Highly efficient methyl ketone synthesis with photoactivated acetone and olefins assisted by Mg(II)-exchanged zeolite y

Article abstract of DOI:10.1021/jo902321f

(Figure Presented) We previously found that photoirradiation of an acetone/water mixture containing olefins affords the corresponding methyl ketones highly efficiently and selectively via a water-assisted C-C coupling between the acetonyl radical and olefins (Org. Lett. 2008, 10, 3117-3120). The reaction proceeds at room temperature without any additives and has a potential to be a powerful method for methyl ketone synthesis. Here we report that an addition of Mg²⁺-exchanged zeolite Y (MgY) to the above photoreaction system accelerates the methyl ketone formation, while maintaining high selectivity. Ab initio molecular orbital calculation reveals that the accelerated methyl ketone formation is due to the electrostatic interaction between Mg²⁺ and excited-state acetone. This leads to a charge polarization of the carbonyl moiety of excited-state acetone and accelerates the hydrogen abstraction from ground-state acetone (acetonyl radical formation). This promotes efficient addition of the acetonyl radical to olefins, resulting in methyl ketone formation enhancement. Adsorption experiments reveal that accumulation of olefins inside the zeolite pore also affects efficient radical addition to olefins. The present process successfully produces various methyl ketones with very high yield, and the MgY recovered can be reused for further reaction without loss of activity.

Full text of DOI:10.1021/jo902321f

pubs.acs.org/joc
Highly Efficient Methyl Ketone Synthesis with Photoactivated Acetone
and Olefins Assisted by Mg(II)-Exchanged Zeolite Y
Daijiro Tsukamoto, Yasuhiro Shiraishi,* and Takayuki Hirai
Research Center for Solar Energy Chemistry and Division of Chemical Engineering, Graduate School of
Engineering Science, Osaka University, Toyonaka 560-8531, Japan
shiraish@cheng.es.osaka-u.ac.jp
Received October 31, 2009
We previously found that photoirradiation of an acetone/water mixture containing olefins affords
the corresponding methyl ketones highly efficiently and selectively via a water-assisted C-C coupling
between the acetonyl radical and olefins (Org. Lett. 2008, 10, 3117-3120). The reaction proceeds at
room temperature without any additives and has a potential to be a powerful method for methyl
ketone synthesis. Here we report that an addition of Mg2þ-exchanged zeolite Y (MgY) to the above
photoreaction system accelerates the methyl ketone formation, while maintaining high selectivity. Ab
initio molecular orbital calculation reveals that the accelerated methyl ketone formation is due to the
electrostatic interaction between Mg2þ and excited-state acetone. This leads to a charge polarization
of the carbonyl moiety of excited-state acetone and accelerates the hydrogen abstraction from
ground-state acetone (acetonyl radical formation). This promotes efficient addition of the acetonyl
radical to olefins, resulting in methyl ketone formation enhancement. Adsorption experiments reveal
that accumulation of olefins inside the zeolite pore also affects efficient radical addition to olefins.
The present process successfully produces various methyl ketones with very high yield, and the MgY
recovered can be reused for further reaction without loss of activity.
1. Introduction
molecular oxygen,2 but these processes require noble metal
catalysts. Other ketone synthesis methods, such as Wacker
oxidation3 and Suzuki-Miyaura cross-coupling,4 also
require Pd-based catalysts. Development of new ketone
synthesis methods with inexpensive reactants and catalysts
is therefore currently in focus.
Ketone is one of the most important chemicals in the
synthesis of natural products and pharmaceutical materials.
Traditional alcohol oxidation processes require stoichio-
metric amounts of inorganic oxidants with concomitant
formation of copious heavy-metal waste.1 Recent advances
in oxidation catalysts allow clean alcohol oxidation with
Earlier, we proposed a photochemical process for methyl
ketone synthesis with acetone and olefins as reactants.5
*To whom correspondence should be addressed. Fax: þ81-6-6850-6273.
Tel: þ81-6-6850-6271.
(3) (a) Cornell, C. N.; Sigman, M. S. Inorg. Chem. 2007, 46, 1903–1909.
(b) Cornell, C. N.; Sigman, M. S. J. Am. Chem. Soc. 2005, 127, 2796–2797. (c)
Mitsudome, T.; Umetani, T.; Nosaka, N.; Mori, K.; Mizugaki, T.; Ebitani,
K.; Kaneda, K. Angew. Chem., Int. Ed. 2006, 45, 481–485. (d) ten Brink,
G.-J.; Arends, I. W. C. E.; Papadogianakis, G.; Sheldon, R. A. Chem.
Commun. 1998, 2359–2360.
(4) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
(5) Shiraishi, Y.; Tsukamoto, D.; Hirai, T. Org. Lett. 2008, 10, 3117–
3120.
(1) (a) Cainelli, G.; Cardillo, G. Chromium Oxidants in Organic Chemistry;
Springer: Berlin, Germany, 1984. (b) Ley, S. V.; Madin, A. In Comprehensive
Organic Synthesis; Trost, B. M., Fleming, I., Ley, S. V., Eds.; Pergamon: Oxford,
UK, 1991; Vol. 7, p 251.
(2) (a) ten Brink, G.-J.; Arends, I. W. C. E.; Sheldon, R. A. Science 2000,
287, 1636–1639. (b) Graves, C. R.; Zeng, B.-S.; Nguyen, S. T. J. Am. Chem.
