GB2161479A - Herbicidal crotonate derivatives - Google Patents

Abstract

Hydroxyprop-2-yl-4-[5-(2,4-disubstituted phenoxy)-2-substituted phenoxy] crotonate derivatives useful as herbicides and at lower dosages as plant growth regulators are represented by the general formula: <IMAGE> wherein R<1> and R<2> are independently hydrogen or lower alkyl; X is halo; Y is halo or trifluoromethyl; and Z is nitro or halo; and compatible salts thereof.b

Description

SPECIFICATION Herbicidal crotonate derivatives This invention relates to hydroxyprop-2-yl 4-[5-(2,4-disu bstituted phenoxy)-2-substituted phenoxy] crotonates and to the use of such compounds as herbicides. At lower dosage rates, the compounds can be applied as plant growth regulators.

A number of diphenoxy type herbicides are described in various publications. For example, U.S. Patent No. 4,163,661 discloses herbicidal alkyl esters of 4-methyl-4-{4-(4-trifluoromethylphenoxy)-phenoxy] crotonic acid; U.S. Patent No. 4,093,446 discloses herbicidal 4-trifluoromethyl-4'-nitrodiphenyl-2'alkoxyethers and U.S. Patent No. 4,134,753 discloses herbicidal 4-halo-4'-nitro-3'-alkanoyloxy diphenyl ethers. Other diphenoxy ether herbicides are described in U.S. Patent 4,221,581 and published German application 2905458. U.S. Patent No.4,419,123 discloses multisubstituted diphenoxy ether herbicides and set forth an extensive testing of various substituents which may be meta to the phenoxy linkage.

In prior U.S. Patent 4,414,017 and British Patent No. 2,079,271, we disclosed herbicidal esters and salts of 4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-crotonic acid. European Patent Application No.

34,120 discloses similar compounds and the 2-chlorophenoxy analogs thereof.

The present invention provides herbicidal compounds having both pre- and post-emergence activity against both grassy weeds and broad-leaf plants. The compounds have especially excellent pre-emergence activity against broad-leaf plants and have sufficient selectivity that they may be effectively and safely apply to control broad-leaf weeds in certain grassy crops; notably rice.

The compounds of the present invention can be represented by the general formula:

wherein R1 and R2 are independently hydrogen or lower alkyl, i.e. alkyl having 1 to 4 carbon atoms; Xis halo; Yis halo or trifluoromethyl; and Z is nitro or halo.

Compatible salts of the above compounds are also encompassed within the invention.

The compounds have an asymmetric carbon atom and can exist as optical isomers. The compounds also exist as geometric isomers with respect to the double bond. The above formula is intended to encompass the respective individual isomers as well as mixtures thereof and the respective isomers as well as mixtures thereof are encompassed within the invention.

In a further aspect, the invention provides a herbicidal composition comprising a compatible carrier and a herbicidally effective amount of a compound of Formula (I), or a compatible salt thereof, or mixtures thereof.

The present invention also provides a method of preventing or controlling the growth of unwanted vegetation, which comprises treating the growth medium and/or the foliage of such vegetation with a herbicidally effective amount of at least one compound of Formula (I) and/or at least one compatible salt thereof.

In another aspect, the present invention provides a plant growth regulating composition comprising a compatible carrier and a plant growth regulating amount of a compound of Formula (I), a compatible salt of Formula (I), or a mixture thereof, effective to alter the normal growth pattern of said plant.

The present invention also provides a method of regulating plant growth which comprises treating the growth medium and/or the foliage of such vegetation with a plant growth regulating effective amount of a compound of formula (I) and/or a compatible salt thereof, effective to alter the normal growth pattern of said plants.

The present invention also provides chemical intermediates and processes for preparing the compounds of Formula (I).

