US3414611A - Method for the resolution of racemic glutamic acid and its salts - Google Patents

Description

Dec. 3, 1968 GENTARO NOYQR] ET AL 3,414,611

METHOD FOR THE RESOLUTION OF RACEMIC GLUTAMIC ACID AND ITS SALTS Filed July 21, 1965 2 Sheets-Sheet l c 5 J PL 5g; 6 B. G b

Temperafure 6) United States Patent 3,414,611 METHOD FOR THE RESOLUTION OF RACEMIC GLUTAMIC ACID AND ITS SALTS Gentaro Noyori, Tokyo, Makoto Honda, Musashino-shi, and Teiko Watanabe, Tokyo, Japan, assignors to Asahi Kasei Kabushiki Kaisha, Kita-ku, Osaka, Japan, and The Noguchi Institute, Itabashi-ku, Tokyo, Japan Filed July 21, 1965, Ser. No. 474,217 Claims priority, application Japan, July 24, 1964, 39/ 41,739 16 Claims. (Cl. 260534) ABSTRACT OF THE DISCLOSURE For resolving racemic glutamic acid, the racemic acid is added to a solution containing the D- or L-form. The opposite form then goes into solution and the form originally contained in the solution remains in solid phase and is separated.

This invention relates to a phy-sicochemical method for the resolution of racemic glutamic acid and its salts whose solubilities in water are greater than those of their optical isomers. More particularly, this invention provides a method for resolving a racemic modification into both optically active forms and obtaining both active forms of high optical purity which comprises adding racemic for-m crystals to a solution containing racemic glutarnic acid or its salts (hereinafter in this specification and the claims, called racemic form) and one of the optical isomers, L- or D-for-m, so as to completely dissolve the opposite isomer, D- or L-form, component (the antipode of the active form, which is present in the solution from the beginning) in the added racemic form crystals and to make at least one part of the active form, L- or D-form component remain in solid phase, thereafter cooling the obtained slurry to make the active form, L- or D-form, crystals grow thereby resolving the racemic form in the solution, and separating solid from liquid and if desired repeating the above operation. An object of this invention is to provide an industrially convenient resolution method concerning racemic glutamic acid and its salts.

Racemic glutamic acid and its salts whose solubilities in water are greater than those of their optically pure isomers include compounds such as tree glutamic acid, glutamic acid hydrochloride, monoammonium salt of glutamic acid and the like.

The physicochemical resolution known hitherto as an industrially convenient resolution method for racemic form is an application of crystallization and can be considered as a kind of separation method resorting to fractional crystallization. Its resolution operation is an application of a crystallization operation. The resolution step consists of unit operations such as heat exchanging (heating, cooling), stirring, dissolving, crystallization, solid-liquid separation, similar to those in a general crystallization process. The resolution step can be divided into the following three elements.

(1 Existence of resolution seeds The existence of crystal nuclei which work as the starting point of crystal growth is essential in the crystallization. Likewise, the existence of one active form of nuclei (hereinafter called resolution seeds) which are the same kind as the desired active form to be crystallized in solid phase is essential.

As one of the conventional methods for making resolution seeds exist in a solution of racemic form there is the so-called seeding method which is known and in which seed crystals are added to the racemic form solution.

3,414,611 Patented Dec. 3, 1968 (2) Growth of resolution seeds (3) Solid-liquid separation A step by which to separate the desired active form in the solid phase from the racemic form, the opposite isomer being undesired and the solvent remaining in liquid phase.

The conventional physicochemical resolution methods are characterized depending on how the above three operation elements are combined. For example, they are characterized by seeding a supersaturated solution of racemic form with an active form crystals (Japan patent application publication No. 14,706/ 1962) or cooling a saturated solution of racemic form after seeding with an active form crystals (Japan patent application publication No. 2,972/ 1961), whereafter resolution is carried out.

The above-mentioned physicochemical resolution methods have been proposed as industrially convenient methods. The necessary factors of the industrially convenient methods are noted in the following:

(A) Good reproducibility. This requires being able to control sufiiciently the resolution operation.

(B) High efficiency. This requires high yield per unit solvent amount and unit time and high optical purity of obtained crystals. In order to increase optical purity, it is necessary to prepare seed crystals of each isomer in high optical purity, to prevent crystallization of the un desired antipode and the racemic form during resolution and to control particle size of obtained crystals thereby to reduce the amount of mother liquor retained by the filter cake after a filtration.

(C) Facile industrial working. This means that most factors can be controlled, that simple operations are employed, that the apparatus is simple, that scale-up is easy, etc.

(D) Economical. Particularly, this requires that expensive reagents not be employed, that the apparatus is simple, that the operation is of high efiiciency and so on.

