A high-performance selective oxidation system for the facile production of fine chemicals

Article abstract of DOI:10.1039/b618090f

Mn^IIIAlPO-5 and Cr^VIAlPO-5 redox (microporous) catalysts are effective, in the presence of dissolved acetylperoxyborate (APB) under mild conditions (333-373 K), and much superior to the titanosilicate, TS-1 (also a single-site heterogeneous catalyst), in the selective oxidation of primary, secondary, benzylic and other unsaturated alcohols, p-cymene, methyl cyclohexene and other speciality organics which are of value in the fine-chemical and pharmaceutical industries. The Royal Society of Chemistry.

Full text of DOI:10.1039/b618090f

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COMMUNICATION
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A high-performance selective oxidation system for the facile production
of fine chemicals{
Robert Raja,*a John Meurig Thomas,*b Mike Greenhill-Hooperc and Violeta Doukovad
Received (in Cambridge, UK) 12th December 2006, Accepted 30th March 2007
First published as an Advance Article on the web 19th April 2007
DOI: 10.1039/b618090f
MnIIIAlPO-5 and CrVIAlPO-5 redox (microporous) catalysts
pharmaceutical contexts, we have found that the widely-used
TS-1 oxidation catalyst is distinctly inferior to MnIII-framework-
are effective, in the presence of dissolved acetylperoxyborate
substituted microporous aluminophosphates (AlPO-5) which we
(and others) earlier described,9,10 along with similar MAlPOs (M ;
CoIII, MnIII, FeIII), in relation to its high performance in the one-
step conversion of cyclohexane to adipic acid.11
We have also shown previously12 that when acetylperoxyborate,
(APB), is dissolved in water it yields, inter alia, a mixture of
hydrogen peroxide and peracetic acid, which, in the presence of a
single-site redox microporous catalyst such as FeIIIAlPO-31 or
MnIIIAlPO-5, releases its active oxygen in the vicinity of the active
site where selective oxidation of the reactant freely ensues. (The
ratio of H2O2 to peracetic acid increases with time after
dissolution, as shown in Figure 2 of ref. 12).
(APB) under mild conditions (333–373 K), and much superior
to the titanosilicate, TS-1 (also a single-site heterogeneous
catalyst), in the selective oxidation of primary, secondary,
benzylic and other unsaturated alcohols, p-cymene, methyl
cyclohexene and other speciality organics which are of value in
the fine-chemical and pharmaceutical industries.
Of the many effective catalytic systems that have emerged1–3 in
recent years to replace stoichiometric ones like CrO3–H2SO4,
pyridinium chlorochromate, KMnO4 and KHSO5 for selective
oxidation4 of organic compounds, one of the most versatile and
powerful is the combination of H2O2 with the single-site5,6
microporous titanosilicate known as TS-1.7,8 An indication of its
utility is seen in Scheme 1.
Typical results for the oxidation of a number of aromatic,
aliphatic and unsaturated alcohols are shown in Table 1. The
oxidation of primary alcohols to their corresponding aldehydes is a
fundamentally important reaction in the laboratory and in
commercial practice. It is of considerable significance in the fine-
chemical industry since vital ingredients and high-value inter-
mediates (such as perfumes) can be so generated. It is worth noting
here that secondary alcohols are generally more reactive compared
to primary alcohols and the Jones oxidation (sodium dichromate–
H2SO4 in acetone) is normally effective here, as over-oxidation is
difficult. With primary alcohols, however, the Jones oxidation is
not very effective as the aldehyde formed is further oxidized to the
acid via the hydrate. Hydroxyapatite-supported palladium
nanoclusters13 have proved effective in the oxidation of activated
alcohols (where the carbon is attached to a phenyl group such as
phenylethanol, and benzyl alcohol), but these catalysts were not
very effective for the oxidation of primary alkyl alcohols such as
1-octanol. Good yields (high turnovers) have been reported with
gold nanocrystals14 using an aqueous base and with biphasic
catalyst systems,15 but the corresponding monoacid and not the
aldehyde was the major product in most cases. Very recently,
Hutchings et al16 have shown that Au/Pd–TiO2 catalysts display
high turnovers and remarkable selectivity (to the aldehyde) for the
oxidation of primary alkyl alcohols and a range of other straight-
chain, benzylic and other unsaturated alcohols.