Illustrations of typical compounds of Formula (I) of the present invention can be had by reference to Examples 1 and 2, set forth hereinbelow. In terms of substituents, the preferred compounds are those wherein Y is trifluoromethyl, X is chloro, Z is nitro or chloro, more preferably nitro, and R1 and R2 are independently hydrogen, methyl or ethyl. More preferably, one of R1 or R2 is hydrogen and the other is hydrogen, methyl or ethyl. Most preferably, P1 is methyl and R2 is hydrogen. The preferred compounds have at least one preferred substituent and more preferably have a combination of two or more preferred substituents.

The compounds of the present invention can be conveniently prepared via reaction of the corresponding di(phenoxy)crotonic acid analogs with propylene oxide. This can be schematically;epresented by the overall reaction equation:

wherein R1, R2, X, Y and Z are as defined hereinabove.

This preparation can be effected by contacting Compound (A) with Compound (B) (propylene oxide) under reactive conditions preferably in an inert organic solvent. It has further been found that good results are obtained when the reaction is further conducted in the presence of a trimethylsulfoxonium halide (e.g.,trimethylsulfoxonium iodide). It is conjectured thatthis improves the reaction by forming the alkyl ester of Compound (A) and liberating hydrogen halide, because the alkyl ester is more readily converted to an alcohol than the acid. Moreover, hydrogen halides catalyze the conversion to the alcohol.

Typically, this process is conducted at temperatures in the range of about from 200 to 150"C, preferably 78" to 105C for about from 1 to 48 hours, preferably, 8to 24 hours using aboutfrom 1 to 25 moles, preferably 1 to 10 moles of propylene oxide per mole of Compound (A). Where a trimethylsulfoxonium halide is used, typically about from 0.10 to 1 mole, preferably 0.15 to 0.50 mole are used per mole of Compound (A).

Typically,trimethylsulfoxonium iodide or bromide is used. Suitable inert organic solvents which can be used include, for example, ethanol, dichloromethane, toluene, 1 ,2-dimethoxyethane, and the like and compatible mixtures thereof.

The starting materials of Formula (A) are generally known compounds and can be prepared by known procedures or obvious modification thereof via the substitution of appropriate solvents and appropriately substituted starting materials. The compounds of Formula A wherein Z is nitro, are, for example, generally described in my prior U.S. Patent No. 4,414,017. The compounds of formula A wherein Z is chloro are generally described in published European Patent Application 34120.

The compatible salts of Formula (I) can be prepared by conventional procedures. For example, the salts can be prepared by treating the compound of Formula (I) with a suitable base, such as, for example, n-butyl-lithium, sodium hydride, potassium hydride, and the like, having the desired cation, to yield the corresponding salt. Additional variations in the salt cation can also be effected via ion exchange with an ion exchange resin having the desired cation.

General process conditions In the above-described processes, it is generally preferable to separate the respective products before proceeding with the next step in the reaction sequence, except where described as an in situ step or unless otherwise expressly stated. These products can be recovered from their respective reaction product mixtures by any suitable separation and purification procedure, such as, for example, recrystallization and chromatography. Suitable separation and purification procedures are,for example, illustrated in the Examples set forth hereinbelow.

Generally, the reactions described above are conducted as liquid phase reaction and hence pressure is generally not significant except as it affects temperature (boiling point) where reactions are conducted at reflux. Therefore, these reactions are generally conducted at pressures of about from 300 to 3,000 mm of mercury and conveniently are conducted at about atmospheric or ambient pressure.

It should also be appreciated that where typical or preferred process conditions (e.g., reaction temperatures, times, mole ratios of reactants, solvents, etc.) have been given, that other process conditions could also be used. Optimum reaction conditions (e.g., temperature, reaction time, mol ratios, solvents, etc.) may vary with the particular reagents or organic solvents used but can be determined by routine optimization procedures.

Where optical isomer mixtures are obtained, the respective optical isomers can be obtained by conventional resolution procedures. Geometric isomers can be separated by conventional separation procedures which depend upon differences in physical properties between the geometric isomers.

Definitions As used herein the following terms have the following meanings unless expressly stated to the contrary: The term "lower alkyl" refers to both straight-and branched-chain alkyl groups having a total of from 1 through 4 carbon atoms and includes primary, secondary and tertiary alkyl groups. Typical lower alkyls include, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl.

