2.4.5- Trichlorophenoxyacetic acid herbicide

Riihimaki V, Sisko A, Hemberg S. 1982. Mortality of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid herbicide applicators in Finland. Scand J Work Environ Health 8 37-42. 

Figure 13.11 Column-switcliing RPLC trace of a surface water sample spiked with eight chlorophenoxyacid herbicides at the 0.5 p-g 1 level 1, 2,4-dichlorophenoxyacetic acid 2, 4-chloro-2-methylphenoxyacetic acid 3, 2-(2,4-diclilorophenoxy) propanoic acid 4, 2-(4-cliloro-2-methylphenoxy) propanoic acid 5, 2,4,5-trichlorophenoxyacetic acid 6, 4-(2,4-dichlorophenoxy) butanoic acid 7, 4-(4-chloro-2-methylphenoxy) butanoic acid 8, 2-(2,4,5-tiichlorophenoxy) propionic acid. Reprinted from Analytica Chimica Acta, 283, J. V. Sancho-Llopis et al., Rapid method for the determination of eight chlorophenoxy acid residues in environmental water samples using off-line solid-phase extraction and on-line selective precolumn switcliing , pp. 287-296, copyright 1993, with permission from Elsevier Science.

Cl4-DBpD) may occur in trace amounts in the herbicide, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) (I, 2). Radiolabeled preparations of this dioxin are needed to facilitate studies of its degradation chemistry, metabolism, and mode of action. 

TJesticides derived from chlorinated phenols (Table I) are among the most prominent of those currently in worldwide use. Several major herbicides have been applied in large quantities in subtropical locations. Cahfornia used more than 1,200,000 pounds of 2,4-dichlorophenoxyacetic acid (2,4-D) and its derivatives in 1970 (I) Hawaii consumed some 465,000 pounds of pentachlorophenol (PCP) in 1968 (2), and the amount of combined butyl esters of 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) released in one area of Cambodia during two months of 1969 was estimated to exceed 77,000 pounds (3). 

TAetection of the highly potent impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), necessitated an environmental assessment of the impact of this contaminate. Information was rapidly needed on movement, persistence, and plant uptake to determine whether low concentrations reaching plants, soils, and water posed any threat to man and his environment. Because of the extreme toxicity of TCDD, utmost precautions were taken to reduce or minimize the risk of exposure to laboratory personnel. Synthesis of uniformly labeled C-TCDD by Muelder and Shadoff (I) greatly facilitated TCDD detection in soil and plant experiments. For unlabeled experiments it seemed wise to use only small quantities of diluted solutions in situations where decontamination was feasible and to rely on the sensitivity afforded by electron capture gas chromatography... 

So far as the author is aware, the first statement of the herbicidal action of 2,4-dichlorophenoxyacetic acid, made in the United States, was in a publication by Hamner and Tukey (14) in 1944. They sprayed 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid on bindweed and obtained a complete kill down to the root tips. At about the same time Hamner and Tukey (13) and Marth and Mitchell (24) demonstrated the effect of 2,4-dichlorophenoxyacetic acid as a differential herbicide on lawns. All plants growing on the lawns (except the grasses) were destroyed with apparently no noticeable ill effect on the grasses. 

Shadoff, L.A., R.A. Hummel, L. Lamparski, and J.H. Davidson. 1977. A search for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in an environment exposed annually to 2,4,5-trichlorophenoxyacetic acid ester (2,4,5-T) herbicides. Bull. Environ. Contam. Toxicol. 18 478-485. 

Many pesticides are moderate to weak acids. Strong acid pollutants are fully ionised at ambient pH. Examples include trifluoroacetic and chloroacetic acids, whose use as herbicides has been banned but which still occur as solvent degradation products [16], or the pesticide 2,4,5-trichlorophenoxyacetic acid (P 2.83). 

Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) dominated the herbicide market up to the late 1960s. These are sometimes called phenoxy herbicides. Phenol is the starting material for 2,4-D. Chlorination via electrophilic aromatic substitution (know the mechanism ) gives 2,4-dichlorophenol. The sodium salt of this compound can react with sodium chloroacetate (Sn2) and acidification gives 2,4-D. 

Dioxins are sometimes—but rarely—produced in nature, most commonly during volcanic eruptions and forest fires. Their most common source in the environment are industrial reactions in which they occur as by-products of other chemical changes or during the incineration of certain synthetic organic compounds. For example, trace amounts of 2,3,7,8-TCDD occur as an impurity in the herbicide Agent Orange (a mixture of 2,4,5-trichlorophenoxyacetic acid [2,4,5-T] and 2,4-dichlorophenoxyacetic acid [2,4-D]), which was... 

