Tetrafluoroethylene telomerization

The higher molecular weight petfluoroalkyl iodides ate prepared by telomerization of tetrafluoroethylene with lower molecular weight perfluoroalkyl iodides (46,48). 

Prepa.ra.tlon There are five methods for the preparation of long-chain perfluorinated carboxyUc acids and derivatives electrochemical fluorination, direct fluorination, telomerization of tetrafluoroethylene, oligomerization of hexafluoropropylene oxide, and photooxidation of tetrafluoroethylene and hexafluoropropylene. 

Fluorinated carboxyflc acids are also prepared by telomerization of tetrafluoroethylene, followed by oxidation (19—21). 

Chloro-2,2,3-trifluoropropionic acid has been prepared by permanganate oxidation of 3-chloro-2,2,3-trifluoropropanol which is one of the telomerization products of chlorotrifluoroethylene with methanol. The present procedure is a modification of one reported earlier and is undoubtedly the method of choice for making propionic acids containing 2 fluorine atoms, i.e., 2,2,3,3-tetrafluoropropionic acid, 3,3-dichloro-2,2-difluoropropionic acid, and 3-bromo-2,2,3-trifluoropropionic acid. When preparing 2,2,3,3-tetrafluoropropionic acid from tetrafluoroethylene, it is desirable to use an additional 50 ml. of acetonitrile and externally applied heat to initiate the reaction. 

The first reactions of fluorinated olefins in C02 reported by DeSimone et al. involved the free-radical telomerization of 1,1 -difluoroethylene29 and tetrafluor-oethylene.30 This work demonstrated the feasibility of carrying out free-radical reactions of highly electrophilic species in solvents other than expensive fluorocarbons and environmentally detrimental chlorofluorocarbons. The work has since been more broadly applied to the synthesis of tetrafluoroethylene-based, nonaqueous grades of fluoropolymers,31,32 such as poly(tetrafluoroethylene-co-peduoropropylvinyl ether) (Scheme 2). These reactions were typically carried out at between 20 and 40% solids in C02 at initial pressures of between 100 and 150 bars, and 30-35°C (Table 10.1). 

Fluoroatcohols. A group of fluorine contg alcohols are available commercially having the general formula H(CFa.GF2)nCH20H, in which n = 1 to 5 They include ales contg C3, C, C7, C9 Ctl, Density of Liquids 1.48-1.66, nD 1.318-1.320 (lowest of all known org compds). Derived by. free radical telomerization of tetrafluoroethylene with methanol. Used as solvents and in org synthesis... 

Romack, T. J. Combes, J. R. DeSimone, J. M. Free-Radical Telomerization of Tetrafluoroethylene in Supercritical Carbon Dioxide. Macromolecules 1995a, 28, 1724-1726. 

Concerning the telomerization, Bedford et al. [47] studied the telomerization of tetrafluoroethylene with IC2F4I and I2. The results are listed in the following table ... 

The only pathway for obtaining a perfectly linear chain as Lichtenberger [133] showed, concerns the telomerization of tetrafluoroethylene with perfluoroalkyl iodides such as C2F5I ... 

Commercial telomerization usually involves the reaction of pentafluoroethyl iodide (telogen) with tetrafluoroethylene oligomers (taxogen) in the presence of a catalyst, to produce a perfluoroalkyl iodide polymer (telomer) ... 

The first reported polymerization of fluoroolefins in carbon dioxide was by Fukui and coworkers [39,40]. Tetrafluoroethylene, chlorotrifluoroethylene,and other fluoroolefins were polymerized in the presence of CO2 using ionizing radiation [39, 40] and free-radical initiators [40]. DeSimone and coworkers reported the homogeneous telomerization of tetrafluoroethylene [41] and vinylidene fluoride [42] in CO2 using AIBN as an initiator. The kinetics of AIBN decomposition in CO2 is well understood [4]. However, peroxide initiators are preferred over azo initiators for producing stable endgroups in fluoroolefins... 

