Note: Descriptions are shown in the official language in which they were submitted.
CA 02650609 2008-10-28
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Porous metal organic framework based on pyrroles and pyridinones
The present invention relates to a process for preparing a porous metal
organic framework
comprising at least one organic compound coordinated to at least one metal
ion.
Crystalline porous metal organic frameworks (MOFs) having defined pores or
pore distribu-
tions and large specific surface areas have been the object of comprehensive
research
activity in recent times.
The best-known porous metal organic frameworks are formed by a metal ion to
which a
dicarboxylic, tricarboxylic or polycarboxylic acid is coordinated so as to
form a coordination
polymer having pores.
Numerous methods have been described in the literature for preparing such
porous metal
organic frameworks based on carboxylic acids.
Thus, for example, US-A 5,648,508 describes microporous metal organic
frameworks
which are prepared under mild reaction conditions from a metal ion and a
ligand in the
presence of a template compound.
A further method of preparing porous metal organic frameworks based on
carboxylic acids
is based on the anodic oxidation of a metal in the presence of a carboxylic
acid to form a
porous metal organic framework. WO-A 2005/049892 describes such metal organic
frameworks based on carboxylic acids.
Owing to the presence of carboxylic acid functions, it is possible to prepare
comparatively
robust porous metal organic frameworks.
It is far more difficult to prepare porous metal organic frameworks in which
the organic
component has no functional groups suitable for framework formation. Here,
coordination is
made possible solely by the organic structure.
Such an organic compound is, for example, imidazole, which has particularly
interesting
properties, especially in respect of its adsorption capability.
CA 02650609 2008-10-28
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X.-C. Huang et al., Angew. Chem. 118 (2006), 1587 - 1589, describe the
preparation of
zinc 2-methylimidazolide and zinc 2-ethylimidazolide and also a metal organic
framework
comprising both 2-ethylimidazolide and 2-methylimidazolide.
Here, the appropriate imidazole in methanol is reacted with a zinc hydroxide
solution in
aqueous ammonia for a period of several days.
Further examples of such organic compounds are triazoles and 2- or 4-
hydroxypyrimidine.
A.M. Goforth et al., J. Solid State Chem. 178 (2005), 2511-2518, describe the
preparation
of porous metal organic frameworks made of up zinc and triazoles, with the
zinc being used
in the form of a zinc fluoride.
J.A.R. Navarro et al., lnorg. Chem. 45 (2006), 2397-2399, describe 2- and
4-hydroxypyrimidine-based metal organic frameworks which are produced from a
precursor
complex. These metal organic frameworks have interesting properties in respect
of their
adsorption capability for water, nitrogen, carbon monoxide and carbon dioxide.
All these organic structures have two ring nitrogens which are capable of
coordinating to a
metal so as to form a porous framework structure, with in each case a nitrogen
atom being
able to be deprotonated to balance the positive charge on the metal ion.
Despite the satisfactory yields and the specific surface areas determined,
there is a need
for improved processes for preparing such metal organic frameworks whose
organic con-
stituent is based on an organic compound of the type described above.
It is therefore an object of the present invention to provide a process for
preparing such
porous metal organic frameworks.
This object is achieved by a process for preparing a porous metal organic
framework com-
prising at least one organic compound coordinated to at least one metal ion,
which com-
prises the step
oxidation of at least one anode comprising the metal corresponding to the at
least one
metal ion in a reaction medium in the presence of the at least one organic
compound,
wherein the at least one organic compound is a monocyclic, bicyclic or
polycyclic ring sys-
tem which is derived from at least one heterocycle selected from the group
consisting of
pyrrole, aipha-pyridone and gamma-pyridone and has at least two ring nitrogens
and is
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unsubstituted or bears one or more substituents selected independently from
the group
consisting of halogen, C1_6-alkyl, phenyl, NH2, NH(C,_6-atkyl), N(C,_6-
alkyl)2, OH, Ophenyl
and OC,-6-alkyl, where the substituents C1_6-alkyl and phenyl are
unsubstituted or bear one
or more substituents selected independently from the group consisting of
halogen, NH2,
NH(C,-6-alkyl), N(C1_6-alkyl)2i OH, Ophenyl and OC1_6-alkyl.
It has surprisingly been found that the provision of the metal ion by means of
anodic oxida-
tion of the corresponding metal in the presence of the at least one organic
compound
makes it possible to form a corresponding porous metal organic framework
which, com-
pared to the synthesis known in the prior art, has a higher specific surface
area and can be
obtained in a higher yield.
The process of the invention involves the anodic oxidation of the at least one
metal which
then enters the reaction medium as cation and reacts with the at least one
organic com-
pound to form a porous metal organic framework. This framework can, for
example, be
separated off by filtration.
The term "electrochemical preparation" as used for the purposes of the present
invention
refers to a preparative process in which the formation of at least one
reaction product in at
least one process step is associated with the migration of electric charges or
the occur-
rence of electric potentials.
The term "at least one metal ion" as used for the purposes of the present
invention refers to
embodiments in which at least one ion of a metal or at least one ion of a
first metal and at
least one ion of at least one second metal which is different from the first
metal is provided
by anodic oxidation.
The present invention also comprises embodiments in which at least one ion of
at least one
metal is provided by anodic oxidation and at least one ion of at least one
metal is provided
via a metal salt, with the at least one metal in the metal salt and the at
least one metal pro-
vided as metal ion by means of anodic oxidation being able to be identical or
different. The
present invention therefore comprises, for example, an embodiment in which the
reaction
medium comprises one or more different salts of a metal and the metal ion
comprised in
this salt or in these salts is additionally provided by anodic oxidation of at
least one anode
comprising this metal. The present invention likewise comprises an embodiment
in which
the reaction medium comprises one or more different salts of at least one
metal and at
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least one metal different from these metals is provided as metal ion in the
reaction medium
by means of anodic oxidation.
In a preferred embodiment of the present invention, the at least one metal ion
is provided
by anodic oxidation of at least one anode comprising this at least one metal
and no further
metal is provided via a metal salt.
In a further preferred embodiment, the metal organic framework prepared by the
process of
the invention comprises only one metal.
The present invention accordingly comprises an embodiment in which the at
least one an-
ode comprises a single metal or two or more metals and in the case of the
anode compris-
ing a single metal, this metal is provided by anodic oxidation and in the case
of the anode
comprising two or more metals, at least one of these metals is provided by
anodic oxida-
tion.
