C O MMU N I C A T I O N S
zeolite
Table 1. Intrazeolite Photooxidation of 1
To effectively suppress the influence of the solvent, kq
slurrya
% conversionc
b
MBc
d
should be approximately 4 times as large as k for hexane (i.e., 4
hν (min)
A/B ratio
4
-1
×
[3.2 × 10 s ]; see Supporting Information). This corresponds
hexane
10
15
14
19
35
30
43
62
81
83/17
98/2
97/3
92/8
93/7
98/2
97/3
95/5
91
97
94
96
88
78
83
82
1
2
3
7
0
0
0
to a zeolite-leveled upper limit for the lifetime of O
2
of 7.5 µs.
1
2
This is slightly less than twice the lifetime of O in water (4.2
µs).16 Using the Einstein equation (〈x 〉 ) 6Dt; where 〈x 〉 is the
mean square molecular displacement) and a very conservative
estimate of the diffusion coefficient, D, for migration of oxygen,
one can calculate that O
2
its lifetime. This implies that O can sample many of more than
2
2
perfluorohexane
10
17
2
3
7
0
0
0
18
1
2
can migrate approximately 370 Å within
1
a
[
1] ) 0.04 M in slurry so that 〈S〉 ) 1.0 in perfluorohexane and
approximately 0.5 in hexane. See Scheme 1 for the structures of A and
B. Mass balance reproducible to (7-8%.
b
5000 zeolite supercages surrounding the locus of its generation.
c
The absence of a dramatic solvent effect on the regiochemistries
1
of the intrazeolite O
2
ene reactions is consistent with the very minor
concentration in both reactions (vide supra), these results indicate
that the reaction rates are approximately the same in hexane and
perfluorohexane slurries. This is a remarkable outcome given the
solvent effect observed in homogeneous media.3
We anticipate that this new synthetic protocol for zeolite
photooxidations will greatly extend the synthetic potential of
intrazeolite photooxidations especially for substrates with low
affinity for the interior of the zeolite. Preparative scale (500 mg)
photooxidations (see Supporting Information) have now been
conducted. In addition, higher intrazeolite concentrations of the
1
fact that the lifetime, τ
∆
, of O
2
is more than 2000 times longer in
perfluorohexane (6.8 × 10 s)10 than in hexane (3.1 × 10 s).
-
2
-5
11
A control reaction in solution verifies that the % conversion is
enhanced in perfluorohexane in comparison to hexane to an extent
consistent with the lifetime difference (see Supporting Information).
4
substrate will inhibit competitive overphotooxidations, and both
The rate of alkene consumption is given by eq 1 and depends
on the concentrations of both the alkene and the
the zeolite and the perfluorohexane can be recycled with little loss
of activity.
1
2
O . The
concentration of the alkene in the interior of the zeolite at a loading
level of 〈S〉 ) 1.0 (one molecule per supercage or eight molecules
per unit cell) can be estimated from the volume of the unit cell
Acknowledgment. We thank the National Science Foundation
and the Italian MIUR for their generous support of this research.
4
3 12
(
1.5 × 10 Å ) as 0.9 M. Under the constant irradiation conditions
Supporting Information Available: A plot of % 1 in the zeolite
1
utilized in these photooxidations, O
2
reaches and maintains a
as a function of equilibration time in hexane and perfluorohexane,
zeolite
q
steady-state concentration given by eq 2. In this equation, κ is the
estimation of k
, and full experimental details (PDF). This material
1
is available free of charge via the Internet at http://pubs.acs.org.
rate of O
removal, k
2
formation, and k
T
is the rate constant for alkene-induced
is the rate constant for solvent-induced removal, and
d
zeolite
1
References
k
q
is the rate constant for zeolite-induced removal of O
solution. Solving for [ O
2
from
(1)
1
2
] and insertion into eq 1 gives eq 3.
(
(
1) Li, X.; Ramamurthy, V. J. Am. Chem. Soc. 1996, 118, 10666-10667.
2) For other examples, see: (a) Robbins, R. J.; Ramamurthy, V. J. Chem.
Soc., Chem. Commun. 1997, 1071-1072. (b) Ramamurthy, V.; Laksh-
minarasimhan, P.; Grey, C. P.; Johnston, L. J. J. Chem. Soc., Chem.
Commun. 1998, 2411-2424. (c) Clennan, E. L.; Sram, J. P. Tetrahedron
d[alkene]
1
-
) k [alkene][ O ]
T
2
dt
2
000, 56, 6945-6950. (d) Stratakis, M.; Froudakis, G. Org. Lett. 2000,
2
, 1369-1372. (e) Clennan, E. L.; Sram, J. P. Tetrahedron 2000, 56,
1
d[ O ]
6945-6950. (f) Clennan, E. L.; Sram, J. P.; Pace, A.; Vincer, K.; White,
2
1
1
zeolite 1
)
0 ) κ - k [alkene][ O ] - k [ O ] - k
[ O2]
S. J. Org. Chem. 2002, 67, 3975-3978.
T
2
d
2
q
dt
(3) Clennan, E. L. Tetrahedron 2000, 56, 9151-9179.