The term "halo" or "halogen atom" or "halide" refers to the group of fluoro, chloro, bromo and iodo.

The term "compatible salts" or "compatible cations" refers to salts which do not significantly alter the herbicidal properties of the parent compound. Suitable salts include cation salts such as, for example, the cation salts of lithium, sodium, potassium, aikali earth metals, ammonia, quaternary ammonium salts, and the like.

The term "room temperature" or "ambient temperature" refers to about 20-25"C.

Utility The compounds of Formula (I) exhibit both pre-emergence and post-emergence herbicidal activity and exhibit especially good herbicidal activity against broadleaf plants.

Generally, for post-emergent applications, the herbicidal compounds are applied directly to the foliage or other plant parts. For pre-emergence applications, the herbicidal compounds are applied to the growth medium, or prospective growth medium, for the plant. The optimum amount of the herbicidal compound or composition will vary with the particular plant species, and the extent of plant growth, if any, and the particular part of the plant which is contacted and the extent of contact. The optimum dosage can also vary with the general location, or environment (e.g., sheltered areas such as greenhouses compared to exposed areas such as fields), and type and degree of control desired. Generally, for both pre- and post-emergent control, the present compounds are applied at rates of about from 0.02 to 60 kg/ha, preferably about from 0.02 to 10 kg/ha.

Also, although in theory the compounds can be applied undiluted, in actual practice they are generally applied as a composition or formulation comprising an effective amount of the compounds(s) and an acceptable carrier. An acceptable or compatible carrier (agriculturally acceptable carrier) is one which does not significantly adversely affect the desired biological effect achieved by the active compounds, save to dilute it. Typically, the composition contains about from 0.05 to 95% by weight of the compound of Formula (I) or mixtures thereof. Concentrates can also be made having high concentrations designed for dilution prior to application. The carrier can be a solid, liquid, or aerosol. The actual compositions can take the form of granules, powders, dusts, solutions, emulsions, slurries, aerosols, and the like.

Suitable solid carriers which can be used include, for example, natural clays (such as kaolin, attapulgite, montmorillonite, etc), talcs, pyrophyllite, diatomaceous silica, synthetic fine silica, calcium aluminosilicate, tricalcium phosphate, and the like. Also, organic materials, such as, for example, walnut shell flour, cotton-seed hulls, wheat flour, wood flour, wood bark flour, and the like can also be used as carriers. Suitable liquid diluents which can be used include, for example, water, organic solvents (e.g., hydrocarbons such as benzene, toluene, dimethylsulfoxide, kerosene, diesel fuel, fuel oil, petroleum naphtha, etc.), and the like.

Suitable aerosol carriers which can be used include conventional aerosol carriers such as halogenated alkanes, etc.

The composition can also contain various promoters and surface-active agents which enhance the rate of transport of the active compound into the plant tissue such as, for example, organic solvents, wetting agents and oils, and in the case of compositions designed for pre-emergence application agents which reduce the leachability of the compound or otherwise enhance soil stability.

The composition can also contain various compatible adjuvants, stabilizers, conditioners, insecticides, fungicides, and if desired, other herbicidally active compounds.

At reduced dosages the compounds of the present invention can be used to alter the normal growth pattern of plants.

The compounds of formula (I) can be applied as plant growth regulators in pure form, but more pragmatically, as in the case of herbicidal application, are applied in combination with a carrier. The same types of carriers as set forth hereinabove with respect to the herbicidal compositions can also be used.

Depending on the desired application, the plant growth- regulating composition can also contain, or be applied in combination with other compatible ingredients such as desiccants, defoliants, surface-active agents, adjuvants, fungicides, and insecticides. Typically, the plant growth regulating composition will contain a total of about from 0.005 to 90 wt. % of the compound(s) of formula (I) depending on whether the composition is intended to be applied directly or diluted first.