Soc. 2006, 128, 12596–12597. (c) Schultz, M. J.; Park, C. C.; Sigman, M. S.
Chem. Commun. 2002, 3034–3035.
1450 J. Org. Chem. 2010, 75, 1450–1457
Published on Web 02/09/2010
DOI: 10.1021/jo902321f
r
2010 American Chemical Society

Tsukamoto et al.
JOCArticle
SCHEME 1. Mechanism of Methyl Ketone Formation with
Photoactivated Acetone and Olefin
enhancement of the radical I formation (enhancement of
H-abstraction by excited-state acetone from ground-state
acetone) is therefore one of the possible ways to accelerate
the methyl ketone formation. There are, however, only a few
reports of acceleration of intermolecular H-abstraction by
excited-state carbonyl compounds.8 Dedinas et al.8a and
Boate et al.8b reported that H-abstraction by the lowest triplet
excited-state (T1) decafluorobenzophenone from 2-propanol
or cyclohexane occurs much faster than that by unmodified
benzophenone. This is due to the enhanced charge polariza-
tion of the T1 carbonyl group upon fluorine substitution. This
implies that enhancement of charge polarization of excited-
state acetone is oneof the ways to accelerate the H-abstraction
from ground-state acetone, although no specific method to
promote charge polarization of excited-state carbonyl com-
pounds has been reported until now.
A few pieces of literature reported the interaction between
carbonyl compounds and metal cations. Ramamurthy and
Turro9 reported that ground-state carbonyl compounds
interact with alkali metal cations within zeolite Y (cation-
carbonyl interaction). This electrostatic interaction leads to
an increase in the electron density of the carbonyl oxygen,
resulting in a charge polarization of the carbonyl group.10
Shailaja et al.11 also studied the effect of alkali cations on the
properties of excited-state acetophenone and clarified that
T1 acetophenone shows a ππ* character within Naþ-ex-
changed zeolite Y, while showing an nπ* character in a bulk
nonpolar solvent. Computational study revealed that this is
due to the stabilized carbonyl n orbital of the T1 acetophe-
none by a cation-carbonyl interaction. These findings imply
that excited-state acetone, if interacted with metal cations
electrostatically, may lead to a charge polarization of the
carbonyl group. This may accelerate the H-abstraction from
ground-state acetone and enable efficient production of
radical I.
In the present work, effects of metal cations on the
photochemical methyl ketone production have been studied.
We found that addition of Mg2þ-exchanged zeolite Y (MgY)
successfully enhances the methyl ketone production, while
maintaining high selectivity. Ab initio molecular orbital
calculation revealed that, as we expected, the enhanced
methyl ketone formation is due to the electrostatic inter-
action between Mg2þ and excited-state acetone within the
zeolite pore. We also describe here that accumulation of
olefins inside the zeolite pore is also an important factor for
efficient methyl ketone formation.
Photoirradiation (300-340 nm) of an acetone/water (6/4
v/v) mixture containing olefins at room temperature affords
the corresponding methyl ketones highly selectively. The
reaction proceeds via the following mechanism, as summar-
ized in Scheme 1. The reaction is initiated by photoexcitation
of acetone. The excited-state acetone promotes an intermo-
lecular hydrogen abstraction (H-abstraction) from ground-
state acetone and produces an acetonyl (I) and 2-hydroxy-
2-propyl radical (II) pair.6 Most of these radical pairs under-
go fast recombination (deactivation to ground-state ace-
tones) or dimerization (formation of acetone dimers).6,7
The methyl ketone is produced by an addition of radial I
to olefin followed by H-abstraction from ground-state ace-
tone. In contrast, radical II reacts with olefin and produces
olefin-derived byproducts. Addition of 40% water to this
system, however, suppresses the formation of acetone dimers
and olefin-derived byproducts. The water addition leads to a
hydration of the respective radicals (I and II) and suppresses
their dimerization. In that, the radical II is strongly hydrated
and thus suppresses the formation of olefin-derived by-
products. These water effects therefore enable selective
methyl ketone formation. The photoprocess exhibits signifi-
cant advantages: (i) noble metal-free, (ii) cheap reactant
(acetone), (iii) mild reaction condition (room temperature).
This process, therefore, has a potential to be one of the
powerful methods for methyl ketone synthesis.
2. Results and Discussion
2.1. Effects of Cation-Exchanged Zeolite Y. The effect of
alkali and alkaline earth metal cation-exchanged zeolite Y on
the methyl ketone formation was studied with 1-hexene (1) as
The purpose of the present work is the acceleration of
methyl ketone production in the above photoprocess. As
shown in Scheme 1, the methyl ketone forms via the addition
of radical I to olefins, where radical I is produced via the
intermolecular H-abstraction from ground-state acetone by
excited-state acetone. Radical I is, however, more or less
deactivated by the recombination of radical pairs.6,7 The
(8) (a) Dedinas, J.; Regan, T. H. J. Phys. Chem. 1972, 76, 3926–3933. (b)
Boate, D. R.; Johnston, L. J.; Scaiano, J. C. Can. J. Chem. 1989, 67, 927–932.
(c) Shoute, L. C. T.; Mittal, J. P. J. Phys. Chem. 1993, 97, 8630–8637.
