Ring-opening of cyclic anhydrides using ionic liquids

Article abstract of DOI:10.3184/030823409X417298

Four novel Bronsted acidic ionic liquids with two different acid sites on the imidazolium cations were synthesised and employed as catalysts and solvents for the ring-opening of cyclic anhydrides to synthesise half-esters. The results showed that these novel Bronsted acidic ionic liquids were efficient and recyclable. Good yields, short reaction times and mild reaction conditions were achieved.

Full text of DOI:10.3184/030823409X417298

JOURNAL OF CHEMICAL RESEARCH 2009
MARCH, 167-169
RESEARCH PAPER 167
Ring-opening of cyclic anhydrides using ionic liquids
Dong Jiang, Yuan Yuan Wang, Yan Nan Xu and Li Yi Dai*
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University,
Shanghai 200062, P. R. China
Four novel Brlilnsted acidic ionic liquids with two different acid sites on the imidazolium cations were synthesised
and employed as catalysts and solvents for the ring-opening of cyclic anhydrides to synthesise half-esters. The
results showed that these novel Brlilnsted acidic ionic liquids were efficient and recyclable. Good yields, short
reaction times and mild reaction conditions were achieved.
Keywords: ionic liquid, ring-opening, half-ester, cyclic anhydride
o
Half-esters are versatile intermediates for the synthesis of
various natural products. General methods for the synthesis
of half-esters or acid-esters involve the esterification or
transesterification with alcohols and the hydrolysis of diesters
with Ba(OH)2 or pig liver esterase. The ring-opening of
cyclic anhydrides with alkoxides is also a popular method
for the synthesis of half-esters. Recently, Sabitha et al. used
the Lewis acid BF3 as a catalyst in the synthesis of half-esters
from cyclic anhydrides. This catalyst was efficient, but also
suffered from some drawbacks. I BF3 is unstable to air and
moisture, making its recovery a significant challenge. When
using BF3 as catalyst, alcohols were used as both reactants
and solvents, so a large amount of alcohol was used, which
was wasteful.
(Y'OH
Vy0R
o
o
¢
OH
OR
o
Scheme
2
Ring-opening of cyclic anhydrides to synthesise
half-esters in ILs.
The development of environmentally friendly catalysts and
media for organic chemistry is an area of great importance.
Ionic liquids (ILs) which are known as environmentally
benign and reusable reagents have attracted growing attention,
due to their particular properties, such as large electrochemical
window, high thermal stability and reusability.2-4The potential
of ILs as green "designer catalysts and media" has become a
practical target for reducing waste and hazards by eliminating
traditional volatile organic media and corrosive catalysts.s-?
Bronsted acidic ILs such as I-hydro-3-methyl-imidazolium
NMR spectra were recorded on a Bruker Avance 500 MHz
spectrometerand tetramethylsilane(TMS) was used as an internal
reference. IR measurementswere performed on a Nicolet Nexus
670 FT-IRabsorptionspectrometer.Elementalanalyseswere carried
out on an ElementarVarioe1III apparatus. The melting point was
determinedon a BiichiB-540instrument.
Synthesis of 3-(1-hydro-imidazolium-3-yl)-propane-l-sulfonate (Him-pS)
(Scheme3)
Under vigorous stirring, imidazole (20 mmol) was dissolved in
acetonitrile(15 mL) and I, 3-propanesulfone(20 mmol)was added
slowly at room temperature.After 12 h, the reaction mixture was
filteredto recoverthe whiteprecipitate.The precipitatewas washed
with acetone(10 mL) three times and dried under reducedpressure
(0.01 torr) at 60°C for I h, giving Him-pS as a white powder
(yield82%).
