IL26540A - Alpha-(2,4-dichlorophenoxy)-propionic acid methyl ammonium salt and its use as a herbicidal agent - Google Patents

Description

26540/2 -TiiV3,»,,r-4,2)-a nsDinn οτ»3ΐοκ V»no Π¾·Ο a-(2, -Dichlorophenoxy)-propionic acid methyl ammonium salt and its use as a kerbicidai PARBE PABRI E BAYER AKTIE &ESKLLSCHAPT C:-25250 The present invention relates to a new alky! ammonium a&lm of 2 , 4-dichlorophenoxypropionic acid and to its use in solid form as herbicidal active compound.

It has already become known that salts of 2 , 4-dichloro- phenoxypropionic acid, e.g. the alkali metal salts, the alkylamine and dialkylamine salts, can be used in the form of aqueous solutions as herbicides (cf. e.g. Austrian Patent Specification No. 217.241» Swiss Patent Specification No. 372.191 and French Patent Specification No. 1.184.025). These salt solutions are prepared from 2, 4-dichlorophenoxypropionic acid and stoichiometric amounts of the appropriate alkali metal hydroxides or amines in water and are put on the market after adjustment to a certain concentration of active compound. For the preparation of the ready-to-use herbicidal spray liquors, these aqueous solutions are diluted to the desired usage concentrations with water.

Compared with solid preparations of active compound, aqueous preparations of active compound exhibit a number of disadvantages which in practise may be considerable. Thus, packaging and transportation of aqueous preparations are substantially costlier and more difficult to effect than those of solid substances.

Moreover, with aqueous solutions there is in winter the risk of freezing of the solutions.

In addition to this there exists the possibility that the active compounds may crystallise out at low temperatures through going below the solubility limit* A particular problem is to be seen here. In general, the aqueous solutions of active compound are put on the market in very concentrated form in order to save transportation costs. However, such aqueous solutions are often particularly sensitive to cooling, because the active compound crystallises out very rapidly.

There exists, therefore, a considerable technological need to replace the aqueous solutions of the salts of 2,4-dichlorophenoxypropionic acid by solid preparations of active compound.

For this reason there has been no lack of attempts to prepare and put on the market salts of 2,4-dichlorophenoxypropionic acid in solid form. However, considerable technical difficulties stood in the way of these attempts.

Thus, the alkali metal salts of 2,4-dichlorophenoxypropionic acid are strongly hygroscopic and therefore cannot be isolated without great difficulties from aqueous solutions. Moreover, they are difficult to handle technically.

The amine salts are not hygroscopic but they cannot be isolated in simple manner either, because in their preparation by the neutralisation of technical 2,4-dichlorophenoxypropionic acid with amines they are obtained in the form of oils and greases and can only with difficulty be made to crystallise. Even when purified acid and anhydrous organic solvents are used, only oils which crystallise very poorly are obtained. Also when aqueous solutions of such amine salts are concentrated by evaporation, greases are obtained which only very slowly become partially crystalline.

We have now found an active herbicidal compound which enables the above disadvantages to be overcome or reduced.

Accordingly, the invention provides the monomethyl ammonium salt of ( 2, 4-dichlorophenoxy)-propionic acid of the formula The invention also provides herbicidal agents in solid form which contain the monomethyl ammonium salt of 2,4-dichlorophenoxypropionic acid and its use for the preparation of ready-to-uee aqueous spray liquors by solution of the herbicidal agents in water and for the preparation of ready-to-use, solid preparations of active compound by dilution of the herbicidal agents with customary extenders.

Surprisingly, the hitherto unknown monomethyl ammonium salt of 2,4-dichlorophenoxypropionic acid can be prepared in solid form in technologically simple manner. This is true not only in respect of the pure 2,4-dichlorophenoxypropionic acid, but also in respect of the technical acid which contains various impurities and is generally obtained in moist form.

The easy production of monomethyl ammonium salt of 2,4-dichlorophenoxypropionic acid in solid form is to be considered as particularly surprising when it is taken into account that it is not possible, either, with ammonia or dimethylamine , monoethyl-amine, diethylamine, triethylamine or the corresponding alkylol-amines, to prepare salts of 2,4-dichlorophenoxypropionic acid which crystallise well from aqueous solution. When such aqueous solutions are concentrated by evaporation, oils are obtained which crystallise only with difficulty or not at all. The obtaining of such salts from organic solvents is not successful either. This is particularly true in respect of the use of technical 2,4-dichlorophenoxypropionic acid which is, however, the only convenient starting material in the industrial-scale preparation.

