Heterogeneously catalysed cleavage of carbon–carbon double bonds with
hydrogen peroxide using calcined heteropolyacids on oxide supports
Christopher D. Brooks, Ling-chu Huang, Moya McCarron and Robert A. W. Johnstone*
Department of Chemistry, University of Liverpool, Liverpool, UK L69 3BX. E-mail: rj05@liverpool.ac.uk
Received (in Cambridge, UK) 27th July 1998, Accepted 13th November 1998
Reaction of an alkene with aqueous hydrogen peroxide and
a catalytic quantity of a heteropolyacid adsorbed onto
magnesium, aluminium or zinc oxide leads to complete,
rapid cleavage of the alkene to give carbonyl compounds.
significant proportions of the final reaction product. In the
poorly nucleophilic solvent, 2-methylpropan-2-ol, no 1-hy-
droxy-2-butoxy derivatives were found and the very small
quantities of 1,2-diol observed as intermediate products pre-
sumably arose from water in the hydrogen peroxide. Although
in MeOH, yields of 1-hydroxy-2-methoxy derivatives reached a
steady value towards the end of reaction, any 1,2-diols produced
at the same time first increased in amount during the early stages
of reaction and then decreased to zero towards the end. For
example, during oxidation of cyclohexene with a PWA catalyst,
maximum intermediate yields of some 7% epoxide and 15%
cyclohexane-1,2-diol were observed during the course of
oxidation, in which 100% of the alkene was converted to other
products; at the end of reaction almost all of the epoxide and
1,2-diol had disappeared. Work-up of this reaction mixture for
non-volatile components showed that the alkene double bond
had been completely cleaved to give adipic acid in high yield
and selectivity (Table 1), which had not been observed by GC
monitoring. Other alkenes behaved similarly (Table 1). It is
clear that these supported heteropolyacids (or their anions on
the supporting oxides and hydroxides) split alkenes efficiently
so as to give complete double-bond cleavage (Scheme 1). Any
Oxidative cleavage of alkenes to ketones, aldehydes or
carboxylic acids is useful synthetically. Reagents for effecting
this reaction include ozone and lead tetraacetate, although the
latter often gives only small yields of cleavage products.1
Alkenes are often cleaved indirectly through intentional or
incidental prior formation of 1,2-diols, followed by further
oxidation. There are many reagents for effecting this last
cleavage, as with sodium bismuthate, osmium tetroxide,
chromium compounds, permanganates and ruthenium oxides.1
All of these reactions are carried out in homogeneous solution
and are generally stoichiometric, or they use expensive oxidants
to recycle precious metal catalysts. Here, oxidative cleavage of
alkenes has been attained through the use of heterogeneous
calcined heteropolyacid catalysts supported on zinc, magne-
sium or aluminium oxide, with hydrogen peroxide as a cheap,
environmentally benign oxidant.
Heteropolyacids are easy to prepare from readily available
tungstates, molybdates and phosphates and are soluble in
organic solvents.2 Those based on molybdenum and/or tungsten
have been used as catalysts for effecting epoxidation of alkenes3
and for ring-opening of epoxides.4 Small yields (5–7%) of
adipic acid have been reported during homogeneous conversion
of cyclohexene to its trans-1,2-diol.3a Similar homogeneous
oxidation of cyclopentene gave a fair to modest yield of
glutaraldehyde.3c In homogeneous two-phase transfer systems,
12-tungstophosphoric acid and hydrogen peroxide have been
reported to give epoxides and 1,2-diols from alkenes. On
extended reaction, some complete cleavage of alkene was
observed.3b
In the present work, 12-molybdophosphoric (PMA), 12-tung-
stophosphoric (PWA) or 6-molybdo-6-tungstophosphoric acid
(PMWA) were deposited onto aluminium, zinc or magnesium
oxide or hydroxide and then calcined to give heterogeneous
catalysts. The alkenes shown in Table 1 were oxidatively
cleaved to give acids, ketones or keto acids in high yields. In the
presence of aqueous hydrogen peroxide and 2-methylpropan-
2-ol as solvent, these catalysts gave very poor and often only
fleeting yields of epoxides and 1,2-diols, unlike analogous
oxidations reported for homogeneous heteropolyacid systems,
from which high yields of epoxide can be obtained.3 As
revealed by gas chromatographic monitoring of the reactions,
the initial alkene disappeared completely from the reaction
medium, but final percentage yields of oxidation products such
as epoxides and 1,2-diols did not remotely match the percentage
disappearance of starting material. Although the formation of
1,2-diols suggested that epoxides were being formed and were
then being ring-opened solvolytically, no significant amounts of
1,2-diols were found at the end of reaction when all the alkene
had disappeared. However, when MeOH was used as solvent,
considerable quantities of 1-hydroxy-2-methoxy derivatives
were found; such solvolysis products are typical of ring-opening
of epoxides by nucleophilic solvents. Unlike the 1,2-diols, the
1-hydroxy-2-alkoxy compounds appear to be stable towards
cleavage under the present reaction conditions and can form
Table 1 Oxidative cleavage of alkenes with supported heteropolyacids and
hydrogen peroxide
Alkene
Heteropolyacida
t/hb Product (% yield)
2,3-Dimethyl-2- PMWA:Mg:C:150/0.5
butene
8
acetonec (91)
Cyclohexene
PMA:Al:C:150/0.5
24
24
adipic acidd (90)
6-ketoheptanoic acidd
(96)
1-Methylcyclo- PWA:Al:C:150/0.5
hexene
Oct-1-ene
Cyclooctene
Styrene
trans-Stilbene
trans-Stilbene
PMWA:Mg:C:150/0.5
PMWA:Al:A:150/0.5
PWA:Al:C:500/4
PWA:Al:C:500/4
PWA:Al:C:500/4
b
4
10
24
24
24
heptanoic acidd (100)
epoxidee
benzoic acid (90)
benzoic acid (92)
f
a
See text for code.
All reactions were carried out at 60 °C in
c
2-methylpropan-2-ol as solvent, except for entry f.
Isolated as its
d
2,4-dinitrophenylhydrazone. Isolated and identified by comparison with
1
e
authentic material for mp, H NMR and mass spectrum. The epoxide of
cyclooctanone is well-known for its resistance to nucleophilic attack. In this
instance, after about 50% conversion of alkene, its epoxide was isolated in
f
30% yield along with some suberic acid (7% yield). This example is
included to show the effect of MeOH as solvent. The bulk of the product
consisted of equal amounts of the enantiomeric pair of 1-hydroxy-
2-methoxy-1,2-diphenylethanes, together with surprisingly only a little of
the meso derivative.
OH
R2
R1
H
R2
R3
R1
H
R2
R3
R2
H2O
O
H2O2
R3
catalyst
H
OH
H2O2
catalyst
R1
HO
R2
R3
R1
R2
R3
H2O2
O
+
O
O
+
O
H
Scheme 1
Chem. Commun., 1999, 37–38
37