Synthesis of fluorinated surfactants

Perfluoroalkanesulfonamides have been claimed as intermediates for the synthesis of fluorinated surfactants. Their synthesis by reaction of the corresponding perfluoroalkanesulfonyl fluoride (or chloride) with liquid ammonia is prototypical for the synthesis of alkylated perfluoroalkane-sulfonamide surfactants. This reaction initially forms a complex ammonium salt as shown in Scheme 18.2. The desired amide is obtained by dissolving the crude product in dioxane and... 

Direct fluorination with elemental fluorine is not practical for commercial synthesis of fluorinated surfactants. Elemental fluorine is extremely reactive and difficult to handle. The heat of formation of the C—bond (about 460 kJ/mol or 110 kcal/mol) and the H—F bond (566 kJ/mol or 135 kcal/mol) exceeds that of the C—C bond (about 348 kJ/mol or 83 kcal/mol) [1]. Hence, the fluorination with elemental fluorine leads to a violent fragmentation of the substrate unless the reaction is carefully controlled and the reaction heat effectively dissipated [2,3]. Commercially important pathways to fluorinated surfactants are electrochemical fluorination, telomerization, and oligomerization of tetrafluoroethylene [4-6]. 

Chapter 1 presents an overview of fluorinated surfactants. The synthesis of fluorinated surfactants is discussed in Chapter 2. Since the space limitations precluded a detailed description of processes, patent citations are augmented by references to Chemical Abstracts. Physical and chemical properties are reviewed in Chapter 3. Chapters 4-7 are devoted to the theory of fluorinated surfactants liquid-vapor and liquid-liquid interface (Chapter 4), solid-liquid interface (Chapter 5), solutions of fluorinated surfactants (Chapter 6), and the structure of micelles and mesophases, including mixed surfactant systems, in Chapter 7. The practical application of fluorinated surfactants is the subject of Chapter 8. Various applications are listed in alphabetical order for easy access to information. Chapter 9 reviews the analytical and physical methods for the investigation of fluorinated surfactants. Chapter 10 examines the environmental and toxicological aspects, including the use of fluorinated surfactants in biological systems. 

Synthesis of Fluorinated Sulfonamides. All compounds presented in this paper were prepared and provided by 3M Company. The general class of compound has been knewn for many years as surfactants (26,27). The general synthetic scheme is as follows ... 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

Per- and poly-fluorinated ether surfactants are the newest commercially available substances in this rapidly expanding group of fluorinated surfactants [33-35]. For example, the phosphate shown in Fig. 4 is used as a grease repellent for food contact paper [36]. Per- and poly-fluorinated polyether carboxylates [37-41] are also used as processing aids in the synthesis of fluoropolymers. Per- and poly-fluorinated polyether silanes are used as surface treatments [42-45]. 

Kausch CM et al (2002) Synthesis, characterization, and unusual surface activity of a series of novel architecture, water-dispersible poly(fluorooxetane)s. Langmuir 18(15) 5933-5938 Dams R (1993) Fluorochemical surfactants for hostile environments. Spec Chem 13(l) 4—6 Shinoda K, Hato M, Hayashi T (1972) The physicochemical properties of aqueous solutions of fluorinated surfactants. J Phys Chem 76(6) 909-914... 

As outlined in Figures 18.1 and 18.2, perfluoroalkanesulfonyl fluorides, especially perfluorooctanesulfonyl fluoride, are industrial intermediates that are converted into the corresponding sul-fonamides. These sulfonamide intermediates are ultimately converted into a whole host of fluorinated surfactants, but have also been used in large quantities for the preparation of surface treatments or paper protectants. The following sections discuss important aspects of the synthesis of perfluoroalkanesulfonamides followed by an overview over the synthesis of selected perfluoroalkanesulfonyl surfactants (Section 18.2.4). 

Cationic PFCA surfactants are obtained through PFCA amides, which are readily obtained from the corresponding PFCA fluorides or chlorides and esters. The synthesis of these surfactants is typically simple and requires only a few synthetic steps however, the amide function of these per-fluorinated amides is relatively labile because of the strong electron-withdrawing effect of the CF2-group adjacent to the amide group, thus posing a limitation for the usefulness of these surfactants. " ... 

Nivet, J.B. et al.. Synthesis and bioacceptability of fluorinated surfactants derived from F-alkylated tertiary amines, Eur. J. Med. Chem., 27, 891, 1992. 

Carnitine is at the origin of two types of fluorinated surfactants. The perfluoroalkyl-acylcarnitines (28) (Scheme 24), obtained with satisfactory yields (44-80%), show good surfactant characteristics [60], The synthesis of Ai-perfluoroalkyl carnitine (29) (Scheme 25) is less efficient, and its physicochemical properties have not been evaluated [61]. The betaines of perfluoro-alkyl a,co-amino acids (30) (Scheme 26) are accessible in a similar manner [62]. They are good surface agents [63]. 

Yong, T.-M., Hems, W.P., van Nunen, J.L.M. et al. (1997) Synthesis of fluorinated block copolymers and their application as novel polymerization surfactants in supercritical carbon dioxide. Chemical Communications, 1811-1812. 

Perfluoroalkyl)ethane thiols have been used as precursors to fluorinated surfactants and products for hydro- and oligophobic finishing of substrates such as textiles and leather (1). The synthesis of 2-(perfluoroalkyl)ethane thiol and a byproduct bis-(-2-perfluoroalkylethane)-disulfide (5-10%) has been practiced via the reaction of 2-(perfluoroalkyl)ethane iodide with thiourea to form an isothiuronium salt which is cleaved with alkali or high molecular weight amine as shown in Equation 1 for 2-(perfluorohexyl)ethane iodide (1). 

The amphiphilic nature is the indispensable attribute of the structure of any surfactant. The nonpolar, "solvophobic" part of fluorosurfactants constitutes usually with perfluoroalkyl, co-hydroperfluoroalkyl or perfluoroether chain of normal or branched structure. Surfactants with semifluorinated carbon chains are not quite effective as the ones with completely fluorinated carbon chains. Usually the optimum perfluorocarbon chain length is from 6 to 10 carbon atoms. Three industrially important methods of fluorosurfactants synthesis are known [123-126] ... 

Table 1.9 Fluorinated surfactants and finishing aids Main suppliers, registered trade names and methods of the Rf synthesis...

LAC Lacroix-Desmazes, P., Andre, P., Desimone, J.M., Ruzette, A.-V., and Boutevin, B., Macromolecular surfactants for supercritical carbon dioxide applications Synthesis and characterization of fluorinated block copolymers prepared by nitroxide-mediated radical polymerization (experimental data by P. Lacroix-Desmazes), J. Polym. Sci. Part A Polym. Chem., 42, 3537, 2004. 

In this chapter, we focus in two kinds of surfactants that so far have not been common as structure-directing agents in the synthesis of mesoporous silica, namely, silicone and fluorinated surfactants, having a hydrophobic chain different from that of conventional hydrocarbon surfactants, which imparts peculiar properties to the systems. 

It should be pointed out that although most of the research works used silica as a model material, fluorinated surfactants can be used for the preparation of a very wide variety of different mesoporous materials, including TiOj [70], aluminophos-phates and Fe- aluminophosphates [71], and Fe-Si oxides [72]. Organic functionalizations can also be obtained in direct synthesis processes. An example is the preparation in a one-step precipitation process, by Rankin et al., of vinyl-functionalized porous silica materials using mixtures ofTEOS and vinyltriethox-ysilane in aqueous solutions of cationic fluorinated surfactants [73]. 

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