4-Amino-2-Fluorobenzoic Acid: Handling & Application Protocol

4-Amino-2-fluorobenzoic acid is a bifunctional fluorinated aromatic building block bearing both a free primary amine and a carboxylic acid group, making it a versatile intermediate for medicinal chemistry, peptide coupling, and bioconjugation applications.

CAS Number

3-Amino-4-fluorobenzoic acid isomer; CAS for 4-Amino-2-fluorobenzoic acid — verify with CoA

Molecular Formula

C₇H₆FNO₂

Molecular Weight

155.13 g/mol

Key Functional Groups

Primary aromatic amine (–NH₂), carboxylic acid (–COOH), aryl fluoride (C–F)

Recommended Storage

Sealed, cool and dry conditions; away from light and moisture

Typical Purity

≥98% (refer to CoA for lot-specific data)

SKU

A120664

Overview and Chemical Properties

4-Amino-2-fluorobenzoic acid (SKU: A120664) is an ortho-fluorinated aminobenzoic acid derivative. The molecule presents three reactive sites: the primary aromatic amine, the carboxylic acid, and the electron-withdrawing aryl fluoride. The fluorine substituent at the 2-position exerts a strong inductive effect, modulating the pKa of the carboxylic acid and the nucleophilicity of the amine, which is exploited in selective coupling reactions.

The compound is a solid at room temperature, typically appearing as a light-colored crystalline powder. It exhibits moderate solubility in polar aprotic solvents such as DMF and DMSO, and limited solubility in water at neutral pH. Solubility in water improves significantly under basic conditions due to deprotonation of the carboxylic acid group.

Safety and Handling Precautions

Before working with 4-Amino-2-fluorobenzoic acid, consult the Safety Data Sheet (SDS) provided with the shipment. The compound contains a primary aromatic amine, which may present sensitization hazards; avoid skin and eye contact and minimize inhalation of dust.

• Personal Protective Equipment (PPE): Wear nitrile gloves, a laboratory coat, and safety goggles. Use a dust mask or work inside a fume hood when weighing.
• Ventilation: All weighing and dissolution steps should be performed in a chemical fume hood.
• Waste Disposal: Dispose of waste in accordance with local environmental and institutional regulations for aromatic amine-containing compounds.
• First Aid: In case of skin or eye contact, rinse thoroughly with water for at least 15 minutes and seek medical advice.

Store the reagent in a tightly sealed container in a cool, dry place away from strong oxidizers, acids, and light sources to prevent degradation and oxidation of the amine group.

Solution Preparation and Dissolution Protocol

The following protocol describes preparation of stock solutions suitable for synthetic or biological assay use.

1. Solvent Selection: For organic synthesis applications, dissolve in anhydrous DMF or DMSO to yield a 0.1–1.0 M stock solution. For aqueous biological applications, prepare a concentrated stock in DMSO (≤10 mM) and dilute into the aqueous buffer of choice; ensure final DMSO concentration does not exceed 0.1% v/v if cytotoxicity is a concern.
2. Weighing: Tare a clean glass vial and weigh the required mass of 4-Amino-2-fluorobenzoic acid (MW = 155.13 g/mol) using an analytical balance inside a fume hood.
3. Dissolution: Add approximately 80% of the target solvent volume to the vial and vortex or sonicate for 2–5 minutes. Add the remaining solvent volume to reach the target concentration.
4. pH Adjustment (aqueous solutions): If poor solubility is observed, adjust pH to 8–9 with dilute NaOH to deprotonate the carboxylic acid and improve dissolution.
5. Filtration: Filter through a 0.22 µm PTFE syringe filter before use if a particulate-free solution is required.
6. Storage of Stock Solutions: Aliquot and store DMSO stocks at –20 °C protected from light; use within 3 months. Aqueous solutions should be freshly prepared.

Application in Organic Synthesis and Bioconjugation

4-Amino-2-fluorobenzoic acid serves as a multifunctional building block in several key application areas:

Amide Bond Formation

The carboxylic acid moiety can be activated using standard coupling reagents such as EDC/NHS, HATU, or DCC/HOBt to form amide bonds with primary or secondary amines. This is routinely used to conjugate the compound to peptides, proteins, or polymer scaffolds. Ensure the free amine is protected (e.g., with Boc or Fmoc groups) if selective carboxylic acid activation is required.

