Process for producing N-phosphonomethylglycine

A process for producing N-phosphonomethylglycine by the oxidation of N-phosphonomethyliminodiacetic acid using a molecular oxygen-containing gas in the presence of a transition metal catalyst.

FIELD OF THE INVENTION 
This invention relates to a process for producing N-phosphonomethylglycine 
by the oxidation of N-phosphonomethyliminodiacetic acid using transition 
metal catalysts. More particularly, this invention relates to a reaction 
using molecular oxygen and a transition metal salt catalyst. 
SUMMARY OF RELATED ART 
It is known in the art that N-phosphonomethylglycine can be produced by 
oxidizing N-phosphonomethyliminodiacetic acid using various oxidizing 
methods. U.S. Pat. No. 3,950,402 discloses a method wherein 
N-phosphonomethyliminodiacetic acid is oxidized to 
N-phosphonomethylglycine in aqueous media using a free oxygen-containing 
gas and a heterogeneous noble metal-based catalyst such as palladium, 
platinum or rhodium. U.S. Pat. No. 3,954,848 discloses the oxidation of 
N-phosphonomethyliminodiacetic acid with hydrogen peroxide and an acid 
such as sulfuric or acetic acid. U.S. Pat. No. 3,969,398 discloses the 
oxidation of N-phosphonomethyliminodiacetic acid using molecular oxygen 
and a heterogeneous activated carbon catalyst. Hungarian Patent 
Application No. 011706 discloses the oxidation of 
N-phosphonomethyliminodiacetic acid with peroxide in the presence of 
metals or metal compounds. 
R. J. Motekaitis, A. E. Martell, D. Hayes and W. W. Frenier, Can. J. Chem., 
58, 1999 (1980) disclose the iron(III) or copper(II) catalysed oxidative 
dealkylation of ethylene diaminetetracetic acid (EDTA) and 
nitrilotriacetic acid (NTA), both of which have iminodiacetic acid groups. 
R. J. Moteakitis, X. B. Cox, III, P. Taylor, A. E. Martell, B. Miles and 
T. J. Tvedt, Can. J. Chem., 60, 1207 (1982) disclose that certain metal 
ions, such as Ca(II), Mg(II), Fe(II), Zn(II) and Ni(II) chelate with EDTA 
and stabilized against oxidation, thereby reducing the rate of oxidative 
dealkylation. 
SUMMARY OF THE INVENTION 
The present invention involves a process for the production of 
N-phosphonomethylglycine comprising contacting 
N-phosphonomethyliminodiacetic acid with a molecular oxygen-containing gas 
in the presence of a transition metal catalyst.

DETAILED DESCRIPTION OF THE INVENTION 
The process of this invention involves contacting 
N-phosphonomethyliminodiacetic acid with a transition metal catalyst in a 
mixture or solution. This mixture or solution is contacted with a 
molecular oxygen-containing gas while heating the reaction mass to a 
temperature sufficiently elevated to initiate and sustain the oxidation 
reaction of N-phosphonomethyliminodiacetic acid to produce 
N-phosphonomethylglycine. 
The transition metal catalyst of the present invention can be any one or 
more of several transition metal compounds such as manganese, cobalt, 
iron, nickel, chromium, ruthenium, aluminum, molybdenum, vanadium and 
cerium. The catalysts can be in the form of salts such as manganese salts, 
e.g., manganese acetate, manganese sulfate; complexes such as 
manganese(II)bis(acetylacetonate) (Mn(II)(acac).sub.2); cobalt salts such 
as Co(II)(SO.sub.4), Co(II)(acetylacetonate), CoCl.sub.2, CoBr.sub.2, 
Co(NO.sub.3).sub.2 and cobalt acetate; cerium salts such as 
(NH.sub.4).sub.4 Ce(SO.sub.4) and (NH.sub.4).sub.2 Ce(NO.sub.3).sub.6, 
iron salts such as (NH.sub.4).sub.2 Fe(SO.sub.4).sub.2, 
iron(III)(dicyano)-(bisphenanthroline).sub.2 -(tetrafluoro)borate salt and 
K.sub.3 Fe(CN).sub.6, and other metal salts such as NiBr.sub.2, 
CrCl.sub.3, RuCl.sub.2 (Me.sub.2 SO), RuBr.sub.3, Al(NO.sub.3).sub.3, 
K.sub.4 Mo(CN).sub.8, VO(acetylacetonate).sub.2 and VOSO.sub.4. The 
catalyst can be added to the N-phosphonomethyliminodiacetic acid in the 
salt form, or a salt may be generated in situ by the addition of a source 
of a transition metal ion such as MnO.sub.2 which dissolves in the 
reaction medium. The Mn(III)chloro(phthalocyaninato), however, is not 
catalytic, possibly because the phthalocyanine ligand covalently bonds to 
the Mn(III) and therefore inhibits the formation of 
N-phosphonomethyliminodiacetic acid/ manganese complex in solution. 
