N-Substituted 3,4-dihydroisoquinolinium ionic liquids as catalysts in alkenes epoxidation reactions

Article abstract of DOI:10.1016/j.apcata.2012.05.017

Because of their high reactivity, epoxides are one of the most important groups of organic compounds. These substances are synthesised primarily by the catalytic oxidation of alkenes in the liquid or gaseous phase. This study investigated new catalytic systems for epoxidation reactions using functionalised ionic liquids. These ionic liquids serve as oxygen transfer agents during the reactions. Several N-substituted 3,4-dihydroisoquinolinium ionic liquids were synthesised, and their potential as catalysts for epoxidation reactions was investigated. Cyclic alkenes such as cyclohexene and cyclooctene were used as model olefins.

Full text of DOI:10.1016/j.apcata.2012.05.017

Applied Catalysis A: General 433–434 (2012) 197–205
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
N-Substituted 3,4-dihydroisoquinolinium ionic liquids as catalysts in alkenes
epoxidation reactions
Stefan Baja,∗, Maciej Bełcha, Mirosław Gibasb
a Silesian University of Technology, Faculty of Chemistry, Department of Chemical Organic Technology and Petrochemistry, Krzywoustego 4 Street, 44-100 Gliwice, Poland
b Silesian University of Technology, Faculty of Chemistry, Department of Organic Chemistry, Bioorganic Chemistry and Biotechnology, Krzywoustego 4 Street, 44-100 Gliwice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Because of their high reactivity, epoxides are one of the most important groups of organic compounds.
These substances are synthesised primarily by the catalytic oxidation of alkenes in the liquid or gaseous
phase. This study investigated new catalytic systems for epoxidation reactions using functionalised ionic
liquids. These ionic liquids serve as oxygen transfer agents during the reactions. Several N-substituted
3,4-dihydroisoquinolinium ionic liquids were synthesised, and their potential as catalysts for epoxidation
reactions was investigated. Cyclic alkenes such as cyclohexene and cyclooctene were used as model
olefins.
Received 12 March 2012
Received in revised form 7 May 2012
Accepted 14 May 2012
Available online 20 May 2012
Keywords:
3,4-Dihydroisoquinolinium ionic liquids
Alkenes epoxidation
© 2012 Elsevier B.V. All rights reserved.
Oxygen transfer agents
1. Introduction
In recent years, ionic liquids have become particularly attrac-
tive because of their physicochemical properties. One of the many
The epoxidation of carbon–carbon double bonds is one of the
most important reactions in organic chemistry. These reactions
can be performed using different types of catalysts, including
compounds and complexes that contain transition metals [1]. In
addition, epoxidation reactions that use organic oxygen trans-
fer agents are interesting. These oxygen transfer agents include
ketones [2,3] and iminium salts [4]. The mechanism of the reaction
with iminium salts is shown in Fig. 1 [5].
Epoxidation involves the initial transfer of an oxygen atom from
the oxidising agent to the carbon–nitrogen double bond of the
iminium group, forming the intermediate oxaziridinium salt [6].
This first step is followed by the transfer of the oxygen atom to the
carbon–carbon double bond of the olefin. In this mechanism, the
iminium salt acts as the oxygen transfer agent [7,8].
interesting areas of study for these compounds is chemical syn-
thesis, in which these compounds can act as auxiliary substances,
such as solvents, extractants and catalysts [11]. Therefore, the syn-
thesis of ionic liquids with an iminium functional group in the
molecule and the potential uses of these ionic liquids in novel and
practical catalytic systems for epoxidation are of interest. In addi-
tion to their catalytic properties in epoxidation reactions, these
substances also possess the other advantages of ionic liquids. We
conducted a study on the preparation of specific N-substituted
3,4-dihydroisoquinolinium ionic liquids, denoted by the general
abbreviation [RDHQM][X], and subsequently investigated the use
of these compounds as catalysts in epoxidation reactions.
2. Experimental
In practice, the following salts are most often used: N-
substituted derivatives of isoquinoline [9,10], derivatives of
binaphthalene [9,10] and pyrrolidine [4,10] (Fig. 2).
2.1. Preparation of 2-(2-bromoethyl)benzaldehyde
These iminium salts are obtained via the condensation of
the corresponding aldehyde with a primary amine in the pres-
ence of an acid catalyst [6,10]. Isoquinolinium salts are obtained
via the oxidation and alkylation of 1,2,3,4-tetrahydroisoquinoline
[5]. Pyrrolidine derivatives are obtained via the reaction of N-
trimethylsilylpyrrolidine with aromatic aldehydes [4].
Preparation of 2-(2-bromoethyl)benzaldehyde is described by
Crosthwaite et al. in [13]. The synthesis was started from 8.0 g
(0.06 mol) of isochroman. A 40% aqueous solution of HBr (18 ml,
2.0 equiv. mol) was added to the crude 1-bromoisochroman. Crude
2-(2-bromoethyl)benzaldehyde was obtained as a red oil (15.35 g
of approx. 75% purity).
2-(2-Bromoethyl)benzaldehyde 2. 1H NMR ıH (300 MHz,
CDCl3; TMS); 3.55–3.64 (4H, m, PhCH2CH2Br), 10.14 (1H, s, PhCHO)
isochroman 1. 1H NMR ıH (300 MHz, CDCl3; TMS); 3.04 (2H, t,
J 5.7 Hz, PhCH2CH2O), 4.77 (2H, s, PhCH2O)
∗
Corresponding author. Tel.: +48 32 2371032; fax: +48 32 2371032.
E-mail address: stefan.baj@polsl.pl (S. Baj).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.05.017

198
S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
O
S
R
R
R
N+
R
R
R
R
HO
HO
O- K+
C
C
C
C
C
C
O
R
O
-
R
R
R
R
R
R
R
N+
O
S
O
K+
O
O
R
O
Fig. 1. The mechanism of olefin epoxidation reactions using iminium salts as catalysts.
2.2. General procedure for the preparation of N-substituted
3,4-dihydroisoquinolinium ionic liquids
[C9H8N]+. Elemental analysis: found: C, 57.4; H, 7.00; N, 4.5%; Calc.
for C13H18NBr: C, 58.2; H, 6.8; N, 5.2%. Density at 20 ◦C: 1.40 g cm−3
.
N-Butyl-3,4-dihydroisoquinolinium
tetrafluorobo-
General procedure for the preparation of N-substituted 3,4-
dihydroisoquinoline derivatives is described also by Crosthwaite
et al. in [13]. Solution of MX salt containing the desired anion
(1.1 equiv. mol) in a minimal amount of acetonitrile, methanol,
water or a mixture of these solvents, was added. This mixture was
stirred for 10–60 min. After the reaction was complete, the solvent
was removed under vacuum, which resulted in the crystallisation
of the by-product, an inorganic salt. The contents of the flask were
diluted with methylene chloride, and the mixture was filtered to
remove the inorganic by-product. The filtrate containing the unre-
acted 2-(2-bromoethyl)benzaldehyde was concentrated on a rotary
evaporator and transferred onto a chromatographic column filled
with silica gel. The aldehyde was eluted with methylene chloride.
After the elution of the aldehyde was complete, the ionic liquid was
eluted with methanol. The methanol was removed using a rotary
evaporator under high vacuum and a temperature of 70–80 ◦C for a
few hours. The finished product was analysed by 1H and 13C NMR,
Mass Spectroscopy and elemental analysis. The melting points of
the solid products were determined.
