Note: Descriptions are shown in the official language in which they were submitted.
1058634
The present invention relates to a process for
producing racemic acid and mesotartaric acid by epoxidation of
an alkali salt of maleic acid with hydrogen peroxide in the
presence of alkali tungstates in an aqueous medium at elevated
temperatures, conversion into the free acid and subsequent hydrol-
ysis.
Several synthetic methods are known for producing
racemic acid from maleic acid by catalytic hydroxylation with
hydrogen peroxide. Thus, for example, free maleic acid is reacted
in aqueous solution with hydrogen peroxide in the presence of
alkali tungstates or molybdates, whereupon the intermediately
formed epoxy succinic acid is hydrolyzed by boiling and the racemic
acid thus formed is recrystallized from hydrolysis solution (see
Church and Blumberg, "Ind. Eng. Chem. 43 (8), 1780 ff"). The
mother liquor of the racemic-acid crystallization is recycled to
the reaction. The recycling and reuse of the mother liquor
after the crystallization is of decisive importance for the
economy of the synthetic production of racemic acid since the
mother liquor contains the tungstate or molybdate catalyst used
as well as a high proportion of maleic acid which cannot be
passed to waste. It is known that this process is carried out
so that approximately 60~ of the maleic acid used is reacted (loc.
cit.) However, the recycling of the mother liquor has great
disadvantages since during its circulation it may become contamin-
ated with impurities, which have an adverse effect onthe quality
of the racemic acid obtained.
It has now been found that on recycling the mother
liquor the rate of epoxidation substantially decreased because of
saturation with tartaric acid (see laid-open German Specification
No. 2,016,668). Further, in the epoxidation the tartaric acid
recycled with the mother liquor is irreversibly oxidized by hydro-
gen peroxide to valueless decomposition products such as formic
1058634
acid, carbonic acid and water (see laid-open German Specification
No. 2 016 668). In fact, according to the process of the laid-
open German Specification No. 2 016 668 attempts were made to
avoid the disadvantages described hereinbefore by, prior to the
recycling of the mother liquor, precipitating the tartaric acid
contained therein as a potassium or calcium salt. However, it
was found that the recovered calcium salt was not completely
free from tungsten and further that the tartaric acid may be
recovered from its salts only with some difficulty. Further,
the tungstate catalyst must be precipitated after several opera-
ting cycles as calcium salt and recovered therefrom or otherwise
its activity diminishes. Yet again the racemic acid obtained
by said process is not sufficiently pure for food purposes. When
racemic acid is to be used instead of tartaric acid in the food
industry, very high purity requirements must be satisfied with
respect to the content of maleic acid and fumaric acid as well
as with respect to the content of traces of heavy metals, i.e.,
in the present case with respect to the content of tungstate and
molybdate.
Since some of the processes described are carried out
with an excess of maleic acid (see Church and Blumberg loc. cit.
and laid-open German Specification No. 2,016,668), the racemic
acid must be crystallized from a solution rich in maleic acid and
is rendered impure by adhering maleic acid. Thus the higher the
yield in which the racemic acid is crystallized the greater the
impurity of the solution. Under the conditions of the reaction,
some of the maleic acid must undergo a change to fumaric acid.
Because of the sparingly solubility of the fumaric acid, said
acid crystallizes out together with the racemic acid, which is
thus rendered impure, and can be separated only with difficulty.
In the known processes the racemic acid obtained must
be crystallized from the solutions, which still contain the entire
-- 2 --
10S8634
catalyst. A complete separation of the catalyst is not possible
since particularly in the case of tungsten, the tungstic acid tends
to adhere to the crystallized racemic acid and renders it impure
until it assumes a blue coloration.
According to the laid-open German Specification No.
1,643,891 it is known that some of the disadvantages can be avoided
by producing calcium tartrate by the catalyzed reaction of acid
calcium maleate with hydrogen peroxide. However, it is difficult
to liberate racemic acid from calcium tartrate, for example, by
reaction with sulphuric acid as in the case of natural tartaric
acid. The solubility products of the gypsum thus obtained and of
calcium tartrate do not differ sufficiently so that losses are
caused by the tartrate content of the gypsum or when an excess of
sulphuric acid is used, then the tartaric acid must be recovered
from a solution containing sulphuric acid, whereby additional
difficulties are caused.
The production of mesotartaric acid from maleic acid
and hydrogen peroxide in the presence of tungstate, i.e., via
cis-epoxy succinic acid, has not been known. Mesotartaric acid
has been obtained, for example, only in the hydrolysis of trans-
epoxy succinic acid (see Kuhn and Ebel, Berichte 58 B, 919 (1925).
The present invention provides a process in which
racemic acid is produced in high yields and with a high degree of
purity, primarily the purity required for food, as well as mesotar-
taric acid while simultaneously recovering the catalyst.
