Biomass-derived γ-valerolactone as an efficient solvent and catalyst for the transformation of CO2 to formamides

Article abstract of DOI:10.1039/c6gc01455k

Efficient conversion of carbon dioxide (CO₂) into valuable chemicals is a very attractive topic. Herein, we conducted the first work on the utilization of biomass-derived γ-valerolactone (GVL) as the solvent and catalyst for transformation of CO₂ with various primary and secondary amines in the presence of phenylsilane (PhSiH₃), and the corresponding desired formamides were produced with high yields without any additional catalyst. Systematic studies indicated that the lactone structure of GVL played a key role in the formation of the active silyl formates and the activation of N-H bonds in amines, thus leading to the excellent performance of GVL for the catalytic reactions.

Full text of DOI:10.1039/c6gc01455k

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DOI: 10.1039/C6GC01455K
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Biomass-derived γ-valerolactone as efficient solvent and catalyst
for the transformation of CO2 to formamides
Received 00th January 20xx,
Accepted 00th January 20xx
Jinliang Song,* Baowen Zhou, Huizhen Liu, Chao Xie, Qinglei Meng, Zhanrong Zhang and Buxing
Han*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Efficient conversion of carbon dioxide (CO2) into valuable and 1,3,2-diazaphospholene,11 etc. Although these catalytic
chemicals is a very attractive topic. Herein, we conducted the first systems could provide good performance, there is no doubt
work on the utilization of biomass-derived γ-valerolactone (GVL) that development of simple, efficient, non-toxic, and
as the solvent and catalyst for transformation of CO2 with various renewable catalytic system for the formylation of amines with
primary and secondary amines in the presence of phenylsilane CO2 to produce formamides is still highly desired.
(PhSiH3), and the corresponding desired formamides were
Nowadays, to search and to use biomass-derived
produced with high yields without any additional catalyst. compounds as sustainable solvents or catalysts has become a
Systematic studies indicated that the lactone structure of GVL hot field.12 An increasing attention is directed to γ-
played a key role for the formation of the active silyl formates and valerolactone (GVL), which is a naturally occurring chemical in
the activation of N-H bonds in amines, and thus leading to the fruits and can also be produced from carbohydrate-based
excellent performance of GVL for the catalytic reactions.
biomass.13 Due to the excellent properties of low toxicity,
biodegradation and low vapor pressure, GVL has been
recognized as a sustainable dipolar aprotic solvent for different
reactions,14 such as biomass conversion,14a Sonogashira
reaction,14d and Heck coupling reactions,14f etc. However, as
far as we know, there is no report on utilization of GVL in CO2
conversion. Herein, we conducted the first work on utilization
of GVL as both solvent and catalyst for synthesis of
formamides from amines, CO2 and organosilanes. It was found
that the formylation of amines with CO2 could be conducted
efficiently without any additional catalysts in GVL.
Transformation of carbon dioxide (CO2) into valuable
chemicals has attracted much attention because CO2 is an
abundant and renewable C1 source.1 In particular, catalytic
formation of C-N bonds with CO2 to generate N-containing
compounds (e.g. formamides, N-methylamines) is significant in
both academia and industry.2 Formamides are important
solvents and intermediates, which are currently produced
using carbon monoxide (CO) in industry.3 Using CO2 as an
alternative of toxic CO for the formylation of amines is an
interesting strategy to produce formamides through the
construction of new C-N bonds.
A benchmark reaction of N-methylaniline with CO2 and
phenylsilane (PhSiH3) to afford N-methylformanilide was
initially carried out to examine the influence of different
Generally, formamides could be synthesized from CO2
and amines with H2 over metal catalysts at elevated
temperature and pressure.4 In recent years, using
organosilanes as reductants to convert CO2 into formamides
under milder conditions has received considerable attention.
