Other Perfluoroalkanes

From the forward and reverse rate constants for reaction (2-6), the enthalpy of reaction was estimated to be 31 kcal/mole by Atkinson and 

McKeagan.13a With Atf°9B C2F4 = -155.0 and AH°29B CF2 = -39.0 kcal/mole, A/f298 c-C3F6 = —225.0 kcal/mole. 

and Ressler20 estimated the enthalpy of reaction to be + 15 kcal/mole at 1100-1400°K for the reaction 

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Tetrafluoromethane and other perfluoroalkanes require radiation of wavelength <100 nm to cause photodissociation of the very strong C—F bond. These species must therefore diffuse upwards to altitudes beyond 100 km before photolysis occurs, and consequently they have atmospheric lifetimes of thousands of years51. 

Oxidation of methyl perfluoroalkyl sulphones with refluxing aqueous potassium permanganate produced the perfluorinated alkanesulphonic acid in 85% yield as the potassium salt (equation 86). On the other hand, attempted oxidation with sodium hypochlorite caused only chlorine substitution (equation 87). Reaction of the new sulphone with aqueous hydroxide gave the same perfluoroalkane sulphonic acid salt (equation 88). 

On the other hand, poly tetrafluoroethylene (PTFE) has been shown to be electrochemically reducible [4]. Very recently, electrochemical reduction of saturated perfluoroalkanes has been observed on an analytical scale and it was found that the reduction potentials of perfluorocycloalkanes are only slightly more negative than those of the corresponding perfluoroaromatics perfluorode-caline (Ep = — 2.60 V vs Ag/O.OIM AgC104) vs. octafluoronaphthalene ( — 2.58 V) perfluoromethylcyclohexane ( — 2.9 V) vs. perfluorotoluene ( - 2.75 V) [5],... 

Strong Brpnsted acids are also available to induce acylations.3,8,9 Perfluoroalkane-sulfonic acids were shown to be highly effective. Certain metal powders, such as Zn, Cu, Al, and Fe, were also found to effect acylations with acyl chlorides. The de facto catalysts are the in situ formed corresponding metal halides.3,8 A number of other catalysts were developed over the years however, many of these are effective only for the acylation of highly reactive aromatics, such as heterocycles.9... 

The reason for the experimentally proven lipophobicity, i.e., the tendency of fluorinated and hydrogenated chains to phase separate, is much less clear than the other effects of fluorination and is still under debate. Mostly it is assigned to the disparity of cohesive energy densities between perfluoroalkanes and alkanes. A reduction of ca. 10% in the interactions between unlike pairs of molecules was estimated by several methods [90]. However, there are also simulations suggesting slightly stronger attractive contributions to the interaction between Rf/Rh pairs compared to the like interactions under certain circumstances [94]. 9 However,... 

A lmost 15 years have elapsed since the initial preparations of trifluoro-methanesulfonanilide (TFMS) and other related perfluoroalkane-sulfonanilides were reported by Brice and Trott (I) and Burdon etal. (2). 

The thermal decomposition of salts of fluorinated acids gives tw o different types of products. depending on the reaction conditions and the type of cation. When the decarboxylation of alkali and alkaline earth metal salts is carried out in the presence of proton donors, such as water, alcohol, aniline, pyridine or other basic solvents, the product of the reaction is a fluorocarbon hydride. This is a general procedure for the preparation of 1 /Z-perfluoroalkanes. ... 

The miscibility of perfluoroalkanes and other perfluoro solvents is low with corresponding hydrocarbon solvents and is exploited in fluorous organic biphasic catalysis.27 In some cases, apolar reactants may be dissolved in the fluorous phase and on conversion to higher polarity products a second immiscible phase is formed. Notable examples of catalyzed reactions that are effectively carried out using the fluorous biphase approach are hydroformylations28 and oxidations.29 It should be noted that fluorous solvents are damaging to the environment, however, as with other catalyst immobilization solvents, if they are not lost from the system no damage to the environment takes place. Fluorous biphase systems have not, as yet, been used on an industrial scale. 

