Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus acids or salts thereof
Patent
1995-07-10
1996-06-18
Dees, Jose'G.
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus acids or salts thereof
C07F 938
Patent
active
055279538
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB94/00018, filed Jan. 6, 1994.
This invention relates to a chemical process and in particular a process for the manufacture of N-phosphonomethyliminodiacetic acid.
N-phosphonomethyliminodiacetic acid is a known compound useful in the manufacture of N-phosphonomethylglycine and certain salts thereof which are active as herbicides.
A typical process for the preparation of N-phosphonomethyliminodiacetic acid is described in U.S. Pat. No. 3,288,846. Thus Example IV describes a process in which the hydrochloride of aminodiacetic acid (a compound referred to herein as iminodiacetic acid) in the presence of concentrated hydrochloric acid and orthophosphoric acid is heated to 100.degree. C. and then reacted with 38% aqueous formaldehyde solution followed by paraformaldehyde. The product is described as N,N-diacetic acid aminomethylenephosphonic acid but is referred to herein as N-phosphonomethyliminodiacetic acid.
Many other processes for the manufacture of N-phosphonomethyliminodiacetic acid are known, including for example that described in United Kingdom Patent No 2 154 589 in which an alkali metal salt of iminodiacetic acid such as the sodium salt is reacted with a strong mineral acid such as sulphuric acid to form the strong mineral acid salt of iminodiacetic acid and the alkali metal salt of the acid (for example sodium sulphate). The strong mineral acid salt of iminodiacetic acid is then reacted with formaldehyde and phosphorous acid and sufficient water to dissolve the alkali metal salt whilst the N-phosphonomethyliminodiacetic acid product is precipitated.
We have now found that, surprisingly, the filtrates from the reaction of iminodiacetic acid with phosphorous acid and formaldehyde may be re-cycled a plurality of times without excessive build-up of by-product, provided that sulphuric acid is used as mineral acid and provided that the starting material is iminodiacetic acid and not an alkali metal salt thereof.
According to the present invention there is provided a process for the manufacture of N-phosphonomethyliminodiacetic acid which comprises:
1) reacting iminodiacetic acid with phosphorous acid and a source of formaldehyde in aqueous solution in the presence of concentrated sulphuric acid;
2) filtering and recovering the N-phosphonomethyliminodiacetic acid product precipitated in stage (1);
3) recovering the filtrates from stage (2) and optionally removing a proportion of the water therefrom;
4) transferring the filtrates from stage (3) to a further reaction stage in which further iminodiacetic acid is reacted with phosphorous acid and a source of formaldehyde in the presence of sulphuric acid; and thereafter
5) repeating stages (1), (2), (3) and (4) in a plurality of re-cycles.
The process of the present invention is well adapted to be operated in a continuous manner, especially at large manufacturing volumes. It is to be understood therefore that stages (1) to (5) above may represent hypothetical stages in a continuous reaction wherein filtrate stream is continuously re-cycled to the reaction vessel (optionally via a water removal stage) and wherein reactants are continuously charged to the reaction vessel and N-phosphonomethyliminodiacetic acid product which precipitates is removed by continuous or semi-continuous filtration.
The use of the re-cycle reaction of the present invention will generally have the effect of reducing the waste/effluent stream produced in the process and of making most effective use of the starting materials.
The source of formaldehyde is suitably either an aqueous solution of formaldehyde or paraformaldehyde, depending on the proportion of water which is desired to be added. If water is removed from the filtrates in stage (3), it may be desirable to use paraformaldehyde in subsequent reaction stages (1), thereby reducing the proportion of water which it is necessary to remove.
The phosphorous acid may be introduced into the reaction as a solid (for example as a flaked solid), as a molten liquid or as an aqueous solution, for example as a
REFERENCES:
patent: 3288846 (1966-11-01), Irani et al.
patent: 3950402 (1976-04-01), Franz
patent: 5023369 (1991-06-01), Fields, Jr.
Jones Raymond V. H.
Rae Graham A.
Ritchie David J.
Standen Michael C. H.
Ackerman Joel G.
Dees Jose'G.
Frazier Barbara S.
Zeneca Limited
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