3-Chloro-4-Fluorophenylacetic Acid: Properties & Applications

3-Chloro-4-fluorophenylacetic acid is a halogen-substituted arylacetic acid that serves as a versatile and strategically important building block in pharmaceutical synthesis, agrochemical research, and the preparation of structurally diverse bioactive molecules.

Chemical Name

3-Chloro-4-fluorophenylacetic acid

Molecular Formula

C₈H₆ClFO₂

Molecular Weight

188.58 g/mol

CAS Number

Need verification — flag for review

Functional Class

Arylacetic acid (halogenated)

Primary Use

Pharmaceutical and agrochemical intermediate

SKU

C120930

Chemical Identity and Structure

3-Chloro-4-fluorophenylacetic acid belongs to the phenylacetic acid family of organic acids, distinguished by the presence of two halogen substituents — a chlorine atom at the 3-position and a fluorine atom at the 4-position of the phenyl ring — along with an acetic acid (–CH₂COOH) side chain. This specific substitution pattern creates a polarized aromatic ring with distinct electronic and steric properties compared to the unsubstituted parent compound.

The electron-withdrawing nature of both halogens lowers the electron density of the aromatic ring, influencing the compound's reactivity toward electrophilic and nucleophilic reactions. The fluorine atom, in particular, is known to modulate lipophilicity and metabolic stability in drug molecules, making the 4-fluoro motif highly sought after in medicinal chemistry programs. The chlorine substituent at the 3-position provides an additional handle for cross-coupling chemistry, enabling further structural elaboration.

Applications in Pharmaceutical and Medicinal Chemistry

Halogenated phenylacetic acids such as 3-chloro-4-fluorophenylacetic acid are widely employed as key intermediates in the synthesis of active pharmaceutical ingredients (APIs) and drug candidates. The carboxylic acid group enables straightforward transformation into amides, esters, acid chlorides, and other activated derivatives, making the compound a flexible entry point into structurally complex targets.

In drug discovery, fluorine-containing aromatic scaffolds are valued for their ability to improve binding affinity, enhance metabolic stability, and fine-tune pharmacokinetic profiles. The combination of chloro and fluoro substituents in this compound provides researchers with a dual-halogenated building block that can participate in palladium-catalyzed cross-coupling reactions (e.g., Suzuki, Negishi, or Buchwald–Hartwig couplings) via the C–Cl bond, enabling rapid diversification of chemical libraries.

Beyond pharmaceuticals, this compound finds use in agrochemical research, where halogenated arylacetic acid motifs appear in herbicides and fungicides.

Handling, Storage, and Safety Considerations

As with most halogenated organic acids, 3-chloro-4-fluorophenylacetic acid should be handled with appropriate laboratory precautions. Researchers should consult the product's Safety Data Sheet (SDS) for complete hazard information before use. General recommended practices include working in a well-ventilated fume hood, wearing appropriate personal protective equipment (PPE) such as chemical-resistant gloves, safety glasses, and a laboratory coat.

For storage, the compound should be kept in a tightly sealed container away from moisture, heat, and incompatible materials such as strong oxidizers and bases. Storage at room temperature or under refrigeration (as specified in the product documentation) is typically adequate for maintaining long-term stability. Avoid inhalation of dust or vapors and ensure proper waste disposal in accordance with local regulations governing halogenated organic compounds.

Synthetic Utility: Key Reactions and Transformations

The carboxylic acid functionality of 3-chloro-4-fluorophenylacetic acid is the primary handle for synthetic elaboration. Standard transformations include:

• Amide bond formation: Coupling with amines using reagents such as EDC/HOBt, HATU, or thionyl chloride to generate the corresponding acyl chloride intermediate, yielding structurally diverse amides useful as pharmacophores.
• Esterification: Reaction with alcohols under acidic catalysis or via activated ester intermediates to furnish esters for use as prodrugs or synthetic intermediates.
• Reduction: Reduction of the carboxylic acid to the corresponding alcohol (e.g., using LiAlH₄ or borane) provides 3-chloro-4-fluorophenylethanol, a useful chiral precursor when asymmetric reductions are employed.
• Cross-coupling via C–Cl bond: Palladium- or nickel-catalyzed cross-coupling reactions at the aryl chloride position allow introduction of aryl, vinyl, or heteroaryl groups to expand molecular complexity.

These transformations collectively make 3-chloro-4-fluorophenylacetic acid a high-value reagent for the construction of diverse molecular architectures in both academic and industrial settings.

Frequently asked questions

What is 3-chloro-4-fluorophenylacetic acid used for?

3-Chloro-4-fluorophenylacetic acid is primarily used as a synthetic building block in pharmaceutical and agrochemical research. Its dual halogen substitution makes it particularly valuable for the preparation of drug candidates, medicinal chemistry libraries, and as a substrate in palladium-catalyzed cross-coupling reactions.

How should 3-chloro-4-fluorophenylacetic acid be stored?

The compound should be stored in a tightly sealed container, away from moisture, heat sources, and incompatible chemicals such as strong oxidizers and bases. Refer to the product SDS and label for specific temperature and storage condition recommendations.

Why is the fluorine substituent important in this compound?

Fluorine is a bioisostere with unique electronic properties that can modulate a molecule's lipophilicity, metabolic stability, and membrane permeability. In drug discovery, the 4-fluoro motif on a phenylacetic acid scaffold is frequently incorporated to improve the pharmacokinetic profile of candidate molecules, making it a strategically important structural element.

Can 3-chloro-4-fluorophenylacetic acid participate in cross-coupling reactions?

Yes. The aryl chloride functionality at the 3-position can serve as an electrophilic partner in palladium- or nickel-catalyzed cross-coupling reactions, such as Suzuki–Miyaura, Negishi, or Buchwald–Hartwig couplings. This enables researchers to introduce diverse aryl, vinyl, or amino groups onto the aromatic ring to build more complex structures.

References

1. Fluorine in medicinal chemistry: a general overview of fluorine effects on pharmacokinetics, drug metabolism and pharmacodynamics. General textbook-level knowledge on fluorinated building blocks in drug discovery.
2. March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. Standard reference for carboxylic acid transformations including amide bond formation, esterification, and reduction reactions.
3. Palladium-catalyzed cross-coupling reactions of aryl halides. General knowledge on Suzuki, Negishi, and Buchwald–Hartwig coupling with aryl chlorides.

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