Structure and Base Catalysis of Supercritical Water in the Noncatalytic Benzaldehyde Disproportionation Using Water at High Temperatures and Pressures

Full text of DOI:10.1002/1521-3773(20010105)40:1<210::AID-ANIE210>3.0.CO;2-7

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[3] K. C. Nicolaou P. S. Baran, R. Kranich, Y.-L. Zhong, K. Sugita, N.
Zou, Angew. Chem. 2001, 113, 208; Angew. Chem. Int. Ed. 2001, 40,
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[4] S. J. Danishefsky, T. Kitahara, C. F. Yan, J. Morris, J. Am. Chem. Soc.
1979, 101, 6996.
[5] S. J. Danishefsky, C. F. Yan, R. K. Singh, R. B. Gammill, P. McCurry,
N. Fritsch, J. C. Clardy, J. Am. Chem. Soc. 1979, 101, 7001.
[6] The DMP-mediated conversion of 8 into quinone 9 was accompanied
by the formation of an epoxide product whose structure was consistent
with epoxidation of the inner diene bond of 9.
[7] A multistep route to this type of diene is known; however, the reaction
requires the presence of chlorine substituents on the aryl ring, see
H. W. Heine, B. J. Barchiesi, E. A. Williams, J. Org. Chem 1984, 49,
2560.
offers exiting possibilities for the development of new
chemical processes.[2] Furthermore, scH2O is a suitable
medium in connection with ªgreenº (environmentally friend-
ly) technology because water is the most environmentally
acceptable and naturally abundant solvent. However, the
microscopic characteristics of scH2O, including the structure
which is closely related to chemical reactivity in scH2O, are
not sufficiently well understood. Hence a better understand-
ing of the structure and nature of scH2O leads to marked
improvements in practical applications such as in the me-
chanical, chemical, and geothermal industries.
Currently in organic synthesis, a matter of primary interest
is the promotion of reaction rates by more ªgreenº chemical
processes. Recently we reported an interesting finding that
scH2O itself successfully functions as an acid in accelerating
pinacol/Beckmann rearrangements.[3] Bröll et al. have briefly
reported a base-catalyzed Cannizzaro-type disproportiona-
tion of formaldehyde in scH2O carried out without a base
catalyst.[4] In addition, our in situ Raman spectroscopy
measurements have indicated that the extent and strength
of hydrogen bonding of scH2O are very different to those in
heated and ambient H2O.[5] This suggests a pronounced
stimulation of the breakdown of monomeric water molecules
under supercritical conditions, which would account for the
acid and base difunctionality of scH2O. We have further
studied the base function of scH2O by conducting a base-
catalyzed disproportionation of benzaldehyde in the absence
of any base catalysts. The rate of such a noncatalytic
disproportionation in scH2O has been found to be several-
hundred-fold larger than in the conventional catalytic reac-
tions, whereas the rates of these reactions in hot water (below
3008C), even at high pressures, are extremely small. In
[8] N. Matsumoto, T. Tsuchida, M. Umekita, N. Kinoshita, H. Iinuma, T.
Sawa, M. Hamada, T. Takeuchi, J. Antibiot. 1997, 50, 900; N.
Matsumoto, H. Iinuma, T. Sawa, T. Takeuchi, S. Hirano, T. Yoshioka,
M. Ishizuka, J. Antibiot. 1997, 50, 906.
[9] N. Matsumoto, N. Agata, H. Kuboki, H. Iinuma, T. Sawa, T. Takeuchi,
K. Umezawa, J. Antibiot. 2000, 53, 637.
[10] N. Matsumoto, A. Ariga, S. To-E, H. Nakamura, N. Agata, S.-I.
Hirano, J.-I. Inoue, K. Umezawa, Bioorg. Med. Chem. Lett. 2000, 10,
865; O. Block, G. Klein, H.-J. Altenbach, D. J. Brauer, J. Org. Chem.
2000, 65, 716; P. Wipf, P. D. G. Coish, J. Org. Chem. 1999, 64, 5053; L.
