Note: Descriptions are shown in the official language in which they were submitted.
PF 72487 CA 02857230 2014-05-28
1
As originally filed
Process for preparing and purifying salts of acrylamido-2-
methylpropanesulfonic acid
Description
The invention relates to a process for preparing salts of acrylamido-
2-methylpropanesulfonic acid free of by-products or low in by-products
(hereinafter,
CAMPS or compound A). The invention relates more particularly to the
preparation of
sodium salt of compound A with a purity of at least 99%, especially at least
99.5%.
To date, purified salts of compound (A) have been prepared using acrylamido-
2-methylpropanesulfonic acid which has already been purified beforehand, but
this
leads to disadvantages. The literature describes numerous processes for
preparation
and for workup of the compound (A) obtained. There are also various known
process
routes for preparation of the salts.
A simple preparation process for compound (A) can be described by the reaction
scheme which follows, in which acrylonitrile in excess as a solvent and
reactant is
reacted with isobutene and sulfuric acid. The sulfuric acid used may also
comprise
varying proportions of free S03. In one embodiment, SO3 and water can also be
added
separately.
CH2 = CH ___________________ ON + (CH3)20 = CH2 + SO3 + H20
0 CH3 0 /
\\
I-12C
N OH
H CH3 (A)
In one embodiment of the preparation process, in a continuous operation,
acrylonitrile
is first fed in and then admixed with isobutene and oleum. However, it is also
possible
to perform a batchwise process (batchwise mode).
B11/72487PC
CA 02857230 2014-05-28
PF 72487
2
Compound (A) is a colorless crystalline solid which is only very sparingly
soluble in
acrylonitrile. For the further processing, the purity of the compound (A) or
salts thereof
is also of particular significance because impurities in the preparation of
polymers and
copolymers from compound (A) or salts thereof can entail very adverse
properties.
More particularly, this relates to the use of compound (A) as a monomer for
preparation
of high molecular weight polymers and copolymers as used, for example, in
mineral oil
production, but also flocculants, as fluid loss polymers and as cementing
polymers.
Patent US 4,337,215 describes a purification process for the preparation of
purified
2-acrylamido-2-methylpropanesulfonic acid. The starting material in the
process is a
crude crystalline precipitate of AMPS which has been obtained from the
reaction
mixture prepared in a known manner by washing the precipitate. The crude
crystals are
dissolved in acetic acid comprising 5 to 40% water. The amount of aqueous
acetic acid
required to completely dissolve the desired amount of compound (A) at 90 C
depends
on the water content. If the aqueous acetic acid has a water content of 10%,
it is used
in an amount of 4 to 5 times the weight of the crude crystals. The purified
crystals are
obtained by filtering the suspension at about 10 to 20 C.
US 4,701,283 discloses processes for preparing compound (A) and salts thereof,
and
copolymer-coated solid materials and copolymer emulsions in which the
copolymer is
prepared by polymerizing compound (A) with another monomer.
US 4,650,614 describes a process for purifying technical-grade 2-acrylamido-
2-methylpropanesulfonic acid, which is obtained by briefly heating the
sulfonic acid in a
slurry with a volatile monohydric alcohol and then recovering the sulfonic
acid by
decanting or another form of separation and subsequently drying the solid
moist
sulfonic acid.
US 6,331,647 describes the preparation and purification of acrylamidosulfonic
acid
monomers.
It is effected by reacting a contaminated acrylamidosulfonic acid with an
aqueous
solution of metal oxides or hydroxides, followed by crystallization.
Disadvantages of the
method are that a quantitative removal can be achieved only with high
complexity due
to the high solubility of the target products in water, and that a
purification of the target
products is made more difficult since some of the impurities crystallize out
of the
solution equally well or even preferentially. Particular mention should be
made here of
the sulfonic acids 2-methyl-2-propene-1-sulfonic acid (isobutenesulfonic acid,
IBSA)
and 2-methylidene-1,3-propenedisulfonic acid (isobutenedisulfonic acid,
IBDSA). Thus,
no high molecular weight polymers are achieved in the polymerization of
compound (A)
B11/72487PC
PF 72487 CA 02857230 2014-05-28
3
or of the sodium salt. A further principle secondary component obtained in the
operation is tert-butylacrylamide (ATB).