(9) (a) Ramamurthy, V.; Turro, N. J. J. Inclusion Phenom. 1995, 21, 239–282.
(10) (a) Del Bene, J. E. Chem. Phys. 1979, 40, 329–335. (b) Raber, D. J.;
Raber, N. K.; Chandrasekhar, J.; Schleyer, P. v. R. Inorg. Chem. 1984, 23, 4076–
4080. (c) Guo, B. C.; Conklin, B. J.; Castleman, A. W., Jr. J. Am. Chem. Soc.
1989, 111, 6506–6510. (d) Remko, M. Mol. Phys. 1997, 91, 929–936.
(11) (a) Shailaja, J.; Lakshminarasimhan, P. H.; Pradhan, A. R.; Sunoj,
R. B.; Jockusch, S.; Karthikeyan, S.; Uppili, S.; Chandrasekhar, J.; Turro,
N. J.; Ramamurthy, V. J. Phys. Chem. A 2003, 107, 3187–3198. (b)
Ramamurthy, V.; Shailaja, J.; Kaanumalle, L. S.; Sunoj, R. B.; Chandrasekhar,
J. Chem. Commun. 2003, 1987–1999.
(6) Nakashima, M.; Hayon, E. J. Phys. Chem. 1971, 75, 1910–1914.
(7) (a) Shimizu, N.; Miyahara, T.; Mishima, M.; Tsuno, Y. Bull. Chem.
Soc. Jpn. 1989, 62, 2032–2039. (b) Przybytek, J. T.; Singh, S. P.; Kagan, J.
J. Chem. Soc., Chem. Commun. 1969, 1224–1225.
J. Org. Chem. Vol. 75, No. 5, 2010 1451

Tsukamoto et al.
JOCArticle
TABLE 1. Results of the Photoreaction of 1 in an Acetone/Water
Mixture with Various Additivesa
entry
additive
LiY
NaY
KY
RbY
CsY
conversion of 1 (%)
GC yield of 10 (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
67
97
93
95
92
90
>99
96
98
90
80
99
99
99
98
47b
69
65
67
65
63
80c
74
71
69
56d
57
48
59
59
MgY
CaY
SrY
BaY
HY
MgMORe
MgZSM-5f
MgCl2
g
FIGURE 1. Optimized geometry of (a) S0 acetone Mg2þ, (b) T1
2þ 3 3 3
g
acetone Mg2þ, and (c) S0 1-hexene (1) Mg systems.
Mg(NO3)2
3 3 3
3 3 3
aReaction conditions: acetone/water (6/4 v/v) mixture (10 mL), 1 (0.2
mmol), cation-exchanged zeolite Y (5 mg, containing ca. 2.6 μmol alkali
or alkaline earth cation), nitrogen (1 atm), λ > 300 nm, photoirradiation
time (6 h). bMass balance was 81%, where 2-octanone (yield: 1.0%) and
2-methyl-2-octanol (0.5%) were produced as minor products. cMass
balance was 82%, where 2-octanone (1.2%) and 2-methyl-2-octanol
(0.7%) were also produced. dMass balance was 78%, where 2-octanone
(0.9%) and 2-methyl-2-octanol (0.6%) were also produced. e5 mg
conversion of 1 and the 10 yield (see footnote of Table 1). This
suggests that nonvolatile or thermally degradable com-
pounds such as carboxylic acids are the main byproducts.
However, it must be noted that the product methyl ketone
(10) is not decomposed by prolonged photoirradiation. This
indicates that the byproducts are not derived from the
product methyl ketone.
(containing 1.6 μmol Mg2þ) was used. f5 mg (containing 1.0 μmol Mg2þ
was used. g26 μmol of Mg salts was used.
)
2.2. Electrostatic Interaction between Excited-State Ace-
tone and Cations. As reported,8 the H-abstraction by T1
decafluorobenzophenone from alcohols and alkanes occurs
faster than that by T1 benzophenone because the fluorine
substitution promotes charge polarization of the carbonyl
group. It is also reported that ground-state carbonyl com-
pounds interact with alkali metal cations within zeolite Y
and this electrostatic cation-carbonyl interaction promotes
a charge polarization of the carbonyl group.9,10 These results
imply that, in the present photoprocess, excited-state acetone
may interact with metal cations and promote charge polar-
ization of the acetone carbonyl. This probably accelerates
the H-abstraction from ground-state acetone (efficient pro-
duction of radical I) and accelerates the methyl ketone
formation (Table 1). To confirm this assumption, ab initio
molecular orbital calculation was performed with the Gauss-
ian 03 programs.12 A simple modeling system consisting of a
free metal cation and S0 or T1 acetone (Figure 1a,b)13 was
a substrate. Table 1 (entries 2-10) summarizes the yields of
2-nonanone (10) obtained by photoirradiation (Xe lamp, λ >
300 nm, 6 h) of an acetone/water mixture (6/4 v/v, 10 mL)
containing 1 (20 mM) under nitrogen atmosphere with
various cation-exchanged zeolite Y (5 mg). In that, the
amount of alkali or alkaline earth cation on zeolite Y is ca.
