Ionic liquid-based routes to conversion or reuse of recycled ammonium perchlorate

Article abstract of DOI:10.1002/chem.200901217

New, potentially green, and efficient synthetic routes for the remediation and/or re-use of perchloratebased energetic materials have been developed. Four simple organic imidazolium- and phosphonium-based Perchlorate salts/ionic liquids have been synthesi

Full text of DOI:10.1002/chem.200901217

FULL PAPER
DOI: 10.1002/chem.200901217
Ionic Liquid-Based Routes to Conversion or Reuse of Recycled Ammonium
Perchlorate
[
a, b]
[a]
[a]
[a, c]
David B. Cordes,
Marcin Smiglak, C. Corey Hines, Nicholas J. Bridges,
[e] [a, e]
[
a, d]
[a, e]
Meghna Dilip,
Geetha Srinivasan, Andreas Metlen,
and Robin D. Rogers*
Abstract: New, potentially green, and
efficient synthetic routes for the reme-
diation and/or re-use of perchlorate-
based energetic materials have been
developed. Four simple organic imida-
zolium- and phosphonium-based per-
chlorate salts/ionic liquids have been
synthesized by simple, inexpensive, and
nonhazardous methods, using ammoni-
um perchlorate as the perchlorate
source. By appropriate choice of the
cation, perchlorate can be incorporated
into an ionic liquid which serves as its
own electrolyte for the electrochemical
reduction of the perchlorate anion, al-
lowing for the regeneration of the chlo-
ride-based parent ionic liquid. The
electrochemical degradation of the haz-
ardous perchlorate ion and its conver-
sion to harmless chloride during elec-
Keywords: ammonium perchlorate ·
electrochemistry · energetic materi-
als · ionic liquids · remediation
35
trolysis was studied using IR and Cl
NMR spectroscopies.
Introduction
materials, and as such, interest in their synthesis has been
[3,4]
growing rapidly in recent years.
The reasons for this are
Many modern energetic materials, even though highly ad-
vanced, and understood in terms of their performance and
behavior, suffer from safety issues and environmental con-
manifold, but some of those most commonly expressed
relate to their advantageous properties such as greater den-
sity and low or negligible vapor pressure under common op-
erating conditions.
[1,2]
cerns.
Organic salts are potential replacement energetic
One of the most common oxidizers used, both in multi-
[5]
component energetic systems and in energetic salts, is the
perchlorate anion. Moreover, one of the recent approaches
to new liquid energetic salts has been to combine perchlo-
rate with nitrogen-rich heterocyclic cations such as triazoli-
[
a] Dr. D. B. Cordes, Dr. M. Smiglak, C. C. Hines, Dr. N. J. Bridges,
Dr. M. Dilip, Dr. A. Metlen, Prof. R. D. Rogers
Department of Chemistry and Center for Green Manufacturing
The University of Alabama
Box 870336, Tuscaloosa, AL 35467-0338 (USA)
Fax : (+1) 205-348-0823
[4]
um, tetrazolium, and more recently, bicyclic azolium salts.
Many of these salts use highly modified heterocyclic cations,
with amino, nitro, and azo substitution of the heterocyclic
ring that often results in the formation of products with
melting points <1008C, referred to as ionic liquids (ILs). By
utilizing a common feature of ILs, that is, their broad liq-
uidus ranges, many of the problems associated with energet-
ic materials may be overcome. Recent developments in en-
E-mail: RDRogers@bama.ua.edu
[
b] Dr. D. B. Cordes
Current address:
Department of Chemistry, Imperial College London
London SW7 2AZ (UK)
[
c] Dr. N. J. Bridges
Current address:
Savannah River National Laboratory
Mail Stop 20, Aiken, SC 29808 (USA)
[3c,6]
ergetic ionic liquids (EILs) research have been reviewed
and the initial results for many of these salts are promising
as energetic materials.
[
d] Dr. M. Dilip
Current address:
Worcester State College, 486 Chandler St.
Worcester MA 01602 (USA)
A number of simpler heterocyclic perchlorate salts have
[7]
also been prepared previously, with imidazolium, 1-meth-
[8]
[9]
ylimidazolium, 1-butyl-3-methylimidazolium, 1,3-dibutyl-
[
e] Dr. G. Srinivasan, Dr. A. Metlen, Prof. R. D. Rogers
The QUILL Research Centre, School of Chemistry
The Queenꢀs University of Belfast
Belfast BT9 5AG (UK)
Fax : (+44) 28-9097-4606
[10]
[11]
imidazolium, and 1-hexyl-3-methylimidazolium cations.
