GB2185015A - Herbicidal diesters - Google Patents

Abstract

Herbicidal diesters formally derived from one mole of a diol esterified with one mole of a first phenoxy alkanoic acid and with one mole of a second phenoxy alkanoic acid. The preferred diester is derived from MCPA, 2,4 -DP and ethylene glycol. The diesters are prepared by esterification of the diol with the two phenoxyalkanoic acids and may be used in combination with the mono and bis-ester by-products of the esterification reaction. The esters may be readily formulated into herbicidal compositions of low volatility which do not suffer from problems of 'drift'.

Description

SPECIFICATION Herbicidal esters This invention relates to esters having herbicial activity.

Many herbicides are in the form of carboxylic acids and/or their alkali metal salts of their esters with a monohydric alcohol. Specific examples are the selective herbicides based on substitued phenoxyacetic, -propionic, and -butyric acids.

The herbicides may be used, for example, as the iso-octyl ester but these esters have the disadvantage that they volatalise and are removed from the site of application. In fact, the ester may be re-deposited in an adjustment field which is obviously undesirable.

EP-A-0032631 seeks to overcome this problem by proposing non-volatile esters of 2-(4chloro-2-methylphenoxy) propionic acid, including inter alia the "polyesters" of the acid with a polyhydric alcohol. The preferred ester is the diester formed with ethylene glycol, this diester being a liquid and easily formulated into a herbical composition for application to crops. We have however found that the glycol diesters of many of the other phenoxy herbidies (e.g. 2,4-D, MCPA, 2,4-DB and MCPB) are relatively insoluble solidus which are difficult to formulate with conventional liquid carriers for spray application.

It is therefore an object of the present invention to provide non-volatile herbicidal esters which are easily formulated.

According to the present invention there are provided herbicidal diesters formally derived from one mole of a diol esterified with one mole of a first phenoxy alkanoic acid and with one mole of a second phenoxy alkanoic acid (different from the first said acid). By formally derived we mean that the ester is effectively the reaction product of the diol and the acids even though the ester is not necessarily prepared from the free acid and the diol. For example, a derivative of the acid could be used.

The invention also provides herbicidal compositions comprising at least one diester as defined in the preceding paragraph formulated with a suitable carrier and/or a surface active agent. Such a composition may also comprise at least one further herbicidaly active compound other than a diester of the invention. We have in fact found that the diesters of the invention are particularly suitable for formulating herbicidal compositions with the solid diesters derived from one mole of a diol and two moles of a phenoxy alkanoic acid.

The invention also provides a method of combatting weeds comprising applying to an area to be treated a herbicidal composition as defined in the preceding paragraph.

The diesters of the invention are preferably derived from phenoxy alkanoic acids of the formula (I)

in which R is lower alkyl (particularly C14 e.g. methyl) or Cl, Rl is H or lower alkyl (particularly C14 e.g. methyl) and n is 0-3.

Specific examples of acids of formula I are listed below.

2,4-D (R=CI; R1=H; n=O) 2,4DP (R=CI; R1=Me; n=O) CMPP (R=Me; Rl=Me; n=O) MCPA (R=Me; R1=H; n=O) 2,4-DB (R=CI; R,=H; n=2) MCPB (R=Me; R,=H; n=2) The diols used to produce the diesters of the invention are preferably selected from ethylene glycol and propylene glycol.

Thus the preferred diesters of the invention are of the general formula (II)

in which R2 is H or methyl R, R1 and n are as defined above, R', R1, and n' are selected from the same group as R, R, and n respectively with the proviso that the two acid residues in the molecule are not the same.

The diesters of the invention are liquids and may be formulated with conventional carriers and/or surface active agents.

We have however surprisingly found that the liquid mixed diesters of the invention may be used to prepare liquid formulations with a solid diester derived from a diol and two moles of a phenoxy alkanoic acid. The solid diester is preferably one which is derived from one of phenoxy alkanoic acids from which the mixed diester has been derived.

More particularly, the mixed diesters of the invention may be prepared by esterifying the two required phenoxy-alkanoic acids with the required diol. This reaction will yield the mixed diester in admixture with mono and bis-esters of the phenoxy-alkanoic acids. This product mixture will comprise the same ratio of acids as the original reaction mixture and may be used for the formulation of the herbicidal composition. Consequently by conducting the reaction using two moles of a mixture of phenoxy-alkanoic acids (in the ratio required for the final product) for each mole of diol it is possible directly to prepare a mixed ester/diester product with the required ratio of acids. This ratio may for example be from 5:1 to 1:5.

As an illustrative example of the invention, we have previously manufactured an iso-octyl ester formulation comprising 35% 2,4-DP and 15% MCPA. This formulation does however give rise to problems due to volatility of the iso-octyl esters. We have found that it is not possible to produce a similar formulation from the ethylene glycol diester of 2,4-DP and the ethylene glycol diester of MCPA because the MCPA diester solidifies as the mixture cools down. When however a composition is prepared from the mixed diester derived from ethylene glycol and one mole of MCPA and one mole of 2,4-DP and a balance of the 2,4-DP diester with etylene glycol (to give the required ratio of acids) the composition remains liquid. This composition may then be formulated with emulsifying agents in the usual way.

The resultant herbicidal composition is substantially non-volatile and does not give rise to problems of 'drift' as is the case with the esters of phenoxy alkanoic acids derived from the monohydric alcohols. The composition may be used on winter or spring sown cereals for the control of broad leaved weeds.