It conventional methods are examined from the above viewpoints, it is seen that they have the inconvenience that isomer crystals (seed crystals) having high optical purity and adequate and uniform particle size must be prepared in advance. Further, in the method in which a supersaturated solution of racemic form is seeded with an active form crystals, the crystal growth rate and the yield are restricted by the degree of supersaturation. If the degree of supersaturation of racemic form is increased in order to increase the yield, notonly does control become difficult clue to occurrence of mimetic crystals, but also obtaining the desired active form crystals of high optical purity becomes dilficult clue to crystallization of the undesired antipode and the racemic form and due to the increasing of amount of the mother liquor retained by the filter cake after filtration as clearly described in Japan patent application publication No. 17,710/ 1961 and No. 9,971/1962. In order to obtain each optical isomer crystal in high optical purity, it is inevitable to employ a method which is not easy to scale-up such as in Japan patent application publication No. 17,710/ 1961 and No. 9,971/ 1962 or to employ peculiar resolution seeds such as in Japan patent application publication No. 15,611/ 1962 some or other such complicated procedure.

The physicochemical resolution methods known hitherto are more industrially convenient than the other known methods, but nevertheless they have still some weak points.

An object of this invention is to provide an industrially convenient and economical resolution method which has the strong points of conventional methods and substantially improves the weak points of the conventional methods.

We made an exhaustive research on the dissolution phenomena of L-, D- and racemic forms, based on the invention of Japan patent application No. 30,625/ 1963 and have established the present invention. Particularly, we found that when into a slightly unsaturated solution containing both L- and racemic forms or containing the L-form alone, racemic form crystals in an amount of as much as twice that of the L-form amount in the solution are added and stirring is effected, the D-form component in the added racemic form crystals is dissolved and entirely transferred into the solution, while nearly all the L-form component is not dissolved and remains in solid phase. This same phenomenon was observed when the D-form was used instead of the L-form in the above procedure.

Table 1 shows the results of carrying out the abovementioned experiments employing crystal type method and tracer method in which glutamic acid hydrochloride labelled with C was used. Hereinafter La (or Du) designates on type L- or D-glutamic acid, L5 (or DB) designates B type L or D-glutamic acid, DL (or) designates racemic glutamic acid anhydrate whose infra-red absorption spectrum and X-ray diffraction chart are in full accord with that of La (or D06), and DL (6) designates racemic glutamic acid anhydrate whose infra-red absorption specrum and X-ray diffraction chart are in full accord with that of L5 (or D/i), DL*-HCl designates racemic glutamic acid hydrochloride whose L-component is labeled with C, and L*-HC1 designates L-glutamic acid hydrochloride labeled with C.

conventional method and were dissolved in a tolueneethanol solvent in order to determine the radioactivity. The radioactivity was less than 1 m,u.c. per 1 g. diethyl ester. For assurance, DL-HCl in the mother liquor was recovered as crystals and their radioactivity was determined in the same way. The result Was 6.6 m c. per 1 g. diethyl ester. This demonstrates clearly that the D-component in the added racemic form crystals dissolved into the solution and the L-component solid.

As a result of. further study on the foregoing discovery, we found that the active form crystals (L-form or D- form) remaining in solid phase can be employed as resolution seeds and that by the combination of their use with the technique of the cooling crystallization method, the resolution operation can be conducted very easily. Thus, a new method was established, which is an improvement over the conventional methods from the point of adding racemic form crystals instead of the desired active form of crystals as resolution seeds to the resolution system for the purpose of creating resolution seeds and at the same time for the purpose of supplying a starting material to be resolved.

In the following, the invention will be explained in more detail, referring to the attached diagram (FIG. 1). FIG. 1 is a diagram illustrating the principle of our operation. The ordinate and abscissa of the diagram show concentration of glutamic acid or its salts and temperature respectively. In FIG. 1, the curve ABE shows solubility of racemic form, the curve BHF shows the saturation curve of a mixture containing C grams of racemic form and some amount of the active form and the curve BG shows change of the total amount of solutes during resolution. The temperature t is the cooling starting temperature, t is the central temperature and is the saturation temperature of C g. of the racemic form, t is the resolution finishing temperature and I is the saturation temperature with respect to the total amount of the racemic form and the active form in the system after the addition of the racemic form crystals. (In this specification and the claims, we define respectively central temperature (t as the saturation temperature with respect to racemic form TABLE 1 Type or kind of added crystals DL (0.) DL Lct+DB (1:1) DL-HCl DL*-HU1 Kind of glutamic acid in solution L L L D L*-HC1 L-HCl Type or kind of crystals remaining in solid phase La LB La DB L-HCl L* H0l Details of some of the experiments are as follows: after the addition of the racemic form for preparing seed 4.7 g. L-glutamic acid were dissolved into 200 g. water, and, at 50 C., 9.4 g. DL (a) were added and stirring was effected for 30 minutes. By water-washing and drying the filter cake after filtration, dry crystals 3.6 g. dry crystals were obtained. By means of infra-red absorption spectrum, X-ray diffraction and microscope, it was shown that the obtained crystals were mostly Lot. The result of determination of optical purity according to the conventional method was 100.9% as L-glutamic acid. If the L-component in the solution had been crystallized by the addition of racemic form crystals, stable type Lt? should have been crystallized. In fact, in the above-mentioned experimental result, unstable type La was present as most of the solid phase. This means that the D-component in the added racemic form crystals dissolved and the L-component remained in solid phase.