It seems likely that the Involvement of (CF2)n species Is also prominent In the plasma polymerization of the other fluorocarbons of F/C52. In a subsequent paper (30) we shall demonstrate that this Is Indeed the case. In an Investigation of metal containing polymers produced In plasmas excited In the series of perfluoroalkanes CjjF2n+2 >3,4). ... 

In addition to polymers there are many other applications of low-molecular-mass fluorochemicals in the electronics industry. Some typical applications of perfluoroalkanes and ethers are listed in Table 4.2. 

McLure, I. A., Thermodynamics of linear dimethylsiloxane-perfluoroalkane mixtures Part 1.—Liquid-liquid coexistence curves for hexamethyldisiloxane-, octamethyltrisiloxane- or decamethyltetrasiloxane-tetradecafluorohexane near the upper critical endpoint and upper coexistence temperatures for 21 other dimethylsiloxane-perfluoroalkane mixtures. J. Chem. Soc., Faraday Trans., 1997, 93, 249-256. 

Similar to perfluoroalkanesulfonic acids, the yield of the fluorination reaction decreases with the increasing chain length of the starting material. For example, the electrochemical fluorination of acetyl fluoride yields 76% of perfluoroacetyl fluoride, whereas the fluorination of octanoyl fluoride yields only 10% of perfluorooctanoyl fluoride. The yield is also lower when the readily available acid chlorides, and not the fluorides, are employed as starting materials. A major side reaction of the fluorination of acid chlorides such as octanoyl chloride is the formation of cyclic products. Other by-products and impurities present in PFCA fluorides obtained by electrochemical fluorination include short-chain PFCA fluorides, perfluoroalkanes, COFj, and HF. Perfluorooctanoyl fluoride, the most important PFCA, was industrially synthesized from the corresponding chloride despite the lower yield and formation of cyclic by-products. ... 

Perfluoroalkane carboxylic and sulfonic acids and their derivatives have been synthesized by Zn-Barbier reactions using iodoperfluoroalkanes in dimethyl-sulfoxide (DMSO) as solvent [71]. A Zn/Cu (100 1) couple was used for most of the reactions but other couples such as Zn-Pb, Zn-Cd or Zn-Hg led to the same results ... 

The Si—O—Si chain will thereafter break and rearrange. The most frequently used acidic catalysts are sulphuric acid, montmorillonite clays activated with sulphuric acid, other mineral acids, alkane- and perfluoroalkane-sulphonic acids, FeCl3 and other Lewis acids. Sulphuric acid is most effective at 84% acid to 8% oleum. Whereas sulphuric acid is used at a concentration of 1 to 2%, the perflu-oroalkanesulfphonic acids are active at concentrations of only 0.1 weight %. With the latter catalysts, temperatures of 25-50 C are used. 

One of the driving forces behind recent developments in the synthesis and characterization of new acids is the requirement to replace mineral acids by reagents and catalysts that will lead to reduction in waste, in other words to an improved atom economy. Thus, HCl used in the synthesis of diamino diphenyl methane, an intermediate in polyurethane production, can be replaced by a silico-aluminate catalyst in which the acid sites of the zeolite are accessible through the external surface. Less conventionally, simple aromatic hydrocarbons can be nitrated using 60-70% nitric acid in the presence of the strong Lewis acids, lanthanide-perfluoroalkane sulfonic acid salts, such as the ytterbium(lll) compounds (VI) and... 

The solubilities of fluorinated surfactants are related to the unusual properties of the fluorine atom and the C—F bond. Fluorine is the most electronegative element and is very difficult to polarize. Fluorine can form a very stable bond with hydrogen or carbon (see Section 3.1). The rigidity of the C— F bond causes stiffening of the perfluoroalkane chain and limits interactions with other molecules. Because of their small size, fluorine atoms can shield the perfluorinated carbon atom without steric stresses. Perfluoromethyl or perfluoromethylene groups therefore form compounds with very weak intermolecular forces. As a consequence of weak interactions, perfluoroalkanes are insoluble in common organic solvents. Perfluo-roalkanes are more hydrophobic than hydrocarbons, evidenced by solubility data CF4 is seven times less soluble in water than CH4 [1,2]. Water is almost 7 times less soluble in perfluoroheptane than in heptane on a equal weight basis [3] and 25 times more on a molar basis. 

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