US 6,331,647 discloses a purification of the salt used with reference to the
reduction in
the peaks in an HPLC chromatogram. There is no mention of any sulfonic acids.
There
is likewise no discussion of the use of the purified salt for the preparation
of high
molecular weight polymers. It is not shown that the purification gives rise to
any
positive effect in use.
US-A 2010/274048 describes a process for preparing the compound (A), in which
a
product comprising less than 100 ppm of 2-methyl-2-propeny1-1-sulfonic acid
and less
than 100 ppm of 2-methylidene-1,3-propylenedisulfonic acid is obtained. The
purification is effected here primarily through crystallization -
subsequently, the content
of the troublesome secondary components is reduced down to the desired target
content by controlled washing and drying steps. Subsequently, the (A) obtained
can be
converted to the desired salt by reaction with bases analogously to the prior
art.
Another disadvantage of this process is the complex purification cycle with
high capital
costs.
It is an object of the present invention to provide a simple and improved
process for
preparing salts of compound (A) with high purity. More particularly, the
content of
organic impurities which have a disruptive influence in the polymerization is
to be
minimized.
These salts of acrylamido-2-methylpropanesulfonic acid are of significance as
monomers for preparation of very high molecular weight homopolymers and
copolymers. Various by-products of the preparation of compound (A) can lead to
unwanted products in the polymerization.
This object is achieved by a process for preparing salts of acrylamido-2-
methylpropanesulfonic acid (A) comprising the steps of:
a) preparing a solution of a contaminated salt of acrylamido-2-
methyl-
propanesulfonic acid (A) in an anhydrous organic solvent (L) using at least
one basic component (B) selected from the group of alkali metal oxides,
alkaline earth metal oxides, alkali metal hydroxides, alkaline earth metal
hydroxides and amines of the general formula (I)
NRa Rb Rc (I)
where the Ra, Rb and R radicals are each independently:
hydrogen, C1-C4-alkyl, hydroxy-C1-C4-alkyl or C1-C4-alkoxy,
B11/72487PC
PF 72487 CA 02857230 2014-05-28
4
where the molar ratio of compound (A) to the basic component (B) is
_ . preferably 1:1 to 1:3,
b) optionally partly removing the organic solvent (L) at a pressure in the
range
from 0.001 to 2 bar (abs),
c) recovering the dissolved salt of compound (A) by crystallization or by
precipitation, by altering the temperature and/or the pressure and/or the
concentration of the salt in the solution,
d) optionally drying the purified salt of acrylamido-2-
methylpropanesulfonic
acid (A).
The invention also relates to a process wherein the anhydrous solvent (L) used
is a
solvent from the group of: methanol, ethanol, propanol, butanol, acetonitrile,
acetone,
DMF, or a mixture of at least two of these solvents.
The invention also relates to a process wherein, in step a), an alkali metal
salt of
acrylamido-2-methylpropanesulfonic acid, especially the sodium salt, is used.
The invention also relates to a process wherein, in step a), a salt of
acrylamido-2-
methylpropanesulfonic acid (A) with an amine of the formula (I), especially a
trimethylammonium salt, is used.
The invention also relates to a process wherein, in step b), at least 50% by
weight of
the organic solvent (L) is removed at a pressure in the range from 0.001 to
0.5 bar
(abs).
The invention also relates to a process wherein, in step b), at least 60% by
weight of
the organic solvent (L) is removed while feeding in a gas, especially air.
The invention also relates to a process wherein, in step a), the solvent (L)
used is an
anhydrous C1-C3-alcohol, and, in step c), the purified salt is obtained from
an alcoholic
solution by temperature changes.
The invention also relates to a process wherein, in step c), the purified salt
is obtained
from the organic solution by pressure changes.
The invention also relates to a process wherein, in step c), the purified salt
is obtained
from the organic solution by changing the concentration and/or by adding a
further
organic component (NL).
B11/72487PC
PF 72487 CA 02857230 2014-05-28
The invention also relates to a process wherein at least steps a) and c) are
repeated
more than once. These steps (dissolution with anhydrous base, optional removal
of the
organic solvent and recovery of the salt) can be repeated, for example, 2 to
10 times,
especially 2 to 5 times, as a result of which a higher purity can be achieved
in each
5 case.