Furthermore, the present invention comprises an embodiment in which at least
two anodes
are used, with these being able to be identical or different. Each of the at
least two anodes
here can comprise a single metal or two or more metals. It is possible here
for, for exam-
ple, two different anodes to comprise the same metals but in different
proportions. It is
likewise possible, for example, in the case of different anodes for a first
anode to comprise
a first metal and a second anode to comprise a second metal, with the first
anode not com-
prising the second metal and/or the second anode not comprising the first
metal.
The metal or the metals are elements of Groups 2 to 15 of the Periodic Table
of the Ele-
ments. For the purposes of the present invention, preferred metal ions are
selected from
the group of metals consisting of copper, iron, aluminum, zinc, magnesium,
zirconium, tita-
nium, vanadium, molybdenum, tungsten, indium, calcium, strontium, cobalt,
nickel, plati-
num, rhodium, ruthenium, palladium, scandium, yttrium, a lanthanide, manganese
and rhe-
nium. iron, copper, zinc, nickel and cobalt are more preferred. Particular
preference is
given to zinc.
A lanthanide comprises La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and
Lu.
As metal ions which are provided in the reaction medium by anodic oxidation,
particufar
mention may be made of Cu2+, Cu+, N i2, , Ni+, Fe 3, , Fe2+, Co3+, Co2+, Zn2+,
Mn3+, Mn2+
,
AI3+' Mg2+, SC3+, Y3+, Ln3+, RE,'3+, V3+, In3+, Cca2+, Sr2+, Pt2+, TiO2+,
TI4+, ZrO2+, Zr4+,
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Ru3+, Ru2+, Mo3+ W3+ Rh2+, Rh+, Pd2+ and Pd+. Particular preference is given
to Zn2+,
Cu2+, Cu+, Fe2+, Fe3+, Ni2+, Ni+, Co3+ and Co2+. Very particular preference is
given to Zn2+.
The present invention accordingly also provides a process as described above
in which a
copper-comprising and/or a nickel-comprising and/or a cobalt-comprising and/or
a zinc-
comprising and/or an iron-comprising anode is used as metal ion source.
In a preferred embodiment, the present invention also provides a process as
described
above in which a zinc-comprising anode is used as metal ion source.
The nature of the anode used in the process of the invention can in principle
be chosen
freely as long as it is ensured that the at least one metal ion can be
provided in the reaction
medium by anodic oxidation to allow formation of the porous metal organic
framework.
Preference is given to, inter alia, anodes in the form of a rod and/or a ring
and/or a disk, for
example an annular disk, and/or a plate and/or a tube and/or a bed of loose
material and/or
a cylinder and/or a cone and/or a frustum of a cone.
In a preferred embodiment, the process of the invention is carried out using
at least one
sacrificial anode. The term "sacrificial anode" as used for the purposes of
the present in-
vention refers to an anode which is at least partly dissolved during the
course of the proc-
ess of the invention. Embodiments in which at least part of the dissolved
anode material is
replaced during the course of the process are also encompassed here. This can
occur, for
example, by at least one fresh anode being introduced into the reaction system
or, in a
preferred embodiment, an anode being introduced into the reaction system and
being fed
further into the reaction system either continuously or discontinuously during
the course of
the process of the invention.
Preference is given to using anodes which consist of the at least one metal
serving as
metal ion source or comprise this at least one metal on at least one suitable
support mate-
rial in the process of the invention.
The geometry of the at least one support material is essentially not subject
to any restric-
tions. It is possible to use, for example, support materials in the form of a
woven fabric
and/or a sheet and/or a felt and/or a mesh and/or a rod and/or a candle and/or
a cone
and/or a frustum of a cone and/or a ring and/or a disk and/or a plate and/or a
tube and/or a
bed of loose material and/or a cylinder.
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Possible support materials according to the invention are, for example, metals
such as at
least one of the abovementioned metals, alloys such as steels or bronzes or
brass, graph-
ite, felt or foams.
Very particular preference is given to anodes which consist of the at least
one metal serv-
ing as metal ion source.
The nature of the cathode used in the process of the invention can in
principle be chosen
freely as long as it is ensured that the at least one metal ion can be
provided in the reaction
medium by anodic oxidation.
In a preferred embodiment of the process of the invention, the electrically
conductive elec-
trode material of the at least one cathode is selected so that no interfering
secondary reac-
tion takes place in the reaction medium. Preferred cathode materials are,
inter alia, graph-
ite, copper, zinc, tin, manganese, iron, silver, gold, platinum or alloys such
as steels,
bronzes or brass.
As preferred combinations of the anode material serving as metal ion source
and the elec-
trically conductive cathode material, mention may be made by way of example
of:
Anode Cathode
Zinc Zinc
Zinc Steel
Zinc Iron
Copper Copper
Magnesium Copper
Cobalt Cobalt
! ron Steel
Copper Steel
The geometry of the at least one cathode is essentially not subject to any
restrictions. It is
possible to use, for example, cathodes in the form of a rod and/or a ring
and/or a disk
and/or a plate and/or a tube.
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For the purposes of the present invention, it is possible to use essentially
any of the types
of cell customary in electrochemistry. Very particular preference is given in
the process of
the invention to an electrolysis cell which is suitable for the use of
sacrificial electrodes.
It is in principle possible to use, inter alia, divided cells having, for
example, a parallel
arrangement of electrodes or candle-shaped electrodes. As separation medium
between
the cell compartments, it is possible to use, for example, ion-exchange
membranes,
microporous membranes, diaphragms, filter fabrics composed of materials which
do not
conduct electrodes, glass frits and/or porous ceramics. Preference is given to
using ion-
exchange membranes, in particular cation-exchange membranes, and among these
preference is in turn given to using membranes which comprise a copolymer of
tetrafluorethylene and a perfluorinated monomer comprising sulfonic acid
groups.
In a preferred embodiment of the process of the invention, preference is given
to using one
or more undivided cells.
The present invention therefore also provides a process as described above
which is car-
ried out in an undivided electrolysis cell.
Very particular preference is given to combinations of geometries of anode and
cathode in
which the facing sides of the anode and cathode form a gap having a
homogeneous thick-
ness.
In the at least one undivided cell, the electrodes are, for example, arranged
parallel to one
another, with the electrode gap having a homogeneous thickness in the range,
for exam-
ple, from 0.5 mm to 30 mm, preferably in the range from 0.75 mm to 20 mm and
particu-
larly preferably in the range from 1 to 10 mm.
