Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus acids or salts thereof
Reexamination Certificate
2002-02-04
2003-03-04
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus acids or salts thereof
Reexamination Certificate
active
06528680
ABSTRACT:
The present invention relates to a process for the preparation of phosphonomethylglycine from N-phosphonomethyliminodiacetic acid N-oxide.
Phosphonomethylglycine, which is known under the common name glyphosate, is a potent phytotoxic compound which is employed as herbicide.
EP-A-439445 describes the preparation of phosphonomethylglycine starting from N-phosphonomethyliminodiacetic acid. The latter is oxidized with a peroxide in aqueous solution, if appropriate in the presence of a catalytically acting quantity of a water-soluble molybdenum compound, to give the intermediate N-phosphonomethyliminodiacetic acid N-oxide. The N-oxide is subsequently converted into phosphonomethylglycine in the presence of a catalytic quantity of a metabisulfite compound and a water-soluble molybdenum compound.
EP-A-464017 also describes a process for the preparation of phosphonomethylglycine starting from phosphonomethyliminodiacetic acid using the same process steps. The oxidation to give the abovementioned N-oxide is carried out with a peroxide in the presence of a water-soluble molybdenum or tungsten compound. The conversion into phosphonomethylglycine is then carried out using iron, zinc, aluminum, vanadium or copper in the form of the metal or using a vanadium salt, iron(II) salt or copper(I) salt as catalyst.
Finally, EP-A-464018 also describes a process for the preparation of phosphonomethylglycine, the oxidation of the phosphonomethyliminodiacetic acid being carried out with a peroxide in the presence of a water-soluble tungsten compound or a mixture of a water-soluble tungsten and molybdenum compound as catalyst. The N-oxide is then brought into contact with iron metal, a water-soluble vanadium compound, an iron(II) salt or a mixture of a water-soluble sulfide, sulfite or bisulfite compound and a water-soluble molybdate compound and converted into phosphonomethylglycine.
The processes described in the prior art have in common that the catalyst is introduced into an initial charge of an aqueous solution of the N-oxide. On an industrial scale, the control of these methods requires great complexity since the gas which is formed upon conversion of the N-oxide into phosphonomethylglycine is liberated in an uncontrolled fashion and, moreover, the temperature of the reaction mixture climbs sharply.
It is an object of the present invention to provide a process for the preparation of phosphonomethylglycine which can be controlled, even on an industrial scale.
We have found that this object is achieved by a process for the preparation of phosphonomethylglycine in which N-phosphonomethyliminodiacetic acid N-oxide is brought into contact with a catalytically active quantity of at least one catalyst, selected from amongst a thionyl halide, ammonium dithionite or an alkali metal dithionite, a dialkyl sulfite, sulfur dichloride, sulfur dioxide and sulfurous acid, in a reaction chamber in the presence or absence of a cocatalyst by metering the N-oxide into the reaction chamber in such a way that always at least 50% of the N-oxide metered into the reaction chamber are converted.
N-Phosphonomethyliminodiacetic acid N-oxide is known and can be prepared by a plurality of processes. For example, it can be synthesized in accordance with U.S. Pat. No. 3,950,402 or U.S. Pat. No. 3,954,848 or in accordance with HU 187,347 using peroxides in the presence of compounds of silver, iron, tin, lead, manganese or molybdenum. However, the N-oxide is preferably prepared by one of the processes described in the European Patent Applications EP 439445 A, EP 464017 A or EP 464018 A, where N-phosphonomethyliminodiacetic acid is brought into contact with a peroxide such as hydrogen peroxide, performic acid, peracetic acid, perbenzoic acid, peroxytrifluoroacetic acid, benzoyl peroxide, benzenepersulfonic acid and the like. Hydrogen peroxide is preferably used, in particular in at least stoichiometric quantities based on N-phosphonomethyliminodiacetic acid. The hydrogen peroxide is generally employed in a concentration in the range of 10 to 70% by weight, in particular 30 to 70% by weight. The reaction temperature is generally in the range of approximately 0° C. to 80° C., in particular approximately 20° C. to approximately 70° C.