hydrogen sulfate
([Hmim]HS04),
I-hydro-3-methyl-
imidazolium tetrafluoroborate
3-(3-sulfopropyl)-imidazolium
([Hmim]BF4), I-methyl-
hydrogensulfate
([HSOr
pmim]HS04) and I-methyl-3-(3-sulfopropyl)-imidazolium
tetrafluoroborate ([HSOrpmim]BF4) have been used as
satisfactory catalysts and solvents in many organic reactions.S-IO
Traditionally, the acidic IL had only one acid site on the
imidazolium cation, the acid sites on the imidazolium cations of
[Hmim]HS04 and [Hmim]BF4 were N-H, while the acid sites
on the imidazolium cations of [HSOrpmim ]HS04 and [HSOr
pmim]BF4were -S03H. Here, four novel Bronsted acidic ILs
with these two different acid sites on the imidazolium cations
(Scheme 1) were synthesised and used as catalysts and solvents
for the ring-opening of cyclic anhydrides to form half-esters
(Scheme 2). The results of experiments showed that these ILs
were efficient and recyclable. Good yields, short reaction times
and mild reaction conditions were achieved.
Him-pS: M.p. 191-192°C. 'HNMR (500MHz,DP):8 2.21-2.25
(m, 2H,NCH
(t, J = 7 Hz, 2H, NCH
lH, NCHCHN),8.65 (s, lH, NCHN). l3CNMR (125 MHz, DP):
825.1 (NCH CH CH2), 47.4 (NCH CH CH2), 47.9(NCH CH CH2),
2
CH
2
CH2), 2.83 (t,J = 7 Hz, 2H, NCH
2
CH
2
CH2), 4.29
2
CH CH2), 7.35 (s, lH, NCHCHN), 7.45 (s,
2
2
2
2
2
2
2
120.3 (NCHCHN), 122.6 (NCHCHN), 135.3 (NCHN). IR (KEr
disc):v 3435 (O-H), 3180 (N-H), 3114 (C-H), 1654 (C=C), 1580
(C=N), 1191(S=O), 1036(S=O),631 (S-o), 523 (C-S).Anal. Calcd
for C6HION203S: C, 37.89; H, 5.30; N, 14.73.Found: C, 37.82; H,
5.39;N, 14.82%.
Synthesis of I-hydro-3-(3-sulfopropyl)-imidazolium
hydrogensulfate
([HSOrpHimjHSO.;) and I-hydro-3-(3-sulfopropyl}-imidazolium
4-methyl-benzenesulfonate ([HSOrpHimjp- TSA) (Scheme4)
Under vigorous stirring,Him-pS (20 mmol) was dissolvedin water
(30 mL) and conc. sulfuric acid (20 mmol) or toluene-p-sulfonic
acid (20 mmol) was added slowly at room temperature.Then the
systemwas slowlyheatedup to 80°C for 2 h, the waterwas removed
under reduced pressure (0.01 torr) at 80°C for 6 h, giving [HSOr
pHim]HS04 or [HSOrpHim]p-TSAas a viscousliquid(yield98%).
Experimental
Imidazole(99%), I, 3-propanesulfone (99%) and other chemicals
(AR) were commercially available and used without any further
purification.
o
O ~I!,O
+0
Scheme
1
Cationic structure of novel Br(ljnsted acidic ILs.
* Correspondent.E-mail:Iydai@chem.ecnu.edu.cn
Scheme
3
Synthesis of Him-pS.

168 JOURNAL OF CHEMICAL RESEARCH 2009
[HS03-pHim]HS04 : X= HS04-
[HS03-pHim]p-TSA: X= -o-S03-
[HS03-pHim]BF4: X= BF4-
[HS03-pHim]H2P04 : X=H2P04-
[HSO;-pHimjHS04: 'H NMR (500 MHz, DP):o 1.93-1.96 (m, 2H,
under reduced pressure to give the half-ester. Then the half-ester
was characterised by FT-IR and 'H NMR.ll-'8 IL was reused after
removal of water under reduced pressure (0.01 torr) at 80°C for 5 h.
