Replacement by fluorine

Heterogeneous vapor-phase fluorination of a chlorocarbon or chlorohydrocarbon with HP over a supported metal catalyst is an alternative to the hquid phase process. Salts of chromium, nickel, cobalt or iron on an A1P. support are considered viable catalysts in pellet or fluidized powder form. This process can be used to manufacture CPC-11 and CPC-12, but is hampered by the formation of over-fluorinated by-products with Httle to no commercial value. The most effective appHcation for vapor-phase fluorination is where all the halogens are to be replaced by fluorine, as in manufacture of 3,3,3-trifluoropropene [677-21 ] (14) for use in polyfluorosiHcones. 

Similar preference in replacement by fluorine of tertiary versus secondary and secondary versus primary hydrogens is observed in the fluorination of alkanes with chlorine trifluoride in 1,2-difluorotetrachloroethane at room temperature (Table 3). Skeletal rearrangements accompany the fluorination [31]... 

In bicyclic systems, bridgehead hydrogens are most resistant to replacement by fluorine Cobalt trifluonde converts l//-nonafluorobicyclo[3.2.0]hept-6-ene to... 

Amino groups bound to sulfur can be replaced by fluorine via diazotization. In contrast to carboxylic acid amides, fluorodediazoniation of aromatic sulfonamides IS readily accomplished to give sulfonyl fluorides in high yields [52, 7S (equation 16) Tetrazotization-fluorination of sulfanilamide can also be effected to give a 38% yield of p-fluorobenzenesulfonyl fluoride [52],... 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

The rate constants of kn and kx obtained using Eq. (24) reveal that (i) the activity of Fem-TAMLs in bleaching Safranine O (k ) increases more than 10-fold when the tail ethyl groups of la are replaced by fluorine atoms in lk. The rate constant kn for lk equals l(rM 1s 1 at 25°C, a value that corresponds to those found for the reactivity of horseradish peroxidase Compound II... 

Polytetrafluorethylene or PTFE (sometimes called TFE) is the most commonly used, the best known and, perhaps, has the highest performance, with excellent performance/ cost ratios. Its main drawback is the impossibility of processing it by conventional molten-state methods. All the hydrogen atoms of polyethylene are replaced by fluorine, leading to the following formula ... 

Halogenated extinguishing agents are hydrocarbons where one or more hydrogen atom is replaced by fluorine, chlorine, bromine, or iodine atoms. The substituted atom is not only rendered nonflammable, but it acts as a very efficient... 

FLUOROCARBONS. Compounds of carbon and fluorine-analogs of hydrocarbons in which the hydrogen has been replaced by fluorine. 

The fluoropolymer family consists of polymers produced from alkenes in which one or more hydrogens have been replaced by fluorine. The most important members of this family are polytetrafluoroethylene (PTFE) (XLVII), polychlorotrifluoroethylene (PCTFE) (XLVIII), poly(vinyl fluoride) (PVF) (XLIX), poly(vinylidene fluoride) (PVDF) (L) copolymers of... 

To appreciate the significance of these two new compounds one must recall the striking properties of carbon compounds in which hydrogen is completely replaced by fluorine. The products are characterized by great chemical inertness, but have physical properties which are similar in many respects to those of the hydrocarbons. This is illustrated by the following summary (Table 3) of the boiling points of fluorocarbons and hydrocarbons of the two series C F2 +2 and... 

In aromatic series, when hydrogen atoms are replaced by fluorine atoms or by fluoroalkyl groups, an enhancement of the log P occurs (Table 3) [13]. The CF3, CF3O and CF3S groups are the most hydrophobic substituents known. They are widely used in crop science [41]. 

First, we consider the fluorinated analogues of natural amino acids, where at least one or several hydrogen atoms have been replaced by fluorine atoms. Then we consider amino acids substituted by a fluoroalkyl group, as the sole structural modification, with special focus on a-fluorinated amino acids. Lastly, we give an outline of polypeptides and proteins in which fluorinated amino acids have been incorporated. 

Hydrogen atoms bonded to nitrogen, as well as those attached to carbon, are replaced by fluorine upon perfluorination of primary and secondary amines (Fig. 37) [101, 102]. Perfluorinated tertiary amines have also been prepared (Figs. 38 and 39) [78,103]. 

Elemental fluorine can be used to replace relatively electron rich C-H bonds by C-F. In particular, tertiary hydrogen atoms which are remote from electron withdrawing substituents can be selectively replaced by fluorine and, where there is more than one tertiary hydrogen atom in the substrate, that with the higher electron density is replaced (Fig. 44). In contrast, where there is an electron withdrawing group close to tertiary hydrogen, very little reaction with fluorine takes place and, consequently, when one fluorine atom has been introduced into a molecule further reaction is often inhibited. 

Of course this need not necessarily be the case, as in any mechanism where species are attached to an anode, changes in their electronic make-up, resulting from hydrogen replacement by fluorine, might be expected to cause variations in the adsorption forces with possible desorption into the electrolyte as a consequence. 

It should be noted that this molecule has two ether linkages that give flexibility to the molecular structure. In addition, the bulky -Cl groups in P6FDA are replaced by fluorine atoms, lire 8c of lOFEDA (157.5 ppm from I MS) was almost the same as that of P6FDA (157.6 ppm), so this dianhydride should have higher reactivity than unfluorinated and partially fluorinated dianhydrides. 

When diphenylacetylene dissolved in cold chloroform reacts with iodine monofluoride suspended in trichlorofluoromethane, the iodine atoms in the primary addition product are easily replaced by fluorine to give l,1,2,2-tetrafluoro-1,2-diphenylethane (60%) along with benzil (10%). Since the C —Br bond is stronger than the C —I bond, the reaction of bromine monofluoride with diphenylacetylene gives 1,1-dibromo-2,2-difluoro-1,2-diphenylethane (65%) and benzil (15%). 

Unlike bromine trifluoride (vide infra), chlorine monofluoride is capable of substituting fluorine for chlorine without catalysts in compounds eliminating chlorine via the intermediate formation of stable carbocations. Chlorine is easily replaced by fluorine at — 50 to — 10 C in /m-butyl chloride and at the secondary carbon atom in 1.2-dichloropropane and 1,2,3-tri-chloropropane.107... 

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