Sulfonic acid-functionalized ionic liquids as metal-free, efficient and reusable catalysts for direct amination of alcohols

Article abstract of DOI:10.1002/adsc.201100886

A series of sulfonic acid-functionalized (SO₃H-functionalized) ionic liquids was synthesized and used as metal-free, highly selective and efficient catalysts for the direct amination of alcohols. Notably, the activities of the series of SO₃H-functionalized ionic liquids were compared and a 92% isolated yield was obtained using 3-tetradecyl-1-(butyl-4- sulfonyl)imidazolium trifluoromethanesulfonate ([BsTdIM][OTf]) as the catalyst. Importantly, the catalytic system has wide substrate scope including benzylic, allyl, propargylic, aliphatic alcohols with sulfonamide, amide, carbamate, aromatic amine and N-heterocyclic compounds. Interestingly, the system was also suitable for a multi-gram scale direct amination of alcohols. Additionally, the reusable nature of [BsTdIM][OTf] makes this protocol more attractive and avoids the disposal and neutralization of acidic catalysts. Moreover, preliminary experiments indicated that this reaction should proceed via an S_N1 pathway. Copyright

Full text of DOI:10.1002/adsc.201100886

FULL PAPERS
DOI: 10.1002/adsc.201100886
Sulfonic Acid-Functionalized Ionic Liquids as Metal-Free,
Efficient and Reusable Catalysts for Direct Amination of
Alcohols
Feng Han,a,b Lei Yang,a,* Zhen Li,a and Chungu Xiaa,*
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences, Lanzhou 730000, Peopleꢀs Republic of China
Fax : (+86)-931-827-7088; phone: (+86)-931-496-8129; e-mail: lyang@licp.cas.cn or cgxia@licp.cas.cn
Graduate School of the Chinese Academy of Sciences, Beijing 100039, Peopleꢀs Republic of China
b
Received: November 15, 2011; Revised: January 12, 2012; Published online: April 16, 2012
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100886.
Abstract: A series of sulfonic acid-functionalized N-heterocyclic compounds. Interestingly, the system
(SO3H-functionalized) ionic liquids was synthesized was also suitable for a multi-gram scale direct amina-
and used as metal-free, highly selective and efficient tion of alcohols. Additionally, the reusable nature of
catalysts for the direct amination of alcohols. Nota- [BsTdIM]ACTHNUTRGNEU[GN OTf] makes this protocol more attractive
bly, the activities of the series of SO3H-functional- and avoids the disposal and neutralization of acidic
ized ionic liquids were compared and a 92% isolated catalysts. Moreover, preliminary experiments indicat-
yield was obtained using 3-tetradecyl-1-(butyl-4- ed that this reaction should proceed via an SN1 path-
sulfonyl)imidazolium
trifluoromethanesulfonate way.
([BsTdIM][OTf]) as the catalyst. Importantly, the
ACHTUNGTRENNUNG
catalytic system has wide substrate scope including
benzylic, allyl, propargylic, aliphatic alcohols with Keywords: alcohols; amination; ionic liquids; sulfon-
sulfonamide, amide, carbamate, aromatic amine and ic acid-functionalized ionic liquids
Introduction
On the other hand, the carbocation process shown
in path C seems to be more attractive. Various Lewis
Amination is a powerful method for the synthesis of acids, such as triflate salts,[5] BiCl3,[6] FeCl3,[7] InBr3,[8]
amine derivatives, which are highly important inter- NaAuCl4,[9] MoCl5,[10] MoO
mediates because of their relevance for the synthesis
of various pharmaceuticals and fine chemicals.[1]
Nowadays, there are several methods to fulfil the
transformation.[2] At present, a good alternative ap-
proach is to use alcohols as the alkylating agents to
react with various amines as listed in Scheme 1. Obvi-
ously, the direct amination of alcohols (Scheme 1,
paths B and C) is more competitive than the protocol
of pre-activating alcohols (Scheme 1, path A) from
the viewpoints of atom economy, green chemistry and
sustainable development, since water is the only reac-
tion by-product therein. In path B, transition metals
with additives or ligands are essential, appropriate
complexes are needed to realize the high performance
of the late transition metals, and 3–5 equivalents of
nucleophiles should be added, all of which make this
protocol complicated.[4]
(acac)2,[11] Ca(NTf2)2,[12]
2ACHUTNGTRENNUG ACHUTNGTRENNUGN
Scheme 1. Methods for the amination of alcohols.