The invention further provides acrylamido-2-methylpropanesulfonic acid (A), or
a salt
thereof, preparable or prepared by a process as described. The free compound
(A) can
be prepared from the salt.
The invention also relates to acrylamido-2-methylpropanesulfonic acid (A) or a
salt with
a purity of at least 99.5%, especially with a purity of at least 99.8%.
Preference is given
to using sodium salts, especially with a purity of at least 99.9%.
The invention also relates to the use of acrylamido-2-methylpropanesulfonic
acid (A)
prepared by a process as described for preparation of copolymers.
Proceeding from a contaminated compound (A), the present invention can prepare
various high-purity salts of acrylamido-2-methylpropanesulfonic acid
comprising only
very small amounts of impurities, for example isobutenesulfonic acid (IBSA)
and/or
isobutenedisulfonic acid (IBDSA).
The content of these isobutenesulfonic acid (IBSA) and/or isobutenedisulfonic
acid
(IBDSA) by-products should preferably be a maximum of 100 ppm in total,
especially a
maximum of 70 ppm, preferably a maximum of 50 ppm. The invention also provides
a
sodium salt of compound (A) containing less than 100 ppm in total of (IBSA)
and
(IBDSA).
In step a) of the process, nonaqueous solutions of an alkali metal oxide or
alkaline
earth metal oxide, of an alkali metal hydroxide or alkaline earth metal
hydroxide and/or
of an organic amine of the general formula NRa Rb Rc are used. The Fe, Rb and
R`
radicals are each independently hydrogen atoms, or alkyl, hydroxyalkyl or
alkoxy
radicals having 1 to 4 carbon atoms.
In general terms, the invention is a process for preparing and purifying the
salts of
compound (A), in which a nonaqueous solution or suspension of an oxide,
hydroxide
or amine is used. The reaction of the contaminated compound (A) with the basic
component in an organic solvent gives rise to a salt.
The invention also relates to a process which is easy to implement in
technical terms
B11/72487PC
PF 72487 CA 02857230 2014-05-28
= 6
for obtaining a high-purity salt of compound (A), especially with a purity of
greater than
99%, especially greater than 99.5%, often greater than 99.7%.
This high-purity salt is suitable as a monomer for preparation of high
molecular weight
copolymers or homopolymers of this monomer. The polymers prepared are
suitable, inter
alia, as drilling aids, flocculants, fluid loss polymers and cementing
polymers.
To prepare the salts, for example, essentially organic solutions, especially
alcoholic
solutions, of an alkali metal oxide or alkaline earth metal oxide or alkali
metal hydroxide
or alkaline earth metal hydroxide or of an amine are used. The metal
hydroxides of the
metals of group IA and group IIA of the Periodic Table of the Elements are
preferred.
Specific examples of these metals are lithium, sodium, potassium, magnesium
and
calcium.
The particularly preferred metal of group IA is sodium, and the particularly
preferred
metal of group IIA is magnesium. Among the metal hydroxide solutions,
preference is
given to using an alcoholic solution of sodium hydroxide.
It is also possible to use a nonaqueous solution of an amine of the
abovementioned
general formula NRaRbRc. It is also possible to use an alcoholic solution of
ammonia.
The expression "essentially organic solution" means in the present context
that the
predominant solvent (L) is organic and water is present in the solvent only to
an extent
not exceeding 0.5% by weight, especially not exceeding 0.2% by weight, often
less
than 0.1% by weight.
Suitable anhydrous organic solvents in principle are alcohols, aldehydes,
ketones,
nitriles, esters and ethers having 1 to 4 carbon atoms, amides such as
dimethylformamide, or sulfoxides such as dimethyl sulfoxide. Preference is
often given
to lower alcohols.
The reaction of compound (A) with a base (B) gives a salt. There are no
technical
problems in the case of use of a molar excess of base (B). An excess of, for
example,
1 mol% to about 20 mol% is possible. In order to achieve salt formation, the
basic
component (B) can be admixed with compound (A) or vice versa. The salt
formation is
exothermic, and the heat which arises can be used to solubilize a maximum
amount of
salt in the solvent. The salt solution is generally subsequently cooled and a
solid salt is
obtained as purified product, for example by crystallization.
