Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1994-10-21
1996-06-25
Dees, Jose G.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562576, C07C22900
Patent
active
055301592
DESCRIPTION:
BRIEF SUMMARY
The preparation of .beta.-alaninediacetic acid or its alkali metal or ammonium salts
The present invention relates to a novel process for preparing .beta.-alaninediacetic acid (Ia) or its alkali metal or ammonium salts (Ib).
The compounds Ia and Ib are, just like nitrilotriacetic acid or ethylenediaminetetracetic acid and the salts of these amino polycarboxylic acids, important for forming complexes.
It is known to prepare .beta.-alaninediacetic acid by reacting chloroacetic acid with .beta.-alanine (G. Schwarzenbach et al., Helv. Chim. Acta 32 (1949), 1184). Also known are the cyanomethylation of .beta.-alanine to give .beta.-alaninediacetonitrile (V. G. Yashuniskii et al., Zh. Vses. Kim. Obschestva im D. I. Mendeleeva 10 (1965), 105) and the reaction of iminodiacetic acid with acrylamide to give .beta.-alanine-N-acetamide-N-acetic acid (DE-A 27 27 755).
The two processes mentioned first require .beta.-alanine, which is relatively difficult to obtain, as starting material and entail a plurality of stages, while the addition of iminodiacetic acid, which is easily obtained from ammonia, hydrocyanic acid and formaldehyde, onto acrylamide provides, just like the cyanomethylation of .beta.-alanine, only a derivative of .beta.-alaninediacetic acid, from which the acid is obtained only by subsequent hydrolysis of the cyano group or of the amide moiety.
Furthermore, DE-A 38 29 859 discloses a process for preparing .beta.-alaninediacetic acid by reacting iminodiacetic with acrylic acid.
Since .beta.-alaninediacetic acid and its salts are mainly used to form complexes, for example in detergents and cleaners, or in the photographic industry, as well as in cosmetic and pharmaceutical compositions, high purities are required.
Although equimolar reaction of iminodiacetic acid or its salts with acrylic acid gives high yields (up to 98% according to DE-A 38 29 859), the resulting products still contain unreacted acrylic acid and/or iminodiacetic acid or the salts thereof, which can be removed only with loss of yield, e.g. by recrystallization or by elaborate extraction processes. For the same reason, of course, it is inappropriate to use an excess of one starting material. The other processes, because of the reversibility of the Michael addition of iminodiacetic acid onto acrylic acid, likewise result in iminodiacetic and acrylic acid at the temperatures used (60.degree. C.).
It is an object of the present invention to prepare the title compounds Ia and Ib by a simple and economic process without special purification steps with a purity such that the final product contains less than 0.5% iminodiacetic acid and less than 0.1% acrylic acid.
We have found that this object is achieved by a process for preparing .beta.-alaninediacetic acid (Ia) or its alkali metal or ammonium salts (Ib) which comprises reacting iminodiacetic acid with acrylonitrile or C.sub.1 -C.sub.4 -alkyl acrylates in weakly acid to weakly basic aqueous medium and subsequently hydrolyzing the nitrile or ester moiety to the acid or a salt.
The iminodiacetic acid or its salts, especially the sodium or potassium salt, ought to have a minimum purity of about 95% by weight, preferably of about 99% by weight, since otherwise the purity of the final product might be impaired. However, iminodiacetic acid or its salts can easily be obtained in such purity even on the industrial scale.
The acrylonitrile or the acrylates are stabilized in a conventional way, e.g. with 50 ppm hydroquinone monomethyl ether or hydroquinone.
The reactants, iminodiacetic acid and acrylate or acrylonitrile, are expediently used in the molar ratio of from 1:0.95 to 1:2, preferably from 1:1.0 to 1:1.5.
The solvent is usually water. However, in the reaction of acrylates it is also possible to use a mixture of water and alcohol, preferably the alcohol corresponding to the acrylate used. An alcohol content of 20% by weight in the solvent mixture is adequate in this case.
The content of iminodiacetic acid in the complete aqueous mixture is generally from 10 to 40, preferably from 20 to 30, % by
REFERENCES:
patent: 5068416 (1991-11-01), Baur et al.
patent: 5130476 (1992-07-01), Baur et al.
Kneip Michael
Oftring Alfred
Schneider Juergen
BASF - Aktiengesellschaft
Dees Jos,e G.
Williams Rosalynd A.
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