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Sulfonic Acid-Functionalized Ionic Liquids as Metal-Free, Efficient and Reusable Catalysts
Scheme 2. SO3H-functionalized ionic liquids used in the direct amination of alcohols.
iridium pincer catalyst,[13] Pd catalyst,[14] AuCl/ catalyst for the direct nucleophilic substitution of al-
AgSbF6,[15] as well as Brønsted acids, such as p-tolue- cohols with aniline, amide, sulfonamide, and 1,3-dicar-
nesulfonic acid or polymer-bound p-toluenesulfonic bonyl compounds.[23] Although significant progress
acid,[16] proton-exchanged montmorillonite,[17] dode- has been made, metal zinc was still used in the cata-
cylbenzenesulfonic acid[18], HClO4·SiO2,[19] and cal- lytic system and substrate scope also needed to be fur-
ix[4]resorcinarenesulfonic acid[20] have been employed ther expanded. In addition, using Amberlyst-15 im-
to achieve this transformation. Unfortunately, the re- mobilized in [BMIM][BF4] ionic liquid as an recycla-
ported catalytic systems working through carbocation ble reagent for the direct substitution of alcohols with
mechanism often suffered from one or more disad- various nitrogen nucleophiles was also described by
vangtages, including poor reactivity (low catalytic ac- Bhanage and co-workers.[24] However, the use of an
tivity and selectivity, and relatively narrow substrate ionic liquid as a solvent was required in order to
scope), and insufficient environmental friendliness obtain higher yields of the products. Except for that,
(difficult catalyst reusability, excessive nucleophile the direct amination of alcohols catalyzed by ionic liq-
utilization, and disposal and neutralization of strong uids is still relatively rare. Therefore, it is significant
acidic catalysts).
and innovative to develop a metal-free, efficient and
To overcome the above defects, novel efficient and reusable ionic liquid catalyst system, which is applica-
environmentally-friendly acidic catalysts need to be ble to a wide scope of alkylating agents and nucleo-
developed for the direct amination of alcohols. Ionic phile classes for direct N-alkylation with alcohols.
liquids naturally come into view due to their excellent
An alkanesulfonic acid group-functionalized ionic
properties, such as very low or practically no vapor liquid, which was recently developed with the com-
pressure and remarkable solubility behavior, as well bined advantages of liquid acids and solid acids, for
as designability by varying their structure to manipu- example, uniform acid sites, stability in water and air,
late parameters like density, solubility etc. and to easy separation and reusability,[25] seems to be an
achieve a specific purpose.[21,22] Recently, Zhu and co- ideal option. In our continuing effort for developing
workers developed the zinc-based ionic liquid acidic ionic liquid-catalyzed reactions,[26] a series of
([CHCl][ZnCl2]2) bearing dual roles as an efficient SO3H-functionalized ionic liquids derived from pyri-
Adv. Synth. Catal. 2012, 354, 1052 – 1060
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FULL PAPERS
Table 1. Screening the activities of SO3H-functionalized
dine, phosphonium, guanidine, imidazole, pyrrolidine
and morpholine (Scheme 2) was synthesized and ap-
plied to the direct amination of alcohols as metal-
free, recyclable, selective and efficient catalysts. To
our delight, the catalytic system has wide substrate
scope including benzylic, allyl, propargylic, aliphatic
alcohols with sulfonamide, amide, carbamate, aromat-
ic amine and N-heterocyclic compounds with moder-
ate to quantitative isolated yields. Moreover,
ionic liquids.[a]
[BsTdIM]ACHTUNGTRENNUNG[OTf] exhibited the best activity and could
be reused at least six times without significant loss of
activity, which effectively avoided the disposal and
neutralization of the acidic catalysts after reaction.
