Koch carbonylation using silver trifluoromethanesulfonate

Article abstract of DOI:10.1016/S0040-4039(02)01945-7

Koch carbonylation was carried out using silver trifluoromethanesulfonate (AgOTf). Tertiary alcohols were transformed into the corresponding carboxylic acids in good yield under carbon monoxide atmosphere (5 MPa: initial pressure) at 150°C. It can be assumed that under these reaction conditions, a strong acid, in which a silver(I) cation participates, would be generated from AgOTf.

Full text of DOI:10.1016/S0040-4039(02)01945-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 7871–7874
Koch carbonylation using silver trifluoromethanesulfonate
Hajime Mori,*,† Aya Mori, Qiang Xu and Yoshie Souma*
National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
Received 11 July 2002; revised 31 July 2002; accepted 6 September 2002
Abstract—Koch carbonylation was carried out using silver trifluoromethanesulfonate (AgOTf). Tertiary alcohols were trans-
formed into the corresponding carboxylic acids in good yield under carbon monoxide atmosphere (5 MPa: initial pressure) at
150°C. It can be assumed that under these reaction conditions, a strong acid, in which a silver(I) cation participates, would be
generated from AgOTf. © 2002 Elsevier Science Ltd. All rights reserved.
The transformation from carbon monoxide with alco-
hols or olefins and H2O to carboxylic acids is well
known as Koch carbonylation1 and is a glamorous
process from the standpoint of atom economy.
Although the reaction is usually carried out under
severe conditions such as high CO pressure, high tem-
perature and strong acid media, some modified meth-
ods have recently been developed. As milder reaction
conditions, we have already found that at ambient
temperature and pressure, the Cu(I), Ag(I), Au(I),
Pd(I), Pt(I), and Rh(I) carbonyl cations generated in
concentrated H2SO4 work well as a catalyst for Koch
carbonylation.2 From both the industrial and environ-
mental points of view, we and other groups have also
reported the carbonylation of alcohols over solid acids
such as H-zeolite,3 sulfated zirconia,4 Nafion-H,5 and
an acidic ion-exchange resin6 and much attention has
focused on a convenient and environmentally benign
process for Koch carbonylation.
reaction catalyzed by the BINAP–AgOTf complex
shows remarkable progress for its application.9 During
the investigation of a new process for Koch carbonyla-
tion, we found that the carbonylation using a catalytic
amount of AgOTf smoothly proceeded and AgOTf,
weak and soft Lewis acid, gave better results than the
common hard Lewis acids. Furthermore in this process
no workup operation such as extraction and neutraliza-
tion was required to obtain carboxylic acids, similar to
the previous study using solid acids.3–5 In this report, as
a new application of AgOTf and a novel and conve-
nient process for Koch carbonylation, we describe the
carbonylation of alcohols or olefins and H2O with
carbon monoxide over AgOTf to form carboxylic acids.
The activity of various Lewis acids for the conversion
of tert-butyl alcohol to pivalic acid, was first investi-
gated. The reaction was carried out in a stainless steel
autoclave at 150°C under carbon monoxide (5 MPa:
initial pressure) atmosphere for 18 h using hexane as
the solvent. The obtained results are summarized in
Table 1. The highest yield of carboxylic acids was
achieved using AgOTf, while the other silver salts
(AgOAc and Ag2SO4) completely lacked any catalytic
activity (entries 1–3). These results suggest that the
acidity of the conjugated acid of the silver salts would
be of great importance. Among the common hard
Lewis acids, BF3·Et2O gave moderate results, while
AlCl3 and TiCl4 were inert for this reaction (entries
4–7). The Lewis acidity did not directly affect the yield
of the carboxylic acids. The active species generated in
situ from AgOTf will be discussed below.
Silver(I) salts have been widely used for the oxidation
and the activation of carbon–halogen and carbon–
sulfide bonds. Silver trifluoromethanesulfonate (AgOTf)
is, in particular, a common reagent for O-glycosylation
as a promoter and its application for glycoside chem-
istry has been significantly explored.7 Compared with
the application described above, the utilization of
AgOTf for acid-catalyzed reactions8 is quite limited,
although the recent report on the enantioselective aldol
Keywords: Koch reaction; silver trifluoromethanesulfonate; tert-car-
boxylic acid.
