WO2022048717A1

WO2022048717A1 - Metribuzin formulations and use of peroxide in such formulations

Info

Publication number: WO2022048717A1
Application number: PCT/DK2020/050244
Authority: WO
Inventors: Morten Pedersen
Original assignee: Alfa Smart Agro
Priority date: 2020-09-03
Filing date: 2020-09-03
Publication date: 2022-03-10

Abstract

Metribuzin is a member of the class of 1,2,4-triazine herbicides. Metribuzin and metribuzin products and formulations are known to carry or develop during storage an offensive mercaptan and sulfide type smell. Mercaptan and sulfide type compounds are not only bad smelling, they are toxic to human beings. The current invention relates to the use of peroxides as additives to metribuzin and metribuzin products and formulations. The peroxides added reduce or eliminate the mercaptan and sulfide type smell and compounds. The peroxides do not to a significant degree destabilize the metribuzin.

Description

METRIBUZIN FORMULATIONS AND USE OF PEROXIDE IN SUCH FORMULATIONS

DESCRIPTION

The present invention relates to metribuzin formulations, solid or liquid, comprising metribuzin as the active ingredient or as one of more active ingredients and the usual formulation carriers and auxiliary agents. The invention further relates to the use of one or more peroxides as an additive or additives to metribuzin products and formulations for reducing the content of bad-smelling and toxic mercaptan and sulfide type compounds in the products and formulations without a simultaneous reduction of the chemical stability of the metribuzin present therein.

Oxidizing agents such as peroxides are used for removing noxious and offensive smell of organophosphate insecticides such as malathion (US Pat No 3,714,301; US Pat No 2,962,521; US Pat 2,879,284; GB Pat 960,013; WO Pat 97125076; US Pat 6,121,478).

In US patent 6,121,478 it is shown that the addition of peroxide to malathion formulations not only eliminates the formation of mercaptan and sulfide type products. The peroxide addition also reduced the formation of the toxic degradation product isomalathion and improved the chemical stability of the malathion in the formulation.

As regards the chemical stability of organophosphate insecticides such as malathion, autocatalytic reactions are a key issue. It means one or more of the degradation products formed during storage of the insecticides act as a catalyst accelerating the degradation of the insecticide further.

According to WO Pat 2002032228 A2, it has been suggested to apply a combination of peracid and hydrogen peroxide to preserve crop protection products, e.g. metribuzin products. The key topic of this document is to preserve the inner surface of packaging material against microbiological growth.

Metribuzin is a member of the class of 1,2,4-triazine herbicides. It is well know that metribuzin and metribuzin products and formulations when stored cany or develop a bad odour. This odour is probably due to the presence or formation of decomposition products of the mercaptan, such as methyl mercaptan, or sulfide type. It is known that there is an offensive mercaptan and sulfide type smell involved when handling and applying metribuzin and metribuzin products and formulations.

The formation or presence of mercaptan and sulfide type degradation products in metribuzin and in metribuzin products and formulations is not only a matter of an offensive smell during handling and application. Methyl mercaptan is toxic to human beings and because methyl mercaptan is a gas, human beings can be exposed orally and dermally and especially through inhalathion. The acute methyl mercaptan LCso inhalathion value for rats were in the range 643 - 1428 ppm (Public Health Statement for Methyl Mercaptan, Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE Atlanta, GA 30341, 1992; Toxicological Profile for Methyl Mercaptan, Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE Atlanta, GA 30341, 1992; Pub Chem, Open Chemistry Database, Methyl Mercaptan). For dimethyl sulfide the acute LCso inha- lathion value for rats was 102 ppm (Dimethyl sulfide, Safety Data Sheet, Chevron Philips Chemical Company, 2018).

Metribuzin is considered to be a persistent pesticide in the environment. Therefore, studies have been done to find methods to degrade metribuzin (A. Khan et al., Titanium oxide - mediated Photocatalysed Degradation of two herbicides derivatives chloridazon and metribuzin, International Journal of Chemical Engineering, vol. 2012, 8 pages; S. Chauhan and P. Kumari, Biomimetic oxidation of metribuzin with hydrogen peroxide catalyzed by 5,10,15,20-tetra-arylporphyrinatoirom (III) chlorides, Tetrahedron Letters, 48(29), 5035-5038, 2007; O. Yahiaoui et al., Evaluating removal of metribuzin pesticide from contaminated groundwater using an electro-chemical reactor combined with ultraviolet oxidation, Desalination, 270, 84-89, 2011). In these studies peroxide was applied to degrade metribuzin.

Based on the results of the metribuzin degradation studies mentioned above, it could not be considered a good idea to use peroxides as a deodorizer in metribuzin and in metribuzin products and formulations. It was expected peroxides would destabilize and degrade metribuzin.

