Fluorine-containing fine chemicals are beginning to be upgraded

Fluorinated surfactants (abbreviated as FS) are surfactants with special properties that have been gradually commercialized in recent years. Unlike ordinary surfactants, FS uses perfluoroalkyl or perfluorovinyl groups, or partially fluorinated alkyl groups as the hydrophobic components in the surfactant structure; thereafter, appropriate linking groups and hydrophilic groups are introduced as needed. Depending on the properties of these hydrophilic groups, FS products of various types such as anionic, cationic, non-ionic, and amphoteric types are produced. 1 Properties of FS: Due to the structural uniqueness of FS, fluorine atoms replace the hydrogen atoms in the hydrophobic groups of conventional surfactants, transforming the C–H bond structure into a C–F bond structure. As a result, it exhibits some of the excellent properties characteristic of fluorocarbons, and it also has both hydrophobic and oleophobic properties. The high surface activity of FS depends on the extremely strong hydrophobicity of the carbon-fluorine bonds in its molecules and the low intermolecular cohesion. It can reduce the surface tension of water to very low values, with only a small concentration being required. The typical application concentration of surfactants with hydrocarbon chains is between 0.1% and 1%; at this level, the surface tension of the aqueous solution can only be reduced to 30–35 dynes/cm. On the other hand, when the concentration of surfactants with fluorocarbon chains is between 0.005% and 0.1%, the surface tension of the aqueous solution can be reduced to below 20 dynes/cm. Furthermore, FS exhibits good surface activity in organic solvents as well; in particular, the introduction of N-substituted perfluorooctanamides enables hydrocarbon solvents to have their surface tension reduced by 5–15 dynes/cm. The excellent thermal stability and chemical inertness of FS are mainly due to the fact that, when fluorocarbon chains replace the hydrophobic groups in hydrocarbon chains, the bond energy of C-F bonds (116 kcal/mol) is greater than that of C-H bonds (99.5 kcal/mol); thus, C-F bonds are more stable and less likely to break. Furthermore, when fluorine atoms replace hydrogen atoms, the larger size of fluorine atoms compared to hydrogen atoms results in the C–C bonds being protected due to the shielding effect of fluorine. As a result, even those C–C bonds that originally had relatively low bond energies become stable, which endows FS with chemical and thermal stability that hydrocarbon surfactants lack. For example, the operating temperature of C9F17OC6H4SO3K can be around 300°C, while its intermediate, C9F17OC6H5, does not decompose even when treated in 50% sulfuric acid or 25% sodium hydroxide solution at 80°C for 48 hours. Studies have shown that the high surface activity of FS is due to the weak van der Waals forces between its molecules; the low tension required for the surfactant molecules to move from the aqueous solution to the surface of the solution leads to their accumulation in large quantities on the surface, resulting in strong surface adsorption. Such compounds exhibit low affinity not only for water but also for hydrocarbons, which gives them hydrophobic and oleophobic properties. However, they do not have a strong effect on the interfacial tension at the oil/water interface. By using FS in combination with hydrocarbon surfactants, it is possible to take advantage of FS’s ability to selectively adsorb on the water surface, thereby reducing the surface tension ； Hydrocarbon surfactants can adsorb at the oil/water interface, reducing the interfacial tension, which necessarily improves the wetting properties of the aqueous solution. 2 Applications of FS: Given the characteristics of FS, it has strong applicability in certain fields, with various uses particularly in the industrial sector. A brief overview of the usage categories of FS listed in Table 1. Brief introduction to some applications: 2.1 Dispersant: FS can be used as a dispersant in the dispersion polymerization of various fluororesins. FS is used as a dispersant in the emulsion dispersion polymerization of fluorine-containing monomers such as tetrafluoroethylene, trichlorofluoroethylene, and vinylidene fluoride. According to rough estimates, by around 1980, the amount of FS used in the emulsion polymerization of tetrafluoroethylene was approximately 80 tons per year. According to data from Nippon Asahi Glass Co., in the early 1980s, the amount of FS used in Japan for manufacturing dispersed fluororesins had reached 5 tons per year. Other studies have reported that FS can also be used in the reaction process of PVC. 2.2 Fire extinguishing agents: The application of FS in fire extinguishing agents can be divided into three types – \"light water\" fire extinguishing agents, fluoroprotein foam fire extinguishing agents, and apolar solvent fire extinguishing agents. The time required to completely extinguish a fire using these agents is within 90 seconds, with some agents enabling suppression of the fire in less than 45 seconds. 