Formic acid: A promising bio-renewable feedstock for fine chemicals

Article abstract of DOI:10.1002/adsc.201200748

In light of the growing scarcity of petroleum-based raw materials, carbon dioxide (CO₂) is becoming increasing attractive as organic carbon source. In this perspective, formic acid (HCOOH) might be an interesting bio-renewable solution to store, transport, and activate carbon dioxide for the synthesis of value-added chemicals. Herein, HCOOH has been successfully used as C₁ building block for the synthesis of a library of alcohols via a catalysed oxo-synthesis, under green experimental conditions. Copyright

Full text of DOI:10.1002/adsc.201200748

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DOI: 10.1002/adsc.201200748
Formic Acid: A Promising Bio-Renewable Feedstock for Fine
Chemicals
Manuel G. Mura,a Lidia De Luca,a Giampaolo Giacomelli,a
and Andrea Porcheddua,*
a
Dipartimento di Chimica e Farmacia, Universitꢀ degli Studi di Sassari, via Vienna 2, 07100 Sassari, Italy
Fax : (+39)-079-229-559; e-mail: anpo@uniss.it
Received: August 21, 2012; Published online: November 8, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200748.
Abstract: In light of the growing scarcity of petrole-
um-based raw materials, carbon dioxide (CO2) is
becoming increasing attractive as organic carbon
source. In this perspective, formic acid (HCOOH)
might be an interesting bio-renewable solution to
store, transport, and activate carbon dioxide for the
synthesis of value-added chemicals. Herein,
HCOOH has been successfully used as C1 building
block for the synthesis of a library of alcohols via
a catalysed oxo-synthesis, under green experimental
conditions.
Recently, Tominaga et al.[5] have first designed
a new hydroformylation pathway, exploiting a reverse
water gas shift reaction (RWGSR), which use CO2 in
place of CO as a reactant. In their studies, after
screening several catalysts,[5a] they have shown that
only clustered ruthenium carbonyl compounds,[6] such
as Ru3(CO)12, in the presence of LiCl as promoter,[7]
catalyse both the reduction of CO2 to CO, and olefin
hydroformylation. In spite of the remarkable results
recently reported for hydrogen release from formic
acid,[8] much less attention has been paid to the use of
HCOOH as feedstock for organic chemicals. In this
regard, we believe that in situ generated CO2 and H2
by catalytic decomposition of formic acid would make
this oxo-synthesis process more interesting and versa-
tile, avoiding all the safety issues related to the use
and management of gaseous reagents (Scheme 1). In
Keywords: carbon dioxide (CO2); formic acid
(HCOOH); ionic liquids; syngas; triruthenium do-
decacarbonyl [Ru3(CO)12]
Nowadays, a lot of non-natural compounds represent-
ed by drugs, detergents, and plastics etc. contribute to
progress and improvement of quality of life. However,
the increasing shortage of fossil resources, and unfav-
ourable effects of carbon dioxide on climate, forces us
to face serious environmental and resource prob-
lems.[1] In future, alternative organic carbon sources
need to be developed in order to ensure the supply of
raw materials. In this perspective, carbon dioxide,
which has long been considered as a waste, is now be-
Scheme 1. Use of HCOOH as syngas source in hydroformy-
lation process.
coming increasingly attractive as a C1 building block addition, the use of formic acid instead of syngas
for energy products and chemicals.[2] Even if CO2 is would render hydroformylation reactions easier to
an abundant, cheap, and totally renewable feedstock[3] perform even on a small scale.
compared to CO, the latter species is mainly used as
Herein, we wish to report our recent studies con-
primary carbon source to synthesise value-added cerning the use of formic acid in hydroformylation re-
products. The activation of CO2 by catalytic hydroge- actions under greener experimental conditions. As
nation appears interesting as it increases the low reac- first step, we have designed a set of experiments in
tivity of carbon dioxide and overcomes some unfav- order to establish the best operating parameters (tem-
ourable thermodynamic aspects (DG8298 = +33 perature, solvent effect and relative kinetics, etc.) con-
kJmolÀ1).[4]
cerning the Ru3(CO)12/LiCl-promoted formic acid de-
composition.