In a preferred embodiment, it is possible, for example, to arrange a cathode
and an anode
parallel to one another so that an electrode gap having a homogeneous
thickness in the
range from 0.5 to 30 mm, preferably in the range from 1 to 20 mm, more
preferably in the
range from 5 to 15 mm and particularly preferably the range from 8 to 12 mm,
for example
in the region of about 10 mm, is formed in the resulting cell. This type of
cell will, for the
purposes of the present invention, be referred to as a "gap cell".
In a preferred embodiment of the process of the invention, the above-described
cell is used
as a bipolar cell.
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Apart from the above-described cell, the electrodes are employed individually
or a plurality
of them are stacked in a likewise preferred embodiment of the process of the
invention. In
the latter case, the electrodes are referred to as stacked electrodes which
are connected in
a bipolar series in what is accordingly referred to as a stacked plate cell.
Particularly when
the process of the invention is carried out on an industrial scale, preference
is given to us-
ing at least one pot cell and particularly preferably stacked plate cells
connected in series
whose in-principle structure is described in DE 195 33 773 Al.
In the preferred embodiment of the stacked plate cell, preference is given,
for example, to
arranging disks of suitable materials, for example copper disks, parallel to
one another so
that a gap having a homogeneous thickness in the range from 0.5 to 30 mm,
preferably in
the range from 0.6 to 20 mm, more preferably in the range from 0.7 to 10 mm,
more pref-
erably in the range from 0.8 to 5 mm and in particular in the range from 0.9
to 2 mm, for
example in the region of about 1 mm, is in each case formed between the
individual disks.
Here, the distances between the individual disks can be identical or
different, but in a par-
ticularly preferred embodiment the distances between the disks are essentially
equal. In a
further embodiment, the material of a disk of the stacked plate cell can
differ from the mate-
rial of another disk of the stacked plate cell. For example, one disk can be
made of graphite
and another disk can made of copper, with the copper disk being connected as
anode and
the graphite disk being connected as cathode.
Furthermore, preference is given for the purposes of the present invention to
using, for
example, "pencil sharpener" cells as are described, for example, in J.
Chaussard et al.,
J. Appl. Electrochem. 19 (1989) 345-348. Particular preference is given to
using pencil
sharpener electrodes having rod-shaped, feedable electrodes in the process of
the invention.
Accordingly, the present invention also provides, in particular, a process as
described
above which is carried out in a gap cell or stacked plate cell.
Cells in which the electrode spacing is less than or equal to 1 mm are
referred to as capil-
lary gap cells.
In likewise preferred embodiments of the process of the invention, it is
possible to use elec-
trolysis cells having, for example, porous electrodes made of beds of metal
particles or
having, for example, porous electrodes composed of metal meshes or having, for
example,
electrodes composed of both beds of metal particles and metal meshes.
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In a further preferred embodiment, electrolysis cells which have at least one
sacrificial an-
ode having a circular disk-shaped cross section and at least one cathode
having an annu-
lar cross section, with particular preference being given to the diameter of
the preferably
cylindrical anode being smaller than the internal diameter of the cathode and
the anode
being located in the cathode in such a way that a gap of homogeneous thickness
is formed
between the outer surface of the cylindrical anode and the interior surface of
the cathode
which at least partly surrounds the anode, are used in the process of the
invention.
For the purposes of the present invention, it is also possible to reverse the
polarity so that
the original anode becomes the cathode and the original cathode becomes the
anode. In
this process variant, it is possible, for example, when suitable electrodes
which comprise
different metals are chosen, firstly to make available one metal as metal
cation by means of
anodic oxidation and to make available a further metal in a second step after
reversal of the
polarity. It is likewise possible to bring about the reversal of polarity by
application of AC
current.
It is in principle possible to carry out the process batchwise or continuously
or in mixed op-
eration. The process is preferably carried out continuously, in particular in
at least one flow
cell.
The voltages employed in the process of the invention can be matched to the
respective at
least one metal of the at least one anode serving as metal ion source for the
porous metal
organic framework and/or to the properties of the at least first organic
compound and/or, if
appropriate, to the properties of the at least one solvent described below
and/or, if appro-
priate, to the properties of the at least one electrolyte salt described below
and/or to the
properties of the at least one cathodic depolarization compound described
below.
In general, the voltages per electrode pair are in the range from 0.5 to 100
V, preferably in
the range from 1 to 40 V and particularly preferably in the range from 1.5 to
20 V. Exam-
ples of preferred ranges are from about 1.5 to 10 V or from 10 to 20 V or from
20 to 25 V or
from 10 to 25 V or from 4 to 20 V or from 4 to 25 V. The voltage can be
constant over the
course of the process of the invention or can change continuously or
discontinuously over
the course of the process.
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For example, if copper is being oxidized anodically, the voltages are
generally in the range
from 3 to 20 V, preferably in the range from 3.5 to 15 V and particularly
preferably in the
range from 4 to 15 V.
The current densities occurring in the preparation according to the invention
of the porous
organic framework are generally in the range from 0.01 to 1000 mA/cm2,
preferably in the
range from 0.1 to 1000 mA/cm2, more preferably in the range from 0.2 to 200
mA/cm2,
more preferably in the range from 0.3 to 100 mA/cm2 and particularly
preferably in the
range from 0.5 to 50 mA/cm2.
The process of the invention is generally carried out at a temperature in the
range from 0 C
to the boiling point, preferably in the range from 20 C to the boiling point,
of the respective
reaction medium or of the at least one solvent used, preferably under
atmospheric pres-
sure. It is likewise possible to carry out the process under superatmospheric
pressure, with
pressure and temperature preferabiy being chosen so that the reaction medium
is prefera-
bly at least partly liquid.
In general, the process of the invention is carried out at a pressure in the
range from 0.5 to
50 bar, preferably in the range from 1 to 6 bar and particularly preferably at
atmospheric
pressure.
Depending on the type and physical state of the constituents of the reaction
medium, the
electrochemical preparation according to the invention of the metal organic
framework can
in principle also be carried out without an additional solvent. This is, for
example, the case
particularly when the at least one organic compound in the reaction medium
functions as
solvent.
It is likewise possible in principle to dispense with a solvent and, for
example, carry out the
process of the invention in the melt, with at least one constituent of the
reaction medium
being present in the molten state.
In a preferred embodiment of the present invention, the reaction medium
comprises at least
one suitable solvent in addition to the at least one organic compound and, if
appropriate, to
the at least one electrolyte salt and, if appropriate, to the at least one
cathodic depolariza-
tion compound. The chemical nature and amount of this at least one solvent can
be
matched to the at least one organic compound and/or to the at least one
electrolyte salt
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and/or to the at least one cathodic depolarization compound and/or to the at
least one
metal ion.
