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products can also be extracted with a solvent (e.g. cyclohexane,
hexane, petroleum ether, or toluene), or by azeotropic separation of
the products with steam (steam stripping). The hydrogen chloride
by-product formed in the reaction was lost through the top of the
condenser.
Table 2 The acylations of various aromatic compounds in [bmim][NTf
2
]
(1.0 g) after 18 h, unless otherwise stated
Aromatic (7.5 Acylating agent
mmol)
(5 mmol)
Catalyst
Temp/°C Yield (%)
To determine the relative effectiveness of various metal
bistriflamide catalysts, the reaction of benzoyl chloride with
toluene was chosen as a model. The bistriflamide salts of
magnesium(II), calcium(II), strontium(II), barium(II), tin(II), lead(II),
55a
Ph–Cl
Ph–Cl
Ph–Cl
Ph–F
PhCOCl
PhCOCl
PhCOCl
4-FPhCOCl
PhCOCl
PhCOCl
5% Zn(NTf
5% Co(NTf
2
)
2
2
130
130
130
160
110
110
140
140
60
a
)
2
95
87abc
15% InCl3
bd
e
5% ZnCl
2
2
98
b
manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) were
Anisole
10% ZnCl
80
99
g
prepared12 and 1 mol% of each of these materials were heated with
PhCH
3
1% SnCl
10% Zn(NTf
4
m-Xylene
m-Xylene
Anisole
Anisole
a
PhCO
PhCO
2
H
H
2
)
)
2
2
40f
82f
88
91
c
reactants for up to five days in the absence of solvent. The ionic
liquid [bmim][NTf ] (1 mol%), HNTf (1 mol%) and lithium
2 2
2
10% Co(NTf
5% In(OTf)
5% Hf(OTf)
2
(PhCO)
(PhCO)
2
O
O
3
bistriflamide (1 mol%) were used as controls. All the reactions were
monitored by GC, and some of the results are shown in Table 1. The
reactions were also carried out successfully with a number of
metal(III) and metal(IV) bistriflamide salts, such as those of
aluminium(III), chromium(III), iron(III), indium(III), ytterbium(III),
and cerium(IV), but these materials are poorly characterised, and
their composition is not necessarily as claimed (see for example
2
4
60
p- : o-isomer ratio = 9 : 1. b [emim][NTf
] ionic liquid used. Reaction
2
time 96 h. d Reaction carried out in an autoclave. p- : o- : m-isomer ratio
e
75 : 15 : 8. Reaction carried out for 48 h. g 97% yield after 2 h.
f
=
much lower reaction temperatures (140 °C compared with 250
C). This has the advantage that water is the only by-product, but
14
°
11
ref. ).
The rates of the acylation reactions varied considerably,
longer reaction times are needed.
We are indebted to QUILL (MJE), Cytec (AR), Marie Curie
UH), the EPSRC (BJMcA) and to LINK for financial support, and
depending on which metal bistriflamide was used. Surprisingly,
metals that are not conventionally thought of as being Friedel–
Crafts catalysts gave the best results. This is particularly the case
(
to Dr. Jillian M. Thompson for preliminary studies.
for M(NTf
2 2
) (M = Mn, Co, Ni, or Pb), which for the reactions of
Notes and references
acyl chlorides, give results significantly better than either lanthani-
‡
Data were collected with a Bruker-AXS SMART diffractometer using
de(III) bistriflamides1
cobalt(II) or nickel(II) bistriflamide, was performed in 1-ethyl-
-methylimidazolium bistriflamide [emim][NTf ], the reaction
0,13
or triflates. When this acylation, with a
15a
the SAINT-NT
a
software with graphite monochromated Mo–K radia-
tion. A crystal was mounted onto the diffractometer at low temperature
under nitrogen at ca. 120 K. The structure was solved using direct methods
and refined with the SHELXTL version 5 and the non-hydrogen atoms
were refined with anisotropic thermal parameters. Hydrogen-atom positions
were added at idealised positions with a riding model and fixed thermal
parameters (Uij = 1.2Ueq for the atom to which they are bonded). The
3
2
time was reduced to 0.5 and 1 h, respectively, and the catalyst–ionic
liquid combination could be recycled (95% yield on third recycle).
Without the ionic liquid present, the catalyst gave successively
15b
nd
rd
poorer yields when reused (48% on 2 and 21% on 3 recycle for
Co(NTf . This activity was restored on addition of HNTf . It is
interesting to note that HNTf is a good acylation catalyst in its own
2
2
21
function minimised was S[w(|F
o
| 2 |F
c
| )] with reflection weights w
=
2
)
2
2
2
2
2
2
2
[
s |F
o
| + (g
1
P) + (g
2
P)] where P = [max |F | + 2|F | ]/3. Additional
o c
2
material available from the Cambridge Crystallographic Data Centre
comprises relevant tables of atomic coordinates, bond lengths and angles,
and thermal parameters.
right, and addition of this as a co-catalyst has been observed to
increase the reaction rate. The isolation of the metal bistriflamide
catalyst is not always necessary: the catalyst can be generated in
situ by the addition of a metal compound (e.g. ZnCl
bistriflamide such as the ionic liquid [bmim][NTf ], thus simplify-
ing the experimental procedure (see Table 2). The acylation of
chlorobenzene (Table 2) proceeds efficiently with cobalt(II
bistriflamide or indium(III) chloride in a bistriflamide ionic liquid.