It has now been found that racemic acid can be obtained
in a continuous or discontinuous process in high yields and with
a very high degree of purity in addition to mesotartaric acid by
the reaction of the alkali maleates with aqueous hydrogen peroxide
in the presence of alkali tungstate when the ratio of hydrogen
peroxide to maleic acid is greater than 1 and when thealkali salts
of the cis-epoxy succinic acid so formed together with the alkali
~058634
tungstate are converted into free cis-epoxy succinic acid and free
tungstic acid by passing them over a strongly acid cation
exchanger, when required after destroying the hydrogen peroxide,
whereupon hydrolysis of the free cis-epoxy succinic acid to
racemic acid and mesotartaric acid may be carried out either
in the presence of in the absence of tungstic acid. In the case
of the catalyst-free hydrolysis the tungstic acid is removed by
anion exchangers prior to the hydrolysis and in the case of the
catalyst-containing hydrolysis the tungstic acid is removed with
anion exchangers after the hydrolysis. The racemic acid is then
crystallized from the tungstic-acid-free hydrolysis mixture in a
conventional manner, when required by evaporation of water, and
by reducing the temperature, whereupon the mesotartaric acid
remains in the mother liquor and is removed therefrom by crystal-
lization or by evaporation to dryness, and is recovered when
required in mixture with tartaric acid, non-reacted cis-epoxy
succinic acid and maleic acid while the anion exchanger charged
with the tungstic acid is regenerated in a conventional manner
with a dilute alkali liquor and, if required, the solution of the
alkali tungstates is returned directly to the epoxidation stage,
if desired after treatment with active carbon.
According to the process of the present invention the
dl-tartaric acid is for the first time technically crystallized
from a solution which is practically free from tungstic acid and
is free from maleic acid except for an exceedingly small residue
and therefore can be recovered from this solution with a degree
of purity suitable for food.
It was also found for the first time that mesotartaric
acid is formed in the hydrolysis of cis-epoxy succinic acid
and it was found th~t its proportion is influenced by the manner
in which the hydrolysis is carried out, i.e., by the presence
or absence of the tungstate catalyst.
1058634
By combining the individual steps in accordance with
the invention, i.e., starting from the salts of the maleic acid,
which are reacted with excess hydrogen peroxide in the presence of
the tungstates by recovering both the free cis-epoxy succinic acid
and the free tungstic acid with the aid of cation exhangers as
well as by the hy~rolysis techniques described hereinbefore and
the removal of the tungstic acid by anion exchangers and by
processing the solution by fractional crystallization dl-tartaric
acid is produced having a high degree of purity and the mesotar-
taric acid so obtained is recovered. Further the tungstate
catalyst can be recovered in a very simple manner and virtually
quantitatively and recycled, in aqueous solution, directly to the
epoxidation stage without cumbersome processing. Again, the
process according to the invention can be carried out technically
in a simple manner as only aqueous solutions are used up to the
crystallization of the tartaric acid and the handling of solids,
which as is well known is difficult, is completely avoided.
Sodium, potassium and ammonium compounds, preferably
the sodium compounds are suitable as alkali maleates and alkali
tungstates. The amounts of alkali maleate are such that the
reaction takes place in a homogeneous mediumduring the entire time
of the reaction. When using sodium maleate the reaction solution
should preferably contain lO to 20% by weight of maleic acid.
The molar ratio of hydrogen peroxide to maleic acid
must be between l.01 and 5:1, preferably between l.l and 2:1. A
ratio between l.l and 1.3 : l is particularly favourable. The
starting concentration of the aqueous hydrogen peroxide solution
can be arbitrarily chosen. The excess of hydrogen peroxide should
be such that even in case of losses of hydrogen peroxide due to
decomposition there always is an excess of hydrogen peroxide relative
to maleic acid during the entire reaction.
The reaction is carried out at pH values between 3 and
1058634
5.5, preferably at pH values from 4 to 5 and at temperatures from
70 to 90C, although higher temperatures up to the boiling point
of the aqueous solution and lower temperatures down to the limit
of solubility of the maleate applied or of the epoxy succinate
formed during the reaction are feasible.
The catalyst, i.e., the alkali tungstate may be used
in amounts of 0.5 to 5, preferably 1 to 2 mole %, relative to the
maleic acid used.
The reaction of sodium salts of maleic acid with
hydrogen peroxide in the presence of sodium tungstate to the sodium
salts of cis-epoxy succinic acid also is known (see G.B. Payne,
P.H. Williams, J. org. Chem. 24 (1959), 54), but their conversion
corresponding to the further steps of the process according to
the invention for producing tartaric acid is not known.
In the process according to the invention the alkali
maleate can be used in a prepared form or it can also be formed
_ situ in the reactor. Maleic acid or maleic anhydride can
be used as the starting material.