Alcaraz, G. Macdonald, J. Ragot, N. J. Lewis, R. J. K. Taylor,
Tetrahedron 1999, 55, 3707.
[11] For a previous total synthesis, see N. Matsumoto, H. Iinuma, T. Sawa,
T. Takeuchi, Bioorg. Med. Chem. Lett. 1998, 8, 2945.
[12] Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
no. CCDC-148280. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
.
addition, the participation of the OHꢀ ion, the not OH
radical, in the reaction is strongly suggested from GC-MS and
NMR spectroscopic analysis of the benzyl alcohol product in
the disproportionation using [D6]benzaldehyde as a reactant.
We first demonstrate that the reaction of benzaldehyde to
benzyl alcohol and benzoic acid proceeds in scH2O even in the
absence of any base catalysts. Figure 1 shows the background
corrected IR spectra for reaction mixtures in scH2O (3978C)
and hot water (2778C) at a constant pressure of 25 MPa along
with those for ordinary benzyl alcohol and benzaldehyde
aqueous solutions. These measurements were performed by
real time, in situ FT-IR spectroscopy for benzaldehyde in H2O
introduced into a high-pressure, high-temperature, flow
reactor at a constant residence time of 105.0 s. The spectrum
obtained in scH2O (trace D),shows a new intense band at
1002 cmꢀ1, not present in that of the benzaldehyde solution
(trace A). This strong band can be assigned to the CO
stretching vibration(n1) of the benzyl alcohol formed, and is
not observed in the hot water (trace C) or ordinary water
(trace A) phases. We have further analyzed the absorption
bands around 1700 cmꢀ1 (not shown) can be assigned to the
CO stretching vibrations of benzaldehyde and benzoic acid, in
which the n1 frequency of benzoic acid is somewhat higher
than that of benzaldehyde. In the scH2O an intense band at
1702 cmꢀ1 nearly coincides with that of the authentic benzoic
acid sample, showing unambiguously that benzoic acid is
produced in addition to benzyl alcohol. Detailed analysis of
Structure and Base Catalysis of Supercritical
Water in the Noncatalytic Benzaldehyde
Disproportionation Using Water at
High Temperatures and Pressures**
Yutaka Ikushima,* Kiyotaka Hatakeda, Osamu Sato,
Toshirou Yokoyama, and Masahiko Arai
The physicochemical characteristics of water are greatly
changeable by varying the pressure or temperature under
supercritical conditions,[1] and supercritical water (scH2O)
[*] Dr. Y. Ikushima,[‡] Dr. K. Hatakeda,[‡] Dr. O. Sato,[‡]
Dr. T. Yokoyama
National Industrial Research Institute of Tohoku
4-2-1 Nigatake, Miyagino-ku
Sendai 983-8551 (Japan)
Fax : (‡ 81)22-237-5224
E-mail: ikushima@tniri.go.jp
Dr. M. Arai[‡]
Graduate School of Engineering, Hokkaido University
Kita13-Nishi8, Kita-ku, Sapporo 060-8628 (Japan)
‡
[ ] CREST, JST (Japan Science and Technology Corporation)
4-1-8 Honcho, Kawaguchi 332-0012 (Japan)
[**] This work has been supported by CREST, JST (Japan Science and
Technology Corporation), 4-1-8 Honcho, Kawaguchi 332-0012 (Ja-
pan).
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a ± c),[7a,f] or an intervention of radical intermediates leading
to the formation of [a-2H2]benzyl alcohol (Scheme 1, path-
way b ± d)[7b,c] or the formation of [a-2H]benzyl alcohol
.
(Scheme 1, pathway b ± e).[7d,e] The OHꢀ ion and/or OH
radical species are thus expected to cause this disproportio-
nation using scH2O alone, and undoubtedly arise from the
H2O molecule itself although H2O at ambient conditions does
not provide the benzylic hydrogen of the product.[8] The OHꢀ
ion is required to form the product alcohol in any reaction
mechanisms,[7] and the participation of the OHꢀ ion in the
disproportionation using scH2O has been clearly demonstrat-
ed. On the other hand, the formation of [a-2H]benzyl alcohol
was not identified in this experiment, and one can eliminate
.
completely the possibility of participation of the OH radical,
.