* Corresponding authors. Tel.: +81-73-477-1271; fax: +81-73-477-
2880; e-mail: hmori@wakayama-kg.go.jp
The additives significantly contributed to the carbonyl-
ation (Table 2). Thus, the addition of 5 mmol H2O,
which promotes the formation of carboxylic acids from
† Present address: Industrial Technology Center of Wakayama Prefec-
ture, Ogura 60, Wakayama 649-6261, Japan.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01945-7

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H. Mori et al. / Tetrahedron Letters 43 (2002) 7871–7874
Table 3. Results of the carbonylation of various alcohols
and olefins over AgOTfa
Table 1. Yield of carboxylic acids from tert-butyl alcohol
over various Lewis acidsa
Entry
Catalysts
Yield of carboxylic acids/% Selectivityd/%
Totalb
Pivalic acidc
1
2
3
4
5
6
7
AgOTf
AgOAc
Ag2SO4
BF3·Et2O
TiCl4
26.5
0
0
15
1
1
23.4
0
0
11.6
–
–
88
–
–
77
–
–
AlCl3
Sn(OTf)2
4.3
3.3
77
a Reaction conditions: 120 mL autoclave, tert-butyl alcohol (5 mmol),
catalyst (1 mmol). Hexane (50 mL), CO (5 MPa; initial pressure),
150°C, 18 h.
b Titration yield of total carboxylic acids.
c GC yield.
d 100×(yield of pivalic acid/yield of total carboxylic acids).
the intermediate acyl cation rather than the oligomer-
ization of iso-butene produced by dehydration of tert-
butyl alcohol, improved the yields of the carboxylic
acids, and even the addition of 15 mmol H2O, which is
the 15 times amount of AgOTf, did not significantly
degrade the catalytic activity (entries 2 and 3, Table 2).
Furthermore, the reaction under 0.1 MPa air and 4.9
MPa carbon monoxide doubled the yields of the car-
boxylic acids (entry 4). This remarkable effect would
result from the participation of molecular oxygen dur-
ing the reoxidation of the silver salts, which are reduced
under reducing atmosphere. Unfortunately, synergism
between H2O and air did not appear (entry 5).
170°C) and the carbon monoxide (1–5 MPa) pressure
showed no significant contribution to the yield of the
carboxylic acids. The best yield of pivalic acid was
achieved at 150°C and 5 MPa carbon monoxide.
In order to evaluate the potential of AgOTf, we carried
out the carbonylation with various alcohols and olefins
(Table 3). Primary alcohols such as 1-hexanol, 1-
octanol and tertiary alcohols such as tert-butyl alcohol,
1-adamantanol, and 2-methyl-2-butanol, were trans-
formed into the corresponding ethers and carboxylic
acids in good yield, respectively (entries 1, 2 and 5–7).
For secondary alcohols, complex mixtures, which con-
tain neither ethers nor carboxylic acids, were obtained
(entries 3 and 4). Under the reaction conditions, the
alkyl cation, which reacts with carbon monoxide and
The effect of solvents was also examined under the
same reaction conditions (no additive) and it was found
that the employment of the halogen-containing solvent
CH2Cl2 caused little decrease of the yield of total
carboxylic acids (22.8%) and a low selectivity of pivalic
acid (25%). Variation of the reaction temperature (120–
Table 2. Additive effect on the carbonylation of tert-butyl alcohola
Entry
Additives (mmol)
Yield of carboxylic acids/%
Selectivityd/%
Totalb
Pivalic acidc
1
2
3
4
5
None
H2O (5)
H2O (15)
Air (0.1 MPa)
Air (0.1 MPa) H2O (5)
26.5
36.5
24.0
55.5
54.0
23.4
30.7
18.4
44.0
44.8
88
84
77
79
83
a Reaction conditions: 120 mL autoclave, tert-butyl alcohol (5 mmol), AgOTf (1 mmol), hexane (50 mL), CO (5 MPa: initial pressure), 150°C,
18 h.
b Titration yield of total carboxylic acids.
c GC yield.
d 100×(yield of pivalic acid/yield of total carboxylic acids).

