n-pentane carbonylation with CO on sulfated zirconia: An in situ solid-state 13C NMR study

Article abstract of DOI:10.1070/MC2001v011n01ABEH001345

Using ¹³C CP/MAS NMR, the first evidence has been obtained for n-pentane carbonylation with carbon monoxide into C₆ aldehydes, ketones and carboxylic acids on a sulfated zirconia catalyst.

Full text of DOI:10.1070/MC2001v011n01ABEH001345

, 2001, 11(1), 23–25
n-Pentane carbonylation with CO on sulfated zirconia: an in situ solid-state
13C NMR study
Mikhail V. Luzgin, Alexander G. Stepanov,* Vera P. Shmachkova and Nina S. Kotsarenko
G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation.
Fax: +7 3832 34 3056; e-mail: a.g.stepanov@catalysis.nsk.su
10.1070/MC2001v011n01ABEH001345
Using 13C CP/MAS NMR, the first evidence has been obtained for n-pentane carbonylation with carbon monoxide into C6 aldehydes,
ketones and carboxylic acids on a sulfated zirconia catalyst.
Since the discovery of its strong catalytic activity,1 sulfated
231
n-C5H12
+
13CO
zirconia (SZ) has found potential applications as a catalyst. The
strong acidity of SZ opens up new, yet to be studied feasibility
of its using as a catalyst, especially for light alkanes conver-
sion.2 Among the promising applications of SZ is a direct
conversion of alkanes into carbonyl-containing compounds,
which are of great importance for industrial organic chemistry.
It is a common knowledge that alkanes can be carbonylated
with carbon monoxide in superacids,3 in the presence of poly-
halomethane-based superelectrophilic systems4 and in the pres-
ence of aluminium chloride as the strong solid Lewis acid.5 In
this paper, using in situ solid state 13C NMR spectroscopy,† we
present the first evidence for n-pentane carbonylation with CO
on pure SZ as a catalyst.
*
*
194
*
*
*
*
*
*
*
(a)
*
*
*
*
300
250
200
150
100
24.5
50
0
d/ppm
[2-13C]n-C5H12 + CO
22.5
Figure 1 displays the 13C CP/MAS NMR spectra of the
products formed from n-pentane and CO on SZ at 70 °C.‡ If
unlabelled n-pentane and 13C-labelled carbon monoxide were
coadsorbed [Figure 1(a)], the most intense signal becomes
visible at 231 ppm from the 13C-labelled carbonyl groups of
both aldehydes and ketones, strongly interacting with SZ acid
sites.8 In case of using [2-13C]n-pentane 1 and unlabelled CO,
only 13C-labelled groups were observed in the 13C NMR spectra:
both 2-13CH2 group of 1 and carbon atoms in which the
2-13CH2 group is transformed during the reaction. The fol-
lowing spectral features from the reaction products appeared in
the spectrum [Figure 1(b)]. Besides the signal from the labelled
13CH2 group of unreacted 1 at 24.5 ppm,6,9 two intense signals
at 32.2 and 33.8 ppm [Figure 1(b)] arise from the product of
n-pentane isomerization, isopentane 5 with 13C-labels at the CH
and CH2 groups, respectively.9 Nine signals from the aliphatic
Experimental
33.8
32.2
*
(b)
(c)
*
Simulated
*
*
27.3
29.1
50.8
35.8
36.7
46.3
54.3
43.9
*
×2
*
70 65 60 55 50 45 40 35 30 25 20 15 10
5
0
d/ppm
Figure 1 13C CP/MAS NMR spectra of the products formed from n-pentane
and CO on sulfated zirconia at 70 °C: (a) coadsorption of 13CO and n-C5H12;
(b) coadsorption of the [2-13C]n-C5H12 and CO; (c) simulation of experi-
mental spectrum (b). Asterisks (*) denote spinning side bands.