.
that is, the breakdown of the H2O molecule to H and OH
radicals under supercritical conditions on the assumption that
the disproportionation using scH2O follows reported mecha-
nisms.[7]
Our in situ FT-IR measurements enable us to carry out a
kinetic analysis. The extent of the conversion of benzaldehyde
in the disproportionation reaction changes in proportion to an
increase in the absorbance of the benzyl alcohol formed. In
this study pseudo second-order rate constants have been
determined at temperatures of 20 ± 4278C and pressures of
0.1 ± 25 MPa by assuming that excess OHꢀ is evolved.[9] The
extinction coefficient of the n1 band of benzyl alcohol
determined through the Lambert ± Beer law was assumed to
be independent of temperature. Pressure differences did not
influence the absorbance at temperatures of 20 ± 2008C.
Figure 1. Infrared spectra of aqueous solutions of A) benzyldehyde 208C,
0.1 MPa, B) benzyl alcohol 208C, 0.1 MPa; and of reaction mixtures in the
aqueous, noncatalytic disproportionation of benzaldehyde C) superheated
H2O, 2778C, 25 MPa, D) scH2O, 3978C, 25 MPa. The band at 1002 cmꢀ1 is
assigned to CO stretching vibration (n1) of benzyl alcohol.
the reaction mixture by GC-MS and NMR
spectroscopy at the end of the reaction
supported the formation of benzyl alcohol
and benzoic acid in scH2O. Hence this
in situ observation has first demonstrated
the disproportionation of benzaldehyde to
benzyl alcohol and benzoic acid in scH2O
without base catalysts.
To explore what kind of species causes
the ªnoncatalyticº disproportionation in
scH2O, we attempted the disproportiona-
tion of [D6]benzaldehyde in scH2O at
3978C and 25 MPa. The benzyl alcohol
Scheme 1. A postulated mechanism for the disproportionation of [D6]benzaldehyde in scH2O;
d) D transfer; e) H transfer.
.
.
Figure 2 shows the pseudo second-order rate constants (kp2)
under various conditions: scH2O, hot water, and concentrated
aqueous NaOH solution. A dramatic enhancement in the
reaction rate is seen on carrying out the reaction in scH2O in
the absence of any base catalysts. The reaction in scH2O at
25 MPa and 4278C (Figure 2g) is about 600 times faster than
in 2m NaOH at 608C (Figure 2a).[9] The reaction is greatly
accelerated by raising the temperature in the scH2O region;
however, in hot water below 3008C even at such high
pressures the reaction was not observed to occur for residence
time from 12 to 360 s. The change in the molecular extinction
coefficient of benzyl alcohol with water density might
influence the rate constants. Recent experimental data show
that the extinction coefficient of triplet anthracene in scH2O
decreases with increasing density, by a factor of about 3 ± 4 in
the density range of 0.12 to 0.62 gcmꢀ3 (ref [10]); however, we
product in the disproportionation was analyzed by GC-MS
of the product mixture containing benzaldehyde and the
alcohol, and also by H NMR spectroscopy of the isolated
1
alcohol product. We observed well-defined fragment ions
‡
‡
such as C6D5CD2OH (m/z 115), C6D5CDOH (m/z 113),
‡
‡
‡
C6D5CDO (m/z 112), C6D5CO (m/z 110), C6D5CD2
‡
‡
(m/z 98), C6D5CD (m/z 96), and C6D5C (m/z 94) character-
istic of [a-2H2]benzyl alcohol according to the reported
analysis,[6] whereas signals from the fragments corresponding
to the ionized products of [a-2H]benzyl alcohol were negli-
gible. In addition, the identification by 1H NMR supports the
result from the GC-MS analysis. A generally postulated
mechanism for the disproportionation involves a pre-equilib-
rium addition of OHꢀ to the [a-2H]benzaldehyde and a rate-
determining intermolecular hydride transfer, followed by the
production of [a2H2]benzyl alcohol (Scheme 1, pathway
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4278C at 25 MPa is because of an increase in thermal energy;
however, hot water did not show any reactivity below 3208C,
whereas a marked increase in the rate with increasing
temperature was observed in the near-critical region. Thus,
the rate of reaction did not show a monotonous temperature
dependence, being in agreement with the 1-h values up to
approximately 4008C. Furthermore, even though such a
specific breakdown really occurs near the critical point,
extensive spectroscopic data[5, 11] suggest that the dispersed
phase beyond the critical point contains low aggregates
including monomeric water molecules. Hence, the excellent
performance of the base-catalyzed disproportionation from
the near-critical to supercritical region might be related not
only to the thermal energy contribution but also to monomer-
‡
like water molecules that do not break completely into H and
OHꢀ ions but polarize extremely in the supercritical state.
