Method for production of n-phosphonomethylglycine

Details Method for production of n-phosphonomethylglycine Method for production of n-phosphonomethylglycine

2002-06-24

2004-11-16

McKane, Joseph K. (Department: 1626)

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

Organic compounds

Phosphorus acids or salts thereof

Reexamination Certificate

active

06818793

ABSTRACT:

The invention relates to a process for the preparation of N-phosphonomethylglycine by reacting a hexahydrotriazine compound with a triacyl phosphite, and to intermediates for use in this process.
N-Phosphonomethylglycine (glyphosate), of the following formula,
is a widely employed nonselective herbicide. A large number of processes for the preparation of phosphonomethylglycine are known. One possibility of preparing it exists in reacting hexahydrotriazine deirvatives with phosphorous esters. Thus, U.S. Pat. No. 4,181,300 describes the preparation of hexahydrotriazines of the formula:
and U.S. Pat. No. 4,053,505 the reaction of these hexahydrotriazines with phosphorous diesters and subsequent hydrolysis of the resulting product to give phosphonomethylglycine. It has emerged that both yield and selectivity favoring the monophosphonated product are capable of improvement. Also, phosphorous diesters are very expensive.
EP-A-104 775 (corresponding to U.S. Pat. Nos. 4,425,284, 4,482,504 and 4,535,181) describes the reaction of the above hexahydrotriazines with an acyl halide and the subsequent phosphonation with a phosphorous triester and hydrolysis to give phosphonomethylglycine in accordance with the following equation:
While this process gives relatively good yields of phosphonomethylglycine, it requires not only the use of the expensive phosphorous esters, but additionally the use of carbonyl chloride. In addition, the carbonyl chloride might at most be recovered in the form of the free acid and then reconverted into the acid chloride in a separate step, which considerably increases the costs of the process. Moreover, the alcohol with which the phosphorous acid is esterified cannot be recycled fully since an equivalent of the corresponding alkyl chloride, which is, moreover, toxicologically unacceptable, is formed during the reaction.
U.S. Pat. No. 4,428,888 (corresponding to EP-A-149 294) describes the reaction of the abovementioned hexahydrotriazine with a phosphorous acid chloride in the presence of a strong anhydrous acid, for example hydrogen chloride, and a C
1
-C
6
-carboxylic acid, such as acetic acid. In this manner, a large number of undefined by-products are obtained, and these reduce the phosphonomethylglycine yield and necessitate complicated purification of the product.
U.S. Pat. No. 4,442,044 describes the reaction of a hexahydrotriazine of the formula 5 with a phosphorous acid triester to give the corresponding phosphonate compound, which is used as herbicide.
DD-A-141 929 and DD-A-118 435 describe the reaction of an alkali metal salt of the above hexahydrotriazine (R=for example Na) with a phosphorous diester. However, since alkali salts are sparingly soluble, the conversion rate is only low.
U.S. Pat. No. 5,053,529 describes the preparation of phosphonomethylglycine by reacting the above hexahydrotriazines with phosphorous triesters in the presence of titanium tetrachloride, followed by hydrolysis of the product obtained. The use of titanium tetrachloride makes the preparation considerably more expensive. Moreover, the phosphonomethylglycine yields are unsatisfactory.
U.S. Pat. Nos. 4,454,063, 4,487,724 and 4,429,124 describe the preparation of phosphonomethylglycine by reacting a compound of the formula
in which R
1
and R
2
are aromatic or aliphatic groups with RCOX (X═Cl, Br, I) to give a compound of the formula
reaction of this product with a metal cyanide and hydrolysis of the product obtained. The disadvantages of this method are stated as above in relation to the use of the acid chloride.
Other possible syntheses which have been described are based on the cyanomethyl-substituted hexahydrotriazine of the formula.
U.S. Pat. Nos. 3,923,877 and 4,008,296 disclose the reaction of this hexahydrotriazine derivative with a dialkyl phosphonate in the presence of an acidic catalyst such as hydrogen chloride, a Lewis acid, a carbonyl chloride or a carboxylic anhydride to give a compound of the formula:
Subsequent hydrolysis yields the phosphonomethylglycine, 8 to 10% of the diphosphonomethylated product being formed.
U.S. Pat. Nos. 4,067,719, 4,083,898, 4,089,671 and DE-A-2751631 describe the reaction of cyanomethyl-substituted hexahydrotriazine with a diaryl phosphonate in the absence of a catalyst to give a compound 9 where R″=aryl. This method has he same disadvantages as described above for the use of the carboxyl-substituted hexahydrotriazine 5.
EP-A-097 522 (corresponding to U.S. Pat. Nos. 4,476,063 and 4,534,902) describes the reaction of the hexahydrotriazine 6 with an acyl halide to give 10, the subsequent phosphonation with a phosphorous triester or diester to give 11 and finally the hydrolysis to phosphonomethylglycine as described in the following equation:
The disadvantages are the same as for the processes in which the carboxyl-substituted hexahydrotriazine derivatives are used.
Finally, U.S. Pat. No. 4,415,503 describes the reaction of the cyanomethyl-substituted hexahydrotriazine in a manner which is similar to the process described in U.S. Pat. No. 4,428,888. Again, substantial formation of by-products can be observed.
EP 164 923 A describes an improved hydrolysis of a compound of the formula 11.
It is an object of the present invention to provide a simple and economical process for the preparation of phosphonomethylglycine in which the phosphomethylglycine is additionally obtained in high purity.
We have found that this object is achieved by reacting a hexahydrotriazine derivative with a triacyl phosphite and subsequently hydrolyzing the product obtained to give phosphonomethylglycine.
The present invention therefore relates to a process for the preparation of N-phosphonomethylglycine, wherein
a) a hexahydrotriazine derivative of the formula II
 in which X is CN, COOZ, CONR
1
R
2
or CH
2
OY,
Y is H or a radical which is readily exchangable for H,
Z is H, an alkali metal, alkaline earth metal, C
1
-C
18
-alkyl or aryl, which is unsubstituted or substituted by C
1
-C
4
-alkyl, NO
2
or OC
1
-C
4
-alkyl,
R
1
and R
2
can be identical or different and are H or C
1
-C
4
-alkyl, is reacted with a triacyl phosphite of the formula III
P(OCOR
3
)
3
in which the radicals R
3
, which can be identical or different, are C
1
-C
18
-alkyl or aryl which is unsubstituted or substituted by C
1
-C
4
-alkyl, NO
2
or OC
1
-C
4
-alkyl,
to give a compound of the formula I
in which R
3
and X have the abovementioned meanings and
b) the compound of the formula I is hydrolyzed, and, if X is CH
2
OY, oxidized.
Furthermore, the invention relates to the compounds of the formula I and their preparation in accordance with step a) of the process for the preparation of phosphonomethylglycine.
Alkyl is a linear or branched alkyl chain having preferably 1 to 8 carbon atoms and in particular 1 to 4 carbon atoms. Examples of alkyl are methyl, ethyl, n-propyl, i-propyl, n-butyl,
1
-butyl, sec-butyl, t-butyl, n-hexyl,
2
-ethylhexyl, etc.
Aryl is preferably phenyl and naphthyl.
X is preferably CN or COOZ.
Z is preferably H, alkali metal or C
1
-C
18
-alkyl.
If Y represents a radical which is readily exchangable for H, this preferably takes the form of an aliphatic or aromatic acyl radical or C
1
-C
6
-alkyl group. The aliphatic acyl radical is preferably a C
1
-C
6
—CO radical, and the aromatic acyl radical preferably takes the form of the benzoyl radical.
R
1
and R
2
are preferably H.
The radical R
3
especially preferably takes the form of an aryl radical which can be unsubstituted or substituted as stated above. Especially suitable radicals R
3
are phenyl, p-tolyl and p-nitrophenyl.
The compounds of the formula II are known and can be prepared in the known manner or analogously to known processes, see, for example, the state of the art mentioned at the outset. For example, an amine X-CH
2
—NH
2
can be reacted with a formaldehyde source, such as aqueous formalin solution or paraformaldehyde, for example by dissolving the primary amine in the aqueous formalin solution. The desired hexahydrotriazine can subsequently be obtained by cryst

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