Manganese salts such as Mn(II), Mn(III) or Mn(IV) salts can be used 
individually, however, the reaction displays a delayed reaction initiation 
time (initiation period), e.g., there is a delay before any 
N-phosphonomethylglycine is produced. When a mixture of Mn(II) and Mn(III) 
salts are used as a catalyst system, the initiation is diminished or 
eliminated. A preferred manganese salt catalyst is a mixture of Mn(II) and 
Mn(III) salts in the range of 1:10 to 10:1 mole ratio of the Mn ions. A 
most preferred manganese catalyst salt is a 1:1 mole ratio of Mn(II) and 
Mn(III) ions in the form of manganese acetate salts. A preferred cobalt 
catalyst is a Co(II) salt such as Co(II)(SO.sub.4), Co(II)Cl.sub.2, 
Co(II)Br.sub.2, Co(II)(OH).sub.2 and Co(II)acetate. 
The concentration of the transition metal catalyst in the reaction solution 
can vary widely, in the range of 0.1M to 0.0001M total metal ion 
concentration. For manganese, the reaction appears to have a first order 
dependency on the catalyst concentration, e.g., the reaction rate 
increases linearly as the catalyst concentration increases. The preferred 
concentration is in the range of about 0.01M to about 0.001M, which gives 
a suitably fast rate of reaction that can be easily controlled and favors 
selectivity to N-phosphonomethylglycine. 
The reaction temperature is sufficient to initiate and sustain the 
oxidation reaction, in the range of about 25.degree. C. to 150.degree. C. 
In general, as the reaction temperature increases, the reaction rate 
increases. To achieve an easily controlled reaction rate and favor 
selectivity to N-phosphonomethylglycine, a preferred temperature range is 
about 50.degree. C. to 120.degree. C. and a most preferred is in the range 
of about 70.degree. C. to 100.degree. C. If a temperature of above about 
100.degree. C. is used, pressure will have to be maintained on the system 
to maintain a liquid phase. 
The pressure at which this process is conducted can vary over a wide range. 
The range can vary from about atmospheric (101 kPa) to about 3000 psig 
(207600 kPa). A preferred range is about 30 psig (200 kPa) to about 1000 
psig (about 6900 kPa). A most preferred range is from about 150 psig 
(about 1000 kPa) to 600 psig (about 4140 kPa). 
The oxygen concentration, as designated by the partial pressure of oxygen 
(PO.sub.2), in the reaction affects the reaction rate and the selectivity 
to the desired product, N-phosphonomethylglycine. As the PO.sub.2 
increases, the reaction rate generally increases and the selectivity to 
N-phosphonomethylglycine increases. The PO.sub.2 can be increased by 
increasing the overall reaction pressure, or by increasing the molecular 
oxygen concentration in the molecular oxygen-containing gas. The PO.sub.2 
can vary widely, in the range of from 1 psig (6.9 kPa) to 3000 psig (20700 
kPa). A preferred range is from 30 psig (207 kPa) to 1000 psig (6900 kPa). 
The term "molecular oxygen-containing gas" means molecular oxygen gas or 
any gaseous mixture containing molecular oxygen with one or more diluents 
which are non-reactive with the oxygen or with the reactant or product 
under the conditions of reaction. Examples of such diluent gases are air, 
helium, argon, nitrogen, or other inert gas, or oxygen-hydrocarbon 
mixtures. A preferred molecular oxygen is undiluted oxygen gas. 