There is still a possibility that the reaction mechanisms using
scH2O might be different from those reported.[7] Microscopic
dynamic behavior of water molecules in a shorter time
domain is in any event more important when discussing the
specific reactivities. We have successfully used the 1-h value to
correlate the acid/base reactivity of scH2O. Another possible
Figure 2. The pseudo second-order rate constants (kp2) of the dispropor-
tionation of benzaldehyde. The base catalyst and its concentration, solvent,
pressure, and temperature are a) 2m NaOH aq. solution, 608C;[9] b) no
catalyst, hot water, 25 MPa, 3008C; c) no catalyst, hot water, 25 MPa,
3528C; d) no catalyst, hot water, 19.1 MPa, 3778C; e) no catalyst, scH2O,
25 MPa, 3778C; f) no catalyst, scH2O, 25 MPa, 3978C; g) no catalyst,
scH2O, 25 MPa, 4278C; h) no catalyst, scH2O, 22.1 MPa, 3778C. For our
data 95% confidence limits are provided.
think that this change is not so large when compared
with the marked enhancement of the rate of reaction, by
one or two orders of magnitude, when using scH2O, and
does not prevent us from concluding that the use of
scH2O can significantly promote the rate of organic
synthesis. Under the conditions used, the substrate can
be soluble in the solvent at high pressures and temper-
atures. Increasing the pressure and temperature in-
creases the density of H2O and so decreases the
concentration of substrate in the constant volume of
reaction mixture. This will have a negative effect on the
rate of reaction and so the enhanced reactivity of scH2O
is of great significance.
The change in hydrogen bonding is presumed to be a
key factor for clarifying the temperature and/or pressure
dependence of the rate of the disproportionation. It was
demonstrated that the extent of hydrogen bonding is
reducing uniquely near the critical point (critical
pressure), where dimers and/or monomers are predom-
Figure 3. Relationship between the extent of disappearance of hydrogen bonding,
*
*
) for the benzaldehyde
1-h ( ) and the pseudo second-order rate constant, kp2
(
disproportionation as a function of temperature at a fixed pressure of 25 MPa. For
kp2 values, 95% confidence limits are given by bars.
‡
inant,[11] but monomers, in part, are further broken into H
parameter is the ion product of water (Kw) value; however,
detailed measurements have not yet been made for scH2O
near the critical region, where interesting reaction results
have been obtained.
and OHꢀ ions by the large fluctuations in the water
‡
structure.[5, 11d] That is, the ªlocalº H or OHꢀ ion concen-
tration would be extremely high when the transferring ion
species cannot escape, leading to the maximized rate near the
critical pressure. Hence such an acceleration of the dispro-
portionation is quite peculiar to the supercritical state, and it
is highly possible that the ªspecific breakdownº of H2O to H
and OHꢀ ions under supercritical conditions occurs.