The photocatalytic degradation of widely used herbicides such as 2,4-D (2,4-dichlorophenoxyecetic acid), 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), bentazon (3-isopropyl-1 H-2,l,3-benzothiadiazin-4(3H)-one 2,2-dioxide), S-tiazines, carbetamide ((R)-l-(ethylcarbamoyl)ethyl carbanilate), and monouron (3-(4-chlorophenyl)-l-methoxy-l-methylurea) in water have been... 

Furthermore, the use of Ralstonia eutropha JMP134-containing sensors for the determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been described [118,121]. This sensor was sensitive to 2,4-D and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) with a detection Emit of 40 mg 1 with a response time of 15 s. Moreover, catechol, benzoic acid, and sahcylaldehyde caused higher signals, but no or very little signal was obtained for phenol, biphenyl, and the usual substrates such as glucose, fructose, ethanol, and acetate. 

Our discussion of pesticides has focused primarily on insecticides. In the United States the primary use of pesticides is in the form of herbicides, those pesticides used to control weeds. Approximately 70% of the pesticides used in the United States are herbicides and 20% are insecticides. The use and development of herbicides parallels that of insecticides. The first herbicides were inorganic metal compounds and salts. During World War II organic herbicides were synthesized and their use increased dramatically. One of the first major classes of herbicides synthesized in the mid-1940s was phenoxyaliphatic acids. As this name implies, the phenoxyaliphatic acids contain the benzene ring, oxygen, and an aliphatic acid. The two most common phenoxyaliphatic acids are 2,4 dichlorophenoxyacetic acid, called 2,4-D and 2,4,5 trichlorophenoxyacetic acid, known as 2,4,5-T (Figure 18.10). The numbers in these... 

Dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and their salts and esters are compounds of interest as herbicides used for the destruction of weeds (Figure 56-1). They have been assigned toxicity ratings of 4 or 3, respectively, which place the probable human lethal dosages at 50-500 or 500-5000 mg/kg, respectively. 

Over the last two decades few chemicals have acquired as much notoriety as 2,3,7,8-tetrachlorodibenzo[6,e ] [1,4]dioxin. The compound, commonly referred to as TCDD, or simply but misleadingly as dioxin, is formed as a by-product in the commercial preparation of 2,4,5-trichlorophenol, an intermediate in the manufacture of the bacteriocide hexa-chlorophene and the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). The commercial production of 2,4,5-trichlorophenol, during which TCDD is generated, involves the reaction of 1,2,4,5-tetrachlorobenzene with base TCDD is formed if the product reacts further (Scheme 32). 

The once widely used herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) is prepared... 

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). 

Chlorophenoxy acid herbicides are also widely used to control broadleaf weeds and grass plants. Several immunoassays have been reported for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).246 247 Several immunosensors have been described using a transducing principle similar to the RIANA system already described in this chapter. Thus, Meusel et al.248 reported the use of monoclonal antibodies in a sensor chip to analyze river and lake water samples, obtaining detection limits of 0.1 ig L 1. Moreover, monoclonal antibodies, produced by Cuong et al.,249 were used in a dipstick immunoassay format to analyze pond water samples. When applied to the 2,4-D compound, this semiquantitative method yielded for an IC50 of 6 ug I. and an LOD of 0.5 pg L-1. 

Another herbicide, 2,4,5-trichlorophenoxyacetic acid, is synthesized by starting with the chlorination of benzene to give 1,2,4,5-tetrachloroben-zene, which reacts with caustic to give 2,4,5-trichlorophenol. Conversion to the sodium salt followed by reaction with sodium chloroacetate and acidification gives 2,4,5-trichlorophenoxyacetic acid. Agent Orange is a 1-to-l mixture of the butyl esters of 2,4,5-trichlorophenoxyacetic acid and 2,4,-dichlorophenoxyacetic acid. 

Perhaps the most renowned example is the extensively-used 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), or rather the 2,3,7,8-tetrachlorodibenzo- -dioxin (TCDD) impurity which sometimes accompanies it. During massive use of the herbicide as a defoliant in the Vietnam war, TCDD was found almost by accident to be one of the most toxic synthetic substances ever tested. Soon, it was shown to be present in domestic 2,4,5-T as well as in the chemical warfare agents. Tests in laboratory animals demonstrated that some of the observed levels indeed were quite high enough to cause toxic effects (32). 

There are other herbicides in use which cannot be discussed in detail here, but one particular pair of chemicals should be mentioned. These are 2,4-D and 2,4,5-T, which are abbreviations of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid. These chemicals act like plant growth hormones but cause excessive growth. They are selectively toxic against weeds. Although these herbicides have low toxicity to animals they can be contaminated with the most toxic type of dioxin (2,3,7,8-TCDD), as a result of the manufacturing process. The mixture of 2,4-D and 2,4,5-T was... 

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