Acidic herbicides, derivatives

Bromocresol green (3.8...5.4) aliphatic carboxylic acids[103,187 — 204] triiodobenzoic acid [205], derivatives of barbituric acid [206] amphetamine derivatives [207, 208] phenazones, morazone [209] alkaloids [91, 209] nephopam [210] phenyramidol metabolites [211] diethylalkylacetamide derivatives [212] zipeprol (Mirsol) [213] thalidomide and hydrolysis products [214] cyclohexylamine derivatives [215] herbicide residues [216]... 

D is found in compounds like quinolyl esters of N-substituted dithio-carbamic acids. A wide variety of compounds containing the quinoline system are herbicides. Derivatives and salts of 8-quinolinecarboxylic acid as well as quinolyl carbamates are each useful insecticides. The copper salt of 8-hydroxyquinoline is an effective fungicide. 

Phenoxyalkanoic acid herbicides are not amenable to direct gas chromatographic determination because of the high polarity or low volatility of the compounds and must be converted to their more volatile derivatives. The sensitivity of the electron capture detector towards alkyl esters of 4-chloro-2-methylphenoxy acetic acid, 4-chloro-2-methylphenoxy butyric acid, etc., is very poor. The methyl ester of 4-chloro-2-methylphenoxy acetic acid was 100 times less sensitive to electron affinity detection than the 2,4-D-methyl ester [396]. 

Chau and Terry [397] reported the formation of pentafluorobenzyl derivatives of ten herbicidal acids, including 4-chloro-2-methyl-phenoxyacetic acid [ 396 ]. They found that five hours was an optimum reaction time at ambient temperature with pentafluorobenzyl bromide in the presence of potassium carbonate solution. Bromination [398], nitrification [399] and esterification with halogenated alcohol [396] have also been used to study the residue analysis of 4-chloro-2-methylphenoxy acetic acid and 4-chloro-2-methylphenoxybutyric acid. Pentafluorobenzyl derivatives of phenols and carboxylic acids were prepared for detection by electron capture at very low levels [400,401 ]. 

Lee et al. [187] developed a multi-residue method with a low detection limit for 10 commonly used acid herbicides in non saline waters. The herbicides were Dicamba, MCPA, 2,4-DP, 2,3,6-TBA, 2,4-D, Silvex, 2,4,5-T, MCPB, 2,4,5-DB and Picloram. The method used solvent extraction and the formation of pentafluorobenzyl esters. The derivatives were quantified by capillary column gas chromatography with electron capture detection. The detection limit was 0.05pg L. Recoveries of herbicides from spiked Ontario lake water (0.5-1.Opg L 1) were 73-108% except for Picloram recovery which was 59% at 0.1 pg L 1. 

The phenoxypropionic acid herbicides (Chapter 31) rely on an SN2 reaction to convert the S-2-chloropropionic acid (1) to the ff-2-aryloxy derivative 2.3 These compounds are also available from lactic acid by substitution reactions -lactic acid (3) requires two inversions, whereas S-lactate (4) only requires one (Schemes 22.2 and 22.3).4... 

Phenoxypropionic acid herbicides contain a stereogenic center that can be derived from 2-chloro-propionic acid and include fluazifop-butyl (29) and flamprop (30).245... 

Table II Derivatives of the Chlorophenoxyalkyl Acids and Some Other Acidic Herbicides...

Herbicides that inhibit photosynthetic electron flow prevent reduction of plastoquinone by the photosystem II acceptor complex. The properties of the photosystem II herbicide receptor proteins have been investigated by binding and displacement studies with radiolabeled herbicides. The herbicide receptor proteins have been identified with herbicide-derived photoaffinity labels. Herbicides, similar in their mode of action to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) bind to a 34 kDa protein, whereas phenolic herbicides bind to the 43-51 kDa photosystem II reaction center proteins. At these receptor proteins, plastoquinone/herbicide interactions and plastoquinone binding sites have been studied, the latter by means of a plastoquinone-deriv-ed photoaffinity label. For the 34 kDa herbicide binding protein, whose amino acid sequence is known, herbicide and plastoquinone binding are discussed at the molecular level. 

Both underivatised and methylated samples are examined because uracil herbicides give a mixture of products on methylation and should be chromatographed in their underivatised forms, whereas carboxylic acid pesticides, e.g. chlorinated phenoxy acid herbicides, are best examined as methyl derivatives. 

Miura, M. Terashita, Y. Funazo, K. Tanaka, M. Separation of phenoxy acid herbicides and their enantiomers in the presence of selectively methylated cyclodextrin derivatives by capillary zone electrophoresis. J. Chromatogr., A 1999, 846, 359-367. 

Analysis of Chloronhenoxv Herbicides. Many important target environmental pollutants can only be detected via conventional GC methods by first converting them to derivatives that are less polar and more volatile, e.g., the chlorophenoxy herbicides. A standard EPA method (SW-846 8150) specifies soil extraction and alkaline hydrolysis of any esters present followed by (re) esterification via diazomethane and detection and confirmation by GC/MS. The methylation step is required because the free carboxylic acids will not pass through conventional GC analytical columns. Reversed phase chromatography functions equally well to resolve free carboxylic acids or the corresponding esters and thus can eliminate the diazomethylation step. An interlaboratory check sample provided by the EPA of soil spiked with the chlorophenoxy acid herbicides Silvex and 2,4-D was obtained by our laboratory to demonstrate that LC/MS can offer a simpler and effective method for these compounds. 

The rehydration product of HMF, levulinic acid, is also regarded as a potential biomass derived organic compound [35, 39,40]. Levulinic acid could be utilized as feedstock for several large volume chemicals (Fig. 7), e.g., methyltetrahydrofuran and levulinate esters (fuel additives), delta-amino-levulinic acid (herbicide), and diphenohc acid (replacer for bisphenol A for polycarbonates). 

Phenoxy acid herbicides, sulfonyl ureas, quaternary ammonium derivatives (quats), and aryloxy propanoic acids are the main classes of compounds subjected to capillary zone electrophoresis (CZE). Triazines are also separated using nonaqueous CZE, while low pfCa characterized chlorotriazines require an ion-pair-like solubilization using cationic surfactants (tetradecylammonium bromide, dodecyltrimethyl-ammonium bromide). Chiral selectors are added in CZE for obtaining enantioselectivity. Chiral selectors used for herbicide enantiomeric discrimination are vancomycin, y-cyclodextrin, ethyl carbonate -cyclo-dextrin, cyclohexyl-alkyl-)S-D-maltoside, sulpropyl ether a-cyclodextrin, and hexakis(2,3-di-0-methyl)-a-cyclodextrin. 

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