2,4-Dichlorophenoxyacetic acid
[CAS# 94-75-7]

Identification

• Classification: Biochemical >> Amino acids and their derivatives >> Threonine derivative
• Name: 2,4-Dichlorophenoxyacetic acid
• Synonyms: Amidox; B-Selektonon; U-5043; Crotilin; Decamine; Dicopur; Dicotox; Ipaner; Netagrone; Pennamine; Weedone-2,4-DP; Helena 2,4-D; 2,4-D LV6; Weedar 64A; Chloroxone; BH 2,4-D; Agrotect; Amoxone; Weed Tox; Weedtrol; Emulsamine BK; Envert DT; Dormone
• Molecular Formula: C₈H₆Cl₂O₃
• Molecular Weight: 221.04
• CAS Registry Number: 94-75-7
• EC Number: 202-361-1
• SMILES: C1=CC(=C(C=C1Cl)Cl)OCC(=O)O

Properties

• Density: 1.563 g/cm³
• Melting point: 137-141 °C
• Boiling point: 160 °C (0.4 torr)
• Water solubility: Slightly soluble. Decomposes. 0.0890 g/100 mL

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H302-H317:-H318:-H335:-H412:
• Safety Statements: P261-P264-P264+P265-P270-P271-P272-P273-P280-P301+P317-P302+P352-P304+P340-P305+P354+P338-P317-P319-P321-P330-P333+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin sensitization	Skin Sens.	1	H317
Serious eye damage	Eye Dam.	1	H318
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Acute toxicity	Acute Tox.	4	H312
Respiratory sensitization	Resp. Sens.	1	H334
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Acute toxicity	Acute Tox.	4	H332
Carcinogenicity	Carc.	2	H351
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413

• Transport Information: UN 2765

Discovery and Applications

2,4-Dichlorophenoxyacetic acid, commonly abbreviated as 2,4-D, is one of the most extensively used synthetic auxins and herbicides in agricultural history. It was first developed in the 1940s, during the period of intense research on plant growth regulators and chemical weed control. The chemical structure of 2,4-D mimics that of natural auxins, particularly indole-3-acetic acid, allowing it to selectively disrupt normal plant growth processes. When applied to broadleaf weeds, it induces uncontrolled cell division and elongation, ultimately causing the plant's death while leaving monocot crops like wheat, corn, and rice relatively unharmed.

The initial discovery and testing of 2,4-D were driven by the need to increase crop productivity by eliminating competition from unwanted vegetation. During World War II, its potential for large-scale application in food production gained strategic importance. After the war, it quickly became commercialized and was one of the first herbicides to be produced in large quantities for agricultural use. Its success helped usher in the era of modern chemical weed management, shaping weed control practices for decades to follow.

2,4-D has been applied in various agricultural systems, including cereal grains, maize, sugarcane, and pasture management. Its ability to control a wide range of broadleaf weeds at relatively low application rates made it highly popular. In turf management and lawn care, it has also been widely used to maintain weed-free grass areas. In forest management, it serves as a tool for controlling brush and invasive species. Additionally, 2,4-D has played a role in no-till and conservation tillage systems by allowing weed control without disrupting the soil.

Several forms of 2,4-D are commercially available, including acid, ester, and salt derivatives, which vary in volatility, solubility, and persistence. This flexibility allows for tailored application methods depending on crop type, climate, and environmental conditions. Formulations have been designed to improve efficacy while minimizing environmental impact, and many are compatible with tank mixes for integrated weed control strategies.

Despite its widespread use, 2,4-D has also been the subject of regulatory review and public scrutiny due to concerns about its ecological and human health effects. Environmental fate studies have shown that it can leach into groundwater and affect non-target species if not used properly. Regulatory agencies around the world have established guidelines and safety thresholds for its use, including buffer zones and application timing restrictions, to reduce the risk of drift and contamination. As part of sustainable agriculture, there is ongoing research into improving application technologies and resistance management strategies to maintain the long-term utility of 2,4-D.

The legacy of 2,4-D is significant in both agronomic and scientific contexts. It was instrumental in demonstrating the feasibility of chemical weed control on a global scale and continues to be an important tool in integrated weed management. Advances in biotechnology, including genetically modified crops tolerant to 2,4-D, have extended its utility and opened new avenues for its application.

References

1984. A gas chromatographic method for determination of 2,4-D residues in urine after occupational exposure. Bulletin of Environmental Contamination and Toxicology, 33(6).
DOI: 10.1007/bf01625578

1979. Oxygen consumption in Lepomis machrochirus exposed to 2,4-D or 2,4,5-T. Bulletin of Environmental Contamination and Toxicology, 22(1).
DOI: 10.1007/bf01685512

1971. Pesticide effect on growth and 14 C assimilation in a freshwater alga. Bulletin of Environmental Contamination and Toxicology, 6(1).
DOI: 10.1007/bf01559063