Formation of acetaldehyde via photocarbonylation of methane with CO

Article abstract of DOI:10.1016/j.tetlet.2007.07.131

Direct photocarbonylation of methane to give acetaldehyde occurred when a mixture of methane and CO dissolved in benzene was subjected to UV irradiation at λ < 290 nm. The reaction was accelerated by rhodium RhCl(CO)(PR₃)₂ complexes, where R = alkyl, Ph, or OPh.

Full text of DOI:10.1016/j.tetlet.2007.07.131

Tetrahedron Letters 48 (2007) 7046–7048
Formation of acetaldehyde via photocarbonylation
of methane with CO
a
a
a
a
a
R. Kazimerczuk, T. Wo z´ niewski, M. Borowiak, E. Zimnicka, K. Zwoli n´ ski,
a
b
a
a
a,
*
Z. Rogulski, A. Trzeciak, S. Ostrowski, J. Cz. Dobrowolski and W. Skupi n´ ski
a
Industrial Chemistry Research Institute, Rydygiera 8, 01-793 Warszawa, Poland
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
b
Received 21 March 2007; revised 6 July 2007; accepted 20 July 2007
Available online 27 July 2007
Abstract—Direct photocarbonylation of methane to give acetaldehyde occurred when a mixture of methane and CO dissolved in
benzene was subjected to UV irradiation at k < 290 nm. The reaction was accelerated by rhodium RhCl(CO)(PR ) complexes,
3 2
where R = alkyl, Ph, or OPh.
ꢀ
2007 Published by Elsevier Ltd.
CO insertionintotheC–H bondsofhydrocarbon chainsis
averysimplemethod forthe synthesisofaldehydes. Inves-
tigation of this reaction in the presence of Vaska type
rhodium complexes of general formula RhCl(CO)(PR3)2
ated by the Vaska type rhodium complexes mentioned
above.
The reaction was carried out in a Quartz reactor filled
with a stirred benzene solution saturated with CO and
(
R = alkyl, aryl) resulted in aldehyde formation when
benzene, long-chain alkanes and cyclic alkanes were
CH (10 ml) via irradiation through the reactor wall
4
irradiated with UV light of a wavelength greater than
with a high pressure mercury lamp HOK 400 W—
Phillips. In this way, UV light of the whole spectrum
was introduced to the reaction mixture.
1
3
00 nm.
In the case of methane, direct carbonylation to acetalde-
hydeundernormal pressure occurs as follows(reaction 1):
After running the reaction for 4 h, 0.014 mmol of acetal-
dehyde was obtained (Table 1). This establishes a 0.4%
quantum yield, 0.4% methane conversion and 3.9% con-
CH
4
+ CO!CH
3
CHO
ð1Þ
version of CO (27 mmol of CH and 3.5 mmol of CO
4
4
It is thermodynamically unfavourable—the Gibbs free
energy of the reaction is close to ꢀ15 kcal/mol. As the
calculation indicates, the reaction occurs efficiently
under a pressure of about 4000 atm. Indeed, under these
conditions, acetaldehyde was obtained in the presence of
dissolved in 10 ml of benzene). Beside acetaldehyde, a
trace of benzaldehyde, as the product of benzene car-
bonylation, was present in the post reaction mixture.
To determine which UV light wavelength was responsi-
ble for methane carbonylation, the reaction was carried
out in a Pyrex glass reactor transmitting only UV wave-
ꢁ3
2,3
titanocene catalysts (6.5 · 10 mol/mol Ti).
1
,5
Herein, we report methane carbonylation with CO to
give acetaldehyde, when a mixture of methane and CO
dissolved in benzene was irradiated with UV light of a
wavelength shorter than 290 nm at ambient temperature
under atmospheric pressure. The reaction was acceler-
lengths longer than 290 nm.
under these conditions.
No reaction occurred
To ascertain which irradiation wavelength supports the
carbonylation in the presence of Vaska type rhodium
complex catalysis, the reaction was carried out in Pyrex
and Quartz wall reactors. In the former case, when the
irradiation wavelength was longer than 290 nm, only
benzaldehyde was formed. The largest yield was
obtained for complexes containing alkylphosphines as
Keywords: Methane carbonylation; Acetaldehyde; Rhodium
complexes.
*
Corresponding author. Tel.: +48 22 5682183; fax: +48 22 5682390;
e-mail: wincenty.skupinski@ichp.pl
0040-4039/$ - see front matter ꢀ 2007 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2007.07.131