In the course of a wide-ranging study of the selective oxidation
of a large number of substrates that would yield, by the desired
selective oxidation, materials of value in fine-chemical and
Scheme 1 Illustration of the range of selective oxidations effected by the
titanosilicate, TS-1.
aDepartment of Chemistry, University of Southampton, Highfield,
Southampton, UK SO17 1BJ. E-mail: R.Raja@soton.ac.uk;
Fax: +44-2380-593781; Tel: +44-2380-592144
It is clear (from Table 1) that the redox active centres (MnIII,
CrVI)17 in the aluminophosphate microporous framework (pore
bDepartment of Materials Science, University of Cambridge,
Cambridge, UK CB2 3QZ. E-mail: jmt2@cam.ac.uk;
Fax: +44-1223-740360
IV
diameter 7.3 A) is very much more effective than the Ti active
˚
centre in the microporous silicalite (TS-1) framework (pore
˚
diameter 5.5 A), and that the yields of the desired product with
cRio Tinto Minerals, 2 Place E, Bouilleres, Toulouse, France.
E-mail: Mike.GreenhillHooper@riotinto.com; Tel: +33-561-502036
dBorax Europe Limited, 1A Guildford Business Park, Guildford, UK
GU2 8XG
the first of these catalysts are superior to those of the latter.
Interestingly, in most cases (with the exception of p-cresol and
2-methoxy-4-methyl phenol) non polar solvents (such as dichloro-
methane, DCM) were particularly effective in facilitating high
{ Electronic supplementary information (ESI) available: Experimental and
analytical details, including results on leaching and recycle tests are
provided. See DOI: 10.1039/b618090f
1924 | Chem. Commun., 2007, 1924–1926
This journal is ß The Royal Society of Chemistry 2007

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Table 1 Comparative performance of TS-1 and MnIII/CrVIAlPO-5 in the oxidation of primary, secondary and benzylic alcohols using APBa
Sub :
Conv.b Oxidantb
actual efficiency
T/K t/h mol ratio Solvent (mol%) (mol%) Product distribution (mol%) (actual)
oxidant
Substrate
Catalyst
1-octanol
87.2
43.5
octanal
12.4
12.7
octanoic acid others
CrAlPO-5 343 1 3 : 1
TS-1
DCM 12.6
DCM 56.3
37.9
56.3
0.3
43.5
—
—
413 3 1 : 1
2-octanol
78.0
54.5
2-octanone
21.5
44.5
others
0.5
1.2
MnAlPO-5 368 3 3 : 1
CrAlPO-5 413 3 1 : 1
DCM 21.9
DCM 45.4
65.8
45.4
21.7
TS-1
368 3 3 : 1
DCM
7.2
93.0
7.1
—
benzyl alcohol benzaldehyde benzoic acid others
MnAlPO-5 333 1 3 : 1
3 : 1
CrAlPO-5 333 3 3 : 1
TS-1 343 1 3 : 1
3 : 1
DCM 23.8
DCM 28.7
DCM 11.9
71.5
86.2
35.4
12.5
24.7
76.0
71.0
88.0
96.0
92.0
21.7
25.6
11.7
4.0
1.0
1.4
—
—
—
1.3
1.8
—
—
—
3
DCM
DCM
4.1
8.2
3
8.1
cyclohexanol cyclohexanone e-caprolactone others
MnAlPO-5 333 3 1 : 1
TS-1 333 3 1 : 1
MnAlPO-5 333 3 1 : 3
CrAlPO-5 333 3 1 : 3
DCM 76.4
DCM 65.0
CH3CN 86.3
CH3CN 71.2
CH3CN 67.3
76.4
65.0
86.3
71.2
67.3
23.5
34.8
13.5
28.5
32.5
76.2
64.8
44.1
32.0
67.2
—
—
30.0
36.5
—
—
—
12.0
2.3
—
TS-1
333 3 1 : 3
p-cresol
4-hydroxy-
benzaldehyde benzoic acid catechol
4-hydroxy-
4-methyl
MnAlPO-5 353 3 3 : 1
TS-1 353 3 3 : 1
acetone 9.2
acetone 5.6
27.4
16.9
90.5
94.5
2.6
—
6.7
5.6
—
—
2-methoxy-
4-methyl-
phenol
vanillin
4.5
vanillic acid
0.8
others
0.5
MnAlPO-5 373 3 1 : 1
TS-1 373 3 1 : 1
CH3OH 5.3 5.3
CH3OH No reaction
94.5
1,2,3,6-tetra- aldehyde
hydrobenzyl
alcohol
acid
epoxide/
others
MnAlPO-5 333 1 3 : 1
MnAlPO-5 363 1 1 : 1
DCM 7.2
DCM 36.9
21.5
36.9
92.5
63.0
6.0
2.5
1.3
34.4
—
—
TS-1
Pd/C
Pd/C
333 3 3 : 1
333 1 3 : 1
333 1 3 : 1
DCM No reaction
DCM 10.5
CH3CN 18.0
32.5
54.8
90.0
82.2
8.3
2.2
2.1
—
—
16.0
a
b
Catalyst ; 0.25 g; solid APB ; 3.49 g (10.54 mmol). See ESI{ for further experimental and analytical details.