2.3 Release agents: The release agents prepared or formulated by FS not only provide excellent release properties for thermoplastic polymers, but also exhibit good release performance for thermosetting polymers and silicone-based rubber elastomers. They do not cause any contamination on the parts after demolding, allowing for further processing such as printing, painting, or bonding. Moreover, they can be used multiple times for demolding after just one application. The release agents produced by FS have gradually become part of a series of products, available in both solvent-based and water-based forms. They can be used not only in the processing of organic polymers but also in the manufacturing industry for rigid materials (such as drawing copper and steel pipes, pin pressing, stamping of die-cast parts, etc.). Currently, fluorine-containing (high-performance) release agents have received high praise from users in industries such as plastics and rubber processing. 2.4 Antistatic agent: An antistatic agent developed by FS that combines cleaning and dust prevention functions; tests conducted by relevant authorities have shown that after surface treatment of PVC substrates, their surface resistance is reduced from 1012Ω to 108Ω. This greatly reduces the occurrence of static electricity on the film base surface, thereby minimizing dust accumulation. Using this antistatic agent for cleaning the surfaces of the drum and head in video recorders yields far better results than ordinary cleaners or cleaning tapes, and it can also extend the service life of the drum and head. After cleaning, the volume of a cleaned film or vinyl record can be increased by 3 decibels when played. This antistatic agent can also be used for surface cleaning and dust prevention on household appliances, plastic products, television screens, as well as other high-end furniture and precision instruments, without causing any side effects. At present, our company has already launched this antistatic agent product, “Yin Ciling”, on the market. 2.5 Leveling agents: Adding a small amount of FS to products such as pigments and coatings can prevent setting and improve dispersion. Adding it to coatings and inks can reduce their surface tension, improve wettability, prevent the formation of bubbles, and make the color more uniform. 2.6 Water and oil repellents: The water and oil repellents prepared by FS, when used for surface treatment of natural or synthetic fibers and their products, enable these fibers or products to possess water and oil repellent properties without affecting their inherent physical characteristics. Disposable paper tableware treated with waterproof and oil-resistant agents is now available on the market, addressing the environmental hazards caused by white pollution. 2.7 Other applications: Adding FS to floor wax can improve the shine of the floor, as well as its wear resistance and resistance to pollution. FS can also be used as additives for oil recovery, oil collectors on the sea surface, metal anti-corrosion agents, and metal polishing agents, among other things. 3 Preparation of FS As described earlier, the difference between FS and hydrocarbon surfactants lies mainly in their hydrophobic tail portions; therefore, the preparation process is also carried out in two main steps. First, long-chain fluorides with a certain structure are prepared; the number of carbon atoms in these chains is generally between 6 and 12. Then, based on their chemical properties, and in a manner similar to the preparation of carbon-fluorine surfactants, linking groups and various hydrophilic groups are introduced sequentially to complete the final synthesis of FS. Currently, the methods for industrial production of long-chain fluorides can be essentially summarized into three approaches. a. Electrolytic fluorination method ； b. Copolymerization method ； c. Assembly method. a. Electrolytic fluorination: Long-chain fluorides were first obtained using Simon’s electrolytic fluorination method, and it was the American company 3M that first brought them to market in 1950. In this process route, the acyl chloride or sulfonyl chloride of hydrocarbon alkyl groups can be directly replaced by the corresponding perfluoroalkyl acyl fluoride or sulfonyl fluoride products. Due to the highly intense electrolytic fluorination reaction, C–C bond cleavage occurs easily; as a result, in addition to perfluorinated compounds with the same number of