R. Kazimerczuk et al. / Tetrahedron Letters 48 (2007) 7046–7048
7047
Table 1. The photocatalyzed carbonylation of methane and benzene in the presence of RhCl(CO)(phosphine)
2
a
Phosphine
UV (nm)
PhCHO (mmol)
MeCHO (mmol)
PMe
3
P(iPr)
>290
0.04
—
—
—
3
PBu
3
PCy
3
PPh
3
P(OPh)
3
—
b
k
>290
OS
OS
>290
OS
>290
OS
>290
0.002
—
OS
>290
—
OS
OS
0.08
—
—
0.16
0.24
0.11
15
0.13
0.29
0.15
22
0.03
—
—
0.12
0.28
0.14
21
0.02
—
—
0.09
0.93
0.79
113
0.02
0.47
0.33
48
0.01
0.33
0.19
28
Trace
0.14
—
—
—
—
c
MeCHORh (mmol)
—
—
d
TONRh
—
—
—
—
3
0
.007 mmol Rh, CO/CH = 1:8 (saturated solution in benzene); benzene—10 cm ; 20 ꢁC; 4 h; Mercury lamp: HOK-400 W—Phillips; Me = methyl,
4
iPr = isopropyl, Bu—butyl, Cy—cyclohexyl; Ph—phenyl, PhCHO–benzaldehyde; MeCHO—acetaldehyde.
a
Non-catalyzed reaction.
OS—whole UV spectrum—reaction carried out in a Quartz reactor.
Amount of MeCHO in the catalyzed reaction.
Number of the catalytic acts at one Rh-atom in the catalyzed reaction.
b
c
d
ligands. From these complexes, the best result,
.08 mmol of PhCHO, was obtained in the presence of
RhCl(CO)(PMe ) .
0.79, 0.33 and 0.19 mmol, respectively. Since 0.007
mmol of the rhodium catalyst was used, the TON of
0
the reaction accelerated by RhCl(CO)(PCy ) is greater
3
2
3 2
than 100.
When the reactions were carried out in a Quartz reactor
transmitting the whole UV light range, acetaldehyde and
benzaldehyde were synthesized in higher yields than
when the reaction was run in the absence of the Vaska
type complexes or when the radiation wavelength was
longer than 290 nm (Table 1).
The efficiency of the acceleration resulted in a 1.2%
quantum yield and methane and carbon oxide conver-
sions equal to 3.7% and 21%, respectively.
As mentioned above, under normal pressure, methane
cannot be carbonylated with CO directly to acetalde-
hyde. Here, the reactions investigated must proceed
via formation of an unknown intermediate when meth-
ane and carbon monoxide are irradiated with UV light
of a wavelength shorter than 290 nm. It is known that
methane forms carbene–CH2 and hydrogen radicals,
when irradiated with UV light of a wavelength equal
The situation when carbonylations are running simulta-
neously is typical of photoactivation. Investigation of
benzene and long-chain alkane carbonylations, indi-
cated that they proceeded independently and that there
1
was even a positive synergic effect on the yield.
5
Again, the largest amount of benzaldehyde, 0.16 mmol,
was obtained in the presence of RhCl(CO)(PMe ) .
to 147 nm (reaction 2):
3
2
k ¼ 147 nm
ð2Þ
Å
The largest quantities of acetaldehyde were obtained in
the presence of complexes containing bulky phosphines:
PCy , PPh and P(OPh) = 0.93, 0.47 and 0.33 mmol,
CH
4
! :CH þ 2H
2
The UB3LYP/aug-cc-pVQZ and UMP2/aug-cc-pVTZ
calculations on the possible transformation of :CH to
3
3
3
respectively (Table 1). This indicates that the rhodium
complexes accelerate methane carbonylation.
2
acetaldehyde (Table 2), show that the most probable
reaction pathway involves a ketene which is subse-
quently hydrogenated by the hydrogen radicals liberated
in reaction 2, to give acetaldehyde (Table 2, reactions 3
and 4):
It is reasonable to state that the values mentioned above
are sums resulting from both accelerated and non-accel-
erated reactions. Taking into consideration the latter,
the greatest quantities of acetaldehyde obtained were:
R
Table 2. Free Gibbs energies (G298, 298.15 K, 1 atm, Hartree) of the used substrates and free Gibbs energies (DG298, 298.15 K, 1 atm, kcal/mol) of
postulated reactions, calculated using different computational levels, respectively
Molecule/reaction
UB3LYP/aug-cc-pVQZ
UMP2/aug-cc-pVTZ
H(D)
ꢁ0.513046
ꢁ1.181969
ꢁ113.381278
ꢁ39.173300
ꢁ40.514355
ꢁ152.588247
ꢁ153.877413
11.4
ꢁ0.510475
ꢁ1.166205
ꢁ113.156745
ꢁ39.058268
ꢁ40.386372
ꢁ152.133588
ꢁ153.523295
12.4
H
2
(S)
CO(S)
CH
CH
CH
CH
CH
CH
2
4
2
3
4
4
(T)
(S)
CO(T)
CHO(S)
(S) + CO(S)!CH
3
CHO(S)
(T) + 2H(D))
(S)!(CH
2
197.6
192.7
(CO(S) + CH
2
(T))!CH
CO(T) + 2H(D)!CH
CO(S) + H
(S))!CH
2
CO(T)
CHO(S)
CHO(S)
ꢁ21.1
ꢁ11.7
CH
2
3
ꢁ165.1
ꢁ168.6
(CH
2
2
3
ꢁ23.4
ꢁ19.1
S, D, T stand for singlet, doublet, and triplet states, respectively.