Different catalytic systems have been developed for this kind
of reactions, including copper-diphosphine complex,5 N-
heterocyclic carbenes (NHC),6 ionic liquids,7 1,5,7-
o
solvents at 50 C and 3 MPa CO2 with a reaction time of 12 h
(Table 1). No reaction was occurred without solvent (Entry 1,
Table 1). Among the examined solvents, only GVL and CH3CN
showed activity for the reaction (Entries 14-15, Table 1),
indicating that the solvents affected the formylation reaction
significantly. To our delight, renewable GVL (Entry 14, Table 1)
showed superior activity for the formylation of N-
methylaniline, which was much higher than CH3CN (Entry 15,
Table 1). Meanwhile, increasing reaction temperature was
beneficial for the formylation reaction in GVL (Fig. S1). N-
methylaniline could be fully transformed into N-
methylformanilide with a yield of 96% at 80 oC for 3 h (Entry 16,
Table 1 and Fig. S2a). In contrast, it needed 16 h to complete
triazabicyclo[4.4.0]dec-5-ene,8
iron(II)
salts
with
a
tetraphosphine ligand,9 bis(NHC)-ligated rhodium complexes,10
o
the reaction at 50 C with a N-methylformanilide yield of 95%
(Entry 17, Table 1 and Fig. S2b). Moreover, the pressure of CO2
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also affected the reaction significantly (Fig. S3). The reaction methylaniline (Entry 3, Table 2) needed a shorter reaction time
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activity increased with rising CO2 pressure from 0.1 MPa to 3 to complete the reaction than N-methylDaOniIl:i1n0e.10(E3n9/tCry6G1C,0T1a45b5leK
MPa mainly due to the higher concentration of CO2 in GVL at 2), indicating that electron-donating groups could be beneficial
higher pressure (Entries 16-20, Table 1),15 which improved the for the formylation reaction. In contrast, the reaction time
interaction between CO2 and other reactants. Interestingly, a should be prolonged to 18 h to obtain satisfactory yields for
N-methylformanilide yield of 63% could be obtained even at the substrates with electron-withdrawing groups (Entries 4
o
0.1 MPa CO2 and 80 C with a prolonged reaction time of 16 h and 5, Table 2). Introducing nitro-, a very strong electron-
(Entry 20, Table 1). These findings indicated that GVL was a withdrawing group, into the reactant completely deactivated
superior solvent for the formylation of N-methylaniline with the formylation reaction (Entry 6, Table 2). In addition, para-
CO2 due to its lactone structure, which will be discussed in the substituted N-methylaniline (Entry 3, Table 2) had a higher
subsequent sections. In addition, we found that diphenylsilane reactivity than the ortho-substituted reactant (Entry 7, Table 2)
(Ph2SiH2) showed lower reactivity than PhSiH3 (Entry 21, Table due to the steric hindrance effect of the substituent group.
1), and triethylsilane (Et3SiH) showed no reactivity (Entry 22, Except for the N-methylanilines, the GVL catalytic system was
Table 1). These results indicated the high reactivity of PhSiH3.
also suitable for the aliphatic secondary amines with good
yields of the corresponding formamides, including morpholine,
pyrrolidine, dipropylamine, and dihexylamine (Entries 10-13,
Table 2). However, 4 equivalent of PhSiH3 was required for
aliphatic secondary amines because the higher basicity of
aliphatic amines could improve the decomposition of PhSiH3
into H2. When the mixture of dihexylamine and PhSiH3 was
stirred at room temperature for 2 h, much more H2 was
generated (Fig. S4) than that from the mixture of N-
methylaniline and PhSiH3 (Fig. S5). These control experiments
indicated the effect of aliphatic amines to decompose PhSiH3
into H2.