g. of DL-HCl crystals were added to g. aqueous solution containing'45 g. L*-HCl (radioactivity 2.8 m c. per 1 g. diethyl ester) and kept at 25 C. After stirring for 30 minutes, crystals remaining in solid phase were separated from the solution. The yield of obtained crystals was 87.6 g. in wet state and 83.0 g. in dry state, and the optical purity was 99.8% after correction with respect to inpurities in the mother liquor retained by the crystals. The obtained dry crystals were esterified according to a crystals and for feeding starting material, in other words, the central temperature resides between cooling starting temperature and resolution finishing temperature, and is determined by a definite operating condition, and in fact, is a resolution starting temperature cooling starting temperature (t is defined as a temperature within the range higher than the central temperature and lower than the saturation temperature (r with respect to the total amount of the racemic form and the active form in the system after the addition of the racemic form and resolution finishing temperature (1 as a temperature lower than the central temperature. The resolution finishing temperature means a temperature at which ideally the same amount of the opposite isomer as the amount of the 0 active form present in the original starting material solution are present in the liquid phase at the resolution finishing point.) Now, to the solution containing the racemic form EG (=EI )g and the active form, L- or Dfor m, EG(=EG)g to be starting material for resolution, at a temperature higher than the saturation temperature with respect to the total amount of the racemic form and the active form, L- or D-form, in said solution and not higher than the cooling starting temperature (t (hereinafter called the racemic form addition temperature), the racemic form crystals EJg are added. When the temperature of the solution reaches t the opposite isomer, D- or L form component of the added racemic form crystals entirely dissolves, further HJg of the active form, L- or D-form, also dissolve and the liquid phase reaches saturation with respect to the mixture of the racemic form and the active form, L- or D-form. At this point the solutes in the solution are Jl g of the racemic form and HJg of the active form, L- or D-form, and HIg, of the active component, L- or D- for m, remain in solid phase.

When the slurry thus obtained is cooled down to the equilibrium between solid and liquid reaches point B along the curve BF to make resolution start, and further goes to the point G along the curve BG to make resolution finish. If the resultant slurry is separated into solid and liquid, the active form crystals, L- or D-form crystals G'Ig(=GKg) are obtained and in the mother liquor EG g of the racemic form and EGg of the opposite isomer D- or L-form, remain dissolved. If the racemic form crystals are added again to this mother liquor and a simi lar operation as in the foregoing cycle is carried out, the opposite isomer, D- or L-form remains in solid phase in turn and can be obtained by separation.

Accordingly, this invention provides a racemic resolu tion method which comprises adding racemic form crystals to a solution containing racemic form and L- or D-form, in other words, a mother liquor obtained by optical resolution according to a physicochemical method or a solution having the similar composition therewith, at a tem perature higher than the saturation temperature of said solution and lower than the saturation temperature with respect to the total amount of the racemic form and L or D-form after the addition of the racemic form crystal thereby to dissolve entirely D- or L-form component of the added racemic form crystals to make at least one part of L- or D-form component of the added racemic body crystals remain in solid phase at the cooling starting tem perature, then cooling the resultant slurry down to the resolution finishing temperature lower than the central temperature while L- or D-form crystals are growing, and obtaining L- or D-form crystals by separation.

In working this method, it is possible to select a yield of active form per one cycle or per unit water amount over a considerably wide range by selecting adequately the cooling starting temperature, the central temperature, the resolution finishing temperature, the kinds of starting material such as free glutamic acids and glutamic acid salts and so on in the correlation of these parameters. In the conventional seeding methods in which a racemic supersaturated solution is seeded with the pure active form, the yield is restricted by the degree of supersaturation of the starting material racemic solution. And the degree of supersaturation cannot be made too high because of undesirable possibilities such as development of mimetic crystals, and crystallization of the racemic form and the undesirable form isomer and so on. The method of this invention in a novel are which is a combination of a novel method for forming seeds for resolution and a conventional method of crystallizing by cooling. This invention removes many weak points of conventional methods such as addition of seed crystals, uniform dispersion of the seed crystals in the solution, preparation of seed crystals having high optical purity and uniform particle size, difficulty of crystallizer operation and control and so on. ,With the present invention, controlling is as easy as a process where a racemic saturated solution is seeded with the active form before cooling.

Thus, the method of this invention has the following industrial advantages and working features compared with the conventional methods.