The two predominant routes to such perchlorate-containing
materials have been either through the protonation of a ring
nitrogen using perchloric acid, resulting in the formation of
Chem. Eur. J. 2009, 15, 13441 – 13448
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
13441

thermally unstable, protonated salts, or by metathesis of an
IL precursor with a perchlorate salt, most commonly
AgClO . LiClO also has been described as starting material
The electrochemical remediation of perchlorate ions is
one of the best ways of converting the toxic perchlorate to
the non-toxic chloride ion efficiently. There are several re-
ports on the electro-reduction of perchlorate at various elec-
4
4
[12]
for 1-butyl-3-methylimidazolium perchlorate.
[17–22]
[23–26]
[27]
Both of these methods have disadvantages, with concen-
trated perchloric acid requiring careful handling, and
AgClO , as well as, LiClO , being more expensive than
trodes, for example, Rh,
Al, Ti, Ir, Ru, Re, Tc, and Sn. The literature
Pt,
tungsten carbide,
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
in this area has recently been reviewed. In most of the
above papers, perchlorate reduction is carried out in aque-
ous systems, and to our knowledge, there are no reports on
the electrochemical reduction of the perchlorate anion using
an IL approach.
4
4
would be ideal for large scale preparations, in addition to
the environmental hazard inherent in the use of perchlorate.
We have thus considered direct reuse or recycle of ammoni-
um perchlorate (AP) in the synthesis of new energetic mate-
rials as an interesting option taking into account the two
main advantages of this material: i) higher thermal stability,
and thus ease of handling in comparison to other perchlo-
rate salts and the free acid, and ii) the relative ease of han-
dling or removal of the associated ammonium cation after
the completion of the reaction. Additionally, AP is available
in large quantities from demilitarization of rocket fuels. By
using AP from such sources for the production of new per-
chlorate-based materials, the use of perchloric acid (with the
Given the wide exploration of ILs in electrochemistry, we
felt it was appropriate to study the reduction of perchlorate
in a medium which was both the reagent and the electrolyte.
With such a strategy the perchlorate anion could be reduced
to non-hazardous chloride, regenerating the starting salt
which in return could be exchanged to a perchlorate anion
again, thus creating a regenerative cycle for the remediation
of perchlorate. The advantages of this approach would in-
clude the potentially improved electrochemical stability of
ILs compared to water, no hydrogen/oxygen evolution
during electrolysis if the IL is wisely chosen, good conduc-
tivity, and, most importantly, no requirement for volatile or-
ganic solvents and supporting electrolytes.
hazards associated with its use) or AgClO (with its higher
4
cost) can be avoided.
In order to effectively utilize AP in the synthesis of per-
chlorate-based energetic materials, new synthetic protocols
for the formation of such products are required which allow
for fast and benign (in terms of byproducts) synthesis of the
target materials. Here, we present three potential routes to
incorporate the perchlorate anion into potentially energetic
Results and Discussion
1
-methylimidazolium and phosphonium salts, using AP as
Syntheses of perchlorate salts: Using three different routes
[see Equations (1)–(4)] and AP as the perchlorate source,
we have prepared 1-methylimidazolium perchlorate,
the perchlorate source, including: 1) the reaction of a neu-
tral amine (1-methylimidazole) with AP in aqueous solution,
resulting in the formation of a protonated imidazolium per-
([Hmim]
([C mim] ACHTUNGTRENNUNG[ ClO ], 2), 1-butyl-3-methylimidazolium perchlo-
4
ACHTUNGTNERNU[GN ClO ], 1), 1,3-dimethylimidazolium perchlorate,
4
chlorate ([Hmim]
lation of 1,3-dimethylimidazolium-2-carboxylate
tion with AP to form 1,3-dimethylimidazolium perchlorate
[C mim][ClO ], 2), ammonia, and CO ; and 3) metathesis
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[ClO ], 1) and ammonia gas; 2) decarboxy-
4
1
[13]
by reac-
rate, ([C mim] ACHNUTGTNERNUG[ ClO ], 3), and trihexyl(tetradecyl)phosphoni-
4 4
um perchlorate, ([P66614] ACHTUNGTRENNUNG[ ClO ], 4). All four of these salts
4
were formed in high yields, requiring little purification; 3
and 4 are ILs by definition, while 1 and 2 melt at tempera-
tures above 1008C.
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
1
4
2
of 1-butyl-3-methylimidazolium chloride with AP in water,
forming the insoluble 1-butyl-3-methylimidazolium perchlo-
rate ([C mim]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[ClO ], 3) and water soluble NH Cl. Using
The first, and simplest method involves the reaction of a
neutral amine (1-methylimidazole) with AP in aqueous solu-
tion, resulting in the formation of 1 and ammonia gas which
due to its volatility and thus easy removal, allows a shift in
the reaction equilibrium to completion. Ultimately, the am-
monia generated by this process could be recovered and
reused, making this reaction very atom efficient. The reac-
tion was conducted in water followed by evaporation to
yield a colorless crystalline hygroscopic solid. Protonation of
the imidazole ring was shown to be quantitative both by the
presence of the NH peak, and the shift in position of all the
4
4
4
this same metathesis methodology but with methanol as sol-
vent, trihexyl(tetradecyl)phosphonium perchlorate ([P66614]-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[ClO ], 4) was also prepared. Due to the relative hydropho-
4
bicity of these new salts, one could even envision recycle of
aqueous perchlorate waste streams (for example, from water
washout of rocket engines) by forming an IL and separating
the anhydrous IL phase.
