Highly concentrated aqueous glyphosate compositions

Details Highly concentrated aqueous glyphosate compositions Highly concentrated aqueous glyphosate compositions

2001-04-03

2002-09-24

Clardy, S. Mark (Department: 1616)

Plant protecting and regulating compositions

Plant growth regulating compositions

Organic active compound containing

Reexamination Certificate

active

06455473

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to herbicidal compositions useful in agriculture and related industries. More specifically, the present invention relates to aqueous concentrate compositions containing as active ingredient a salt of the herbicide glyphosate (N-phosphonomethylglycine), and to a method of killing or controlling unwanted vegetation using such compositions.
BACKGROUND OF THE INVENTION
Glyphosate is well known in the art as an effective post-emergent foliar-applied herbicide. In its acid form, glyphosate has a structure represented by formula (I):
and is relatively insoluble in water (1.16% by weight at 25° C.). For this reason it is typically formulated as a water-soluble salt.
Monobasic, dibasic and tribasic salts of glyphosate can be made. However, it is generally preferred to formulate glyphosate and apply glyphosate to plants in the form of a monobasic salt. The most widely used salt of glyphosate is the mono(isopropylammonium), often abbreviated to IPA, salt. Commercial herbicides of Monsanto Company having the IPA salt of glyphosate as active ingredient include Roundup®, Roundup® Ultra, Roundup® Xtra and Rodeo® herbicides. All of these are aqueous solution concentrate (SL) formulations and are generally diluted in water by the user prior to application to plant foliage. Other glyphosate salts which have been commercially formulated as SL formulations include the mono(trimethylsulfonium), often abbreviated to TMS, salt, used for example in Touchdown® herbicide of Zeneca.
Various salts of glyphosate, methods for preparing salts of glyphosate, formulations of glyphosate or its salts and methods of use of glyphosate or its salts for killing and controlling weeds and other plants are disclosed in U.S. Pat. No. 4,507,250 to Bakel, U.S. Pat. No. 4,481,026 to Prisbylla, U.S. Pat. No. 4,405,531 to Franz, U.S. Pat. No. 4,315,765 to Large, U.S. Pat. No. 4,140,513 to Prill, U.S. Pat. No. 3,977,860 to Franz, U.S. Pat. No. 3,853,530 to Franz, and U.S. Pat. No. 3,799,758 to Franz. The aforementioned patents are incorporated herein in their entirety by reference.
Among the water soluble salts of glyphosate known in the literature, but never used commercially before the priority filing date hereof, is the monoethanolammonium (MEA) salt, having a structure represented by formula (II):
in the ionic form predominantly present in aqueous solution at a pH of about 4. This salt is disclosed, for example, by Franz in U.S. Pat. No. 4,405,531 cited above, as one of a very long list of organic ammonium salts of glyphosate useful as herbicides, and, as an example of a monoalkanolammonium salt, is included among the “particularly preferred” compounds disclosed therein. An aqueous solution of the MEA salt of glyphosate can be prepared by reacting approximately equimolar amounts of glyphosate acid and monoethanolamine in an aqueous medium. The reaction is exothermic.
Very few herbicides have been commercialized as their MEA salts. Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is formulated as its MEA salt in certain herbicide products sold by DowElanco under the trademark Lontrel®.
Glyphosate MEA salt has a molecular weight of 230, very similar to that of glyphosate IPA salt (228).
Solubility of glyphosate MEA salt in water is believed not to be recorded in prior art but is readily determined by procedures familiar to those skilled in the art. Similarly, aqueous solutions of glyphosate MEA salt at concentrations greater than about 40% by weight are believed not to have been specifically disclosed, thus any unusual or unpredicted properties of such solutions have not been publicly known. Concentrations expressed as percent by weight herein relate to parts by weight of salt or acid equivalent per 100 parts by weight of solution.