(l) Forming of resolution seeds. It is possible to form resolution seeds pure enough for resolution in the resolution system simply by the addition of racemic form crystals from without the resolution system. In other words, operation of feeding racemic form crystals to be starting material for resolution provides resolution seeds in the resolution system, and accordingly one operation serves the purpose of operations in the conventional methods. Besides, as apparent from the mechanism of resolution seeds formation and examples described later, even if the racemic form crystals (starting material for resolution) to be added contain the active form crystals undesired, they do not give any substantially bad influence on the resolution. On the contrary, in the conventional methods, the content of the opposite isomer crystals undesired in the active form crystal seeds for resolution is very harmful for the resolution, and when the content reaches to some extent the resolution ends unsuccessfully. In our method, a considerable amount of the undesired isomer crystals in the crystals to be added may be up to as much as weight percent of the amount of the excess active form in the original solutibn. Since the formation of resolution seeds in the method of this invention is the result of dissolution of the undesirable antipode component of the racemic form crystals, the formation is very stable thermodynamically and natural. Thus, though the time required for dissolution of the antipode component of the added racemic form crystals depends on agitation efiiciency and temperature of adding racemic form crystals, in practice it may be about 10 minutes and is surely Within 60 minutes. Further, in our method, the size and the quantity of resolution seeds can be controlled by changing the size of the racemic form crystals, and by the cooling starting temperature. This is an important point for controlling of resolution operation and is, an advantage which cannot be seen in the other methods. Further, the optium range of the ratio of the active form to the racemic form in the starting material solution for resolution depends on the central temperature, the cooling starting temperature and the resolution finishing temperature, specifically a solution having the ratio as defined below is preferable.

Weight of active form Weight of racemic f0rm influence to our method, because smaller crystals dissolve before larger ones and only crystals having relatively large particle size remain in solid phase.

The lower limit of the cooling starting temperature, as before mentioned, must be a temperature higher than the central temperature. Preferably it is a temperature at which less than of the desired active form component of the added racemic form crystals remain in solid phase. If it is lower than the central temperature, the opposite undesired isomer component also remains in solid phase and if it is the same as the central temperature, the complete dissolution of the undesired isomer component cannot be expected in practice. In the both cases, the resolution finishes unsuccessfully. The upper limit of the cooling starting temperature, theoretically may be such a temperature as 0.1% of the active form component of the added racemic form crystals remain in solid phase but, practically, a temperature at which more than 1% remain is suitable in interrelation with the over-all crystal growth rate. Further, from the view point of industrial operation, it is preferable that the cooling starting temperature is selected from a range higher than the central temperature by 3 to 30 C.

(2) Growth of resolution seeds. In the method of our invention, the growth stage of resolution seeds following the forming stage is effected by a cooling operation. By selecting the cooling starting temperature based on the number and size of the resolution seeds to suit the crystal growth rate, it is possible to minimize the degree of supersaturation and to prevent occurrence of mimetic crystals during the growing stage. That is to Say, in our method, it is easy to control the growing operation industrially. Further, as a result of the fact that the resolution seeds are a very pure optical isomer and the strength of agitation during the growing operation may be the lowest strength that can mix solid and liquid in a suspension state, it is possible to prevent the formation of crystal nuclei and growth of the undesired opposite isomer or racemic form from the solution and to obtain the desired active form crystals of high purity by resolution. The cooling of the suspension from cooling starting temperature to the resolution finishing temperature is divided into two parts, that is, cooling to the central temperature and cooling from the central temperature. As the cooling to the central temperature corresponds to recrystallization of the active form crystals desired in the solution, the cooling rate is not liimted. While, as upon the cooling from the central temperature, real resolution is effected, an adequate cooling rate should be selected depending on the crystals particle size of the added racemic form crystals and the cooling starting temperature. However, in our method, since no active form crystals are added from the outside of the resolution system, it is possible to make much more amount of resolution seeds exist without lowering resolution efficiency and accordingly it is possible to make the cooling rate (resolution rate) considerably higher, compared with the conventional seeding methods. As a result, there is one advantage that it is possible to make the time until crystallization of the undesired isomer much longer and the resolution operation can be conducted very safely. In short, it is permissible to conduct the crystallization of the desired active isomer under supersaturated conditions under which the racemic form and the undesired isomer hardly crystallized. Specifically, the resolution is effected at a cooling rate lower than 10 C. per minute but higher than 0.05" C. per minute. In addition, it is desirable to effect resolution employing a temperature between from C. to 80 C. as the central temperature, a temperature within the range higher than the central temperature by 3 C. to C. as the cooling starting temperature, and a temperature within the range lower than the central temperature by 2 C. to 40 C. as the resolution finishing temperature.

(3) Solid-liquid separation. When solid-liquid separation is carried out in a resolution process, solutes in the solution are entirely optical impurities against the solid phase. Therefore, one requirement for el'liciently obtaining active form of high purity is to lower the retained amount of the liquid phase as far as possible and thereby to prevent contamination due to retaining of the mother liquor. Solid-liquid separability is influenced by shape, crystal size and crystal size distribution surface intention of solution and so on. According to our method, as before mentioned, by selecting adequately crystal size of starting material racemic from crystals and distribution thereof, and the cooling starting temperature, as well as by controlling crystallization operation, it is possible to obtain crystals suitable for solid-liquid separation. Further, it is possible to shorten the time required for solid-liquid separation and to minimize the influence of lowering purity which is given by possible crystallization of undesired isomer or racemic form during solid-liquid separation, and thereby to easily obtained by separation the active form crystals of high purity from the solution.

