Acetals of N,N-dimethylformamides: Ambiphilic behavior in converting carbon dioxide to dialkyl carbonates

Article abstract of DOI:10.1246/cl.2013.146

Carbon dioxide is immobilized into dialkyl carbonate using acetals of N,N-dimethylformamide under atmospheric pressure. No special treatment with tailor-made catalysts is needed. Use of dimethyl sulfoxide as a solvent is critical. An ambiphilic mechanism is proposed for the direct synthesis of dialkyl carbonates from acetals and carbon dioxide.

Full text of DOI:10.1246/cl.2013.146

doi:10.1246/cl.2013.146
1
46
Published on the web January 26, 2013
Acetals of N,N-Dimethylformamides: Ambiphilic Behavior
in Converting Carbon Dioxide to Dialkyl Carbonates
Yuki Takada, Aki Matsuoka, Ya Du, Hiroshi Naka, and Susumu Saito*1,3
1
1
1
1,2
1
Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8602
2
Research Center for Materials Science, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8602
3
Institute for Advanced Research, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601
(
Received November 2, 2012; CL-121115; E-mail: saito.susumu@f.mbox.nagoya-u.ac.jp)
¹
Carbon dioxide is immobilized into dialkyl carbonate using where one of the [RO] fragments acts as a nucleophile [RO ]
+
7
acetals of N,N-dimethylformamide under atmospheric pressure.
No special treatment with tailor-made catalysts is needed. Use
of dimethyl sulfoxide as a solvent is critical. An ambiphilic
mechanism is proposed for the direct synthesis of dialkyl
carbonates from acetals and carbon dioxide.
and the other [RO] as an electrophile [R ]. Such dual role has
9
been used for practical esterification of carboxylic acids. Jiang
and Hua proposed that DMF ethylene acetals are possible
intermediates in DMF-catalyzed synthesis of cyclic carbonates
from epoxide and CO , and confirmed that DMF dimethyl acetal
2
reacts with CO2 under the same reaction conditions (PCO =
2
5
,10
5
0 atm).
In agreement with their results, exposure of 1a
Production of dialkyl carbonates from alcohol (ROH) and
carbon dioxide (CO2) is an ideal example where CO2 is reused
as a massive C1 resource.1 Dialkyl carbonates are widely used
as major synthetic intermediates for engineering plastics,
electrolyte solvents for lithium ion batteries, organic solvents,
fuel additives, and green reagents.2 Formation of dialkyl
carbonates from CO2 either produces a considerable amount of
(1.0 mmol) to 50 atm pressure of CO for 24 h gave dibenzyl
2
carbonate (2a) in 78% (Table 1, Entry 1). However, only 4% of
2a was obtained under 1 atm pressure of CO2 under otherwise
identical conditions (Entry 2). Unexpectedly, we found that this
reaction is significantly facilitated under atmospheric pressure
using dimethyl sulfoxide (DMSO, Table 1, Entry 3). In the
presence of DMSO, the reaction of 1a with CO2 at 1 atm gave 2a
in 80% NMR yield and 71% isolated yield (Entry 3). Use of
DMSO as a solvent is critical. Other polar solvents such as 1,3-
dimethyl-2-imidazolidinone (DMI) or N-methylpyrrolidone
(NMP) gave lower yields (Entries 4 and 5). Less polar solvents
such as 1,4-dioxane and toluene were ineffective (2a: 0­4%).
Presence of water was detrimental to the formation of dialkyl
carbonates and caused decomposition of 1a into benzyl alcohol
and DMF.
­6
6
3
salt wastes or demands high pressure. In addition, coproduced
water could cause catalyst deactivation and hydrolysis of the
product carbonate, resulting in low productivity. Drawbacks
caused by water can be avoided by using dehydrating agents
2
and/or dehydrated forms of alcohol such as epoxides, acetals
3
b­3e,4b
3a
[of acetone,
methyl acetate, and N,N-dimethylforma-
5
7
mide (DMF) ], and nitriles, but these methods demand either
high pressure (40­2000 atm) of CO2 or large excess of
dehydrating agents. Thus, strategies for salt-free CO2 conversion
under lower pressure are of significant challenge. To address this
issue, we here present synthesis of dialkyl carbonates from an
atmospheric pressure of CO2 using organic compounds, dialkyl
Reactions of CO2 using representative acetals 1b­1g are
listed in Table 2. Under atmospheric pressure of CO , each
2
reaction proceeded to give the corresponding carbonate with
primary alkyl groups 2b­2g in moderate yield (Table 2, 12­
58%). Increasing the CO2 pressure led to higher yield of
products (Table 2, 9 atm: 42­67%; 20 atm: 73­75%). Neither
8
acetals of DMF [1: (CH3)2NCH(OR)2] without special treat-