The unreacted 2-(2-bromoethyl)benzaldehyde could be
removed from the crude product by dissolving the material in
methanol and adding a saturated aqueous sodium hydrogen
sulphate(IV) solution. The sodium hydrogen sulphate forms a
solid adduct with the aldehyde, which can be removed by vacuum
filtration. The filtrate was concentrated with a rotary evaporator
whilst maintaining the vacuum at a temperature of 70–80 ◦C for a
few hours.
rate [BDHQM][BF4] 3b. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 0.97 (3H, t, J 7.5 Hz, N (CH2)3CH3), 1.43 (2H, m, J 7.5 Hz,
N
(CH2)2CH2CH3), 1.90 (2H, m, J 7.5 Hz, N CH2CH2CH2CH3), 3.31
(2H, t, J 8.1 Hz, CH2CH2N), 4.09 (2H, t, J 7.8 Hz, CH2CH2N),
4.22 (2H, t, 7.5 Hz, CH2(CH2)2CH3), 7.29–7.72 (4H, m,
J
N
C6H4 ), 9.76 (1H, s, CH N). 13C NMR (75 MHz, CDCl3; TMS):
ıC/ppm = 13.26, 19.22, 25.07, 29.13 (CH3CH2CH2CH2 ); 48.21,
60.53
( CH2CH2N ); 124.31, 127.96, 128.39, 134.23, 135.80,
137.82 ( C6H4 ); 166.35 (HC
N
). MS EI (70 eV) m/z: 188 (100%)
[C9H9N C4H9]+, 130 (58%) [C9H8N]+. Elemental Analysis: Found:
C, 55.3; H, 7.0; N, 4.55%; Calc. for C13H18NBF4: C, 56.75; H, 6.6; N,
5.1%. mp 43.2–47.3 ◦C (measured by DSC).
N-Butyl-3,4-dihydroisoquinolinium
bis(trifluoromethanesulfonyl)imide [BDHQM][NTf2] 3c. 1H
NMR (300 MHz, CDCl3; TMS): ıH/ppm = 1.00 (3H, t, J 7.5 Hz,
N
m, J 7.5 Hz, N CH2CH2CH2CH3), 3.29 (2H, t, J 8.1 Hz, CH2CH2N),
4.04 (4H, t, J 7.8 Hz, CH2CH2N, N CH2(CH2)2CH3), 7.26–7.85 (4H,
m, C6H4 ), 8.86 (1H, s, CH N). 13C NMR (75 MHz, CDCl3; TMS):
ıC/ppm = 13.28, 19.16, 25.15, 29.40 (CH3CH2CH2CH2 ); 52.08,
61.22 ( CH2CH2N ); 117.67, 121.91 (N(SO2CF3)2); 124.12, 128.29,
(CH2)3CH3), 1.44 (2H, m, J 7.8 Hz, N (CH2)2CH2CH3), 1.89 (2H,
128.99, 134.49, 135.72, 138.76 ( C6H4 ); 167.17 (HC
N ). MS
EI (70 eV) m/z: 188 (100%) [C9H9N C4H9]+, 130 (51%) [C9H8N]+.
Elemental Analysis: Found: C, 38.3; H, 3.4; N, 5.6%; Calc. for
C15H18N2O4S2F6: C, 38.45; H, 3.9; N, 6.0%. Density at 20 ◦C:
1.59 g cm−3
.
N-Hexyl-3,4-dihydroisoquinolinium bromide [HDHQM][Br]
4a. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.87
(3H, t,
Hz,
N
N-Butyl-3,4-dihydroisoquinolinium bromide [BDHQM][Br]
3a. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.96 (3H, t, J
7.5 Hz, N (CH2)3CH3), 1.41 (2H, m, J 7.5 Hz, N (CH2)2CH2CH3),
1.89 (2H, m, J 7.5 Hz, N CH2CH2CH2CH3), 3.28 (2H, t, J 8.1 Hz,
CH2CH2N), 4.06 (2H, t, J 7.8 Hz, CH2CH2N), 4.20 (2H, t, J
7.5 Hz, CH2(CH2)2CH3), 7.29–8.11 (4H, m, C6H4 ), 10.27 (1H, s,
J
6.9 Hz,
CH2CH2 (CH2)3 CH3), 1.93 (2H, m,
CH2 CH2 (CH2)3CH3), 3.36 (2H, t, J 8.1 Hz, CH2CH2N), 4.15
N
(CH2)5CH3), 1.26–1.44 (6H, m,
J
7.8.
N
J
6.9 Hz,
(2H, t, J 7.8 Hz, CH2CH2N), 4.34 (2H, t, J 7.5 Hz, N CH2(CH2)4CH3),
7.32–8.16 (4H, m, C6H4 ), 10.32 (1H, s, CH N). 13C NMR
(75 MHz, CDCl3; TMS): ıC/ppm = 13.79, 22.21, 25.41, 25.74, 27.47;
31.02 (CH3CH2CH2CH2CH2CH2 ); 48.39, 60.81 ( CH2CH2N );
124.47, 127.13, 128.43, 134.60, 135.70, 137.78 ( C6H4 ); 166.70
CH N). 13C NMR (75 MHz, CDCl3; TMS): ıC/ppm = 13.97, 19.45,
25.15, 29.61 (CH3CH2CH2CH2 ); 48.70, 60.02
( CH2CH2N );
124.39, 128.00, 128.45, 134.55, 135.93, 137.84 ( C6H4 ); 166.09
). MS EI (70 eV) m/z: 188 (100%) [C9H9N C4H9]+, 130 (44%)
(HC
N
). MS EI (70 eV) m/z: 216 (100%) [C9H9N C6H13]+, 130
(HC
N
Ph
-
BPh4
N+
CH3
-
ClO4
N+
-
R
BF4
N+
C
CH
3
CH3
H
Fig. 2. Selected examples of iminium salts that are used as catalysts in epoxidation reactions.

S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
199
(39%) [C9H8N]+. Elemental Analysis: Found: C, 59.5; H, 7.4; N,
3.6%; Calc. for C15H22NBr: C, 60.8; H, 7.5; N, 4.7%. Density at 20 ◦C:
1.32 g cm−3
N
CH2 CH2 (CH2)5CH3), 2.98 (2H, t,
J
8.1 Hz,
CH2CH2N),
4.01 (4H, m, J 8.1 Hz, CH2CH2N, N CH2(CH2)6CH3), 7.21–8.22
(4H, m, C6H4 ), 8.80 (1H, s, CH N). 13C NMR (75 MHz, CDCl3;
TMS): ıC/ppm = 13.85, 22.44, 25.93, 27.07, 27.40, 28.72, 28.79,
31.53 (CH3(CH2)6CH2 ); 48.49, 61.33
121.54 (N(SO2CF3)2); 124.05, 125.78, 128.34, 130.48, 134.25,
.