The monomethyl ammonium salt of 2,4-dichlorophenoxypropionic acid is obtained in solid form when acid and amine are brought together in stoichiometric amounts in suitable solvents and the salt which is formed is separated from the solvent in customary manner..

As starting material, not only the pure 2,4-dichlorophenoxypropionic acid, but also in particular the technical acid, is suitable. These technical acids generally contain as impurities about 2 to 8$ isomers and homologuea of 2,4-dichlorophenoxypropionic acid, 0.2 to 1.5. of non-subli able portions and 1 to 5$ of free 2,4-dichlorophenol, In addition, the technical acids contain (depending on the degree of drying) water, for example in amounts of 2 to 10 .

The methylamine may be used as such in gaseous form or in the form of its aqueous solutions or solutions in organic extenders.

The preferred solvent is water. However, organic solvents, such as alcohols, e.g. methanol, ethanol, isopropanol; ethers, e.g. diethyl ether and dioxan; esters, e.g. acetic acid ethyl ester and acetic acid butyl ester; aliphatic hydrocarbons, e.g. petrol; chlorinated aliphatic hydrocarbons, e.g. tetrachloroethane; aromatic hydrocarbons, e.g. benzene and xylene, and chlorinated aromatic hydrocarbons, e.g. mono- or dichlorobenzene, may also be used.

According to a particularly expedient method of preparation, an aqueous monomethylamine solution is neutralised with 2,4-dichlorophenoxypropionic acid or an aqueous suspension of this acid, expediently without abstraction of the neutralisation heat, a clear solution having a temperature of about 50 to 80°C being formed from which, during cooling, the salt precipitates in an easily separable form. It can be separated from the mother liquor by filtration, filtering off with suction, or centrifuging.

The mother liquors which are obtained still contain considerable amounts of the salt in solution, but can be used as solvent for further mixtures, whereby an economic method of working is ensured. Moreover, the aqueous mother liquors may also be used in known manner for the preparation of liquid herbicides. .

When organic solvents are used, it is possible to work not only in homogeneous but also in heterogeneous phase. The monometh lamine ma in these cases be introduced in gaseous form in form of a solution into, the solutions or suspension of the acid The separatio of the salt from the solvents used takes place for example b distilling off the solvent or by filtration or centrifugation i case the salt is insoluble in the solvent.

Irrespective of whether pure 2,4-dichlorophenoxypropionic acid or technical acid is used in these methods of preparation, there are normally obtained directly free-flowing powders which can simply be packaged with the usual equipment and can then, optionally after admixture of extenders, be dispatched without special precautionary measures.

The monomethyl ammonium salt of 2 , -dichlorophenoxypropionic acid is a colourless powder which, isolated from water, melts at 1 7 to 150°C. Recrystallised from isopropanol, it melts at 150 to 152°C. The salt is not hygroscopic.

The monomethyl ammonium salt of 2,4-dichlorophenoxypropionic acid is used, in the same way as the already known salts of 2,4-dichlorophenoxypropiqnic acid, for the control of weeds, in particular for the control of grain weeds such as common chickweed (stellaria media) and cleaver (galium aparine) in grain crops such as wheat, rye, barley and oats.

The herbicidal agents according to the invention should have a particularly high content of active compound because transportation is thereby made particularly simple. In general, the active compound content, with reference to the monomethyl ammonium salt of the acid, lies between 70 and 9-$ by weight.

The remainder may consist for example of impurities which originate from the technical acid. These impurities appear to have no kind of disadvantageous effect when the mixture is used as herbicide.

If the herbicidal agents are to be used later for the preparation of aqueous spray liquors, water-soluble extenders, such as sodium chloride, potassium chloride and sodium sulphate, may also be added to the active compound.

If the herbicidal agents are to be used for the preparation of dusting powders,- they may contain solid extenders.

For the preparation of aqueous spray liquors, the herbicidal agents are expediently dissolved in the necessary amount of water at the place where they are to be used. The ready-to-use spray liquors have in general an active compound content, with reference to the free acid, of 0.1 to 15 , preferably between 1 and 10 .

Application may be effected in conventional manner by squirting or spraying. The amount used may vary. It is generally between 2 to 5 kg. 2,4-dichlorophenoxypropionic acid per hectare.