Entry
Catalyst
Yield [%][b]
1
2
3
4
5
6
7
8
[TG][OTf]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
79
62
77
66
56
67
86
92
77
82
62
79
82
84
84
85
54
57
67
62
60
56
Results and Discussion
The exploratory experiments were started by screen-
ing the activities of SO3H-functionalized ionic liquids
with p-toluenesulfonamide and diphenylcarbinol as
the model substrates. Initially, a series of ILs based on
phosphonium, imidazolium, guanidinium and moÀr-
9
À
pholinium cations and BrÀ, BF4 , OTsÀ, CH3SO3 ,
10
11
12
13
14
15
16
17
18
19
20
21
22
À
HSO4 , camphorsulphonate anions was tested and no
reaction occurred (see the Supporting Information,
Table S1). Fortunately, the reaction could be success-
fully carried out using OTfÀ as the anion and pyridini-
um, phosphonium, guanidinium, imidazolium, pyrroli-
dinium and morpholinium as cations (Table 1). And
only trace of the unwanted by-product ether could be
found in some cases. Higher than 50% yields of the
desired product could be obtained when [TG][OTf],
[LPS][OTf], [LBPS][OTf] and [PyS][OTf] were used
as the catalyst (entries 1–4). Subsequently, the results
indicated that the length of the side chain of the imi-
dazolium and pyrrolidinium cations has a great effect
on the yield (entries 5–16). The yield increased sharp-
ly with the carbon number of the side chain increasing
from one to fourteen and dramatically decreased or
kept the same when further increasing the carbon
number. And 92% yield could be obtained by em-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
G
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
[a]
Reaction conditions: p-toluenesulfonamide: 0.75 mmol,
diphenylcarbinol: 0.5 mmol, catalyst: 20 mol% (referred
to diphenylcarbinol), reaction temperature: 808C, sol-
vent: 1,4-dioxane, 2 mL, reaction time: 3 h.
Isolated yield.
[b]
ploying [BsTdIM][OTf] as the catalyst. However, the ble spectroscopy with 2-nitroanline as the indicator in
length of the side chain seems to have little influence dichloromethane[27] (see the Supporting Information,
on the yield for ionic liquids derived from morpholine Figure S1 and Table S4). Interestingly, it was found
(entries 17 and 18). Besides, the activities of SO3H- that the acidities of the SO3H-functionalized ionic liq-
functionalized imidazole, pyrrolidine and morpholine- uids decreased along with the increase of the carbon
based dicationic ionic liquids were also investigated atom number in the side chain of the imidazole ring
and only moderate yields could be obtained. Addi- of the ionic liquids, while on the contrary, the catalyst
tionally, a control experiment was performed to com- activities increased until a maximum was reached.
pare the catalytic activities between TfOH (trifluoro-
Subsequently, the effects of various reaction param-
methanesulfonic acid) and SO3H-functionalized ionic eters were examined. Preliminary results indicated
liquids. Otherwise, only 56% yield could be obtained that the solvent had a certain impact on the reaction
using TfOH as the catalyst (entry 22), and 42% of (see the Supporting Information, Table S2). Either
bis(diphenylmethyl) ether as an unwanted by-product polar or non-polar solvents showed almost equal good
could be isolated. The acidities of above imidazole- performances and several solvents such as dimethyl
based SO3H-functionalized ionic liquids were evaluat- sulfoxide, dimethylformamide and PEG-400 exhibited
ed from the Hammett acidity function using UV-visi- poor activity, especially no amination product was ob-
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Sulfonic Acid-Functionalized Ionic Liquids as Metal-Free, Efficient and Reusable Catalysts
Table 2. Dependence of the yield on catalyst loading and re-
Table 3. (Continued)
action temperature.[a]
Entry Alcohol
Product
Yield
[%][b]
Entry Catalyst [mol%] Temperature [oC] Yield [%][b]
1
2
3
4
5
6
7
8
20
20
20
20
1
2.5
5
7.5
10
20
30
40
60
100
120
80
80
80
80
80
80
80
31
73
93
95
trace
33
60
82
90
6
7
71
87
9
10
11
92
93
8[c]
19
[a]
Reaction conditions: p-toluenesulfonamide: 0.75 mmol,
diphenylcarbinol: 0.5 mmol, solvent: 1,4-dioxane, 2 mL,
reaction time: 3 h.