Other catalysts were found to be less effective. The acylation of
fluorobenzene with 4-fluorobenzoyl chloride was carried out at 5
4 12 2 8 4 r
Crystal data for C F N O S Zn: M = 625.67, monoclinic, space group
2
) to a source of
P2
1
/n, a = 11.566(6), b = 5.160(2), c = 14.179(7) Å, b = 100.753(10) °,
U = 831.1(7) Å23, Z = 2, m = 2.154 mm21, Rint = 0.0904, transmission
2
range (max, min) = 0.928, 0.588. A total of 3810 reflections were measured
for the angle range 4 < 2q < 50 and 1439 independent reflections were
used in the refinement. The final parameters were wR2 = 0.1892 and R1 =
)
0
b403650f/ for crystallographic data in .cif or other electronic format.
1
2
R. Taylor, Electrophilic Aromatic Substitution, Wiley, Chichester,
990.
C. J. Adams, M. J. Earle, G. Roberts and K. R. Seddon, Chem.
Commun., 1998, 2097.
bar, and gave primarily 4,4A-difluorobenzophenone using zinc(II
chloride dissolved in [bmim][NTf ]. The metal chloride dissolved
)
1
2
in a bistriflamide ionic liquid was found to give similar yields
compared with isolated metal bistriflamide catalysts. Metal bistri-
flamides also catalyse the acylation of aromatic compounds with
carboxylic acids and anhydrides. Zinc(II) and cobalt(II) bistri-
flamide gave similar yields to lanthanide(III) bistriflamides, but at
3
4
J. Matauo, K. Odashima and S. Kobayashi, Synlett., 2000, 403.
Ionic Liquids in Synthesis, ed. P. Wasserscheid and T. Welton, Wiley-
VCH, Weinheim, 2003.
5 J. T. Welch, World Patent WO 9940124, 1999.
6
7
P. A. Grieco and S. T. Handy, Tetrahedron Lett., 1997, 38, 2645.
K. Ishihara, Y. Karumi, M. Kubota and H. Yamamoto, Synlett., 1996,
Table 1 The variation of yield with time for the reaction of benzoyl chloride
(5 mmol) with toluene (7.5 mmol) at 110 °C with no solvent
8
39.
8
9
K. Mikami, O. Kotera, Y. Motoyama, H. Sakaguchi and M. Maruta,
Synlett., 1996, 171.
J. Nishikido, H. Nakajima, T. Saeki, A. Ishii and K. Mikami, Synlett.,
Catalyst (1.0 mol%)
Time/h
Yield (%)
LiNTf
Mg(NTf
2 2
Ca(NTf )
2
120
48
120
120
120
5
< 5
99
< 5
31
65
99
99
99
99
99
91
95
0
1
998, 1347.
2 2
)
1
1
1
1
1
1
0 F. Duris, D. Barbier-Baudry, A. Dormond, J. R. Desmurs and J. M.
Bernard, J. Mol. Catal. A, 2002, 188, 97.
1 C. G. Frost, J. P. Hartley and D. Griffin, Tetrahedron Lett., 2002, 43,
2 2
Sr(NTf )
Ba(NTf )
2 2
4
789.
2 2
Mn(NTf )
2 M. J. Earle, B. J. McAuley, A. Ramani, J. M. Thompson and K. R.
Seddon, World Patent, WO02072519, 2002.
3 M. J. Earle, B. J. McAuley, A. Ramani, J. M. Thompson and K. R.
Seddon, World Patent, WO02072260, 2002.
4 M. Kawamura, D.-M. Cui, T. Hayashi and S. Shimada, Tetrahedron
Lett., 2003, 44, 7715.
5 (a) SAINT-NT, program for data collection and data reduction, Bruker-
AXS, Madison, WI, 1998; (b) G. M. Sheldrick, SHELXTL Version 5.0,
A System for Structure Solution and Refinement, Bruker-AXS, Madison,
WI, 1998.
Co(NTf )
2 2
3
4
Ni(NTf
Cu(NTf
2
)
2
2
)
2
72
48
48
6
120
48
2
2 2
Zn(NTf )
Sn(NTf
Pb(NTf
2
)
)
2
2
2
[
bmim][NTf
HNTf
2 2 2
Co(NTf ) –HNTf
2
]
2
97
97
C h e m . C o m m u n . , 2 0 0 4 , 1 3 6 8 – 1 3 6 9
1369