Table 1. Formylation of N-methylaniline using CO2 as the carbon source to
produce N-methylformanilide.a
T
(oC)
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
80
50
80
50
80
50
50
t
C
(%)b
0
Y
(%)b
0
S
(%)c
--
Entry
Solvent
(h)
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
3
1
2
None
Ethyl acetate
Dodecane
Tetrahydrofuran
CH2Cl2
1
0
--
3
5
1
--
4
3
1
--
5
2
0
--
Table 2. Formylation of various secondary amines using CO2 as the carbon
source.a
6
CH3CH2OH
Dimethyl carbonate
1,4-Dioxane
Butyl ether
Methylbenzene
Chloroform
Carbon tetrachloride
Acetone
4
1
--
Time
(h)
Conversion
(%)b
Yield
(%)b
7
3
0
--
Entry
Reactant
Product
8
2
0
--
N
NH
NH
1
3
2.5
2
100
100
100
77
89
0
96
98
95
70
83
0
9
3
0
--
CHO
10
11
12
13
14
15
16
17
18d
19d
20e
21f
22g
2
0
--
N
2
CHO
N
6
2
--
4
1
--
H3CO
Cl
H3CO
NH
3
CHO
3
0
--
N
Cl
NH
4
24
24
12
3
GVL
86
19
100
99
80
58
78
12
0
84
16
96
95
76
56
63
11
0
98
84h
96
96
96
97
80h
92
--
CHO
CHO
CHO
CH3CN
Br
N
Br
NH
NH
5
GVL
O2N
N
GVL
16
3
O2N
6
GVL
CHO
NH
N
7
94
97
40
96
98
97
99
92
94
31
91
94
92
94
GVL
16
16
12
12
OCH3
OCH3
GVL
8
3
N
N
H
GVL
CHO
CHO
H
N
GVL
N
9
24
8
aReaction conditions: N-methylaniline, 1 mmol; PhSiH3, 2 mmol; solvent, 1 g; CO2,
CHO
N
10c
11c
12c
13c
H
N
3
MPa. bT=Temperature, t=time, C=conversion, Y=yield. The yields and
CHO
N
conversions were obtained by GC using ethylbenzene as the internal standard.
cS=Selectivity. dThe CO2 pressure was 1 MPa. eThe CO2 pressure was 0.1 MPa. fThe
reductant was Ph2SiH2. gThe reductant was Et3SiH. hThe by-product was mainly
N,N-dimethylaniline, which was formed through the route shown in Scheme S1.
H
N
5
3
3
3
3
NH
NH
N
CHO
4
O
O
N CHO
5
aReaction conditions: Amine, 1 mmol; PhSiH3, 2 mmol; GVL, 1g; temperature, 80
oC; CO2, 3 MPa. bThe conversions and yields were determined by GC using
ethylbenzene as the internal standard. cThe amount of PhSiH3 was 4 equivalent.
Due to the excellent performance of GVL for the
formylation of N-methylaniline with CO2, we expanded the
o
substrate scope to various secondary amines at 80 C in GVL
(Table 2). It was found that the substituent groups of N-
methylanilines had great impact on the reactivity. 4-Methyl-N-
methylaniline (Entry 2, Table 2) and 4-methoxy-N-
Since the newly developed GVL-based catalytic system
was found to be highly effective for the formylation of various
2 | J. Name., 2012, 00, 1-3
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secondary amines with CO2, we further expanded the played a key role for the good performance. We cVoiemwpAratirceledOntlhinee
DOI: 10.1039/C6GC01455K
substrate to different primary amines (Table 3). All of the activity of other lactone-containing compounds with non-
primary amines employed were well tolerated with a reaction lactone-containing esters, including ethyl acetate and ethyl
temperature of 80 oC in GVL. There was a competition levulinate. As shown in Table 4, the examined lactone-
between mono- and bis-formylated products for primary containing compounds (Entries1-4, Table 4), including γ-
amines because both N-H bonds could be reactive. For butyrolactone, δ-valerolactone and ε-caprolactone, showed
aromatic primary amines, the formylation reaction mainly the similar activity with GVL, while ethyl acetate (Entry 2, Table
produced mono-formylated formamides (Entries 1-5, Table 3). 1) and ethyl levulinate (Entry 5, Table 4) gave no formamides,
However, for 4-methoxyaniline (Entry 2, Table 3) and 3,5- indicating the crucial role of the lactone structure. The lactone
dimethylaniline (Entry 3, Table 3), the yields to bis-formylated structure caused GVL to be a dipolar aprotic solvent with strong
products (14% and 12%, respectively) increased due to the polarity. In contrast, ethyl acetate and ethyl levulinate have weaker
electron-donating effect of the methoxy- and methyl- groups. polarity than GVL. Therefore, we speculated that the polarity of