†
General experimental details. A SZ sample of low temperature tetra-
gonal phase with a surface area of 60 m2 g–1 and 9.9 wt.% of SO3
content was synthesised according to the procedure described earlier.6
The SZ sample was calcined at 600 °C in air and at 400 °C in a vacuum
(10–3 Pa) for 2 h. Equal amounts of n-pentane and CO (or n-pentane, CO
and H2O) (ca. 300 µmol g–1 of each coadsorbate) were adsorbed on SZ
in a vacuum at the temperature of liquid nitrogen. After sealing a glass
tube with the SZ sample off from the vacuum system, it was heated at
50–150 °C for 1 h, the initial pressure of CO in the sealed tube could
reach 10 atm at 150 °C. The reaction products were analysed in situ
by 13C CP/MAS NMR in the sealed glass tubes containing the catalyst
with adsorbed reaction products and ex situ by high-resolution 13C NMR
spectroscopy in CDCl3 solution. 13C NMR spectra with cross-polariza-
tion and magic angle spinning (13C CP/MAS NMR) and high-resolution
13C NMR spectra in solution were recorded on a Bruker MSL-400 NMR
spectrometer at room temperature (~23 °C). The conditions used for CP
experiments are described in ref. 7, the spinning rate was 3–4 kHz. A
few thousands of scans have been collected for each spectrum. The
13C chemical shifts for carbon nuclei were measured with respect to
TMS as an external standard. To facilitate NMR analysis, n-pentane
labelled with 13C at the second carbon atom, [2-13C]n-pentane (82%
isotope enrichment), or 13CO (90% isotope enrichment) were used in
NMR experiments. [2-13C]n-Pentane was prepared from [1-13C]ethanol
(82% 13C) via a six-step synthesis.
fragments of the carbonylation products are also readily identi-
fied in this spectrum [Figure 1(b),(c)] at 22.5–54.3 ppm. Six of
them, namely, at 22.5, 29.1, 36.7, 46.3, 50.8 and 54.3 ppm,
originate from 2-methylpentanal 6, 2-ethylbutanal 7, 2-methyl-
pentan-3-one 9 and 3-methylpentan-2-one 10 (see Scheme 1§).
We further confirmed the formation of the aldehydes and
ketones by high-resolution 13C NMR analysis of the products
extracted with Et2O from SZ.¶,††
The less intense signal at 194 ppm [Figure 1(a)], belonging
to 13COOH carboxylic groups,7,11 points to the formation of
carboxylic acids in addition to aldehydes and ketones. The
§
In Scheme 1, 13C chemical shifts for the carbons in the adsorbed initial
[2-13C]n-pentane and reaction products are indicated only above the
carbons with 13C labels expected in these carbon atoms as the result of
the reaction according to Scheme 1.
¶
The products exhibited the following 13C NMR chemical shifts in
CDCl3 solution, d: 6, 13.2 (Me), 13.9 (5-Me), 20.2 (4-CH2), 32.8
(3-CH2), 46.1 (2-CH), 204.7 (C=O); 7, 11.3 (Me), 21.5 (CH2), 55.0 (CH),
204.8 (C=O); 9, 7.7 (Me), 18.3 [(Me)2], 33.4 (CH2), 40.6 (CH), 214.5
(C=O); 10, 11.5 (5-Me), 15.7 (Me), 25.9 (4-CH2), 27.9 (1-Me), 48.7
(3-CH), 212.0 (2-C=O). The data are in complete accordance with the
chemical shifts for these compounds.10
†† The conversion of n-pentane was 41% at 70 °C. The selectivity
towards the reaction products was as follows: 5, 35%; 6, 12%; 7, 8%; 9,
18%; 10, 15%; 11, 5%; 12, 2.5%; and 13, 4%.
‡
To follow selectively the transformation of the initial reactants and for
the identification of reaction products adsorbed on SZ by 13C NMR,
either CO or n-pentane labelled with the 13C isotope were used. In this
case only signals from 13C-labelled carbon atoms in both reactants and
reaction products were preferentially observed in the spectrum.
