2,4,5-Trichlorophenoxyacetic acid

2,4,5-T hit the market in 1948. During its manufacture, serious accidents involving the release of dioxins occurred. As a result of an industrial accident at the Monsanto manufacturing plant in Nitro in 1949, 120 workers were exposed to the reaction mixture and suffered from chloracne . Another serious incident occurred in 1952 at the Boehringer Ingelheim plant in Hamburg Moorfleet, where another 30 workers fell ill with chloracne. In research to optimize 2,4,5-T synthesis in 1968, a reaction vessel exploded in a British laboratory at Coalite Chemicals, killing one worker ^[5] .

During the Vietnam War, 2,4,5-T, partly in the form of its isopropyl and n- butyl ether, was used as the active ingredient of Agent Orange , Agent Green , Agent Pink and Agent Purple . In these mixtures, pollution was contained between 0.02 and 15 mg / kg of 2,3,7,8-TCDD , which turned out to be there due to the imperfection of the production technology of 2,4,5-trichlorophenoxyacetic acid. The amount of 2,3,7,8-TCDD expended during the Vietnam War is estimated at 166 kg ^[6] .

Between 1971 and 1974, a specialized company in Missouri improperly disposed of oily residues from 2,4,5-T production. Instead of recycling them, they sprayed it at racetracks to bind the dust. Horses are very sensitive to dioxins, more than 50 animals died. The remains of the mixture were sprayed on the streets of Times Beach. During the 1982 flood, sidewalks treated with oily residues washed away into homes. The population was evacuated, and the state bought a significant part of the land ^[5] .

2,4,5-T, like its related 2,4-dichlorophenoxyacetic acid, are essentially synthetic auxin plant hormones. They cause excessively fast growth, which leads to the death of the plant.

In the 1970s and 1980s, 2,4,5-T under the trade name Tormona was used against woody plants for the so-called forest cleaning. In combination with other herbicides, it is also used for growing crops , on pastures and lawns. It is usually sold in the form of a powder of water-soluble salts of alkali metals or ammonium, as well as 2,4,5-T esters in the form of concentrated emulsions .

In Germany, the use of this herbicide has been prohibited since 1988 ^[1] , as well as in Austria and Switzerland ^[7] .

To prepare this substance, tetrachlorobenzene and 2,4,5-trichlorophenol are mixed with chloroacetic acid at a temperature of about 140–20 ° C, resulting in the formation of 2,4,5-trichlorophenoxyacetic acid. If the temperature rises sharply in the last stage of the reaction, toxic dioxins are formed.

2,4,5-T enters the body primarily through the skin or digestive tract. It acts on the mucous membranes and skin, irritating them greatly, and this effect is explained by the presence of 2,3,7,8-TCDD in the preparation. After oral administration, the general health condition worsens. The substance damages the nervous and cardiovascular systems. Volunteers who took 2,4,5-T in doses up to 5 mg / kg body weight showed no clinical symptoms. They only reported a metallic taste in their mouths. In animal studies, the semi-lethal dose (LD ₅₀ ) was 100 mg / kg body weight for dogs, 500 mg / kg for rats, and about 800 mg / kg for mice ^[1] . Studies of chronic toxicity in most cases did not track the extent to which 2,4,5-T was contaminated with dioxins. In animal experiments, chronic exposure caused damage to the liver and kidneys. The permissible daily dose for humans was set at 0.03 mg / kg body weight. Pure 2,4,5-trichlorophenoxyacetic acid is believed to have no teratogenic , mutagenic, or carcinogenic properties ^[1] .

On average, 2,4,5-T contains about 10 ppm of dioxins ^[5] .

The compound decomposes in plants after removing the residue of acetic acid by hydroxylation of a benzene ring. The storage time in the soil after applying 1.5 kg of 2,4,5-T per ha is estimated at 2 months. The herbicide has been classified as non-toxic to bees. LC ₅₀ for rainbow trout for the esters of the drug was determined to be 12 mg with a duration of exposure of 24 hours ^[8] .

For analytical detection, residues of 2,4,5-trichlorophenoxyacetic acid are extracted with chloroform and converted by trichloridapyridine to trichlorophenol by purification of the extract. The resulting trichlorophenol can be quantified quantitatively by reaction with 4-aminoantipyrine and potassium ferricyanide . Alternatively, the purified 2,4,5-T extract can be esterified with dimethyl sulfate and determined by gas chromatography ^[8] .