Moreover, the ortho-substituted substrates, such as 2,6- solvents could affect the reaction activity. In order to prove this, we
diisopropylaniline (Entry 4, Table 3) and 2-methoxyaniline conducted 1H-NMR characterization for the N-methylaniline and
(Entry 5, Table 3), could show a higher selectivity to mono- PhSiH3 in different deuterated solvents (CDCl3, d6-benzene, CD3CN
1
formylated products (>95%) because of the steric hindrance and d6-DMSO). From Fig. S6, it was found that the H signals of N-H
1
effect of the substituent groups. Compared with aromatic proton in N-methylaniline appeared at different positions. The H
primary amines, the aliphatic primary amines gave higher signals shifted to the down field following the order: d6-DMSO ˃
selectivity to bis-formylated products due to the high basicity CD3CN ˃ CDCl3 ˃ d6-benzene, indicating that solvents with high
of the aliphatic primary amines (Entries 6-9, Table 3). For polarity could activate the N-H bond in N-methylaniline through
example, the yield of the mono-formylated product from solvation and polarization. This effect could tune the
octylamine was only 50% (Entry 9, Table 3).
basicity/nucleophilicity of N-methylaniline, and thus was helpful for
the formylation reaction. Meanwhile, the H signals of Si-H proton
1
in PhSiH3 showed an opposite order: d6-DMSO < CD3CN < CDCl3< d6-
benzene (Fig. S7) because the H in PhSiH3 was hydridic, suggesting
the activation of Si-H bonds by solvents with high polarity, which
was beneficial for the insertion of CO2 to Si-H bonds to form the
active silyl formates. In order to support this argument furtherly,
a mixture of PhSiH3 (3 mmol), GVL (1 g) and CO2 (3 MPa) was
Table 3. Formylation of various primary amines using CO2 as the carbon
source.a
Time
(h)
Conversion
(%)b
Yield
(%)b
91
5
Entry
1
Reactant
Product
2a
3a
2b
3b
2c
3c
2d
o
NH2
treated at 80 C in the absence of amines (Scheme S2). The
3
3
3
98
100
96
1a
silyl formates could be obviously detected by GC-MS (Fig. S8)
after a reaction time of 4 h. When N-methylaniline (1 mmol)
was added into the above treated mixture, N-
methylformanilide with a yield of 45% could be obtained at 80
oC with a reaction time of 4 h. In contrast, no silyl formates
were detected when the mixture was changed into PhSiH3 (3
mmol), ethyl levulinate (1 g) and CO2 (3 MPa). Moreover, the
formylation of N-methylaniline with CO2 was also conducted in
83
14
80
12
95
H3CO
NH2
2
3
1b
NH2
1c
NH2
4
5
97
3d
2
1d
NH2
2e
3e
2f
93
5
5
6
4
5
100
97
o
OCH3
1e
the mixture of CH3CN (1 g) and GVL (0.1 g) at 50 C for 12 h.
79
16
83
13
81
10
50
22
The yield of N-methylformanilide could reach 89%, which was
much higher than the result obtained in pure CH3CN (Entry 15,
Table 1). These results above suggested that high polarity of
GVL was beneficial for the formation of the active silyl
formates and the activation of N-H bonds in amines, which
could promote the formylation significantly. In addition, we
confirmed that no N-methylformanilide was formed without
PhSiH3 and no reaction occurred between GVL and PhSiH3.
On the basis of the experimental results, a possible
mechanism for GVL-promoted formylation of various amines
with CO2 and PhSiH3 to produce formamides was proposed
(Scheme 1). In the catalytic cycle, GVL activated the Si-H bond
in PhSiH3 by the effect of solvation and polarization, which also
could activate the N-H bond in amines. CO2 was inserted into
the activated Si-H bond to form the active species, silyl
formates. Then, the nucleophilic N atom in amines attacks the
carbon atom of silyl formates. Finally, formamides were
NH2
1f
3f
2g
3g
2h
3h
2i
H3CO
Cl
7
3
98
NH2
1g
8
6
94
NH2
1h
9c
1i
12
74
NH2
3i
aReaction conditions: reactant, 1 mmol; PhSiH3, 2 mmol; GVL, 1 g; temperature,
80 oC; CO2, 3 MPa. bThe conversions and yields were obtained from 1H NMR using
mesitylene as the internal standard. cThe amount of PhSiH3 was 4 equivalent.