selectivites towards the desired product (i.e. to the corresponding
aldehyde or ketone) compared to polar (aprotic) solvents (such as
tetrahydrofuran, acetonitrile or acetone). The choice of solvent and
substrate:oxidant mole ratio play a significant influence in the
oxidation of cyclohexanol to either cyclohexanone or e-caprolac-
tone. It also noteworthy (Table 1) that the combination of APB
and a strategically designed single-site redox nanoporous catalyst is
effective in catalyzing reactions of major significance in the fine-
chemical industry. For example, vanillin is used extensively in the
food industry as a flavouring and antibacterial agent, and is an
important constituent in non-food items such as air fresheners and
body lotions. Benzaldehyde, on the other hand, finds extensive use
in synthesizing other organic intermediates, ranging from phar-
maceuticals (e.g. mandelic acid), plastic additives, photographic
chemicals and certain aniline dyes. The single-site microporous
aluminophosphate catalyst (MnIIIAlPO-5), in combination with
APB, is much superior in performance and affords higher selec-
tivities to the desired aldehydes compared to TS-1. Further, in the
oxidation of 1,2,3,6-tetrahydrobenzyl alcohol (1,2,3,6-tetrahydro-
benzaldehyde is an important intermediate for producing epoxy
monomers that have applications in high-speed photocurable
coatings, adhesives and printing ink applications), the combination
of APB and MnIIIAlPO-5 produces yields that are much higher
than TS-1 (which is inactive for this reaction), and selectivities that
are comparable to conventionally-used Pd/C catalysts.
We have also compared MnIIIAlPO-5 with TS-1 in the
epoxidation of both cyclohexene and 1-methyl-cyclohexene and
in the selective oxidation of p-cymene (Table 2). In general,
epoxidation reactions with a number of catalysts (including the
Shell (TiIV–SiO2 catalyst) is markedly sensitive to deactivation by
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Table 2 Comparative performance of MnIIIAlPO-5 and TS-1 in the oxidation of olefins and p-cymene using APBa
Sub :
oxidant
Conv.b
actual
T/K t/h (mol ratio) Solvent mol%
Oxidantb
efficiency
mol%
Substrate Catalyst
Product distribution (mol%) (actual)
cyclohexene
67.5
68.0
85.0
77.9
epoxide
31.9
30.8
6.7
16.7
12.2
diols
0.5
1.1
3.4
2.9
others
—
—
5.0
2.5
—
MnAlPO-5 333
MnAlPO-5 333
MnAlPO-5 333
3
3
3
3
3
3 : 1
3 : 1
3 : 1
3 : 1
3 : 1
DCM
CH3CN 31.8
15.1
CH3CN 22.0
32.3
96.9
95.3
45.3
67.3
45.9
—
TS-1
TS-1
333
333
DCM
15.3
32.6
84.5
3.0
1-methyl-1-
cyclohexene
67.3
68.3
76.5
epoxide
others
MnAlPO-5 333
MnAlPO-5 333
MnAlPO-5 333
3
3
3
3
3
3 : 1
3 : 1
3 : 1
3 : 1
3 : 1
DCM
97.8
94.4
71.2
85.3
36.1
31.0
29.0
5.4
5.2
7.5
1.5
2.5
18.3
23.1
4.4
CH3CN 31.5
23.7
CH3CN 28.0
—
TS-1
TS-1
333
333
71.5
87.8
DCM
12.0
p-cymene
cuminaldehyde 4-isopropyl-
benzoic acid
others
MnAlPO-5 373
MnAlPO-5 373
3
1
1
1
3 : 1
1 : 1
1 : 1
3 : 1
acetone
acetone
acetone No reaction
acetone No reaction
6.9
9.2
19.8
9.2
93.0
90.6
5.0
9.0
0.5
0.3
1.3
—
TS-1
TS-1
373
373
a
b
Catalyst ; 0.25 g; solid APB ; 3.49 g (10.54 mmol). See ESI{ for further experimental and analytical details.