Summarizing the advantages of our method hereinbefore mentioned, our method does not require any preparation of the both of extremely optically pure isomers for seeding which is a weak point of the conventional seeding methods, it does not require a procedure to add active form crystals into the resolution system from the outside, and it further can effect the supply of racemic form crystals to be starting material for resolution and the formation of resolution seeds in the same one operation, and can employ a method having an ideal crystallization process, that is, growing of active form crystals present from the beginning by cooling, though taking a dissolution proce dure. In our method, merely by supplying starting material racemic form crystals to the filtrate containing an excessive amount of one active form, for example D-form, from which the opposite isomer crystals, for example L- form crystals, has been resoluted and separated, thereby to dissolve L-form component, and then cooling the slurry, the resolution operation is carried out very smoothly and easily for obtaining D-form crystals.

Thus, according to our resolution method, by a continuous operation of heating, feeding racemic form crystals, cooling and separating L- or D-form crystals followed by again heating, feeding racemic form crystals, cooling and separating D- or L-form crystals, it is possible to resolve and separate alternately each of the two isomers, L- and D- form crystals, from racemic form crystals. Upon resolution, no procedure to add any active form in any state to any system of the cycle from the outside is required. Our method can he worked by a very simple procedure of merely supplementing racemic form crystals, starting material for resolution, from the outside and then the same amount of an isomer desired as added racemic form crystals by selection of the resolution condition. Further, according to our method, by employing an ideal procedure lowering temperature for crystallization of active form, which preclude the occurence of mimetic crystals, and other useful procedure, it is possible to produce in good yield and in good efiiciency each of the two optical isomers having high purity from their racemic modification. In short, our method has many excellent industrial advantages.

EXAMPLE 1 The resolution starting material solution consisting of racemic glutamic acid hydrochloride 350 g., L-glutamic acid hydrochloride g. and water 500 g. in a beaker with jacket for recycling heating or cooling water was controlled at 60 C. and thereto were added with stirring 170 gram of of racemic glutamic acid hydrochloride crystals as resolution starting material. The resultant slurry was maintained at 60 C. for 30 minutes and thereafter cooling was started. Stirring was continued while cooling and the slurry was cooled at 25 C. over 25 minutes, and then within 10 minutes was completed separation into solid and liquid. For the solid-liquid separation was employed a basket centrifuge, and dehydration was effected for 3 minutes with 3,000 rpm. The moisture content of the crystals obtained is 3.2 weight percent (based on wet crystals). By drying without water washing,l67.4 gram of L-glutamic acid hydrochloride of optical purity (OP) 97.1% were obtained. If correcting in respect to contamination due to retained mother liquor gives, the corrected value of optical purity is 100.3%, the yield of pure isomer is 95.7% and the yield of the crystals is 98.5%.

The values, moisture content, yield of dry crystals, yield of pure isomer and corrected value of optical purity were calculated from the following equation:

Moisture content of crystals (percent) 2 (1- Wg/Wl) X Yield of dry crystals (percent) W /Wo) X100 Yield of pure isomer (percent) :OPX W /W x 100 Corrected value of optical purity (percent) :OPX W /{W W(C +2C /100} where W=wt. of retained moisture by obtained crystals W wt. of added racemic form crystals W =wt. of obtained wet crystals W wt. of obtained dry crystals C -racemic form concentration in mother liquor after filtration (g./ 100 ml. H O) C =excess isomer concentration in mother liquor after filtration (g./ 100 ml. H O) The above operation and results will be explained, referring to the accompanying drawing FIGURE 2 which shows theoretical resolution operation diagram. For convenience, in the following explanation, calculated values per 100 g. water of glutamic acid hydrochloride described in the above example will be employed.

In FIGURE 2 line ABE represents solubility curve of racemic form solely, line FHB represents saturated curve on total amount of racemic form and excess isomer at higher temperatures than 50 C., in the case of dissolving active form in the solution of racemic form at concentration C curve BG shows change of total amount of the solutes during resolution, and line PQE represents saturated curve at higher temperatures than 25 C. in the case of dissolving active form in the solution of racemic form at concentration C respectively, wherein C is 104 g./O g. H 0, and C is 70 g./100 g. H O. The cooling starting temperature 2 is 60 C., the central temperature t is 50 C., and the resolution finishing temperature t is 25 C. 1