NCH2CH2CH2), 2.55 (t, J = 6 Hz, 2H, NCH2CH2CH2), 4.01 (t, J = 7 Hz,
2H, NCH2CH2CH2), 7.10 (s, lH, NCHCHN), 7.18 (s, lH, NCHCHN),
8.39 (s, lH, N CHN). BCNMR(125 MHz, DP):o 24.8 (NCH2CH2CH2),
47.1 (NCH2CH2CH2), 47.7 (NCH2CH2CH2), 119.7 (NCHCHN), 122.4
(NCHCHN), 135.5 (NCHN). IR (liquid film):v 3432 (O-H), 3150
(N-H), 2982 (O-H), 1666 (C=C), 1582 (C=N), 1231 (S=O), 1031
(S=O), 853 (S-o), 580 (C-S). Anal. Calcd for C6H12N207S2:C, 25.00;
H, 4.20; N, 9.72. Found: C, 25.12; H, 4.26; N, 9.76%.
Examples:
Methyl hydrogen phthalate: '2 'H NMR (500 MHz, CDC13):o 3.90
(s, 3H, CH3), 7.38-7.56 (m, 2H, 2CH), 7.65 (d, J = 7 Hz, lH, CH),
7.90 (d, J= 8 Hz, lH, CH), 11.97 (s, lH, OH); IR (KEr disc):v 3080
(O-H), 2950 (CHrH), 1740 (C=O), 1692 (C=O), 1601 (C=C), 1291
(C-o).
Benzyl hydrogen phthalate:'s 'H NMR (500 MHz, CDC13):o 5.32
(s, 2H, CH2), 7.19-7.30 (m, 5H, CH2Ph), 7.41-7.56 (m, 2H, 2CH),
7.68 (d, J= 8 Hz, lH, CH), 7.92 (d, J= 8 Hz, lH, CH), 11.88 (s, lH,
OH); IR (KEr disc):v 3046 (O-H), 3013 (C-H), 1726 (C=O), 1695
(C=O), 1605 (C=C), 1288 (C-O).
[HSO;-pHimjp-TSA:
'H NMR (500 MHz, DP):o 2.00-2.05
(m, 2H, NCH2CH2CH2), 2.06 (s, 3H, CH3), 2.66 (t, J = 7 Hz, 2H,
NCH2CH2CH2), 4.06 (t, J = 7 Hz, 2H, NCH2CH2CH2), 7.02 (d,
J = 8 Hz, 2H, CHC(CH3)CH), 7.15 (s, lH, NCHCHN), 7.23 (s,
lH, NCHCHN), 7.40 (d, J = 8 Hz, 2H, CHC(S03H)CH), 8.44 (s,
lH, NCHN). BC NMR (125 MHz, DP):o 20.5 (NCH2CH2CH2),
25.1 (CH3), 47.3 (NCH2CH2CH2),
47.9 (NCH2CH2CH2),
119.4
Methyl hydrogen maleate:'6 'H NMR (500 MHz, CDC13):o 3.86
(s, 3H, CH3), 6.43 (d, J = 3 Hz, 2H, CH=CH), 12.10 (s, lH, OH);
IR (liquid film):v 3442 (O-H), 3060 (C-H), 2966 (CHrH), 1735
(C=O), 1662 (C=O), 1638 (C=C), 1246 (C-o).
Benzyl hydrogen maleate:17 'H NMR (500 MHz, CDC13):o 5.27
(s, 2H, CH2), 6.63 (d, J = 4 Hz, 2H, CH=CH), 7.26-7.39 (m, 5H,
CH2Ph), 11.93 (s, lH, OH); IR (KEr disc):v 3415 (O-H), 3040
(C-H), 3016 (C-H), 1732 (C=O), 1690 (C=O), 1632 (C=C), 1262
(C-o).
(NCHCHN), 122.2 (NCHCHN), 125.3 (CHC(S03H)CH), 129.4
(CHC(CH3)CH), 135.0 (NCHN), 139.7 (CHC(S03H)CH), 142.3
(CHC(CH3)CH). IR (liquid film):v 3435 (O-H), 3146 (N-H), 2965
(O-H), 1677 (C=C), 1551 (C=N), 1225 (S=O), 1034 (S=O), 820
(S-o), 568 (C-S). Anal. Calcd for CBH,8NP6S2: C, 43.07; H, 5.02;
N, 7.73. Found: C, 42.88; H, 5.16; N, 7.68%.
