Herbicides chlorinated phenoxyacetic acid

Chlorinated phenols were first synthesized in the 19 century. The most characteristic properties of these compounds are related to their antiseptic features. At present, 19 chlorinated phenols are known. For industrial use, the most important congeners are 2,4-dichlorophenol, 2,4,5-trichlorophenol, and pentachlorophenol, PCP. The first of these continues to be commercially important in the production of chlorinated phenoxyacetic acid herbicides and 2,4,5-trichlorophenol is also used as the precursor of the antiseptic hexachlorophene through condensation with formaldehyde. 

During the short time of their application in the early 1980s, DLI interfaces were often applied for substance-specific analysis [60] of various types of pesticides and herbicides (triazines, carbamates, organophosphorus compounds) [61-67], chlorinated phenoxyacetic acids, phenylureas, analides (alachlor, propachlor and aldi-carb) [63]. 

Since the 1930s almost all the pesticides which have been developed are organic compounds, with notable examples being DDT, the chlorinated phenoxyacetic acid and bipyridyl herbicides, and glyphosate. 

A selective herbicide that kills broad-leaf weeds is made by chlorinating phenoxyacetic acid. Is the substituent an activating or deactivating group ... 

Haugland RA, DJ Schlemm, RP Lyons, PR Sferra, AM Chakrabarty (1990) Degradation of the chlorinated phenoxyacetate herbicides 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid by pure and mixed bacterial cultures. Appl Environ Microbiol 56 1357-1362. 

Other carboxylic acids that have become popular herbicides, though they are not phenoxyacetic acid derivatives, are dicamba and glyphosate or Roundup . Notice that dicamba does have a methoxy group and two chlorines, so it is similar to 2,4-D. Glyphosate is used on cotton and... 

Renberg [169] used an ion exchange technique for the determination of chlorophenols and phenoxyacetic acid herbicides in soil. In this method, the soil extracts are mixed with Sephadex QAE A-25 anion exchanger and the adsorbed materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl or 2-chloroethyl esters for gas chromatography. 

T (2,4,5-trichlorophenoxyacetic acid) ester formulation to a complex mixture of successively less-chlorinated phenoxyacetic esters, and Que Hee, et al. (16) reported a similar dechlorination of 2,4-D (2,4-dichlorophenoxyacetic acid). The toxic 2,4,5-T impurity, TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), was dechlo-rinated in a herbicide ester deposit on a sunlit leaf surface within a few hours (Figure 5) (17). 

Applications of this technique are growing and include the analysis of mixtures of pesticides and herbicides, including oiganophosphorus, phenoxyacetic acid, caibamate, urea types, mixtures of various types of organic compounds, alkylbenzene sulphonates, polyethylene glycols, nonylphenyl ethoxylates, dioctadecylmethyl ammonium, ozonisation products and chlorination products. 

In addition to its use in resins and adhesives, phenol is also the starting material lor the synthesis of chlorinated phenols and the food presen -atives BHT (butylated hydrox5rtoluene) and BHA (butylated hydroi -anisole). Pentachlorophenol, a widely used wood preservative, is prepared by reaction of phenol with excass C12- The herbicide 2,4-D (2,4-dich)oro-phenoxyacetic acid) is prepared from 2,4-dichlorophenol, and the hospital antiseptic agent hexachlorophene is prepared from 2,4,5-trichlorophenol. 

The multiple chlorination of another oxygen-substituted compound, phenoxyacetic acid, leads to a useful product. Chlorination with two equivalents of chlorine provides 2,4-dichlorophenoxy acetic acid, which is the herbicide 2,4-D. The oxygen substituent again activates the ring and directs the chlorination to the ortho and para positions. 

Uses 2,4-D is a chlorine-substituted phenoxyacetic acid herbicide used for postemergence control of annual and perennial broad-leaved weeds in fruits, vegetables, turfs and ornamentals. 

A case of palmoplantar keratoderma, scleroderma and chloracne was reported in an agricultural worker who had been a weed sprayer for 5 years. He had used 2,4,5-trichlorophenoxyacetic acid and/or 2,4 dichloro-phenoxyacetic acid, both of which may contain chlorinated dibenzodioxins as impurities. He also had been chronically exposed to multiple other, non-chloracne associated herbicides, some of which have been associated with scleroderma. Safety equipment was not utilized (Poskitt et al. 1994). 

The metabolism of the herbicide 2,4-dichlorophenoxyacetic acid by A. niger has been examined. The major metabolite was 2,4-dichloro-5-hydroxyphenoxy-acetic add. This was accompanied by a minor product, 2,5-dichloro-4-hydroxy-phenoxyacetic add, in which a chlorine migration had taken place. 

---