N-Hexyl-3,4-dihydroisoquinolinium
tetrafluorobo-
rate [HDHQM][BF4] 4b. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 0.87 (3H, t, J 6.9 Hz, N (CH2)5CH3), 1.25–1.42 (6H,
( CH2CH2N ); 117.29,
m,
N
J
7.8 Hz,
N CH2CH2 (CH2)3 CH3), 1.91 (2H, m, J 6.9 Hz,
137.50 ( C6H4 ); 166.05 (HC
N ). MS EI (70 eV) m/z: 244 (34%)
[C9H9N C8H17]+, 130 (26%) [C9H8N]+. Elemental Analysis: Found:
C, 42.3; H, 5.1; N, 5.3%; Calc. for C19H26N2O4S2F6: C, 43.5; H, 5.0;
CH2 CH2 (CH2)3CH3), 3.32 (2H, t, J 7.8 Hz, CH2CH2N), 4.11
(2H, t, J 8.1 Hz, CH2CH2N), 4.22 (2H, t, J 7.5 Hz, N CH2(CH2)4CH3),
7.33–8.05 (4H, m, C6H4 ), 9.57 (1H, s, CH N). 13C NMR
(75 MHz, CDCl3; TMS): ıC/ppm = 13.73, 22.16, 25.18, 25.66, 27.33,
30.92 (CH3CH2CH2CH2CH2CH2 ); 48.26, 60.86 ( CH2CH2N );
124.39, 127.99, 128.38, 134.38, 135.81, 137.83 ( C6H4 ); 166.45
N, 5.3%. Density at 20 ◦C: 1.51 g cm−3
.
N-Dodecyl-3,4-dihydroisoquinolinium
[DodDHQM][Br] 6a. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 0.88 (3H, t, 6.9 Hz, (CH2)11CH3), 1.24 (18H,
CH2CH2(CH2)9CH3), 1.93 (2H, m, 6.9 Hz,
CH2CH2(CH2)9CH3), 3.36 (2H, t, J 7.8 Hz, CH2CH2N), 4.15 (2H,
bromide
J
N
(HC
N
). MS EI (70 eV) m/z: 216 (100%) [C9H9N C6H13]+, 130
m,
N
J
6.9 Hz,
N
J
(51%) [C9H8N]+. Elemental Analysis: Found: C, 58.2; H, 7.3; N, 4.2%;
Calc. for C15H22NBF4: C, 59.4; H, 7.3; N, 4.6%. Density at 20 ◦C:
t, J 8.1 Hz, CH2CH2N), 4.34 (2H, t, J 7.5 Hz, N CH2(CH2)10CH3),
1.48 g cm−3
.
7.34–8.16 (4H, m, C6H4 ), 10.28 (1H, s, CH N). 13C NMR
(75 MHz, CDCl3; TMS): ıC/ppm = 13.91, 22.45, 25.36, 26.08, 27.50,
28.94, 29.10, 29.19, 29.31, 29.39, 29.48, 31.67 (CH3(CH2)10CH2 );
48.34, 60.81 ( CH2CH2N ); 124.44, 127.94, 128.37, 134.53, 135.69,
N-Hexyl-3,4-dihydroisoquinolinium
bis(trifluoromethanesulfonyl)imide
[HDHQM][NTf2]
4c. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.88
(3H, t,
7.8 Hz,
J
6.9 Hz,
CH2CH2 (CH2)3 CH3), 1.88 (2H, m,
7.8 Hz,
4.00 (4H, m, J 8.1 Hz, CH2CH2N, N CH2(CH2)4CH3), 7.35–7.82
(4H, m,
C6H4 ), 8.83 (1H, s, CH N). 13C NMR (75 MHz,
N
(CH2)5CH3), 1.26–1.38 (6H, m,
J
137.72 ( C6H4 ); 166.63 (HC
N ). MS EI (70 eV) m/z: 300 (85%)
[C9H9N C12H25]+, 130 (100%) [C9H8N]+. Elemental Analysis:
Found: C, 64.6; H, 8.7; N, 3.9%; Calc. for C21H34NBr: C, 66.3; H, 9.0;
N, 3.7%. mp 64.0–67.4 ◦C (measured by DSC).
N
J
6.9 Hz,
N
CH2 CH2 (CH2)3CH3), 3.26 (2H, t,
J
CH2CH2N),
N-Dodecyl-3,4-dihydroisoquinolinium
rate [DodDHQM][BF4] 6b. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 0.86 (3H, t, 6.9 Hz, (CH2)11CH3), 1.24 (18H,
CH2CH2(CH2)9CH3), 1.90 (2H, m, 6.9 Hz,
CH2CH2(CH2)9CH3), 3.31 (2H, t, J 7.8 Hz, CH2CH2N), 4.08 (2H,
tetrafluorobo-
CDCl3; TMS): ıC/ppm = 13.69, 22.18, 25.02, 25.62, 27.34, 30.88
(CH3CH2CH2CH2CH2CH2 ); 48.46, 61.29 ( CH2CH2N ); 117.36,
121.61 (N(SO2CF3)2); 124.08, 128.28, 128.76, 134.29, 135.88,
J
N
m,
N
J
6.9 Hz,
N
J
138.61 ( C6H4 ); 166.09 (HC
N ). MS EI (70 eV) m/z: 216 (100%)
[C9H9N C6H13]+, 130 (31%) [C9H8N]+. Elemental Analysis: Found:
C, 40.7; H, 4.4; N, 5.0%; Calc. for C17H22N2O4S2F6: C, 41.1; H, 4.5;
t,J 8.1 Hz, CH2CH2N), 4.18 (2H, t, J 7.5 Hz, N CH2(CH2)10CH3),
7.31–8.01 (4H, m, C6H4 ), 9.57 (1H, s, CH N). 13C NMR (75 MHz,
CDCl3; TMS): ıC/ppm = 13.99, 22.54, 25.19, 26.11, 27.46, 28.96,
29.20, 29.27, 29.39, 29.56, 29.55, 31.75 (CH3(CH2)10CH2 ); 48.23,
N, 5.6%. Density at 20 ◦C: 1.69 g cm−3
.
N-Octyl-3,4-dihydroisoquinolinium
bromide
[OcD-
HQM][Br] 5a. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = .85
61.00
( CH2CH2N ); 124.44, 128.02, 128.47, 134.43, 135.85,
(3H, m,
7.8 Hz,
J
7.5 Hz,
N
(CH2)7CH3), 1.21–1.32 (10H, m,
J
137.90 ( C6H4 ); 166.48 (HC
N
). MS EI (70 eV) m/z: 300 (100%)
[C9H9N C12H25]+, 130 (72%) [C9H8N]+. Elemental Analysis: Found:
C, 64.5; H, 8.9; N, 3.3%; Calc. for C21H34NBF4: C, 65.1; H, 8.9; N,
3.6%. mp 58.0–60.3 ◦C (measured by DSC).
N
CH2CH2 (CH2)5 CH3), 1.93 (2H, m,
J
7.2 Hz,
N
CH2 CH2 (CH2)5CH3), 3.33 (2H, t, J 8.1 Hz, CH2CH2N), 4.15
(2H, t,J 7.2 Hz, CH2CH2N), 4.30 (2H, t, J 7.5 Hz, N CH2(CH2)6CH3),
7.26–8.11 (4H, m, C6H4 ), 10.38 (1H, s, CH N). 13C NMR
(75 MHz, CDCl3; TMS): ıC/ppm = 13.98, 22.50, 26.08, 26.60, 27.35,
28.89, 29.01, 31.64 (CH3(CH2)6CH2 ); 50.46, 62.01 ( CH2CH2N );
126.48, 127.00, 127.34, 127.82, 129.95, 133.42 ( C6H4 ); 166.50
N-Dodecyl-3,4-dihydroisoquinolinium
bis(trifluoromethanesulfonyl)imide
1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.87 (3H, t, J 6.6 Hz,
(CH2)11CH3), 1.25 (18H, m, J 7.2 Hz, N CH2CH2(CH2)9CH3),
[DodDHQM][NTf2]
6c.
