Note: Descriptions are shown in the official language in which they were submitted.
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5-13686/~
Process for producin~ N-phosphonomethylglycine
_.
The present invention relates to a novel process ~or producing
N-phosphonomethylglycine of the formula I
Ho\~oL
~ -CH NH-CH -COOH (I~
by reaction of aminomethanephosphonic acid with glyoxal in an aqueous
medium in the presence of sulfur dioxide.
N-Pllosphonomethylglycine is a herbicide which has a very wide spectrum
and which has little or no residual effects. The production and use
thereof are described in the U.S. Patent Specification No. 3,799,758.
It is known that on reaction of glycine, formaldehyde and
phosphorous acid in the molar ratio of 1:1:1, there is formed, instead
oE the desired N-phosphonomethylglycine mainly N,N-bis-phosphono
methylglycine (cp. U.S. Patent Specification No. 3,956,370). This
product can then be converted electrolytically (U.S. Patent
Specification No. 3,835,000) into phosphonomethylglycine.
In order to overcome the difficulties associated with the afore-
mentioned process, it has been suggested that N-phosphonomethyl-
glycine be produced by a process comprising firstly reacting an
N-substituted glycine with formaldehyde and phosphorous acid to the
corresponding N-substituted N-phosphonomethylglycine, and
subsequently detaching from this the substituent originally present on
., a~
L
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the nitrogen atom. There is thus described for example in the U~S.
Patent Specification No. 3,956,370 the production of N-phosphono-
methylglycine by reaction of N-benzylethylglycinate with formaldehyde
and phosphorous acid with simultaneous hydrolysis of the ester group
to give N-benzyl-N-phosphonomethylglycine and subsequent removal of
the benzyl group, as benzyl bromide, with strong hydrobromic acid.
N-Yhosphonomethylglycine is obtained in this manner in a yield of
about l,o %. This process is not advantageous for commercially
producing N-phosphonomethylglycine on account of the low yield and in
view of the lacrimatoric action of the benzyl bromide formed as a
by-product.
It is therefore the object of the present invention to provide a process
by which N-phosphonomethylglycine can be produced in good yield and
with the formation of by-products which are easy to handle and
environmentally favourable.
It is suggested according to the invention to produce N-phosphonomethyl-
glycine by reacting aminomethanephosphonic acid of the formula II
HO\~
/P-CH2-NH2 (II),
HO
in an aqueous medium, with glyoxal of the formula III
OHC-CHO (III)
in the presence of sulfur dioxide, and isolating the resulting
product.
There are two preferred procedures in performing the reaction
according to the invention.
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The Eirst advantageous procedure for the reaction is to suspend the
aminomethanephosphonic acid and glyoxal in water, and to
subsequently introduce sulEur dioxide into the suspension.
In this proceclure the introduction of the sulfur dioxide gas can be
performed with or without cooling oE the reaction solution. The
reaction mixture is however advantageously cooled to 0 to 30C,
particularly to 5 to 20C, during the time the sulfur dioxide gas is
being introduced. The amount of sulfur dioxide gas introduced is so
regulated that the amount is hetween that required to clarify the
suspension and that sufficing to saturate the mixture. A saturation
of the reaction solution with sulfur dioxide is however an advantage.
The second advantageous procedure for the reaction is to suspend the
aminomethanephosphonic acid in water and to subsequently introduce the
glyoxal and the sulfur dioxide into the suspension simultaneously.
In this procedure the addition of the glyoxal and the sulfur dioxide
gas is with advantage performed in a pre-heated suspension of amino-
methanephosphonic acid. The temperature of the suspension is
preferably 30 to 90C, and in particular 35 to 75C.
The amount o~ sulfur dioxide employed in this typ of procedure may
be less than the equivalent necessary to form the bis-adduct with
glyoxal. Preferred amounts of sulfur dioxide are 0.3 to 1.5 mole
per mole of glyoxal. Most preferred are 0.5 to 1.0 mole sulfur dioxid
gas per mole of glyoxal.
After completion of the introduction of the sulfur dioxide, resp. the
glyoxal and the sulfur dioxide, required, in both procedures the
solution is heated to a temperatur of between 60 and 1~0C. A
temperature of between 85C and the boiling temperature of the
reaction mixture is advantageous. The reaction solution is heated for
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a period of 5 to 120 minutes. Reaction times of 15 to 60 minutes, and
in particular of 20 to 40 minutes, are advantageous. The sulfur
dioxide gas introduced is again liberated during heating and can be
recovered.
The employed glyoxal can be used, in the reaction according to the
invention, both as an aqueous solution of the monomer and as polymer.
