PhCHO + Mn(III)
PhCO• + O2
PhCO• + H+ + Mn(II)
PhCOOO•
PhCOOOH + PhCO•
2PhCOOH
C6H10O + PhCOO•
C6H10O + PhCOOH
PhCOOH + PhCO•
PhCOO• + OH– + Mn(III)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
into the reactor no epoxidation ensues under the conditions
given in Table 1.
We thank the EPSRC, UK for financial support (rolling grant
to J. M. T.), the Royal Commission for the Exhibition of 1851
for a Research Fellowship to R. R., and Professors J. M. van
Hooff and R. A. van Santen for sending us a copy of
H. F. W. J. van Breukelen’s Eindhoven thesis, 1998.
PhCOOO• + PhCHO
PhCOOOH + PhCHO
PhCOOO• + C6H10
PhCOOOH + C6H10
PhCOO• + PhCHO
PhCOOOH + Mn(II)
Scheme 1
Notes and references
1 C. Bolm, G. Schlingloff and K. Weickhardt, Angew. Chem., Int. Ed.
Engl., 1994, 33, 1848.
2 T. Yamada, T. Takai, O. Rhode and T. Mukaiyama, Chem. Lett., 1991,
1.
3 R. Raja and J. M. Thomas, Chem. Commun., 1998, 1841.
4 G. Sankar, R. Raja and J. M. Thomas, Catal. Lett.,1998, 55, 15.
5 R. Raja, J. M. Thomas and G. Sankar, Chem. Commun., 1999, 525.
6 P. A. Wright, S. Natarajan, J. M. Thomas, R. G. Bell, P. L. Gai-Boyes,
R. H. Jones and J. Chen, Angew. Chem., Int. Ed. Engl., 1992, 31,
1472.
7 P. A. Barrett, G. Sankar, C. R. A. Catlow and J. M. Thomas, J. Phys.
Chem., 1996, 100, 8977.
8 J. M. Thomas, R. Raja, G. Sankar and R. G. Bell, Nature, 1999, 398,
227.
9 B. Kraushaar-Czarnetzki, W. G. M. Hoogeroorst, R. R. Andrea, C. A.
Ameis and W. H. J. Stork, J. Chem. Soc., Faraday Trans., 1991, 87,
891.
10 L. E. Iton, I. Choi, J. A. Desjardins and V. A. Moroni, Zeolites, 1989, 9,
535.
11 H. F. W. J. van Breukelen, M. E. Gerritsen, V. M. Ummels, J. S. Broens
and J. H. C. van Hooff, Stud. Surf. Sci. Catal., 1996, 105, 1029.
12 M. P. J. Peeters, M. Basio and P. Leijten, Appl. Catal. A: Gen., 1994,
118, 51.
13 T. C. Chou and C. C. Lee, Ind. Eng. Chem., Fundam., 1985, 24, 32.
14 S. A. Maslov and E. A. Blyumberg, Russ. Chem. Rev., 1976, 45, 155.
15 G. Sankar, F. Rey, J. M. Thomas, G. N. Greaves, A. Corma, B. R.
Dobson and A. J. Dent, J. Chem. Soc., Chem. Commun., 1994, 2279.
16 R. D. Oldroyd, J. M. Thomas, T. Maschmeyer, P. A. MacFaul, D. W.
Snelgrove, K. U. Ingold and D. D. M. Wayner, Angew. Chem., Int. Ed.
Engl., 1996, 35, 2787.
means of initiating the free-radical reactions leading to
epoxidation.
Benzaldehyde molecules may freely enter the large (ca. 650
m2 g21) internal surfaces of both MAlPO-36 and MAlPO-5
catalysts, thereby generating11,13 first PhCO· and then the
PhCOOO· radicals which, from the sequence of steps shown in
Scheme 1, lead to the formation of benzoic acid and cyclohex-
ene oxide. In this sequence, reaction (5) is known14 to proceed
much faster than reaction (6). This free-radical based epoxida-
tion of cyclohexene (and the other alkenes listed in Table 1) is
mechanistically quite distinct from the radical-free epoxidation
of alkenes15–17 using alkyl hydroperoxides and titanosilicate
catalysts.
Other aldehydes may also be used as sacrificial oxidants
provided they are small enough to gain access to the active sites
situated at the inner surface of the molecular sieve catalyst.
Benzaldehyde is itself too large to enter Mn (or Co)-AlPO-18,
but hexanal is not. Although it diffuses less rapidly into the
MAlPO-18 structure than benzaldehyde does in AlPO-36, it
nevertheless functions efficiently in epoxidising hex-1-ene.
The experimental conditions chosen for this study—the
concentration of catalytically active redox ions at the inner
surface of the molecular sieve (arbitrarily set at 4 atom%), the
ratio of reactants, the amount of catalyst, temperature, pressure,
etc.—have not been optimised for maximal conversion and
selectivity. There is considerable scope for achieving improve-
ments in catalytic performance. Note also that under the
reaction conditions employed here, the framework-substituted
transition-metal-ions are not leached out during use. When the
solid catalyst is removed by filtration and the reactants returned
17 R. Murugavel and H. W. Roesky, Angew. Chem., Int. Ed. Engl., 1997,
36, 477.
Communication 9/01127G
830
Chem. Commun., 1999, 829–830