N
(HC
N
). MS EI (70 eV) m/z: 244 (37%) [C9H9N C8H17]+, 130 (49%)
1.88 (2H, m, J 6.6 Hz, N CH2CH2(CH2)9CH3), 3.27 (2H, t, J 8.1 Hz,
CH2CH2N), 4.00 (4H, t, J 7.5 Hz, CH2CH2N, N CH2(CH2)10CH3),
7.38–7.81 (4H, m, C6H4 ), 8.79 (1H, s, CH N). 13C NMR (75 MHz,
CDCl3; TMS): ıC/ppm = 14.05, 22.62, 25.04, 26.03, 27.44, 28.86,
29.24, 29.27, 29.39, 29.53, 29.61, 31.85 (CH3(CH2)10CH2 ); 48.46,
61.39 ( CH2CH2N ); 117.25, 121.49 (N(SO2CF3)2); 124.03, 128.31,
[C9H8N]+. Elemental Analysis: Found: C, 64.0; H, 8.5; N, 4.2%;
Calc. for C17H26NBr: C, 62.95; H, 8.1; N, 4.3%. Density at 20 ◦C:
1.45 g cm−3
.
N-Octyl-3,4-dihydroisoquinolinium
tetrafluorobo-
rate [OcDHQM][BF4] 5b. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 0.86 (3H, m, J 6.9 Hz, N (CH2)7CH3), 1.25–1.41 (10H,
m, J 7.8 Hz, N CH2CH2 (CH2)5 CH3), 1.90 (2H, m, J 6.9 Hz,
128.85, 134.33, 135.82, 138.71
( C6H4 ); 166.08 (HC N ).
MS EI (70 eV) m/z: 300 (100%) [C9H9N C12H25]+, 130 (20%)
[C9H8N]+. Elemental Analysis: Found: C, 48.8; H, 5.3; N, 4.2%;
Calc. for C23H34N2O4S2F6: C, 47.6; H, 5.9; N, 4.8%. Density at 20 ◦C
N
CH2 CH2 (CH2)5CH3), 3.31 (2H, t, J 8.1 Hz, CH2CH2N), 4.09
(2H, t,J 8.1 Hz, CH2CH2N), 4.20 (2H, t, J 7.5 Hz, N CH2(CH2)6CH3),
7.21–8.16 (4H, m, C6H4 ), 9.70 (1H, s, CH N). 13C NMR (75 MHz,
CDCl3; TMS): ıC/ppm = 13.88, 22.44, 26.38, 27.19, 27.58, 28.81,
1.60 g cm−3
N-iso-pentyl-3,4-dihydroisoquinolinium
PDHQM][Br] 7a. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.86
(3H, q, 6.9 Hz, (CH2)2CH(CH3)2), 1.00 (3H, q, 6.9 Hz,
(CH2)2CH(CH3)2), 1.71 (2H, q, J 6.9 Hz, N CH2 CH2 CH(CH3)2),
1.85 (1H, m, 6.9 Hz, (CH2)2 CH (CH3)2), 3.38 (2H, t,
CH2CH2N), 4.18 (2H, t, 7.8 Hz, CH2CH2N), 4.32
7.8 Hz, CH2 CH2CH(CH3)2), 7.33–8.12 (4H, m,
CH N). 13C NMR (75 MHz, CDCl3;
.
bromide
[i-
29.01, 31.59 (CH3(CH2)6CH2 ); 50.00, 61.60
( CH2CH2N );
124.50, 126.97, 127.51, 127.98, 130.11, 134.53 ( C6H4 ); 166.92
J
N
J
(HC
N
). MS EI (70 eV) m/z: 244 (23%) [C9H9N C8H17]+, 130 (43%)
N
[C9H8N]+. Elemental Analysis: Found: C, 62.3; H, 8.1; N, 4.35%;
J
N
J
Calc. for C17H26NBF4: C, 61.6; H, 7.9; N, 4.2%. Density at 20 ◦C:
7.8 Hz,
(2H, t,
J
1.38 g cm−3
.
J
N
N-Octyl-3,4-dihydroisoquinolinium
C6H4 ), 10.36 (1H, s,
TMS): ıC/ppm = 22.13, 26.76, 28.81, 31.46 ((CH3)2CHCH2CH2 );
50.00, 63.20 CH2CH2N ); 125.93, 126.63, 128.40, 131.11,
136.58, 137.70 ( C6H4 ); 170.11 (HC ). MS EI (70 eV) m/z: 202
(19%) [C9H9N–CH2CH2CH(CH3)2]+, 130 (39%) [C9H8N]+. Elemental
bis(trifluoromethanesulfonyl)imide
[OcDHQM][NTf2]
5c. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.86
(
(3H, m,
7.8 Hz,
J
6.9 Hz,
N
(CH2)7CH3), 1.19–1.27 (10H, m,
J
N
N
CH2CH2 (CH2)5 CH3), 1.63 (2H, m,
J
6.9 Hz,

200
S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
Analysis: Found: C, 60.4; H, 7.6; N, 4.5%; Calc. for C14H20NBr: C,
136.26, 138.54 ( C6H4 ); 164.55 (HC N ). MS EI (70 eV) m/z: 214
59.6; H, 7.2; N, 5.0%. Density at 20 ◦C: 1.63 g cm−3
.
(100%) [C9H9N C6H11]+, 130 (74%) [C9H8N]+. Elemental Analysis:
Found: C, 40.6; H, 3.7; N, 5.3%; Calc. for C17H20N2O4S2F6: C, 41.3;
N-iso-pentyl-3,4-dihydroisoquinolinium
tetrafluorobo-
rate [i-PDHQM][BF4] 7b. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 0.96 (6H, m, J 6.9 Hz, N (CH2)2CH(CH3)2), 1.68 (2H,
H, 4.1; N, 5.7%. Density at 20 ◦C: 1.27 g cm−3
.
q,
N
J
6.9 Hz,
N CH2 CH2 CH(CH3)2), 1.78 (1H, m, J 6.9 Hz,
2.3. NMR spectra
(CH2)2 CH (CH3)2), 3.37 (2H, t, J 7.8 Hz, CH2CH2N), 4.04 (2H,
t, J 7.8 Hz, CH2CH2N), 4.50 (2H, t, J 7.8 Hz, N CH2 CH2CH(CH3)2),
NMR spectra were performed using Varian Unity Inova Plus
spectrometer, 300 MHz for 1H spectra and 75 MHz for 13C spec-
tra. All samples were dissolved in CDCl3 99.8% atoms of deuterium
with 0.03 vol.% of TMS.
7.39–8.08 (4H, m, C6H4 ), 9.70 (1H, s, CH N). 13C NMR
(75 MHz, CDCl3; TMS): ıC/ppm = 21.82, 25.91, 27.53, 31.91
((CH3)2CHCH2CH2 ); 48.87, 59.98 ( CH2CH2N ); 124.18, 125.90,
127.80, 130.47, 135.71, 137.66 ( C6H4 ); 166.04 (HC
N ). MS
EI (70 eV) m/z: 202 (16%) [C9H9N CH2CH2CH(CH3)2]+, 130 (37%)
[C9H8N]+. Elemental Analysis: Found: C, 58.1; H, 6.9; N, 4.3%;
Calc. for C14H20NBF4: C, 58.15; H, 7.0; N, 4.85%. Density at 20 ◦C:
2.4. Differential scanning calorimetry (DSC)
DSC were performed using 822e DSC Mettler Toledo Differential
Scanning Analyzer. Sample of [RDHQM][X] (2–4 mg) was heated
from 25 to 400 ◦C at a heating rate of 10 ◦C min−1 under nitrogen
atmosphere.