It can now be disclosed that glyphosate MEA salt has been determined to have a solubility in pure water at 20° C. of about 64% by weight, that is, about 47% glyphosate acid equivalent (a.e.) by weight. This is very similar to the solubility of the IPA salt. Thus a simple aqueous solution concentrate of glyphosate MEA salt can readily be provided at a concentration of, for example, 46% a.e. by weight, comparable to that commercially obtainable with glyphosate IPA salt, as in the aqueous solution concentrate available from Monsanto Company under the name MON 0139.
A major advantage of the IPA salt over many other salts of glyphosate has been the good compatibility in aqueous solution concentrate formulations of that salt with a wide range of surfactants. Glyphosate salts generally require the presence of a suitable surfactant for best herbicidal performance. The surfactant can be provided in the concentrate formulation, or it can be added by the end user to the diluted spray composition. The choice of surfactant has a major bearing on herbicidal performance. For example, in an extensive study reported in Weed Science, 1977, volume 25, pages 275-287, Wyrill and Burnside found wide variation among surfactants in their ability to enhance the herbicidal efficacy of glyphosate, applied as the IPA salt.
Beyond some broad generalizations, the relative ability of different surfactants to enhance the herbicidal effectiveness of glyphosate is highly unpredictable.
Surfactants tending to give the most useful enhancement of glyphosate herbicidal effectiveness are generally but not exclusively cationic surfactants, including surfactants which form cations in aqueous solution or dispersion at pH levels of around 4-5 characteristic of SL formulations of monobasic salts of glyphosate. Examples are long-chain (typically C
12
to C
18
) tertiary alkylamine surfactants and quaternary alkylammonium surfactants. The term “alkyl” as conventionally used herein in describing surfactant structures includes unsaturated as well as saturated hydrocarbyl chains. An especially common tertiary alkylamine surfactant used in aqueous solution concentrate formulations of glyphosate IPA salt has been the very hydrophilic surfactant polyoxyethylene (15) tallowamine, i.e., tallowamine having in total about 15 moles of ethylene oxide in two polymerized ethylene oxide chains attached to the amine group as shown in formula (III):
where R is a mixture of predominantly C
16
and C
18
alkyl and alkenyl chains derived from tallow and the total of m+n is an average number of about 15.
For certain applications, it has been found desirable to use a somewhat less hydrophilic alkylamine surfactant, such as one having less than about 10 moles of ethylene oxide, as suggested in U.S. Pat. No. 5,668,085 to Forbes et al., for example polyoxyethylene (2) cocoamine. That patent discloses illustrative aqueous compositions comprising such a surfactant together with the IPA, ammonium or potassium salts of glyphosate.
A wide variety of quaternary ammonium surfactants have been disclosed as components of aqueous solution concentrate formulations of glyphosate IPA salt. Illustrative examples are polyoxyethylene (2) cocoammonium chloride, disclosed in European Patent No. 0 274 369, polyoxyethylene (15) cocoammonium chloride, disclosed in U.S. Pat. No. 5,317,003, and various quaternary ammonium compounds having formula (IV):
(R
1
)(R
2
)(R
3
)N
+
—CH
2
CH
2
O—(CH
2
CH(CH
3
)O)
n
H Cl
−
  (IV)
where R
1
, R
2
and R
3
are each C
1-3
alkyl groups and n is an average number from 2 to 20, disclosed in U.S. Pat. No. 5,464,807.
PCT Publication No. WO 97/16969 discloses aqueous solution concentrate compositions of glyphosate, in the form of the IPA, methylammonium and diammonium salts, comprising a quaternary ammonium surfactant and an acid salt of a primary, secondary or tertiary alkylamine compound.
Other cationic surfactants which have been indicated as useful in aqueous solution concentrate compositions of glyphosate salts include those disclosed in PCT Publication No. WO 95/33379. It is further disclosed in PCT Publication No. WO 97/32476 that highly concentrated aqueous compositions of glyphosate salts can be made with certain of these same cationic surfactants, with the fu

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