It must also be pointed out here, that perchlorate is con-
sidered to be environmentally and toxicologically hazardous.
This anion has been identified to interfere with the human
thyroid glands and hence to suppress the formation of sever-
al iodine-containing hormones.
Protection Agency (EPA) set a limit of 15 ppb perchlorate
for drinking water; however, the discussions on that topic
1
1-methylimidazole peaks in the H NMR spectrum. The IR
[14]
À
The U.S. Environmental
spectrum showed one peak in the [ClO ] stretching region,
4
À1
a strong and broad peak at 1044 cm , with a shoulder at
[15]
À1
À
1005 cm , consistent with the symmetry of the [ClO ]
4
[16]
[37]
are controversial. We have thus considered that our ap-
proach to reuse AP could also be utilized as a remediation
strategy for AP.
anion being slightly altered, probably by hydrogen-bond-
ing. An additional peak was observed at 3081 cm indica-
tive of the protonation of the imidazole ring.
À1
[36]
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Chem. Eur. J. 2009, 15, 13441 – 13448

Recycled Ammonium Perchlorate
FULL PAPER
morph transition, and its rever-
sibility indicated it to be poly-
trophic.
Compound 2 proved to be
comparably unstable and the
TGA experiment resulted in an
energetic decomposition at
2
628C. DSC runs were there-
fore not conducted past 1508C,
up to which temperature no
thermal transitions were ob-
served. In 3, only a glass transi-
tion at T =À778C was ob-
g
served. The DSC of 4 showed a
melting point at 24.78C and
The second method involves utilization of a previously re-
ported protocol for the formation of a permanent cation,
that is, the preparation of imidazolium-based salts via the
decarboxylation reaction of 1,3-dimethylimidazolium-2-car-
from this standpoint it can be classified as an IL.
In TGA investigations, all salts showed stability at lower
temperatures with almost no mass loss observed below
2008C. Compound 1 exhibited a two-step decomposition
with T5%decomp =2418C, and an onset temperature for the
second decomposition step of 4958C. Salt 2 showed a more
violent decomposition with T5%decomp =2448C, after which a
steady rate of decomposition was observed until 2628C
when it underwent extremely rapid, energetic decomposi-
tion. Compound 3 exhibited T5%decomp =2828C. Above this
temperature the IL showed a steady rate of decomposition
up to 3108C, when it underwent very rapid, total decomposi-
[13]
boxylate. When reacted with AP, this compound is trans-
formed to [C mim][ClO ], 2, and easily removable gaseous
ACHTUNGTRENNUNG
1
4
by-products ammonia and CO . The Krapcho decarboxyla-
2
tion of 1,3-dimethylimidazolium-2-carboxylate was carried
out in a mixture of EtOH and DMSO. Evaporation of the
solvents gave 2 as a colorless, crystalline, extremely hygro-
scopic solid, in quantitative yield. The decarboxylation of
1
13
the zwitterion was confirmed by both the H and C NMR
1
spectra; the H NMR showing a resonance for the C2
tion. Compound 4 decomposes in one step with T5%decomp
254.58C.
=
1
3
À
proton, and the C NMR showing neither R-COO nor
À
2À
[
HCO ] /
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[CO ] species. Production of pure 2 was con-
In contrast to these materials, AP itself generally shows a
3
3
[40]
firmed by single crystal X-ray diffraction (Figure 1).
The compounds 3 and 4 were prepared by metathesis of
NH ClO with [C mim]Cl in water or with [P66614]Cl in meth-
more controllable thermal decomposition,
which begins
around 1308C, but below its phase-transition temperature of
~2408C, does not undergo complete decomposition. While
it is regarded as more generally thermally stable than
NH NO , the stability of AP does depend on a variety of
4
4
4
anol, respectively. The IL products phase separated from
the corresponding solution to give 3 as a pale yellow viscous
liquid and 4 as a clear liquid that transformed into a white
solid at around 208C. AgCl precipitation tests were negative
4
3
factors, including method of crystallization, preliminary
treatment of crystals, how long they have been stored, and
the purity of the salt.
À
indicating the absence of Cl in each product to the limit of
detection. The lack of an absorption band for water in the
IR spectra after drying and the measured water contents of
X-ray structure: Crystals suitable for X-ray crystallographic
analysis of 2 were obtained by the vapor diffusion of diethyl
ether into a dry ethanol solution of 2. Despite the use of
perfluorinated oil, 2 showed signs of rapid absorption of
water from the air, and likely recrystallized once placed in
the liquid nitrogen stream on the diffractometer. However,
no water was found in the crystal structure.