[b]
Isolated yield.
9[c]
24
49
65
tained employing PEG-400 as the solvent probably
because of the existence of the hydroxy group inhibit-
ing the reaction. Additionally, control experiments
were carried out to test the influence of the reaction
temperature and the results are summarized in
Table 2. It was apparent that the yield remarkably in-
creased when the temperature increased from 408C
to 808C (entries 1, 2 and 10) and there was no signifi-
cant change when further increasing the temperature
(entries 3 and 4). Besides, the dependence of the yield
on catalyst loading was also examined. Unfortunately,
10[c]
11[c]
12[d]
75
[a]
Reaction conditions: p-toluenesulfonamide: 0.75 mmol,
alcohol: 0.5 mmol, catalyst: [BsTdIM][OTf], 10 mol%
(referred to alcohol), reaction temperature: 808C, sol-
vent: 1,4-dioxane, 2 mL, reaction time: 3 h.
Isolated yield.
Table 3. Catalytic N-alkylation of p-toluenesulfonamide and
4-nitroaniline with different alcohols.[a]
[b]
[c]
Entry Alcohol
Product
Yield
[%][b]
4-Nitroaniline as
N source, [TG][OTf] as catalyst,
10 mol%; reaction temperature: 1408C, reaction time:
24 h.
[d]
4-Nitroaniline as N source, [BsTdIM][OTf] as catalyst,
10 mol%; reaction temperature: 1208C, reaction time:
12 h.
1
2
90
89
only traces of product could be acquired with 1 mol%
catalyst loading (entry 5). It could easily be seen that
catalyst loading also had a great influence on yield
with variation of loading from 2.5 to 10 mol% (en-
tries 6–9); whereas the yield slightly changed with cat-
alyst loadings in the range of 10–30 mol% (entries 9–
11). As a whole, the optimized reaction conditions
3
84
were 10 mol% [BsTdIM]
and 2 mL of 1,4-dioxane.
ACHTUNGERTN[NUNG OTf] as the catalyst, 808C
4
5
65
87
To examine the utility and generality of the catalyst
system for the direct amination, the scope of the reac-
tion with respect to alcohols including benzylic, allyl,
propargylic and aliphatic alcohols, and tertiary alco-
hols was first investigated and the results are listed in
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Table 4. Catalytic N-alkylation of diphenylcarbinol (a) or
(E)-1,3-diphenylprop-2-en-1-ol (e) with different N sour-
Table 4. (Continued)
Entry N Source
R3OH Time
[h]
Product/Yield
[%][b]
ACHTUNGTRENNUNG
ces.[a]
Entry N Source
R3OH Time
[h]
Product/Yield
[%][b]
28
a
a
3
3
20a/87
21a/89
1
2
a
e
3
3
1a/90
1e/87
29
[a]
Reaction conditions: N source: 0.75 mmol, diphenylcarbi-
nol or (E)-1,3-diphenylprop-2-en-1-ol: 0.5 mmol, catalyst:
[BsTdIM][OTf], 10 mol% (referred to alcohol), reaction
temperature: 808C, solvent: 1, 4-dioxane, 2 mL.
Isolated yield.
Reaction temperature: 1208C, reaction time: 24 h.
a-Phenylethanol (k) as alcohol, reaction temperature:
1208C, reaction time: 24 h.
3
a
3
2a/85
4
5
a
e
3
3
3a/83
3e 93
[b]
[c]
[d]
6[c]
7
a
e
24
2
4a/76
4e/99
[e]
Room temperature.
8
e
3
5e/89
Table 3. Obviously, the electronic properties of the
substituent group had no significant influence on the
activities of diphenylcarbinol derivatives (entries 1–3).