The reaction of compound (A) with the base (B) to give a salt is effected at a
temperature of 0 C to 80 C. Preference is given to performing the salt
formation at a
B11/72487PC
PF 72487 CA 02857230 2014-05-28
7
temperature of about 5 to about 50 C and especially of about 10 to about 40 C.
The molar ratio of compound (A) to base (B) in the salt formation depends on
the nature of
the base (B). If the base (B) is a metal of group IA, the molar ratio of
(A):(B) is about 1:1 to
2, preferably 1:1 to 1.10 and especially about 1:1 to 1.05. If the base (B) is
a metal of group
IIA, the molar ratio of (A):(B) is about 2:1 to 2, preferably 2:1 to 1.10 and
especially about
2:1 to 1.05. If the base (B) is an amine of the general formula NRaRbRc, the
ratio of moles
of compound (A) to the nitrogen atoms of base (B) is about 1:1 to 2,
preferably 1:1 to 1.10
and especially about 1:1 to 1.05.
The salt formed in this way is present in an organic solution. The solution
can
optionally be filtered to remove solid impurities. The salt of compound (A)
can be
recovered by subjecting the organic solution, for example, to changes in
temperature
and/or pressure and/or concentration.
It is also possible to add a further organic component (NL), for example a
compound in
which the salt of compound (A) is very sparingly soluble.
By increasing the temperature, optionally under reduced pressure, a portion of
the
solvent (L) is often removed, as a result of which the amount of salt present
rises
relative to the amount of solvent remaining. The removal of solvent at
elevated
temperature can be simplified by reducing the pressure. However, solvent (L)
can also
be removed by reducing the pressure at room temperature. By reducing the
temperature, the salt is removed due to the change in solubility of the salt
as a function
of temperature.
In each case, the salt can be obtained by oversaturating the organic solution.
Two
methods for achieving such an oversaturation are changing the temperature and
crystallization by stripping off the solvent. In the method of changing the
temperature, a
saturated solution is cooled to lower the solubility of the desired salt in
the solvent (L).
As a result of the lowering of the solubility, the salt crystallizes out of
the solution. In
the method of crystallization by stripping off the solvent, the solvent (L) is
removed
from the solution, either by heating or by reduced pressure, or a combination
of heating
and reduced pressure.
The reduced amount of solvent brings about the crystallization of the desired
salt. The
crystallization by changing the temperature and stripping off the solvent can
be
effected batchwise or continuously.
It is often advantageous that the organic solution is kept at a temperature
from -20 to
about 45 C. Temperatures above 45 C can lead to rapid formation of by-
products, or
B11/72487PC
PF 72487 CA 02857230 2014-05-28
8
else to the formation of polymers. Temperatures below about -20 C sometimes
cause
problems in the isolation of the salt from the organic solution.
In order to prevent polymerization, it may be helpful to use a polymerization
inhibitor.
Polymerization inhibitors are commercially available. A preferred
polymerization
inhibitor is hydroquinone monomethyl ether. In an evaporative crystallization,
the
solvent is distilled off under reduced pressure (less than 1 bar) to reduce
the distillation
temperature and to minimize by-product formation. A constant flow of a gas,
for
example of purge air or of another oxygen-comprising gas, can be supplied to
the
distillation operation.
The purity of the salts of compound (A) obtained in the process according to
the
invention can be determined, for example, by spectroscopic methods, for
example
H NMR and C-13 NMR.
Another possibility is a chromatographic removal (e.g. HPLC) of the by-
products
present in small amounts, which can then be determined quantitatively by means
of
standard methods.
The examples and claims which follow illustrate the invention.
Example 1
There follows an illustrative description of the preparation process for
compound (A) in
an acrylonitrile solvent on a customary laboratory scale, though the process
can also
be performed on a large scale:
15.5 mol (820 g) of acrylonitrile (AN) are initially charged at a temperature
of -10 C,
then two reaction mixing pumps are used together to supply 2.5 mol (140 g) of
isobutene (boiling point is -7.1 C) at a rate of 0.6 g/min, and 2.1 mol of
oleum (205.8 g)
at a rate of 22-28 ml/h. The supply takes about 3.5 h.