0.17% w/w (3) and 0.12% w/w (4) indicated the materials
to be quite hydrophobic. The IR spectra showed a strong
À
À1
and broad peak in the [ClO ] stretching region (1068 cm ,
4
À1
3
; 1081 cm , 4) for each compound consistent with the sym-
metry of the [ClO ] anion being unbroken.
À
[37]
4
Thermal investigations: All four salts were examined by
The compound crystallizes in the monoclinic space group
DSC and TGA using a standard protocol. From the DSC of
P2 /c where the asymmetric unit of the salt contains one full
1
[38,39]
1
, a melting point of 1488C (lit. 154–1588C)
was ob-
cation and anion, unusual given the symmetry of both ions.
The closest contact is through the C2 proton in the cation to
O3 in the perchlorate anion (Figure 1). Close contacts about
each ion reveal that the cation interacts with five anions,
three of which are via the three hydrogen atoms on C1,
each to separate perchlorate anions. The anion similarly in-
teracts with five cations, two of which are to O3. O1, O2,
and O4 each interact with one cation. Additionally, the imi-
dazolium cations stack in parallel pairs that alternate in ori-
served, with an additional transition observed at 28C. This
melting point is a bit lower than the one found in the litera-
ture, and we assume that this may be caused by the com-
poundꢀs high hygroscopicity and thus fast absorption of
water from the atmosphere. However, no detailed informa-
tion on the methods used to determine the melting-point
range was provided in the literature. From its appearance,
the transition at 28C was identified as a solid-state poly-
Chem. Eur. J. 2009, 15, 13441 – 13448
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13443

R. D. Rogers et al.
Figure 2. Electrochemical behavior of [P66614
]
A
H
U
G
R
N
U
G
4
] on a Au electrode vs.
+
À1
=
1 4
Figure 1. Crystal structure of [C mim] ACHNUTRTGENNGNU[ ClO ] (2) showing (A) the asym-
metric unit with the dominating interaction of the most acidic proton in
the cation (C2-H) with the perchlorate anion indicated; the interactions
(
distances less than the sum of the van der Waalsꢀ radii minus 0.1 ꢂ) to
4
Figure 3. Electrochemical behaviour of [P66614] ACHTUNETGRNNUNG[ ClO ] on a Pt electrode vs.
the (B) cation and (C) anion; and (D) the packing down the crystallo-
graphic c axis showing the distinct cationic and anionic layers (hydrogen
atoms were omitted).
+
À1
Ag/Ag at 508C and 100 mVs ; ~ = À3.0 to 3 V, * = À3 to 3.5 V, & =
À3 to 4 V.
The electrocatalytic reduction of perchlorate on Pt follows
[42]
entation with other pairs of cations. Distinct cationic and
anionic layers are found to form in the (0 À1 1) plane. The
combination of these various interactions gives rise to a
skewed NaCl-type of packing arrangement for the salt.
the mechanism depicted below, where desorption of the
intermediates is negligible and platinum acts as a sacrificial
anode. Perchlorate is reduced stepwise to chloride, while the
platinum counter electrode is simultaneously oxidized by
the oxygen produced. The formation of PtO (a dark-brown
2
Electrochemical reduction of perchlorate: To test the ability
of a perchlorate-based IL to serve as reagent and electro-
solid that is soluble in aq. KOH) in the anode chamber was
observed.
lyte, we chose [P66614
]
A
H
U
G
R
N
N
[ClO ] (4) since the phosphonium
This is, to the best of our knowledge, the first report of
the electro-reduction of perchlorate from a system using
4
cation is electrochemically more stable than imidazolium
[41]
cations,
and this provides a wider electrochemical
window. The cyclic voltammetry (CV) experiments carried
out with neat 4 indicated that the perchlorate anions can be
+
reduced on both gold (at À1.3 and À2 V vs Ag/Ag ) and on
platinum (at À0.5 and À1 V with a hump at À1.8 V) electro-
des (see Figures 2 and 3). When the potential range was in-
creased (À3.5 to 6 V) while using the gold electrodes, the
perchlorate ions were adsorbed on the gold electrode sur-
face which passivated the electroactive area and eventually
reflected on the electrochemically inert behavior at both
anodic and cathodic sides of the CV. Using platinum electro-
des, when the potential window was increased, the current
increased on the reduction peaks, showing that the electro-
reduction of perchlorate was progressing.
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Recycled Ammonium Perchlorate
FULL PAPER
ILs. In aqueous systems, the reduction of perchloric acid
leads to the evolution of hydrogen which may significantly
reduce the amount of perchlorate being transformed to
[43]
chloride. In our study, there are no acidic protons present
and consequently no hydrogen evolution, allowing the elec-
tro-reduction of perchlorate to proceed uninterrupted.