However, the yield sharply decreased due to the
steric hindrance when employing (2-chlorophenyl)-
9
a
e
k
3
3
24
6a/81
6e/79
6k/63
10
11[d]
12[c]
13
e
a
3
3
7e/81
8a/89
AHCTUNGTREG(NNUN phenyl)methanol as the substrate (entry 4). Besides,
allyl or propargylic alcohols also showed good activi-
ties with 71–87% yields (entries 5–7). Interestingly,
aliphatic alcohols usually exhibiting poor activities
still reacted smoothly with 4-nitroaniline when using
[TG]ACTHNUTRGENU[GN OTf] as the catalyst and enhancing the tempera-
ture to 1408C (entries 8–10). And a-phenylethanol
also showed moderate activity with 4-nitroaniline as
the N source (entry 11). However, the desired prod-
ucts cannot be obtained when using tertiary alcohols
as the substrates (see the Supporting Information,
Table S3). To our delight, benzylic primary alcohols
with donating groups could make the reaction occur
well, wherein 4-nitroaniline serves as the N source
(entry 12).
Next, a series of N sources including sulfonamide,
amide, carbamate, aromatic amines and various N-
heterocyclic compounds was investigated with diphe-
nylcarbinol or (E)-1,3-diphenylprop-2-en-1-ol as the
alkylating reagent. The reactions of sulfonamide com-
pounds with diphenylcarbinol or (E)-1,3-diphenyl-
prop-2-en-1-ol proceeded smoothly with above 80%
yields within 3 h (Table 4, entries 1–5, 7 and 8). And
the yield of the reaction of methanesulfonamide and
diphenylcarbinol could reach up to 76% after pro-
longing the reaction time to 24 h (entry 6). As for an
amide as the N sources for the reaction, aliphatic
amides could be completely transformed (entries 14–
16) and aromatic amides exhibited slightly poorer ac-
tivities (entries 9, 10, 12, 13). Additionally, cyclic
amides also showed good activities and nearly quanti-
tative yields could be obtained using pyrrolidin-2-one
14
15
16
e
e
e
3
3
3
9e/98
10e/99
11e/95
17
18
e
e
1.5
3
12e/98
13e/71
19
20
a
e
3
3
14a/86
14e/85
21
e
3
15e/93
22
23
a
e
3
0.3
16a/75
16e/98
24
25
e
e
3
1
17e/90
18e/99
26
a
e
3
0.25
19a/96
19e/93
27[e]
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Sulfonic Acid-Functionalized Ionic Liquids as Metal-Free, Efficient and Reusable Catalysts
Scheme 3. [TG]ACHTUNTRGNEUNG[OTf]-catalyzed direct amination of k.
Figure 1. X-ray structure of 2-benzhydryl-5-phenyl-2H-tetra-
zole 19a (hydrogen atoms are omitted for clarity, crystal
data see the Supporting Information, 3).
that the nucleophilic attack was achieved through an
SN1 pathway and not an SN2 pathway.
Another practical feature of the designed catalyst
system is the facile separation of the product and the
as the substrate within 1.5 h (entry 17). However, ex- recyclability of the catalyst. To test the catalyst reusa-
tending the cycle of the cyclic amide would decrease bility, the reaction was carried out in the presence of
the yield even after prolonging the reaction time to a catalytic amount of [BsTdIM][OTf] under the opti-
3 h (entry 18). Besides, 75–98% yields are achieved mal reaction conditions with p-toluenesulfonamide
for the amination of diphenylcarbinol or (E)-1,3-di- and diphenylcarbinol as the substrates. After each
phenylprop-2-en-1-ol with carbamate (entries 19–23). cycle, the catalyst and the product were separated in
There is nearly no difference in activities using either deionized water and the crude product was washed
diphenylcarbinol or (E)-1,3-diphenylprop-2-en-1-ol as three times with deionized water. Then the water
the alkylating agent with ethyl carbamate as the N layer containing the catalyst was concentrated and
source (entries 19 and 20). However, significant differ- dried under reduced pressure at 808C for 24 h in
ences existed on employing oxazolidin-2-one as the N order to be reused directly. The results shown in
source and quantitative yields could be afforded Figure 2 indicated that the isolated yield of the prod-
within 0.3 h (entries 22 vs. 23). On the other hand, the uct 1a was almost consistent after six runs and
amination of diphenylcarbinol or (E)-1,3-diphenyl- [BsTdIM][OTf] could be reused at least six times
prop-2-en-1-ol with azole compounds was also suc- without significant loss of the activities. Likewise,
cessfully with >90% yields (entries 24–27). Surpris- good catalyst reusability could also be achieved with
ingly, a 93% yield could be attained for the reaction benzamide and diphenylcarbinol, p-toluenesulfon-
of 5-phenyltetrazole and (E)-1,3-diphenylprop-2-en-1-
ol even at room temperature for 0.25 h (entry 27).