Conceivable solvents are in principle all solvents or solvent mixtures in
which the starting
materials used in the process of the invention can be at least partly
dissolved or suspended
under the chosen reaction conditions such as pressure and temperature. For the
purposes
of the present invention, the term "solvent" also comprises solvent mixtures.
Examples of
solvents used are, inter alia,
- water;
- alcohols having 1, 2, 3 or 4 carbon atoms, e.g. methanol, ethanol, n-
propanol, iso-
propanol, n-butanol, isobutanol, tert-butanol;
- carboxylic acids having 1, 2, 3 or 4 carbon atoms, e.g. formic acid, acetic
acid, propi-
onic acid or butanoic acid;
- nitriles such as acetonitrile or cyanobenzene;
- ketones such as acetone;
- at least singularly halogen-substituted lower alkanes such as methyl
chloride or 1,2-
dichloroethane;
- acid amides such as amides of lower carboxylic acids such as carboxylic
acids hav-
ing 1, 2, 3 or 4 carbon atoms, e.g. amides of formic acid, acetic acid,
propionic acid
or butanoic acid, for example formamide, dimethylformamide (DMF), diethylforma-
mide (DEF), t-butylformamide, acetamide, dimethylacetamide, diethylacetamide
or t-
butylacetamide;
- cyclic ethers such as tetrahydrofuran or dioxane;
- N-formylamides or N-acetylamides or symmetrical or unsymmetrical urea
derivatives
of primary, secondary or cyclic amines such as ethylamine, diethylamine,
piperidine
or morpholine;
- amines such as ethanolamine, triethylamine or ethylenediamine;
- dimethyl sulfoxide;
- pyridine;
- trialkyl phosphites and phosphates;
and mixtures of two or more of the abovementioned compounds.
The reaction medium preferably comprises an organic solvent which may, if
appropriate, be
present in admixture with water; the organic solvent particularly preferably
comprises an
alcohol.
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The term "organic solvent" as used above includes both pure organic solvents
and organic
solvents which comprise small amounts of at least one further compound such
as, prefera-
bly, water. In this case, the water contents of the abovementioned solvents
are in the range
up to 1% by weight, preferably in the range up to 0.5% by weight, particularly
preferably in
the range from 0.01 to 0.5% by weight and very particularly preferably in the
range from 0.1
to 0.5% by weight. For the purposes of the present invention, the term
"methanol" or "etha-
nol" or "acetonitrile" or "DMF" or "DEF" also encompasses, for example, a
solvent which
may in each case particularly preferably comprise water in an amount of from
0.1 to 0.5%
by weight. However, the at least one further compound can also be of a
different chemical
nature. In particular, it does not have to be a customary solvent. Mention may
be made by
way of example of stabilizers. If a mixture of organic solvents with water is
present, it is of
course possible for higher proportions of water to be present in the solvent
mixture.
Preferred solvents in the process of the invention are methanol, ethanol,
acetonitrile, DMF
and DEF or a mixture of two or more of these compounds. Very particular
preference is
given to methanol, ethanol, DMF, DEF and a mixture of two or more of these
compounds
as solvent. Methanol is especially preferred.
In a preferred embodiment, at least one protic solvent is used as solvent.
This is preferably
used when, inter alia, the cathodic formation of hydrogen is to be achieved in
order to avoid
the redeposition described below on the cathode of the at least one metal ion
provided by
anodic oxidation.
However, a protic solvent can also be dispensed with for the purposes of the
present inven-
tion since the at least one organic compound has at least one ring nitrogen to
which, at
least as represented by a limiting formula, a hydrogen atom is bound and can
be split off
and reduced.
For example, in the case of methanol being used as solvent, the temperature
for the proc-
ess of the invention under atmospheric pressure is generally in the range from
0 to 90 C,
preferably in the range from 0 to 65 C and particularly preferably in the
range from 15 to
65 C.
For example, in the case of ethanol being used as solvent, the temperature in
the process
of the invention under atmospheric pressure is generally in the range from 0
to 100 C,
preferably in the range from 0 to 78 C and particularly preferably in the
range from 25 to
78 C.
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In the process of the invention, the pH of the reaction medium is set so that
it is favorable
for the synthesis or the stability or preferably for the synthesis and the
stability of the
framework. For example, the pH can be set by means of the at least one
electrolyte salt.
If the reaction is carried out as a batch reaction, the reaction time is
generally in the range
up to 30 hours, preferably in the range up to 20 hours, more preferably in the
range from 1
to 10 hours and particularly preferably in the range from 1 to 5 hours.
The at least one organic compound is a monocyclic, bicyclic or polycyclic ring
system
which is derived from at least one heterocycle selected from the group
consisting of pyr-
role, alpha-pyridone and gamma-pyridone and has at least two ring nitrogens
and is un-
substituted or bears one or more substituents selected independently from the
group con-
sisting of halogen, Ct_6-alkyl, phenyl, NH2, NH(C1_6-alkyl), N(C1_6-alkyl)2,
OH, Ophenyl and
OC1_6-alkyl, where the substituents C1_6-alkyl and phenyl are unsubstituted or
bear one or
more substituents selected independently from the group consisting of halogen,
NH2,
NH(C1_6-alkyl), N(C1_6-alkyl)2, OH, Ophenyl and OC1_6-alkyl.
For the purposes of present invention, the term "C1_6-alkyl" refers to an
alkyl group having
from 1 to 6 carbon atoms. Examples are methyl, ethyl, n-propyl, i-propyl, n-
butyl, i-butyl,
sec-butyl, t-butyl, pentyl, hexyl. Preferred radicals are methyl and ethyl. If
a substituted Ct_6-
alkyl radical is present, at least one hydrogen atom is replaced by another
substituent.
Furthermore, for the purposes of the present invention, the term "halogen"
refers to fluo-
rine, chlorine, bromine or iodine. Preference is given to fluorine and
chlorine.
As indicated above, the organic compound is a monocyclic, bicyclic or
polycylic ring system
which is derived from at least one heterocycle selected from the group
consisting of pyr-
role, alpha-pyridone and gamma-pyridone. All these three heterocycles have a
ring nitro-
gen which in at least one limiting structure bears a hydrogen atom which can
be split off. It
is thus possible to deprotonate pyrrole, alpha-pyridone or gamma-pyridone.
This forms a
negative charge which can at least partly balance the positive charge of the
at least one
metal ion.