H. Mori et al. / Tetrahedron Letters 43 (2002) 7871–7874
7873
H2O to form carboxylic acids, was generated only from
the tertiary alcohols, while a substitution and an
oligomerization were the main reactions for the primary
and secondary alcohols, respectively. The results using
Nafion-H under similar conditions,5 in which the
smooth conversion from primary and secondary alco-
hols to a carboxylic acid was observed, apparently
indicate that the acidity of the reaction media would
not be enough for the generation of the carbocation
from the primary and secondary alcohols. Olefins with
an equal amount of H2O were also converted to the
corresponding carboxylic acid under the same reaction
conditions, although the yields of the carboxylic acids
were lower than that of the alcohol due to the signifi-
cant oligomerization (entries 8 and 9).
salts of heteropoly acids supported on silica showed
high catalytic activity for the isomerization of hexane in
the presence of hydrogen rather than the parent acids,12
which are commonly used for various acid-catalyzed
reactions as a solid acid catalyst. Based on the detailed
investigation of their behavior under hydrogen atmo-
sphere, they explained the unique phenomenon that the
generation of a Brønsted-acid from the silver salts of
heteropoly acids easily occurred and the mobility of
protons in them was greater than that in the parent
acids. From AgOTf, as described above, a strong acid
and reduced silver metal would be generated. Taking
the difference between AgOTf and metal oxide clusters
on silica into consideration, the mobility of protons is
not an important factor in our case. In the presence of
air, reduced silver metal would be partly reoxidized to
silver(I) cations and the formation of cationic silver(I)
carbonyl complexes, which effectively catalyze Koch
reaction in H2SO4,2a is expected in the reaction media.
In fact, the carbonyl complexes were observed by IR
measurement in the silver salts of heteropoly acids and
the silver-exchanged zeolites under low carbon monox-
ide pressure.10,12,13 Judging from the consideration
described above, it seems that in our reaction condi-
tions (4.9 MPa carbon monoxide and 0.1 MPa air), a
strong acid produced from AgOTf cooperates with
silver(I) carbonyl complexes to catalyze Koch reaction.
Although we performed IR measurement to catch the
carbonyl complexes generated in situ, any such active
species have not been trapped yet. The positive effect of
water on the redox behavior of silver cations in silver
exchanged zeolites was also reported10,13 and in the
present case, water would work at the promotion of the
formation of carboxylic acids from acyl cation and
might contribute to the acceleration of the reduction of
a silver(I) cation, along with the formation of a
Brønsted-acid.
Taking the Lewis acidity of AgOTf into consideration,
it is curious that AgOTf was effective for Koch car-
bonylation which is usually performed under a strong
Brønsted-acid media such as concentrated H2SO4. In
general, silver(I) compounds show an easily reduced
character and under the carbon monoxide atmosphere,
the generation of a Brønsted-acid from the silver-
exchanged zeolites, have already been proposed.10 Judg-
ing from the previous report, in our case, the reduction
of AgOTf, which causes the generation of an acid such
as trifluoromethanesulfonic acid (TfOH), probably
occurred.11 In order to compare the acid generated in
situ with TfOH, we carried out the carbonylation of
tert-butyl alcohol, using TfOH under several reaction
conditions (Table 4). Although the reaction using
TfOH under the same conditions gave better results
than that of AgOTf, the effect of additives was com-
pletely different between TfOH and AgOTf. Thus, the
addition of water and air was advantageous for AgOTf,
while for TfOH the opposite effects due to the additives
appeared. Generally speaking, the addition of H2O,
which reduces the acidity of a strong acid, and of air,
which causes the side reactions such as oxygenation by
molecular oxygen, are unfavorable for Koch carbonyla-
tion as shown in the reaction by TfOH. The results
obtained here suggest that not trifluoromethanesulfonic
acid but an acid, in which a silver(I) cation would
participate, would be generated in situ under the reac-
tion media. Ono and co-workers reported that the silver
In conclusion, we have demonstrated the novel applica-
tion of AgOTf for Koch carbonylation and found that
it worked well for the synthesis of tert-carboxylic acids
from tertiary alcohols and of ethers from primary alco-
hols. The attempt described here provides a new insight
into its use in synthetic organic chemistry.