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Adv. Synth. Catal. 2012, 354, 3180 – 3186

Formic Acid: A Promising Bio-Renewable Feedstock for Fine Chemicals
In a continuous set-up, an NMP solution of formic ducted in two separate glass reactors contained into
acid and HCOONa in the presence of the ruthenium a single autoclave as shown in Figure 3.
cluster catalyst together with LiCl was placed in
Formic acid decomposed into chamber-reactor
a thermostatically controlled autoclave, and the tem- 1 (outer vessel), while the hydroformylation occurred
perature varied (58CminÀ1) from 258C up to 2008C. into chamber-reactor 2 (inner vessel). Therefore the
Once the temperature reached 1308C, an exponential outer reactor was charged with an NMP solution of
growth of pressure was observed, which stabilized HCOOH/HCOONa,[13] and LiCl in the presence of
after about 10 min (Figure 1, HCOOH/HCOONa, Ru3(CO)12; whereas cyclohexene, Ru3(CO)12 and LiCl
10:1 line). A GC analysis showed that the formic acid promoter in NMP were added to the inner reactor.
was completely and selectively decomposed into CO2
and H2.[9] No change was observed at temperatures
higher than 1508C. The results showed that the de-
composition rate of formic acid was relatively low in
the presence of solo HCOOH and became more pro-
nounced after the addition of a small quantity of
HCOONa (Figure 1). Here, the 30/1 molar ratio of
HCOOH/HCOONa was identified as the ideal pro-
portion for achieving high conversion and relatively
fast reaction rate (Figure 1, HCOOH/HCOONa 30:1
line).[10] The role of solvent in governing the decom-
position rates of formic acid was also studied in the
130–1608C range. It is noteworthy that when the reac-
tion was carried out without solvent the rate of
formic acid decomposition increased from a few mi-
nutes into 1 h.
The resulting reddish-brown catalytic mixture could
be recycled more than 5 times without substantial loss
of activity (Figure 2).
Figure 2. Catalyst recycling diagram for decomposition of
The decomposition of formic acid into syngas re- formic acid.
started again by adding fresh HCOOH at the end of
each run.[11] Once setting up the selective degradation
of formic acid to CO2 and H2, we have focused our at-
tention on the carbon dioxide reduction to CO and
the subsequent hydroformylation of alkenes. Since
formic acid is known for its ability to react with ole-
fins giving formic acid esters,[12] the HCOOH decom-
position and the hydroformylation reaction were con-
Figure 1. Decomposition of formic acid as a function of
HCOOH/HCOONa ratio. Reaction conditions: HCOOH
(212 mmol), Ru3(CO)12 (0.1 mmol), LiCl (0.5 mmol), NMP
(15 mL), 1508C.
Figure 3. The gas-producing (outer vessel) and gas-consum-
ing chamber (inner vessel).
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Manuel G. Mura et al.
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reducing undesired hydrogenation (Table 1, compare
entries 10 vs. 11–15). The chloride anion stabilizes the
Ru3(CO)12 catalyst avoiding precipitation of metal
catalyst, while NTf2 anion promotes the solubilisation
of the olefin in ILs.[20]
In a typical experiment, the reaction with HCOOH
was carried out at 1508C in a stainless steel autoclave
by applying the above described two-chamber system
Scheme 2. Hydroformylation of cyclohexene using HCOOH
as syngas source.
The autoclave was heated up to 1508C and kept at (one inside the other, see Figure 3). The external
this temperature for 24 h, up to complete conversion chamber was charged with the gas-releasing system
of cyclohexene,[14] to give cyclohexylmethanol[15] in using 8 mL of HCOOH (212 mmol), HCOONa
51% isolated yield (Scheme 2).[16] When operating in (7 mmol), ruthenium cluster complex Ru3(CO)12
a single chamber system, cyclohexylmethanol was in- (0.1 mmol) as a catalyst, and LiCl (0.5 mmol) as a pro-
stead recovered in very low yields (<10%).
