[Agr. Biol. Chem., Vol. 28, No. 9, p. 646•`649, 1964]

A New Crystalline form of Monosodium L-Glutamate

By Hiromasa MARUYAMA, Tsuyoshi FUJIWARA and Kuniharu TAKENOUCHI

Ajinomoto Co. Inc., Kawasaki Factory, Kawasaki

Received March 19, 1964

A new crystalline form of monosodium L-glutamate, which is different from the known monoso- dium L-glutamate monohydrate crystal in external appearance, density, X-ray diffraction pattern, solubility, and water of crystallization, has been crystallized from ca. 73 weight per cent aqueous methanol solution at ca. 18°C. It was identified as the dihydrate from the determination of water of crystal lization based on Karl Fischer's method. The newly found crystals are extremely unstable in air, aqueous solution, and the mother liquor, because of rapid transformation into the stable monohydrate, whereas they can be kept in a considerably stable condition in absolute ethanol and acetone.

INTRODUCTION 2. Procedure and Results Monosodium L-glutamate is most commonly (1) Crystallization obtained as the monohydrate, while it sometimes 1500 ml of absolute methanol and 300 ml of water crystallizes as the pentahydrate1) at temperatures were poured into a 21-flask. To the prepared ca. 80 weight per cent aqueous methanol, 200 ml of 37.5 weight below -0.8°C. The authors found that unstable per cent monosodium L-glutamate monohydrate aqueous crystals of monosodium L-glutamate dihydrate, solution is slowly added with stirring at room temperature, whose constitution was decided by quantitative ca. 18°C. When addition is finished, nothing appears in analysis of water of crystallization based on Karl the immediately solution. After a few hours' stirring, Fischer's method, crystallize from ca. 73 weight several grams of resultant transparent rectangular plate per cent aqueous methanol solution at ca. 18°C can be recognized. Stirring after a lapse of 5 to 15 appearaing as thin transparent rectangular plates minutes subsequent to the nucleate brings about crystal as shown in Fig 1 lization of rhombic prisms to the known monohydrate, . Although these crystals could not be subjected and at the same time the educed crystals in rectangular to detailed studies by X-ray crystallography plate begin to lose transparency, resulting in a perfect transformation into the monohydrate. In the composition because of the quite rapid transformation into described above, the newly formed crystals are coming the monohydrate, some information obtained as out, and in the other case only the monohydrate is to this new crystal will be reported. obtained. EXPERIMENTALAND DISCUSSION The photograph of the new crystals is shown in Fig. 1, which was taken by Nikkon's Shadow Graph model-VI 1. Materials (50 x magnification). The sketch of the external appearance MonosodiumL-glutamate monohydrate was a com- of the new crystals observed through a microscope is mercialproduct. illustrated in Fig. 2. Each axis direction in Fig. 2 was T-N, 7.49%; [a]_??_,25.16 (2N-HCI) decided from the extinction observed through a polari Methanol,ethanol, isopropanol, butanol, acetone, chloro zing microscope. form, and ethyl ether wereall commercialmaterials of The density of the new crystal is ca. 1.37 g/cm3. guaranteedgrade. (2) Transformation As described above, the new crystals are readily trans- I) Tetsuo Ogawa, Japanese Pat. No. 178,476 (1948, 12, 17). formed into the stable monohydrate in the mother liquor. A New Crystalline form of Monosodium L-Glatumate 647

FIG. 1. The Crystals of Monodium L-Glutamate Dihydrate.

new crystals in various solvents were left to stand at room temperature, and the progress of the transformation was observed through Nikkon's Shadow Graph. The results of observation were shown in Table I. Table I. THE RESULTSOF OBSERVATIONABOUT A RATE OF TRANSFORMATIONINTO THE MONOH YDRATEAFTER SUBSTITUTINGTHE MOTHER LIQUORBY ANOTHERSOLVENT (%)

FIG. 2. A Sketch of the Monosodium L-Glutamate Dihydrate Crystal.

When they exposed to the air after being filtered from the mother liquor, they are also rapidly transformed into the monohydrate, resulting in complete lose of trans parency.Providedthatthe transformation proceedsin solid phase, inhibition will be diffiult. On the assumption that the transformation is caused by recrystallization in the saturat ing body, just as in the case of the ƒ¿-ƒÀ transformation of L-glutamic acid2), this phenomenon may be prevented by substituting the surrounding mother liquor for such (3) X-ray Diffraction Pattern solvents as alcohols, acetone, or ether which have little As these transparent rectangular crystals are very small ability to dissolve monosodium L-glutamate. The mother and extremely unstable, X-ray oscillating or Weissenberg liquor of the slurry of the new crystals was decanted photographs for the purpose of the determination of its before beginning of the transformation. Then either unit cell, could not be taken. absolute methanol, ethanol, isopropanol, butanol, acetone, Therefore, the powder method of X-ray diffraction chloroform, or ethylether was added, and the liquor was applied to the ethanol-wet crystals only to determine was decanted again. By repeating this procedure several the difference in the crystal structures between the known times, the surrounding mother liquor was completely monohydrate and the newly found crystal. The X-ray substituted by another solvent. The suspensions of the diffraction pattern of the new crystals is illustrated in