5.2 ꢀ 10-4 mol g-1. Without zeolite (entry 1), the yield of 10 is
47%. Addition of alkali or alkaline earth metal cation-
exchanged zeolite Y (entries 2-10) leads to an increase in
the 10 yield (>63%). Among them, alkaline earth cations,
especially lighter cations, show higher activity, where Mg2þ
-
exchanged zeolite Y (MgY) shows the highest 10 yield (80%,
entry 7). As shown in entry 11, Hþ-exchanged zeolite Y (HY)
shows low 10 yield (56%), indicating that the 10 production
enhanced by alkali and alkaline earth cation-exchanged
zeolite Y is mainly due to their cations. The zeolite Y frame-
work is also important for efficient methyl ketone produc-
tion. As shown in entries 12 and 13, the 10 yields obtained
with Mg2þ-exchanged Mordenite (MgMOR, 57%) and
ZSM-5 (MgZSM-5, 48%) are much lower than that obtained
with MgY (80%). In addition, as shown in entries 14 and 15,
the use of homogeneous Mg salts such as MgCl2 and Mg-
(NO3)2 also shows low 10 yields (59%). These results suggest
that both Mg2þ and zeolite Y framework are necessary for
efficient methyl ketone production.
(12) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant,
J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi,
M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma,
K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford,
S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; and Pople, J. A. Gaussian 03, Revision B.05; Gaussian, Inc.,
Wallingford, CT, 2004. (b) Dennington, R., II; Keith, T.; Millam, J.; Eppinnett,
K.; Hovell, W. L.; Gilliland, R. GaussView, Version 3.09; Semichem, Inc.,
Shawnee Mission, KS, 2003.
As shown in Table 1, the 10 yields are lower than the
conversion of 1, indicating that byproducts are produced
during reaction. This is because, as shown in Scheme 1,
several side reactions occur. GC-MS analysis detected some
of the byproducts, such as 2-methyl-2-octanol and 2-octa-
none. The yields of these compounds are, however, much
lower than those expected from the difference between the
(13) Sunoj, R. B.; Lakshminarasimhan, P.; Ramamurthy, V.; Chandrasekhar,
J. J. Comput. Chem. 2001, 22, 1598–1604.
1452 J. Org. Chem. Vol. 75, No. 5, 2010

Tsukamoto et al.
JOCArticle
TABLE 2. Calculated Binding Affinities (ΔE) and Distances between Metal Cations and S0 Acetone, T1 Acetone, or S0 1-Hexene (1) a
S0 acetone
T1 acetone
S0 1-hexene (1)
b
c
b
c
d
ΔE (kcal mol-1
)
ΔE (kcal mol-1
)
ΔE (kcal mol-1 b
)
˚
distance (A)
˚
distance (A)
˚
distance (A)
cations
Mg2þ
Ca2þ
Sr2þ
Ba2þ
Liþ
118.9
80.8
66.4
56.9
48.8
35.1
25.5
21.0
18.2
1.84
2.21
2.42
2.62
1.79
2.18
2.55
2.83
3.06
75.5
38.1
23.8
32.1
29.5
20.5
14.2
11.3
9.6
1.88
2.21
2.40
2.74
1.90
2.30
2.66
2.96
3.11
87.7
46.1
32.8
25.5
23.8
16.4
9.0
2.19
2.66
2.95
3.19
2.21
2.63
3.07
3.47
3.74
Naþ
Kþ
Rbþ
Csþ
6.5
5.1
aCalculations were performed at the MP2/6-31þG(d) level for H, C, O, Li, Na, K, Mg, and Ca and at the MP2/LAVCP* level for Rb, Cs, Sr, and Ba.
bΔE = E(molecule Mnþ) - (E(molecule) þ E(Mnþ)), where E denotes the SCF energies. cThe core-core distance between metal cation and carbonyl
3 3 3
oxygen. dThe distance between the metal cation and the CdC bond of 1. Cartesian coordinates of the respective systems and the data for
E(molecule Mnþ) are summarized in the Supporting Information.
3 3 3
employed for the calculation. Table 2 summarizes the bind-
ing affinities between cations and S0 or T1 acetone, calculated
based on the second order Moller-Plesset (MP2) theory.14
The binding affinities for both S0 and T1 acetones increase
with cations in the following order: Mg2þ > Ca2þ > Sr2þ
>
Ba2þ > Liþ > Naþ > Kþ > Rbþ > Csþ. This indicates that
both S0 and T1 acetones strongly associate with alkaline
earth cations, especially lighter cations, with the strongest
affinity with Mg2þ. This trend is consistent with the trend of
10 yield (Table 1) obtained by reaction with various cation-
exchanged zeolite Y (Mg2þ > Ca2þ > Sr2þ > Ba2þ ≈ Liþ >
Kþ > Naþ ≈ Rbþ > Csþ). These data indicate that the
electrostatic affinity between the ground- or excited-state
acetone and metal cations is closely related to the efficiency
of methyl ketone formation.
Figure 2 summarizes the electron densities of carbonyl
carbon and oxygen atoms of T1 acetone, when interacted
with the respective cations. Upon interaction with cations,
the electron densities of carbonyl carbon decrease, while
those of carbonyl oxygen increase. This indicates that elec-
trostatic interaction with cations indeed leads to a charge
polarization of the T1 acetone carbonyl. The difference
between the electron densities of carbonyl carbon and oxy-
gen of T1 acetone becomes more apparent when interacted
with alkaline earth cations, especially Mg2þ, in the order of
FIGURE 2. Calculated electron densities of carbonyl carbon and
oxygen atoms of T1 acetone, when interacted with alkali or alkaline
earth cations. The electron densities of S0 acetone when interacted
with cations are shown in Figure S1 (Supporting Information). The
detailed calculation data are summarized in Table S1 (Supporting
Information).
