Method of preparing N-phosphonomethyl glycine

Details Method of preparing N-phosphonomethyl glycine Method of preparing N-phosphonomethyl glycine

1998-12-07

2000-09-19

Geist, Gary

Organic compounds -- part of the class 532-570 series

Organic compounds

Phosphorus acids or salts thereof

C07F 938

Patent

active

06121485&

DESCRIPTION:

BRIEF SUMMARY
This application is the national phase of PCT/EP97/03955 filed Feb. 22, 1997.
The subject matter of the invention is a method of preparing N-phosphonomethyl glycine from aminomethylphosphonic acid or one of its salts.
N-phosphonomethyl glycine (glyphosate) has been in use for more than 20 years as a systemic herbicide, the action of which is based on inhibition of the plant enzyme 5-enolpyruvylshikimat-3-phosphate synthetase (EPSP synthetase) and thus of aromatic amino acid synthesis.
Of the many syntheses which have been developed for N-phosphonomethyl glycine, technical significance has been attached, amongst other reactions, to reactions in which an amino component is hydroxymethylated or cyanomethylated by reacting it with formaldehyde or with formaldehyde and hydrocyanic acid respectively.
A familiar disadvantage of the hydroxymethylation and cyanomethylation of primary amines is that one usually obtains mixtures of mono- and di-substituted products.
According to the Polish patent PL 156 933, for example, in which aminomethylphosphonic acid is reacted with formalin and sodium cyanide at a pH of 10, and the initially formed nitriles are subsequently hydrolysed, one obtains not only the main product N-phosphonomethyl glycine, but also the by-product N-phosphonomethyliminodiacetic acid. U.S. Pat. No. 4,221,583 describes the reaction of aminomethylphosphonic acid with formaldehyde and sodium cyanide at pH levels of 6.6 to 9.7; in this case, the yield of N-phosphonomethylglyconitrile is only 65%.
During hydroxymethylation and analogous reactions of primary amines it should be possible to prevent the formation of di-substituted products by introducing a protective group temporarily into the amine. A synthesis of this kind, in which N-phosphonomethyl glycine is obtained from glycine, is disclosed in European patent 112 580. When glycine is reacted with sodium carbonate, it is first converted into the sodium salt of the corresponding carbamic acid. Subsequent reaction with formalin and diethyl phosphite leads to formation of N-carboxy-N-(O,O'-diethylphosphonomethyl)glyconitrile, from which N-phosphonomethyl glycine is obtained by way of hydrolysis. However, the 36% yield from this method is also extremely low.
The object of the invention is thus to provide a technically uncomplicated method of preparing N-phosphonomethyl glycine, which does not have the disadvantages of the prior art and with which high yields of high-purity compound are obtained.
This object is established according to the invention in that desirable with the addition of lyes, is reacted with an alkali carbonate and/or alkali hydrogencarbonate or with carbon dioxide and a lye, hydroxymethylated with formaldehyde, N-hydroxymethyl-N-phosphonomethylcarbamic acid, if necessary or desirable with addition of a lye, are reacted with hydrocyanic acid and/or a cyanide and treated with acids and converted by means of hydrolysis and decarboxylation into N-phosphonomethyl glycine.
Surprisingly, one obtains an excellent yield of high-purity N-phosphonomethyl glycine in this way, with relatively uncomplicated technical equipment. What is especially surprising is that during the reaction only very small proportions (<0.5%) of N-phosphonoethyliminodiacetic acid are formed, and none is contained in the isolated N-phosphonomethyl glycine.
According to the invention, N-phosphonomethyl glycine is prepared from aminomethylphosphonic acid in a number of steps; however, as per a special embodiment, the intermediates need not be isolated and the entire process can be carried out as a one-pot reaction.
In the first step a), aminomethylphosphonic acid or one of its salts in water--if necessary or desirable with the addition of lyes--is reacted with an alkali carbonate and/or alkali hydrogencarbonate, or with carbon dioxide and a lye; the amino group is carboxylated, and salts of N-phosphonomethylcarbamic acid are formed, having the formula (I): ##STR1##
Since the reaction ensues in water, it is preferable to use a water-soluble alkali carbonate and/or alkali hydro

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patent: 5679843 (1997-10-01), Hodgkinson
patent: 5750774 (1998-05-01), Miyata
patent: 5948937 (1999-09-01), Worley

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