After the epoxidation reaction the hydrogen peroxide
and the other peroxide compounds, such as per tungstates are, if
required removed. For removing the peroxide compounds known
chemical reactions and the known decomposition of these compounds
which is catalyzed by metals can be used. The operation is pref-
erably so carried out such that the solution is not rendered
impure and a catalyst containing platinum on a solid support is
used, for example, 0.01 to 5% by weight of platinum on a chemically
inert support material having very few pores and consisting of
more than 90~ of SiO2, preferably 0.05 to 0.5% of Pt. With this
catalyst the peroxide compounds can be decomposed in the solutions
concerned at temperatures from 20 to 100C, preferably from 60
to 80C, under standard pressure.
A particularly preferred manner of carrying out the
1058634
process up to the stage of the peroxide decomposition is explained
hereafter with reference to the accompanying drawing in which,
Figure l is a flow sheet of the process according
to one embodiment of the present invention.
An aqueous solution of hydrogen peroxide and maleic
acid is fed through pipe 17 and an aqueous solution of sodium
tungstate and a solution of caustic soda are fed through pipe 18
into a continuously operated reactor, which works as an ideal
vessel with stirrer with complete remixing of the solution, which
is kept at a constant temperature by a heat exchanger. From the
reactor l the solution flows into a reactor 2, which is basically
equipped in the same way as reactor 1 and into which, if required,
additional aqueous solution of caustic soda can be fed through
the pipe 20 in order to adjust to a desired pH value. Oxygen,
which may be formed by decomposition of hydrogen peroxide exhausts
respectively through the pipes l9 and 21.
The reaction mixture leaving the reactor 2 is fed to a
secondary reaction zone, asa flow pipe in the form of 3 through
pipe 22. The reacted mixture is fed through pipe 23 from pipe
3 found from below into the column 4. Column 4 is filled with
a decomposition catalyst and the oxygen formed by decomposition
leaves the column 4 through the pipe 24 while the solution flows
through the pipe 25 into an intermediate tank 5, in which it must
be kept at a temperature above the temperature of crystallization
of the dissolved solids.
As strongly acid cation exchangers for producing the
free cis-epoxy succinic acid all the commercial types, primarily
those based on polystyrene, or polystyrene divinly benzene, may
be used, preferably those containing free sulphonic-acid groups.
For successfully carrying out the process it is immaterial whether
known parallel-flow, counterflow or continuous ion-exchange
processes are used. However, it is advantageous to carry out the
1~58634
regeneration of the cation exchange resin in a counterflow to the
charging, whereby the process is not limited. In this manner the
known advantages of the counterflow process, such as low residual
content of alkali in the exchanged solution and low requirement
of regenerating agent, and thus its greater economy are utilized.
Methods which avoid the exchanged solution being too highly diluted
with the wash water obtained in the regeneration of the exchange
resins are particularly favourable since the water of dilution
must be additionally evaporated in the subsequent processing.
A particularly preferred method of producing the cis-
epoxy succinic aid by ion exchange is also set forth in Figure 1.
The solution in the tank 5 is fed at a temperature
above the crystallization temperature through the pipe 26 and
from below into column 6, filled with ion exchange resin. From
column 6 the solution is fed through pipe 26a into a similar column
7, which is operated as a fine purifier. An aqueous solution of
the epoxy-succinic acid and tungstic acid runs off at the top
of the column 7 through pipe 27. The column 6 is preferably
operated until alkali escapes, whereupon the pipe 26 is switched
over to column 7, a freshly regenerated column 8 serving as the
fine purifier and column 6 then is in turn regenerated. When
this manner of carrying out the process is continued a quasi-
continuous flow can be obtained. It was found to be favourable
that the exchange bed be so dimensioned that the operation is
carried out below a velocity of flow at which the resin is
suspended or fluidized which fluidization tends to detract from
the ion exchange. This method also does not require additional
technical devices for operating countercurrent filters (see K.
Dorfner, ion exchangers, Walter de Gruyter & Co., Berlin (1970).
The method described above can be carried out in a particularly
simple manner, especially in association with the process according
to the invention since, primarily, the reaction in the-reactors 1,
1058634
2, 3 and 4 defines the concentration and the mass flow (per hour)
of the solution to be exchanged by the cation exchange columns
6, 7 and 8 so that higher mass flows per hour which cause the
suspension of the resin and reduce the efficiency of the exchange
are not required.
The washing of an exhausted exchange column and its re-
generation will now be explained hereafter with reference to
Figure 1, using column 8 as an example. This method has proved to
be particularly advantageous with respect to saving wash water
and preventing the product solution from being diluted too much
while the losses of product are only low. Thus, the process can
be so carried out that the solution in the column is displaced
by a subsequent solution. It is merely necessary to take precau-
tions that the regenerating acid is not mixed with the flow of
product.