strongly coordinating ligands, especially water. The rationale
behind choosing TS-1 for comparison (in the epoxidation
reactions) was that, TS-1, due to its hydrophobicity, would be
less susceptible for deactivation in the presence of water, and has
been proven to be a good epoxidation catalyst using aqueous
peroxides (H2O2). Although TS-1 does exhibit some activity for
the epoxidation reaction, it is distinctly inferior in terms of overall
selectivity for the desired epoxide product compared to
MnIIIAlPO-5 as a single-site catalyst. More significantly, it did
not exhibity any appreciable activity for the oxidation of p-cymene
under comparable conditions (Table 2). The choice of solvent in
the epoxidation reactions, again has a moderate influence, but
reactions carried out in the absence of an organic solvent were
inferior both in terms of activity and selectivity. Further,
experiments analogous those reported earlier,12,17 were carried
out to rule out the possibility of leaching.{
Many other organic compounds that yield products such as
vitamins, fragrances, flavours and general pharmaceutical and
agrochemical intermediates have been selectively oxidized using
APB and an appropriate single-site solid catalyst.18,19 From Tables
1 and 2, it is clear that acetylperoxyborate (APB) in combination
with a single-site microporous AlPO-based catalyst is dintinctly
superior (1-octanol being the only exception), both in terms of
activity and selectivity, to the widely-used microporous single-site
titanosilicate (TS-1), for the oxidation of alcohols and for the
epoxidation of olefins. The high activities, selectivities and the
relatively mild conditions employed with the former of these
catalysts, coupled with ease of transport, storage and stability of
the solid oxidant, augurs well for the future use of APB in
conjunction with other single-site catalysts for fine-chemical,
pharmaceutical and agrochemical applications.18,20
Notes and references
1 Modern Oxidation Methods, ed. J.-E. Ba¨ckvall, Wiley-VCH, Weinheim,
2005.
2 N. Theyssen, Z. Hou and W. Leitner, Chem.–Eur. J., 2006, 12,
3401.
3 J. M. Thomas and R. Raja, Catal. Today, 2006, 117, 22.
4 J. Clayden, N. Greeves, S. Warren and P. Wothers, Organic Chemistry,
Oxford University Press, 2001.
5 J. M. Thomas, R. Raja and D. W. Lewis, Angew. Chem., Int. Ed., 2005,
44, 6456.
6 M. Anpo and J. M. Thomas, Chem. Commun., 2006, 3273.
7 B. Notari, Adv. Catal., 1996, 41, 253; M. Taramasso, G. Perego and
B. Notari, US Pat, 4410501, 1983; I. E. Maxwell, Stud. Surf. Sci. Catal.,
1996, 101, 1.
8 C. R. A. Catlow, S. A. French, A. A. Sokol and J. M. Thomas, Phil.
Trans. R. Soc. London, Ser. A, 2005, 363, 913.
9 J. M. Thomas and R. Raja, Chem. Commun., 2001, 675.
10 J. H. Yu and R. Xu, Chem. Soc. Rev., 2006, 35, 593.
11 R. Raja, G. Sankar and J. M. Thomas, J. Am. Chem. Soc., 1999, 121,
11926; M. Dugal, G. Sankar, R. Raja and J. M. Thomas, Angew.
Chem., Int. Ed., 2000, 39, 2310.
12 R. Raja, J. M. Thomas, M. Xu, K. D. M. Harris, M. Greenhill-Hooper
and K. Quill, Chem. Commun., 2006, 448.
13 K. Mori, T. Hara, T. Mizugaki, K. Ebitani and K. Kaneda, J. Am.
Chem. Soc., 2004, 26, 10657.
14 F. Porta and L. Prati, J. Catal., 2004, 224, 397.
15 Fine Chemicals through Heterogeneous Catalysis, ed. R. A. Sheldon and
H. van Bekkum, Wiley-VCH, Weinheim, 2001; R. Neumann and
M. Levin-Elad, Appl. Catal., A, 1995, 122, 85.
16 D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu, A. F. Carley,
A. A. Herzing, M. Watnabe, C. J. Kiely, D. W. Knight and
G. J. Hutchings, Science, 2006, 311, 362.
17 W. Buijs, R. Raja, J. M. Thomas and H. Wolters, Catal. Lett., 2003, 91,
253.
18 M. Greenhill-Hooper, R. Raja and J. M. Thomas, British. Pat. Appl.,
0423586.7, 2004; WO Pat. Appl 2006043075 A1, 2006.
19 R. Raja, J. M. Thomas, M. Greenhill-Hooper, S. L. Ley and R. G. Bell,
manuscript in preparation.
We thank National Chemical Laboratory, India, for supplying
us with a sample of TS-1.
20 R. Raja, J. M. Thomas and M. Greenhill-Hooper, manuscript in
preparation.
1926 | Chem. Commun., 2007, 1924–1926
This journal is ß The Royal Society of Chemistry 2007