carbon atoms as the organic starting materials, short-chain perfluorinated compounds and other types of by-products are also formed, which leads to a low overall yield of products. Companies that use this reaction to produce FS include 3M in the United States, Dainippon Ink in Japan, and Tohoku Fertilizer, among others. b. Copolymerization method: The copolymerization reaction of fluoroolefins was first proposed by Professor Haszeldine in the UK. Subsequently, the American company Du Pont developed a metathesis reaction using iodine pentafluoride and tetrafluoroethylene to produce perfluoroalkyl sulfonates. Although the yield of this reaction is high, the final product is a mixture with different chain lengths (with a wide distribution of the n value). By appropriately selecting a suitable reaction process and controlling the reaction conditions, it is possible to ensure that the n value remains within the desired range (n: 2–4), thereby stopping further progression of the reaction. To reduce the excessive formation of unwanted high-boiling substances (n>6). There are many other substances that can be used as copolymerization agents, and a large number of patents have been published in this field of research; their respective reaction formulas are as follows. Companies such as DuPont in the United States, Covestro in Switzerland, Asahi Glass and Daikin in Japan use the copolymerization method to produce FS. The product obtained from the telomerization reaction is a mixture with varying chain lengths, which allows for the synthesis of fluorocarbon chain hydrophobic groups of different lengths; when used in appropriate proportions, this enhances the surface activity of the final product. c. The metathesis method, developed by the British company ICI, is based on the anionic polymerization of tetrafluoroethylene; preparing long-carbon-chain fluorinated alkyl intermediates is also a method for producing FS. Perfluoroethylene, hexafluoropropylene, and their corresponding epoxides (such as hexafluoropropylene oxide) can undergo anionic polymerization in aprotic polar solvents under the catalysis of fluoride ions, to yield C6–C14 perfluoropolymer oligomers. The product obtained from the oligomerization of tetrafluoroethylene is a mixture of tetra-, pentaa-, hexa-, and hepta-oligomers. ) Of these, pentamers account for about 65% of the entire mixture. Since the fluorine atoms attached to the carbon atoms of the double bond are easily displaced by nucleophiles, the desired linking groups can be introduced through this reaction. The oligomerization of hexafluoropropylene quantitatively produces dimers and trimers. Hexafluoroepoxypropane also readily undergoes oligomerization reactions in the presence of fluoride ions. Companies that produce FS using the oligomerization method include the British company ICI and the Japanese company Neos, among others. Application Areas and Uses:
Chemical Industry: Fire extinguishants, emulsifiers, dispersants, antistatic agents, oil collectors, evaporation inhibitors, leveling agents, release agents, etchants, clog prevention agents, defoamers, plastic modifiers, plastic foaming agents.
Mechanical Industry: Penetrants, cleaning agents, rust inhibitors, water removers, lubricating release agents, metal flaw detection agents, metal surface treatment agents, flux assistants, additives for electroplating baths. Textile industry: waterproof and oil-repellent agents, fabric finishing agents, fiber processing penetrants, fiber oils, detergents, spinning plate cleaners. Inks and coatings: pigment surface treatment agents, levelers, detergents, wetting penetrants, film modifying agents, film protective agents, ink modifying agents. Household products: polish additives, detergents, cleaners, water- and oil-repellent agents, levelers, adsorbents, dust suppressants. Paper industry: oil-resistant treatments, anti-sticking agents, additives for disposable tableware, dispersants. Others: photographic emulsions, antistatic agents, agricultural polyethylene anti-fogging agents, bactericides, dust suppressants, glass anti-fogging agents, levelers. Through the various methods described above for the industrial production of long-chain fluorides, the raw materials necessary for further synthesizing various types of FS are provided. Based on the structural characteristics of these substances, appropriate linking groups and hydrophilic groups can be selected to react with them, ultimately yielding the desired FS product. FS has not been in use as an industrial product for a long time, and its areas of application still need to be further explored. As research and understanding of its properties and applications progress, it is believed that the variety and production volume of such products will continue to increase.