1.43 g cm−3
N-iso-pentyl-3,4-dihydroisoquinolinium
bis(trifluoromethanesulfonyl)imide [i-PDHQM][NTf2]
1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 0.97 (6H, d, J 6.5 Hz,
(CH2)2CH(CH3)2), 1.70 (2H, q, J 6.6 Hz, N CH2 CH2 CH(CH3)2),
1.81 (1H, m, 6.6 Hz, (CH2)2 CH (CH3)2), 3.27 (2H,
CH2CH2N), 4.02 (4H, t, 7.8 Hz, CH2CH2N,
CH2 CH2CH(CH3)2), 7.27–8.06 (4H, m, C6H4 ), 8.89 (1H,
.
7c.
N
2.5. Density measurement
J
N
t,
N
J
7.8 Hz,
J
Into pycnometer of known weight (mpy = 1.93 g) and known vol-
ume (Vpy = 0.18 ml, determinated by water at 20 ◦C) was introduced
an ionic liquid was thermostated in water bath at 20 ◦C for 15 min.
After this time, pycnometer with the ionic liquid was dried and
was weighed (ms, 0.0001 g). For each ionic liquid procedure was
repeated 4 times. Density of the ionic liquid (dIL) was calculated
according to equation:
s, CH N). 13C NMR (75 MHz, CDCl3; TMS): ıC/ppm = 21.89, 25.03,
27.64, 35.98 ((CH3)2CHCH2CH2 ); 48.57, 59.83, ( CH2CH2N );
117.54, 121.80 (N(SO2CF3)2); 124.17, 125.65, 127.60, 130.15,
135.87, 138.44 ( C6H4 ); 166.08 (HC
N ). MS EI (70 eV) m/z:
202 (43%) [C9H9N CH2CH2CH(CH3)2]+, 130 [C9H8N]+ (100%).
Elemental Analysis: Found: C, 38.35; H, 3.7; N, 4.7%; Calc. for
C16H20N2O4S2F6: C, 39.8; H, 4.2; N, 5.8%. Density at 20 ◦C:
dIL = (ms − mpy)Vp−y1
1.62 g cm−3
.
N-Cyclohexyl-3,4-dihydroisoquinolinium bromide [cHD-
HQM][Br] 8a. 1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 1.28–2.23
(10H, m, J 12.9 Hz, J 3.3 Hz, N CH(CH2CH2)2CH2), 3.33 (2H, t, J
7.8 Hz, CH2CH2N), 4.16 (2H, t, J 7.8 Hz, CH2CH2N), 4.47 (1H,
m, J 11.7 Hz, J 3.3 Hz, N CH(CH2CH2)2CH2), 7.32–8.35 (4H, m,
C6H4 ), 10.30 (1H, s, CH N). 13C NMR (75 MHz, CDCl3; TMS):
ıC/ppm = 24.39, 24.60, 25.63; 30.65 (N CH(CH2CH2)2CH2); 46.56,
2.6. General procedure for epoxidation
Sodium bicarbonate (5.0 equiv. mol), tetrabutylammonium
hydrogen sulphate (0.1 equiv. mol), [RDHQM][X] (0.1 equiv. mol),
olefin (0.10 g, 1.0 equiv. mol), water (6 ml) and acetonitrile (9 ml)
were added to a three-necked flask fitted with a reflux con-
denser, a thermometer, a dropping funnel and a magnetic stirrer.
A solution of Oxone® (2.0 equiv. mol) in water was added at
room temperature. Oxone® is the trade name of salts mixture
2KHSO5·KHSO4·K2SO4 in which KHSO5 is an oxidising agent. After
the addition was complete, the reaction mixture was kept at room
temperature for 1 h and then heated to 60 ◦C. The reaction was
maintained at this temperature for 20 h. The conversion of the start-
ing materials was monitored by TLC using dichloromethane as the
eluent and UV light and iodine in trichloromethane to visualise the
signals. After this time, the reaction mixture was cooled to ambient
temperature, and water was added to dissolve the inorganic solids.
The contents of the flask were extracted with methylene chloride
(4 × 15 ml). The organic layer was washed with 1% NaOH solution
(5 × 15 ml) to remove [n-Bu4N][HSO4] and dried over anhydrous
magnesium sulphate. The drying agent was removed by filtration,
and the organic solvent was evaporated under high vacuum at
30–35 ◦C. The final product was analysed by 1H and 13C NMR spec-
troscopy.
70.08
( CH2CH2N ); 124.75, 127.80, 128.45, 135.05, 136.02,
137.69 ( C6H4 ); 165.35 (HC
N
). MS EI (70 eV) m/z: 214 (69%)
[C9H9N C6H11]+, 130 (100%) [C9H8N]+. Elemental Analysis: Found:
C, 61.0; H, 7.0; N, 4.3%; Calc. for C15H20NBr: C, 61.2; H, 6.9; N, 4.8%.
mp 162.9–168.2 ◦C (measured by DSC).
N-Cyclohexyl-3,4-dihydroisoquinolinium
roborate [cHDHQM][BF4] 8b. 1H NMR (300 MHz, CDCl3;
TMS): ıH/ppm = 1.26–2.20 (10H, m, 12.9 Hz, J 3.3 Hz
CH(CH2CH2)2CH2), 3.29 (2H, t, 7.8 Hz, CH2CH2N), 4.11
(2H, t, J 7.8 Hz, CH2CH2N), 4.28 (1H, m, J 11.7 Hz, J 3.6 Hz,
tetrafluo-
J
N
J
N
CH(CH2CH2)2CH2), 7.31–8.16 (4H, m, C6H4 ), 9.71 (1H, s,
CH N). 13C NMR (75 MHz, CDCl3; TMS): ıC/ppm = 24.42, 24.65,
25.47; 30.57 (N CH(CH2CH2)2CH2); 46.55, 70.30 ( CH2CH2N );
124.67, 127.87, 128.50, 134.80, 136.20, 137.82 ( C6H4 ); 165.16
(HC
N
). MS EI (70 eV) m/z: 214 (41%) [C9H9N C6H11]+, 130
(100%) [C9H8N]+. Elemental Analysis: Found: C, 58.8; H, 6.7;
N, 4.4%; Calc. for C15H20NBF4: C, 59.8; H, 6.7; N, 4.65%. mp
68.1–71.9 ◦C (measured by DSC).
1,2-Epoxycyclohexane 9b. 1H NMR (300 MHz, CDCl3; TMS):
ıH/ppm = 1.15–1.18 (2H, m, CH2CH2CH2CH2 ), 1.33–1.38 (2H, m,
N-Cyclohexyl-3,4-dihydroisoquinolinium
bis(trifluoromethanesulfonyl)imide
1H NMR (300 MHz, CDCl3; TMS): ıH/ppm = 1.25–2.18 (10H,
m, 13.2 Hz, J 3.6 Hz, CH(CH2CH2)2CH2), 3.24 (2H, t,
7.8 Hz, CH2CH2N), 4.05 (3H, m, J 7.8 Hz, CH2CH2N, J 3.6 Hz,
[cHDHQM][NTf2]
8c.
CH2CH2CH2CH2 ), 1.74–1.76 (2H, m,
1.85–1.88 (2H, m, CH2CH2CH2CH2 ), 3.04–3.06 (2H, m,
HC
CH). 13C NMR (75 MHz, CDCl3; TMS): ıC/ppm = 19.45
CH2CH2CH2CH2 ), 24.12 CH2CH2CH2CH2 ), 52.01
(HC CH).