7048
R. Kazimerczuk et al. / Tetrahedron Letters 48 (2007) 7046–7048
:
CH þ CO ! CH @C@O
ð3Þ
ð4Þ
best result was obtained in the presence of the
RhCl(CO)(PCy ) complex.
2
2
Å
3
2
CH
2
@C@O þ 2H ! CH
3
CHO
The negative values of the Gibbs free enthalpy calcu-
lated for reactions 2 and 3 (Table 2) indicate, that the
reactions proceed spontaneously under the experimental
conditions.
Acknowledgements
Financial support from the State Committee for Scien-
tific Research (KBN—Project PBZ/KBN/018/T09/99/
1a) is gratefully acknowledged.
Since the Vaska type rhodium complexes absorb UV
6
–8
light at 365 nm,
they dissociate into unsaturated
three-coordinated RhCl(PR ) complexes (reaction 5):
3
2
References and notes
k ¼ 365 nm
RhClðCOÞðPR
ð5Þ
3
Þ2 ! RhClðPR
3
Þ2 þ CO
1. Sakakura, T.; Sodeyama, T.; Sasaki, K.; Wada, K.;
Tanaka, M. J. Am. Chem. Soc. 1990, 112, 7221.
which are very active species and probably they also
accelerate reactions 3 and 4.
2
3
. Grigoryan, E. A. Kinet. Katal. 1999, 40, 389 (Chem. Abstr.,
1999, 131, 157 487).
. Enikolopyan, N. S.; Menchikova, E. N.; Grigoryan, E. A.
DAN SSSR 1986, 219, 110 (Chem. Abstr., 1987, 107, 96 293
z).
The calculated energy for reaction 2 is ca. 190 kcal/mol,
which corresponds to 145 nm wavelength energy. This is
in very good agreement with the literature data. As we
mentioned above, the UV light of this wavelength splits
4
. Clever, H. L.; Baffino, R. In Techniques in Chemistry VIII;
Duck, M. R. J., Ed.; Solution and Solubilities Part I; John
Wiley & Sons: London, 1975; p 379.
5
methane to methyl carbene and two hydrogen radicals.
5
. Paszyc, W. Photochemistry Fundamentals (in Polish),
PWN: Warszawa, 1983.
Thus we conclude that methane can be carbonylated to
6
. Spillett, C. T.; Ford, P. C. J. Am. Chem. Soc. 1989, 111,
1932.
acetaldehyde when a CH and CO saturated solution of
4
benzene is irradiated with UV light of a wavelength
of 145 nm. The reaction can be accelerated by
RhCl(CO)(PR ) rhodium Vaska type complexes. The
7. Brady, R.; Flynn, B. R.; Geoffroy, G. L.; Gray, H. B.;
Peone, J., Jr.; Vaska, L. Inorg. Chem. 1976, 15, 1485.
8. Wink, D. A.; Ford, P. C. J. Am. Chem. Soc. 1987, 109, 436.
3
2