The invention will be illustrated by way of example only with reference to the following Examples and Comparative Examples.

Comparative Example 1 4019 (2 mols) MCPA, 629 (1 mol) ethylene glycol and 300 ml xylene were azeotroped until esterification was complete and the xylene was removed under vacuum to a boiler temperature of 180 C. After recrystallisation the product (bis-MCPA ethylene glycol ester) was found to be solid of melting point 77"C.

The above procedure was repeated using 470g (2 mols) dichloroprop in place of the MCPA.

The product obtained was a brown viscous oil of almost pure diester (i.e. bis Dichloroprop ethylene glycol ester).

An emulsifiable formulation of the above two esters was made as follows: 213.59 bis MCPA ethylene glycol ester (=2009 MCPA) 4429 bis Dichloroprop ethylene glycol ester (=4009 D.P.) 1109 Emulsifying Agents Xylene (to 1000ml) On standing, this mixture solidified at room temperature and on heating clarified at 45"C.

Example 1 200g MCPA, 400g Dichloroprop, 849 ethylene glycol and 300 ml xylene were axeotroped until esterification was complete and xylene was removed under vacuum to a boiler temperature of 1800C. The product was a brown viscous oil with the following analysis.

(1) 0.9% mono MCPA ethylene glycol ester (2) 4.1% mono Dichloroprop ethylene glycol ester (3) 10.7% bis MCPA ethylene glycol ester (4) 38.5% bis Dichloroprop ethylene glycol ester (5) 44.0% MCPA/Dichloroprop ethylene glycol ester The structural formulae of the above products are shown below.

The oil remained liquid at room temperature and did not solidify at --14"C.

A formulation corresponding to the formulation of Comparative Example 1 was prepared by mixing the oil with 1109 Emulsifying Agents and xylene to 1000ml (thereby yielding a composition equivalent to 2009 MCPA and 4009 Dichloroprop).

This formulation was a mobile brown liquid which did not deposit any crystals at - 14"C. The difference in melting points between the formulations of Comparative Example 1 and Example 1 renders the use of the latter practicable.

The formulation of Example 1 may be used on winter and spring cereals at a rate of 2.8 litres (in 100 to 200 litres of water) per hectare at a pressure of not more than 2.7 bars for the control of a variety of broad leaved weeds.

Weeds controlled.

Annual weeds up to young plant stage.

Annual nettle, charlock, common chickweed, cleavers, corn buttercup, fat-hen, field pennycress, wild radish (runch), shepherd's-purse.

Annual weeds at seedling stage.

Annual sowthistle, black-bindweed, cornflower, common fumitory, hempnettle, common orache, poppy, redshank, wild turnip.

Annual weeds checked.

Cranesbill, corn spurrey, groundsel, knotgrass, scentless mayweed, speedwell.

Perennial weeds controlled or checked.

Daisy, broad leaved dock, creeping buttercup, creeping thistle, curled dock, dandelion, horsetail, plantain.

The above list is those weeds most commonly found in cereal crops, but is not exclusive of other weeds which may be found occasionally in these crops.

Other uses could be exploited such as grassland, amenity grass and industrial locations.

Claims (12)

1. Herbicidal diesters formally derived from one mole of a diol esterified with one mole of a first phenoxy alkanoic acid and with one mole of a second phenoxy alkanoic acid.

2. Herbicidal diesters as claimed in claim 1 wherein the diol is selected from ethylene glycol and propylene glycol.

3. Herbicial diesters as claimed in claim 1 or 2 wherein the first and second phenoxy alkanoic acids are each selected from compounds of the formula I

in which R is lower alkyl or Cl, R1 is H or lower alkyl, and N is O to 3.

4. Herbicidal diesters of the general formula (II)

where R2 is H or methyl R and R' are lower alkyl or Cl, R, and R1, are H or lower alkyl, and n and n' are 0-3 with the proviso that the two acid residues in the molecule are not the same.

5. Herbicidal diesters. as claimed in claim 4 wherein one phenoxy alkanoic residue is derived from MCPA (R=Me, R1=H, n=O) and the other is derived from 2,4-DP (R'=CI, R1,=Me, n'=O).

6. A herbicidal diester mixture comprising a first diester as claimed in any one of claims 1 to 4 and- a second diester derived from one mole of a diol and two moles of a phenoxy alkanoic acid.

7. A herbicidal diester mixture wherein the phenoxy alkanoic acid of the second diester is the same as one of the phenoxyl alkanoic acids of the first diester.

8. A herbicidal composition comprising a herbicidal diester as claimed in any one of claims 1 to 5 or a diester mixture as claimed in claim 6 or 7 together with a carrier and/or a surface active agent.

9. A method of combatting weeds comprising applying to an area of land to be treated a composition as claimd in claim 8.

10. A method as claimed in claim 9 for the control of weeds in winter or spring sown cereals.

11. A method of preparing a herbicidal ester as claimed in claim 1 comprising esterifying a diol with a first phenoxy alkanoic acid (or ester forming derivative thereof) and a second phenoxy alkanoic acid (or ester forming derivative thereof).

12. A method as claimed in claim 11 wherein the diol is ethylene glycol or propylene glycol, and the first and second phenoxy alkanoic acids are selected from compounds of he formula I, or ester forming derivatives thereof.

in which R is lower alkly or Cl, R1 is H or lower alkly and n is 0-3.