CH2CH2CH2CH2 ),
J
N
J
O
(
(
N CH(CH2CH2)2CH2), 7.27–7.83 (4H, m, C6H4 ), 8.84 (1H, s,
CH N). 13C NMR (75 MHz, CDCl3; TMS): ıC/ppm = 24.39, 24.53,
O
1,2-Epoxycyclooctane 10b. 1H NMR (300 MHz, CDCl3;
TMS): ıH/ppm = 1.25–1.63 (8H, m, CH2CH2CH2CH2CH2CH2 ),
25.25; 30.63 (N CH(CH2CH2)2CH2); 46.70, 70.70 ( CH2CH2N );
117.28, 121.52 (N(SO2CF3)2); 124.23, 128.16, 128.78, 134.38,
2.11–2.17 (4H, m,
CH2CH2CH2CH2CH2CH2 ), 2.91 (2H, m,

S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
201
Table 1
Results of the syntheses of 3,4-dihydroisoquinolinium N-substituted bromides.
Product
No.
Reaction time (h)
Yielda (%)
Melting pointb (◦C)
Densityc (g cm−3
)
[BDHQM][Br]
[HDHQM][Br]
[OcDHQM][Br]
[DodDHQM[Br]
[i-PDHQM][Br]
[cHDHQM][Br]
3a
4a
5a
6a
7a
8a
6
16
47
24
20
16
84
73
65
71
91
81
–
–
–
1.40
1.32
1.45
–
1.63
–
52–54
–
168–171
a
Yield was determined for isolated products.
b
c
Melting point of solids measured by capillary apparatus.
Density of liquid products measured by pycnometer at 20 ◦C.
O
CH). 13C NMR (75 MHz, CDCl3; TMS): ıC/ppm = 25.48
Table 3
HC
Effect of the type of atom on the chemical shift, ıH, (300 MHz, CDCl3; TMS) of the
(
CH2CH2CH2CH2CH2CH2 ), 26.19 ( CH2CH2CH2CH2CH2CH2 ),
hydrogen atom of the CH
N
group.
26.44 ( CH2CH2CH2CH2CH2CH2 ), 55.50 (HC
O CH).
Cation
Anion
[Br]−
[BF4]−
[NTf2]−
3. Results and discussion
[BDHQM]+
10.27 ppm
10.32 ppm
10.38 ppm
10.28 ppm
10.36 ppm
10.30 ppm
9.76 ppm
9.57 ppm
9.70 ppm
9.57 ppm
9.70 ppm
9.71 ppm
8.86 ppm
8.83 ppm
8.80 ppm
8.79 ppm
8.89 ppm
8.84 ppm
[HDHQM]+
[OcDHQM]+
[DodDHQM]+
[i-PDHQM]+
[cHDHQM]+
3.1. Synthesis of N-substituted 3,4-dihydroisoquinolinium ionic
liquids
A number of ionic liquids were obtained that contained the
iminium group C
N R. These substances are built from 3,4-
dihydroisoquinolinium N-substituted cations that possess different
substituents on the nitrogen atom.
is a solid having a melting point of 168–171 ◦C. The remaining
3,4-dihydroisoquinolinium N-substituted bromides that were
obtained meet the defining criterion of ionic liquids [11].
The anion for each of the synthesised bromides was exchanged
for tetrafluoroborate [BF4]− and bis(trifluoromethylsulfonyl)imide
[NTf2]−. These anions are commonly used in ionic liquids. The reac-
tions were conducted as shown in Fig. 5.
Table 2 shows the results of these syntheses. As in the case of the
bromides, most of the products containing the [BF4]− and [NTf2]−
anions were liquids with relatively high density at room temper-
ature, in the range between 1.27 and 1.69 g cm−3. Under these
conditions, [DodDHQM][BF4] and [cHDHQM][BF4] were solids with
melting points lower than 100 ◦C. Therefore all of the compounds
met the defining criterion of ionic liquids [11].
They were obtained from isochroman (1) through a multi-
step process (Fig. 3) [12,13]. An essential starting material for the
synthesis of these derivatives is 2-(2-bromoethyl)benzaldehyde
(2) [9], which was obtained as the product of the bromina-
tion of isochroman (1) [13]. Crude 2-(2-bromoethyl)benzaldehyde
was reacted with primary amines to yield the desired 3,4-
dihydroisoquinolinium N-substituted bromides (3a–8a). Fig. 4
shows the structures of the [RDHQM][Br] compounds that were
synthesised and the abbreviations used in the remainder of this
paper.
Table
1 shows the results of the synthesis of the 3,4-
dihydroisoquinolinium N-substituted bromides (3a–8a). The reac-
tion time for the condensation of the aldehyde with the primary
amine depends largely on the type of the amine utilised; the dura-
tion of the reaction also considerably influences the final yield of
the product.
3.2. NMR data of N-substituted 3,4-dihydroisoquinolinium ionic
liquids
The greatest yields were obtained for [i-PDHQM][Br] (91%),
[BDHQM][Br] (84%) and [cHDHQM][Br] (81%). When using larger
amines, longer reaction times were required to obtain high yields.
At ambient temperature, some of the bromides were obtained
as liquids with relatively high densitiy, in the range between
1.32 and 1.63 g cm−3. An exception is [cHDHQM][Br] (8a), which
The [RDHQM][X] structure was characterised using 1H and 13
C
NMR. The identity of the anion in the ionic liquid considerably influ-
ences the chemical shifts of the hydrogen atoms that are connected
to the carbon atom of the iminium group [14,15]. The 1H NMR data
for these atoms are presented in Table 3.
Table 2
Results of the reaction in which [Br]− was exchanged for [BF4]− or [NTf2]−
.
Product
No.
Reaction time (min)
Yielda (%)
Melting pointb (◦C)
Densityc (g cm−3
)
[BDHQM][BF4]
3b
3c
4b
4c
5b
5c
6b
6c
7b
7c
8b
8c
10
30
30
60
60
60
10
30
60
60
60
60
69
60
45
50
57
81
72
38
79
87
63
50
37–40
–
–
–
–
–
56–58
–
–
–
74–77
–
–
[BDHQM][NTf2]
[HDHQM][BF4]
[HDHQM][NTf2]
[OcDHQM][BF4]
[OcDHQM][NTf2]
[DodDHQM][BF4]
[DodDHQM][NTf2]
[i-PDHQM][BF4]
[i-PDHQM][NTf2]
[cHDHQM][BF4]
[cHDHQM][NTf2]
1.59
1.48
1.69
1.38
1.51
–
1.60
1.43
1.62
–
1.27
a
Yield was determined for isolated products.
b
c
Melting point of solids measured by capillary apparatus.
Density of liquid products measured by pycnometer at 20 ◦C.

202
S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
Br
CCl4
HBr 40% aq
~ 0,5h
+ Br2
O
O
O
~ 2,5h
O
(1)
(2)
(2)
Br
Br
Br-
X-
R-NH2
EtOH
MX
+
+
N
CH3CN/H2O
N
R
R
(3a - 8a)
(3b,c - 8b,c)
CH
-
b, X-= BF4
3
3a, R= n-Bu
4a, R= n-He
5a, R= n-Oc
6a, R= n-Dod
7a, R= H C
3
-
c, X-= NTf2
CH
3
8a, R=
Fig. 3. Synthesis of [RDHQM][X] from isochroman.
Br-
Br-
N+
N+
CH
CH
3
3
[BDHQM][Br] (3a)
[DodDHQM][Br] (6a)
Br-
N+
Br-
N+
CH
CH
3
3
[HDHQM][Br] (4a)
[
i-PDHQM][Br]
CH
3
(7a)
Br-
Br-
N+
CH
N+
3
[cHDHQM][Br]
(8a)
[OcDHQM][Br] (5a)
Fig. 4. Structures of the obtained [RDHQM][Br] compounds with their abbreviations.