The contents of the column 8 is returned first to
the tank 5 through the pipe 28, the tank 9 and the pipe 29 and
then rewashed with preconcentrated wash water from tank 10, pipe
31 and column 8. The discharge from column 8 also returns to
the tank 5 through the pipe 28, tank 9 and pipe 29, whereupon
it is rewashed with distilled water through the pipe 32. This
discharge is fed to the tank 10 through the pipe 28, tank 9 and
pipe 30 and is reused in the next cycle. The subsequent regener-
ation with rewashing can be carried out in a conventional manner,
for example, with dilute hydrochloric acid, as defined by the resin
producers, through the pipes 33/34 and 35. It is advantageous
to drain the last wash water and to charge the empty column 8 in
order to avoid unnecessary dilution of the product.
The aqueous solution of epoxy succinic acid and tungstic
acid which is obtained after the cation exchanger and still contains
small amounts of non-reacted maleic acid and small amounts of
tartaric acid is then reacted to form tartaric acid at temperatures
1058634
from 50 to 200C, preferably at temperature~ from 100 to 150C.
The procedure may be such that the solution, through the pipe 27,
is boiled directly in the tank 11, for example, for 5 hours under
reflux. However, the procedure may also be such that the solution
from pipe 27 is passed through the pipe 37 to the anion exchangers
13 and 14 at temperatures of approximately 20 to 95C. These
temperatures are limited by the stability of the anion exchangers.
The solution of the epoxy succinic acid, which is free from tungstic
acid and is discharged through the pipe 40, is then hydrolyzed.
The hydrolysis of aqueous cis-epoxy-succinic acid solution is known
(see R, Kuhn and F. Ebel, Ber. 58 B, 919 (1925); G. Wode, Svensk
Kem. Tids. 40, 221 (1928) and C.A. 23 (1929, 2344 as well as laid-
open German Specification 2 400 767).
Surprisingly it was found that the proportion of mesotar-
taric acid, which is unexpectedly formed in the hydrolysis of the
cis-epoxy succinic acid, depends on whether the hydrolysis is carried
out prior to or after the anion exchange. This is so much more
surprising since according to R. Kuhn et al. (loc. cit.) and the
laid-open German Specification No. 2,400,767 even in the hydrolysis
of an aqueous solution of cis-epoxy succinic acid, which correspon-
ds to the solution obtained after the anion exchanger in the process
according to the invention, only dl-tartaric acid is formed.
However, according to the process of the invention it
was found that the proportion of mesotartaric acid formed can be
substantially reduced when the hydrolysis is carried out in the
presence of 0.1 to 5, preferably 1 to 2 mole % of tungstic acid
relative to the cis-epoxy succinic acid, i.e., prior to the anion
exchange as will be seen from Examples 4 and 5 given hereinafter.
According to the process of the invention it is also
possible to so adjust the conditions according to requirements that
selectively more or less mesotartaric acid is formed. Thus,
depending on requirements, more or less dl-tartaric acid can be
-- 10 --
1058634
obtained and in cases in which dl-tartaric acid can be used only
insufficiently or not at all it can be made up or replaced by
mesotartaric acid. For example, this is the case when the
solubility of the dl-tartaric acid is not sufficient for specific
purposes. Since the dl-tartaric acid differs from the natural
tartaric acid by its substantially poorer solubility while the
solubility of mesotartaric acid is close so that of natural
tartaric acid, a solution having higher proportions of mesotartaric
acid can be produced whenever the solubility of the dl-tartaric
acid is not sufficient for the purpose concerned in a technical
field of application, as for example, in the building material
industry or in the galvanic industry.
The use of anion exchangers for removing tungstate-
containing compounds even in the presence of polybasic, complex-
forming acids, such as citric acid, is known per se (see D. Shishkov,
E. Koleva, Doklady, Bolg. Akad. Nauk 17 (10) 909 (1964) and C.Z.
(1966) 27-538). It was found that there usually is a possibility
of purifying racemic-acid solutions by passing them over anion
exchangers. Any type of commercial anion exchanger can be used,
preferably weakly basic anion exchangers based on polystyrene or
polystyrene/divinyl benzene and having macroporous structures and
amino functions as exchange-active groups.
In the process according to the invention it is immater-
ial whether the anion exchange is carried out by means of a known
parallel-flow, counterflow or continuous ion-exchange process.
This exchange process is also shown in Figure 1, i.e., in the
columns 12, 13 and 14 which can be correspondingly controlled as
described for the cation exchange in the columns 6, 7 and 8.
Accordingly three columns are used which are charged from below in
a counterflow to the regeneration. Two of these columns are in
series connection while the third column is in the regeneration.