Mg2þ > Ca2þ > Sr2þ > Ba2þ > Liþ > Naþ ≈ Kþ
>
Rbþ > Csþ. This trend is almost consistent with the trend
of 10 yield (Table 1). As reported,8 charge polarization of
T1 carbonyl compounds accelerates the intermolecular
H-abstraction. The above calculation results clearly indicate
that the electrostatic interaction between Mg2þ and excited-
state acetone enhances the charge polarization of acetone
carbonyl and, hence, accelerates the H-abstraction from
ground-state acetone. This therefore promotes efficient
radical I formation and enhances the methyl ketone forma-
tion. As reported,11 hydrated zeolite makes the interaction of
the cations with guest molecules ineffective. However, the
experimental results (Table 1) and the calculation results
(Figure 2) indicate that, in the present process, the acetone
molecules indeed interact with Mg2þ within zeolite even in
the hydrated conditions.15
(14) (a) Head-Gordon, M.; Pople, J. A.; Frisch, M. J. Chem. Phys. Lett.
1988, 153, 503–506. (b) Frisch, M. J.; Head-Gordon, M.; Pople, J. A. Chem.
Phys. Lett. 1990, 166, 275–280. (c) Frisch, M. J.; Head-Gordon, M.; Pople,
J. A. Chem. Phys. Lett. 1990, 166, 281–290.
(15) Phosphorescence analysis usually provides important information
on the nature of the excited-state carbonyl compounds within zeolite (ref 11).
However, in the present case, the analysis does not provide clear information
on the nature of excited-state acetone within MgY in the absence and
presence of water. Figure S2 (Supporting Information) shows phosphores-
cence spectra of acetone measured at 77 K. In a diethyl ether/2-propanol
glass, a distinctive emission assigned to acetone phosphorescence appears at
455 nm: Borkman, R. F.; Kearns, D. R. J. Chem. Phys. 1966, 44, 945–949. In
contrast, acetone adsorbed on MgY shows a red-shifted emission at 493 nm.
As reported in the following, the red-shifted emission is assigned to the
phosphorescence of the protonated acetone formed by a reaction with acidic
hydroxyl groups on zeolite: Bosacek, V.; Kubelkova, L. Zeolites 1990, 10,
64–65. A similar emission red shift is observed on highly acidic HY. In
contrast, no emission red shift is observed on less acidic CsY: Okamoto, S.;
Nishiguchi, H.; Anpo, M. Chem. Lett. 1992, 1009–1012. These data support
the protonation of acetone within MgY. Addition of water to the MgY
sample leads to a blue shift of the emission (λmax = 467 nm). This is probably
because, as reported in the following, hydration of zeolite weakens its acidity
and suppresses the protonation of acetone: Ward, J. J. Phys. Chem. 1968, 72,
4211–4213. These indicate that the zeolite acidity strongly affects the acetone
phosphorescence. A clear explanation as to how the cation affects the nature
of the excited acetone within zeolite in the absence and presence of water,
therefore, cannot be made.
It is well-known that alkali and alkaline earth cations
interact with the π electron of olefins (cation-π interaction).11
Clark16 reported that efficient alkyl radical addition to ethy-
lene in the gas phase with Liþ-exchanged zeolite Y is due to
the cation-π interaction between Liþ and ethylene, which
decreases the activation energy of the radical addition. This
implies that, also in our photoprocess, the cation-π inter-
action between Mg2þ and olefins is likely to contribute to the
(16) (a) Clark, T. J. Chem. Soc., Chem. Commun. 1986, 1774–1776. (b)
Clark, T. J. Am. Chem. Soc. 2006, 128, 11278–11285.
J. Org. Chem. Vol. 75, No. 5, 2010 1453

Tsukamoto et al.
JOCArticle
TABLE 3. Cylindrical Dimensions of Olefins and Their Effect on the Methyl Ketone Formation Enhancement (YMgY/Ynone
)
aDetermined according to a literature procedure (ref 17). bThe ratio of methyl ketone yields obtained with and without MgY. cReaction conditions:
acetone/water (6/4 v/v) mixture (10 mL), olefin (0.2 mmol), MgY (5 mg), nitrogen (1 atm), λ > 300 nm, photoirradiation time (6 h). dPhotoirradiation
time (2 h) was employed because 6 h of irradiation converts almost all of 3 even without MgY. e0.05 mmol of olefin was used because of low solubility in
solution. The detailed results are summarized in Table S2 (Supporting Information).
methyl ketone formation enhancement. This possibility,
however, can be ruled out by the following results. Table 2
shows the binding affinities between cations and 1-hexene (1)
alkaline earth cations exist within the supercage of zeolite Y,11
meaning that the H-abstraction between excited- and ground-
state acetones occurs inside the zeolite pores and produces
radical I there. To clarify whether the addition of radical I to
olefins occurs inside the zeolite pore or not, the effect of the size
of olefins on the reaction was studied with various olefins (1-8).
Table 3 shows the size of these olefins determined in terms of a
minimum cylindrical dimension.17 The pore system of zeolite Y
calculated with use of an 1 free cation system (Figure 1c).
