Synthesis and Properties of 1H,1H,2H,2H-Perfluorooctanesulphonic acid

1H,1H,2H,2H-Perfluorooctanesulphonic acid is a low-melting-point solid characterized by notable acidity and exceptional chemical stability, exhibiting insolubility in aqueous media but good solubility in alcoholic organic solvents and dimethyl sulfoxide. With its combination of pronounced acidic character and robust chemical inertness, 1H,1H,2H,2H-Perfluorooctanesulphonic acid represents a functionally versatile compound whose solubility profile facilitates its processing and application across various chemical environments. 1H,1H,2H,2H-Perfluorooctanesulphonic acid serves as a crucial intermediate in organic fluorine synthesis, advanced chemical synthesis, and the production of fluorinated surfactants, functioning as both an organic intermediate and an electroplating intermediate. As a key aliphatic compound specifically employed in the synthesis of fluorinated surfactants, 1H,1H,2H,2H-Perfluorooctanesulphonic acid plays an indispensable role in the development of specialized surface-active agents with unique physicochemical properties derived from its distinct perfluorinated molecular structure. 

Synthesis

The present invention relates to a one-step synthesis method for producing 1H,1H,2H,2H-Perfluorooctanesulphonic acid, comprising the following sequential steps: (1) charging a reaction vessel with perfluorohexylethyl sulfonate salt; (2) heating to 100–110 °C and maintaining this temperature range for 20–30 minutes; (3) cooling to 50–55 °C and dropwise adding fuming sulfuric acid at a weight ratio of perfluorohexylethyl sulfonate salt to fuming sulfuric acid of 1:1–3; (4) after complete addition, reacting at 80–90 °C with stirring for 4–6 hours; (5) cooling to allow phase separation, where the lower layer consists of fuming sulfuric acid and the upper layer contains sulfate salts and solid 1H,1H,2H,2H-Perfluorooctanesulphonic acid; (6) adding excess methanol to the upper mixture and heating under reflux for 30–40 minutes; (7) cooling, filtering to remove sulfate salts, and finally distilling methanol to obtain the purified product. This one-step synthetic approach provides a simplified process characterized by mild reaction conditions and low operational cost, while affording the target compound in high yield and purity. [1]

Properties

The sulfonic acid unit within the structure of 1H,1H,2H,2H-Perfluorooctanesulphonic acid exhibits significant acidity, enabling it to undergo acid-base neutralization reactions with common basic substances such as organic amines.

Figure1: Neutralization of 1H,1H,2H,2H-Perfluorooctanesulphonic Acid with Organic Amines

In a 1.5 mL Eppendorf vial, 1 mL of a 10% (w/w) aqueous solution of 6:2 1H,1H,2H,2H-Perfluorooctanesulphonic acid (100 mg, 0.23 mmol, 1 equiv.) was combined with an excess of 25% (v/v) aqueous ammonia solution (200 μL, 2.68 mmol, 1.2 equiv.), and the resulting mixture was shaken thoroughly before being placed—with the lid left open—in a desiccator containing anhydrous calcium chloride under non-evacuated conditions for three days, after which the crystalline product was isolated by filtration. [2]

Chemical Applications

1H,1H,2H,2H-Perfluorooctanesulphonic acid serves as a substitute within the perfluoroalkyl substance (PFAS) class, sharing structural similarities with the compounds it aims to replace; however, comprehensive toxicity assessments for such alternatives remain incomplete. The resulting uncertainties, combined with the higher release rates of alternative chemicals during processes like electroplating—where PFOS is more readily removed by activated carbon compared to alternatives such as 1H,1H,2H,2H-Perfluorooctanesulphonic acid—make it challenging for industries to clearly ascertain the benefits of switching to these substitutes. 1H,1H,2H,2H-Perfluorooctanesulphonic acid serves as a critical additive for maintaining operational safety and environmental compliance in industrial plating applications by significantly reducing the emission of toxic airborne particulates. [3]

Synthesis of Chromium Mist Inhibitor

The present invention discloses a preparation method for a chromium mist suppressant. This invention utilizes a perfluorohexylethyl halide as the starting material, which undergoes reaction with a thiocarboxylate to synthesize perfluorohexylethyl thiocarboxylate, followed by nitric acid oxidation to yield 1H,1H,2H,2H-Perfluorooctanesulphonic acid. The prepared 1H,1H,2H,2H-Perfluorooctanesulphonic acid is obtained with high yield exceeding 92% and purity up to 98%, accompanied by high material utilization efficiency without generation of by-products such as thioethers or olefins. Furthermore, the preparation process employed in this invention is easily scalable for industrial production, safe, environmentally friendly, and simple to operate. [4]

Reference

[1] Liu J G. One-step synthesis method of 1H,1H,2H,2H-perfluorooctanesulphonic acid: CN201811550138.3[P].

[2] Freilinger, Johanna; et al, Ammonium 6:2 fluorotelomer sulfonate: crystal structure, thermal analysis and use as internal standard in PFAS analysis, Journal of Molecular Structure 2025, 1327, 141232.

[3] Peter Fantke, From incremental to fundamental substitution in chemical alternatives, Sustainable Chemistry and Pharmacy

2015, 1:1-8.

[4] Zhang H C, Zhang L S, Wang W L, et al. A preparation method for chromium mist suppressant: CN202211612409.X[P].