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2,4,5-Trichlorophenoxyacetic acid

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2,4,5-Trichlorophenoxyacetic acid
2,4,5-Trichlorophenoxyacetic acid
Names
IUPAC name
(2,4,5-Trichlorophenoxy)acetic acid
Other names
2,4,5-Trichlorophenoxyacetic acid
2,4,5-T
Trioxone
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.068 Edit this at Wikidata
KEGG
RTECS number
  • AJ8400000
UNII
  • InChI=1S/C8H5Cl3O3/c9-4-1-6(11)7(2-5(4)10)14-3-8(12)13/h1-2H,3H2,(H,12,13) checkY
    Key: SMYMJHWAQXWPDB-UHFFFAOYSA-N checkY
  • InChI=1/C8H5Cl3O3/c9-4-1-6(11)7(2-5(4)10)14-3-8(12)13/h1-2H,3H2,(H,12,13)
    Key: SMYMJHWAQXWPDB-UHFFFAOYAR
  • Clc1cc(OCC(=O)O)c(Cl)cc1Cl
Properties
C8H5Cl3O3
Molar mass 255.48 g/mol
Appearance Off-white to yellow crystalline solid
Density 1.80 g/cm³, 20 °C
Melting point 154-158 °C
238 mg/kg (30 °C)
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T), a synthetic auxin, is a chlorophenoxy acetic acid herbicide used to defoliate broad-leafed plants. It was developed in the late 1940s and was widely used in the agricultural industry until being phased out, starting in the late 1970s due to toxicity concerns. Agent Orange, a defoliant used by the U.S. in the Vietnam War, was equal parts 2,4,5-T and 2,4-D (2,4-dichlorophenoxyacetic acid). "The U.S. military had tested Agent Orange in Thailand between April 1964 and June 1965 with the full knowledge of the Thai authorities."[citation needed]

2,4,5-T itself has low toxicity, with oral LD50 of 389 mg/kg in mice and 500 mg/kg in rats. However, the manufacturing process for 2,4,5-T contaminates this chemical with trace amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD is a carcinogenic persistent organic pollutant with long-term effects on the environment. With proper temperature control during production of 2,4,5-T, TCDD levels can be held to about .005 ppm. Before the TCDD risk was well-understood, early production facilities lacked proper temperature controls and individual batches tested later were found to have as much as 60 ppm of TCDD.

In 1970, the United States Department of Agriculture halted the use of 2,4,5-T on all food crops except rice, and in 1985, the EPA terminated all remaining uses in the US of this herbicide. The international trade of 2,4,5-T is restricted by the Rotterdam Convention. 2,4,5-T has since largely been replaced by dicamba and triclopyr.

Apart from agricultural uses, 2,4,5-T was also a major ingredient in Agent Orange, a herbicide blend used by the U.S. military in Vietnam between January 1965 and April 1970 as a defoliant. Because of TCDD contamination in the 2,4,5-T component, it has been blamed for serious illnesses in many US veterans and Vietnamese civilians who were exposed to it. Agent Orange often had much higher levels of TCDD than 2,4,5-T used in the US.

References

1. Tschirley FH. Defoliation in Vietnam. Science. 1969;163:779-786.

2. Orians GH, Pfeiffer EW. Ecological effects of the war in Vietnam. Science. 1970;168:544-554.

3. Neilands JB, Orians GH, Pfeiffer EW, Vennema A, Westing AH. Harvest of Death: Chemical Warfare in Vietnam and Cambodia. New York: Free Press; 1972.

4. Gochfeld M. The other victims of the Vietnam war. BioScience. 1975;25:540-541.

5. Westing AH, ed. Herbicides in War. The Long Term Ecological and Human Consequences. London: Taylor and Francis; 1984.

6. Schecter AJ, Tong HY, Monson SJ, Goss ML. Levels of 2,3,7,8-TCDD in silt samples collected between 1985-86 from rivers in the North and South of Vietnam. Chemosphere. 1989;19:547-550.

7. Schecter AJM, Dai LC, Thuy LTB, et al. Agent Orange and the Vietnamese: the persistence of elevated dioxin levels in human tissues. Am J Public Health. 1995;85:516-522.

8. Kahn PC, Gochfeld M, Nyugen M, Hansson M, Rappe C, Velez H. Dioxins and dibenzofurans in blood and adipose tissue of Agent Orange-exposed Vietnam veterans and matched controls. JAMA. 1988;259:1661-1667.

9. Fingerhut MA, Halperin WE, Marlow DA, et al. Cancer mortality in workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin. N Engl J Med. 1991;324:212-218.

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