For the purposes of the present invention, the term "derive" means that the
monocyclic,
bicyclic or polycyclic ring system has at least one substructure which
corresponds to pyr-
CA 02650609 2008-10-28
-14-
role, alpha-pyridone or gamma-pyridone. Furthermore, two or all three
heterocycles can
also be present as substructure in the ring system.
For the purposes of the present invention, the term "derive" also means that
the three
abovementioned heterocycles can occur not in neutral form but, if appropriate,
also as an-
ion or cation so that the oxidation can also occur in the presence of these
ions.
Furthermore, it should be noted that at least one of the heterocycles which
represents a
substructure of the ring system is deprotonated during the reaction.
Furthermore, for the purposes of the present invention, the term "derive"
means that the
substructure of at least one of the three heterocycles can bear substituents
and one or
more ring carbons can be replaced by a heteroatom.
Of course, the ring system can also be one of the heterocycles pyrrole, alpha-
pyridone or
gamma-pyridone itself or the ring system can likewise be made up of
substructures which
are selected exclusively from the group consisting of pyrrole, alpha-pyridone
and gamma-
pyridone. In this case too, the above-described modifications are possible.
Finally, it should be noted that at least one hydrogen which in at least one
limiting structure
is not the hydrogen bound to said nitrogen is replaced by a bond by means of
which the
respective heterocycle is bound to the remainder of the ring system.
If a monocyclic ring system is present, this is derived from pyrrole or alpha-
pyridone or
gamma-pyridone.
However, the ring system can also be a bicyclic ring system. This is the case
when, for
example, two rings which are joined to one another via a covalent single bond
or via a
group R are present in the ring system. Here, one ring has to be derived from
pyrrole, al-
pha-pyridone or gamma-pyridone.
R can be -0-, -NH-, -S-, -N=N- or an aliphatic branched or unbranched
saturated or unsatu-
rated hydrocarbon which has from 1 to 4 carbon atoms and may be interrupted by
one or
more atoms or functional groups selected independently from the group
consisting of -0-, -
NH-, -S- and -N=N-.
Furthermore, the bicyclic ring system can be a fused ring system.
CA 02650609 2008-10-28
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Examples are, in particular, benzo-fused derivatives derived from pyrrole,
alpha-pyridone
and gamma-pyridone.
In addition, the bicyclic ring system can be a bridged ring system.
The ring system can likewise be a polycyclic ring system which has, for
example, 3, 4 or
more rings. Here, the rings can be joined via a covalent single bond and/or a
group R
and/or be fused and/or be present as a bridged ring system.
The ring system has at least two ring nitrogens. Here, at least one of the two
ring nitrogens
is that nitrogen which is present in the ring derived from pyrrole, alpha-
pyridone or gamma-
pyridone. In addition, at least one further ring nitrogen has to be present.
If the ring system
is one which has more than one ring, the at least second ring nitrogen can
also be present
in the ring derived from pyrrole, alpha-pyridone or gamma-pyridone or, if the
at least one
further ring is not derived from one of these three heterocycles, may be
located in this ring.
The at least two ring nitrogens are preferably present in one ring of the ring
system.
In this case, the ring is derived from pyrazole, imidazole, pyridazin-2-one or
pyrimidin-2-one
or pyrimidin-4-one.
In addition to the two ring nitrogens, further ring nitrogens can be present.
For example, the
ring system can have 3, 4, 5 or more ring nitrogens.
If more than two ring nitrogens are present, all ring nitrogens can be present
in one ring of
the ring system or can be distributed over more than one ring up to all rings
of the ring sys-
tem.
If, for example, three ring nitrogens are present, these are also preferably
present in the
ring which is derived from pyrrole, alpha-pyridone or gamma-pyridone. The
resulting sub-
structure of the ring can then be derived, for example, from a triazole, such
as 1,2,3-triazole
or 1,2,4-triazole.
In addition, the ring system can have further heteroatoms in the ring. These
can be, for
example, oxygen or sulfur. However, preference is given to no further
heteroatoms in addi-
tion to nitrogen being present.
CA 02650609 2008-10-28
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If the ring system has more than one ring, this ring can be saturated or
unsaturated. The at
least one further ring preferably has an at least partially conjugated double
bond system or
is aromatic in nature.
The ring system can be unsubstituted.
The ring system can also have one or more substituents. If a plurality of
substituents are
present, these can be identical or different.
The substituents bound to the ring system can be halogen, C1_6-alkyl, phenyl,
NH2, NH(C,_6-
alkyl), N(C1_6-alkyl)2, OH, Ophenyl or OC1_6-alkyl.
If at least one of the abovementioned substituents of the ring system is a
C1_6-alkyl or
phenyl, these can likewise be unsubstituted or bear one or more substituents.
When a plu-
rality of substituents are present, it is also possible here for them to be
identical or different.
These are selected from the group consisting of halogen, NH2, NH(C1_6-alkyl),
N(C1_6-alkyl),
N(C1_6-alkyl)2, OH, Ophenyl and OC1_6-alkyl.
If the group C1_6-aikyl occurs more than once, these alkyl groups can be
identical or differ-
ent.
For the purposes of the present invention, the hydroxy or keto group of alpha-
pyridone and
gamma-pyridone is not counted as a substituent since this group is necessarily
present in
the ring in order to obtain, at least for one limiting structure, a ring
nitrogen bound to hydro-
gen.
Preference is given to the substituents bound to the ring system having no
further substitu-
ents.
Preferred substituents bound to the ring system are C,_6-alkyl, phenyl, NH2
and OH. C1_6-
alkyl and NH2 are more preferred. Particular preference is given to C1_6-
alkyl.
In a further preferred embodiment, the ring system is selected from the group
consisting of
CA 02650609 2008-10-28
-17-
~ N ~ NN \ II \ \ I Na
\
N
N N N N N
H H H H
,
N~N N
N N N N N H
H H H H
I ~ x ( ) ~ N ~ ) i
N / N N N N N N'N N \N N
H H H H H
eN N-NN N NNUNN ~NH
H u TN-T u N O
U
N I\ ~ NN N~
N N
H H H H O
H
Xo
N)
NH
0
Further preferred ring systems are an imidazole, benzimidazole, triazole,
2-hydroxypyrimidine or 4-hydroxypyrimidine.
The at least one organic compound is very particularly preferably selected
from the group
consisting of 2-methylimidazoie, 2-ethylimidazole, benzimidazole, 1,2,4-
triazole, 3-amino-
1,2,4-triazole, 3,5-diamino-1,2,4-triazole, 2-hydroxypyrimidine and 4-
hydroxypyrimidine and
their deprotonated forms.