Now, if racemic form crystals 34 g. (C -C ar added to a solution consisting of L-form 17 g. (C -C racemic form 70 g. (C and water 100 g. at a temperature higher than the saturation temperature 2.2; of said solution and lower than 1' that is, 60 C., D-fiorm component 17 g. (C C of the racemic form crystals dissolve and further g. (C C of L-form component 17 g. dissolve and L-form crystals of 2 g. (C C re main in solid phase. In other words, thus obtained suspension is represented by point I, in which 2 g. of L-form crystals are in solid phase and 15 g. of L-form and 104 g. (C of the racemic form and 100 g. of water are in liquid phase. The amount of total glutamic acid hydrochloride in the resolution system become 121 g. (C and the saturation temperature of the system is t If the resulting suspension is cooled starting from 60 C., solid-liquid relation changes theoretically along the curve HB and reaches B, in which state 17 g. (C C of L-form are crystallized out in solid phase and 104 g. (C of racemic form are dissolved in liquid phase. Further, if cooling is continued, resolution of racemic form is effected along the curve BG showing solid-liquid relation. When reaching the resolution finishing temperature t C.), 34 g. (C -C of L-form crystals are in solid phase, and in liquid phase 70 g. (C of racemic form exist in saturated condition and 17 g. (C -C of D-form exist in supersaturated condition. After solidliquid separation, theoretically 34 g. of L-form can be recovered as crystals while 187 g. of mother liquor (D- form 17 g., racemic form 70 g. and water 100g.) to be resolution material solution for the successive cycle can be obtained. The saturation temperature of the mother liquor is t 10 EXAMPLE 2 The similar operation as in Example 1 was carried out except controlling the temperature of the starting material solution at 53:1 C. and adding the starting material racemic form crystals at 52-54 C. Wet crystals 168 g. having moisture content 2.3% were obtained. The crystals, which have been dryed as they were, were L- glutamic acid hydrochloride of optical purity 97.8%. The corrected value of optical purity of dry crystals was 100.1%, and the yield of dry crystals was 96.6%.

EXAMPLE 3 The similar operation in Example 1 was carried out except that the temperature of the starting material solution, the temperature for adding racemic form crystal and the cooling starting temperature were all 55il C. Wet crystals 18 g. having moisture content 5.8% were obtained. The crystals, which have been dryed as they Were, were L-glutamic acid hydrochloride of optical purity 94.1%. The corrected optical value of dry crystals is 99.9%, the yield of dry crystals is 100.4% and the yield of the pure L-isomer is 98.0%.

EXAMPLE 4 Racemic glutamic acid hydrochloride crystals 500 g. were added at C. to 3,250 g. of glutamic acid hydrochloride solution (its composition: L-glutamic acid hydrochloride 7.7%, racemic glutamic acid hydrochloride 47.1%, and water 45.2%) in the stirring vessel of 3 volume having jacket type and inner coil type heat exchangers. After stirring was carried out at the rate of 300 r.p.m. for 30 minutes, the stirring was reduced to the rate of r.p.m. and cooling was carried out at the rate of 12 C. per minute. When the temperature of slurry was lowered to 25 C., cooling was stopped, and thereafter within 5 minutes solid and liquid were separated using a basket centrifuge. The crystals were dryed as they were, that is, without washing and their specific rotation was determined.

The resultant filtrate was introduced again into the stirring vessel used in the foregoing cycle, and the similar operation as in the foregoing cycle was carried out. In this time the stirring vessel was not washed and some slurry of the foregoing cycle remained attached thereto, and therefore, the active form of the foregoing cycle that is some L-form crystals remained attached to the stirring vessel. The amount of added starting material racemic form crystals was reduced correspondingly to the lost amount of the filtrate. The similar operation as in the. foregoing cycle was repeated 8 times in total except that time between the addition of racemic form crystals and the coolingstarting (the time maintained at 60 C.) was changed as shown in Table 2. The results were as shown in Table 2.

TABLE 2 Starting Material Obtained Crystals Time Main- Amount of Amount of Repeated Cycle tained at Starting Racernie Amount Moisture Yield Optical Sort 60 0. (min.) Material Form of Wet Content of Dry Purity of Solution Crystals Crystals (Percent) Crystals (Percent) Active (gram) Added (gram) (Percent) Form First Cycle 30 3, 250 500 499 3. 8 96. 0 96. 9 L-form 2nd Cycle 30 3, 490 511 3. 7 100.5 97. 1 D-form 15 3, 140 483 529 4. 2 105. 0 96. 4 L-forrn 15 3, 090 475 481 2. 9 98. 3 96. I D-form 45 3, 050 470 482 3. 4 99. 0 95. 2 L-form 45 3, 000 462 488 3. 4 102. O 96. 3 D-form 30 2, 950 454 474 3. 2 101. 0 95. 7 L-forrn 3O 2, 900 446 466 3. 7 100. 5 97. 2 D-form 1 1 l2 3. EXAMPLE glutamic acid in the filtrate 500 g. was 81 g. as free acid, about 5 g. of which were L-glutamic acid.

Using the similar apparatus as in Example 1, 20 g. of DL (0:) type glutamic acid were added to the solution about 1,490 g. at 55 C. containing L-glutamic acid g. racemic glutamic acid 47 g., were added and EXAMPLE 8 Except that glutamic acid hydrochloride aqueous solution 300 g. having a composition shown in Table 3 was the slurry was stirred for 40 minutes. Thereafter cooling used as the starting material solution, and that the coolwas effected at the rate of 0.25 C. per minute. Still ing starting temperature (the same temperature as the during cooling, stirring was continued. At 40 C. solid racemic form crystals addition temperature), the resolua-nd liquid were separated. Moisture content of wet tion finishing temperature and the cooling time were crystals was 2.7%. After the crystals were dried as they 10 selected as shown in Table 3, the similar operation as were, that is, without washing, the optical purity was in Example 1 was carried out and the results shown 99.2% and the yield was 17.6 g. The infrared absorption in Table 3 were obtained.

