Polymer immobilised TEMPO (PIPO): An efficient catalyst for the chlorinated hydrocarbon solvent-free and bromide-free oxidation of alcohols with hypochlorite

Article abstract of DOI:10.1039/a909690f

PIPO, a readily prepared polymer immobilised TEMPO, can be employed as an efficient recyclable heterogeneous catalyst for the chlorinated hydrocarbon solvent-free and bromide-free bleach oxidation of a variety of alcohols and polyols.

Full text of DOI:10.1039/a909690f

Polymer immobilised TEMPO (PIPO): an efficient catalyst for the chlorinated
hydrocarbon solvent-free and bromide-free oxidation of alcohols with
hypochlorite
Arn e´ Dijksman, Isabel W. C. E. Arends and Roger A. Sheldon*
Laboratory for Organic Chemistry and Catalysis, Department of Biotechnology, Delft University of Technology,
Julianalaan 136, 2628 BL Delft, The Netherlands. E-mail: secretariat-ock@stm.tudelft.nl
Received (in Cambridge, UK) 9th December 1999, Accepted 7th January 2000
PIPO, a readily prepared polymer immobilised TEMPO, can
be employed as an efficient recyclable heterogeneous cata-
lyst for the chlorinated hydrocarbon solvent-free and
bromide-free bleach oxidation of a variety of alcohols and
polyols.
proved to be an effective catalyst for oxidations of alcohols with
hypochlorite using the Anelli protocol. †
Primary and secondary aliphatic and benzylic alcohols were
smoothly converted to the corresponding aldehydes and ketones
2 2
in CH Cl (Table 1). Under these conditions the system was
homogeneous as PIPO is soluble in dichloromethane. In
contrast, in the absence of solvent (entry 3) PIPO was an active
heterogeneous catalyst. The heterogeneous nature of the
catalyst was confirmed in a filtration experiment, in which the
reaction mixture was filtered after 10 min. The filtrate showed
no activity at all during 1 h after filtration. The residue,
however, could be reused at least twice as a catalyst. The minor
loss of activity ( < 5%) observed is probably due to mechanical
losses occurring during filtration of the small amount of
catalyst.
2
The use of stable nitroxyl radicals, such as TEMPO, as catalysts
for the oxidation of alcohols to aldehydes, ketones and
1
carboxylic acids is well documented. Typically, these trans-
formations employ 1 mol% of the nitroxyl radical and a
stoichiometric amount of a terminal oxidant, e.g. sodium
2
3
hypochlorite, MCPBA (m-chloroperbenzoicacid), sodium
4
5
bromite, trichloroisocyanuric acid and oxygen in combination
with CuCl or RuCl (PPh ) . In particular, the TEMPO-bleach
2 3 3
6
7
protocol using bromide as co-catalyst introduced by Anelli
2
et al. is finding wide application in organic synthesis. Although
only a small amount of catalyst is used, recyclability is an issue
and several heterogeneous TEMPO systems have been re-
Table 1 PIPO-catalysed oxidation of alcohols with bromide/hypo-
chloritea
8
8g
ported. For example, MCM-41 and silica-supported TEM-
Entry
Substrate
Product
t/min Conv.(%)b Sel.(%)b
8h,i
PO
have been applied in oxidation reactions using hypo-
chlorite as the oxidant. The preparation of these catalysts
involves initial functionalisation of the support followed by
covalent attachment of a 4-substituted TEMPO.
Here, we report the use of a readily prepared polymer
immobilised TEMPO as a catalyst for alcohol oxidations. It was
derived from a commercially available oligomeric, sterically
hindered amine, poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-
1
2
3
4
5
a
Octan-1-ol
Octan-2-ol
Octanal
Octan-2-one
20
20
45
> 99
> 99
95
> 99
> 99
> 99
> 99
> 99
> 99
> 99
c
Benzyl alcohol Benzaldehyde 20
1-Phenylethanol Acetophenone 20
0
.8 mmol substrate, 2.5 mg PIPO (1 mol% nitroxyl), 2 ml CH
.5 M KBr solution (10 mol%), 0.14 g KHCO , 2.86 ml 0.35 M
hypochlorite solution (1.25 equiv.), 0 °C. Conversion and selectivity
2 2
Cl , 0.16 ml
0
3
1
,3,5-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidinyl)-
b
imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl-
imino]], better known as Chimassorb 944 (MW ≈ 3000; see
Scheme 1 for structure). This compound is used as an
antioxidant and a light stabiliser for plastics. It contributes
c
2
determined by GC using n-hexadecane as internal standard. No CH Cl2
(solvent-free).
Further investigation revealed that the use of bromide was not
necessary. Thus, in contrast to the conventional TEMPO-bleach
oxidations, which use dichloromethane as solvent and bromide
significantly to the long term heat stability of polyolefins and
has broad approval for use in polyolefin food packaging.9
2
as a co-catalyst, PIPO catalyses the oxidation of a variety of
alcohols in the absence of organic solvent and using only a
hypochlorite solution (0.35 M, pH 9.1) as the oxidant (Table 2).
However, under these conditions primary aliphatic alcohols
such as octan-1-ol, gave low selectivities to aldehydes owing to
over-oxidation of octanal to octanoic acid (entry 1). This
problem was circumvented by using MTBE as the organic
solvent, in which PIPO is not soluble, affording an increase in
selectivity to 94% (entry 2). Here again, filtration experiments
confirmed that this system was heterogeneous, analogous to the
solvent-free conditions.
Scheme 1 Synthesis of PIPO.
In addition to primary and secondary aliphatic alcohols
(entries 2–7), benzylic alcohols were also efficiently oxidised
(entries 9 and 10), complete conversion being observed within
30 min. In competition experiments, the catalyst showed a
marked preference for primary alcohols (entries 8 and 11). This
Nitroxyl radicals are normally prepared by treating the
2 4 2
analogous secondary amine with Na WO ·2H O and hydrogen
peroxide.10 In the case of Chimassorb 944, the same procedure
was applied resulting in the formation of an oligomeric TEMPO
2
(
Scheme 1). Probe-MS data revealed that the mass of each
is analogous to the already reported homogeneous and
segment increased by 30 owing to transformation of two
secondary amine moieties into the corresponding nitroxyl
radicals. This new polymer immobilised TEMPO, further
referred to as PIPO (polyamine immobilised piperidinyl oxyl),
heterogeneous8h TEMPO systems. Chirality on the a-position is
not affected during oxidation as shown by the selective
oxidation of (S)-2-methylbutan-1-ol to (S)-2-methylbutanal
(entry 12).11
Chem. Commun., 2000, 271–272
This journal is © The Royal Society of Chemistry 2000
271