The chemical shifts relative to TMS of the hydrogen atoms of
the CH group for compounds containing the same anion were
values due to specific anions (ıH([Br]−) ıH([BF4]−) ≈ 0.65 ppm;
N
ıH([BF4]−) ıH([NTf2]−) ≈ 0.83 ppm;
ıH([Br]−) ıH([NTf2]−)
very similar (∼10.32 ppm for [Br]−, ∼9.67 ppm for [BF4]− and ∼8.84
for [NTf2]−), regardless of the cation structure. In the series of syn-
thesised compounds, the chemical shifts of this hydrogen atom
were not affected by the characteristics of the substituent (length
and shape of the hydrocarbon chain) on the nitrogen.
≈1.48 ppm) was so large that the compounds can be easily
differentiated based on the 1H NMR spectra. This effect is caused
by the differences in the cation-anion interactions and the for-
mation of hydrogen bonds between these ions, as in the case
of imidazolium ionic liquids [16]. When a proton is part of a
hydrogen bond, a reduction in the shielding effect and a shift of the
signal towards a higher value are observed. Amongst the anions
utilised, the bromide ion interacts most strongly with the cation,
In contrast, the influence of the anion on the chemical
shift of this hydrogen was clear. Amongst compounds con-
taining the same cation, the variation in the chemical shift
-
Br-
BF4
N+
NaBF4
+
NaBr
N+
10-60 min, CH3CN/H2O
R
R
(3b - 8b)
(3a - 8a)
(3a - 8a)
-
Br-
LiNTf2
NTf2
N+
30-60 min, CH3CN
+
LiBr
N+
R
R
(3c - 8c)
Fig. 5. Synthesis of [RDHQM][BF4] and [RDHQM][NTf2] from [RDHQM][Br].

S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
203
Table 4
Chemical shift ıC (75 MHz, CDCl3; TMS) of the carbon atom of the CH
Table 6
N
group.
Results of cyclohexene and cyclooctene epoxidation using [RDHQM][X] ionic liquids
as catalysts.
Cation
Anion
[Br]−
Catalyst
[RDHQM][X]
Catalyst Product yield/%
No.
[BF4]−
[NTf2]−
[BDHQM]+
166.09 ppm
166.70 ppm
166.50 ppm
166.63 ppm
170.11 ppm
165.35 ppm
166.35 ppm
166.45 ppm
166.92 ppm
166.48 ppm
166.04 ppm
165.16 ppm
167.17 ppm
166.09 ppm
166.05 ppm
166.08 ppm
166.08 ppm
164.55 ppm
1,2-
1,2-Epoxycyclooctane
(10b)
[HDHQM]+
[OcDHQM]+
[DodDHQM]+
[i-PDHQM]+
[cHDHQM]+
Epoxycyclohexane
(9b)
[BDHQM][BF4]
[BDHQM][NTf2]
[HDHQM][Br]
3b
3c
4a
4b
4c
5a
5b
5c
6a
6b
6c
8b
8c
46
42
63
50
73
63
54
67
46
46
59
63
59
44
39
44
44
58
39
35
51
39
31
47
28
35
[HDHQM][BF4]
[HDHQM][NTf2]
[OcDHQM][Br]
[OcDHQM][BF4]
[OcDHQM][NTf2]
[DodDHQM][Br]
[DodDHQM][BF4]
[DodDHQM][NTf2]
[cHDHQM][BF4]
[cHDHQM][NTf2]
whereas the other two anions have weaker interactions [17]. These
interactions explain the differences in the chemical shifts of the
proton of the iminium group; that is, this chemical shift depends
on the type of the anion in the ionic liquid. The second reason for
the differences in the chemical shifts of the hydrogen atom of the
CH
N
group may be the structure of the anion. Anions that
possess a larger number of atoms ([NTf2]−, [BF4]−) exert stronger
shielding effects on this atom, and thus, the signal appears at a
lower chemical shift. The signals of the remaining hydrogen atoms
in the various cations were almost identical.
Conditions: 0.1 equiv. mol calatyst, 2.0 equiv. mol Oxone®, 5.0 equiv. mol Na2CO3,
0.1 equiv. mol [n-Bu4N][HSO4], solvent acetonitrile/water = 1.5/1.0, temperature
60 ◦C, reaction time 20 h. Yield was determined for isolated products.
For the carbon atom of the iminium group (Table 4), a clear effect
of the identity of the anion on the chemical shift was not observed.
This carbon atom is linked with the more electronegative nitrogen
atom by a double bond and has a higher chemical shift of approxi-
mately 166–167 ppm. For [cHDHQM][X] ionic liquids, we observed
a slight shift in the signal of this carbon atom towards the stronger
field. This observation may be explained by the cyclic structure of
the substituent on the nitrogen atom.
liquids were those with [NTf2] anions, and they underwent decom-
position in temperature above 300 ◦C. It is typically characteristic
for ionic liquids [20].
3.4. Application of the synthesised ionic liquids as catalysts in
olefin epoxidation
An essential element of this study was the investigation of the
potential use of the synthesised [RDHQM][X] ionic liquids as cata-
lysts for epoxidation. Earlier, Philip C. Bulman Page et al. described
application of the tetraphenylborate 3,4-dihydroisoquinolinium N-
substituted salts as the efficient catalysts in olefins epoxidation
reactions [21].
For our experiments, model alkenes such as cyclohexene (9a)
and cyclooctene (10a) were selected. The epoxidation products of
these alkenes have practical applications. 1,2-Epoxycyclohexane
(cyclohexene oxide, CHO, 9b) is widely used in the chemistry and
technology of polymers. The copolymerisation of CHO with carbon
dioxide provides to biodegradable poly(cyclohexene carbonate)s
[22]. In addition, CHO is used to modify polymeric resins that
contain amino groups [23] and is used in the synthesis of pes-
ticides, pharmaceuticals and dyestuff [24]. 1,2-Epoxycyclooctane
(cyclooctene oxide, COO, 10b) has applications in the chemistry
of organosilicon compounds [25,26]. Both of these epoxides may
be easily converted into the corresponding vicinal diols, which are
important intermediates in organic synthesis [27] and in polymer
chemistry [28].
The epoxidation reactions were performed in the presence
of [RDHQM][X] as a catalyst at a concentration of 10 mol% rela-
tive to the alkene. Potassium peroxymonosulphate (KHSO5) was
used as the oxidising agent (Fig. 6). The solvent for these reac-
tions was a mixture of acetonitrile and water in a 1.5/1.0 ratio
by volume. In addition, tetrabutylammonium hydrogen sulphate,
[n-Bu4N][HSO4], was utilised.
Table 6 shows the results of these reactions. The reactions
were monitored by TLC. After 20 h, the starting materials were not
observed in the reaction mixtures. The separated products of the
reactions were characterised by 1H and 13C NMR spectroscopy.
The major products of these reactions were the epoxides: 1,2-
epoxycyclohexane and 1,2-epoxycyclooctane. The reaction yields
were determined for the isolated products and varied from
30 to 70%. In some cases of cyclohexene epoxidation, a trace
amount of 1,2-cyclohexanediol was observed, as indicated by the
3.3. Thermal properties of N-substituted
3,4-dihydroisoquinolinium ionic liquids
The thermal properties for synthesised [RDHQM][X] ionic liq-
uids were investigated. The temperatures associated with phase
transitions were measured by Differential Scanning Calorimetry
(DSC), in the range 25–400 ◦C. The results of the analysis are shown
in Table 5.