The first exchange column is operated preferably up to the discharge
1058634
of tungsten while the second exchange column, which is always
freshly regenerated, serves for fine purification. At variance
with the cation exchange, one of the usual countercurrent techni-
ques, for example, the fluidized bed process, must be applied
(see Dorfner loc. cit.). The regeneration and washing of an
exhausted column are described with reference to Figure 1, using
the column 12 as an example, that is to say a most favourable
method. The contents of the column 12 is displaced first with
distilled water through pipe 47 and returned by way of the pipe 39
for use in the anion exchangers 13 or 14. As little water as
possible is used so that the product is not unnecessarily diluted.
Usually 1 to 5 bed volumes of water are sufficient. Then, as
recommended by the resin producers, theregeneration is carried out
with dilute solution of caustic soda through the pipe 48/49 and
the regenerate is washed with water until it is free from alkali.
The regenerate running off through pipe 50 contains the tungstate
catalyst in addition to small amounts of tartaric acid, epoxy-
succinic acid and maleic acid and/or their sodium salts. In a
diluted aqueous solution said tungstate catalyst can be returned
to the reaction stage almost quantitatively and can be used, for
example, for preparing the mixture in pipe 18.
It is required to install at least sufficient anion
exchange resin in the columns 12, 13 and 14 such that the regener-
ation and the washing of an anion exchange column by the capacity
of the installed resin occurs only so infrequently so that the
amount of water introduced with the wash water and with the dilute
solution of caustic soda and returend through pipe 50 can be used
for the production of the solution fed into the reactors l and 2
through pipes 17, 18, and 20.
Prior to its reuse the regnerate in pipe 50 is treated
with active carbon since it was found that when carrying out the
process continuously yellowish-brown impurities are occasionally
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10S8634
adsorbed to the anion exchange resin. During the regeneration of
the resin said impurities get into the regenerate in pipe 50 and
render it impure. The purification can be so carried out that 0.05
to 1% by weight, preferably 0.1 to 0.4~ by weight of active carbon,
relative to the solution, is stirred in, preferably at room
temperature. After a period of 5 minutes to 5 hours the solution
is filtered off the active carbon and the completely uncolored
solution is reused. Temperatures higher or lower than room temper-
ature can also be used. Methods other than the stirring-in method,
for example, columnar methods, in which the colored solution
is passed over an active-carbon tower, can also be used.
The solution present in pipe 40 after hydrolysis and
anion exchange can then be processed. Such solution is essentially
free from tungstic acid and contains the entire dl-tartaric acid
as well as corresponding amountsof mesotartaric acid and possibly
unreacted epoxy succinic acid in addition to small amounts of
maleic acid, which was either not reacted or not separated at
the anion exchanger, or traces of fumaric acid (see Church and
Blumberg loc. cit.).
If required, after evaporating water, the solution is
cooled, the racemic acid is filtered off, rewashed with water and
subsequently dried. For example, after evaporating to dryness,
the mesotartaric acid can be recovered in mixture with non-crystal-
lized racemic acid and the residual contents of maleic acid cis-
epoxy succinic acid. The evaporation is suitably carried out at
temperatures between 40 and 50C, preferably between 60 and 110C
and the crystallization at temperatures from 1 to 25C.
In order to produce particularly pure racemic acid, the
solution is suitably subjected to fractional crystallization. For
this purpose, in a preferred manner of carrying out the process
(see Fig. 1) the solution is passed from the pipe 40, for example,
to a rotary evaporator 15, in which a partial amount of water is
- 13 -
10581634
distilled off through pipe 41, under vacuum or pressure.
The amount of water depends on the concentration of the
solution of racemic acid, mesotartaric acid, cis-epoxy succinic
acid and maleic acid coming from the anion exchanger and on the
expected degree of purity of the racemic acid. The solution with
increased concentration is fed to a crystallization and filtration
stage through pipe 43 so that racemic acid which had been once
crystallized is obtained in pipe 45 and the aqueous mother liquor
(referred to hereafter as Mula I) is obtained in pipe 46. The
pipes 42 and 44 serve merely for ventilation and for maintaining
the pressure.
The Mula I thus obtained can then be evaporated in a
corresponding manner to a further racemic acid fraction, which can
have a lower degree of purity corresponding to the solubility and
concentration of the other components. The number of fractions
can be chosen arbitrarily. However, it is favourable to crystallize
not more than 2 to 4 fractions and to evaporate the last mother
liquor to dryness.
