Wiley-VCH: Wein-
heim, Germany, 2001.
3) Kirk-Othmer Encyclopedia of Chemical Technology; Wiley: New York,
982; p 432.
4) (a) About 2.8 kg of ammonium sulfate is generated per kilogram of
cyclohexanone oxime produced. (b) Bellussi, G.; Perego, C. Cattech 2000, 4,
III
19
(
2 3 2
of NH OH from NH and O at the redox (Co ) site.
1
We note, in particular that deliberate increase of the concentra-
tion of Br o¨ nsted sites in Co(Mn)AlPO-36 (cf. G with A and H
with B) significantly enhances the production of ꢀ-caprolactam;
no ꢀ-caprolactam (3) is ever produced with MAlPO-18 catalysts,
even when the Br o¨ nsted active center concentration is increased
(
4
.
(
5) Taramasso, M.; Perego, G.; Notari, B. U.S. Pat. 4,410,501, 1983.
6) Roffia, P.; Padovan, M.; Leofanti, G.; Mantegazza, M. A.; De Alberti,
(
G.; Tanszik, G. R. U.S. Pat. 4,794,198, 1988.
(
(
(
(
7) Degussa, DE 2003269, 1970.
8) Armor, J. N. J. Catal. 1981, 70, 72.
(15) Wright, P. A.; Natarajan, S.; Thomas, J. M.; Bell, R. G.; Gai-Boyes,
P. L.; Jones, R. H.; Chen, J. Angew. Chem., Int. Ed. Engl. 1992, 31, 1472.
(16) Barrett, P. A.; Sankar, G.; Catlow, C. R. A.; Thomas, J. M. J. Phys.
Chem. 1996, 100, 8977.
(17) Thomas, J. M.; Raja, R.; Sankar, G.; Bell, R. G. Nature 1999, 398,
227.
9) Thomas, J. M. Angew. Chem., Int. Ed. 1999, 38, 3588.
10) Thomas, J. M.; Raja, R.; Sankar, G.; Bell. R. Acc. Chem. Res. 2001,
4, 191.
3
(
11) Thomas, J. M.; Raja, R. Chem. Commun. Feature Article 2001, 675.
12) Dugal, M.; Sankar G.; Raja, R.; Thomas, J. M. Angew. Chem., Int.
(
Ed. 2000, 39, 2310.
(18) Zecchina, A.; Spoto, G.; Bordiga, S.; Geobaldo, F.; Petrini, G.;
Leofanti, G.; Padovan, M.; Mantegazza, M.; Roffia, New Frontiers in
Catalysis; Guzci, L., Ed.; Elsevier: Amsterdam, 1993; p 719.
(
13) Raja, R.; Sankar G.; Thomas, J. M. Angew. Chem., Int. Ed. 2000, 39,
2
313.
(14) Raja, R.; Thomas, J. M.; Sankar, G. J. Chem. Soc., Chem. Commun.
(19) NH
2
2 3
and O at a Co active site (such as Co AlPO-18).
OH was not formed when the reaction was carried out in NH
I
I
I
I
1
999, 525.
1
0.1021/ja011001+ CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/31/2001

8154 J. Am. Chem. Soc., Vol. 123, No. 33, 2001
Communications to the Editor
Table 1. Solvent-Free Ammoximation of Cyclohexanone:
Performance of Various Catalysts and Oxidantsa
product selectivityb
mol %)
(
conv
mol
solid molecular
sieve
t
ꢀ-capro-
I.D.