It is well known from the literature, that high thermal stability
is the characteristic properity for ionic liquids [18,19]. As resulted
from Table 5, all investigated [RDHQM][X] ionic liquids were sta-
ble to temperature of approximately 200 ◦C. The most stable ionic
Table 5
Results of thermal analysis of sythesised [RDHQM][X].
Product
No.
Melting point
(◦C)a
Tonset (◦C)b
Tendset (◦C)b
[BDHQM][Br]
3a
3b
3c
4a
4b
4c
5a
5b
5c
6a
6b
6c
7a
7b
7c
8a
8b
8c
–
223.1
236.4
328.9
216.6
244.3
302.8
229.4
238.3
323.2
228.7
223.5
311.6
312.6
239.9
302.0
217.8
263.0
319.6
294.5
299.6
398.7
299.4
354.4
435.0C
310.6
305.0
413.4C
286.5
325.5
397.4
376.2
291.7
405.2C
281.5
307.1
384.7
[BDHQM][BF4]
[BDHQM][NTf2]
[HDHQM][Br]
43.2–47.3
–
–
–
–
–
–
–
64.0–67.4
58.0–60.3
–
–
–
–
[HDHQM][BF4]
[HDHQM][NTf2]
[OcDHQM][Br]
[OcDHQM][BF4]
[OcDHQM][NTf2]
[DodDHQM][Br]
[DodDHQM][BF4]
[DodDHQM][NTf2]
[i-PDHQM][Br]
[i-PDHQM][BF4]
[i-PDHQM][NTf2]
[cHDHQM][Br]
[cHDHQM][BF4]
[cHDHQM][NTf2]
162.9–168.2
68.1–71.9
–
a
Melting point measured by DSC.
The decomposition temperature determined by DSC.
The decomposition temperature determined by TGA.
b
C

204
S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
O
S
X-
or
or
HO
HO
O- K+
+
N
O
R
(9a)
(10a)
(10b)
O
-
X-
O
S
O
+
O
O
+
O
K
N
R
O
(9b)
Fig. 6. Epoxidation of cyclohexene and cyclooctene using [RDHQM][X] ionic liquids as catalysts.
H2O + H+A-
H
OH+2
HO
+ A-
H
O+
H
+
O
O+
H +
H
OH+2
H
OH
H
O+
OH
H
OH+2
+
+
HO
H
H
OH
OH
Fig. 7. Mechanism of 1,2-cyclohexanediol formation under aqueous acidic conditions.
corresponding weak signals in the NMR spectra (1H NMR 300 MHz,
CDCl3, TMS: ıH/ppm = 4.14, 2H, s, OH; 13C NMR 75 MHz, CDCl3,
TMS: ıC/ppm = 77.15, C OH). The presence of water and acidic sub-
stances in the reaction system promotes epoxide ring-opening and
diol formation [29], as shown in Fig. 7.
When comparing the results of the epoxidation reactions of
model alkenes using the same catalyst, the yield for the epoxida-
tion of cyclohexene was higher than that for cyclooctene in all of
the experiments; this result conflicts with the literature data [30].
In the cyclooctene epoxidation, secondary epoxide ring-opening
by-products were not observed. In the absence of the undesir-
able side reactions, the lower yield of 1,2-epoxycyclooctane may
be caused by the more difficult extraction and purification of this
epoxide.
duration of the reaction between 2-(2-bromoethyl)benzaldehyde
and the primary amine was critical and strongly influenced the final
yield of the product. A longer reaction time should be utilised for
bulkier amines.
At ambient temperature, most products were high-density liq-
uids, and only compounds with a relatively large cation and a small
anion were solids. This relationship is characteristic of all types of
ionic liquids.
The 1H NMR and 13C NMR spectra of the obtained isoquinolin-
ium ionic liquids were determined. The type of anion influenced
the chemical shift of the hydrogen on the carbon of the iminium
group. For specific types of anions, this signal fell within a very nar-
row and characteristic range, and substances built from the same
cation and different anions can be easily identified.
All of obtained [RDHQM][X] ionic liquids are stable to tempera-
ture of approximately 200 ◦C. The most stable are compounds with
[NTf2] anion. [RDHQM][NTf2] decomposes in temperature above
300 ◦C. Slightly different of melting point value, measured by DSC
and capillary apparatus was observed.
The synthesised [RDHQM][X] ionic liquids were tested as cat-
alysts for the epoxidation of cyclohexene and cyclooctene at a
concentration of 10 mol% relative to the alkene. The yield var-
ied from 30 to 70%, but was higher for cyclohexene in all of
the experiments. The starting materials were not detected in the
reaction mixture after 20 h. The identity of each product was
determined based on the 1H NMR and 13C NMR spectra. The reac-
tions selectively produced the corresponding epoxides. In some of
the cyclohexene epoxidation reactions, secondary epoxide ring-
opening and hydrolysis to form 1,2-epoxycyclohexanediol was
observed, but the extent of this side reaction was very small. Unde-
sirable side reactions were not observed in the epoxidation of
When comparing series of ionic liquids with the same
cation, the best results were observed for compounds containing
the hydrophobic bis(trifluoromethylsulfonyl)imide anion [NTf2]−
instead of [BF4]− or [Br]− in most cases. For the [BDHQM]+ (3b, 3c)
and [cHDHQM]+ (8b, 8c) series of ionic liquids, the yields of prod-
ucts were comparable for both anions, and a clear effect of the type
of anion was not observed.
Our results show that the synthesised N-substituted 3,4-
dihydroisoquinolinium ionic liquids may have uses as catalysts in
olefin epoxidation.
4. Conclusions
Ionic liquids that contain an iminium group were synthesised
based on an N-substituted 3,4-dihydroisoquinolinium cation and
anions that are typically used in this type of compound, [Br]−,
[BF4]− and [NTf2]−. The synthesis consisted of several steps. The

S. Baj et al. / Applied Catalysis A: General 433–434 (2012) 197–205
205
cyclooctene. For both of the epoxidated alkenes, the best results
were observed when using ionic liquids that contained the [NTf2]−
anion.
[12] P. Bulman Page, G. Rassias, D. Bethnell, M. Schilling, J. Org. Chem. 63 (1998)
2774–2777.
[13] J. Crosthwaite, V. Farmer, J. Hallett, T. Welton, J. Mol. Catal. A: Chem. 279 (2008)
148–152.
[14] P. Bonhote, A. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grätzel, Inorg.
Chem. 35 (1996) 1168–1178.
Acknowledgment
[15] R. Giernoth, D. Bankmann, N. Schlörer, Green Chem. 7 (2005) 279–282.
[16] K. Dong, S. Zhang, D. Wang, X. Yao, J. Phys. Chem. A 110 (2006) 9775–9782.
[17] S. Lin, M. Dang, C. Chang, S. Lue, Tetrahedron 60 (2004) 9441–9446.
[18] H. Ngo, K. LeCompte, L. Hargens, A. McEwen, Thermochim. Acta 357–358 (2000)
97–102.
This work was co-financed by the Ministry of Science and Higher
Education (grant no. N N209 149236).
[19] A. Amarasekara, O. Owereh, J. Therm. Anal. Calorim. 103 (2011) 1027–1030.
[20] N. Meine, F. Benedito, R. Rinaldi, Green Chem. 12 (2010) 1711–1714.
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[22] J. Kim, C. Cowman, A. LaPointe, U. Wiesner, G. Coates, Macromolecules 44 (2011)
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