And the structure of the corresponding product 19a
has been elucidated by X-ray and is described in
Figure 1, which indicates that the alkylation takes
place at the N-2 position of tetrazole.[28] Finally, the
activities of aromatic amines were also tested and
about 90% yields could be obtained (entries 28 and
29).
In addition to an evaluation of the scope and limi-
tations of the SO3H-functionalized ionic liquid-cata-
lyzed direct amination, some preliminary mechanistic
investigations were performed. Optically active alco-
hol k with >99% ee was treated with 20 under the
specified reaction conditions and racemic product 20k
was observed as anticipated (Scheme 3). Although the
exact reaction mechanism is not quite clear at the
moment, the amination under our catalytic system
seems to proceed by a carbocation intermediate,
which was attacked by the nucleophile (N source).
The above chirality-transfer experiment supported tion of p-toluenesulfonamide and diphenylcarbinol.
Figure 2. Recyclability of [BsTdIM]ACTHNUTRGNEUNG[OTf] in direct amina-
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Feng Han et al.
FULL PAPERS
erenced to CHCl3 (d=7.26) or D2O (d=4.88). GC-MS anal-
yses were performed using an Agilent 6850 system (FID).
Silica gel (200–300 microns) was used for all chromato-
graphic separations. High resolution mass spectra (HR-MS)
were recorded on a Bruker MicroTOF-QII mass instrument
(ESI). Anhydrous organic solvents were dried and stored
under nitrogen. All other chemicals used for synthetic pro-
cedures were reagent grade or better. Solutions were con-
centrated under vacuum with a rotary evaporator and the
residue was purified using a silica gel column unless speci-
fied otherwise. All reactions were monitored by TLC with
silica gel-coated plates and detection was conducted by UV
absorption (254 nm). And the synthetic procedure for
SO3H-functionalized ionic liquid was in accordance with the
references.[26b,29]
Scheme 4. Large-scale direct amination of diphenylcarbinol.
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Supporting Information, Figure S2, Figure S3, and
Figure S4.)
From the standpoint of practical applications,
a large-scale direct amination of alcohols would be
significant. As shown in Scheme 4, the present proto-
col could be carried out on a multigram scale. N-
Procedure for 3-Tetradecyl-1-(butyl-4-sulfonyl)-
imidazolium Trifluoromethanesulfonate
([BsTdIM][OTf])
1-Tetradecylimidazole (5.28 g, 0.020 mol) and 1,4-butanesul-
tone (2.25 mL, 0.022 mol) were charged into a 100-mL
round-bottom flask. Then the mixture was stirred at 408C
for 10 h. After washing the salt with ether and toluene to
remove any unreacted starting materials, the solid was dried
under vacuum. Then, a stoichiometric amount of trifluoro-
methanesulfonic acid (1.80 mL, 0.020 mol) was added drop-
wise and the mixture stirred for 12 h at 808C, resulting in
the formation of 3-tetradecyl-1-(butyl-4-sulfonyl)imidazoli-
um trifluoromethanesulfonate ([BsTdIM][OTf]). The ionic
liquid phase was then washed repeatedly with toluene and
ether to remove non-ionic residues, and dried under vacuo.
The product [yield: 10.8 g (98%)] was formed quantitatively
and in high purity as assessed by NMR, IR and mass spec-
Benzhydryl-4-methylbenzenesulfonamide
(2.54 g,
75%) could be obtained just by filtration and recrys-
tallization. And the by-product ether (0.25 g, 7%) was
isolated from the filtrate.