Table 2 PIPO-catalysed oxidation of alcohols with hypochloritea
Notes and references
Conv.
Sel.
(%)
† General procedure for the oxidation of alcohols with PIPO as catalyst: in
a glass reaction vessel was placed 2.5 mg of PIPO (8 mmol based on
t/min (%)b
b
Entry
1
Substrate
Product
21
complete functionalisation; degree of functionalisation = 3.2 mmol g ).
Octan-1-ol
Octan-1-ol
Hexan-1-ol
Octan-2-ol
Hexan-2-ol
Octan-3-ol
Cyclooctanol
Octan-1-ol/
octan-2-ol
Benzyl alcohol
1-Phenylethanol
Benzyl alcohol/
Octanal
Octanal
Hexanal
45
45
45
45
45
45
90
80
89
99
99
70
100
86/ < 1
50d
94
95
> 99
> 99
> 99
> 99
96
2 2
Then a CH Cl solution (2 ml) of the alcohol (0.4 M) and n-hexadecane
c
(0.12 M; as internal standard) was added followed by an aqueous solution
(0.16 ml) of KBr (0.5 M). After the cooling of the reaction mixture to 0 °C,
2.86 ml of aqueous NaOCl (0.35 M and buffered by the addition of 0.14 g
2
3
c
4
5
6
7
Octan-2-one
Hexan-2-one
Octan-3-one
Cyclooctanone 45
Octanal/ 45
octan-2-one
Benzaldehyde 30
Acetophenone 30
Benzaldehyde/ 30
acetophenone
3
KHCO to pH 9.1) was added. Then, the reaction mixture was vigorously
shaken for 45 min. After destroying the excess of hypochlorite with
Na
Na
2
SO
SO
3
, the reaction mixture was extracted with diethyl ether, dried over
and analysed on GC (Chrompack CP-WAX 52 CB column; 50 m
c
8
2
4
3 0.53 mm).
9
100
100
95/4
> 99
> 99
> 99
‡ Procedure for the oxidation of methyl a-D-glucopyranoside with PIPO as
1
1
0
1
catalyst: in a glass reaction vessel was placed 15.7 mg of PIPO (50 mmol
based on complete functionalisation; degree of functionalisation = 3.2
21
1
-Phenylethanol
mmol g ) and 200 mg methyl a-D-glucopyranoside (1.03 mmol). Then, 8
1
2
(S)-2-Methyl-
butan-1-ol
(S)-2-Methyl- 45
butanal
90
> 99
ml of aqueous NaOCl (0.56 M and brought to pH 9.5 with an aqueous 1 M
hydrochloride solution) was added. During the reaction the pH was kept
constant at 9.5 by automatic titration with a 0.1 M KOH solution. When the
hydroxide consumption stopped (1.3 equiv. of hydroxide were consumed),
a
0
3
.8 mmol substrate, 2.5 mg PIPO (1 mol% nitroxyl), 0.14 g KHCO , 2.86
b
ml 0.35 M hypochlorite solution (1.25 equiv.), 0 °C. Conversion and
selectivity determined by GC using n-hexadecane as internal standard.
ml MTBE as solvent. Octanoic acid and octyl octanoate as side
products.
Na
2 3
SO was added to destroy the excess of hypochlorite. The crude mixture
c
2
was analysed using HPLC.
d
1
A. E. J. de Nooy, A. C. Besemer and H. van Bekkum, Synthesis, 1996,
153 and references therein; J. M. Bobbitt and M. C. L. Flores,
1
Heterocycles, 1988, 106, 509.
2
3
P. L. Anelli, C. Biffi, F. Montanari and S. Quici, J. Org. Chem., 1987,
5
2, 2559.
J. A. Cella, J. A. Kelley and E. F. Kenehan, J. Org. Chem., 1975, 40,
1
3
860; S. D. Rychovsky and R. Vaidyanathan, J. Org. Chem., 1999, 64,
10.
Scheme 2 Oxidation of methyl a-D-glucopyranoside using PIPO/NaOCl.
4
T. Inokuchi, S. Matsumoto, T. Nishiyama and S. Torii, J. Org. Chem.,
1990, 55, 462.
Carbohydrates are also oxidised by the PIPO/NaOCl system
