CA1052119A - Herbicide formulations - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

This invention discloses novel aqueous solutions of the dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid. The concentration of the acid is 650 to 800 grams per liter of solution as its dimethylamine salt and are stable at quite low temperatures e.g. - 11°C. The solutions are thus useful as herbicidal concentrates for agricultural use. The preferred con-centration range for the 2-methyl-4-chlorophenoxyacetic acid is from 750 to 800 grams per liter of solution as its dimethylamine salt.

Description

05'~1~9 1 The present invention relates to solutions containing

2-methyl-4-chlorophenoxyacetic a~id a~ its dimethylamine salt, and more particularly to concentrated solutions of the same.
The chlorinated phenoxyalkanoic acids are well known for their herbicidal properties, and have been used in agri-culture as selective weed killers, for example in certain types of cereal crops. In order to apply these herbicides effectively ~ . , .
to the crops it is desirable that they should be evenly dis-persed in water. The resultant mixture can thereafter be sprayed in accurately controlled amounts on to the crop.
.
One method which enables such herbicides to be dis-persed in water is by making a water soluble salt of the chlor-inated phenoxyalkanoic acid. Typical such salts are the sodium, potassium and dimethylamine salts. In order to enable farme~s to use the water soluble salts conveniently, they are usually ~ ! ~
supplied as concentrated solutions. The farmer can easily pour ;-the required v~lume of concentrated solution into a pred~eter-mined quantity of water, and then spray the resulting mixture on to the crop.
It is usual to supply to the farmer the most concen~ `
trated solution of the salt which does not crystallise in cold water. The use of this maximum concentration avoids the wasted expense of the transportation of unnecessary extra weight and , ,.
the use of large containers. ~`~
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Many chlorophenoxyalkanoic acids are used in avery day commercial operations. A typical such acid is the highly : : ~
active herbicide 2-methyl-4 chlorophenoxyacetic acid; the commercially-available orm o this is the Technical Grade acid, which is referred to herein as "MCPA".
The commercially-available forms o MCPA usually contain between 92 1/2 and 96 1/2~ by weight of the active ;~-.

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1 2-methyl-4-chlorophenoxyacetic acid, and in these products the 2-methyl-6-chlorophenoxyacetic acid is the major isomeric im-, . .
purity. The Technical Grade acid used in the Examples herein-after contained 95% by weight of 2-methyl-4-chlorophenoxyacetic acid, together with other isomers and chlorinated phenoxy acids of which 2-methyl-6-chlorophenoxyacetic acid (3% ~y weight) and 2-methyl-4,6-dichlorophenoxyacetic acid (1% by weight) were the most important.

MCPA can be formulated as a solution of its sodium salt, its potassium salt or its dimethylamine salt. The highest concantration which has ade~uate low temperature properties for a sodium salt formulation is equivalent to 250 grams of MCPA
per litre of solution. As its potassium salt the equivalent ;~-MCPA concentration can be increased to 400 grams per litre of `
solution. As its dimethylamine salt, a solution containing the equivalent of 500 gxams per litre of MCPA has a crystallising point at about minus 11C, and this has been generally con~
sidered to be the highest concentration which can be safely supplied to the farmer. :
We have now surprisingly found, contrary to expecta~

tions, that solutions containing very high acid equivalent concentrations of MCPA dimethylamine salt in water are remark~
ably stable; the salt will remain in solution without signifi-cant crystallisation even when cooled down to very low tem~
peratures. More specifically, it has been surprisingly found ~ ~;
that a solution containing, in the form of its dimethylamine salt, the equivalent of 727 g/litre of MCPA remains a free ~ . :. .
flowing liquid even after 2 1/2 days at a temperature as low as minus 25C. ;~
Accordingly, there is pxovided by the present inven- ~~
tion an aqueous solution of the dimethylamine salt of 2-methyl- `
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1 4-chlorophenoxyacetic acid wherein the concentration of the said salt is equivalent to from 650 to ~00 grams of the free acid per litre of solution.
The word "stable" is used herein to mean that the solutions do not suffer any significant crystallisation at ' temperatures down to minus 11C.
Preferably a solution of the dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid in accordance with this invention will contain the eguivalent of from 750 to 800 grams of the acid per litre of solution, and a preferred concentra-tion is about 800 grams acid ~as its dimethylamine salt) per - litre of solution.
The invention also proviaes a process for the preparation of a solution as described above, which process comprises reacting a concentrated solution of dimethylamine in water, for example a s~lution containing 500 grams or more of the amine per litre, with the 2-methyl-4-chlorophenoxyacetic ,,., ~:
acid in its solid state, with stirring and cooling as necessary, and thereafter diluting the resulting solution, if desired, to yield a concentrated solution in accordance with the invention.
In order to produce these highly concentrated dimethyl-amine salt solutions it may be more convenient to increase the concentration of dimethylamine by using the amine in its gaseous form. ~;
We do not understand the reason why these very con~
centrated solutions of the dimethylamine salt of ~-meth~1-4-chlorophenoxyacetic acid exhibit the stated properties. We have considered it possible that the solutions ma~ be supersaturated at low temperatures, and that they are in fact meta-stable, but ~; -3~ this seems not to be the case. -~
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~ ~5 ~ ~9 1 The following Table illustrates the crystallisation behaviour of solutions of MCPA dimethylamine salt at reduced temperatures.
. .