When processing the last mother liquor it was found to
be favourable that said mother liquor contains as little cis-
epoxy succinic acid as possible since this acid does not readily
crystallize and tends to stick, thus rendering the processing
more difficult. However, since even at high reaction rates of 98
to 99% of cis-epoxy succinic acid in the mother liquors during the
hydrolysis the concentration increases distinctly, it is, technical-
ly speaking, particularly favourable to carry out the evaporation
under conditions at which the hydrolysis of the epoxy succinic acid
is continued (see Example 2 hereinafter)in order to avoid long
reaction times for the actual hydrolysis in the tank 11. For example,
a mother liquor can be subjected, with advantage, to an after-
saponification (see Example 3 hereinafter) since at this point the
total volumne of the solution is distincltly lower than that of the
- 14 -
~058634
solution in the only hydrolysis in tank 11 and since thus only
small tanks are required.
As mentioned hereinbefore, the advance in the art of
the process according to the invention lies first in the produc-
tion or racemic acid, which is very pure with respect to maleic
acid, fumaric acid and impurities caused by the catalyst.
According to Deutsches Arzneimittelbuch 7, for natural
tartaric acid and maximum content of heavy metals (in terms
of lead) of 20 p.p.m. is admissible. The tungsten content of the
dl-tartaric obtained by means of the process according to the
invention is lower than S p.p.m. According to the US Food Chemical
Index of 1966, dl-malic acid, which is produced from maleic
acid and is used in the food sector, may contain a maximum of 0.05%
by weight of maleic acid and 0.7% by weight of fumaric acid.
The dl-tartaric obtained according to the process of the invention
contains less than 0.02% by weight of maleic acid and fumaric
acid and thus has the degree of purity required for food. Moreover,
as mentioned hereinbefore, the process according to the invention
is technically easy to carry out since only aqueous solutions
are used up to the crystallization of the tartaric acid. Further,
the recovered catalyst can be immediately returned to the
reaction stage.
The present invention will be further illustrated by
way of the following Examples.
Example 1
The process is carried out in an apparatus corresponding
to Figure 1. The data hereafter relate to a continuous procedure
upon reaching the steady state.
2.27 moles/h of maleic acid and 2.76 moles/h of H2O2 in
820 g/h of an aqueous solution are fed to reactor 1 through pipe
17 and 3.6 moles/h of NaOH and 0.032 mole/h of Na2WO4 in 830 g/h
of an aqueous solution are fed to reactor 1 through pipe 18.
1058634
Small amounts of an acid mixture recycled through pipe 50 are
also fed to reactor 1. Moreover, 80 g/h of an aqueous solution
with 0.395 mole/h of NaOH are additionally added in reactor 2
through 20. The reactors 1, 2 and 3 are operated at a temperature
of approximately 80C. The operating volume of reactor 1 is
1650 ml and that of reactor 2 is 1280 ml. The secondary reaction
zone 3 consists of a tube having a length of 5.40 m and a
diameter of 38 mm. The tube is packed with 4 mm Raschig rings.
The column 4 is operated at approximately 80C and con-
sists of a tube (38 mm diameter), which is filled with 1100 ml of
a catalyst consisting of 0.1% of platinum on a chemically inert
support having very few pores. More than 90% of said support
consists of silicon dioxide. The granular size of said support is
between 3 and 5 mm.
The residual content of H2O2 in the mass flow in the pipe
23 is approximately 0.6%. Upon leaving the decomposition catalyst
the hydrogen peroxide in the pipe 25 is almost quantitatively
destroyed. Approximately 1720 g/h of an aqueous solution, which
contains approximately 0.011 mole/h of maleic acid and 0.25 mole/h
of tartaric acid in the form of their sodium salts in addition
to cis-epoxy succinic acid flow through pipe 25 into the intermediate
tank 5, which is kept at a temperature of 40C. The solution is
fed to the cation exchangers 6 and 7 through pipe 26, which is
heated to approximately 40C. The diameter of the exchange columns
is 10 mm. The columns are filled with approximately 11 litres
of a cation exchanger, based on polystyrene containing free sulphon-
ic acid groups, and a small amount of inert resin. In the swollen
state the exchange resin fills approximately 95% of the free space
between two sieve plates.
At the beginning of the charging cycle column 4 is
filled with product and column 7 is emptied after the regeneration.
An average of 3500 to 4000 g/h is conveyed at a constant flow
- 16 -
~058634
from the tank 5 corresponding to the feed through pipes 25 and
29. As soon as the sodium ions start to break through at the top
of the column 6 the flow through pipe 26 is switched over to
column 7, from where it is conveyed to the completely regenerated
column 8. The washing and regenerating of an exhausted column is
explained hereafter,using the column 8 as an example. First, the
column 8 is emptied into tank 9 through pipe 28. From tank 9 the
flow is returned to tank 5 through pipe 29. The preconcentrated
wash water in tank 10 is then used for rewashing. The discharge is
also returned to tank 5 by way of the tank 9. The column 8 is then
rewashed with 4.5 kg of water completely free from salt. This
water is returned through pipe 28 tank 9 and pipe 30 to tank 10.