moter. Once the formic acid was completely decom-
Further investigations were performed aimed to im- posed to CO2 and H2, the subsequently RWGSR and
prove these results and to establish a greener strategy. oxo-synthesis occurred in the inner glass reactor,
Therefore, we have studied the influence of several which contained the catalyst Ru3(CO)12 (0.1 mmol)
non-conventional solvents, including ionic liquids dissolved in a mixture of two ionic liquids [bmim]Cl
(Table 1). In search of the best reaction solvent for (2.5 mmol), [bmim]NTf2 (2.5 mmol)], and cyclohex-
the preparation of cyclohexylmethanol, an improved ene (10 mmol). The autoclave was held at 1508C for
yield was observed employing Peg-OMe (Table 1, 24 h with stirring. After cooling and bulb-to-bulb dis-
entry 8),[17] but more impressive results were obtained tillation, cyclohexylmethanol was recovered in 86%
using ionic liquids[18] (Table 1, compare entry 8 and isolated yield (Table 1, entry 11).
11). This is most likely due to the increased solubility
The yields of cyclohexylmethanol significantly in-
of CO2 in ionic liquid salts[19] compared to other sol- creased on increasing the concentration of Ru3(CO)12
vents. A binary mixture of ionic liquids [bmim] [Cl+ from 0.05 up to 0.1 mmol, beyond which no significant
NTf2] was successfully used as reaction medium for variation was observed.
the chemoselective hydroformylation of olefins thus
Table 1. Solvent effect on the ruthenium catalysed hydroformylation of cyclohexene with HCOOH.[a]
Entry
Solvent
Promoter
Conv. [%][b]
Alcohol Yield [%][c]
1
2
3
4
5
6
7
8
NMP[d]
LiCl
LiCl
A
LiCl
LiCl
LiCl
LiCl
LiCl
–
–
–
–
–
100
95
94
95
95
96
96
95
95
72
95
97
88
99
99
51
54
41
23
32
52
56
65
58
51
86
69[j]
63
72
60
DMPU[e]
CPME[f]
Peg-OH (200)
Peg-OH (400)
DGBE[h]
tetraglyme
Peg-OMe (500)
T
[bmim][Cl][g]
9
[Cl+BF4][i]
ACHTUNGTRENNUNG
10
11
12
13
14
15
N
E
G
A
R
T
N
A
–
–
[a]
Reaction conditions: (chamber 1) HCOOH (212 mmol), HCOONa (7 mmol), Ru3(CO)12 (0.1 mmol), LiCl (0.5 mmol);
(chamber 2) cyclohexene (10.0 mmol), ILs (5 mmol) or solvent (3 mL), Ru3(CO)12 (0.1 mmol), 1508C, 24 h.
Determined by GC analysis.
Isolated yield.
NMP=N-methyl-2-pyrrolidone.
DMPU=N,N-dimethypropyleneurea.
CPME=cyclopentyl methyl ether.
bmim=1-butyl-3-methyl-imidazolium.
DGBE=diethylene glycol dibutyl ether.
dmim=1-decyl-3-methylimidazolium.
Reaction carried out at 1858C.
[b]
[c]
[d]
[e]
[f]
[g]
[h]
[i]
[j]
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Formic Acid: A Promising Bio-Renewable Feedstock for Fine Chemicals
Table 2. Hydroformylation of alkenes using HCOOH as non-conventional syngas surrogate.[a]
Entry
Alkene
Conv.[b]
Alcohol Yield [%][c]
n/i ratio [%][b]
1
2
3
4
5
6
7
8
cyclohexene
cyclooctene
1-hexene
2-hexene
3-hexene
2-methyl-1-hexene
3,3-dimethyl-1-butene
1-octene
1-decene
1-dodecene
vinylcyclohexane
95
96
95
95
96
95
96
94
94
95
94
95
98
96
96
97
96
97
86
85
74
76
75
71
83
70
67
55
81
63
15
5
–
–
85/15
83/17
82/18
100/0
100/0
80/20
81/19
79/21
82/18
–
77/23
–
81/19
100/0
100/0
100/0
9
10
11
12
13
14
15
16
17
18
bicycloACTHUNGTRENUN[NG 2.2.1]hept-2-ene
styrene
vinylanisole
allylbenzene
a-methylstyrene
4-fluoro-a-methylstyrene
a,2-dimethylstyrene
79
71
68
65
[a]
Reaction conditions: (chamber 1) HCOOH (212 mmol), HCOONa (7 mmol), LiCl (0.5 mmol), Ru3(CO)12 (0.1 mmol);
(chamber 2) [bmim]Cl (2.5 mmol), [bmim]NTf2 (2.5 mmol), Ru3(CO)12 (0.1 mmol), alkene (10.0 mmol), 1508C, 24 h.