One of the above-described organic compounds can be used in the formation of
the porous
metal organic framework. However, it is likewise possible to use a plurality
of such organic
compounds.
CA 02650609 2008-10-28
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However, preference is given to only one of the above-described organic
compounds which
participates in the formation of the framework being used.
Accordingly, a preferred embodiment of the process of the invention for
preparing a porous
metal organic framework is obtained when the porous metal organic framework
comprises
only one organic compound of the type described above.
The at least one organic compound is used in a concentration which is
generally in the
range from 0.1 to 30% by weight, preferably in the range from 0.5 to 20% by
weight and
particularly preferably in the range from 2 to 10% by weight, in each case
based on the
total weight of the reaction system minus the weight of the anode and the
cathode. Accord-
ingly, the term "concentration" in this case comprises both the amount of the
at least one
organic compound dissolved in the reaction medium and, for example, any amount
of the
at least one organic compound suspended in the reaction medium.
In a preferred embodiment of the process of the invention, the at least one
organic com-
pound is added continuously and/or discontinuously as a function of the
progress of the
electrolysis and in particular as a function of the decomposition of the anode
or liberation of
the at least one metal ion and/or as a function of the formation of the porous
metal organic
framework.
It is also possible for further organic compounds whose presence is
advantageous for the
formation of a desired structure to be added as templates to the electrolyte.
In a particularly preferred embodiment of the process of the invention, the
reaction medium
comprises at least one suitable electrolyte salt. Depending on the at least
one organic
compound used and/or any solvent used, it is also possible in the process of
the invention
to carry out the preparation of the porous metal organic framework without any
additional
electrolyte salt.
The electrolyte salts which can be used in the process of the invention are
essentially not
subject to any restrictions. Preference is given to using, for example, salts
of mineral acids,
sulfonic acids, phosphonic acids, boronic acids, alkoxysulfonic acids or
carboxylic acids or
of other acidic compounds such as sulfonamides or imides.
Possible anionic components of the at least one electrolyte salt are
accordingly, inter alia,
sulfate, monoalkylsulfate such as monomethylsulfate, nitrate, nitrite,
suifite, disulfite, phos-
CA 02650609 2008-10-28
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phate, hydrogenphosphate, dihydrogenphosphate, diphosphate, triphosphate,
phosphite,
chloride, chlorate, bromide, bromate, iodide, iodate, carbonate or
hydrogencarbonate.
Possible cation components of the electrolyte salts which can be used
according to the
invention are, inter alia, alkali metal ions such as Li+, Na+, K+ or Rb+,
alkaline earth metal
ions such as Mg2+, Ca2+, Sr2+ or Ba2+, ammonium ions or phosphonium ions.
As ammonium ions, mention may be made of quaternary ammonium ions and
protonated
monoamines, diamines and triamines.
Examples of quaternary ammonium ions which are preferably used according to
the inven-
tion are, inter alia,
- symmetrical ammonium ions such as tetraalkylammonium preferably bearing C1-
C4-
alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-
butyl, e.g.
tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylam-
monium, or
- unsymmetrical ammonium ions such as unsymmetrical tetraalkylammonium prefera-
bly bearing C,-C4-alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-
butyl, isobu-
tyl, tert-butyl, for example methyltributylammonium, or
- ammonium ions bearing at least one aryl such as phenyl or naphthyl or at
least one
alkaryl such as benzyl or at least one aralkyl and at least one alkyl,
preferably C1-C4-
alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-
butyl, e.g.
aryltrialkylammonium such as benzyltrimethylammonium or
benzyltriethylammonium.
In a preferred embodiment, sodium methylsulfate or tributylmethylammonium-
methylsulfate
is used as electrolyte salt in the process of the invention.
In one, inter alia, preferred embodiment of the process of the invention, it
is possible for
compounds which are used for formation of the porous metal organic framework
to be in-
troduced into the reaction medium via the cationic and/or anionic component of
the at least
one electrolyte salt. In particular, at least one organic compound which is
comprised in the
resulting porous metal organic framework can be introduced via at least one
electrolyte salt
in the process of the invention.
CA 02650609 2008-10-28
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In an embodiment of the process of the invention, it is thus possible to
introduce the metal
ion into the reaction medium via the cationic component of the at least one
electrolyte salt
in addition to the at least one anode as metal ion source. It is likewise
possible for at least
one metal ion which is different from the at least one metal ion introduced by
means of an-
odic oxidation in terms of the valence of the cation and/or the type of metal
to be introduced
into the reaction medium via the cationic component of the at one electrolyte
salt.
The present invention accordingly also provides a process as described above
in which the
at least one electrolyte salt comprises a salt of the at least one organic
compound.
In the process of the invention, the concentration of the at least one
electrolyte salt is gen-
erally in the range from 0.01 to 10% by weight, preferably in the range from
0.05 to 5% by
weight and particularly preferably in the range from 0.1 to 3% by weight, in
each case
based on the sum of the weights of all electrolyte salts present in the
reaction medium and
more preferably based on the total weight of the reaction medium without
taking into ac-
count the anodes and cathodes.
If the process of the invention is carried out as a batch process, the
reaction medium com-
prising the starting materials is generally made available first, electric
current is subse-
quently applied and the medium is then circulated by pumping.
If the process is carried out continuously, a substream is generally branched
off from the
reaction medium, the porous metal organic framework comprised therein is
isolated and
the mother liquor (the remaining reaction medium) is recirculated.
In a particularly preferred embodiment, the process of the invention is
carried out so that
redeposition on the cathode of the metal ion liberated by anodic oxidation is
prevented.
According to the invention, this redeposition is, for example, preferably
prevented by using
a cathode which has a suitable hydrogen overvoltage in a given reaction
medium. Such
cathodes are, for example, the abovementioned graphite, iron, copper, zinc,
tin, manga-
nese, silver, gold, platinum cathodes or cathodes comprising alloys such as
steels, bronzes
or brass.
Furthermore, the redeposition is, according to the invention, preferably
prevented by, for
example, using an electrolyte which promotes the cathodic formation of
hydrogen in the
reaction medium. In this respect, preference is given, inter alia, to an
electrolyte which
comprises at least one protic solvent. Preferred examples of such solvents
have been
CA 02650609 2008-10-28
-21-
given above. Particular preference is given here to alcohols, in particular
methanol and
ethanol.
Furthermore, the redeposition is, according to the invention, preferably
prevented by, for
example, at least one compound which leads to cathodic depolarization being
comprised in
the reaction medium. For the purposes of the present invention, a compound
which leads
to cathodic depolarization is any compound which is reduced at the cathode
under given
reaction conditions.