In making solid ready-to-use preparations, the herbicidal agents according to the invention may be mixed with the customary solid extenders such as natural stone powders, e.g. kaolins, argillaceous earths, talcum and chalk, or synthetic stone powders such as highly dispersed silicic acid and silicates. The concentration of active compound generally lies between 0.1 and 10 , preferably between 1 and 5 , in each case with reference to the free acid. In this instance, too, the amount used generally varies between 2 and 5 kg. acid per hectare.

L Example lOOg. of a technical 2,4-dichlorophenoxypropionic acid of the following composition are introduced, with stirring, into 50 ml. of an approximately 25% aqueous solution of monomethylamine: 83.9 pure acid .2 isomeric and homologous acids 0.8 non-sublimable portions 3.0 free 2,4-dichlorophenol 7.1% water A clear solution is obtained which is adjusted to a pH-value of 7.5 to 8.5 by further addition of amine or acid. During cooling of the solution, which has a temperature of about 50 to 55°C» colourless crystals are precipitated which after about 5 hours are filtered off with suction at aboutl5 to 20°C. After the crystalline product which. as been filtered off has dried in the air, about 55 to 65 g. of a light-grey to colourless powder which melts at about 147 to 150°C are obtained. These crude crystals have the following analytical composition: 93.8% pure methyl ammonium salt of 2,4- dichlorophenoxypropionic acid (= 82.9% pure acid) 2.9% isomeric and homologous acids 0.1% insoluble residue 0.7% 2,4-dichlorophenol 2.5% water The salt can be purified by dissolving it in isopropanol and allowing it to crystallise, colourless crystals being obtained which melt at 150 to 152°C. The elementary analysis of these crystals gives the following values: G10H13°3N<3½ (molecular weight 266) 0 H 0 N CI Calculated: 45.20 4.88 18.10 5.26 26.70 $> Pounds 44.81 4.89 18.07 5.42 27.12 & The technical product obtained can be used directly as herbicidal agent. If it is to serve subsequently for the preparation of aqueous spray liquors , finely powdered or crystalline sodium chloride may also be added, expediently in an amount of up to 10 to 20$, with reference to the final mixture.

In the same way, the active compound according to the invention may be prepared by dropwise addition of an approximately 33$ aqueous solution of monomethylamine to an aqueous suspension of 2 ,4-dichlorophenoxypropionic acid.

The yield of solid is determined by the dilution which is used and by the temperature at which filtration with suction is effected. The mother liquor obtained may be used as it is as diluent for further mixtures. The salt described may also be prepared by introducing gaseous methylamine in stoichiometric amounts into solutions or suspensions of 2,4-dichlorophenoxypropionic acid in organic solvents.

The insoluble salt can be separated from the solvents by filtration or centrifugation.

In case the salt is partly soluble in organic solvents, the solvent must be distilled off after neutralisation. The salt obtained does not differ in its physical properties from that prepared from water.

In a similar way, the compound according to the invention may be prepared by introducing 0.6 kg. gaseous or liquid monomethyl amine into a suspension of 4.7 leg. 2,4-dichlorophenoxypropionic acid in 10 1. chlorobenzol at a temperature of about 50°C. The temperature of the mixture is kept between 60 and 75°G. The addition of the amine is stopped as soon as the pH of the reaction mixture is about 8.5, in general between 7.5 and 9.5. The reaction mixture is then cooled to room temperature while stirring and the precipitated salt is removed either by suction or by cen-trifugation. After the remaining chlorobenzol is removed from the salt in vacuo, 4.8 to 5. kg. of the monomethylamine salt of 2. -dichldrophenoxypropionic acid are obtained. Pp. 148 - 351 °C. The mother liquor can be used for further mixtures.

- The salts prepared i this manner have a content of 90 to 9$ by weight of pure monomethyl ammonium salt of 2 , 4-dichlorophenoxypropionic acid. These salts may be used as herbicidal agents directly or after admixture with water soluble salts or solid extenders.

Post-emergence test To produce a suitable preparation of active compound, 1 part by weight of active compound is mixed with the number of parts by weight of water which are necessary for the desired end concentration.

Test plants of about 5 - 15 cm height are sprayed with the preparation of the active compound until just dew moist. After three weeks, the degree of damage to the plants is determined and characterised by the values 0 - 5» which have the following meaning: " 0 no effect 1 a few slightly burnt spots 2 marked damage to leaves 3 some leaves and parts of stalks partially dead 4 plant partially destroyed plant completely dead.