The column is then regenerated with 13.5 kg of a 6.5% by weight
hydrochloric acid through the pipe 33/34 and rewashed with 15
litres of water, which is completely free from salt. On the average,
the washing and regenerating operation must be repeated every
4.5 to 5 hours.
From pipe 27 an average of approximately 2700 g/h of
an aqueous solution of cis-epoxy succinic acid containing 11 mole
~ of tartaric acid, relative to the total acid, traces of maleic
acid and the entire tungstic acid flows to the tank 11 in a
concentration of 0.84 mole of dibasic acid per 1000 g. The
washing operation at the cation exchanger merely resulted in a
dilution of approximately 64% of the initial concentration of losses
amounting to approximately 0.5% of the material applied. In tank
11 the solution is boiled for 5 hours under reflux at approximately
100C. In order to make the further operation continuous, a second
tank is run in parallel in a two point control arrangement (not
shown).
On completing the hydrolysis and cooling to room
temperature, 2700 g/h of an aqueous solution are passed through
pipe 37/38 from below over the anion exchange columns 13, 14. The
1058634
anion exchange columns 13 and 14 are in cascade connection.
Along with the aqueous solution 2.03 moles/h of racemic acid,
0.13 mole/h of mesotartaric acid, 0.06 mole/h of cis-epoxy succinic
acid and 0.01 mole/h of maleic acid as well as the entire tungsten
catalyst are conveyed. Three columns having inside diameters of
approximately 43 mm are used as anion exchangers and filled with
approximately 1.3 litres of a macroporous, monofunctional weakly
basic anion exchange resin based on polystyrene, occupying
(in the non-charged state) approximately 60% of the space between
two sieve plates. The ion exchange is carried out according to
the fluidized bed process. After 24 hours when the tungsten
breaks through a column is regenerated as previously described and
is switched, as a fine purification column, behind the column
which is operated to the change-over point as a fine purification
column.
The washing and regenerating operation is described here-
after, using the column 12 as an example. First, the column con-
tents is displaced with 3.5 kg of water, which is completely free
from salt, through pipe 47 and returned through pipe 39. Accord-
ing to the data provided by the resin producer, 3.2 kg of a 4% by
weight solution of caustic soda are used for regenerating through
the pipe 48/49, whereupon 5.2 kg of water, which is completely
free from salt, are used for washing until the solution is free
from alkali. In order to prevent the product from being diluted,
the water level is always kept only slightly above the resin.
In order to remove a yellow colouration, the aqueous
regenerate is treated for approximately 30 minutes with 0.2% of
pulverized active carbon and then filtered off the active carbon,
whereupon it is returned through the pipe 50 for reuse.
On the average per unit of time 2.23 moles/h of dibasic
acids and approximately 2500 g/h of water flow through pipe 40 and
are fed to a rotary evaporation 15, in which approximately 1400 ml
- 18 -
105~634
of water per hour are evaporated in vacuo at a temperature of
approximately 80C through pipe 41. The solution, whose concentra-
tion is thus increased, is discontinuously cooled in a vessel
with stirrer (not shown) to approximately 5C. The crystallized
racemic acid is filtered off and twice rewashed with 10% by
weightof cold distilled water, relative to the solids. Upon
drying (converted into gram per hour) 209g/h, i.e., 61,5% (rela-
tive to maleic acid) of a racemic acid containing a maximum of
2 to 3 p.p.m. of tungsten and less than 0.02% of maleic acid and
fumaric acid are obtained.
Approximately 1200 g/h of the mother liquor of this
first inlet state still contain 96% of racemic acid, 19.5 g of
mesotartaric acid, 7.9 g of cis-epoxy succinic acid and 1.1 g
of maleic acid. On evaporating approximately 800 ml/h of water at
approximately 80C, followed by crystallization at approximately
5C and rewashing with cold water as in the first crystallization
and drying, 74 g/h of dl-tartaric acid (21.6% relative to maleic
acid) containing approximately 0.02 to 0.03% of maleic acid,
less than 0.02% of fumaric acid and less than 5 p.p.m. of tungsten
are obtained.
The mesotartaric acid fraction of 15.1%, relative to
maleic acid, can be obtained by evaporation to dryness. It contains
38.5% by weight of mesotartaric acid in addition to 43.5% by
weight of racemic acid, 15.6% by weight of epoxy succinic acid
and 2.4% by weight of maleic acid. The mixture as such can be
used industrially. However, it can also be purified by further
fractional crystallization and the racemic acid can be separated
more completely.
From the regenerate of the ion exchanger in pipe 50,
8.9 kg of a solution containing 247.7 g of sodium tungstate, i.e.,
99.75% of the amount used, and samll amounts of the sodium salts of
acid encountered in the reaction are obtained every 24 hours.