– 23 –

, 2001, 11(1), 23–25
194
n-C5H12
+
13CO + H2O
Me *CH CH2 CH2 Me
2a
– H–
24.5
176
*
Me *CH2 CH2 CH2 Me
Me *CH2 CH2 CH Me
SZ
*
2b
*
*
*
(a)
*
Me *CH2 CH CH2 Me
300
250
200
150
100
50
0
3
d/ppm
Me
[2-13C]n-C5H12 + CO + H2O
Me *CH CH2
*CH2 Me
*C *CH2 Me
Me
4a,b
+ H–
(b)
(c)
Experimental
*
*
Me
32.2
33.8
*CH *CH2 Me
Me
5
Simulated
+ CO, H–
Me *CH CH2 *CH2 Me
35.8
43.9
22.5
20
2
46.3
27.3
30
*
O
H
22.5
50.8
[O]
Me *CH2 CH2 *CH
C
100 90
80
70
60
50
40
10
0
Me
d/ppm
6
Figure 2 13C CP/MAS NMR spectra of the products formed from n-pentane,
CO and water on sulfated zirconia at 150 °C: (a) coadsorption of 13C-label-
O
22.5
43.9
Me *CH2 CH2 *CH
C
led CO, unlabelled n-C5H12 and water; (b) coadsorption of [2-13C]n-C5H12
,
OH
unlabelled CO and water; (c) simulation of experimental spectrum (b).
Me
Asterisks (*) denote spinning side bands.
11
+ CO, H–
Thus, the following processes occur in the interaction of
n-pentane with CO on SZ (see Scheme 1). Two secondary
carbenium ions 2 and 3, which seem to be generated via
hydride abstraction from n-pentane by SZ, react further with
CO and the hydride ion to produce 6 and 7. In addition,
n-pentyl cation 2 undergoes isomerization giving rise to tertiary
isopentyl cation 4, from which 5 evolves. 2,2-Dimethylbutanal
8, whose formation from 4 could be expected, was not detected.
Instead, two ketones 9 and 10 are generated according to the
well-known property of aldehydes with a carbonyl group at-
tached to a quaternary carbon atom to rearrange in liquid
acid3(b),13 and in the presence of solid AlCl35(c),5(e),14 by an alkyl
shift to form the corresponding ketone.
Me *CH2 CH CH2 Me
3
O
H
O
22.5
27.3
[O]
Me *CH2 CH
C
Me *CH2 CH
C
OH
Me CH2
Me CH2
7
12
Me
+ CO, H–
*C *CH2 Me
Me
4
Acids 11–13 seem to be formed by partial oxidation of
aldehydes15 6, 7 and 8 with SZ sulfate groups,16 complete
oxidation of aldehydes to acids occurs in the presence of
water.15
Me
Me *CH2 *C
Me
O
O
35.8
46.3
[O]
C
Me *CH2 *C
C
H
OH
There are two alternative routes for aldehyde formation from
n-pentane. One of them involves hydride abstraction from the
alkane with the formation of carbenium ions 2 and 3, the
subsequent formation of oxocarbenium ions, which are further
reduced under acidic hydride-transfer conditions. The other
implies direct formylation of the alkane by the formyl cation
[H+CO].3(b) Evidence for the reaction of n-pentane carbonyla-
tion by the first route is the formation of 5, which implies
hydride abstraction from 1 to form intermediate cations 2 and 4.
The formation of intermediate formate species on SZ with a
signal at 176 ppm from the –HCO fragment17 [Figure 2(a)] is in
Me
Me
8
13
O
C
O
C
Me
Me
46.3
36.7
29.1
54.3
*CH
*CH2 Me
Me *CH2 *CH
Me
Me
9
10
Scheme 1
signals from 13C-labelled aliphatic carbons of the acids at 22.5,
27.3, 35.8, 43.9 and 46.3 ppm belong to 2-methylpentanoic 11,
2-ethylbutanoic 12 and 2,2-dimethylbutanoic 13 acids‡‡ (see
Scheme 1§).