Starting materials for the synthesis of all perfluoroalkyl iodonium reagents are the perfluoroalkyl iodides, which themselves play a central role as building blocks in fluoroorganic chemistry. The iodides are available either by pyrolysis of the silver salts of perfluoroalkyl carboxylic acids in the presence on iodine [14] or - on a more technical scale - by iodofluorination of tetrafluoroethylene [15] with the iodine-IFp system [16] and subsequent radical telomerization of tetrafluoroethylene with the resulting intermediate perfluoroalkyl iodides [17] (Scheme 2.143). 

Scheme 2.143 Synthesis of perfluoroalkyl iodides by the Hunsdiecker route (top), based on the electrochemical fluorination of carboxylic acid derivatives (Rp = CF3 (CF2)9CF3) and the industrial telomerization route (bottom) based on tetrafluoroethylene as the central intermediate.

Anionic telomerization of tetrafluoroethylene with fluoride ion in an aprotic solvent yields mainly tetramer, perfluoro-3,4-dimethylhex- 3-ene, pentamer (57), the major product, and hexamers, mostly (58) and (59). The ICI work on the preparation of novel surface-active agents from, in particular, the pentamer (57) has been... 

Scheme 93 AIBN - initiated telomerization of vinylidene fluoride and tetrafluoroethylene in sc-COp.

Tetramethyldiphosphine adds photochemically to vinyl and vinylidene fluoride to give the bisphosphines Me2P-CH2-CXF-PMe2 (X H or F), and tetrakis(trifluoromethyl)diphosphine similarly adds thermally (at 50 Q or photochemically to the same olefins and to tetrafluoroethylene. Free-radical additions of trifluorothioacetic acid to the olefins CHF CF2, CHarCFa, and CH2 CHF (see p. 138) have been described only one-way addition was observed. Bis(trifluoromethyl) disulphide adds to fluoro-olefins with u.v. Irradiation in Pyrex or silica apparatus in the vapour phase to yield a variety of 1 1 and telomeric adducts. The products are consistent with the following mechanism ... 

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]. 

The starting materials of the telomerization process are tetrafluoroethylene and a perfluoroalkyl iodide. Of the various perfluoroalkyl iodides used in telomerization processes, pentafluoroethyl iodide is the most important (see Section 2.3). The one-step process for manufacturing pentafluoroethyl iodide is based on the addition of iodine fluoride to tetrafluoroethylene. Iodine fluoride, IF, is too unstable to be isolated and is therefore formed from iodine pentafluoride and iodine in situ. Iodine pentafluoride is synthesized from iodine and elemental fluorine [12] ... 

Haszeldine [62,63] allowed trifluoromethyl iodide to react with ethylene and obtained oligomers of the type CF3[CH2CH2] I (n = 1, 2, and 3). The reaction of trifluoromethyl iodide with tetrafluoroethylene, catalyzed by ultraviolet (UV) irradiation, yielded short-chain polymers of the general formula CF3[CF2CF2] I, where n = 1-10. Some of the members of the telomeric series were isolated. 

Commercial telomerization of tetrafluoroethylene with pentafluoroethyl iodide was developed by the Du Pont Company [65,66]. The telogen, pentafluoroethyl iodide, is prepared by reacting iodine pentafluoride and iodine with tetrafluoroethylene [13,14] (see Section 2.1) ... 

Telomerization of tetrafluoroethylene with pentafluoroethyl iodide produces a mixture of even-carbon-numbered telomers differing in their overall carbon chain length ... 

Numerous modifications of the original Du Pont telomerization process have been patented [67-79]. Fluorides, such as HF/SF4, SbF3/SbF5, or IF5/AICI3, used in older telomerization processes as catalysts [4], are corrosive and have been replaced by selected metal salts dissolved in amines or solid metal salt-amine complexes. Hauptschein [67] has prepared telomers by reacting tetrafluoroethylene with a secondary iodide, having two same or different perfluoroalkyl groups, at 150-220°C under pressure. A Ciba patent [68] discloses telomerization of per-... 

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