Afurther understanding of the invention can be had in the following non-limiting Preparation and Example(s). Wherein, unless expressly stated to the contrary, all temperatures and temperature ranges refer to the Centigrade system and the term "ambient" or "room temperature" refers to about 20-25"C. The term "percent" or "%" refers to weight percent and the term "mole" or "moles" refers to gram moles. The term "equivalent" refers to a quantity of reagent equal in moles, to the moles of the preceding or succeeding reactant recited in that example in terms of finite moles orfinite weight or volume.Where given, proton-magnetic resonance spectrum (p.m.r. or n.m.r.) were determined at 60 mHz, signals are assigned as singlets (s), broad singlets (bs), doublets (d), double doublets (dd), triplets (t), double triplets (dt), quartets (q), and multiplets (m); and cps refers to cycles per second. Also where necessary examples are repeated to provide additional starting material for subsequent examples.

EXAMPLES EXAMPLE 1 3-Hydroxyprop-2-yl-4-J5-(2-chloro-4-trffluorometh ylphenoxy)-2-nitrophen oxy]-4-m eth ylcro tonate In this example, a mixture containing 10.9 g of 4-[5-(2-cloro-4-trif luoromethylphenoxy)-2-nitrophenoxy]-4- methylcrotonic acid, 10 g of propylene oxide and 1 g of trimethylsulfoxonium iodide in 150 ml of ethanol was refluxed for 24 hours and then filtered. The filtrate was evaporated and the residue redissolved in ethyl ether and again evaporated. The residue was chromatographed over silica gel eluting with mixtures of ethyl ether and petroleum ethers affording the title compound as an oil Elemental Analysis Carbon: Calc. - 51.49%, Found 51.66%; Hydrogen: Calm. - 3.92%, Found - 4.32%; Nitrogen: Calc. - 2.86%, Found - 2.86%.

Similarly, by applying the above procedures to the corresponding crotonic acid analogs, the following compounds can be prepared: 3-hydroxyprop-2-yl-4-[5-(2-fluoro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-4-methyicrotonate; 3-hydroxyprop-2-yl-4-[5-(2-bromo-4-trifluoromethyl phenoxy)-2-nitrnphenoxy]4-methylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-iodo-4-trifluoromethylphenoxy)-2-nitrophenoxy]-4-methylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-fluornphenoxy)-2-nitrnphenoxyl-4-methylcrotonate; 3-hyd roxyprop-2-yl-4-[5-(2-iodo-4-chlorophenoxy)-2-nitrophenoxyj-4-methylcrotonate; 3-hydroxyprop-2-yi-4-[5-(2-fluoro-4-bromophenoxy)-2-nitrophenoxy1-4-methylCrotonate; 3-hydroxyprop-2-yl-4-[5-(2,4-dichlorophenoxy)-2-nitrophenoxy]-4-methylCrotonate;; 3-hydroxyprop-2-yl-4-[5-(2,4-dífluorophenoxy)-2-nitrophenoxy]-4-methylCrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-crotonate; 3-hydroxyprop-2-yl-4-[5-(2-iodo-4-trifluoromethylphenoxy)-2-nitrophenoxyj-crotonate; 3-hydroxyprop-2-yl-4-[5-(2-iodo-4-trifluoromethylphenoxy)-2-nitrophenoxyj-crotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-fl I uorophenoxy)-2-nitrophenoxy]-crotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy1-3-methylorotonate; 3-hydrnxyprop-2-yl-4-[5-(2-brnmo-4-iodophenoxy)-2-n itrophenoxy]-3-methylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-4-ethylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-chioro-4-trifl uo romethylphenoxy)-2-nitrophenoxy]-3-ethylorotonate;; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-4-propylCrotonate; 3-hydroxyprop-2-yl-4-[5-(2-ch loro-44rifluoromethylphenoxy)-2-nitrophenoxyj-3-butylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-4-isopropylCrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxyj-34-butylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-44rifl uoromethylphenoxy)-2-nitrophenoxy]-3,4-dimethylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethyl phenoxy)-2-nitrophenoxy]-3,4-dibutylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy-2-nitrophenoxy]-3-ethyl-4-propylCrotonate;; 3-hydrnxyprop-2-yl-4-l5-(2-chlorn-4trifluornmethylphenoxy)-2-chlornphenoxy]-4methylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-bromo-4-trifluoromethyl phenoxy)-2-chlorophenoxy]-4-methylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-iodo-4-trifluoromethylphenoxy))-2-chlorophenoxy]-4-methylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-fluorophenoxy)-2-chlorophenoxy]-4-methylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-iodo-4-chlorophenoxy)-2-chlorophenoxy]-4-methylorotonate; 3-hydroxyprop-2-yi-4-[5-(2-fluoro-4-bromophenoxy)-2-chlorophenoxy]-4-methylCrotonate; 3-hydroxyprop-2-yl-4-[5-(2,4-dichlorophenoxy)-2-chlorophenoxy]-4-methyicrotonate; 3-hydroxyprop-2-yl-4-[5-(2,4-difluorophenoxy)-2-chlorophenoxy]-4-methylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-crotonate;; 3 hydroxyprop-2-yl-4-{5-(2-iodo-4-trifluoromethylphenoxy)-2-chlorophenoxy]-crotonate, 3-hydroxyprop-2-yl-4-[5-(2-iodo-4-trifluoromethylphenoxy)-2-chlorophenoxy]-crotonate; 3 hydroxyprop-2-yl-4-[5-(2-chloro-44luorophenoxy)-2-ch lorophenoxy]-crotonate; 3-hyd roxyprop-2-yl-4-[5-(2-chloro-4-trifl uoromethylphenoxy)-2-chlorophenoxy]-3-methylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-bromo-4-iodophenoxy)-2-chlorophenoxy]-3-methylcrotonate 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxyj-4-ethylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-3-ethylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-4-propylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethyl]-2-chlorophenoxyl-3-butylcrotonate;; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-4-isopropylcrotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-3-t-butylcrotonate, 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-3,4-dimethylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-3,4-dibutylorotonate; 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-chlorophenoxy]-3-ethyl-4- propylcrotonate.