When the reaction was carried out in the presence of water,
carboxylic acids 11–13 were formed as the only products of
n-pentane carbonylation. No signals from aldehydes and ketones
were observed (Figure 2).§§
‡‡ The carboxylic acids extracted with Et2O from the catalyst reveal the
following 13C NMR chemical shifts in CDCl3 solution, d: 11, 13.9
(5-Me), 16.8 (Me), 20.5 (4-CH2), 35.9 (3-CH2), 39.4 (2-CH), 183.9
(1-COOH); 12, 11.8 (Me), 24.9 (CH2), 49.0 (CH), 183.3 (COOH); 13,
9.2 (Me), 24.5 [(Me)2], 33.3 (CH2), 42.6 (C), 185.4 (COOH). The data
are in complete accordance with the chemical shifts for these com-
pounds.12
§§ In the presence of water, the conversion of n-pentane was 40% at
150 °C with the following selectivity: 5, 83%; 11, 5%; 12, 5%; and 13, 7%.
– 24 –

, 2001, 11(1), 23–25
6
V. M. Mastikhin, A. V. Nosov, S. V. Filimonova, V. V. Terskikh, N. S.
Kotsarenko, V. P. Shmachkova and V. I. Kim, J. Mol. Catal., 1995,
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M. V. Luzgin, A. G. Stepanov, A. Sassi and J. Sommer, Chem. Eur. J.,
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D. H. Barich, J. B. Nicholas, T. Xu and J. F. Haw, J. Am. Chem. Soc.,
1998, 120, 12342.
A. G. Stepanov, V. N. Sidelnikov and K. I. Zamaraev, Chem. Eur. J.,
1996, 2, 157.
favour of the second route. The formyl cation can be formed
from formate as an equilibrated species. To date, we cannot
elucidate by which of the two routes the carbonylation occurs.
We assume that both routes for aldehyde formation are pos-
sible, similarly to the case with isobutane carbonylation on SZ.18
In conclusion, this work represents the first example of
n-pentane carbonylation on a SZ catalyst. This study opens up
new possibilities of using SZ catalysts for direct carbonylation
of alkanes to produce valuable chemical products (carboxylic
acids, aldehydes and ketones).
7
8
9
10 G. E. Hawkes, K. Herwig and J. D. Roberts, J. Org. Chem., 1974,
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11 A. G. Stepanov, M. V. Luzgin, V. N. Romannikov, V. N. Sidelnikov and
K. I. Zamaraev, J. Catal., 1996, 164, 411.
12 P. A. Couperus and A. D. Clague, Org. Magn. Reson., 1978, 11, 590.
13 (a) S. Danilow and E. Vanus-Danilowa, Ber. Dtsch. Chem. Ges. B,
1926, 59, 377; (b) G. A. Olah, D. H. O’Brien and M. Calin, J. Am.
Chem. Soc., 1967, 89, 3582.
14 G. A. Olah, A. Burrichter, G. Rasul, G. K. S. Prakash, M. Hachoumy
and J. Sommer, J. Am. Chem. Soc., 1996, 118, 10423.
15 R. T. Morrison and R. N. Boyd, Organic Chemistry, Allyn & Bacon,
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16 T. H. Clingenpeel, T. E. Wessel and A. I. Biaglow, J. Am. Chem. Soc.,
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17 (a) T. M. Duncan and R. W. Vaughan, J. Catal., 1981, 67, 49; (b) N. D.
Lazo, D. K. Murray, M. L. Kieke and J. F. Haw, J. Am. Chem. Soc.,
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18 A. G. Stepanov, M. V. Luzgin, A. V. Krasnoslobodtsev, V. P. Shmachkova
and N. S. Kotsarenko, Angew. Chem., Int. Ed. Engl., 2000, 39, 3658.
This research was supported by the Russian Foundation for
Basic Research (grant no. 99-03-32454). We are grateful to
A. V. Krasnoslobodtsev for his assistance in the extraction
experiments and to V. N. Zudin for the synthesis of 13C-labelled
n-pentane.
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Received: 22nd June 2000; Com. 00/1671
– 25 –