The Current Status of Organic Fluorine Fine Chemicals and Fluorine Chemical Industry in Our Country Organic fluorine chemicals mainly include basic fluorocarbons, fluoropolymers, organic fluorine fine chemicals, as well as hydrofluoric acid, which is an important raw material for production. 　　1.1 Basic fluorocarbons Basic fluorocarbons include fluorinated alkanes such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). They are primarily used as refrigerants in refrigerators and air conditioners, as blowing agents in plastics, as cleaning agents for electronics, in aerosols, and as Halon fire extinguishing agents. In 1995, China’s production capacity for basic fluorocarbons was 120,000 tons per year, with an actual output of 60,000 tons per year; of this amount, approximately 50,000 tons were chlorofluorocarbon refrigerants. Currently, the domestic demand for chlorofluorocarbon refrigerants is approximately 100,000 tons per year. As the use of Freon was gradually phased out, China built a large number of production facilities for ODS substitutes during the Ninth Five-Year Plan period, with production reaching over 80,000 tons in 1999. 　　2.2 Fluoropolymers Fluoropolymers mainly include fluororesins and fluororubbers. In 1995, China’s production capacity for fluoropolymers was 0.6 million tons per year, with a production volume of around 0.40 million tons per year. The main product was PTFE, accounting for about 80% of the total output; these products were mainly in the form of medium-grained suspensions of medium to low quality ； Fluororubber accounts for 3%. At present, neither the variety nor the quantity of fluoropolymers can meet domestic demand. Conservatively estimated, the current domestic demand for fluoropolymers is 5,000 tons of PTFE, 500 tons of PVDF, 600 tons of FEP, 200 tons of ETFE, 200 tons of PFA, 10,000 tons of fluororubber, and other fluoropolymers; the potential market is therefore very large. 　　In the development of fluoropolymers, institutions such as the Shanghai Institute of Organic Chemistry of the Chinese Academy of Sciences, the Shanghai Institute of Organic Fluorine Materials, and the Sichuan Chenguang Chemical Research Institute have carried out extensive work and achieved numerous results from industrial-scale tests; some of these are now moving toward commercialization. 　　1.3 Organic Fluorine Fine Chemicals Organic fluorine fine chemicals include fluorine-based pesticides, fluorine-based pharmaceuticals, fluorine dyes, fluorinated aromatic intermediates, fluorinated surfactants, and fluorine-based inert fluids, among others. 　　(1) Fluoropharmaceuticals are the most actively developed, as fluorinated organic compounds possess specific biological activities and compatibility with living organisms, resulting in drugs containing fluorine having several times greater efficacy than ordinary drugs. Currently, there are nearly a hundred fluorine-containing pharmaceuticals that have been commercialized or are under development worldwide. Some important products include the sedative haloperidol ； Antitumor drug fluorouracil ； Anti-inflammatory drug diflunisal ； Hormonal drugs: fludrocortisone, flucinonide, fluocinolone, fludicasone ； Antiarrhythmic drug flecainide ； Antifungal drugs fluconazole, flucytosine ； The anticancer drug fludarabine phosphate ； The hypnotic drug flumazenil ； The anti-asthma drug flunisolone ； The antidepressant fluoxetine (Prozac, the best-selling antidepressant in the world) ； The weight-loss drug fluoxetine. 　　(2) Fluorine pesticides: Since the 1970s, China has begun research on fluorine-containing pesticides. Herbicides such as pretilachlor, fluazifop-P-butyl, and ethofenpropargate, as well as insecticides such as flufenoxuron, chlorantraniliprole, and fluorinated pyrethroids have been developed. Among these, fluazifop-P-butyl has been put into industrial production, while compounds such as gor, hexaflumuron, and chlorantraniliprole are also produced on a large scale. Pesticides derived from heterocyclic compounds already possess strong properties, and the introduction of fluorine further enhances these properties. For example, the performance of the herbicide pyrifluzifol (Stablecide), which is made from fluorinated pyridine derivatives, has increased by more than a factor of two ； The insecticide chlorfluoruron possesses both insecticidal and sterilizing effects. At present, the variety and quantity of fluorinated pesticides available in the country do not meet market demand, resulting in a heavy reliance on imports. 　　