JPS6072856A - Production of high-purity s-carboxymethyl-l-cysteine - Google Patents

Abstract

PURPOSE:An acidic solution of S-carboxymethyl-Lcystein (SCMC) and an alkali or an alkaline solution of SCMC are mixed in a crystallization tank as the pH is kept constant to effect neutralization crystallization to obtain the titled compound of high purity, meeting the ignition residue test. CONSTITUTION:An acidic solution of SCMC and an alkali or an alkaline solution of SCMC, or an alkali solution of SCMC and an acid or an acidic solution of SCMC are added in portions into the crystallization tank, as the pH is kept near the isoelectric point (pH 2.8) under stirring to effect neutralization crystallization so that extreme supersaturation of SCMC does not occur locally to give the objective compound.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides S-cal? A method for obtaining oxymethyl-L-cysteine (hereinafter abbreviated as SCMC) as a highly pure crystal, in other words, the purpose is to eliminate impurities and inorganic salts that fail the ignition residue test. The present invention relates to a method for purifying SCMC.

Neutralization crystallization is used to purify SCMC, but conventionally, an acid (or alkali) solution of SCMC is poured into a crystallization tank in advance, and then an alkali (or acid) is added dropwise. In the neutralization crystallization method that adjusts the concentration, an extremely supersaturated state of SCMC occurs locally in the crystallization tank, and therefore only fine crystals including aggregated crystals can be obtained.

Such fine crystals have a large amount of adhering mother liquor, and inorganic salts derived from the mother liquor are incorporated, resulting in the ignition residue test being outside the standard. Furthermore, it is difficult to remove this adhering mother liquor by simply washing the crystals.

As a countermeasure to the above problem, it is thought that the concentration of each solution or one of the solutions during crystallization may be diluted to prevent sudden local supersaturation, but this would result in an oversized apparatus. Therefore, it cannot be said to be an industrially suitable method.

As a result of further research, the present inventor has determined that an acid (or alkali) solution of SCMC and an alkali (or acid) or an alkali (or acid) solution of SCMC are locally SCMC in a crystallization tank.
We have completed the method of the present invention, which allows for neutralization crystallization to obtain industrially applicable high-purity SCMC by adding solid solutions little by little while stirring to avoid extremely supersaturation of MC. .

Embodiments of the present invention will be further described below.

The concentration of the SCMC solution is 10 g/dl to 40 g/d7 when subjected to neutralization crystallization using an acid or alkali solution of SCMC and an alkali or acid solution! The front and back are
In addition, when subjecting to neutralization crystallization using an acid or alkali solution of SCMC and an alkali or acid solution of SCMC, 511/d7! An industrially appropriate concentration is around 30 y/at. Here, the acid may be hydrochloric acid, sulfuric acid, etc., and the alkali may be sodium hydroxide, ammonia, etc.

The solid solution to be subjected to neutralization crystallization is locally SC in the crystallization tank.
In order to prevent the extremely supersaturated state of MC from occurring, in other words, to make the - in the crystallization tank uniform, for example, depending on the scale, it is necessary to simultaneously drop the solid solution under stirring. good.

Neutralization, as well as the isoelectric point of SCMC (pH = 2.8
) or around it, and at such a pH value, the isolation yield of SCMC crystals will be high. Note that during crystallization, seed crystals may be used as necessary. The crystallization temperature is
Considering thermal decomposition of SCMC, the temperature is preferably around 5 to 60°C. After the neutralization is completed, stirring is further continued as necessary to sufficiently precipitate SCMC.

In order to separate the precipitated crystals from the mother liquor, a known method may be appropriately employed. For example, high purity SCMC containing no inorganic salts can be obtained by cooling, separating and drying.

According to the present invention, the crystal is about 50 times thicker (300 μm to 50 μm) and has no aggregated crystals than the conventional crystal (Fig. 2).
A SCMC crystal (FIG. 3) with a diameter of 0 μm) was obtained, and this crystal is a high-quality SCMC crystal that hardly incorporates inorganic salts and passes the ignition residue test.

I'll keep it tight. One dropping funnel (A) contains SCMC.
Add an alkali (or acid) or an alkali (or alkali) solution of SCMC to the other dropping funnel 0), and add the alkali (or acid) solution of SCMC from the dropping funnel 0) to the crystallization tank while stirring. Always drip at a constant speed, using the dropping funnel (
From B), crystallization is performed by dripping so that the − of the crystallization tank is constant.

After completion of the dropwise addition, the mixture is further stirred if necessary, and after the SCMC crystals have been thoroughly analyzed, the mixture is cooled for one separation and dried to obtain high-purity SCMC containing no inorganic salts.

Example 1 24g of SCMC crystals (ignition residue: 020%) in 1.5NH
C1, was dissolved in 240 ml of water, and this solution was dropped at a rate of 6 ml/min into a 40° C. crystallization tank containing 200 ml of water. On the other hand, 27% NaOH was added to -
was added dropwise so that the amount remained at 3 throughout.

During this period, the mixture was stirred to make the - in the crystallization tank uniform, and after completion of the 90% neutralization, 8CMC crystals 211ii' were obtained by cooling, separating by filtration, and drying. This crystal had a purity of 99.5% or more and an ignition residue of 0.05%.

Example 2゜ 24 g of the same SCMC crystal as in Example 1 was heated to 3N.

(5) Dissolve in 120ml of NaOH and add 200rfL of this solution.
The mixture was dropped at a rate of 3 ml/min into a 10°C crystallization tank containing 1 liter of water and SCMC crystal IF (ignition residue 0.05%). On the other hand, 35% HCl was added to the crystallizer until -2
was added dropwise so as to maintain it throughout. Meanwhile, stirring was continued.

After the neutralization was completed, fiscMc crystal 22II was obtained by cooling, filtering and drying.

The purity of this crystal is over 99.5%, [α)%0=-32
5°.

The ignition residue was 0.05.

[Brief Description of the Drawings] Figure 1 shows the apparatus used to carry out the present invention, and Figure 2 (photograph) shows a micrograph (X
100) Figure 3 (photo) shows S produced by the method of the present invention.
It is a micrograph (X100) of an example of CMC crystal. Patent applicant: Ajinomoto Co., Inc. (6) Figure 1 Figure 2 Figure 3, 9□＼

Claims (1)

[Claims] S-, Cal? An acid (or alkali) solution of oxymethyl-L-cysteine and an alkali (or acid) solution or an alkali (or acid) solution of S-carboxymethyl-L-cysteine are placed in a crystallization tank, and - is kept constant in the crystallization tank. While stirring, add the solid solution little by little at the same time.
1. A method for producing S-cal-xymethyl-L-cysteine, which comprises neutralizing and crystallizing cal-xymethyl-L-cysteine.