EXAMPLE 2 Sodium salt of 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-2- methyicrotonate The title compound can be prepared by the following procedure.

0.54 g of sodium hydride (50%) is added portionwise to a stirred solution containing 5.5 gm (0.0112 mole) of 3-hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-2-methylcrotonate in 100 ml of anhydrous ethyl ether at room temperature under a nitrogen atmosphere. After the evolution hydrogen ceases two drops of ethanol are added to destroy unreacted sodium hydride. The reaction mixture is filtered through magnesium sulfate. The filtrate is then evaporated, under vacuum, to afford the title compound as the residue.

Similarly, by applying the above procedure to the compounds illustrated in Example 1, the corresponding sodium salts thereof can be prepared.

EXAMPLE 3 In this example, the title compound of Example 1 was tested for pre-emergent and post-emergent activity against a variety of grasses and broad-leaf plants, including one grain crop and one broad-leaf crop using the procedures described hereinbelow.

Pre-emergent herbicide test Pre-emergence herbicidal activity was determined in the following manner.

A test solution of the compound was prepared as follows: 355.5 mg of test compound was dissolved in 15 ml of acetone. 2 ml of acetone containing 110 mg of a nonionic surfactant was added to the solution. 12 ml of this stock solution was then added to 47.7 ml of water which contained the same nonionic surfactant at a concentration of 625 mg/l.

Seeds of the test vegetation were planted in a pot of soil and the test solution was sprayed uniformly onto the soil surface at a dose of 27.5 micrograms/cm2. The pot was watered and placed in a greenhouse. The pot was watered intermittently and observed for seedling emergence, health of emerging seedlings, etc., for a 3-week period. At the end of this period, the herbicidal effectiveness of the compound was rated based on the physiological observations. A 0-to-100 scale was used, 0 representing no phytotoxicity, 100 representing complete kill. The results of these tests are summarized in Table 1.