analogous to TEMPO/NaOCl.12 For example, methyl a-
5 C.-J. Jenny, B. Lohri and M. Schlageter, Eur. Pat., 0775684A1, 1997.
D
-
6
7
8
M. F. Semmelhack, C. R. Schmid, D. A. Cort e´ s and S. Chou, J. Am.
Chem. Soc., 1984, 106, 3374.
A. Dijksman, I. W. C. E. Arends and R. A. Sheldon, Chem. Commun.,
glucopyranoside afforded methyl a- -glucopyranosiduronate
D
in 70% yield (Scheme 2).‡ As in the case of the oxidation of
simple alcohols, filtration experiments confirmed that the
catalyst is truly heterogeneous. Further investigation in the field
of carbohydrate oxidations using PIPO/NaOCl is in progress
and will be reported on in due course.
1
999, 1591.
(a) T. Osa, U. Akaba, I. Segawa and J. M. Bobbitt, Chem. Lett., 1988,
423; (b) Y. Kashiwagi, H. Ono and T. Osa, Chem. Lett., 1993, 257; (c)
1
T. Osa, Y. Kashiwagi and Y. Yanagisawa, Chem. Lett., 1994, 367; (d)
F. MacCorquodale, J. A. Crayston, J. C. Walton and J. Worsfold,
Tetrahedron Lett., 1990, 31, 771; (e) T. Osa, Y. Kashiwagi, J. M.
Bobbitt and Z. Ma, in Electroorganic Synthesis, Marcel Dekker Inc.,
New York, 1991, p. 343; (f) D. Brunel, P. Lentz, P. Sutra, B. Deroide,
F. Fajula and J. B. Nagy, Stud. Surf. Sci. Catal., 1999, 125, 237; (g) M. J.
Verhoef, J. A. Peters and H. van Bekkum, Stud. Surf. Sci. Catal., 1999,
6,7
Besides hypochlorite, oxygen can also be used as oxidant.
Unfortunately, in contrast to homogeneous TEMPO the combi-
7
2 3 3
nation of PIPO and RuCl (PPh ) in chlorobenzene is not able
to catalyse the aerobic oxidation of octan-2-ol, probably owing
to coordination of ruthenium to the polyamine. On the other
6
hand, in combination with CuCl/O
2
in DMF, it is capable of
1
25, 465; (h) A. Heeres, H. A. van Doren, K. F. Gotlieb and I. P.
completely oxidising benzyl alcohol to benzaldehyde within 2
h. This system, however, is limited to benzylic and allylic
alcohols as for homogeneous TEMPO.
Bleeker, Carbohydr. Res., 1997, 299, 221; (i) C. Bolm and T. Fey,
Chem. Commun., 1999, 1795.
9 See: http://www.pidc.org.tw/enst/e-11.htm
In summary we have developed a recyclable heterogeneous
catalyst for the bleach oxidation of alcohols and polyols. In
contrast to previously reported systems, neither a chlorinated
hydrocarbon solvent nor a bromide is necessary to achieve good
activity. A further advantage of our system is that the catalyst is
readily prepared from inexpensive and commercially available
raw materials. We believe that it will find wide application in
organic synthesis.
10 E. G. Rozantsev and V. D. Sholle, Synthesis, 1971, 190.
11 For bleach oxidation of (S)-2-methylbutan-1-ol with homogeneous
TEMPO, see: P. L. Anelli, F. Montanari and S. Quici, Org. Synth., 1990,
6
9, 212.
2 A. E. J. de Nooy, A. C. Besemer and H. van Bekkum, Tetrahedron,
995, 51, 8023; A. E. J. de Nooy, A. C. Besemer and H. van Bekkum,
1
1
Carbohydr. Res., 1995, 269, 89; N. J. Davis and S. L. Flitsch,
Tetrahedron Lett., 1993, 34, 1181.
We gratefully acknowledge IOP (Innovation-Oriented Re-
search Program) for financial support.
Communication a909690f
272
Chem. Commun., 2000, 271–272