The oxidation of N-phosphonomethyliminodiacetic acid is particularly preferably carried out in the presence of a catalytic quantity of a water-soluble molybdenum compound or a water-soluble tungsten compound or a mixture of these. Suitable molybdenum compounds are known to the skilled worker, and it is only necessary for them to be soluble in the reaction medium. Useful molybdenum compounds are, for example, alkali metal molybdates such as sodium molybdate, ammonium molybdate or alkali metal or ammonium polymolybdates such as ammonium or sodium dimolybdate.
Suitable tungsten compounds are also known to the skilled worker, and all that is required is for them to be soluble in the reaction medium. Useful tungsten compounds are, for example, tungstic acid, 1,2-tungstatophosphate and barium tungstate. Ammonium tungstate and alkali metal tungstates such as sodium tungstate and potassium tungstate are preferred.
The catalyst quantity can vary within wide limits. In general, approximately 0.01 to approximately 5.0% by weight, preferably approximately 0.01 to approximately 3.0% by weight of catalyst are used, based on the weight of N-phosphonomethyliminodiacetic acid.
The peroxide is generally employed in at least stoichiometric quantities. It is preferred to use a small excess, in particular approximately 1.02 to 1.20 mole equivalents, especially preferably 1.05 to 1.15 mole equivalents, based on the quantity of phosphonomethyliminodiacetic acid.
The oxidation of the N-phosphonomethyliminodiacetic acid takes place in aqueous medium, the N-phosphonomethyliminodiacetic acid first being suspended but at least partially dissolving during the course of the oxidation. The N-phosphonomethyliminodiacetic acid is expediently employed in high concentration, for example in the form of an up to 60% by weight, in particular up to 50% by weight, aqueous suspension. The N-phosphonomethyliminodiacetic acid is preferably employed in such a quantity that a solution is present after the oxidation has ended. The transition from suspension to solution indicates that the oxidation reaction has essentially ended since the N-oxide is much better soluble in water than the N-phosphonomethyliminodiacetic acid.
The conversion of the N-oxide to the desired phosphonomethylglycine is preferably effected starting from an aqueous solution of the N-oxide. The catalyst is also preferably used in the form of an aqueous solution. Sulfur dioxide can be employed as a gas, either as such or diluted with an inert gas such as nitrogen. Catalysts which are preferably used are sulfur dioxide or sulfurous acid, thionyl chloride, a dialkyl sulfite, in particular a di-C
1
-C
4
-alkyl sulfite such as dimethyl sulfite, or an alkali metal dithionite, in particular sodium dithionite, or mixtures of these.
The conversion of the N-oxide into phosphonomethylglycine is preferably effected in the presence of a cocatalyst to increase the conversion rate. Suitable cocatalysts are, for example, water-soluble vanadium salts such as vanadyl sulfate or water-soluble iron(II) salts such as iron(II) sulfate or iron(II) chloride. However, it is preferable to use a water-soluble molybdenum compound such as ammonium molybdate or an alkali metal molybdate such as sodium molybdate or an ammonium polymolybdate or alkali metal polymolybdate such as ammonium dimolybdate or sodium dimolybdate as cocatalyst. It is particularly preferred to use the same cocatalyst for the oxidation of the N-phosphonomethyliminodiacetic acid and for the subsequent conversion of the N-oxide, in particular one of the abovementioned molybdenum compounds.
In general, at least 0.01% by weight of catalyst is used, based on the amount of N-oxide. As a rule, an amount of 10% by weight, preferably not more than 8% by weight of catalyst can be employed, based on the N-oxide. The amount is preferably in the ra
Aust Nicola Christiane
Butz Thomas
Fischer Martin
BASF - Aktiengesellschaft
Keil & Weinkauf
Vollano Jean F.
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