Nucleophilic Aromatic Substitution (SNAr)

The aryl fluoride at the 2-position is activated toward nucleophilic aromatic substitution due to the combined electron-withdrawing effects of the adjacent carboxylic acid and amino groups. Reaction with thiolates, phenolates, or amines under mild basic conditions can yield diverse biaryl ether, thioether, or diarylamino products useful in drug discovery.

Diazotization and Diazonium Chemistry

The primary aromatic amine can be diazotized under cold acidic conditions (NaNO₂, HCl, 0–5 °C) to generate the corresponding diazonium salt, which serves as an intermediate for azo coupling, Sandmeyer reactions, or introduction of other functional groups at the 4-position.

Pharmaceutical Intermediate

The compound is used as a building block in the synthesis of fluorinated heterocyclic drugs, kinase inhibitor scaffolds, and labeled probes, where the fluorine atom contributes to metabolic stability and lipophilicity tuning.

Quality Verification and Analytical Characterization

Upon receipt, verify the identity and purity of 4-Amino-2-fluorobenzoic acid (A120664) using the following analytical methods:

• HPLC Purity: Typical purity is ≥98% by HPLC. Run a reversed-phase C18 column with a water/acetonitrile gradient (0.1% TFA modifier) and compare retention time to reference standard.
• NMR Characterization: ¹H NMR (400 MHz, DMSO-d₆) should show characteristic signals for the aromatic protons (2H, dd pattern reflecting fluorine coupling), NH₂ broad singlet, and COOH proton. ¹⁹F NMR will show a single resonance for the aryl fluoride. Actual chemical shifts should be verified against the CoA.
• Mass Spectrometry: ESI-MS should give [M+H]⁺ = 156.1 and [M–H]⁻ = 154.0, consistent with MW 155.13 g/mol.
• Melting Point: Confirm melting point against the value stated in the Certificate of Analysis (CoA) supplied with each lot.
• Visual Inspection: The material should appear as a uniform, light-colored powder. Discoloration may indicate oxidation of the amine; do not use degraded material.

Always refer to the lot-specific Certificate of Analysis (CoA) available from Aladdin Scientific for authoritative specification data.

Frequently asked questions

What solvents are recommended for dissolving 4-Amino-2-fluorobenzoic acid?

4-Amino-2-fluorobenzoic acid dissolves well in polar aprotic solvents such as DMF and DMSO. For aqueous applications, prepare a DMSO stock and dilute into buffer, or adjust the aqueous solution pH to 8–9 with dilute NaOH to improve solubility by deprotonating the carboxylic acid.

How should 4-Amino-2-fluorobenzoic acid be stored to maintain stability?

Store the solid compound in a tightly sealed container in a cool, dry place away from light, moisture, strong oxidizers, and acids. DMSO stock solutions should be aliquoted and stored at –20 °C protected from light, and used within 3 months. Aqueous solutions should be freshly prepared on the day of use.

Can the aryl fluoride in 4-Amino-2-fluorobenzoic acid be used in nucleophilic aromatic substitution?

Yes. The aryl fluoride at the 2-position is activated toward nucleophilic aromatic substitution (SNAr) due to the electron-withdrawing effects of the neighboring carboxylic acid group and the nitrogen substituent. It can react with thiolates, phenolates, and amines under mild basic conditions to introduce diverse functional groups, making it valuable in medicinal chemistry and materials science.

Is selective functionalization of the amine or carboxylic acid possible?

Yes, selective functionalization is achievable through orthogonal protection strategies. The amine can be protected with Boc or Fmoc groups prior to carboxylic acid activation with standard coupling reagents. Conversely, the amine can be selectively acylated or diazotized while the carboxylic acid remains free. Careful control of reagent stoichiometry and reaction conditions is essential.

What quality documentation is available for A120664?

Aladdin Scientific provides a lot-specific Certificate of Analysis (CoA) for A120664, which includes purity by HPLC, appearance, and other characterization data. An SDS is also available for safety information. Contact Aladdin Scientific customer service or visit the product page to download these documents.

References

1. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford, 2012. (General reference for amide coupling, SNAr, and diazotization reactions.)
2. Küenburg, B. et al. Development of a pilot-scale synthesis of the anti-tumour agent combretastatin A-4 using fluoroaromatic SNAr chemistry — general reference for SNAr on activated fluoroarenes. (Illustrative literature; verify specific citation details.)
3. Aladdin Scientific Certificate of Analysis, 4-Amino-2-fluorobenzoic acid, SKU A120664. (Lot-specific; obtain from Aladdin Scientific product page.)

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