Based on this success, Pt was chosen as the material for
the working electrode for subsequent bulk electrolysis ex-
periments. As platinum is a very expensive material, nickel
could be used as a sacrificial anode in bulk studies as shown
[43]
by Rusanova et al., for aqueous systems.
The bulk electrolysis experiment was carried out at À2 V
+
versus Ag/Ag by chronoamperometry for 120 min on a Pt
3
5
Figure 5. Cl NMR spectra recorded during the electrolysis of [P66614]-
[ClO ] to determine the degradation of perchlorate ions and accumula-
tion of chloride ions. The peak at ~0 ppm is attributed to the external
electrode at room temperature. During this bulk electrolysis
of 4, the electrochemical degradation of the perchlorate ions
and their conversion into chloride ions was studied using IR
A
H
U
G
R
N
U
G
4
standard 1.0m NaCl in D
2
O. The peak at ~50 ppm is attributed to the
À
35
presence of [Cl] anions formed over time by electrolysis.
(
Figure 4) and Cl NMR (Figure 5). Samples were taken
from the electrolytic cell periodically after 15, 30, 45, 90,
and 105 min of electrolysis for analyses, and were also tested
with AgNO for the presence of chloride. The observed pre-
3
cipitation level of AgCl increased with the time of electroly-
sis, suggesting an increase in the chloride ion concentration
in the electrolyte with time.
As electrolysis time increased, the peak for perchlorate was
diminished and the peak for chloride became prominent.
The complete disappearance of the perchlorate peak in
3
5
the Cl NMR does not, however, support that all perchlo-
rate anions have been converted to chloride during this
short period of time. It is because the resolution of the per-
chlorate peak even in pure 4 was very poor when compared
to that in AP, perhaps because of the rather high viscosity of
the sample, or due to the lower symmetry of the phosphoni-
+
[44]
um cation, compared to NH4
.
However, the substantial
decrease of the size of this peak in comparison to the in-
À
creasing size of the Cl peak allows us to speculate that sub-
stantial conversion is taking place.
To the best of our knowledge we are the first to report
the electrochemical degradation of perchlorate ions using an
IL strategy while simultaneously recycling back the parent
IL. It is conceivable that due to the simplicity of the system
and ability to recover the starting material [P66614]Cl, that
can later be reconverted back to 4, using up further AP, the
developed system could be used in a continuous fashion in
the process of perchlorate removal and conversion to innoc-
uous chloride (Scheme 1).
Conclusions
4
Figure 4. IR spectra of [P66614] AHCTUNGTERNNUNG[ ClO ] in acetonitrile before (0 min) and
Three new routes have been shown for the synthesis of or-
ganic perchlorate salts of simple nitrogen heterocycles and a
quaternary phosphonium compound, using AP as the source
of perchlorate. Specifically, new preparative routes have
been determined for the easy preparation of 1-methylimid-
azolium perchlorate, 1,3-dimethylimidazolium perchlorate,
1-butyl-3-methylimidazolium perchlorate, and trihexyl(tetra-
decyl)phosphonium perchlorate. The synthetic routes pro-
ceed in a single step from the chosen precursors, and pro-
duce the desired products in high yield and purity. Most im-
portantly, the electrochemical remediation of the perchlo-
after (105 min) electrolysis (top) and magnification of the perchlorate
peak recorded during the electrolysis to monitor the degradation of per-
chlorate ions (bottom).
In the IR spectra (1 mm solutions of electrolyte, [P66614]-
ACHTUNGTRENNUNG[ ClO ], in acetonitrile), the intensity of the perchlorate peak
4
À1
at 1081 cm decreased with time of electrolysis, reflecting
À
35
the reduction of the [ClO4] ions. In the Cl NMR spectra,
À
the peak around 1000 ppm was assigned to the [ClO ]
anion, and the peak at 50 ppm was assigned to the Cl ion.
4
À
Chem. Eur. J. 2009, 15, 13441 – 13448
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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13445

R. D. Rogers et al.
The water content of compound 4 was
determined using a Cou-Lo Aquamax
from GRScientific (Bedfordshire, UK)
Karl-Fischer titrator. Electrospray
mass spectrometry and elemental anal-
ysis were performed on an LCT Pre-
mier from Waters using an Advion
nanomate injection system (Manches-
ter, UK), and
Series II CHNS/O Elemental Analyser
Shelton, CT), respectively.
a PerkinElmer 2400
(
Thermogravimetric analyses: Decom-
position temperatures for compounds
1
–3 were measured in the dynamic
heating regime using TA Instru-
a
ments (New Castle, DE) TGA 2950
Thermogravimetric Analyzer under
dried air. Samples were heated from
room temperature to 6008C under
À1
constant heating at 58C min
in
1
0 mm platinum sample pans (Instru-
ments Specialists Inc., Twin Lakes,
WI) that were flame treated before
each data collection. Compound 4 was
analyzed with the same procedure but
Scheme 1. Possible AP IL reuse/remediation strategies.
using a TA Instruments (West Sussex,
UK) TGA Q 5000 analyzer. Decom-
position temperatures (T5%decomp) were determined from the onset to
wt% mass loss in an isocratic TGA experiment.
rate ion from an ionic liquid leading to a potential perchlo-
rate removal/remediation cycle was achieved. This could
lead to a continuous process for converting perchlorate to
chloride ions using a strategy where an IL serves as both re-
agent and electrolyte. A few such strategies based on the re-
sults reported here are illustrated in Scheme 1.