(
(
(
4) Shailaja, J.; Sivaguru, J.; Robbins, R. J.; Ramamurthy, V.; Sunoj, R. B.;
(2)
Chandrasekhar, J. Tetrahedron 2000, 56, 6927-6943.
5) Lakshminarasimhan, P.; Thomas, K. J.; Johnston, L. J.; Ramamurthy, V.
Langmuir 2000, 16, 9360-9367.
6) Wilson, S. R.; Yurchendo, M. E.; Schuster, D. I.; Yurchendo, E. N.;
Sokolova, O.; Braslavsky, S. E.; Klihm, G. J. Am. Chem. Soc. 2002, 124,
d[alkene]
κk
T
[alkene]
-
)
(3)
zeolite
dt
k [alkene] + k + k
q
T
d
1977-1981.
(7) (a) Horv a´ th, I. T.; R a´ bath, J. Science 1994, 266, 72-75. (b) Horv a´ th, I.
It is tempting to suggest that the high concentration of the alkene
in the interior of the zeolite quantitatively traps all of the O
T. Acc. Chem. Res. 1998, 31, 641-650.
1
(8) Lim, K. H.; Grey, C. P. J. Chem. Soc., Chem. Commun. 1998, 2257-
2
such
1
zeolite
2258.
that k
T
[alkene] . (k
d
+ kq ). Consequently, the lifetime of O
) would have no influence on the rate of product
2
(
9) (a) Staley, R. H.; Beauchamp, J. L. J. Am. Chem. Soc. 1975, 97, 5920-
(τ
∆
) 1/k
d
5921. (b) Caldwell, J. W.; Kollman, P. A. J. Am. Chem. Soc. 1995, 117,
4177-4178.
formation. If this scenario is correct, the rate of alkene consumption
should also be independent of the concentration of the alkene (eq
). However, examination of Table 1 shows that doubling the
intrazeolite concentration of 1 by changing the slurry solvent from
(
10) Schmidt, R.; Afshari, E. Ber. Bunsen-Ges. Phys. Chem. 1992, 96, 788-
94.
(11) Rodgers, M. A. J. J. Am. Chem. Soc. 1983, 105, 6201-6205.
7
3
(
12) Cozens, F. L.; O’Neill, M.; Schepp, N. P. J. Am. Chem. Soc. 1997, 119,
583-7584.
13) Calculated using the k
7
hexane to perfluorohexane nearly doubles the % conversion. In
(
T
value for (E)-2-methyl-2-butenoic acid: Vever-
3
-1 13
Bizet, C.; Dellinger, M.; Brault, D.; Rlougee, M.; Bensasson, R. V.
Photochem. Photobiol. 1989, 50, 321-325.
addition, comparing k
T
[4] (6.1 × 10 s
)
d
to k for hexane (3.2
4
-1
1
-1
×
10 s ) and perfluorohexane (1.47 × 10 s ) demonstrates that
(
14) Wilkinson, F.; Helman, W. P.; Ross, A. B. J. Phys. Chem. Ref. Data 1995,
zeolite
q
k
T
[alkene] cannot be greater than (k
d
+ k
), at least in hexane.
24, 663-1021.
zeolite
(15) Foote, C. S. In Singlet Oxygen; Wasserman, H. H., Murray, R. W., Eds.;
Academic Press: New York, 1979; Vol. 40, Chapter 5, pp 139-171.
As an alternative explanation, we suggest that kq
which would also have the effect of removing any influence of the
identity of the slurry solvent on the reaction rate. We believe that
the framework aluminum tetrahedra, AlO
d
> k ,
(
16) Schmidt, R.; Afshari, E. Ber. Bunsen-Ges. Phys. Chem. 1992, 96, 8-794.
(17) Ellison, E. H.; Thomas, J. K. Langmuir 2001, 17, 2446-2454.
-
7 2
-1
-
(18) D(O
2
) ) 3 × 10 cm s is approximately 2 orders of magnitude smaller
4
, are responsible for the
than that in water. See ref 17 for a discussion of the ability of zeolites to
inhibit diffusion. Grossweiner, L. I. Photochem. Photobiol. 1977, 26,
309-311.
zeolite
q
-1
1
-
deactivation, k
, of O
2
. Other anions such as azide (N
CN) are known to be potent charge-
3
, k
q
)
.8 × 10 M s-1 in CH
9
14
4
3
15
1
transfer quenchers of O
2
.
JA027053W
J. AM. CHEM. SOC.
9
VOL. 124, NO. 38, 2002 11237