2þ3 3 3
The affinity of 1 with Mg (87.7 kcal mol-1) is comparable
to that of T1 acetone (75.5 kcal mol-1), but much lower than
that of S0 acetone (118.9 kcal mol-1). This indicates that
Mg2þ interacts with ground-state acetone more strongly
than 1. In addition, in the present photoprocess, a larger
number of acetone molecules exist as compared to 1, where
the ratio of acetone/1 is 410/1 (mol/mol). These data suggest
that, in the present photoprocess, electrostatic interaction
between cations and olefins is negligible. This therefore
leaves the electrostatic interaction between cation and
excited-state acetone and the corresponding H-abstraction
enhancement as the predominant factor for methyl ketone
formation enhancement.
˚
consists of a spherical supercage with a 13.4 A diameter,
11
connected through a window with a 7.6 A diameter. The
˚
˚
˚
length and width of 1-6 olefins are less than 8.9 A and 5.4 A,
respectively, which are smaller than the diameter of supercage
and window, respectively. This indicates that these olefins can
diffuse into the pore of zeolite Y. In contrast, the length of 7
˚
˚
(14.8 A) and the width of 8 (8.0 A) are larger than the diameter
of supercage and window, respectively, suggesting that these
olefins are difficult to diffuse inside the pore.
2.3. Role of the Zeolite Y Framework. As shown in Table 1,
MgMOR, MgZSM-5, and homogeneous Mg2þ salts are less
effective, indicating that the zeolite Y framework is also
important for efficient methyl ketone formation. Alkali or
(17) (a) Morkin, T. L.; Turro, N. J.; Kleinman, M. H.; Brindle, C. S.;
Kramer, W. H.; Gould, I. R. J. Am. Chem. Soc. 2003, 125, 14917–14924. (b)
Chen, Y.-Z.; Wu, L.-Z.; Zhang, L.-P.; Tung, C.-H. J. Org. Chem. 2005, 70,
4676–4681.
1454 J. Org. Chem. Vol. 75, No. 5, 2010

Tsukamoto et al.
JOCArticle
Table 3 shows the ratio of methyl ketone yields (YMgY
/
Ynone) obtained by photoreaction of respective olefins with
and without MgY. In the case of small olefins (1-6), the
YMgY/Ynone ratio is larger than 1, indicating that methyl
ketone formation is indeed enhanced with MgY. In contrast,
the ratio for large olefins (7 and 8) is almost 1, indicating that
MgY is ineffective for the reaction of these olefins. These
suggest that small olefins can diffuse inside the zeolite pores
and react efficiently with the radical I formed there, resulting
in efficient methyl ketone formation. In contrast, large
olefins are difficult to diffuse inside the pores and result in
almost no acceleration of methyl ketone formation. These
suggest that the uptake of olefins inside the MgY pores is an
important factor for reaction enhancement.
The importance of olefin uptake inside the zeolite pore is
further supported by adsorption experiments. This was
performed by stirring an acetone/water (6/4 v/v) mixture
containing the respective olefins with MgY at 298 K for 6 h.
The degree of olefin adsorption onto MgY was defined as a
distribution ratio, D,18 as follows:
FIGURE 3. Relationship between distribution ratio, D, and the
ratio of methyl ketone yields (YMgY/Ynone) obtained with and with-
out MgY for reaction of the respective olefins (1-8). The detailed D
data are summarized in Table S2 (Supporting Information).
SCHEME 2. Schematic Representation of the Mechanism of
Methyl Ketone Formation within MgY
D ¼ ðC0 -CeÞ=Ce
ð1Þ
where C0 is the initial concentration of olefin in the solution
and Ce is the equilibrium concentration of olefin in the
solution. Figure 3 shows the relationship between D and
the ratio of methyl ketone yield (YMgY/Ynone). The large size
7 and 8 olefins show low D (<0.10) and low YMgY/Ynone
(almost equal to 1) values. In contrast, the small size 1-6
olefins show high D (>0.68) and high YMgY/Ynone values.
These results indicate that the large olefins are difficult to
diffuse inside the zeolite pore and, hence, are less adsorbed
onto the internal zeolite surface. In contrast, small olefins
can diffuse inside the pores and are adsorbed well.19 The
small olefins accumulated inside the pores of MgY, there-
fore, react efficiently with radical I formed there, resulting in
enhanced methyl ketone formation. These findings clearly
suggest that the olefin accumulation inside the MgY pore
also contributes to efficient methyl ketone formation.20
As shown in Table 1, MgMOR and MgZSM-5 scarcely
enhance the methyl ketone formation. This is because the
narrow pore size of MOR and ZSM-521 suppresses the
diffusion of olefins and hence suppresses the addition of
radical I to olefins. It is well-known that the effective pore
size of zeolites is usually defined with the Spaciousness Index
(SI), which is the ratio of isobutane/n-butane formed during
hydrocracking of n-butylcyclohexane.22 The SI values of
MOR and ZSM-5 are 7.5 and 1.0, respectively, whereas the
value of zeolite Y is more than 20. The adsorption test further
confirms this. The distribution ratio, D, of 1 on MgMOR
and MgZSM-5 is determined to be 0.06 and 0.01, respec-
tively, whereas that on MgY is 1.21. This clearly indicates
that, on MOR and ZSM-5, olefins are scarcely accumulated
inside the pores. As shown in Table 1, homogeneous Mg salts
are also ineffective for methyl ketone formation, indicat-
ing that the olefin accumulation within the MgY pore is
significantly important for methyl ketone formation
enhancement.