TABLE 3 Starting Material Solution Resolution Condition Obtained by Crystals Starting Material, Cooling Amount of Starting Resolution Optical Content of Total [L-Form] Racemic Temperature Finishing Cooling Amount Purity Glutamic Acid Form C.) Temperature Time Obtained (Percent) Hydrochloride (Percent) lRacemic Form] Crystals (Raccmic C.) (min) (gram) (As L-Form) Added Form (gram) Addition Temperature) 50. 4 0. 246 70 70 35 3o 69. 4 93. s 47. 1 0. 203 56 5s 29 70 57. 1 so. 2 42. 9 0. 204 54 50 17 35 52v 4 95. 5 42. 2 0. 207 51 3o 16 20 4e. 7 97. 0

spectrum and the X-ray diffraction chart show that the EXAMPLE 9 obtained crystals was a-type L-glutamic acid. The mother liquor contained, 0.53 g. equivalent of D-glutamic acid per 100 ml. of the solution.

Then using the above mother liquor, and adding thereto glutamic acid 20 g. Of *DL type in place of DL (a) type, the similar operation as in the foregoing cycle was carried out. Wet crystals 21.2 g. having moisture content 8.6% were obtained. The crystals, 3 which have been obtained by drying as they were, were TABLE 4 D-glutamic acid of optical purity 98.7%. The type of crystal was ,8 type. Thus apparent difference was ob- Except that racemic glutamic acid hydrochloride crystals having crystal size distribution (CDS) shovm in Table 4 were added as the starting material, and that the racemic form addition temperature and the cooling starting temperature were both 58 C., the similar opera tion as in Example 1 was carried out and the results shown in Table 4 were obtained.

Obtained Dry Crystals 'th as 0 sin ra emic lutamic Moisture Cr 1 Ser.ved comparing W1 the c e f L a C g CSD or Racemic Content of Si e of 361121 of DL (00) type. 40 Form C(rystabs Added Obwtained kgnount Optical 80 wt.

mes ct tained Purity percent EXAMPLE 6 (Crystals) (gram) ((L-Form) of percent percent) obtained To the solution 400 g. at 36 C. consisting of L- crystals glutamic acid 6.8%, racemic glutamic acid 39.2%, ammonia 5.7% and water 46.3%, were added 67.3 g. of 40-60 3.4 169 96,7 100-150 3. 1 170. 5 97. 2 0. 2-0. 7

crystals Of racemic glutamlc acld m n 'a m l salt 200 pass 9 5 1 7 90AE (1) mono-hydrate. The slurry was stirred for 45 minutes, 1 and then cooled down at the rate of 0.4 C. per minute. Imposslme to classlfy' When the temperature of slurry was lowered to 15 C., EXAMPLE l0 cooling was stopped. Stirring was still continued for 5 H minutes and then solid and liquid were separated. 74.5 Except that the raflemlc f Crystals addltlon of wet crystals were obtained These wet crystals perature and thecoolmg starting temperature were both contained 601 g of mono ammonium Salt of glutamic C., and coollng was conducted respectively from 55 acid. The optical purity of L-glutamic acid mono-am- 50 y r 0 mlnutes from 50 C, to 25 C, over 5 monium Salt including water content was In 55 minutes, the similar operation as in Example lwas carried other words, 665 g ofL g1utamic acid mono ammonium out. Wet crystals 172.5 g. were obtained. The crystals 1t d t a 0 ticl urit 91 67 were after drying were 161.5 g. and were L-glutamic acid Sa mon y me p a P y 0 hydrochloride of optical purity 93.8%.

tained.

EXAMPLE 7 We claim:

1. A method for the resolution of racemic glutamic To the solution 610 g. containing racemic glutamic acid and Salts thereof, Said method comprising Preparing id 50 L l t i a id 6 1 d 50 of mono. as a starting material solution for resolution of mother sodium salt of racemic glutamic acid (without water of liquor obtained by the resolution Of the racemic form Of crystallization) :and regulated at C, were added a member Selected from the group Consisting of racemic racemic glutamic acid unhydrate crystals 10 g. and the 65 glutamic acid and salts thereof, the solubility in water of mixture was maintained at 65 C. with stirring for about i h is gr ter than that Of each of the pure isomers an hour. The resulting slunry was cooled down to 55 C. and recovering one of the or D-fofms y P Y at the rate of 0.1 C. per minute and immediately the chemical means and in which an excess of one of the crystals were separated by vacuum filter. After water D- or L-forms and the racemic form coexist; adding washing and then drying of crystals, were obtained 1, racemic form crystals to the starting material solution :glutamic acid 11.4 g. having optical purity 98.6%. Sucat a temperature higher than the saturation temperature cessively to the mother liquor, 11 g. of racemic glutamic of the starting material solution but less than a cooling acid unhydrate crystals and then the similar operation starting temperature; thereafter maintaining the starting as the above was conducted. 10.7 g. of D-glutamic acid material solution at the cooling starting temperature to having optical purity 98.8% were obtained. The total thereby cause the L- or D-form antipode component of the added racemic form crystals to completely dissolve with at least a part of the other D- or L-form component of the added racemic form crystals remaining in solid phase and forming a suspension; then cooling the resulting suspension to a resolution finishing temperature lower than a central temperature of 1580 to cause the dissolved D- or L-form of the first said solution to crystallize out and continuing the resolving .of the racemic form to cause further of the latter form to crystallize out; and recovering said crystals by separation and obtaining a mother liquor in which the racemic form and antipode form coexist, said mother liquor being the starting material for resolution in a succeeding cycle.