A
oxidant (h) (%) TONg oxime lactam others
II
III
c
Co Co AlPO-36
O
O
2
6
0
6
0
6
0
6
0
6
0
6
0
6
13.1 217
20.2 322
15.0 245
23.6 381
9.5 167
17.9 289
10.0 160
19.0 308
7.8 135
12.9 215
8.6 140
15.8 254
12.4 108
73.9
54.2
75.8
57.0
81.7
76.7
81.5
65.4
45.6
36.4
39.8
41.1
44.0
33.9
48.4
36.2
28.4
26.9
91.7
86.5
17.7
21.1
16.9
20.2
7.9
10.2
24.5
7.3
22.8
12.0
13.3
8.3
15.9
38.6
55.3
38.4
40.6
19.5
22.7
19.5
18.0
72.3
73.0
8.5
2
2
2
2
2
2
II
III
B
C
D
E
F
Mn Mn AlPO-36
2
II
III
Co Co AlPO-36 TBHP
10.0
10.1
18.2
16.3
14.7
20.8
18.4
36.2
42.9
31.3
45.2
-
II
III
Mn Mn AlPO-36 TBHP
II
III
d
Co Co AlPO-36
H
H
O
O
2
2
2
2
O
2
2
II
III
Mn Mn AlPO-36
O
II
III
G
H
Mg Co AlPO-36
II III
III
20 21.5 212
Figure 1. (A) In M M AlPO-36 (M ≡ Co, Mn), the framework M
II
III
II
Mg Mn AlPO-36
6
0
13.7 136
23.0 262
ions are the redox active centers (A
1
), whereas M ions have associated
2
ionizable OH bonds attached to the framework and these are the Br o¨ nsted
II
I
J
K
Co AlPO-36
O
O
O2
2
2
20 1.9
20 2.2
28
15
II
(
B
1
) acid sites. Mg ions in the framework also have neighboring ionizable
II
II
Mg Co AlPO-36
-
III
III
OH ions (B
2
sites). (B) In M AlPO-18 all the framework M ions are
CoIIIAlPO-18
6
21.5 367
-
II
II
20 32.4e 550
6
again redox active centers: there are no Co (or Mn ) framework sites.
-
13.7
II
III
2
Mg framework ions again have neighboring (B ) Br o¨ nsted sites.
L
Co AlPO-18
TBHP
no reaction
2
0
6
0
6
III
M
N
Co AlPO-18
H
2
O
2
19.7 333
28.0 477
19.9 274
65.8
59.3
90.4
87.5
32.0
81.5
-
-
-
-
-
-
34.0
41.4
9.5
12.3
67.4
19.2
(
cf. N and K) solely because the oxime (2) is too large to gain
f
2
access to these centers via the 3.8 Å pore apertures; for the same
reason there is no conversion at all of 1 to 2 or 3 when TBHP is
used as oxidant with Co AlPO-18, as this peroxide is also too
MgIICoIIIAlPO-18 O2
20 31.7 412
III
O
P
no catalyst
O2
20 1.2
32.6
-
-
no catalyst +
O
2
6
bulky to reach the redox active centers; with O
smaller pore CoAlPO-18 (catalyst K) gives higher conversion of
to the oxime (2) than with catalysts A or B because of the
2
as oxidant, the
h
2
NH OH‚HCl
a
Cyclohexanone: oxidant (H
2
O
2
, TBHP) ≡ 3:1 (mol); catalyst ≡
1
0
.5 g; Air ≡ 3.5 MPa; cyclohexanone: NH
3
≡ 1:3 (mol); T ≡ 328 K;
higher concentration of the redox active centers in the former;
b
we may categorically rule out the “imine” mechanism2
0,21
cyclohexanone = 50 g; mesitylene (internal standard) ≡ 2.5 g. Oxime
for the
6 5
formation of the oxime (2), according to which C H dNH is a
≡
cyclohexanone oxime (2); others ≡ mainly high molecular weight
conjugated products formed through aldol condensation of cyclohex-
necessary intermediate. Since this species is also too large to enter
the pores of the Co AlPO-18 (which smoothly yields 2 from 1
with a mixture of air and NH
direct conversion of 1 with NH
centers alone (see catalysts I, J) are not enough to effect the
conversion of 1 to 2 {and hence to 3}. Indeed, the meagre extent
of conversion (1.9% mol) is the same as is observed when no
catalyst is present (cf. I and O); but when hydroxylamine
hydrochloride is added to this mixture, conversion of 1 to the
oxime (2) {only} is very high, further confirming that the
hydroxylamine mechanism prevails.
c
anone plus some polycaprolactam and water. The reaction mixture
III
was colorless, indicating that very little tar is produced. d The reaction
mixture was brownish yellow, suggesting possible formation of tar.