Synthesis of I-hydro-3-(3-sulfopropyl)-imidazolium tetrafiuoroborate
([HSO;-pHimj BF.;)
dihydrogen phosphate ([HSO;-pHimj H
and
I-hydro-3-(3-suljopropyl)-imidazolium
PO.;) (Scheme 4)
2
Under vigorous stirring, Him-pS (20 mmol) was dissolved in water
(30 mL) and fluoboric acid (20 mmol) or phosphoric acid (20 mmol)
was added slowly at room temperature. The system was stirred for 12h
at room temperature, then the water was removed under reduced
pressure (0.01 torr) at 80°C for 6 h, giving [HSOrpHim]BF4 or
[HSOrpHim]H2P04 as a viscous liquid (yield 99%).
Results and discussion
Four novel Bronsted acidic ILs were synthesised and identified by
'H NMR, BC NMR and FT-IR. All of these ILs contained two
different acid sites on the imidazolium cations, one acid site was
N-H and the other was -S03H, as shown in Scheme 1. Each had the
potential to be used as an acidic catalyst in organic reactions.
The ring-opening of cyclic anhydrides to synthesise half-esters
was carried out in these Bronsted acidic ILs [HSOrpHim]HS04,
[HSOrpHim]BF4, [HSOrpHim]H2P04
The results are listed in Table 1 showing good yields, and confirming
that these ILs are efficient catalysts and solvents for the ring-opening
of cyclic anhydrides to form half-esters.
From the results in Table 1, it is shown that the yields of half-esters
using [HSOrpHim]H2P04 and [HSOrpHim]p-TSAas
[HSO;-pHimjBF4:
'H NMR (500 MHz, DP):o 2.13-2.16 (m,
2H, NCH2CH2CH2), 2.75 (t, J = 7 Hz, 2H, NCH2CH2CH2), 4.20 (t,
J= 7 Hz, 2H, NCH2CH2CH2), 7.30 (s, lH, NCHCHN), 7.37 (s, lH,
NCHCHN), 8.57 (s, lH, NCHN). BC NMR (125 MHz, DP):o 25.0
(NCH2CH2CH2), 47.0 (NCH2CH2CH2), 47.8 (NCH2CH2CH2), 119.9
(NCHCHN), 122.6 (NCHCHN), 135.6 (NCHN). IR (liquid film):
and [HSOrpHim]p-TSA.
V
3436 (O-H), 3161 (N-H), 2991 (O-H), 1665 (C=C), 1583 (C=N),
1221 (S=O), 1128 (B-F), 1043 (S=O), 844 (S-O), 592 (C-S). Anal.
Calcd for C6HllNP3F4SB: C, 25.92; H, 3.99; N, 10.08. Found: C,
25.80; H, 4.06; N, 10.01%.
catalysts and
solvents were a little higher than those using [HSOrpHim ]HS04 and
[HSOrpHim]BF4. The acidities ofILs containing HS04- and BF4'
should be stronger than those ofILs containing H2P04' and p- TSA' .19
We supposed that when using the strongly Bronsted acidic ILs
[HSOrpHim]HS04 and [HSOrpHim]BF4 as catalysts and solvents,
the esterification of half-esters with excess alcohols to synthesise
diesters was much easier than that using the weaker Bronsted acidic
[HSO;-pHimjH
2
P04:
'H NMR (500 MHz, DP):o 1.97-2.01 (m,
2H, NCH2CH2CH2), 2.60 (t, J = 8 Hz, 2H, NCH2CH2CH2), 4.06 (t,
J= 6 Hz, 2H, NCH2CH2CH2), 7.14 (s, lH, NCHCHN), 7.22 (s, lH,
NCHCHN), 8.42 (s, lH, NCHN). BC NMR (125 MHz, DP):o 24.9
(NCH2CH2CH2), 47.2 (NCH2CH2CH2), 47.7 (NCH2CH2CH2), 119.8
(NCHCHN), 122.5 (NCHCHN), 135.5 (NCHN). IR (liquid film):
V
3430 (O-H), 3151 (N-H), 2972 (O-H), 1656 (C=C), 1583 (C=N),
1225 (S=O), 1169 (p=0), 1040 (S=O), 853 (S-O), 592 (C-S). Anal.
