Fluorination, solubility increase

In the case of fluorinated molecules, it is important to differentiate the lipophilic character from the hydrophobic character. Both these characters are in tune for nonfluorinated molecules, but they diverge when the number of fluorine atoms increases in a molecule. It is generally recognized that fluorination induces an increase in the lipophilicity. However, this has only been demonstrated for aromatic compounds, and more specifically when fluorine atoms are in the a position of atoms, or groups bearing n electrons (Table 1.8)." Conversely, the presence of fluorine atoms in an aliphatic molecule provokes a decrease in the lipophilicity, while it can enhance the hydrophobicity. This phenomenon is so important that highly fluorinated molecules are not soluble in organic solvents or in water and constitute a third phase. 

The trichloride reacts violently with fluorine to form the trifluoride.4 Chlorine dissolves readily at low temperatures without reaction (see p. 110), the gas being expelled on warming.5 Iodine also dissolves without reaction,6 the solubility increasing with temperature, thus ... 

C o solubility increases in the similar sequence, from iodobenzene to chlorobenzene. The exception is fluorobenzene in which C6o solubility is lower than in iodobenzene. Apparently, in the case of interaction between fluorobenzene and C6o fullerene the factor of high fluorine electronegativity prevails. Moreover, as Table 3 indicates the fluorobenzene nitration gives rise to mainly para-isomer and very little ort/zo-isomers. Consequently, the entire negative charge is localized in the /jara-position in a fluorobenzene molecule. Therefore, as with Cgo solubility in alkyl derivatives of benzene (Table 2), one can anticipate that for the C6o molecule that is an electrophilic reagent, the ortho-position will be the more preferential location for electrophilic attack than the /w/ra-position. 

Queiroz synthesized diarylamines in the benzothiophene series, where the ligand BINAP was used to achieve the Pd-catalyzed amination in medium to high yields [156]. The diarylamines 96 were used in materials with electronic or luminescent properties. These compounds were further cyclized to provide substituted thienocarbazoles, which are bioisosteres of natural antitumoral DNA intercalating compounds. The presence of fluorine atoms increased the solubility of these molecules [156]. 

Fluorinated compounds are highly soluble - fluorinated tails increase solubility. 

The amidation reaction carried out with DCCI/Al-hydroxy-succinimide [18,19] or DCCI/hydroxy-benzotriazole [20,21] as coupling agents yields less than 15% of the corresponding amides. The utilization of BOP [22,23] as activating agent for the fluorinated acid increases the yields to 20-30%. The hydrolysis step is also not very efficient, so the overall yield of compound 3 (Scheme 5) is less than 10%. Moreover, the products are poorly soluble in water (<10 mol L ), even at high pH values [24]. 

Potential artificial oxygen carriers, based on new water-soluble fluorinated polymers, were obtained by using FOXARs (see also Scheme 59 in Sect. 3.3) to introduce fluorinated pendants in the a,p-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) and polyethylenglycol-PHEA (PHEA- PEG) biocompatible polymers. The introduction of the fluorinated moiety increased the polymer s oxygen-dissolving ability without compromising its biocompatibility which was checked by an in vitro viability assay [4]. 

Another way of applying the selective extraction method directly on the initial solution is to produce a solution of low acidity. This can be achieved by using the hydrofluoride method for fluorination and decomposition of raw material. As was discussed in Paragraph 8.2.2, the raw material is fluorinated by molten ammonium hydrofluoride yielding soluble complex fluorides of ammonium and tantalum or niobium. The cake obtained following fluorination is dissolved in water, leading to a solution of low initial acidity that is related for the most part to the partial hydrolysis of complex fluoride compounds. The acidity of the solution is first adjusted to ensure selective tantalum extraction. In the second step, the acidity of the raffinate is increased to provide the necessary conditions for niobium extraction. 

The chelatoborates LiB(C6H4 xFt 02)2 (x = 0, 1,4) are sufficiently soluble in various solvents and yield chemically stable solutions. Figure 14 shows the results of conductivity measurements at concentrations of about 1 mol L 1 in DME solvent, showing that a conductivity increase of about 440 percent at 35 °C and of about 240 percent at -45°C can be obtained with increasing fluorination of the salt. 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

Because the fluoride ion is so small, the lattice enthalpies of its ionic compounds tend to be high (see Table 6.6). As a result, fluorides are less soluble than other halides. This difference in solubility is one of the reasons why the oceans are salty with chlorides rather than fluorides, even though fluorine is more abundant than chlorine in the Earth s crust. Chlorides are more readily dissolved and washed out to sea. There are some exceptions to this trend in solubilities, including AgF, which is soluble the other silver halides are insoluble. The exception arises because the covalent character of the silver halides increases from AgCl to Agl as the anion becomes larger and more polarizable. Silver fluoride, which contains the small and almost unpolarizable fluoride ion, is freely soluble in water because it is predominantly ionic. 

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