2. A method for the resolution of racemic glutamic acid and salts thereof, said method comprising preparing as a starting material solution for resolution of mother liquor in which coexist the racemic form and an excess of one of the L- or D-forms of a member selected from the group consisting of glutamic acid and glutamic acid salts, the racemic forms of which have a solubility in water greater than that of each of the pure isomers; adding racemic form crystals to the starting material solution at a temperature higher than the saturation temperature of the starting material solution but less than the cooling starting temperature; thereafter maintaining the starting material solution at the cooling starting temperature to cause the D-. or L-form antipode component of the added racemic form crystals to completely dissolve with at least a part of the other L- or D-form component of the added racemic form crystals remaining in solid phase and forming a suspension; then cooling the resulting suspension to a resolution finishing temperature lower than a central temperature of 15 -80 C. to cause the dissolved L- or D-form of the first said solution to crystallize out and continuing the resolving of the racemic form to cause further of the D- or L-form to crystallize out; and recovering the resulting crystals by separation and obtaining a mother liquor in which racemic form and an excess of the D- or L-form antipode coexist, said mother liquor being the starting material for resolution in a succeeding cycle.

3. The method of claim 1 in which the racemic form, D-form and L-form are glutamic acid hydrochloride.

4. The method of claim 2 in which the racemic form, D-form and L-form are glutamic acid hydrochloride.

5. The method of claim 1 in which the racemic form, D-form and L-form are glutamic acid monoammonium salt.

6. The method of claim 2 in which the racemic form, D-form and L-form are glutamic acid monoammonium salt.

7. The method of claim 1 in which the racemic form crystals to be added are crude racemic modification crystals which contain L- or D-form crystals in an amount not higher than 80 weight percent of the excess D- or L- form in the starting material solution for resolution.

8. The method of claim 2 in which the racemic form crystals to be added are crude racemic modification crystals which contain D- or L-form crystals in an amount not higher than 80 weight percent of the excess L- or D- form in the starting material solution for resolution.

9. The method of claim 1 in which the cooling starting temperature is a temperature higher than the central temperature by 3 C. to 30 C.

10. The method of claim 2 in which the cooling starting temperature is a temperature higher than the central temperature by 3 C. to 30 C.

11. The method of claim 1 in which the resolution finishing temperature is a temperature lower than the central temperature by 3 C. to 40 C.

12. The mthod of claim 2 in which the resolution finishing temperature is a temperature lower than the central temperature by 3 C. to 40 C.

13. The method of claim 1 in which the mean rate of cooling the slurry below the central temperature is lower than 10 C./minute but more than 0.05 C./minute.

14. The method of claim 2 in which the mean rate of cooling the slurry below the central temperature is lower than 10 C./minute but more than 005 C./minute.

15. The method of claim 1 in which the racemic form, D-form :and L-form are glutamic acid hydrochloride, the central temperautre is a temperature between 20 C. and C., the cooling starting temperature is a temperature higher than the central temperature by 5 C. to 30 C., the resolution finishing temperature is a temperature lower than the central temperature by 5 C. to 35 C., and the mean rate of cooling the slurry below the central temperature is lower than 10 C./minute but more than 0.1 C./minute.

16. The method of claim 2 in which the racemic form, D-form and L-form are glutamic acid hydrochloride, the central temperature is a temperature between 20 C. and 70 C., the cooling starting temperautre is a temperature higher than the central temperature by 5 C. to 30 C., the resolution finishing temperature is a temperature lower than the central temperature by 5 C. to 35 C., and the mean rate of cooling the slurry below the central temperature is lower than 10 C./miuute but more than 0.1" C./minute.

References Cited UNITED STATES PATENTS 2,940,998 6/1960 Ogawa et al. 260-534 FOREIGN PATENTS 1,335,192 7/ 1963 France.

OTHER REFERENCES Akashi: J. Chem. Soc. of Japan, vol. 83, pages 417- 425, April 1962.

JAMES A. PATTEN, Primary Examiner.

ALBERT P. HALLUIN, Assistant Examiner.

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