Haloxyfop esters

Eksteen, F.H., A.F.P. Cairns, and P.J. Pieterse (2004). Cross resistance of ryegrass to glyphosate, paraquat and haloxyfop-r methyl ester in the Western Cape. 4th International Weed Science Congress, p. 48, S15MT08P00. 

Experiments were conducted to determine how quickly a low concentration (1.4 /zM) of an aryloxyphenoxypropanoate, haloxyfop (2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]-propanoic acid) (Fig.l) could affect lipid metabolism. We used leaf discs as experimental material because it would mitigate effects of herbicide uptake and translocation. Maize (Zea mays) leaf discs were prepared as previously described (15) and incubated in C-acetate. At various times, discs were removed and cell constituents were separated into organic and aqueous soluble fractions (16). Within 30 min of application, 1.4 /zM of either the free acid or the methyl ester of haloxyfop inhibited lipid... 

Figure 2. Comparison of control (O), 1.4 /zM haloxyfop methyl ester ( ), or 1.4 /iM haloxyfop free acid (A) on l C-acetate incorporation into lipids in maize leaf discs.

The activity of ACCase extracted from maize was inhibited by both tralkoxydim and haloxyfop acid in a concentration dependant manner (Fig. 4). The concentration that inhibited activity by 50% (I50) was about 1 / M for both compounds. These values are similar to those recently reported by others (2.3). The methyl ester of haloxyfop was more than 100 fold less inhibitory than the free acid (Fig. 4), which is consistent with the methyl ester being deesterified in the plant. The data presented in Fig. 2 suggest that the deesterification occurs rapidly in leaf tissue. 

Figure 4. Effect of haloxyfop methyl ester (A), haloxyfop free acid (O), and tralkoxydim ( ) on acetyl CoA carboxylase activity from maize.

Halogenated aiyloxyphenoxypropionic acids are a new class of herbicides used for the selective removal of grass species. In commercial preparations, they are present as alkyl esters. In negative-ion ESI, haloxifop, fluazifop, and diclofop all show similar behaviour. The deprotonated molecule is the base peak in the spectrum. Weak formate and acetate adducts occur, and a fragment due to the loss of the propionate part [45]. The analysis of fluazifop and its butyl ester, fenoxaprop, quizalofop and haloxyfop and their ethyl esters, and diclofop and its methyl ester was reported. The free acids were analysed in negative-ion mode, and the esters in positive-ion mode. The esters showed sodium and potassium adducts next to the protonated molecules. The adduct formation was suppressed by the addition of 25 mmol/1 formic acid to the mobile phase. The influence of the orifice potential on the appearance of their mass spectra was studied [46-47]... 

To optimize analytical results in the separation process TBA was used as the ion pairing agent in the quantitative analyses of phenoxy acid derivatives such as MCPA, 2,4-D, mecoprop, dichlorprop, 2,4,5-T, MCPB, 2,4-DB and 2,4,5-TP in drinking and surface water samples [529]. Under the same conditions, ion-pairing with TBA fluoride [531] or ammonium acetate [532], the arylphenoxypropionic herbicides fluazifop, fenoxaprop, quizalofop, haloxyfop and diclofop and some of their Me, Et and Bu-esters were determined in surface, ground water or drinking water [531] or in soil [532] by ESI-LC-MS in SIM mode. Recoveries and detection limits were reported. 

Oxyphenoxyacid esters Cycloxydim, diclofop-methyl, fenoxaprop-ethyl, fluazifop-butyl, haloxyfop-methyl, quizalofop-ethyl... 

The ethoxyethyl ester of haloxyfop 2-(4-((3-chloro-5-(tri-fluoromethyl)-2-pyridinyl)oxy)phenoxy) propanoic acid belongs to the p-oxyphenoxypropanoate herbicide family. The mode of action of this herbicide is unsufficiently known. In this study the influence of haloxyfop-ethoxyethyl on lipid metabolism was investigated. 

Figure 5.3. Examples of other herbicides which interfere with respiration and mitochondrial membranes. Diclofop and haloxyfop are the active free acids of their parent methyl esters (see Chapter 3).

Their results demonstrated the importance of structure (and adjuvant) in controlling the penetration mechanism. Cuticle penetration by haloxyfop, haloxyfop-methyl, haloxyfop-ethyl, and fluazifop-butyl without COC followed BP kinetics, being impeded by an initial fast penetration stage. With the exception of haloxyfop, the addition of COC to the formulation simplified the penetration kinetics to SP. The BP behavior in the absence of COC may be due to the relatively rapid penetration of Ortho X-77, leaving the polar pyridinyloxy ester on the leaf surface. These polar esters may require the assistance of the surfactant and/or COC to facilitate cuticle penetration. In contrast, the behavior of quizalofop-methyl and diclofop-methyl was SP in the presence or absence of COC. 

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