The manner in which the solution or mixture of the 
N-phosphonomethyliminodiacetic acid is contacted with molecular oxygen can 
vary greatly. For example, the N-phosphonomethyliminodiacetic acid 
solution or mixture can be placed in a closed container with some free 
space containing molecular oxygen and shaken vigorously or agitated by 
stirring. Alternatively, the molecular oxygen can be continuously bubbled 
through the solution or mixture containing the transition metal catalyst 
using a straight tube or a tube with a fritted diffuser attached to it. 
The process of this invention only requires actively contacting the 
molecular oxygencontaining gas with the aqueous solution or mixture of the 
N-phosphonomethyliminodiacetic acid containing a transition metal 
catalyst. 
The initial pH (pHi) of the reaction affects the reaction rate and the 
selectivity to N-phosphonomethylglycine. For example, with manganese, as 
the initial pH increases, the reaction rate increases, but the selectivity 
to N-phosphonomethylglycine decreases. The pHi of the reaction can vary 
widely, in the range of about 0.1 to about 7. A preferred range is about 1 
to about 3 with mangnaese and about 0.1 to 3 with cobalt. A most preferred 
pH is the unadjusted pH of N-phosphonomethyliminodiacetic acid in a water 
solution which varies with the N-phosphonomethyliminodiacetic acid 
concentration and the reaction temperature. 
The oxidation reaction can take place in a solution or slurry. For a 
solution, the initial concentration of the N-phosphonomethyliminodiacetic 
acid in the reaction mass is a function of the solubility of the 
N-phosphonomethyliminodiacetic acid in a solvent at both the desired 
reaction temperature and the pHi of the solution. As the solvent 
temperature and pH changes, the solubility of the 
N-phosphonomethyliminodiacetic acid changes. A preferred initial 
concentration of the N-phosphonomethyliminodiacetic acid is a saturated 
slurry containing a solvent system at reaction conditions, which maximizes 
the yield of N-phosphonomethylglycine in the reaction mass. A preferred 
concentration of N-phosphonomethyliminodiacetic acid is in the range of 
about 1 to 50 wt. %. It is, of course, possible to employ very dilute 
solutions of N-phosphonomethyliminodiacetic acid, or slurries and 
mixtures. 
The reaction is typically carried out in an aqueous solvent. The term 
aqueous solvent means solutions containing at least about 50 weight % 
water. The preferred aqueous solvent is distilled, deionized water. 
The following examples are for illustration purposes only and are not 
intended to limit the scope of the claimed invention. 
EXAMPLES 
A series of runs were made to oxidize N-phosphonomethyliminodiacetic acid 
to N-phosphonomethylglycine. The reactions were conducted in a modified 
Fisher-Porter glass pressure apparatus or an Engineer Autoclave 300 ml 
pressure reactor in which a stirrer was installed in the head, as were 
three additional valved ports that were used as a sample port, a gas 
inlet, and a purged gas outlet. The stirrer maintained sufficient 
agitation to afford thorough gas-liquid mixing. The temperature was 
controlled by immersing the reactor in a constant temperature oil bath. 
The indicated amount of transition metal catalyst was dissolved or 
suspended in a distilled, deionized water solution containing the 
indicated amount of N-phosphonomethyliminodiacetic acid. The reactor was 
sealed and heated to the indicated reaction temperature, then pressurized 
to the indicated PO.sub.2 with oxygen gas. Agitation was initiated. 
The selectivity (mole %) to N-phosphonomethylglycine was determined by 
dividing the moles of N-phosphonomethylglycine produced by the total moles 
of N-phophonomethyliminodiacetic acid consumed and multiplying by 100. The 
yield (mole %) of N-phosphonomethylglycine was determined by dividing the 
moles of N-phosphonomethylglycine produced by the total moles of starting 
M-phosphonomethyliminodiacetic acid and multiplying by 100. 
EXAMPLES 1 THROUGH 8 
Examples 1 through 8, shown in Table 1, show the effect of varying the 
manganese catalyst concentration. In examples 1-4 the reaction temperature 
was 90.degree. C., the PO.sub.2 was 100 psig (690 kPa), the initial 
N-phosphonomethyliminodiacetic acid concentration was 0.1M. The catalyst 
was a mixture of Mn(II) and Mn(III) acetate salts in a 1:1 mole ratio of 
Mn(II) and Mn(III). Examples 5-8 were run at the same conditions as 1-4, 
except that the PO.sub.2 was 450 psig (3100 kPa) and the reaction 
temperature was 80.degree. C. and the catalyst was Mn(II) acetate. 