ment with catalysts.
We first tested N,N-dimethylformamide dibenzyl acetal (1a)
for CO2 trapping under atmospheric pressure (Table 1). DMF
acetals 1 are ambiphilic, reasonably reactive organic compounds
Table 2. Synthesis of dialkyl carbonates (2) from acetal 1 and
CO2
a
Table 1. Synthesis of dibenzyl carbonate (2a) from acetal 1a
P
CO2
Yield
/%
32/42/75
12/50
a
Entry
1
RO
2
b
and CO2
/
atm
N(CH3)2
O
N(CH3)2
1
4
/2/3
/5
1b
1c
1d
1e
CH
3
O
1/9/20
1/9
2b
2c
2d
2e
+
CO2
+
solvent, 100 °C, 24 h
4 9
n-C H O
RO
OR
RO
OR
O
H
1
PCO2
2
DMF
6/7/8
9/10
H
2
2
C=CHCH
2
O
1/9/20
1/9
54/67/73
58/62
Yield of 2a/%b
H
C=C(CH )CH O
3
2
Entry
PCO /atm
Solvent
2
c
c
1
2
3
4
5
50
1
1
1
1
none
none
DMSO-d6
DMI
NMP
78
4
80 [71]
53
30
11 /12
1f
1/9
2f
48/59
O
c
d
13
1g
1
2g
47
O
aConditions: 1a (R = Bn, 1 mmol), CO2 (1 or 50 atm), and
anhydrous solvent (2.0 mL) at 100 °C for 24 h in a 30 mL-
a
Conditions: 1 (1 mmol), CO2 (1­20 atm), and anhydrous
b
DMSO-d6 (2.0 mL) at 100 °C for 24 h. Determined by
μ
1
c
d
PTFE [poly(tetrafluoroethylene)] reaction vessel (Teflon ).
H NMR. In the presence of geraniol (8 mmol). In the
presence of nerol (1 mmol).
b
1
c
Determined by H NMR. Isolated yield.
Chem. Lett. 2013, 42, 146­147
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1
47
E/Z stereoisomers nor regioisomers for 2f or 2g was detected
cantly decreased the energies for TS1, TS2, and 4b by 7.1, 24.9,
¹
1
(
<5%, Entries 11­13).
and 106.1 kcal mol , respectively (Figure S3). These results are
consistent with the better performance of DMSO than other less
polar solvents.
The ambiphilic mechanism for the reaction of CO2 with 1
is clearly different from that of the conventional dehydrative
1
8
18
When O-labeled CO2 (C[ O]2) was reacted with acetal
1
8
1
a, the two O atoms were embedded into carbonate 2a, in
1
8
which one O was in the C=O and the other in one of the C­Os
of 2a (eq 1).
synthesis of dialkyl carbonates from alcohols and CO , in which
18O
2
C[18O]2
one oxygen atom of CO2 would be incorporated into dehydrat-
ing agents. Two thus far unrecognized concepts, polar aprotic
reaction media and the ambiphilic nature of acetals, should
provide an insight into advanced research on artificial chemical
fixation of CO2 under low pressure.
1
a
+
ð1Þ
DMSO, 100 °C
18OBn
2­4
BnO
[18O2]2a, 18O/16O = 9:1, 49%
8O/16O = 9:1, 1 atm 24 h
1
This conclusion was ascertained by high-resolution mass
spectrometry (HR-MS) and infrared (IR) absorption spectra for
11
2
1
2
a (Table S1). A crossover experiment using a 1:1 mixture of
a and 1d ([1]0 = 0.50 M) yielded three different carbonates 2a,
d, and 3 in a ratio of 4.5:1.0:2.5 (eq 2).
This work was supported by a Grant-in-Aid for Scientific
Research B (General) from MEXT, and by funds from Asahi
Glass, Asahi Kasei Chemicals, Daiso, Kuraray, Mitsubishi
Chemical, Mitsui Chemicals, Nissan Chemical Ind., and
Sumitomo Chemical. H.N. thanks the Nagoya University (NU)
Science Foundation for funding. Y.D. acknowledges GCOE in
Chemistry, NU for financial support. The authors wish to thank
Prof. R. Noyori (NU) for fruitful discussions and Y. Yamazaki
(NU) for technical assistance.
O
CO2, 1 atm
1
a + 1d
:1
2a + 2d
+
ð2Þ
DMSO, 100 °C
24 h
O
OBn
1
3
4
4% (4.5:1.0:2.5)
When a mixture of 1a and 1d (or 2a and 2d) was heated without
CO2 under otherwise identical reaction conditions, no inter-
change occurred between the benzyloxy and allyloxy groups.
These results imply a stepwise mechanism: the reaction of
1 with CO2 forms an intermediary ion pair
(CH3)2NCH(OR)] [ROCO2] (4), and subsequent recombina-
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+
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‡
(CH3)2N
O
O
O
(CH3)2N
C+
C
O
1
b + CO2
0.0)
7
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+
H3CO
H
–
–O
OCH3
(
H3CO
H
CH3
TS1 (+16.8)
4b (+1.6)
‡
H
H3CO
8
9
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autoclave, 110 °C, 15 h. Product: 2b (82% yield). See ref. 5.
Supporting Information is available electronically on the CSJ-Journal
Web site, http://www.csj.jp/journals/chem-lett/index.html.
CH3)2N C+
H
(
C
O
2b + DMF
(–16.6)
O
C
O–
H H
TS2 (+10.0)
Figure 1. A simplified pathway of the reaction of 1b with CO
to give 2b and DMF. Energies (¦E, in kcal mol , PCM,
= 46.7 for DMSO) at B3LYP/6-31+G** are relative to the
sum of energies of 1b and CO2.
2
1
0
¹
1
¾
11
11
Chem. Lett. 2013, 42, 146­147
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/