In order to obtain a high yield, it is oE advantage to keep the amount
of water as small as possible, since the reaction product is soluble
in water. The Eurther addition oE water ~as ~olvent can be dispensed
with in particular when dilute aqueous solutions of glyoxal are
being used.
In the reaction according to the invention~ the sulfur dioxide can
also be in the bound form instead of being in the form of sulfur
dio~ide gas. Especially suitable in this respect are alkali metal
salts and alkaline-earth metal salts of sulfurous acid, particularly
hydrogen sulfite of sodium, potassium or calcium.
Using the procedure of adding the glyoxal to a suspension of amino-
methanephosphonic acid and an alkali metal hydrogen sulfite very
small amounts of the hydrogen sulfite may be used. Even amounts of less
than 0.05 mole of sodium hydrogen sulfite per mole of glyoxal do not
lower the yield dramatically. In this case a heating of the reaction
mixture to temperatures above 75C is not advisable, in order to avoid
an evolution of sulfur dioxide gas, which would stop the reaction
before having achieved a reasonable conversion of the starting
materials. The reaction still works at concentrations of 0.01 mole of
alkali metal hydrogen sulfite per mole of glyoxal, but the reaction
rates become slower with decreasing concentrations. Reaction times
required may be up to 3 hours when low concentrations of alkali metal
hydrogen sulfite are employed.
Also adducts of glyoxal and sulfurous acid, cmd salts tllereof, can be
used as starting products for the reaction according to the invention.
Suitable in a particular manner for this purpose is the commercially
obtainable glyoxal-bis-(sodium hydrogen sulfite) hydrate.
The substitution of sulfur dioxide by salts thereof or by reaction
products of these with glyoxal is advantageous with respect to
carrying out the process of the invention in the laboratory by
virtue of the greater ease of operation; however, also in the case of
applying the process on a commercial scale, the use of sulfur dioxide
gas is of advantage Eor reasons of cost, in particular because the
sulEur dioxide released again during the reaction can be recovered and
re-utilised in the reaction of the following reaction batch~
An advantageous embodiment of the process according to the invention
comprises saturating at 5 to 20C the suspension of aminomethane-
phosphonic acid and glyoxal in water with sulfur dioxide, heating the
formed solution at 85 to 105C for 20 to 40 minutes, and isolating
the product by crystallisation.
Another advantageous embodiment of the process according to the
invention comprises introducing at 30 to 90C into a suspension of
aminomethanephosphonic acid simultaneously glyoxal and sulfur
dioxide, heating the formed solution at 85 to 105C for 20 to 40
minutes, and isolating the product by crystallisation.
Another advantageous embodiment of the process according to the
invention comprises adding at temperatures not above 75C glyoxal to
a suspension of aminomethanephosphonic acid and at least 0.01 mole of
alkalimetal hydrogen sulfite, heating the mixture of temperatures
not above 75C for 0.5 to 3 hours and isolating the product by
crystallisation.
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The reactants, aminomethanephosphonic acid and glyoxal, are as a
rule reacted in equimolar amounts.
The Examples which follow serve to further illustrate the present
invention.
Example 1: Sulfur dioxide gas is introduced at 10 to 15C, with
vigorous stirring and with cooling" into a suspension of 11.1 g
(0.1 mol) of aminomethanephosphonic acid and 11.4 ml (0.1 mol) of
40 % aqueous glyoxal in 40 ml of water until a clear solution has
formed. ~fter further stirring at room temperature for half an hour,
the solution is refluxed for halE an hour, in the course of which an
intense evolution of sulfur dioxide occurs, and the solution turns
darlc brown. The reaction mixture is afterwards cooled to 5C; the
formed precipitate is separated, washed with a small amount of ice-
water and recrystallised from water. The yield is 8.1 g (48%) of
pure N-phosphonomethylglycine; decomposition: 236C.
Example 2: A suspension of 11.1 g (0.1 mol) of aminomethane-
phosphonic acid and 702 g (0.1 mol) of 80 % polymeric glyoxal in
40 ml of water is treated with sulfur dioxide and further processed
in the manner described in Example l; yield: 7.7 g (45.5 %) of
N-phosphonomethylglycine; decomposition: 244C.
Example 3: Sulfur dioxide gas is introduced, without cooling and
with vigorous stirring, into a suspension of 11.1 g (0.1 mol) of
aminomethanephosphonic acid and 7.2 g (Ool mol) of 80 % polymeric
glyoxal in 40 ml of water until saturation is attained, in the course
of which the solution turns yellowish-orange and the temperature
rises to 42C. The solution is subsequently stirred and refluxed,
during which time the colour of the solution becomes dark brown. The
solution is filtered hot and then cooled to 5C; the precipitate is
afterwards separated, washed with a small amount of ice-cold water
and dried. The resulting yield is 10,6 g (62.8%) of N-phosphono-
methylglycine; decomposition: 235C.