TABLE 1 
______________________________________ 
Effect of Varying Catalyst Concentration 
Yield of 
Selectivity Initial N--Phosphono- 
to N--phospho 
Manganese Reaction 
methyl glycine 
Ex- nomethyl- Concen- Rate (Male %) 
am- glycine tration (Velocity, 
at indi- 
ples (Mole %) (M) M/hr) cated time (h) 
______________________________________ 
1 58 0.008 0.23 53(6) 
2 82 0.004 0.10 75(6) 
3 84 0.002 0.05 18(11/4) 
4 63 0.001 0.016 45(6) 
5 83 0.02 0.30 83(2/3) 
6 83 0.0067 0.10 81(1/2) 
7 70 0.004 0.07 68(6) 
8 74 0.002 0.034 68(6) 
______________________________________ 
The data indicated that the reaction rate increases with the catalyst 
concentration. There appeared to be a first-order dependence of the 
reaction rate on the catalyst concentration. 
EXAMPLES 9 THROUGH 13 
Examples 9 through 13, shown in Table 2, illustrate the effect of initial 
pH on the reaction rate and selectivity to N-phosphonomethylglycine for a 
manganese catalyst. The reaction temperature was 80.degree. C., the 
PO.sub.2 was 100 psig (690 kPa), the initial 
N-phosphonomethyliminodiacetic acid concentration was 0.1M, the reaction 
times are indicated and the manganese ion concentration was 0.004M. The 
mixture of manganese salts was the same as used in Example 1. The initial 
pH was adjusted using sodium hydroxide or sulfuric acid solutions. THe 
data indicate that as the initial pH increases, the reaction rate 
increases, but the selectivity to N-phosphonomethylglycine decreases. 
TABLE 2 
______________________________________ 
Effect of Varying Initial pH 
Yield of Selectivity 
Initial N--phosphonomethyl 
to N--phos- 
Reaction glycine (Mole %) 
phonomethyl 
Exam- Initial Rate at indicated time 
glycine 
ple pH (M/h) (h) (Mole %)(h) 
______________________________________ 
9 1.20 0.0103 31(6) 49(6) 
10 1.35 0.015 56(5) 66(5) 
11 1.80 0.11 41(21/2) 44(21/2) 
12 2.30 0.14 36(21/2) 37(21/2) 
13 3.50 0.32 39(39) 41(1/2) 
______________________________________ 
EXAMPLES 14 THROUGH 16 
Examples 14 through 16, shown in Table 3, illustrate the effect of reaction 
temperature on reaction rates and selectivity to N-phosphonomethyl glycine 
for a manganese catalyst. The PO.sub.2 was 450 psig, the initial 
N-phosphonomethyliminodiacetic acid concentration was 0.1M and the 
manganese ion concentration was 0.067M. The form of the manganese salt was 
Mn(II)SO.sub.4. and the pH was the unadjusted pH of the acid solution. 
The data indicated that as the reaction temperature increased, the reaction 
rate increased. 
TABLE 3 
______________________________________ 
Effect of Varying Temperature 
Selectivity to 
N--phosphono- 
Yield 
methyl of N--phosphono- 
Initial glycine methyl glycine 
Temper- Reaction (Mole %) at 
(Mole %) at 
Exam- ature Rate indicated indicated time 
ple (.degree.C.) 
(M/hr) time (h) (h) 
______________________________________ 
14 70 0.035 77 (5) 75(5) 
15 80 0.093 83 (11/2) 81(11/2) 
16 90 0.310 80 (1/2) 77(1/2) 
______________________________________ 
EXAMPLES 17 THROUGH 22 
Examples 17 through 22, shown in Table 4, illustrate the effect of PO.sub.2 
on selectivity to N-phosphonomethylglycine for a manganese catalyst. The 
reaction temperature was 80.degree. C., the initial 
N-phosphonomethyliminodiacetic acid concentration was 0.1, the reaction 
time was as indicated which allowed for almost complete conversion of the 
N-phosphonomethyliminodiacetic acid, and the manganese ion concentration 
was 0.006M. The form of the manganese salt was Mn(II)SO.sub.4 and the pHi 
was the unadjusted pH of the acid solution. 
The data indicated that as the PO.sub.2 increased, the selectivity to 
N-phosphonomethylglycine increased. 