Figure 3 shows the change in the rate constant with
temperature at a fixed pressure of 25 MPa, together with
the extent of the disappearance of hydrogen bonding (1-h) of
water determined by our Raman spectroscopic data.[5] The
rate constant increases with increasing temperature above the
near-critical region despite the loss in OHꢀ ion activity
anticipated from the Raman data.[5] The significant increase in
the rate constant with increasing temperature from 397 to
Experimental Section
‡
The reactions were performed under ambient to scH2O conditions using a
high-pressure, high-temperature flow-reaction system with a short-path-
length (20 mm) FT-IR cell operable at 5008C and 50 MPa. Details of the FT-
IR system used are described elsewhere.[3b] An aqueous solution of
benzaldehyde (0.05m) was introduced into the system in the range of flow
rates of 0.07 to 0.7 mLminꢀ1 (the residence time from 12 to 360 s) using a
high-pressure liquid pump, pressure control was achieved by a back-
pressure regulator. The temperature was then raised to the desired value.
Once stabilized, 50 spectra (4 cmꢀ1 resolution) were accumulated in one
destination file. Each file was rationed against the spectrum of pure H2O
under the same conditions. Furthermore, all of the products were
212
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qualitatively identified by using 1H NMR spectroscopy and GC-mass
spectrometry.
established.[2] The understanding of the structure and the
reactivity of silylnickel species[3] is indispensable for the
development of new catalytic methodologies. Although a
number of mononuclear silylmetal complexes are known for
all Group 10 metals, structurally characterized silylene-bridg-
ed dinuclear complexes have been reported only for plati-
num[4] and palladium.[5, 6] These dinuclear species are consid-
ered to play important roles in catalytic processes. For
example, silylene-bridged Pt2Si2 rings are potential key
intermediates in the platinum-catalyzed dehydrocoupling of
hydrosilanes.[4b±d] Here we report on the reaction of 1,2-
disilylbenzene (1) with nickel(0) complexes, which led to the
isolation of the dinuclear (m-silylene)(silyl)nickel(iii) com-
plexes [{1,2-C6H4(SiH2)(SiH)}2Ni2(R2PCH2CH2PR2)2] (R ˆ
Me or Et), which contain the first structurally characterized
four-membered Ni2Si2 rings. The short contact between the
SiH2 and m-SiH moieties revealed by X-ray crystallography
Received: July 31, 2000 [Z15561]
[1] a) NBC/NRC Steam Tables (Eds.: L. Haar, J. S. Gallagher, G. S. Kell),
Hemisphere, New York, 1984; b) High-Temperature Aqueous Solu-
tions: Thermodynamic Properties (Eds.: P. R. J. Fernandez, H. R.
Corti, M. L. Japer), CRC, Boca Raton, 1992; c) R. W. Shaw, T. B. Brill,
A. A. Clifford, C. A. Eckert, E. U. Franck, Chem. Eng. News 1991, 69
(51), 26.
[2] P. E. Savage, Chem. Rev. 1999, 99, 603.
[3] a) O. Sato, Y. Ikushima, T. Yokoyama, J. Org. Chem. 1998, 63, 9100;
b) Y. Ikushima, O. Sato, K. Hatakeda, T. Yokoyama, M. Arai, Angew.
Chem. 1999, 111, 3087; Angew. Chem. Int. Ed. 1999, 38, 2910; c) Y.
Ikushima, O. Sato, K. Hatakeda, T. Yokoyama, M. Arai, J. Am. Chem.
Soc. 2000, 122, 1908.
[4] D. Bröll, C. Kaul, A. Krämer, P. Krammer, T. Richter, M. Jung, H.
Vogel, P. Zehner, Angew. Chem. 1999, 111, 3180; Angew. Chem. Int.
Ed. 1999, 38, 2998.
[5] Y. Ikushima, K. Hatakeda, N. Saito, M. Arai, J. Chem. Phys. 1998, 108,
5855.
ꢀ
suggests the possibility of Si Si bond formation, which indeed
[6] a) S. Meyerson, P. N. Rylander, E. L. Eliel, J. D. McCollum, J. Am.
Chem. Soc. 1959, 81, 2606; b) E. L. Eliel, J. D. McCollum, S.
Meyerson, P. N. Rylander, J. Am. Chem. Soc. 1961, 83, 2481.
[7] a) C. G. Swain, A. L. Powell, T. J. Lynch, S. R. Alpha, R. P. Dunlap, J.
Am. Chem. Soc. 1979, 101, 3576, and refs therein; b) E. C. Ashby, D. T.