The above results indicated that GVL-based catalytic
system was highly efficient for the formylation of various
amines using CO2 as the carbon source. To gain insight into the
reasons for the excellent performance of GVL and the reaction
mechanism, we performed some control experiments. In the
reaction system, we thought that the lactone structure of GVL
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formed by the formation of new C-N bond between amines
and CO2.
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DOI: 10.1039/C6GC01455K
Table 4. Formylation of N-methylaniline using CO2 as the carbon source to
produce N-methylformanilide in various lactone-containing solvents.a
Entry
Solvent
Conversion (%)b
Yield (%)b
Selectivity (%)
1
2
3
4
5
γ-Valerolactone
γ-Butyrolactone
δ-Valerolactone
ε-Caprolactone
Ethyl levulinate
86
87
85
89
3
84
85
83
85
0
98
97
98
96
--
Scheme 2. Conversion of CO2 with o-phenylenediamine, 2-aminothiophenol
and 2-aminophenol. Reaction conditions: substrate, 1 mmol; CO2, 3 MPa;
GVL,
1 4 mmol for o-
g; reaction temperature, 80 oC; PhSiH3,
phenylenediamine and 2 mmol for 2-aminothiophenol and 2-aminophenol.
aReaction conditions: N-methylaniline, 1 mmol; PhSiH3, 2 mmol; solvent, 1 g; CO2,
3 MPa; temperature, 50 oC; reaction time, 12h. bThe yields and conversions were
obtained by GC using ethylbenzene as the internal standard.
Conclusions
In summary, renewable GVL is an efficient solvent and catalyst
for the formylation of various amines with CO2 using PhSiH3 as
the hydrogen source without using any additional catalyst, and
the yields of the formamides are very high. Meanwhile,
benzimidazole, benzothiazole and benzoxazole could also be
synthesized via the reactions of CO2 with o-phenylenediamine,
2-aminothiophenol, and 2-aminophenol in GVL, respectively.
Control experiments indicated that the lactone structure of
GVL contributed significantly to the excellent performance by
promoting the formation of the active silyl formates and the
activation of N-H bonds in amines. We believe that the
efficient and greener route to produce formamides has great
potential of application, and using the special structure of GVL,
some other new routes to transform CO2 into value-added
chemicals can be developed.
Scheme 1. Possible reaction mechanism for GVL-promoted formylation of
various amines using CO2 as the carbon source with PhSiH3.
Delighted by the excellent performance of GVL for the
formylation of amines, we explored the application of GVL to
convert CO2 with o-phenylenediamine, 2-aminothiophenol and
2-aminophenol,17 respectively (Scheme 2). It was found that o-
phenylenediamine could be completely transformed into
benzimidazole and N-formylbenzimidazole by the formation of
new C-N bonds at 3 MPa CO2 and 80 oC with a reaction time of
5 h and the yields of the two products were 57% and 36%,
respectively. Meanwhile, 97% of 2-aminothiophenol could be
converted into benzothiazole with a yield of 89% by the
construction of C-N and C-S bonds simultaneously at the same
reaction conditions with o-phenylenediamine. In addition,
benzoxazole with a yield of 79% could be produced from 2-
aminophenol (conversion=95%) and CO2 by the generation of
Acknowledgements
The authors thank the National Natural Science Foundation of China
(21533011, 21133009, 21003133, 21321063), Chinese Academy of
Sciences (KJCX2.YW.H30).
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Green Chemistry
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View Article Online
DOI: 10.1039/C6GC01455K
Graphical abstract
γ-Valerolactone acts as both solvent and catalyst for N-formylation of various amines
with CO2 to formamides in the presence of phenylsilane without any additional
catalysts.