Surprisingly this turned out not to be the case. Peroxide can be used in metribuzin and in metribuzin products and formulations improving the odour and reducing the content of toxic mercaptan and sulfide type degradation products, without destabilizing the metribuzin.

A peroxide based method for effectively improving the odour and reducing the formation of toxic mercaptan and sulfide type degradation products in metribuzin and metribuzin products and formulations is to the best of our knowledge not described in the literature.

It has surprisingly been found that the addition of peroxides to metribuzin and metribuzin products and formulations considerably reduces the concentration of toxic and offensive smelling mercaptans and sulfide degradation products, even after prolonged storage at elevated temperatures. Likewise, it has most surprisingly been found that said addition of peroxides does not impair the chemical stability of metribuzin as it would have been expected in view of the above-mentioned papers (A. Khan et al., Titanium oxide - mediated Photocatalysed Degradation of two herbicides derivatives chloridazon and metribuzin, International Journal of Chemical Engineering, vol. 2012, 8 pages; S. Chauhan and P. Kumari, Biomimetic oxidation of metribuzin with hydrogen peroxide catalyzed by 5,10,15,20-tetra-arylporphyrinatoirom (III) chlorides, Tetrahedron Letters, 48(29), 5035-5038, 2007; O. Yahiaoui et al., Evaluating removal of metribuzin pesticide from contaminated groundwater using an electro-chemical reactor combined with ultraviolet oxidation, Desalination, 270, 84-89, 2011).

Accordingly, the metribuzin and metribuzin products and formulations of the present invention are characterized in that to the products are added 0.01 - 10, preferrebly 0.05 - 3 and in particular 0.3 - 1.5 percentage by weight of one or more peroxides. In the use according to the invention the above stated amounts of peroxides are applied. Said addition will reduce the content of mercaptans and sulfide type degradation products to more acceptable levels without destabilizing the metribuzin. Autoxidation of peroxide into water and oxygen may limit the effect of the peroxide on the content of mercaptan and sulfide type products. The autoxidation may, however, be considerably limited by the addition of stabilizing agents which stabilize the peroxide without limiting its effect on lowering the content of mercaptan and sulfide type products in the metribuzin formulations. Examples of peroxide stabilizing agents are e.g. EDTA, salicylic acid, propylgallate, acetanilide, 8- hydroxyquinoline, phenacetin and mixtures thereof.

Crosslinked polyacrylic acid thickening agents work well in the formulations invented. However, the thickening effect of cross-linked polyacrylic acid thickening agents can be damaged by oxygen. Therefore, the application of an autoxidation stabilizing agent can be of importance for metribuzin formulations containing hydrogen peroxide and a crosslinked polyacrylic acid, e.g. Carbopol 980. It may be an advantage to use a combination of peroxides with different solubility properties and different distribution coefficients between the phases in metribuzin formulations in order to reduce the content of mercaptan and sulfide type products as much as possible.

The addition of peroxide(s) alone or in combination with peroxide stabilizing agent(s) makes it possible to produce metribuzin products and formulations having a more acceptable concentration of mercaptan and sulfide type products.

The metribuzin products and formulations according to the invention may besides metribuzin also contain one or more other pesticides.

The exact mechanism behind the present invention, i.e. the improvement of the smell and the reduction of the toxicity of metribuzin products and formulations by the addition of peroxides, is not known.

The invention is further illustrated by the following examples.

Example 1

An odour improvement was observed for the formulations in the table above containing hydrogen peroxide. Both initially and after storage at room temperature, at 45°C, at 54°C, and at 0°C a reduced odour of mercaptan and sulfide type was observed. The formulations not containing hydrogen peroxide had a quite strong mercaptan and sulfide type odour. As regards the formulations containing 10 g/1 hydrogen peroxide, the Carbopol 980 containing formulation had a better odour, i.e. less mercaptan and sulfide type odour, than the formulation containing xanthan gum. It was speculated the difference in odour could be due to a reaction between hydrogen peroxide and xanthan gum. The formulation containing 10 g/1 hydrogen peroxide and Carbopol 980 had improved odour even after storage for 2 weeks at 54°C and after several months of storage at room temperature. The concentration of metribuzin in the formulations listed in the table was measured before and after storage at elevated temperatures, i.e. 45°C for 12 weeks and 54°C for 2 weeks. The chemical stability of metribuzin was excellent. There were no signs of metribuzin degradation in the formulation samples containing hydrogen peroxide. Whether or not the presence of hydrogen peroxide reduced the rate of autocatalytic reactions is not known.