Example 4: A suspension of 15.6 g (0.055 mol) of glyoxal--bis-
(sodium hydrogen sulfite) hydrate and S.5 g (0.05 mol) oE amino-
methanephosphonic acid in 30 ml of water is refluxed with stirring.
The evolution of sulfur dioxide commences when the temperature
reaches 85C; a clear solution is formed and is refluxed for
40 minutes. ~fer cooling of the reaction mixture to room temperature,
11 ml (0.11 mol) of 32 % hydrochloric acid are added, and the
mixture is concentrated by evaporation. The oily residue is triturated
with 40 ml of 36% hydrochloric acid; the salt which has
precipitated is then separated, and the solution is again concentrated
by evaporation. The oil obtained is crystallised by the addition
of 150 ml of ethanol. This suspension is neutralised to Congo red by
propylene oxide being added; the precipitate is separated, washed
with ethanol and dried. Recrystallisation from water yields 4.5 g
(53.2 %) of N-phosphonomethylglycine; decomposition: 228C.
Example 5: A suspension of 22.2 g (0.2 mol) of aminomethane-
phosphonic acid and 58 g (0.2 mol) of glyoxal-bis-(sodiumhydrogen
sulfite) hydrate in 80 ml aqueous 5 N hydrochlorid acid is heated
slowly, while stirring, until the temperature reaches 95C. When
the temperature at the interior of the reaction vessel reaches 70C,
a strong evolution of sulfur dioxide occurs and the colour of the
solution becomes light brown. After the gas-evolution has ceased,
the reaction mixture is boiled for 0.5 hour under reflux, and then
slowly cooled down to 0C.The precipitation that falls out, is
filtered off, washed with icecold water and with acetone and then
dried. Thus 20.2 g (59.8%) of N-phosphonomethylglycine is obtained,
which melts while decomposing at 236~C.
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Example 6: 26 g (0.4 mol) Sulfur dioxide gas and 58 g of a 40 %
aqueous solution of glyoxal t0.4 mol) are simultaneously introduced
at a temperature of 40C into a suspension of 4~s.4 g (0.4 mol)
of aminomethanephosphonic acid in 160 ml of water. The resulting
solution is refluxed for 30 minutes, in course of which an evolution
of sulfur dioxide occurs. The solution is then cooled to 5C; the
formecl precipitate is separated, washed with a small amount of ice-
water and dried. The resulting yield is 44 g (65 %) of N-phosphono
methylglycine; decomposition: ~250"C.
26 g (0.4 mol) Sulfur clioxide gas and 58 g of a 40 %
aqueous solution of glyoxal (0.4 mol3 are simultaneously introduced
at a temperature of 60C into a suspension of 44.4 g (0,4 mol) of
aminomethanephosphonic acid in 160 ml of water. The resulting
solution is refluxed for 30 minutes, in course of which an
evolution of sulfur dioxide occurs. The solution is then cooled to
5C; the Eormed precipitate is separated, washed with a small amount
of ice-water and dried. The resulting yield is 50 g (74 %) of
N-phosponomethylglycine; decomposition:~250C.
Example 8- 13 g (0.2 mol) Sulfur dioxide gas and S8 g of a 40 %
aqueous solution of glyoxal (0.4 mol) are simultaneously introduced
at a temperature of 60C into a suspension of 44,4 g (0.4 mol) of
aminomethanephosphonic acid in 160 ml of water. The resulting
solution is refluxed for 30 minutes, in course of which an evolution
of sulfur dioxide occurs. The solution is then cooled to 5C; the
formed precipitate is separated, washed with a small amount of ice-
water and dried. The resulting yield is 50 g (74 %) of N-phosphono-
methylglycine; decomposition: ~ 250C.
Example 9: 50.5 g of a 40 % aqueous solution of glyoxal (0.334 mol)
is dropwise added to a solution of 37.1 g (0.334 mol) of amino-
methanephosphonic acid and 2.6 g (0.016 mol) of sodium hydrogen
sulfite in 150 ml of water at a temperature of 60C. Stirring of the
mixture at the same temperature is continued for l hour; the
mixture is cooled to 5C; the forMed precipitate is separated, washed
with a small amount of ice-water and dried. The resulting yield is
37.6 g (67 %) of N-phosphonomethylglycine; decomposition:
~250~C.