5
Differential scanning calorimetry: DSC scans for compounds 1–3 were
conducted on a TA Instruments Model 2920 Modulated DSC calorimeter
(New Castle, DE) cooled with a liquid nitrogen cryostat. Data were col-
lected at constant atmospheric pressure. Samples between 8 and 13 mg
were placed in fresh aluminum pans (PS1007, hermetic sample pans, In-
strument Specialists Inc., Twin Lakes, WI) and massed using a Cahn C-
3
5 microbalance (Thermo Electron Corp., Waltham, MA). An empty pan
was used as a reference in the DSC. The dry box of the DSC was flushed
with dry nitrogen to prevent condensation and crystallization from ambi-
ent moisture upon cooling of the sample. The following protocols were
Experimental Section
À1
CAUTION! Although no problems were encountered in the synthesis or
characterization of these salts, all perchlorate salts should be treated as
potentially explosive, and should be prepared in small amounts under
good control. Energetic decomposition of perchlorate-based systems can
be initiated by a variety of external stimuli (e.g., impact, electrostatic dis-
charge), and care should be taken during all handling of such materials.
used on all samples. For solids; an initial heating rate of 58Cmin to
508C below the T5%decomp determined by TGA was followed by a 5 min
À1
isotherm. A cooling rate of 58Cmin to À308C was followed by a 5 min
isotherm, with the cycle repeated twice. For liquids; an initial cooling
À1
rate of 58Cmin to À1108C was followed by a 5 min isotherm. A heat-
À1
ing rate of 58Cmin to 1208C was followed by a 5 min isotherm, with
the cycle repeated twice. Compound 4 was analyzed following a similar
procedure but using a TA instruments (West Sussex, UK) DSC Q 2000
analyzer.
General: All chemicals unless otherwise stated were purchased from Al-
drich Chemical Company (Milwaukee, WI) and used without further pu-
rification. Water was deionized (DI) in house above 18 MW cm using a
Barnstead (Dubuque, IA) deionization system. Infrared spectra for com-
X-ray crystallography
À1
pounds 1–3 were recorded as neat samples from 4000–650 cm on a
À1
Crystal data: [C
ic, P2
1
mim]
A
H
U
G
R
N
U
G
4
] (2); C
5
H
9
N
2
O
4
Cl; 196.59 gmol ; monoclin-
Perkin–Elmer (Waltham, MA) Spectrum 100 FT-IR spectrometer fitted
with a Universal ATR Sampling Accessory; spectra for compound 4 were
measured as neat samples for the characterization of the pure compound,
and as 1 mm solutions in acetonitrile for the monitoring of the perchlo-
1
/c; T=173 K; a=6.2666(6), b=17.0452(17), c=7.8173(8) ꢂ, b=
3
À3
9
2.580(2)8; Z=4; V=834.16(14) ꢂ ; 1=1.565 gcm ; R
1 2
, wR [I>2s(I),
1
550 flections]=0.0302, 0.0809; R , wR (all data, 5110 reflections, 1703
1
2
unique)=0.0335, 0.0832; GooF=1.070. Data were collected on a Bruker
CCD area detector-equipped diffractometer (Madison, WI) using graph-
ite monochromated MoKa radiation (l=0.71073 ꢂ). The single crystal
was coated in Paratone-N (Hampton Research, Laguna Niguel, CA) per-
fluorinated oil, mounted on a glass fiber and transferred to the goniome-
ter for data collection. The crystal was cooled to À1008C using a cold ni-
À1
rate degradation, from 4000–650 cm on a Perkin–Elmer (Dublin, Ire-
land) Spectrum 100 FT-IR Spectrometer. The solvent signals were sub-
tracted (as background) from the spectra.
NMR data for compounds 1–3 were recorded in [D
6
]DMSO at 258C on a
5
00 MHz Bruker (Billerica, MA) AX500 spectrometer, with tetramethyl-
1
silane (TMS) as the internal standard for H (500 MHz) or the solvent as
the internal standard for C (125 MHz). NMR data of compound 4 were
trogen gas stream. The structures was solved and refined using the
1
3
[45]
SHELXTL software package
and absorption corrections were made
[
46]
collected from the neat sample, on a Bruker (Coventry, UK) 500DRX
using SADABS. The structure was refined by full-matrix least squares
on F . All non-hydrogen atoms were readily located and their positions
1
spectrometer with capillary [D
6
]DMSO as the external standard for
H
2
1
3
(
500 MHz) and C NMR (125 MHz). No standard was used to record
the P NMR (202 MHz). A solution of 1.0m NaCl in D O served as ex-
2
refined anisotropically, while all hydrogen atoms were found from differ-
ence Fourier maps and isotropically refined without restraint.