Example 2

During storage at room temperature and at elevated temperatures, i.e. 45°C and 54°C, the viscosity dropped in a metribuzin formulation containing 10 g/1 hydrogen peroxide and the thickener xanthan gum (Example 1, formulation number 7). A similar drop in viscosity was not seen in the formulation containing 10 g/1 hydrogen peroxide and Carbopol 980 (Example 1, formulation number 3). For the two formulations without hydrogen peroxide (Example 1, formulation number 5 and 6) a viscosity drop was not observed during storage at room temperature and at elevated temperatures, i.e. 45°C and 54°C. Having a product with a constant viscosity is usually desirable. Example 3

Metribuzin is often formulated as a suspension concentrate, i.e. metribuzin is suspended as particles typically in water. It is highly desirable that the particle size remains stable during storage of formulations, because reduced biological activity, nozzle and filter blockage during application and formation of sediment in the packaging containers can be the result of particle growth during storage.

In the table below the particle size stability is shown for some commercial metribuzin 600 g/1 suspension concentrates and for a metribuzin 600 g/1 suspension concentrate containing hydrogen peroxide 10 g/1 and Carbopol 980 (Example 1, formulation number 3).

Particle size in micrometer (Mean V / D90%, LASER particle size analyzer). Metribuzin saturated water was used when measuring the particle size.

According to the results in the table above, the metribuzin 600 g/1 suspension concentrate containing 10 g/1 hydrogen peroxide and Carbopol 980 had excellent particle size stability both at 0°C and at 54°C. According to the results in the table, the formulation was even better than commercially available metribuzin formulations. In the commercial product II a sticky sediment was observed after storage. No sediment or sticky sediment was present in the product containing 10 g/1 hydrogen peroxide and Carbopol 980, neither before nor after storage at room temperature, at 0°C or at 54°C.

Example 4

The formulations from example 1 containing 6 or 10 g/1 hydrogen peroxide and xanthan gum or

Carbopol 980 as thickening agent were tested for spontaniety and suspensibility according to the CIPAC guidelines. Both a low, 0.6 g metribuzin per liter spray liquid, and a high metribuzin concentration, i.e. 3.3 g metribuzin per liter spray liquid, in various water types, were tested. The spon- taniety and suspensibility were tested in formulation samples stored at room temperature and in formulation samples stored at 0°C for 7 days and at 54°C for 2 weeks. In all cases both the sponta- niety and the suspensibility were in the range 98.5 - 107%. It is both surprising and encouraging the samples tested had excellent spontaniety and suspensibility properties despite the presence of a quite strong oxidizing agent, i.e. hydrogen peroxide, in the formulations.

Example 5

The metribuzin formulations mentioned in example 4 were tested for wet sieve residue according to the CIPAC guideline. A 71 micrometer pore size sieve was applied. All formulation samples, stored at room temperature, at 0°C and at 54°C, had wet sieve residues far below 2% w/w. It means the formulations fulfilled the wet sieve residue requirements in the United Kingdom.

Example 6

In crop safety laboratory and field tests it was checked that hydrogen peroxide up to 15 g/1 in formulations did not damage the crops sprayed.

Example 7

A series of metribuzin 600 g/1 suspension concentrates contaning 10 g/1 hydrogen peroxide and Carbopol 980 were produced. The pH was varied in the range 4 - 9. Best odour reducing effect was achieved at neutral pH, i.e. 7. It may be due to the improved chemical stability of peroxides at neutral pH.

Claims

PATENT CLAIMS

1. A metribuzin water based, partly water based or solid product comprising metribuzin, at least one of a carrier and an auxiliary agent and 0.01 to 15 percent by weight of at least one peroxide.

2. A product according to claim 1 containing 0.1 to 5 percent by weight of at least one peroxide.

3. A product according to claim 1 containing 0.2 to 3 percent by weight of at least one peroxide.

4. A product according to claim 1, wherein the peroxide is hydrogen peroxide.

5. A product according to claim 1 comprising a thickening agent, wherein the thickening agent is a cross-linked polyacrylic acid.

6. A process for reducing the content of sulfides and mercaptans, especially methyl mercaptan, by adding 0. 1 to 5 percent by weight of at least one peroxide as an additive to a metribuzin water based, partly water based or solid product.

7. A metribuzin water based, partly water based or solid product comprising metribuzin, at least one of a carrier and an auxiliary agent and 0.01 to 15 percent by weight of at least one peroxide, wherein the peroxide or peroxides are stabilized against autoxidation by including a stabilizing agent.

8. A metribuzin water based, partly water based or solid product comprising metribuzin, at least one of a carrier and an auxiliary agent and 0. 1 to 5 percent by weight of at least one peroxide, wherein the peroxide or peroxides are stabilized against autoxidation by including a stabilizing agent.

9. A metribuzin water based, partly water based or solid product comprising metribuzin, at least one of a carrier and an auxiliary agent and 0.2 to 3 percent by weight of at least one peroxide, wherein the peroxide or peroxides are stabilized against autoxidation by including a stabilizing agent.

10. A product according to claim 6, wherein the stabilizing agent is selected from the group consisting of EDTA, salicylic acid, propyl gallate, acetanilide, 8 -hydroxy quinoline, phenacetin, and mixtures thereof.