TABLE 4 
______________________________________ 
Effect of Varying PO.sub.2 
Yield of 
N--phospho- 
Selectivity nomethyl 
to N--phosphono- 
glycine 
methyl glycine 
(Mole %) 
(Mole %) at the 
PO.sub.2 at the indica- 
indicated 
Example psig (kPa) ted time (h) time (h) 
______________________________________ 
17 40(210) 56(6) 54(6) 
18 70(450) 65(6) 63(6) 
19 100(690) 68(6) 66(6) 
20 130(890) 75(6) 73(6) 
21 225(1550) 81(2) 78(2) 
22 450(3100) 83(11/2) 81(11/2) 
______________________________________ 
EXAMPLES 23 THROUGH 29 AND CONTROL 1 
Examples 23 through 29 and Control 1, shown in Table 5, illustrate the 
effect of varying the form of the manganese catalyst on selectivity to 
N-phosphonomethylglycine. The reaction temperature was 90.degree. C., the 
PO.sub.2 was 100 psig (700 kPa), the initial concentration of 
N-phosphonomethyliminodiacetic acid was 0.1M, the manganese concentration 
was 0.004M and the reaction time was 1 h. The pHi was the unadjusted pH of 
the acid solution. 
The Mn(III)chloro-(phthalocyaninato) (Control 1) was not catalytic. 
TABLE 5 
______________________________________ 
Effect of Varying Form of Manganese 
Selectivity to 
N--phosphonomethyl 
glycine (Mole %) 
Selectivity 
Example 
Form at 1 h. at 6 h. 
______________________________________ 
23 .sup.1 Mn(II)/Mn(III) 
43 75 
24 Mn(II)acetate 
18 75 
25 Mn(III)acetate 
20 75 
26 Mn(II)sulfate 
16 75 
27 .sup.2 Mn(II)(acac) 
20 75 
28 .sup.3 MnCl.sub.2.4H.sub.2 O 
82 -- 
29 .sup.3 MnO.sub.2 
70 73 
Control 
.sup.4 Mn(III) 
1 &lt;10 
______________________________________ 
.sup.1 Mn acetate, 50/50 mole ratio Mn(II)/Mn(III) 
.sup.2 Mn(II)bis(acetylacetonate) 
.sup.3 PO.sub.2 = 450 psig (3100 kPa) at 80.degree. C. and Mn 
concentration was 0.0lM. 
.sup.4 Mn(III)chloro-(phthalocyanato) 
EXAMPLES 30 THROUGH 42 
Examples 30 through 42, shown in Table 6, further illustrate the present 
invention. The initial pH, unless otherwise indicated, was the unadjusted 
pH at reaction temperature, the PO.sub.2, unless otherwise indicated, is 
100 psig (690 kPa), the initial concentration of 
N-phosphonomethyliminodiacetic acid was 0.1M, and the manganese catalyst 
was the mixture used in Example 1. 
TABLE 6 
__________________________________________________________________________ 
Run Time 
Catalyst Temperature 
Yield Conversion 
Example 
(h) Concentration(M) 
(.degree.C.) 
(Mole %) 
(Mole %) 
__________________________________________________________________________ 
30 1 .01 90 10 96 
31 1 .02 80 42 97 
32 l.sup.a 
.007 80 32 91 
33 2 .01 70 8 95 
34 2 .007 80 65 95 
35 2.sup.b 
.007 70 74 96 
36 2.sup.c 
.007 80 25 75 
37 2.sup.d 
.007 80 22 63 
38 2 .004 90 42 80 
39 2 .002 90 60 75 
40.sup.e 
21/2 .007 80 85 100 
41.sup.f 
1 .007 80 95 97 
42.sup.g 
5 .07 80 19 84 
__________________________________________________________________________ 
.sup.a pHi = 2.3 
.sup.b PO.sub.2 = 130 psig(810 kPa) 
.sup.c PO.sub.2 = 40 psig(275 kPa) 
.sup.d pHi = 1.35 
.sup.e PO.sub.2 = 225 psig(1545 kPa) 
.sup.f PO.sub.2 = 450 psig (3100 kPa) 
.sup.g Catalyst was Mn(II)acetylacetonate, the PO.sub.2 was 450 psi(3000 
kPa) and the initial concentration of N--phosphonomethyliminodiacetic aci 
was 0.5M. 