Post-emergent herbicidal test The test compound was formulated in the same manner as described above for the pre-emergent test.

This formulation was uniformly sprayed on 2 similar pots containing plants 2 to 3 inches tall (except wild oats, soybean and watergrass which were 3 to 4 inches tall) (approximately 15 to 25 plants per pot) at a dose of 27.5 microgram/cm2. After the plants had dried, they were placed in a greenhouse and then watered intermittently at their bases as needed. The plants were observed periodically for phytotoxic effects and physiological and morphological responses to the treatment. After 3 weeks, the herbicidal effectiveness of the compound was rated based on these observations. A 0-to-100 scale was used, 0 representing no phytotoxicity, 100 representing complete kill. The results of these tests are summarized in Table 2.

TABLE 1 Pre-Emergence Herbicidal Activity Application Rate: 27.5 micrograms/cm2, unless otherwise noted Broad-Leaf Plants Grasses Compound % Phytotoxicity % Phytotoxicity No. Lambs quarter Mustard Pig weed Soybean Watergrass Crab grasps Wild Oats Rice 1 100 100 100 100 100 93 93 95 TABLE 2 - Post-emergence Herbicidal Activity Application Rate: 27.5 micrograms/cm2, unles otherwise noted Broad-Leaf Plants Grasses Compound % Phytotoxicity % Phytotoxicity No. Lambs quarter Mustard Pig weed Soybean Watergrass Crab grasps Wild Oats Rice 1 100 100 100 45 50 35 50 40 Obviously, many modifications and variations of the invention described hereinabove and beiow in the claims can be made without departing from the essenee and scope thereof.

Claims (15)

1. Compounds represented by the general formula:

wherein R1 and R2 are independently hydrogen or lower alkyl (as hereinbefore defined); Xis halo; Y is halo ortrifluoromethyl; and Z is nitro or halo; and compatible salts (as hereinbefore defined) thereof.

2. Compounds as claimed in Claim 1, wherein Y is trifluoromethyl.

3. Compounds as claimed in Claim 1 or 2, wherein X is chloro.

4. Compounds as claimed in Claim 1,2 or 3, wherein one of R1 or R2 is hydrogen and the other is hydrogen, methyl or ethyl.

5. Compounds as claimed in Claim 4, wherein R2 is hydrogen and R1 is methyl.

6. Compounds as claimed in Claim 1, 2, 3,4, or 5, wherein Z is nitro or chloro.

7. 3-Hydroxyprop-2-yl-4-[5-(2-choro-4-trifluoromethylphenoxy)-2-nitrophenoxy]-4-methylorotonate.

8. 3-Hydroxyprop-2-yl-4-[5-(2-chloro-4-trifluoromethyl phenoxy)-2-chlorophenoxy]-4-methylcrotonate.

9. Compounds as claimed in Claim 1 ,as described in the foregoing Example 1 or 2.

10. A herbicidal composition comprising a herbicidally effective amount of at least one compound as claimed in Claim 1 and a compatible carrier (as herein before defined) therefor.

11. A herbicidal composition comprising a herbicidally effective amount of the compound claimed in Claim 7 and a compatible carrier (as hereinbefore defined) therefor.

12. A method of preventing or controlling the growth of unwanted vegetation, which comprises applying a herbicidally effective amount of at least one compound as claimed in Claim 1 to the foliage and/or growth medium of said vegetation.

13. A method of preventing or controlling the growth of unwanted vegetation, which comprises applying a herbicidally effective amount of the compound claimed in Claim 7 to the foliage and/or growth medium of said vegetation.

14. A plant growth regulating composition which comprises a compatible carrier (as hereinbefore defined) and an amount of a compound as claimed in Claim 1 effective to alter the normal growth pattern of a plant.

15. A method of regulating the growth of plants which comprises applying to the foliage of said plants and/or their growth medium an amount of a compound as claimed in Claim 1 effective to alter the normal growth pattern of said plants.