Determined by GC analysis.
Isolated yields.
[b]
[c]
The effect of temperature was investigated too. The down to 55% for 1-dodecene (Table 2, entries 3, 8–
best results were observed at 1508C (Table 1, com- 10).
pare entry 11 and 12), while below 1308C the catalytic BicycloCATHNUGTRNE[NGU 2.2.1]hept-2-ene also proved to be an appli-
activity dropped considerably, and at higher tempera- cable substrate for this hydroformylation and was
ture a rise in the component of hydrogenated product converted to the corresponding alcohol in good yield
(cyclohexane) was detected.[21] Nevertheless, the com- (Table 2, entry 12). Significant differences in the reac-
peting hydrogenation side reaction of cyclohexene tivity of vinylarenes have been observed. Styrene and
was much less significant than hydroformylation, vinylanisole (Table 2, entries 13 and 14) did not pro-
which remains the dominating process. A key advant- vide any useful result since they underwent mainly
age of this procedure was that the final alcohol could the hydrogenation reaction, while a-methylstyrene re-
be easily removed from the ionic liquids making the acted satisfactorily giving 3-phenyl-1-butanol in good
whole process more efficient, and less time-consuming yield (71%; Table 2, entry 16). In general, under the
to perform. Once having removed water and any best experimental conditions, olefins showed the fol-
other organic substances by distillation, the resulting lowing reactivity order: cyclic alkenes>1-alkenesꢀa-
mixture containing the active catalytic species was methylstyrene@styrene.
successfully reused several times. The catalytic activity
The regioselectivity is another interesting and at-
appeared to be very robust; it remained constant tractive feature of this oxo synthesis. The hydroformy-
during the first recycle and continued almost un- lation of different 1-alkenes gave preferentially the
changed for 5 recycles.[22]
linear alcohol with almost 80:20 selectivity, except in
Having such efficient conditions for the hydrofor- the case of 2-methyl-1-hexene (Table 2, entry 6), 3,3-
mylation reaction, we have then extended the proce- dimethyl-1-butene (Table 1, entry 7), a-methylstyrene
dure to other substrates in order to test the scope and and its derivatives that, owing to their steric hin-
limitations of the present reaction protocol. We were drance, provided only the linear product (Table 2, en-
pleased to see that hydroformylations of substrates tries 16–18). It is noteworthy that the hydroformyla-
other than cyclohexene proceeded in all cases in good tion of internal olefin substrates such as 2- and 3-
to high yields. Various aliphatic and aromatic olefins hexene did not give the expected products, but a mix-
were hydroformylated in good yields (Table 2). For 1- ture of 1-heptanol and 2-methyl-1-hexanol, the same
hexene, 1-octene, and 1-decene, high conversions and products that were isolated by hydroformylation of 1-
good yields were observed, whereas on increasing the hexene (Scheme 3).
hydrocarbon chain length of the alkene the yields fall
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Manuel G. Mura et al.
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Scheme 3. Hydroformylation of internal alkenes.
fetti sul SNC di una libreria di donatori di nitrossido derivati
dall’acido di Piloty”, Legge Regionale 7 Agosto 2007, N. 7:
“Promozione della Ricerca Scientifica e dell’Innovazione
Tecnologica in Sardegna”.
