G. A. Echeverría et al. · Ammonium Acesulfamate
739
Table 2. Assignment of the FTIR spectrum of ammonium
acesulfamate .
The weak and very weak bands found at 2100, 2025
and 1935 cm could not be assigned with certainty.
Thus, they probably originate also from combination
or overtone modes.
a
−1
Band position (cm 1)
−
Proposed assignment
3
2
2
1
1
1
1
1
1
1
1
1
9
8
8
7
6
5
5
242 vs, 3062 s, br
ν3(NH4+
)
+
849 w
2ν4(NH4 )
100 vw, 2025 w, 1935 w
see text
765 sh
ν4 +ν6( NH4+
)
Experimental Section
660 vs, 1590 sh/1569 vs
ν(C=O)+ν(C−C)ring
459 m, 1431 w
393 vs
370 s
288 vs
171 vs/1158 sh
080 s
021 s
46 vs
61 s
21 s
δ(CH3)+ν4( NH4+
δ(CH3)
)
Materials and measurements
ν(NC)+ν(OC)+δ(CCH)
νas(SO2)
νs(SO2)+ν(SN)
δ(CH3)
Potassium acesulfamate was supplied by Fluka and am-
monium carbonate, along with the other employed reagents
were from Merck, analytical grade, and were used as pur-
chased. Elemental analysis of the compound was performed
with a Carlo Erba model EA 1108 elemental analyzer. The
infrared absorption spectra were recorded on a FTIR Bruker
EQUINOX-55 spectrophotometer in the spectral range be-
ν(OC)+ν(SN)
ν(OC)+ν(C−CH3)
τ(ring)
ν(SN)+ν(C−C)+δ(NCO)
34 vs
55 vs
63 m
τ(ring)
−
1
tween 4000 and 400 cm , using the KBr pellet technique.
δ(ring)
NMR spectra were recorded in D O using a Bruker Avance
δ(SO2)+δ(ring)
δ(ring)
2
47 m, 521 m, 434 m
300 instrument. Chemical shifts are reported in ppm down-
1
field from tetramethylsilane. H NMR spectra were recorded
a
vs, very strong; s, strong; m, medium; w, weak; vw, very weak; br,
1
3
at 300 MHz and C NMR spectra at 75 MHz.
broad; sh, shoulder.
Synthesis of the compound
Acesulfamic acid was prepared as described by Velaga et
al. [22], as follows: To 5.00 g of potassium acesulfamate dis-
solved in a small portion of water (ca. 15 mL), 6 mL of con-
centrated HCl was added drop-wise. The generated acid was
extracted with 20 mL of ethyl acetate. After evaporation of
the solvent in air a colorless solid was deposited. It was re-
crystallized twice from ethyl acetate, generating a deposit of
needle-like colorless crystals, after slow evaporation of the
be assigned to the split anti-symmetric ν stretching
3
+
vibration of NH , although the symmetric mode,
4
ν1, is eventually also activated and overlapped by
the ν components. The antisymmetric deformational
3
mode of the cation, ν , is overlapped by other rela-
4
−1
tively strong bands in the region around 1400 cm
.
This band multiplet is somewhat more complex in the
present case than for the corresponding potassium salt.
Interestingly, no evidences are found for an activation
◦
solvent in air (m. p. 122 – 124 C).
For the synthesis of the ammonium salt, 0.33 g (2.0 mmol)
of the symmetric deformation, ν , although a weak of acesulfamic acid was dissolved in 15 mL of distilled wa-
2
−1
◦
shoulder seen at ca. 1690 cm , on the high energy ter and heated to 75 C. To this solution, 0.10 g (1.0 mmol) of
side of the strong 1660 cm band, may be eventually (NH4)2CO3 was slowly added, under constant stirring. After
−
1
related to this mode.
this addition, the solution was stirred for another 30 min at
the same temperature, and finally it was left to evaporate in
air. After a few days a colorless powder, highly soluble in
water, was collected and recrystallized from water (yield: ca.
The activation of some combination and overtone
modes is usually regarded as a proof that the NH4+
cation does not rotate freely in the crystal structure [20,
0.25 g). The purity of the salt was confirmed by elemental
2
1], as is the case in the compound investigated here.
analysis and NMR spectroscopy. – Analysis: C H N O S
4
8 2 4
One of the expected overtones is clearly seen as a weak
(
180.18): calcd. C 26.64, H 4.44, N 15.55; found C 26.58,
−1
band at 2849 cm , which can be assigned to 2ν .
4
1
H 4.50, N 15.50. – H NMR: δ (ppm) = 2.02 (s, 3H, CH ),
5
1
−
1
3
The very weak feature observed at 1765 cm may
be related to one of the expected combinations in-
13
.58 (s, 1H, =C–H). – C NMR: δ (ppm) = 18.96 (CH3),
00.98 (=C–H), 164.18 (>C=O), 172.22 (=C–Me). These
volving ν and an external (lattice) mode located at
4
data are practically identical to that measured for the potas-
sium salt and also to those reported for choline acesulf-
amate [17]. Single crystals adequate for X-ray diffraction
−1
about 360 cm (ν + ν in Waddington’s nomencla-
ture [20]). The other usually observed combination
4
6
−
1
mode (ν + ν ) is expected at around 3070 cm and studies were selected from the crystalline mass employing
2
4
is surely overlapped by the strong ν components.
a microscope.
3
Brought to you by | Purdue University Libraries
Authenticated
Download Date | 6/6/15 11:02 AM