During the supply, the temperature rises constantly up to 2.7 C, while cooling
with a
thermostat (-10 C). The end of the supply is followed by warming to a
temperature of
20 C and stirring for a period of 10 min. This forms a milky suspension of
compound
(A) in the excess acrylonitrile solvent, and it is also possible in some cases
for residues
of isobutene and SO3 to be present.
The purification of compound (A) can be performed by crystallization as
follows:
The described milky suspension of compound (A) in excess acrylonitrile solvent
is
discharged from the reaction reactor and introduced into a second reactor. The
reaction reactor is rinsed once again with 550 ml of acetic acid (96%) and
likewise
B11/72487PC
PF 72487 CA 02857230 2014-05-28
9
supplied to the second redactor. The reaction mixture in the second reactor is
admixed
with 20 ml of water and heated under reflux (to about 87 C). The mixture is
stirred
under reflux for 10 min and then cooled. The precipitated compound (A) is
filtered off
with suction.
The solid can be dried at 70 C in a drying cabinet over several hours. This
gives
369.4 g of compound (A), which corresponds to a yield of 85%. The product,
however,
still comprises several % by weight of impurities.
.In the process according to the invention, in contrast, a contaminated
suspension of
compound (A) (obtained directly without purification or removal from the
reaction of
acrylonitrile, isobutene and oleum) is reacted with a substantially anhydrous
solution of
a base, preferably alkali metal hydroxides or alkaline earth metal hydroxides,
in one or
more polar solvents (L), for example methanol, ethanol, isopropanol, butanols,
acetonitrile, acetone, DMF or the like. Preference is given to using an
anhydrous
alcohol (preferably methanol) or a mixture consisting predominantly of alcohol
(preferably methanol).
A reaction with gaseous ammonia or trialkylamines as base (B) to give the
corresponding ammonium salts is also possible.
The resulting solution or else suspension of the salt in the organic solvent
comprises
impurities which can be removed by purification methods, for example
extraction or
crystallization. Therefore, a preferred procedure consists in the
recrystallization of the
resulting sodium salt from an organic solvent or else a mixture of two or more
organic
solvents.
In contrast to crystallization in an aqueous system, the desired product is
obtained in a
relatively high purity (greater than 94%). Especially the !BSA and IBDSA
impurities
which lead to chain termination in the polymerization and hence to a polymer
of lower
molecular weight are depleted by the process according to the invention.
The same applies to a further preferred procedure in which the still-
contaminated
product is first filtered and then washed with an organic solvent. A product
is obtained
in much higher purity than in the case of performance of the same procedure in
an
aqueous system.
A further advantage of working in a substantially anhydrous system is that the
removal
of the solvent or of the solvent mixture is distinctly simplified. The product
is also
obtained in a crystalline form which is easy to filter. It can be dried in a
simple manner.
B11/72487PC
PF 72487 CA 02857230 2014-05-28
= 10
In contrast, a crystallization from an aqueous system gives a product which is
much
harder to filter. The drying is also complex.
Example 2:
Preparation of the sodium salt of compound (A) (NaATBS,
anhydrous) directly from the reaction mixture
Acrylonitrile, isobutene and oleum were reacted with one another as described
above
to give an about 25% suspension of crystalline ATBS in acrylonitrile.
This solution was admixed at 5 C in a controlled manner with a solution of
NaOH in dry
methanol (18% NaOH in Me0H) until pH = 7.8 was attained. This gave a
homogeneous, pale yellowish solution with an NaATBS content of approx. 16.7%
by
weight (determination by calibrated HPLC), which was processed further
directly.
Example 3: Preparation of NaATBS from a substantially anhydrous
system
About 50 g of solvent were removed at room temperature under reduced pressure
and
while introducing air into the reaction solution from 100 g of a solution,
obtained
according to example 1, of NaATBS (16.77% by weight) in acrylonitrile and
methanol.
This gave a suspension of colorless, readily filterable NaATBS. The product
was
separated from the residual solvent by filtration and washed with further
acrylonitrile/methanol. This left 17.3 g of slightly contaminated, finely
crystalline
NaATBS (purity 94%). The proportion by weight of IBSA was 0.43%, the
proportion by
weight of ATB 1.7%.