(3) The introduction of fluorine from fluorine dyes can enhance the luster and vividness of the dyes, as well as improve their resistance to sunlight, water, and organic solvents. When F-type reactive dyes containing fluorochloropyrimidine-type active groups replace K-type and KN-type screen printing dyes, their reactivity, color fastness, and other properties are significantly improved. **The dye intermediate 2,6-difluoro-3-nitropyridine also has antibacterial properties and can be used as a additive in chewing gum. 　　In terms of fluorine-containing dyes, various types have been synthesized in China, including bright red-based VD, orange-based RD, fluorine-containing lake pigments, polyfluorocyanine, thermosensitive dyes, and FT2. Beijing Institute of Fashion Technology offers technologies such as polyfluorocyanuretane and thermosensitive dyes. 　　(4) Organic fluorine intermediates Organic fluorine intermediates mainly include aromatic fluorides and aliphatic fluorides, among which aromatic fluorides predominate. Aromatic fluorides include: polyfluorobenzenes ； Chloro, bromo, iodofluorobenzenes ； Fluorinated *** compounds ； Fluoroanilines ； Fluorophenols ； Fluorobenzaldehydes ； Fluorophenylpropanoids ； Fluorobenzoic acids ； Chlorinated benzoals ； Fluorotoluenes and other fluorobenzenes ； and monotrifluorotoluenes ； Bis(trifluorotoluene) derivatives ； Flupyridines ； Trifluoromethylpyridines and the like. 　　Aromatic fluorides are important intermediates in the synthesis of pharmaceuticals, pesticides, and dyes; for example, 2,4-dichlorofluorobenzene is used in the synthesis of anti-infective quinolone drugs such as ciprofloxacin, ofloxacin, and norfloxacin ； Use of p-fluorophenol in the synthesis of the anti-inflammatory and antirheumatic drug thioindic acid, as well as the aldose reductase inhibitor sobinil ； Fluorobenzoyl chloride is used in the synthesis of fluvastatin sodium, a drug for cardiovascular and cerebrovascular diseases ； 3-Chloro-4-fluoroaniline is used in the synthesis of fluoroquinolone-class antibacterial drugs ； 4-Bromo-2-fluoroaniline is used in the synthesis of the anti-inflammatory drug ibuprofen ； 4-Chloro-4-fluorobenzene is also used in the synthesis of the medical anthelmintic flubendiazole ； Furthermore, the aliphatic fluoride bromofluoromethane is an important intermediate for the cephalosporin drug cefluzamide. 　　All of the above are currently emerging or best-selling products with promising market prospects; therefore, despite the high prices of their corresponding intermediates, they remain highly competitive in the market. To reduce costs, the international market for intermediates is being shifted to Asia. Among them, the domestic and international market prospects for 2,4-dichlorofluorobenzene, 3-chloro-4-fluoroaniline, and trifluorotoluene are quite optimistic, with large production scales as well. In China, the domestic demand for 2,4-dichlorofluorobenzene, which is used as a raw material for ciprofloxacin, amounts to 2,000–3,000 tons; the United States, Japan, Germany, and Italy all need to import it ； There is also a significant shortage of 3-chloro-4-fluoroaniline, an important intermediate for quinolone drugs. 　　(5) Fluorinated surfactants and fluorinated compound treatment agents Fluorinated surfactants are widely used as cleaning agents for electronic components, anti-fogging agents, release agents, leveling agents in the silk textile industry, and additives for giving metals a glossy finish ； Furthermore, it can also be used as an additive in fire extinguishants, pesticide additives, paint additives, etc. Fluorine-containing chromium-suppressing mist agents can effectively suppress the chromium mist generated during the chromium plating process, thereby protecting workers’ health. Fluorine-containing compound treatment agents are divided into leather treatment agents, fabric treatment agents, and paper treatment agents; they have a wide range of applications, with global market consumption reaching 5,000 tons per year, and there are many different types available. The domestic production of the above products is virtually non-existent. 　　(6) Fluorine-inert fluids (fluorine oils, fluorine greases): Fluoroalkyl compounds possess high chemical and thermal stability. Fluorine oils can withstand temperatures of 250–360°C, and they also feature low-temperature fluidity, high density, good lubricity, non-flammability, and low surface tension. Their main applications include lubricating valves that are exposed to strong oxidizing agents in the nuclear industry and aerospace technology, lubricating valves for corrosive fluids, use as oil in special diffusion pumps, as fluids for flow meters and pressure gauges, as shock-absorbing fluids in rocket gyroscopes, as dielectrics and coolants in the electrical industry, and as testing liquids in the electronics industry.