In the present process, the methyl ketones formed within the
MgY pores successfully diffuse out to a bulk solution, while the
olefins are accumulated. The distribution ratio, D, ofthemethyl
ketones, 10 (2-nonanone) and 20 (1-cyclopentyl-2-propanone)
on MgY, is very low (3.24 ꢀ 10-3 and 3.45 ꢀ 10-3), while the
values for the corresponding olefins 1 and 2 are very high (1.21
and 0.68). This is because ketones are more polar and have
higher solubility in an aqueous solution than the corresponding
olefins.23 The mechanism of MgY-assisted methyl ketone
formation can therefore be shown schematically in Scheme 2.
The electrostatic interaction between Mg2þ and excited-state
acetone accelerates the radical I formation. Radical I reacts
efficiently with olefins accumulated inside the MgY pore and
accelerates the methyl ketone formation. The methyl ketones
formed smoothly diffuse out of the pores.
(18) Shiraishi, Y.; Saito, N.; Hirai, T. J. Am. Chem. Soc. 2005, 127, 12820–
12822.
(19) Adsorption of substrates onto the solid surface depends on the
affinity of substrates for the surface and the solubility of substrates in
solvents: Wright, E. H. M.; Pratt, N. C. J. Chem. Soc., Faraday Trans. 1
1974, 70, 1461–1471. In the present case, acetone/water mixture has a poor
solubility of olefins and, hence, allows olefin adsorption onto zeolite. This is
confirmed by adsorption experiments of 1 with MgY (Figure S3; Supporting
Information): the adsorption of 1 onto MgY in pure acetone is almost zero,
but an increase in water content of the solution leads to an increase in the
adsorption amount.
(20) It must be noted that, as shown in Table 3 and Figure 3, there is no
linear relationship between the methyl ketone yield enhancement and the size
or the adsorption degree of olefins. This suggests that the electronic structure
of olefins (reactivity with the radical I) is also the important factor for methyl
ketone production as well as the size and adsorption degree of olefins.
(21) Abbot, J.; Wojciechowski, B. W. J. Catal. 1984, 90, 270–278.
(22) (a) Weitkamp, J.; Ernst, S.; Kumar, R. Appl. Catal. 1986, 27, 207–
210. (b) Chen, C.; Finger, L. W.; Medrud, R. C.; Kibby, C. L.; Crozier, P. A.;
Chan, I. Y.; Harris, T. V.; Beck, L. W.; Zones, S. I. Chem.;Eur. J. 1998, 4,
1312–1323.
(23) Tewarl, Y. B.; Miller, M. M.; Waslk, S. P.; Martlre, D. E. J. Chem.
Eng. Data 1982, 27, 451–454.
J. Org. Chem. Vol. 75, No. 5, 2010 1455

Tsukamoto et al.
JOCArticle
TABLE 4. Effect of MgY on the Photochemical Methyl Ketone Formationa
aReaction conditions: acetone/water (6/4 v/v) mixture (10 mL), olefin (0.2 mmol), MgY (5 mg), nitrogen (1 atm), λ > 300 nm. bQuantum yields of the
methyl ketone formation. cReused after run 13. dReused after run 14.
2.4. Synthesis of Various Methyl Ketones with MgY. As
summarized in Table 4, the present photoprocess with MgY
successfully produces various kinds of methyl ketones. Both
acyclic and cyclic methyl ketones are produced with much
higher yields as compared to that obtained without MgY.
Quantum yields of the methyl ketone formation with MgY
(0.12-0.39) are much higher than that obtained without
MgY (0.08-0.16). The quantum yields are higher than those
of other photochemical reactions for organic synthesis
(<0.07),24 indicating that the present photoprocess proceeds
highly efficiently. The MgY used in this process can easily be
recovered by a simple centrifugation. As shown in entries
13-15, the MgY recovered can be reused without loss of
activity at least twice. Applying the basic concept presented
here with MgY may help realize methyl ketone synthesis in
an economically and environmentally friendly way.
reactants have been studied. The methyl ketone formation is
much enhanced with MgY. This is due to the combination of
electrostatic interaction between Mg2þ and excited-state
acetone and accumulation of olefins inside the MgY pore.
The electrostatic interaction between Mg2þ and excited-state
acetone accelerates the H-abstraction from ground-state
acetone and enhances the acetonyl radical formation. In
that, olefins with a size smaller than the zeolite pore are
accumulated inside the pores and react efficiently with the
acetonyl radical formed there. The present process enables
the synthesis of various kinds of methyl ketones, where MgY
is reusable without loss of activity. The present photoprocess
allows clean and efficient synthesis of methyl ketones with
cheap reactants (olefin, acetone, water) and without noble
metal catalysts. The basic concept presented here with MgY
may become one of the powerful methods for methyl ketone
synthesis.
3. Conclusions
4. Experimental Section
Effects of Mg2þ-exchanged zeolite Y (MgY) on the photo-
chemical methyl ketone synthesis with acetone and olefin as
Materials. All of the materials used were of the highest
commercial quality and were used without further purification.