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Weight/Volume Concentration Temperature at which of MCP~ (measured as free crystallisation commences acid equivalent) - grams per litre . .. , . .. , 660 below -18C

750 below -22C

915 Plus 56C
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The present invention also provides a method o~
treating weeds in agricultural crops, using 2-methyl-4-chloro-phenoxyacetic acid, by employing an aqueous solution of the dimethylamine salt, as described above,-and thereafter, prior ~`
; to applyiny the herbicide to the crop, diluting the concen-O trated solution to the required concentration for the applica-tion.
In ordex to utilise a concentrated solution o~ the invention it is first diluted with water before spraying on the crops and weeds. In a normal practical situation the water `
- .:
available for dilution contains dissolved salts, in particular those derived ~rom calcium and magnesium. The calcium salt of MCPA is only slightly soluble in water, and when-the solu--tions of the present invention are diluted with hard water this calcium salt may precipitate. This precipitation can cause spra~

nozzle blockages, uneven application and reduced effectiveness o~ the herbicide. -~;~

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1 The precipitation of calcium and other metal salts can be hindered by including in the concentrated solution se~uestrants and other adjuvants which may "chelate" or other- -wise suppress the effect of the calcium or other metal ians in the diluting water. Many well known se~uestrants and other adjuvants have been tried in a variety of concentratlons and have been found to be effective in suppressing the precipitation of these hard water salts. Of particular value are the citrate and heptonate ions. These can conveniently be added in the form of ammonium citrate (e.g. at 4% weight/weight) or sodium hepton-ate.
The present invention will be further illustrated by the *ollowing Examples.
Example I

A quantity of crystalline MCPA dimethylamine salt was prepared by prolonged storage in a vacuum desiccator over a strong dessicant (magnesium perchlorate).
Separately, a sample o~ an aqueous solution of the -dLmethylamine salt of MCPA at a concentration of 73% weight/ ;

volume ~730 gpl Technical Grade frea acid equivalent; a~out 694 gpl of pure free acid) was prepared by-dissolving MCPA in a concentrated solution of dimethylamine in water tth~ me~hod of the present invention). The formed sample was cooled to ; minus 14C, and then seeded with a small quantity of the -~
` crystals prepared as described above. It was then stored for ~ ~
three days at between minus 14C and mînus 15C. No further ~ ;
crystallisation took place, and the seeding crystals were seen to have dissolved at the end of the period.
For comparison, a sample of aqueous MCPA dimethyl~
amine salt solution (50~ weight/volume, or 500 gpl Technical ;~` ' ' ~

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t Grade free acid equivalent, or 475 gpl of pure free acid) stored at between minus 14C and minus 15C with the other sample was found to be more than half full of crystals at the end of three days even though no seeding crystals had been added.
Example 2 , .
A stable solution containing 810 gpl of MCPA (770 gpl of pure free acid), in the form of the dimethylamine salt, was made by dissolving MCPA in a concentrated solution of dimethyl-amine in water. This solution had a pH value of 7.7. When 5 mls ~
of this solution were diluted with 95 mls of water containing -342 ppm of hardness a brown precipitation was soon formed. This `~
precipitate settled after a short time to the bottom of the dilution vessel. -`
, For comparison, in another sample of the concenkrated MCPA dimethylamine salt solution was dissolved 4~ weight/weight `~;
ammonium citrate. The pH value of the resulting solution was- `~ -7.5. This solution was tested by dilution in the same way as described above. In this case no precipitate formed, and even 18 hours later the solution was still bright and clear o~
sediment. ~ ~

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Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A stable aqueous solution of the dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid, wherein the concen-tration of the said salt is equivalent to from 650 to 800 grams of the free acid per litre of solution.

2. A solution as claimed in claim 1, wherein the con-centration of the salt is equivalent to from 750 to 800 grams free acid per litre of solution.

3. A solution as claimed in claim 2, wherein the con-centration of the salt is equivalent to 800 grams free acid per litre of solution.

4. A solution as claimed in any one of claims 1 to 3, which contains a sequestrant or adjuvant which suppresses the precipitation of hard water salts of 2-methyl-4-chlorophenoxy-acetic acid when the solution is diluted with hard water.

5. A solution as claimed in any one of claims 1 to 3, which contains a sequestrant which comprises a compound which provides ions selected from the group consisting of citrate ion heptonate ions.

6. A solution as claimed in any one of claims 1 to 3, which contains a sequestrant selected from the group consisting of ammonium citrate and sodium heptonate.

7. A process for preparing a stable solution of the di-methylamine salt of 2-methyl-4-chlorophenoxyacetic acid which comprises reacting an aqueous dimethylamine solution with the acid in its solid state, and, if necessary, diluting the re-sulting solution with water to yield a solution in accordance with claim 1.

8. A process as claimed in claim 7, wherein the concen-tration of the dimethylamine solution is at least 500 grams per litre.

9. A process as claimed in claim 8, wherein gaseous di-methylamine is reacted with the resulting solution before dilution thereof.

10. A method of herbicidally treating a crop, which method comprises diluting a solution as claimed in claim 1 with water to yield a dilute solution containing the desired concen-tration of the dimethylamine salt of 2-methyl-4-chlorophenoxy-acetic acid, and then applying the dilute solution to the crop.