EXAMPLES 43 THROUGH 65 
Examples 43 through 65, shown in Table 7, illustrate the use of cobalt 
catalysts in the present invention. The initial concentration of 
N-phosphonomethiminodiacetic acid was 0.1M and the catalyst was 
Co(II)(SO.sub.4). The pH was the unadjusted pH of the 
N-phosphonomethyliminodiacetic acid of the solution, unless otherwise 
indicated when it was adjusted with sodium hydroxide or sulfuric acid 
solution. 
TABLE 7 
__________________________________________________________________________ 
Cobalt Catalysts 
Catalyst 
Run Time 
Concentration 
Temperature 
Yield Conversion 
Example 
(h) (M) (.degree.C.) 
(Mole %) 
(Mole %) 
pH PO.sub.2 (psi) 
__________________________________________________________________________ 
43 5.5 0.02 80 73 100 unadjusted 
450 
44 3.0 0.02 85 85 100 " 450 
45 1.75 0.02 90 75 100 " 450 
46 5.5 0.02 85 90 100 " 450 
47 5 0.02 85 98 100 " 1000 
48 2.0.sup.a 
0.02 85 21 31 " 450 
49 5.5 0.02 85 74 98 " 300 
50 3.0.sup.b 
0.036 90 87 100 " 450 
51 4.0.sup.c 
0.048 80 64 97 " 450 
52 5.0.sup.d 
0.125 85 52 99 " 450 
53 18.sup.f 
0.5 100 16 100 6.25 100 
54 18.sup.e 
0.5 100 28 98 1.80 100 
55 18.sup.e 
0.5 100 16 100 2.25 100 
56 18.sup.e 
0.5 100 0 100 4.00 100 
57 18.sup.e 
0.5 100 35 98 1.09 100 
58 18.sup.e 
0.5 100 9.9 22 0.77 100 
59 18.sup.e 
0.5 100 17 98 1.7 100 
60 18.sup.e 
0 100 0 98 9.00 100 
61 18.sup.e 
0.01 100 20 40 0.44 100 
62 2.sup.f 
0.01 100 28 98 1.80 100 
63 2.sup.g 
0.01 100 26 98 1.80 100 
64 18.sup.h 
0.01 100 26 98 1.74 100 
65 5.sup.i 
0.2 85 66 99 1.7M 450 
__________________________________________________________________________ 
.sup.a The catalyst was Co(III)(acetylacetonate).sub.3. 
.sup.b The initial N-phosphonomethyliminodiacetic acid concentration was 
0.3M. 
.sup.c The initial N-phosphonomethyliminodiacetic acid concentration was 
0.4M. 
.sup.d The initial N-phosphonomethyliminodiacetic acid concentration was 
1.0M. 
.sup.e The initial N-phosphonomethyliminodiacetic acid concentration was 
0.5M, the catalyst was CoCl.sub.2. 
.sup.f The initial N-phosphonomethyliminodiacetic acid concentration was 
0.5M and the catalyst was Co(NO.sub.3).sub.2. 
.sup.g The initial N-phosphonomethyliminodiacetic acid concentration was 
0.5M and the catalyst was cobalt acetate. 
.sup.h The initial N-phosphonomethyliminodiacetic acid concentration was 
0.5M and the catalyst was CoBr.sub.2. 
.sup.i The initial N-phosphonomethyliminodiacetic acid concentration was 
0.4M. 
EXAMPLES 66 THROUGH 85 
Examples 66 through 85, shown in Table 8, illustrate iron catalysts 
suitable for the present invention. The PO.sub.2 was 100 psi (690 kPa), 
the catalyst concentration was 0.01M, the reaction temperature was 
100.degree. C., the run time was 18 h, and the initial concentration of 
the N-phosphonomethyliminodiacetic acid was 0.5M, which formed a slurry. 
When NaBr was added, the concentration was also 0.01 M. 