Figure 1 shows an HPLC spectrum of the resulting product (A). It is evident in
the
HPLC spectrum that numerous unwanted secondary components, for example tert-
butylacrylamide, acrylonitrile, IBSS and IBDSS, are also present. It is thus
difficult to
obtain a polymer with sufficiently high molecular weight from the
polymerization of such
a product. The abscissa of the HPLC spectrum shows the time (0 to 17.5
minutes), the
ordinate the intensity.
Example 4:
Purification of NaATBS by crystallization from organic solvents
(substantially anhydrous reaction regime)
About 503 g of distillate were removed under reduced pressure and while
introducing
air into the reaction solution from 809 g of a solution, obtained according to
example 1,
of NaATBS (16.77% by weight) in acrylonitrile and methanol. 383 g of acetone
were
added to the remaining 306 g of solution and the mixture was cooled to 0 C.
After a
period of 15-20 min, NaATBS began to precipitate in the form of white
crystals. The
resulting precipitate was removed by filtration, washed with acetone and dried
cautiously at 70 C. This gave purified NaATBS of purity >> 95%, which no
longer
comprised any ATB and in which the proportion of IBSA had been reduced to 0.3%
by
weight. Repeated use of the method (recrystallization, washing) and drying at
110 C
B11/72487PC
PF 72487 CA 02857230 2014-05-28
11
led to NaATBS of high purity which was suitable for the preparation of
polymers of high
molecular weight.
Figure 2 shows an HPLC spectrum of the resulting product (A). It is evident in
the
HPLC spectrum that the level of unwanted secondary components has been
distinctly
reduced. More particularly, the IBSS and IBDSS secondary components which are
troublesome in the polymerization of monomer (A) have been reduced to < 100
ppm.
The abscissa of the HPLC spectrum shows the time (0 to 16 minutes), the
ordinate the
intensity.
Figure 3 shows an NMR spectrum of the resulting product (A). It is evident in
the NMR
spectrum that the resulting product has a very high purity. The abscissa of
the NMR
spectrum shows the shift (220 to 0 ppm) and the type of signal (s, d, t or q).
Such a
purified salt of compound (A) is suitable for preparation of polymers of high
molecular
weight.
Comparative example 1: Crystallization of sodium salt of compound (A)
NaATBS from water (analogously to US 6,331,647)
100 g of water were removed under reduced pressure and while introducing air
into the
reaction solution from 440 g of a 50% solution of NaATBS in water.
A viscous, honeylike precipitate was obtained, which was separable from the
filtrate by
filtration only with difficulty. The filtercake was dried at 35 C under
reduced pressure.
By repeating the procedure several times, a total of 224 g of slightly
contaminated
NaATBS (purity 94%) was obtained, which, after drying, was present as an
amorphous
solid. The proportion by weight of IBSA was 0.43% - thus, a salt of compound
(A)
obtained in such a way is unsuitable for achieving polymers of high molecular
weight.
The salt of compound (A) also comprised 4-5% by weight of water of
crystallization,
which could not be removed from the solid even by drying.
Comparative example 2: Purification of salt of compound (A)
NaATBS by crystallization from aqueous solution with
organic solvents
200 g of an about 50% solution of NaATBS in water (stabilized with 100 ppm of
MEHQ,
proportion by weight of IBSA approx. 0.4%) was admixed with 400 ml of acetone
at
20 C while stirring.
This gave a fine white precipitate which was removed from the mother liquor by
filtration. After cautious drying at 70 C, the solid was analyzed by
calibrated HPLC.
This gave a purity of NaATBS of 84.8% by weight with a proportion by weight of
IBSA
of 3.9%. This procedure thus enriched the unwanted IBSA secondary component.
B11/72487PC
PF 72487 CA 02857230 2014-05-28
12
Thus, the resulting product (A) (NaATBS) is unsuitable for achieving polymers
with high
molecular weight.
Figure 4 shows an HPLC spectrum of the resulting product (A). It is evident in
the
HPLC spectrum that numerous unwanted secondary components, for example tert-
butylacrylamide, acrylonitrile, IBSS and IBDSS, are present. The abscissa of
the HPLC
spectrum shows the time (0 to 17.5 minutes), the ordinate the intensity. Thus,
it is not
possible to obtain a polymer with sufficiently high molecular weight from the
polymerization of such a product.
B11/72487PC