3
), the dominant mechanism entails
OH to 2; and Br o¨ nsted active
e
f
Turnover efficiencies based on moles of O
2
consumed = 91%. H
2 2
O
2
g
efficiency = 85%. TON ) mol of substrate converted per mol of
h
metal (Co, Mn, or Mg) in the catalyst. Cyclohexanone: NH
1:1 (mol).
2
OH‚HCl
≡
23
mixture of cyclooctane and cyclohexanone along with NH
3
and
III
II
air over a Co Mg AlPO-18 catalyst. Unsurprisingly, there is no
conversion whatsoever of the cyclooctane molecule, as it is too
large to gain access into the interior of the catalyst where the
Our results also demonstrate that the MAlPO catalysts that we
vast majority of the active sites are located. The NH , however,
2
gains ready access to such active sites, where NH OH is first
3
10-14,17
have developed for this and other oxidations
function in a
genuinely heterogeneous manner and not seemingly sosbecause
22
produced before subsequently reacting with cyclohexanone to
produce the oxime (2). When the active sites are deliberately
leached22 using acetic acid as a solvent, considerable oxidation
of the cyclooctane now occurs (the main products being cyclo-
octanol, cyclooctanone, and cyclooctanoic acid), in addition to
III
III
the active entities (e.g., Co or Mn ions in this instance) do
not leach out and then simply adhere to the molecular sieve where
they would operate as loosely bound homogeneous catalysts. If
III
III
the Co or Mn were leached out, we would have seen
appreciable conversion using TBHP with catalyst L, yet there
2 3 2
the formation of NH OH from NH . The NH OH, now, reacts
II
was none. Moreover, if Mg ions were leached out, they would
not only with cyclohexanone to produce the corresponding oxime,
but also with the cyclooctanone to give its oxime. Clearly acetic
acid as a solvent results in homogeneous as well as heterogeneous
catalysis.
have catalyzed the Beckmann rearrangement of 2 to ꢀ-caprolactam
catalyst N), but again none of the latter is formed. In a separate
experiment (with reaction conditions analogous to those of H, in
Table 1) the solid catalyst was filtered off from the reaction
mixture (when hot) after 4 h, and the reaction was continued with
the resulting filtrate for a further 16 h. No further conversion to
-caprolactam was observed, and the filtrate analyzed by ICP/
AAS analysis revealed only trace amounts of Mn and Mg (<3
ppb and <5 ppb, respectively). Finally, we took an equimolar
(
Acknowledgment. We thank the EPSRC (UK) for a rolling grant to
J.M.T.
Supporting Information Available: Kinetics data showing the
ꢀ
II
III
2 3 2
formation of NH OH from NH and O using Mg Mn AlPO-36 (PDF).
This material is available free of charge via the Internet at http://pubs.acs.org.
JA011001+
(
20) Reddy, J. S.; Sivasanker, S.; Ratnasamy, P. J. Mol. Catal. 1991, 69,
83.
21) Peroxydicyclohexylamine (PDCA), believed by some workers20 to be
the key byproduct in the imine mechanistic path, was not observed.
22) Raja, R.; Sankar, G.; Thomas, J. M. J. Am. Chem. Soc. 1999, 121,
1926.
III
III
3
(23) It has been previously established22 that the redox centres (Co , Mn )
(
present in these molecular sieves catalyze the oxidation of cyclic alkanes by
2
2,24
a free-radical mechanism.
(
(24) MacFaul, P. A.; Ingold, K. U.; Wayner, D. D. M.; Que, L., Jr. J. Am.
Chem. Soc. 1997, 119, 10594.
1