TABLE 8 
__________________________________________________________________________ 
Iron Catalysts 
Yield Conversion 
Example 
Catalyst (mole %) 
(mole %) 
pH 
__________________________________________________________________________ 
66 Fe(SO.sub.4).sub.2 
21 36 6.25 
67 " 18 28 10.0 
68 " 6 14 5.0 
69 Fe(SO.sub.4).sub.2 + NaBr 
5 6 3.0 
70 " 12 14 5.0 
71 " 26 40 6.25 
72 " 28 84 7.0 
73 " 29 84 8.0 
74 " 37 83 9.0 
75 iron(III)(dicyano)bis 
6 12 6.25 
(o-phenanthroline) tetrafluoroborate 
salt 
76 " 8 10 7.0 
77 " 3 12 9.0 
78 " 3 12 10.0 
79 K.sub.3 Fe(CN).sub.6.sup.a 
3 14 3.0 
80 " 8 24 5.0 
81 " 21 46 6.3 
82 " 30 76 7.0 
83 " 37 80 9.0 
84 " 32 80 10.0 
85 Fe(SO.sub.4).sub.2 + Al(NO.sub.3).sub.3 
21 72 6.0 
__________________________________________________________________________ 
.sup.a Run time is 8 h. 
EXAMPLES 86 THROUGH 106 AND CONTROL 2 
Examples 86 through 106 and Control 2, shown in Table 9, illustrate nickel, 
chromium, ruthenium, aluminum, and molybdenum catalysts appropriate for 
the present invention. The conditions are as for those given in Table 8. 
The catalyst for Control 2, CuCl.sub.2, appeared to be ineffective. 
Table 9 
______________________________________ 
Nickel Chromium, Ruthenium, Aluminum 
and Molybdenum Catalysts 
Yield Conversion 
Examples 
Catalyst (mole %) (mole %) 
pH 
______________________________________ 
86 NiBr.sub.2 0.2 22 5.0 
87 " 0.2 10 4.0 
88 " 10 34 7.0 
89 " 9 38 8.4 
90 " 8 34 10.4 
91 CrCl.sub.3 1 12 1.26 
92 " 4 16 2.0 
93 " 16 76 3.0 
94 " 0.1 14 4.0 
95 " 12 52 5.0 
96 " 4 22 7.0 
97 " 13 58 6.25 
98 RuBr.sub.3 70 8 6.25 
99 " 18 34 10.0 
100 RuBr.sub.2 (Me.sub.2 SO).sub.4 
34 62 6.25 
101 " 25 48 11.0 
102 Al(NO.sub.3).sub.3 
11 34 6.25 
103 Al(NO.sub.3).sub.3 + NaCl 
12 16 6.25 
Control 2 
CuCl.sub.2 0.2 14 6.25 
104 K.sub.4 Mo(CN).sub.8 
4 22 4.0 
105 " 32 48 6.0 
106 " 10 30 9.0 
______________________________________ 
EXAMPLES 107-109 
Examples 107 through 109 shown in Table 10, illustrate vanadium catalysts 
suitable for the present invention. The reaction temperature was 
70.degree. C., the PO.sub.2 was 100 psi (690 kPa), the initial 
concentration of N-phosphonomethyliminodiacetic acid was 0.5M, the 
catalyst concentration was 0.033M. 
TABLE 10 
______________________________________ 
Vanadium Catalysts 
Run 
Time Yield Conversion 
Examples 
Catalyst (h) (mole %) 
(mole %) 
______________________________________ 
107 VO(acetylacetonate).sub.2 
2 40 67 
108 VOSO.sub.4 (hydrate) 
2.25 42 94 
109 VOSO.sub.4 (hydrate).sup.a 
5 54 91 
______________________________________ 
.sup.a The initial concentration of N--phosphonomethyliminodiacetic acid 
was 0.15 M and the concentration of catalyst was 0.015 M. 
EXAMPLES 110 AND 111 
Examples 110 and 111 shown in Table 11 illustrate cerium catalysts suitable 
for the present invention. The reaction temperature was 90.degree. C. and 
the PO.sub.2 was 130 psi (897 kPa). 
TABLE 11 
__________________________________________________________________________ 
Cerium Catalysts 
N--phosphonomethyl- 
Catalyst 
iminodiacetic acid 
Run Time 
Concentration 
Concentration 
Yield 
Conversion 
Example 
Catalyst (h) (M) (M) (mole %) 
(mole %) 
__________________________________________________________________________ 
110 Ce(NH.sub.4).sub.4 (SO.sub.4).sub.4 
3 0.1 1.0 7 45 
111 Ce(NH.sub.4).sub.4 (SO.sub.4).sub.4 
3 0.01 0.1 30 80 
__________________________________________________________________________