CCDC 730659 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
3
1
3
5
ternal standard for the Cl NMR (49 MHz) experiments.
Water content of compound 3 was measured by Karl-Fischer titration
with an EM Science Aquastar V1b Titrator (Hiranuma Sangyo, Japan).
13446
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 13441 – 13448

Recycled Ammonium Perchlorate
FULL PAPER
1
3
Electrochemistry: All electrochemistry experiments were carried out at
room temperature unless stated otherwise, using a computer controlled
Autolab PGSTAT (Eco Chemie B.V., The Netherlands) potentiostat. A
conventional three electrode electrochemical system consisting of a plati-
num disc as a working electrode, platinum coil as a counter electrode,
A
T
N
T
N
U
G
2 3 6
CH ); C NMR (125 MHz, [D ]DMSO, 258C, TMS):
2
3
2
2
2
2
3
3
À
À1
4
] ), 842, 751 cm ; MS: m/z (%): 83.07 (25)
+ +
+
+
À
3
and Ag/Ag as the reference electrode was used. The counter and refer-
ence electrode compartments were filled with the same electrolyte as the
[Hmim] , 139.1 (100) [C
4
mim] , 239.2 (30) [M+H] , 82.9 (5) [ClO
] ,
À
À
97.0 (15) [dimim] , 98.9 (100) [ClO
4
] . The compound appears to be
bulk ([P66614
]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[ClO
4
]), but were separated from the bulk electrolyte by a
slightly hygroscopic, as the elemental analysis suggests that a substoichio-
metric hydrate formed after several days with contact to the atmosphere:
glass frit. This reduces the contamination of the bulk electrolyte by the
by-products from the counter electrode during electrolysis. For voltam-
metric measurements, working electrodes purchased from BioAnalytical
Systems (Warwickshire, UK) were used. Prior to each experiment, the
electrodes were polished on soft lapping pads with alumina slurry of size
elemental analysis calcd (%) for
39.52, H 6.42, N 11.52; found: C 39.41, H 6.23, N 11.32.
Synthesis of [P66614 [ClO ] (4): A mixture of [P66614]Cl (Cytec, Niagara
Falls, Canada) (4.07 g, 7.8 mmol) and NH ClO (0.922 g, 7.8 mmol) in
8 15 2 4 2
C H N ClO ꢃ0.25H O (243.2): C
]ACHTUNGTRENNUG
4
4
4
1
and 0.3 mm and then washed with distilled water and dried by com-
pressed air. All samples were degassed with Ar prior to measurement.
Synthesis of [Hmim][ClO ] (1): NH ClO (0.50 g, 4.3 mmol) was dis-
solved in DI water (3 mL). N-Methylimidazole (0.44 mL, 0.35 g,
.3 mmol) was dissolved in DI water (1 mL), the solutions were mixed
and stirred overnight. The water was evaporated under a N gas stream
MeOH (10 mL) containing a few drops of water was stirred at room tem-
perature. A phase separation was observed after 15 min (precipitation of
NH
4
Cl), but the stirring was continued overnight to ensure the comple-
Cl . The organ-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
4
4
4
tion of the reaction. The product was extracted using CH
2
2
ic phase was washed until chloride free, and the solvent was removed in
vacuo. The product was dried under high vacuum at 358C overnight to
give a colorless liquid that slowly crystallized (91%). M.p. (DSC) 24.78C,
4
2
to give an off-white solid. A further portion of DI water was added and
the evaporation repeated. The solid material was dried under high
vacuum at room temperature to give the desired product as a white hy-
groscopic solid in quantitative yield (0.76 g). M.p. (DSC) 1488C, onset
for 5% decomposition T5%decomp =2418C, second decomposition Tdecomp
4
NCHN), 7.48 (s, 1H, NCHCHN), 7.38 (s, 1H, NCHCHN), 7.07 ppm (brs,
1
2
1
single
decomposition
T
5%decomp =254.58C;
H NMR
(500 MHz,
),
]DMSO, 258C): d=
[
D
6
]DMSO, 258C): d=2.17 (m, 8H, PCH
2
), 1.34 (m, 48H, CH
2
1
3
0
.88 ppm (m, 12H, CH
3
); C NMR (125 MHz, [D
), 30.02 (CH ), 29.81 (CH
), 28.61 (CH
), 17.46 (d, CH
); P NMR (202 MHz, [D ]DMSO, 258C): d=34.96 ppm; Cl NMR
6
3
1.27 (CH
2
), 30.36 (CH
2
2
2