2) Yoshiki Sakata, This journal, 25, 835 (1961). Fig. 3 in comparison with that of the transformed material 648 Hiromasa MARUIYAMA, Tsuyoshi FUJIWARA and Kuniharu TAKENOUCHI

FIG. 3. X-ray Diffraction Pattern of the Monosodium L-Glutamate Dihydrate Crystals.

FIG. 4. X-ray Diffraction Pattern of the Transformed Crystals (the Monosodium L-Glutamate Monohydrate Crystals).

FIG. 5. Isothermal Triangular Diagram, the System shown in Fig. 4. The X-ray diffraction pattern shown L-C5H5N04.Na-CH3OH-H20, at 25•Ž in Fig. 4 was perfectly identical with that of monosodium

L-glutamate monohydrate crystals. the aqueous solution is in the unstable supersaturated (4) Water of Crystallization zone of monosodium I:glutamate monohydrate, the new As the new crystals were transformed into the mono- crystals recrystallize very rapidly into the monohydrate hydrate in air, the water of crystallization could be de in the aqueous solution; therefore, the solubility in water termined only by Karl Fischer's method with application cannot be measured. Accordingly, phase equilibria in of the sample wetted with ethanol. Some of the crystal ternary system, i.e. C5H8NO4.2H20-CH3•@ OH-H20, at wetted with ethanol, were weighed as rapids as possible. 25°C was represented on an isothermal triangular diagram. At the same time others were weighed and then heated The result of measurement is illustrated in Fig. 5 in in a thermostat for three hours at 95°C, resulting in comparison with phase equilibria in C5H8N04. Na. H20- perfect transformation into the monohydrate. From the CH3OH-H2O. loss on heating, the reduced weight of the sample was applied to the determination of the water of crystal DISCUSSION lization. The results of measurements are shown Table II. The new crystals were found to be monso-

From the results in Table II, it is concluded that the dium L-glutamate dihydrate judging from mol

new crystals contain two molecules of water of crystal cular number of the water of crystallization

lization. determined by Karl Fischer's method.

TABLE II. THE WATER OF CRYSTALLIZATION As monsodium L-glutamate dehydrate could be OF THE NEW CRYSTALS separated only from the very highly supersatu

rated methanol aqueous solution with respect to

the monohydrate, they seem to be very unstable.

This phenomenon has been recognized as the

Ostwald's Law of Stage : in other words, when

a chemical system is left in an unstable state,

it tends not to change into the most stable state,

but into a transient stable modification whose

formation from the original state is accomplished

by the smallest loss of free energy. Therefore,

(5) Solubility in Methanol Aqueous Solution the new crystalline modification seems to be As the saturated concentration of the new crystals in transient and is transformed readily into the A New Crystalline form of Monosodium L-Glutamate 649 stable crystalline form, monosodium L-glutamate other solvents due to its relatively high dissolv monohydrate. This transformation is considered ing ability. Judging from the extent of solvent to be the recrystallization of the dihydrate as the action, a more inhibitory effect should be ex saturating body into the monhydrate caused by pected for isopropanol, butanol, chloroform, the difference in solubility, since the velocity and ethylether than for ethanol and acetone, but of transformation varies with the state of sur- the fact is contrary. The reason for this result rounding solvents as showh in the observed is not clear, but it is reasonable that one of causes results in Table 1. The dehydrate crystals are is imperfect substitution of the solvents due to more stable in ethanol and acetone than in their more hydrophobic properties relative to methanol, isopropanol, butanol, chloroform, and ethanol and acetone. ethylether, while they undergo transformation Acknowledgment. The authors wish to express immediately in air, aqueous solution, and mother their sincere thanks to Mr. S. Inagawa, Manag liquors. It is essential, for preventing this trans- ing Director and Superintendent of Kawasaki formation caused by the recrystallization in the Factory of Ajinomoto Co., Inc., for his encou mother liquor, that the surrounding solvent does ragement, to Mr. N. Nagashima for help with not dissolve the dihydrate crystals perfectly. the X-ray diffraction and to Miss F. Akino for Thus, methanol should be less suitable than the the Karl Fischer analysis.