The active compounds, their concentrations and the results obtained can be seen from the following Tables Post-emergence test Active compound Concentration of Wheat Oats Bar active substance 2,4-dichlorophenoxypropionic acid as potassium salt 0.2 0 ( known) 1 0 0.1 0 0 0 0.05 0 0 0 Monomethylamine salt 1o by weight (with reference to 2,4-dichlorophenoxypropionic acid) Le A 9698

Claims (24)

HAVING HOW particularly described and ascertained the nature of our • said invention and in what manner the same is to he performed, we , declare that what we claim is:- ;

1. Monomethyl ammonium salt of i-(2, 4-dichlorophenoxy)- propionic acid.

2. Solid monomethyl ammonium salt of <_j(-(2,4-dichlorophenoxy)- propionic acid.

3. A process for the production of the salt of Claim 1 or 2 comprising reacting monomethylamine and 2 , 4-dichlorophenoxy- propionic acid.

4. The process of Claim 3 in which the reactants are used in substantially stoichiometric proportions.

5. The process of Claim 3 or 4 in which gaseous monomethylamine is reacted with a suspension or a solution of the acid.

6. The process of Claim 3 or 4 in which a solution of monomethylamine is reacted with the acid or with a suspension or a solution of the acid.

7. The process of Claim 3 or 4 in which an aqueous monomethylamine solution is neutralised with the acid or an aqueous suspension of the acid to form a substantially clear solution having a temperature from 30 to 80°C, and the solution is cooled so as to precipitate the salt.

8. The process of Claim 3 or 4 in which a suspension of 2.4- dichlorophenoxypropionic acid in chlorobenzene is reacted with gaseous or fluid monomethylamine until the pH of the mixture has reached the value of 7.5 to 9.5, and the precipitated salt is separated by filtration or centrifugation.

9. The process of Claim 3, substantially as hereinbefore described in the Example.

10. Monomethyl ammonium salt of ο-(2, 4-dichlorophenoxy)- propionic acid, produced by the process of any of Claims 3 to 9.

11. Solid herbicidal agents comprising monomethyl salt of ( -(2, 4-dichlorophenoxy)-propionic acid in admixture with a diluent or extender.

1 2. The solid herbicidal agents of Claim 1 1 , comprising φ from 70 to 99$ of the salt, by weight of the agents.

1 3. The solid herbicidal agents of Claim 1 in the form of ready-to-use powders comprising an amount of the salt equivalent to from 0. 1 to 10$ of the acid by weight of the agents.

14. The solid herbicidal agents of Claim 1 3 comprising an amount of the salt equivalent to from 1 to 5$ of the acid, by weight of the agents.

1 5. A process for the preparation of the herbicidal agents of any of Claims 1 1 to 1 4 , comprising admixing the salt with a diluent or extender.

1 6. Liquid herbicidal agents comprising monomethyl salt of d-{ 2 , 4-dichlorophenoxy)-propionic acid: dissolved or suspended in a liquid diluent.

1 7. Liquid herbicidal agents comprising monomethyl salt of -{ 2 „ -dichlorophenoxy)-propionic acid in the form of an aqueous solution of the salt.

18. Ready-to-use liquid herbicidal agents comprising an aqueous solution of monomethyl salt of < -( 2 , 4-dichlorophenoxy)-propionic acid in which the concentration of the salt is equivalent to from 0. 1 to 1 5$ of the acid, by weight of the solution.

1 9. Liquid herbicidal agents of Claim 18 in which the concentration of the salt . is equivalent to from 1 to 1 0$ of the acid, by weight of the solution.

20. A process for the preparation of the herbicidal agents of any of Claims 1 6 to 1 9 , comprising dissolving or suspending the salt in a liquid diluent which may be water. Le A 9698 - 14 -

21. A method of combating weeds in a crop area, comprising applying to the area monomethyl salt of <X-(2,4-dichlorophenoxy)-propionic acid alone or in admixture with a solid or liquid diluent or carrier.

22. A method of combating weeds in a crop area, comprising applying to the area the ready-to-use herbicidal agents of any of Claims 13, H, 18 or 19.

23. The method of Claim 21 or 22 in which an amount of monomethyl salt of o-(2,4-dichlorophenoxy)-propionic acid is applied which is equivalent to from 2 to 5 kilograms of the acid per hectare.

24. Soil, whenever treated with monomethyl ammonium salt of tfC-( 2, 4-dichlorophenoxy)-propionic acid, alone or in admixture with a solid or liquid diluent or carrier. Dated this 19th day of September, 1966 For t Ap lic an s