K.K. Laali, V.J. Gettwert / Journal of Fluorine Chemistry 107 (2001) 31±34
33
Table 2
One-pot diazotization/fluorodediazoniation
a
a
Ionic liquid
NOX (X)
PF
RarNH
2
(R)
RArN X yield (%)
2
Temperature (8C)
RArF yield (%)
[
bmim][PF
6
]
6
H
H
100
100
100
96
100
70
100
100
100
b
BF
BF
4
[
emim][BF
4
]
4
2,4,6-(Me)
3
a
Determined by 1H NMR.
b
Counterion exchange with ionic liquid.
�
tion of ArN2 BF4 salts in [emim][CF CO ], [emim][OTs]
3
corresponding ¯uoaromatic and some NEtiPr whereas the
2
2
and [emim][OTf] ionic liquids offered the opportunity to see
if these novel, highly ionizing, polar media could encourage
the formation of a solvent separated ion-pair, whereby the
Schiemann reaction would compete with nucleophile
quenching by the ionic liquid counter-ion. NMR monitoring
ionic liquid phase contained the [HNEtiPr ][BF ] salt.
4
2
3.1.2. Typical run for [bmim][PF6]
The procedure was similar to 3.1.1. In this case, counter-
ion exchange occurs to give [bmim][BF ], but this does not
4
(
proton chemical shifts of the imidazolium core are counter-
create any limitation. The resulting [emim][PF /BF ] is
4
6
ion dependent) showed, however, that on mixing metathesis
occurs; subsequent dediazoniation produces the esters
slowly transformed into [emim][BF ] after several ¯uoro-
4
dediazoniation reactions.
(
nucleophile quenching products) (see Table 1).
Other aspects of ArN2 chemistry in ionic liquid solvents
are under investigation in our laboratory.
3.1.3. Reaction in [emim][X] other than X BF and PF
4
6
The ionic liquid (3.0 mmol) was charged into a Schlenk
tube. The diazonium salt (0.5 mmol) was added and stirred.
In most cases the salt dissolves in the ionic liquid in which
1
3
. Experimental section
case counterion exchange could be determined by H NMR.
The mixture was subsequently heated until gas evolution
was observed. It was kept at this temperature for 1±3 h until
The [emim][X] ionic liquids (X BF , OTf), NOBF and
4
4
1
NOPF were high purity commercial samples (Aldrich)
6
dediazoniation was complete ( H NMR).
which were used as received. Diazonium salts were prepared
by conventional diazotization (NaNO /HBF ) and precipi-
tation from MeCN/ether [23±25]. The [emim][CF COO]
3.1.4. Product characterization and yield determination
Product characterization was based on NMR (and GC). In
cases where the H uÈ nig base was not used (see Table),
isolated yields were determined after ether extraction and
following the removal of solvent. The NMR yields refer to
direct analysis of the reaction mixtures without work-up,
showing complete disappearance of the diazonium salt and
presence of only the resonances belonging to the ¯uoroarene
product and the ionic liquid solvent. In cases where authen-
tic ¯uoroarenes were available, the identity of the products
were further con®rmed via GC analysis.
2
4
3
and [emim][OTs] were prepared from [emim][Cl] by reac-
tion with sodium tri¯uoroacetate and silver tosylate, respec-
tively, whereas [bmim][CF COO] was synthesized via
3
[bmim][Cl] and NaCF CO2 [26]. Ether was dried over
3
sodium whereas other solvents were used without puri®ca-
tion. All reactions were carried out in Schlenk tubes.
1
H NMR spectra were recorded in [D ]acetone and
6
[D ]chloroform at room temperature using a Bruker
3
AMX 300 instrument.
GC analysis were performed with an HP-5890 capillary
GC instrument.
3.2. One-pot diazotization/fluorodediazoniation
3
3
.1. Fluorodediazoniation
Nitrosonium salt (NOPF6 or NOBF ; 0.6 mmol) was
4
added to [emim][PF ] or [emim][BF ] (5.0 mmol) and the
6
4
.1.1. Typical run for [emim][BF4]
The [emim][BF ] (990 mg, 5.0 mmol) was charged into a
solution was cooled to 08C in an ice bath. The aniline
(0.6 mmol) was added slowly and the mixture stirred for
30 min at 08C (viscous ionic liquid) and for 12 h at RT. The
4
Schlenk tube and diazonium salt (0.5 mmol) was directly
added and the mixture stirred. In most cases, the salt is
soluble in the ionic liquid. The mixture was heated until gas
evolution was observed. Heating was continued for 1±3 h
until dediazoniation was complete (assayed by H NMR),
after which one equivalent of the H uÈ nig base (0.5 mmol
1
progress of diazotization was monitored by H NMR. Once
complete, the reaction mixture (solution or suspension) was
heated until gas evolution was observed. It was kept at this
temperature for 1±3 h until the dediazoniation was complete
1
1
( H NMR), after which one equivalent of the H uÈ nig
base (0.6 mmol NEtiPr ) was added and the solution
was extracted with ether. The ether phase contained the
NEtiPr ) was added and the solution was extracted with
2
2
ether. Based on NMR analysis, the ether phase contained the