As cathodic depolarizers, preference is given, inter alia, to compounds which
are hy-
drodimerized at the cathode. Examples of particularly preferred compounds of
this type are
acrylonitrile, acrylic esters and maleic esters such as, more preferably,
dimethyl maleate.
Further preferred cathodic depolarizers are, inter alia, compounds which
comprise at least
one carbonyl group which is reduced at the cathode. Examples of such compounds
com-
prising carbonyl groups are, for instance, ketones such as acetone.
As cathodic depolarizers, preference is given, inter alia, to compounds which
have at least
one nitrogen-oxygen bond, a nitrogen-nitrogen bond and/or a nitrogen-carbon
bond which
is/are reduced at the cathode. Examples of such compounds are, for instance,
compounds
having a nitro group, compounds having an azo group, compounds having an azoxy
group,
oximes, pyridines, imines, nitriles and/or cyanates.
It is also possible in the process of the invention to combine at least two of
the abovemen-
tioned measures for preventing the cathodic redeposition. For example, it is
possible to use
both an electrolyte which promotes the cathodic formation of hydrogen and an
electrode
having a suitable hydrogen overvoltage. It is likewise possible both to use an
electrolyte
which promotes the cathodic formation of hydrogen and to add at least one
compound
which leads to cathodic depolarization. It is likewise possible both to add at
least one com-
pound which leads to cathodic depolarization and to use a cathode having a
suitable hy-
drogen overvoltage. Furthermore, it is possible both to use an electrolyte
which promotes
the cathodic formation of hydrogen and to use an electrode having a suitable
hydrogen
overvoltage and also to add at least one compound which leads to cathodic
depolarization.
CA 02650609 2008-10-28
-22-
Accordingly, the present invention also provides a process as described above
in which
cathodic redeposition of the at least one metal ion is at least partly
prevented by means of
at least one of the following measures:
(i) use of an electrolyte which promotes the cathodic formation of hydrogen;
(ii) addition of at least one compound which leads to cathodic depolarization;
(iii) use of a cathode having a suitable hydrogen overvoltage.
The present invention therefore likewise provides a process as described above
in which
the electrolyte (i) comprises at least one protic solvent, in particular an
alcohol, more pref-
erably methanol and/or ethanol.
As has been indicated above, these measures are not absolutely necessary since
hydro-
gen deposition can in principle be possible and a satisfactory conductivity
can in principle
be present as a result of the at least one organic compound.
In a particularly preferred embodiment, the process of the invention is
carried out in the
circulation mode. For the purposes of the present invention, this
"electrolysis circuit" is any
procedure in which at least part of the reaction system present in the
electrolysis cell is
discharged from the electrolysis cell, if appropriate subjected to at least
one intermediate
treatment step such as at least one thermal treatment or addition and/or
removal of at least
one component from the discharged stream and recirculated to the electrolysis
cell. For the
purposes of the present invention, such an electrolysis circuit is
particularly preferably
combined with the use of a stacked plate cell, a tube cell or a pencil
sharpener cell.
The porous metal organic framework is typically present as a suspension. The
framework
can be separated off from its mother liquor. This separation can in principle
be effected by
means of all suitable methods. The framework is preferably separated off by
solid-liquid
separation, centrifugation, extraction, filtration, membrane filtration,
crossfiow filtration,
diafiltration, ultrafiltration, flocculation using flocculants such as
nonionic, cationic and/or
anionic auxiliaries, pH shift by addition of additives such as salts, acids or
bases, flotation,
spray drying, spray granulation or evaporation of the mother liquor at
elevated tempera-
tures and/or under reduced pressure and concentration of the solid.
The reaction medium separated off from the porous metal organic framework
(mother liq-
uor) can be discarded. However, it is preferably recirculated to the reaction
so that it is re-
used for the oxidation.
CA 02650609 2008-10-28
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The separation can be followed by at least one additional washing step, at
least one addi-
tional drying step and/or at least one additional calcination step.
If at least one washing step is carried out in the process of the invention,
washing is pref-
erably carried out using at least one solvent employed in the synthesis.
If at least one drying step is carried out in the process of the invention, if
appropriate after
at least one washing step, the framework solid is generally dried at
temperatures in the
range from 20 to 200 C, preferably in the range from 40 to 120 C and
particularly prefera-
bly in the range from 56 to 60 C.
Preference is likewise given to drying under reduced pressure, in which case
the tempera-
tures can generally be selected so that the at least one washing liquid is at
least partly,
preferably essentially completely, removed from the crystalline porous metal
organic
framework and the framework structure is at the same time not destroyed.
The drying time is generally in the range from 0.1 to 15 hours, preferably in
the range from
0.2 to 5 hours and particularly preferably in the range from 0.5 to 1 hour.
The at least one washing step which can be carried out if appropriate and the
at least one
drying step which can be carried out if appropriate can be followed by at
least one calcina-
tion step in which the temperatures are preferably selected so that the
structure of the
framework is not destroyed.
It is possible, for example, for at least one template compound which may, if
appropriate,
have been used for the electrochemical preparation according to the invention
of the
framework to be removed at least partly, preferably essentially
quantitatively, by, in particu-
lar, washing and/or drying and/or calcination.
The process of the invention for preparing a porous metal organic framework is
typically
carried out in water as solvent with addition of a further base. As a result
of the preferred
use of the organic solvent, it is not necessary to use such a base.
Nevertheless, the solvent
for the process of the invention can be selected so that it itself is basic,
but this is not abso-
lutely necessary for carrying out the process of the invention. In addition,
the organic sol-
vent can be present in admixture with water.
CA 02650609 2008-10-28
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It is likewise possible to use a base. However, preference is given to not
using any addi-
tional base.
In addition to or as an alternative to the abovementioned calcination and/or
washing steps,
the removal of the at least one organic compound (ligand) from the pores of
the porous
metal organic framework can be effected by treatment of the framework formed
with a fur-
ther solvent. Here, the ligand is removed in a type of "extraction process"
and may, if ap-
propriate, be replaced by a solvent molecule in the framework. This mild
method is particu-
larly useful when the ligand is a high-boiling compound.
The treatment preferably takes at least 30 minutes and can typically be
carried out for up to
2 days. This can occur at room temperature or elevated temperature. It is
preferably carried
out at elevated temperature, for example at at least 40 C, preferably 60 C.
The extraction
is more preferably carried out at the boiling point of the solvent used (under
reflux).
The treatment can be carried out in a simple vessel by slurrying and stirring
of the frame-
work. It is also possible to use extraction apparatuses such as Soxhlet
apparatuses, in par-
ticular industrial extraction apparatuses.