Commercially unavailable methyl ketones (20, 30, 40, 60, and 80)
(24) Leigh, W. J.; Srinivasan, R. Acc. Chem. Res. 1987, 20, 107–114.
1456 J. Org. Chem. Vol. 75, No. 5, 2010

Tsukamoto et al.
JOCArticle
were synthesized according to a literature procedure25 and used
as standards for GC analysis. The details are summarized in the
Supporting Information with the obtained NMR charts
(Figures S4-S9). Alkali and alkaline earth metal cation-
exchanged zeolite Y were synthesized according to a literature
procedure26 with NaY (Tosoh Corp.; HSZ-320NAA; SiO2/
Al2O3 = 5.5; BET surface area, 700 m2 g-1) as follows: NaY
(3 g) was refluxed for 24 h in water (30 mL) containing 10 wt %
respective metal salts (LiNO3, KNO3, RbCl, CsCl, MgCl2,
Ca(NO3)2, Sr(NO3)2, BaCl2). The resulting solid was recovered
by filtration, washed with water, and dried for 12 h at 100 °C.
This procedure was repeated three times. MgMOR and
MgZSM-5 were obtained in a similar manner, using NaMOR
(Japan Reference Catalyst.; JRC-Z-M15; SiO2/Al2O3 = 15; 426
m2 g-1) supplied from the Catalyst Society of Japan and
NaZSM-5 (Tosoh Corp.; HSZ-820NAA; SiO2/Al2O3 = 23.3;
340 m2 g-1). HY (Tosoh Corp.; HSZ-331HSA; SiO2/Al2O3 = 6;
650 m2 g-1) was used as received.
Photoreaction. Each olefin was dissolved in an acetone/water
mixture (6/4 v/v; 10 mL) within a Pyrex glass tube (φ 10 mm;
capacity, 20 cm3). Zeolite material (5 mg) was added to the
solution and dispersed well by ultrasonication for 5 min. The
tube was sealed with a rubber septum cap, purged with nitrogen
gas, and photoirradiated with magnetic stirring by a Xe lamp
(2 kW; light intensity, 32.1 mW m-2 at 300-340 nm). After the
reaction, the sample was subjected to centrifugation, and the
solution obtained was analyzed by GC-FID. The quantum yield
for methyl ketone formation was determined with a trans-
stilbene actinometer (Φ = 0.45 in benzene),27 where a 313 nm
emission line was irradiated with a high-pressure Hg lamp (300
W, light intensity, 3.1 mW m-2),28 filtered through a potassium
chromate solution consisting of K2CrO4 (0.27 g L-1) and
K2CO3 (1 g L-1).
(MP2) theory.14 Geometries were fully optimized at the MP2/6-
31þG(d) level for H, C, O, Liþ, Naþ, Kþ, Mg2þ, and Ca2þ
atoms and at the MP2/LAVCP* level for Rbþ, Csþ, Sr2þ, and
Ba2þ atoms. Calculation of the T1 acetone was performed using
the basis set with the diffuse and polarization functions accord-
ing to a literature procedure,29 where the initial guess of T1
acetone was generated by selecting an appropriate orbital
occupancy and the nature of the electronic state was checked
graphically with the molecular orbital.13 The optimized struc-
ture was then used for frequency calculation. The binding
affinities were calculated with the MP2 theory according to a
literature procedure,10a without the basis set for superposition
error corrections. The electron densities were determined by the
natural population analysis.30
Cylindrical Dimensions of Olefins. The length and width
of olefins were determined according to a literature procedure
using the MM2 program within the Chem3D-Pro software
(CambridgeSoft, Inc.).17 Molecular dynamics annealing calcula-
tions were performed first to obtain a lowest energy structure,
where the cooling rate was 1 kcal/atom/ps and the final tempera-
ture was 300 K, respectively. The minimization of the molecular
energy was performed to a minimum rms gradient of 0.1. The
relevant axes of the resulting structure were determined graphi-
˚
cally, and 1.0 A was added to these distances to take into account
the dimensions of the exterior hydrogen atoms.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (No. 19760536) from the
Ministry of Education, Culture, Sports, Science and Techno-
logy, Japan (MEXT). We thank the Division of Chemical
Engineering for the Lend-Lease Laboratory System.
Supporting Information Available: Synthesis of standard
methyl ketones, supplementary data (Figures S1-S9 and Tables
S1 and S2), and Cartesian coordinates and SCF energies for
calculated structures. This material is available free of charge via
the Internet at http://pubs.acs.org.
Ab Initio Calculations. Calculations were performed with the
Gaussian 03 program based on second-order Moller-Plesset
(25) Linker, U.; Kersten, B.; Linker, T. Tetrahedron Lett. 1995, 51, 9917–
9926.
(26) Kaanumalle, L. S.; Shailaja, J.; Robbins, R. J.; Ramamurthy, V.
J. Photochem. Photobiol. A 2002, 153, 55–65.
(27) Lewis, F. D.; Johnson, D. E. J. Photochem. 1977, 7, 421–423.
(28) Shiraishi, Y.; Saito, N.; Hirai, T. J. Am. Chem. Soc. 2005, 127, 8304–
8306.
(29) Foresman, J. B.; Head-Gordon, M.; Pople, J. A. J. Phys. Chem. 1992,
96, 135–149.
(30) Read, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1995, 83,
735–746.
J. Org. Chem. Vol. 75, No. 5, 2010 1457