-- 19 --
1~58634
This solution-made up with caustic soda solution, water
and very small amounts of sodium tungstate-results in a mixture
which i9 fed into the reaction stage directly through the pipe 18.
Example 2
A flow of 2500 g/h of H2O and an average of 2.23 moles/h
of dibasic acids are drawn off through pipe 40, as explained in
Example 1, but the flow is then fed to a rotary evaporator having
an operating content of 1950 ml. In said rotary evaporator
approximately 1400 ml of water are evaporated under pressure at
a boiling temperature of 112C, followed by processing as
described in Example 1. Thus, in the first crystallization 62.5%
of racemic acid (relative to maleic acid) of corresponding purity
are obtained. After the secondevaporation and crystallization,
which is carried out as in Example 1, 22% of racemic acid having
the same purity as in Example 1 are obtained. Then, on evapora-
tion to dryness a mixture of mesotartaric acid (6%), racemic
acid (6%), maleic acid (0.5%) and epoxy succinic acid (0.3%),
each percentage relative to maleic acid used is obtained.
In contrast to Example 1, in which a mesotartaric acid
fraction containing 15.6~ of epoxy succinic acid is obtained,
the mesotartaric acid fraction obtained in the present case
contains only 2.1% of epoxy succinic acid, the difference being
converted into racemic acid and mesotartaric acid. Moreover,
a less tacky product is thus obtained, facilitating the processing.
Example 3
In order to improve the reaction with respect to epoxy
succinic acid, a secondary hydrolysis of the mother liquor of the
second crystallization can be carried out as is evident from this
example.
1 litre of the mother liquor of the second crystalliza-
tion obtained according to example 1 was boiled in a glass flask
for 5 hours under reflux. The solution contained 1.01 moles of
- 20 -
1058634
a mixture of dibasic acids per 1000 g. The mixture consisted of
15.5 mole ~ of maleic acid, 35 mole % of racemic acid, 37 mole %
of mesotartaric acid and 12.5 mole % of epoxy succinic acid. After
5 hours of secondary hydrolysis the solution contained 14.5 mole
% of maleic acid, 42 mole % of racemic acid, 39 mole % of mesotar-
taric acid, 1 mole % of fumaric acid and approximately 3.5 mole
of epoxy succinic acid.
The rate of reaction in the secondary hydrolysis, rela-
tive to epoxy succinic acid, is 72%, whereby additional racemic
acid and mesotartaric acid are formed.
Example 4
A solution obtained according to Example 1 through
pipe 27 was nDt hydrolysed but was first passed over an anion
exchanger, as generally described in Example 1.
The solution contained 0.97 mole of a mixture of dibasic
acid per 1000 g, i.e., 0.20 mole of tartaric acid per 1000 g and
0.75 mole of epoxy succinic acid per 1000 g. The tungsten content
of the solution was lower than 2 p.p.m. (not detectable). After
the hydrolysis at 95C the product distribution, relative to the
initial content of epoxy succinic acid and tartaric acids, was
as follows:
-
mole % of mesotartaric epoxy succinic selectivity of
dl-tartaric acid acid mesotartaric
mlnutes acid acid, relative
to tartaric
acids formed
210 S9 9 32 13.2
285 65 11 24 14.5
403 70 14 16 16.7
1390 83 17 (< 0.5) 17
According to the procedure described in Example 1 a
selectivity of 6% of mesotartaric acid relative to tartaric
acids formed at a rate of reaction of epoxy succinic acid of 97%
105863~
was attained.
The analytical data in Example 4 were obtained with
the aid of a method of nuclear resonance.
Example 5
300 g of a solution, which contained 1.31 moles of
dibasic acids per 1000 g and had been produced analogously
to the product obtained by way of the pipe 27 in Example 1, had
a content of 0.013 moles of tungstic acid per 1000 g. The solution
was boiled in a glass flask for 5 hours with reflux.
Relative to the acid applied, 4.3 mole % of epoxy
succinic acid, 9.2 mole % of mesotartaric acid and 86.4 mole %
of dl-tartaric acid were obtained. The selectivity of mesotartaric
acid, relative to tartaric acids formed, was 9.6%.
The same solution was passed over a weakly basic,
macroporous anion exchanger based on polystyrene with exchange-
active amino groups and after the exchange it contained less than
2 p.p.m. of tungsten. The acid concentration was 1.335 moles of
dibasic acid per 1000 g of solution. 300 g of the solution were
boiled for S hours under reflux. After processing, 64.1 mole %
of dl-tartaric acid, 17.2 mole % of mesotartaric acid and 18.3
mole % of epoxy succinic acid of the acids applied were obtained.
The selectivity of mesotartaric acid was 21.2%, relative to
tartaric acids formed.
The analytical results of Example 5 were obtained by
fractional crystallization on evaporating and identifying the
fractions.