Coleman, M. Gamasa, Tetrahedron Lett. 1983, 24, 851; c) E. C. Ashby,
D. T. Coleman, M. Gamasa, J. Org. Chem. 1987, 52, 4079; d) S.-K.
Chung, J. Chem. Soc. Chem. Commun. 1982, 480; e) J. Weiss, Trans.
Faraday Soc. 1941, 37, 782; f) C. G. Swain, A. L. Powell, T. J. Lynch,
S. R. Alpha, R. P. Dunlap, J. Am. Chem. Soc. 1979, 101, 3584.
[8] C. R. Hauser, P. J. Hamrick, Jr., A. T. Stewart, J. Org. Chem. 1956, 21,
260.
takes place in a similar reaction of 1-(dimethylsilyl)-2-
silylbenzene (2) with [Ni(dmpe)2] (dmpe ˆ 1,2-bis(dimethyl-
phosphanyl)ethane).
[9] Y. Saeki, K. Negoro, S. Ichiyasu, Nippon Kagaku Kaishi 1985, 931.
[10] M. J. Kremer, K. A. Connery, C. M. DiPippo, J. Feng, J. E. Chateau-
neuf, J. F. Brennecke, J. Phys. Chem. A 1999, 103, 6591.
[11] a) N. Matsubayashi, C. Wakui, M. Nakahara, Phys. Rev. Lett. 1997, 78,
2573; b) M. M. Hoffmann, M. S. Conradi, J. Am. Chem. Soc. 1997, 119,
3811; c) H. Ohtaki, T. Radnai, T. Yamaguchi, Chem. Soc. Rev. 1997, 26,
41; d) Yu. E. Gorbaty, A. G. Kalinichev, J. Phys. Chem. 1995, 99, 5336.
Previously, we reported that treatment of
1 with
[Ni(dmpe)2] results in the dimeric bis(silyl)nickel(ii) complex
3 and the first tetrakis(silyl)nickel(iv) complex 4a.[7] A similar
reaction under somewhat different conditions led to the
formation of a new dimeric NiIII complex. While studying 3 by
variable-temperature NMR spectroscopy in [D8]toluene, we
observed, upon heating the solution to 808C, a color change
from pale yellow to orange and the emergence of new weak
Isolation of Dinuclear (m-Silylene)(silyl)nickel
1
signals in the H and 31P NMR spectra. Further heating at
ꢀ
Complexes and Si Si Bond Formation on a
1108C for 30 min gave a new complex 5a, which could be
isolated as orange crystals (34%) by crystallization from
benzene. The similar complex 5b, ligated by 1,2-bis(diethyl-
phosphanyl)ethane (depe), was also obtained directly from 1
and [Ni(PEt3)2(depe)] (1:Ni ˆ 1:1.05); the reaction proceeded
even at room temperature and gave 5b as the main product
(49% yield). The 29Si NMR spectrum of the crude mixture
showed the presence of the tetrakis(silyl)nickel(iv) complex
Dinuclear Nickel Framework**
Shigeru Shimada, Maddali L. N. Rao,
Teruyuki Hayashi, and Masato Tanaka*
Palladium and platinum complexes are versatile catalysts
for the transformation of organosilicon compounds.[1] How-
ever, the utility of nickel complexes has not been as well
4b as
a
side product [d ˆ ꢀ2.11 (dd, 2J(Si,Pcis) ˆ 20,
2
2J(Si,Ptrans) ˆ 101 Hz), 3.03 (t, J(Si,P) ˆ 16 Hz)].
[*] Prof. M. Tanaka, Dr. S. Shimada, Dr. M. L. N. Rao, Dr. T. Hayashi
National Institute of Materials and Chemical Research
Tsukuba, Ibaraki 305-8565 (Japan)
Fax: (‡81)298-61-4430
E-mail: mtanaka@home.nimc.go.jp
[**] We are grateful to the Japan Science and Technology Corporation
(JST) for financial support through the CREST (Core Research for
Evolutional Science and Technology) program and for a postdoctoral
fellowship to M.L.N.R.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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