), 29.61 (CH
2
), 29.01
), 28.05 (CH ),
3
), 13.89 (CH ), 13.80 ppm
=
1
(CH
2
), 28.93 (CH
2
), 28.68 (CH
2
2
2 2
), 22.06 (CH
958C; H NMR (500 MHz, [D
6
]DMSO, 258C, TMS): d=8.51 (s, 1H,
2
1.77 (CH
2
), 20.48 (d, CH
2
2
3
1
35
1
3
(CH
3
6
H, NH), 3.78 ppm (s, 3H, NCH
3 6
); C NMR (125 MHz, [D ]DMSO,
(
49 MHz, D
n˜
720 cm ; MS: m/z (%): 483.5 (100) [P66614] , 82.9 (5) [ClO
2
O, 25 8C, NaCl): d=1010.80 ppm; selected IR (neat sample):
58C, TMS): d=136.48 (NCHN), 122.72 (NCHCHN), 122.18
À
=
2955, 2923, 2854, 1465, 1412, 1378, 1215, 1081 ([ClO
4
] ), 812,
(
NCHCHN), 34.45 ppm (CH
3
) ; selected IR (neat sample): n˜ = 3154,
À1
+
À
À
3
] , 98.9 (100)
À
4
[ClO ] , 202.9 (95) [P66H] ; elemental analysis calcd (%) for
3
1
116, 3081, 3022, 2976, 2880, 1587, 1550, 1439, 1308, 1280, 1044 ([ClO
4
] ),
À
À
4
005 ([ClO ] ), 931, 914, 856, 747 cm ; MS: m/z (%): 83.06 (100)
+
À1
+
À
PC32H
68ClO
4
(583.3): C 65.89, H 11.75; found: C 66.32, H 11.88.
[
[
Hmim] , 265.06 (90) [Hmim
ClO
2
ClO
4
] , 82.9 (35) [ClO
3
] , 98.9 (100)
À
4
] .
Synthesis of [C
was prepared according to the literature method.
.3 mmol) was dissolved in DMSO/EtOH 3:1 (2.5 mL) and added to a
warmed solution of 1,3-dimethylimidazolium-2-carboxylate (0.60 g,
.3 mmol) dissolved in EtOH (2 mL). The mixture was heated to 708C
and then stirred for 3 d. The solvent was removed under high vacuum to
leave the desired product as a white and extremely hygroscopic solid in
quantitative yield. X-ray quality crystals were grown by the diffusion of
diethyl ether vapor into a solution of 2 in dry EtOH. The melting point
was not determined. Due to the discovered instability of the investigated
compound (the TGA experiment resulted in an energetic decomposi-
tion), the DSC experiment was not conducted above 1508C, to which
temperature no thermal transition was recorded. Onset temperature for
1 4
mim] ACHTUNGTRENNUNG[ ClO ] (2): 1,3-Dimethylimidazolium-2-carboxylate
[
47]
4 4
NH ClO (0.50 g,
4
Acknowledgements
4
This research was supported by a grant from Amtec Corporation and the
Air Force Office of Scientific Research (Grant F49620-03-1-0357).
[
[
1] E. T. Urbansky, Environ. Sci. Pollut. Res. Int. 2002, 9, 187–192.
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tion); H NMR (500 MHz, [D
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3
1
3
NCHN), 7.65 (s, 2H, NCHCHN), 3.84 ppm (s, 6H, NCH
3
); C NMR
]DMSO, 258C, TMS): d=136.93 (NCHN), 123.34
NCHCHN), 35.58 ppm (CH ).
mim][ClO ] (3): NH
solved in DI water (3 mL). [C mim]Cl (BASF, Ludwigshafen, Germany)
0.74 g, 4.3 mmol) was dissolved in DI water (1 mL) and added with ini-
tial mixing. The mixture was left to stand for 2 h. The water was evapo-
rated under a N gas stream to give a mixture of solid and liquid residue.
The liquid was separated from the solid by extraction with CH Cl , and
the solvent removed in vacuo. The resulting viscous liquid was taken up
in CH Cl and extracted with DI water until the washing water did not
form a precipitate when tested with a solution of AgNO . The CH Cl
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(
(
125 MHz, [D
6
3
Synthesis of [C
4
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
4
4 4
ClO (0.50 g, 4.3 mmol) was dis-
4
(
2
2
2
2
2
3
2
2
was removed in vacuo and the resulting pale yellow viscous liquid dried
under high vacuum at room temperature to give the desired product
(
0.91 g, 89%). No melting point was detected in the compoundꢀs DSC
trace, but a glass transition was observed at T
=À778C; onset for 5%
decomposition T5%decomp =2828C; H NMR (500 MHz, [D ]DMSO, 258C,
TMS): d=9.10 (s, 1H, NCHN), 7.77 (s, 1H, NCHCHN), 7.70 (s, 1H,
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1
Received: May 7, 2009
Published online: November 9, 2009
1
13448
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 13441 – 13448