Chlorthal-dimethyl: Properties, Uses & Safety Overview

Chlorthal-dimethyl is a chlorinated phthalate ester herbicide widely used as a pre-emergent weed control agent and analytical reference standard in environmental and agricultural research.

IUPAC Name

Dimethyl 2,3,5,6-tetrachloroterephthalate

Common Synonyms

DCPA; Dacthal; dimethyl tetrachloroterephthalate

Molecular Formula

C₁₀H₆Cl₄O₄

Molecular Weight

331.96 g/mol

CAS Number

1861-32-1

Physical State

White to off-white crystalline solid at room temperature

Application Class

Pre-emergent herbicide; analytical reference standard

Chemical Identity and Physical Properties

Chlorthal-dimethyl (CAS 1861-32-1), commonly abbreviated as DCPA and marketed historically under the trade name Dacthal, is the dimethyl ester of 2,3,5,6-tetrachloroterephthalic acid. Its molecular formula is C₁₀H₆Cl₄O₄, giving a molecular weight of approximately 331.96 g/mol. The compound appears as a white to off-white crystalline powder at room temperature.

Chlorthal-dimethyl exhibits low water solubility, which contributes to its persistence in soil and its suitability as a pre-emergent herbicide. It is soluble in common organic solvents such as acetone, dichloromethane, and ethyl acetate, facilitating its use in analytical sample preparation and standard solution preparation in the laboratory.

The presence of four ring-chlorine substituents and two ester groups confers chemical stability under normal storage conditions, though the compound should be protected from prolonged exposure to strong bases, which can promote ester hydrolysis.

Herbicidal Mechanism and Agricultural Background

Chlorthal-dimethyl functions as a pre-emergent (pre-plant or at-planting) herbicide, meaning it is applied to soil before weed seeds germinate rather than targeting established plants. Its primary mode of action involves disruption of cell division (mitosis) in germinating seedlings, inhibiting the formation of the mitotic spindle and thereby preventing normal root and shoot elongation in susceptible weed species.

Historically, DCPA was registered and widely used in the United States and other countries for control of annual grasses and certain broadleaf weeds in crops such as broccoli, Brussels sprouts, cabbage, cotton, strawberries, and turf. It is particularly effective against crabgrass (Digitaria spp.) and other annual grass species.

Because chlorthal-dimethyl is not systemic and has limited post-emergent activity, its efficacy is highly dependent on proper soil incorporation or rainfall after application to move the compound into the weed seed germination zone.

Laboratory and Research Applications

In the research setting, chlorthal-dimethyl (SKU: C111305) is primarily employed as an analytical reference standard and certified research reagent. Key laboratory applications include:

• Environmental monitoring: Quantification of DCPA residues in soil, water, and sediment samples by gas chromatography (GC) or GC-MS methods, supporting environmental fate and ecotoxicology studies.
• Food and agricultural residue analysis: Determination of herbicide residues in crop commodities and food matrices in compliance with regulatory guidelines (e.g., EPA, EU MRL frameworks).
• Method development and validation: Preparation of calibration standards and spiked matrix samples for development and validation of multi-residue pesticide analytical methods.
• Toxicological research: In vitro studies investigating the compound's potential endocrine-disrupting properties and metabolic pathways, including formation of its hydrolysis metabolites monomethyl tetrachloroterephthalate (MTP) and tetrachloroterephthalic acid (TCPA).

For analytical work, stock solutions are typically prepared in acetone, methanol, or ethyl acetate at known concentrations, then diluted gravimetrically into matrix-matched calibration standards.

Safety, Handling, and Regulatory Considerations

Researchers working with chlorthal-dimethyl should observe standard laboratory safety practices appropriate for chlorinated organic pesticide standards:

• Personal protective equipment (PPE): Wear nitrile gloves, a laboratory coat, and safety glasses. Use a fume hood when weighing powders or preparing concentrated solutions to minimize inhalation exposure.
• Storage: Store in a cool, dry, well-ventilated location away from oxidizers and strong bases. Keep containers tightly sealed. Typical storage temperature: room temperature or as specified on the product label.
• Waste disposal: Dispose of chlorthal-dimethyl and contaminated solvents as halogenated organic waste in accordance with applicable local, national, and institutional regulations.
• Regulatory status: The U.S. EPA has classified chlorthal-dimethyl as a possible human carcinogen (Group C) based on animal data. The European Union has reviewed its approval status under pesticide regulation frameworks. Researchers should consult current Safety Data Sheets (SDS) and applicable regulatory databases for the most up-to-date classification and restriction information.

Always consult the product-specific SDS provided by Aladdin Scientific prior to use. The SDS contains authoritative hazard classification, first-aid measures, and disposal guidance.

Frequently asked questions

What is chlorthal-dimethyl used for in a research laboratory?

In research laboratories, chlorthal-dimethyl (DCPA) is primarily used as an analytical reference standard for pesticide residue analysis in environmental, food, and agricultural matrices. It is also used in method development, calibration curve preparation, and toxicological or environmental fate studies.

What solvents are suitable for preparing chlorthal-dimethyl standard solutions?

Chlorthal-dimethyl is soluble in common organic solvents including acetone, dichloromethane, ethyl acetate, and methanol, all of which are suitable for preparing stock and working standard solutions. Water solubility is very low, so aqueous preparations alone are not recommended for analytical standards.

Is chlorthal-dimethyl considered hazardous, and what precautions should be taken?

Yes, chlorthal-dimethyl carries regulatory hazard classifications. The U.S. EPA has classified it as a possible human carcinogen (Group C) based on animal studies. Researchers should use appropriate PPE (gloves, lab coat, eye protection), work in a fume hood, store the compound properly, and dispose of waste as halogenated organic waste. Always consult the current SDS before use.

What analytical techniques are typically used to detect chlorthal-dimethyl residues?

Gas chromatography with electron-capture detection (GC-ECD) and gas chromatography–mass spectrometry (GC-MS) are the most widely used techniques for detecting and quantifying chlorthal-dimethyl residues in environmental and food matrices, owing to the compound's volatility and the sensitivity of these detectors to chlorinated compounds.

References

1. U.S. Environmental Protection Agency. Chlorthal-dimethyl (DCPA) Pesticide Registration Review. EPA Docket.
2. Tomlin, C.D.S. (Ed.). The Pesticide Manual: A World Compendium, 17th ed. British Crop Production Council, 2015.
3. Montgomery, J.H. Agrochemicals Desk Reference, 2nd ed. CRC Press, 1997.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.