Calcd for C6HBN207SP: C, 25.00; H, 4.55; N, 9.72. Found: C, 25.06;
H, 4.50; N, 9.82%.
ILs [HSOrpHim]H2P04
and [HSOrpHim]p-TSA,
thus affording
reduced yields of the half-esters.
Compared with the yields of ethyl hydrogen phthalate using
Bronsted acidic ILs as catalysts and solvents, the yield obtained in
the absence ofILs was very low (entry 6, Table 1) and the solubility
of phthalic anhydride in ethyl alcohol was not good at 60°C without
ILs. This revealed that Bronsted acidic ILs were efficient catalysts and
solvents for the ring-opening of cyclic anhydrides to form half-esters.
One important advantage of using Bronsted acidic ILs is the
possibility of recycling. We examined the synthesis of ethyl hydrogen
phthalate in Bronsted acidic IL [HSOrpHim ]p-TSA. The results of the
recycling experiments are summarised in Table 2, which revealed that
Bronsted acidic ILs used as catalysts and solvents for the ring-opening
of cyclic anhydrides to form half-esters were recyclable. The slight
decline in the yield should be ascribed to the slight loss ofILs.
General procedure for the ring-opening of cyclic anhydrides to
synthesise halfesters
The alcohol (30 mmol), cyclic anhydride (10 mmol) and IL
(10 mmol) were added into a flask and stirred at 60°C. After the cyclic
anhydride had dissolved in the liquid phase, the reaction mixture
was heated for 10 min. Upon completion of the reaction, water
(8 mL) was added to the reaction mixture. The reaction mixture was
extracted with ether (10 mL) three times. Then the ether was added
to a saturated solution of sodium bicarbonate (20 mL) and separated.
The solution of sodium bicarbonate was neutralised with conc. HCl
(8 mL) at O°C and extracted with ether (10 mL) three times, and the
ether was dried by anhydrous sodium sulfate (6 g) and concentrated

JOURNAL OF CHEMICAL RESEARCH 2009 169
Table 1 Results of the ring-opening of cyclic anhydrides to synthesise half-esters in ILs
Entry
Cyclic anhydride
IL
Alcohol
Yield/Yo
[HSOTpHim]HS04
1
2
3
4
5
6
7
8
9
Phthalic anhydride
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Ethyl alcohol
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Methyl alcohol
Ethyl alcohol
85
88
87
88
87
16
87
88
88
89
90
89
91
90
93
94
90
93
92
93
95
82
82
80
84
85
82
83
82
86
85
87
88
89
91
90
85
87
88
90
89
[HSOTpHim]BF4
10
11
[HSOTpHim]HzP04
[HSOTpHim]p-TSA
[HSOTpHim]HS04
[HSOTpHim]BF4
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Maleic anhydride
[HSOTpHim]HzP04
[HSOTpHim]p-TSA
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
Methyl alcohol
Ethyl alcohol
Isopropyl alcohol
Butyl alcohol
Benzyl alcohol
-, No IL added
Table 2 Results of the recycling use of [HSOTpHim]p-TSA in
the synthesis of ethyl hydrogen phthalate
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1
2
3
4
5
6
7
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93
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procedure for the ring-opening of cyclic anhydrides to form half-
esters in these ILshas been developed. The ring-opening of cyclic
anhydrides to form half-esters, using ILs [HSOrpHim] HS04,
[HSOrpHim]BF4, [HSOrpHim]H2P04 and [HSOrpHim]p-
TSA as catalysts and solvents, has several advantages: (1) ILs as
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Received 6 November 2008; accepted 25 January 2009
Paper 08/0283 doi: 10.3184/030823409X417298
Published online: 6 April 2009
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