Physicochemical Properties and Synthetic Methods of 2-Fluorobenzoic acid

2-Fluorobenzoic acid is a fluorinated benzoic acid compound. At room temperature and pressure, it appears as a white to light yellow solid powder, exhibiting significant acidity and good chemical stability. It is insoluble in water and sparingly soluble in ether organic solvents. 2-Fluorobenzoic acid is primarily used as a basic raw material for fine chemical products and has been widely applied as a preservative in food, medicine, and cosmetics. 2-Fluorobenzoic acid is also extensively used in the preparation of various dyes, fungicides, color motion picture films, and various oil-soluble couplers.

Physicochemical Properties

2-Fluorobenzoic acid is slightly soluble in water and soluble in organic solvents such as methanol, diethyl ether, and acetone. Its acidity coefficient (pKa) is 3.27 (at 25 °C). 2-Fluorobenzoic acid is chemically stable at room temperature and should be protected from exposure to high temperatures and strong oxidizing agents.

Synthetic Methods

Method 1

Figure1: Picture of 2-Fluorobenzoic acid

In a 25 mL Schlenk tube equipped with a magnetic stir bar, the primary alcohol (0.3 mmol, 1.0 equiv.) is combined with FeBr₃ (8.9 mg, 10 mol%), Fe(NO₃)₃·9H₂O (12.1 mg, 10 mol%), and 3 mL of acetonitrile, after which the tube is sealed with a rubber stopper and an air balloon is attached to the sidearm; the entire setup is then placed in a photoreactor equipped with a 15 W blue LED, and the mixture is stirred at 500 rpm for 24 hours. Following the reaction, the mixture is dried by the addition of anhydrous Na₂SO₄, subsequently filtered, and the resulting filtrate is purified by flash column chromatography using silica gel with a gradient eluent system of petroleum ether, ethyl acetate, and acetic acid (PE/EA/AcOH = 20/1/0.05 to 2/1/0.1). Finally, the residue is concentrated under reduced pressure to afford 2-fluorobenzoic acid. [1]

Method 2

CuCl (9.0 mg, 0.1 mmol) and 1,10-phenanthroline (54 mg, 0.3 mmol) are added to a 10 mL dry Schlenk tube equipped with a magnetic stirring bar, followed by the introduction of anhydrous DMF (5.0 mL) as the solvent, and the mixture is stirred for 30 min at room temperature under inert conditions. Iodobenzene (123 mg, 1.0 mmol), K₂CO₃ (692 mg, 5.0 mmol), and triethylamine (140 μL, 1.0 mmol) are then added, and the mixture is degassed through two freeze-pump-thaw cycles using liquid nitrogen. A balloon filled with carbon dioxide is attached to the reaction tube, and the Schlenk tube is positioned approximately 6 cm away from a 34 W purple LED and stirred while being cooled by a fan. After 8 hours, the reaction mixture is concentrated under reduced pressure, and 5 mL of 0.2 M aqueous HCl solution is added to the residue, followed by extraction with EtOAc (3 × 5 mL). The combined organic layers are washed with brine and concentrated under reduced pressure, and the resulting crude product is dissolved in 4 mL of Et₂O and extracted with 1 M NaOH (3 × 4 mL). The aqueous layer is washed with hexane (3 × 5 mL), then acidified to pH less than 2 using 5 M HCl and extracted with EtOAc (3 × 5 mL). Finally, the combined organic layers are dried over Na₂SO₄, filtered, and concentrated under reduced pressure to afford 2-fluorobenzoic acid. [2]

Chemical Applications

2-Fluorobenzoic acid primarily serves as an organic synthesis intermediate in the preparation of a wide range of products, including biochemical reagents such as zaragozaic acid A analogs, the fungicide flutriafol, as well as various dyes and color motion picture films, and 2-Fluorobenzoic acid is also frequently employed in the same capacity as an organic synthesis intermediate for the production of biochemical reagents (including zaragozaic acid A analogs), the fungicide flutriafol, along with dyes and color motion picture films.

Reference

[1] Xing, Dong ; et al, Selective Oxidation of Benzyl and Allyl Alcohols to Carbonyl Compounds or Acids Mediated by Iron Photocatalysts, ChemCatChem 2025, 17, e00611.

[2] David, A. John; et al, Photocatalytic carboxylation of aryl halides/alkenes with a copper(I) complex bypassing the demand for dual catalysts, Chemical Communications (Cambridge, United Kingdom) 2025, 61, 17677-17680.

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