Table 4. Comparison of the additive effect between AgOTf and TfOHa
Catalysts
Additives
Yield of carboxylic acids/%
Selectivityd/%
Totalb
Pivalic acidc
AgOTf
None
26.5
55.5
36.5
64.5
42.5
23.5
23.4
44.0
30.7
46.5
31.1
15.9
88
79
84
72
73
68
Air 1 atm
H2O (5 mmol)
None
Air 1 atm
H2O (5 mmol)
CF3SO3H
a Reactions conditions: 120 mL autoclave, tert-butyl alcohol (5 mmol), catalyst (1 mmol). Hexane (50 mL). CO (5 MPa: initial pressure), 150°C,
18 h.
b Titration yield of total carboxylic acids.
c GC yield.
d 100×(yield of pivalic acid/yield of total carboxylic acids).

7874
H. Mori et al. / Tetrahedron Letters 43 (2002) 7871–7874
7. For example: (a) McAuliffe, J.; Hindsgaul, O. J. Org.
References
Chem. 1997, 62, 1234; (b) Kim, N.; Kinghorn, A.; Kim,
D. Org. Lett. 1999, 1, 223; (c) Ercegovic, T.; Meijer, A.;
Magnusson, G.; Ellervik, U. Org. Lett. 2001, 3, 913.
8. For a recent review see: Lewis Acids in Organic Synthesis;
Yamamoto, H., Ed.; Wiley VCH: Weinheim, 2000; Vol.
2, p. 575.
9. (a) Yanagisawa, A.; Nakashima, H.; Ishiba, A.;
Yamamoto, H. J. Am. Chem. Soc. 1996, 118, 4723; (b)
Yanagisawa, A.; Matsumoto, Y.; Nakashima, H.;
Asakawa, K.; Yamamoto, H. J. Am. Chem. Soc. 1997,
119, 9319; (c) Yanagisawa, A.; Matsumoto, Y.; Asakawa,
K.; Yamamoto, H. J. Am. Chem. Soc. 1999, 121, 892.
10. Calzaferri, G.; Sater, N.; Waldek, B. J. Chem. Soc.,
Chem. Commun. 1990, 485.
11. The pH of the water phase obtained by the extraction of
the reaction mixtures was 2.9. Titration of the water
phase by a 0.1N NaOH ethanol solution showed that a
water-soluble acid was almost quantitatively produced
from AgOTf in the reaction media.
12. Baba, T.; Nomura, M.; Ono, Y.; Kansaki, Y. J. Chem.
Soc., Faraday Trans. 1992, 88, 71.
13. Baba, T.; Akinaka, N.; Nomura, M.; Ono, Y. J. Chem.
Soc., Faraday Trans. 1993, 89, 595.
1. New Synthesis with Carbon Monoxide; Falbe, J., Ed.;
Springer: Berlin, 1980, p. 372.
2. Cu, Ag: (a) Souma, Y.; Sano, H. J. Org. Chem. 1973, 38,
3633; (b) Souma, Y.; Sano, H.; Iyoda, J. J. Org. Chem.
1973, 38, 2016; (c) Souma, Y.; Sano, H. Bull. Chem. Soc.
Jpn. 1974, 47, 1717; (d) Souma, Y.; Kawasaki, H. Catal.
Today 1997, 36, 91; (e) Souma, Y.; Sano, H.; Miwa, H.;
Kawasaki, H.; Ichikawa, O. J. Synth. Org. Chem. Jpn.
1990, 48, 92. Au: (f) Xu, Q.; Imamura, Y.; Fujiwara, M.;
Souma, Y. J. Org. Chem. 1997, 62, 1594. Pd: (g) Xu, Q.;
Souma, Y.; Umezawa, J.; Tanaka, M.; Nakatani, H. J.
Org. Chem. 1999, 64, 6306. Rh: (h) Xu, Q.; Nakatani, H.;
Souma, Y. J. Org. Chem. 2000, 65, 1540. Pt: (i) Xu, Q.;
Fujiwara, M.; Tanaka, M.; Souma, Y. J. Org. Chem.
2000, 65, 8105.
3. Xu, Q.; Inoue, S.; Tsumori, N.; Mori, H.; Kameda, M.;
Tanaka, M.; Fujiwara, M.; Souma, Y. J. Mol. Catal. A
2001, 170, 147.
4. Mori, H.; Wada, A.; Xu, Q.; Souma, Y. Chem. Lett.
2000, 136.
5. Tsumori, N.; Xu, Q.; Souma, Y.; Mori, H. J. Mol. Catal.
A 2002, 179, 271.
6. Lange, J.-P.; Petrus, L. Appl. Catal. A 2001, 216, 285.