Conclusions
In summary, a series of SO3H-functionalized ionic liq-
uids derived from pyridine, phosphonium, guanidine,
imidazole, pyrrolidine and morpholine was synthe-
sized and applied to the direct amination of alcohols
without adding any additives. Notably, [BsTdIM]
[OTf] exhibited the best activity and this catalytic
system has a wide substrate scope including benzylic,
allyl, propargylic, aliphatic alcohols with sulfonamide,
amide, carbamate, aromatic amine and various N-het-
erocyclic compounds with moderate to quantitative
isolated yields. Interestingly, the system was also suit-
able for the multigram scale direct amination of alco-
hols. Moreover, preliminary experiments indicated
that the reaction should proceed by an SN1 pathway.
Studies on the developmont of the new catalytic
system for this reaction and applying the catalytic
system for new reactions are in progress in our labo-
ratory.
1
troscopy. H NMR (400 MHz, D2O): d=0.68 (t, J=6.4 Hz,
3H), 1.09–1.15 (m, 22H), 1.59–1.69 (m, 4H), 1.83–1.91 (m,
2H), 2.75 (t, J=7.6 Hz, 2H), 4.04 (t, J=7.6 Hz, 2H), 4.12 (t,
J=7.6 Hz, 2H), 7.37 (s, 1H), 7.47 (s, 1H), 8.78 (s, 1H);
13C NMR (100 MHz, D2O): d=13.7, 21.2, 22.6, 26.2, 28.5,
29.2, 29.5, 29.6, 29.8, 29.9, 30.0, 32.0, 49.0, 49.5, 50.1, 118.2,
121.4, 122.2, 122.6, 135.4; IR: n=3159, 3122, 3095, 2900,
2853, 1573, 1468, 1295, 1246, 1245, 1166, 1120, 1032, 915,
863, 776, 724, 639, 517 cmÀ1; MS (ESI): [m/z]+ =400.8,
AHCTUNGTRENNUNG
[m/z]À =148.9.
Typical Procedure for Direct Amination of Alcohols
and Reuse of [BsTdIM][OTf]
AHCTUNGTERGUN[NN BsTdIM][OTf] (27.5 mg, 10 mol%), alcohol a (92 mg,
0.5 mmol), p-toluenesulfonamide 1 (128.3 mg, 0.75 mmol),
and dry 1,4-dioxane (2.0 mL) were added into the screw-cap
vial. Then the mixture was stirred continuously at 808C for
3 h and monitored by TLC. At the end of the reaction,
10 mL of deionized water were added into the reaction mix-
ture. When the mixture was cooled to room temperature,
the crude product was isolated though simple filtration and
the pure product – N-benzhydryl-4-methylbenzenesulfon-
Experimental Section
General
AHCTUNGTREGaNNUN mide (1a) – was obtained by recrystallization or flash
NMR spectra were recorded on Bruker DRX 400 spectrom-
column chromatography on silica gel as a white solid; yield:
92%; mp 159–1608C. IR: n=3248, 1560, 1495, 1452, 1316,
1161, 1092, 1057, 1028, 940, 812, 748, 702, 676, 571, 548,
1
eters. H NMR (400 MHz) and 13C NMR (100 MHz) spectra
were obtained as solutions in either CDCl3 or D2O. Chemi-
cal shifts are reported in parts per million (ppm, d) and ref-
1
491 cmÀ1; H NMR (400 MHz, CDCl3): d=2.37 (s, 3H), 5.15
1058
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Adv. Synth. Catal. 2012, 354, 1052 – 1060

Sulfonic Acid-Functionalized Ionic Liquids as Metal-Free, Efficient and Reusable Catalysts
(d, J=6.8 Hz, 1H), 5.56 (d, J=6.8 Hz, 1H), 7.09–7.21 (m,
12H), 7.56 (d, J=8.0 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d=21.5, 61.4, 127.2, 127.4, 127.6, 128.5, 129.4, 137.3, 140.5,
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The ionic liquid ([BsTdIM][OTf]) obtained by drying the
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Procedure for Large-Scale Direct Amination of
Diphenylcarbinol
ACHTUNGTRENNUNG[BsTdIM]OTf (0.55 g, 10 mol%), diphenylcarbinol (1.84 g,
10 mmol), p-toluenesulfonamide (2.56 g, 15 mmol), and dry
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We are grateful to the National Science Foundation of China
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