Solvents which can be used are, for example, C1_6-alkanol, dimethyl sulfoxide
(DMSO),
N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), acetonitrile,
toluene, dioxane,
benzene, chlorobenzene, methyl ethyl ketone (MEK), pyridine, tetrahydrofuran
(THF), ethyl
acetate, optionally halogenated C1_200-alkane, sulfolane, glycol, N-
methylpyrrolidone (NMP),
gamma-butyrolactone, alicyclic alcohols such as cyclohexanol, ketones, such as
acetone
or acetylacetone, cyclic ketones, such as cyclohexanone or mixtures thereof.
A C1.6-alkanol is an alcohol having from 1 to 6 carbon atoms. Examples are
methanol,
ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, pentanol,
hexanol and mix-
tures thereof.
An optionally halogenated C1_200-alkane is an alkane which has from 1 to 200
carbon atoms
and in which one or more up to all hydrogen atoms can be replaced by halogen,
preferably
chlorine or fluorine, in particular chlorine. Examples are chloroform,
dichloromethane, tetra-
chloromethane, dichloroethane, hexane, heptane, octane and mixtures thereof.
Preference is given to methanol, ethanol, propanol, acetone, MEK and mixtures
thereof.
CA 02650609 2008-10-28
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A very particularly preferred extractant is methanol.
The solvent used is preferably water-free.
Example 1 Zn"(2-methylimidazolate)2
The electrolyte consisting of 3.0 g of 2-methylimidazole, 4 g of NaMeSO4,
178.6 ml of
methanol and 71.4 ml of water was introduced into the cell circuit. A
conductivity of
4.8 mS/cm was measured.
The cell circuit comprised a tube cell, a glass cooler and a circulating pump.
The pump cir-
culated the electrolyte or the suspension formed at about 100 I/h.
The tube cell comprised a stainless steel tube (length: 10.2 cm, internal
diameter: 1.75 cm)
as cathode and a zinc rod as anode (length: 10.2 cm, diameter: 1.4 cm, surface
area:
45 cm2). The arrangement in the electrolysis cell ensured, by means of various
airtight
seals and screw connections, that the electrodes are positioned concentrically
and guaran-
tee a homogeneous gap all around between cathode and anode through which the
electro-
lyte thermostated to 20 C is pumped.
The cell was operated at a current of 0.5 A and a cell voltage of from 1.5 to
3.2 V for
1.9 hours (0.97 Ah) until a charge transfer of 1 faraday per mole of 2-
methylimidazole had
been reached. During the experiment, the cell was flushed with a stream of
inert gas to
remove hydrogen formed and to rule out formation of an explosive H2/02
mixture.
After the electrolysis was complete, the electrolyte was filtered and washed
with 2 x 50 ml
of MeOH. The crystalline product was dried at 80 C at 5 mbar and 3.4 g of Zn
(2-
methylimidazolate)2 were obtained (yield: 81%). The surface area was
determined by the
Langmuir method in accordance with DIN 66135 and was 1746 m2/g.
Example 2 Zn"(2-methylimidazolate)2
The electrolyte consisting of 76.1 g of 2-methylimidazole, 85.8 g of
methyltributylammo-
nium methylsulfate (MTBS), 1810 g of methanol and 750.2 g of water was
introduced into
the cell circuit. A conductivity of 4.8 mS/cm was measured.
CA 02650609 2008-10-28
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The cell circuit comprised a tube cell, a glass cooler and a circulating pump.
The pump cir-
culated the electrolyte or the suspension formed at about 600 I/h.
The tube cell comprised a stainless steel tube (length: 55 cm, internal
diameter: 5 cm) as
cathode and a zinc rod as anode (length: 55 cm, diameter: 1.94 cm, surface
area:
3.41 cm2). The arrangement in the electrolysis cell ensured, by means of
various airtight
seals and screw connections, that the electrodes are positioned concentrically
and guaran-
tee a homogeneous gap all around between cathode and anode through which the
electro-
lyte thermostated to 29 C is pumped.
The cell was operated at a current of 5.1 A and a cell voltage of from 4.6 to
5 V for
4.8 hours (24.6 Ah) until a charge transfer of 1 faraday per mole of 2-
methylimidazole had
been reached. During the experiment, the cell was flushed with a stream of
inert gas to
remove hydrogen formed and to rule out formation of an explosive H2/02
mixture.
After the electrolysis was complete, the electrolyte was filtered and washed
with 300 ml of
MeOH. The weight of the zinc anode was reduced by 29.0 g. The crystalline
product was
dried at 80 C at 1 mbar and 100.9 g of Zn"(2-methylimidazolate)2 were obtained
(yield:
98%). The surface area was determined by the Langmuir method in accordance
with
DIN 66135 and was 1718 m2/g.
Example 3 Zn"(benzimidazolate)2
The electrolyte consisting of 4.3 g of benzimidazole, 1 g of
methyltributylammonium me-
thylsulfate and 254.7 g of methanol was introduced into the cell circuit. A
conductivity of
0.5 mS/cm was measured.
The cell circuit comprised a tube cell, a glass cooler and a circulating pump.
The pump cir-
culated the electrolyte or the suspension formed at about 200 I/h.
The tube cell comprised a stainless steel tube (length: 10.2 cm, internal
diameter: 1.75 cm)
as cathode and a zinc rod as anode (length: 10.2 cm, diameter: 1.4 cm, surface
area:
45 cm) . The arrangement in the electrolysis cell ensured, by means of various
airtight
seals and screw connections, that the electrodes are positioned concentrically
and guaran-
tee a homogeneous gap all around between cathode and anode through which the
electro-
lyte thermostated to 30 C is pumped.
CA 02650609 2008-10-28
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The cell was operated at a current of 0.2 A and a cell voltage of from 3.0 to
7.9 V for
4.8 hours (0.97 Ah) until a charge transfer of 1 faraday per mole of
benzimidazole had
been reached. During the experiment, the cell was flushed with a stream of
inert gas to
remove hydrogen formed and to rule out formation of an explosive H2/02
mixture.
After the electrolysis was complete, the electrolyte was filtered and washed
with MeOH.
The crystalline product was dried at 50 C at 4 mbar and 9.5 g of
Zn"(benzimidazolate)2*7MeOH were obtained (yield: 98%). After 16 hours at 50 C
in a high
vacuum (loss in mass: 39%), the surface area was determined by the Langmuir
method in
accordance with DIN 66135 and was 465 m2/g.