These results suggest a migration of double bond
along the carbon chain, from the internal to the ter-
minal position, that presumably occurred prior and
significantly much faster than the oxo-synthesis pro-
cess.[23]
In summary, we have shown that HCOOH can be
used as a sustainable source of syngas avoiding all the
safety issues related to the use and management of
gaseous reagents. The cluster complex Ru3(CO)12 was
able to decompose formic acid to syngas and promote
the hydroformylation of various alkenes in a one-pot
reaction. Several aliphatic and aromatic olefins were
hydroformylated in good to high yields. The ionic
liquid containing the catalyst system may be recycled
several times without significant loss of activity and
selectivity. In this regard, we believe that formic acid
could play a key role not only in the energy sector,
but also in supporting the chemical industry as
a green feedstock for chemicals. Further studies are
underway in our laboratory to extend the use of
HCOOH as eco-compatible feedstock in hydroamino-
methylation reactions.
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Experimental Section
General Procedure
8 mL of HCOOH (9.76 g, 212 mmol), 0.48 g of HCOONa
(7.0 mmol), 21 mg of LiCl (0.5 mmol), and 64 mg di
Ru3(CO)12 (0.1 mmol) were put into chamber 1 of the two-
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a red brown solution of Ru3(CO)12 (64 mg, 0.1 mmol) in
[bmim]Cl (0.436 g, 2.5 mmol), and [bmim]NTf2 (1.048 g,
2.5 mmol) contained into chamber 2. The two-chamber
system, so loaded, was placed in a 100-mL stainless steel au-
toclave, that was heated at 1508C and held at that tempera-
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reached, the autoclave was cooled and the excess pressure
released using a needle. The separation and purification of
alcohol was achieved by bulb-to-bulb distillation, silica gel
chromatography or using both the methodologies if necessa-
ry. The products were identified by comparison of spectral
data with those for authentic materials or literature data.
All the experiments were conducted in duplicate.
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Acknowledgements
This work was supported by Regione Autonoma della Sarde-
gna (Grant No. J71 J1 0000250002), Project CRP1 409: “Ef-
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conventional hydroformylation with syngas, only clus-
tered ruthenium carbonyl compounds such as
H4Ru4(CO)12, [PPN]ACHTUNTGREN[NUG RuCl3(CO)3], and Ru3(CO)12 cata-
lyse the hydroformylation with CO2. Among these cata-
lyst precursors, the commercially available and air-
stable Ru3(CO)12 is by far the most widely used, and
one of the most effective: a) T. Mitsudo, T. Kondo, in:
Ruthenium-Catalyzed Reaction with CO and CO2,
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[7] The presence of LiCl is crucial in preventing the de-
composition of the cluster to ruthenium metal. In addi-
tion, it improves the hydroformylation chemoselectivity
supressing undesired olefin hydrogenation. K. Tomina-
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be completely recovered and recycled at the end of re-
action. These results showed good agreement with liter-
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[11] Blank experiments at 1308C were conducted and no
decomposition was observed without catalyst.
[8] The advantage of HCOOH is that it has an energy stor-
age capacity comparable to liquid hydrogen, but it
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[13] The highest CO concentration was observed at 80 bar
CO2/H2 total pressure (ref.[5a]). Therefore, we per-
formed a set of experiments using increasing amounts
of HCOOH in order to generate a final pressure of
80 bar.
[14] Determined by GC-MS analysis.
[15] Cyclohexanecarbaldehyde, the primary hydroformyla-
tion product (detected by GC-analysis), was completely
converted into the corresponding alcohol.
[16] At the end of the reaction, a GC analysis of gaseous
components inside the autoclave confirmed the simul-
taneous presence of CO, H2, and CO2.
[17] PEG-OMe is a cheap, thermally stable, recoverable,
environmentally benign and non-toxic solvent. C.
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the recovery of the final alcohol in higher yield and are
in agreement with literature data (see ref.[5b]).
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[20] We have observed that these two synergistic effects in-
creased the conversion of cyclohexene and the yield of
cyclohexylmethanol. The use of the two liquid ions in
a molar ratio represented a good compromise allowing
[21] At higher temperatures, both the conversion and hy-
drogenation of cyclohexene increased, thereby decreas-
ing the yield of alcohol. At temperatures below 1408C,
the reaction became rather slow. Even at lower temper-
atures, the recovery of aldehyde in significant yield was
rather difficult (<10%).
[22] See Table 3 in the Supporting Information.
[23] Analogous examples of hydroformylation of internal
olefins with CO are reported by several authors. J. F.
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