Fluoroalkyl functional groups

Keywords Silanes fluoroalkyl-functional groups surface modification surface tension adhesion control lubrication silylating agents release agents. 

Hoefling et al. " " and Harrison et al.t" have identified a number of factors influencing the solubility of surfactants in CO2. They concentrated on the functionality of various chelates and surfactants. Even though these solutes have low vapor pressures, they found that solutes with low solubility parameters, and low dipolarity/ polarizability parameters (e.g., with fluoroalkyl functional groups) were more soluble in CO2 than those with opposite properties. Favorable C02-tail interactions aid partitioning into the CO2, bending of the interface about water, and reduced micelle-micelle interactions. They also reported that solutes that were Lewis bases tended to have higher solubilities. 

The per(poly)fluoroalkylation of olefins by per(poly)fluoroalkyl chlorides, initiated by ammonium peroxydisulfate and sodium formate, is also reported. The reaction proceeds smoothly in polar aprotic solvents. The presence of functional groups like sodium car-boxylate or sulfonate in the polyfluoroalkyl chloride appears to facilitate the reaction. This reaction represents the first example of the reactivity of per(poly)fluoroalkyl chlorides. 

The Pummerer rearrangement has also been used to transform the 4-tolylsulfinyl group, which is an effective chiral auxiliary, into other functionalities via the aldehyde. Thus, chiral /> -(ben-7yloxy)-/J-(fluoroalkyl) sulfoxides 11 have been transformed into aldehydes 12 in a two-step process.7,8 The 3,3-difluoro-substituted aldehydes 12 can be converted directly into a variety of other functional groups without isolation. The chiral center at C2 is derived from the corresponding chiral / -oxo sulfoxide, which can be reduced diastereoselectively due to the presence of the chiral 4-tolylsulfinyl group.7,8 Diastereoselective reduction of fluorine-free fi-oxo sulfoxides has been intensively studied, especially in the laboratories of Solladie.9... 

When functional groups are present, the products can be quite complex. Primary and secondary amines give NF2 and NF compounds respectively and fluorination of sulphur compounds gives products in which the sulphur has been oxidised to its maximum valency state of six [149] (Table 2.4). Hydroxy compounds can give fluoroalkyl hypo-fluorites (fluoroxy compounds) (see also Chapter 3, Section IIIB), the corresponding alkyl derivatives not being stable [150, 151] bisfluoroxy derivatives have also been isolated [152-154] (Figure 2.27). 

Schematic representation of the chemical modifications of the silicon oxide network. Inorganic modification with M = Al, Ti, Zr and others, organic modification with R = alkyl, aryl, both without and with additional functional groups, for example fluoroalkyl, or R = bioactive or dyestuff group. 

Fluorine can share three sets of lone-pair electrons with electron-deficient atoms intramo-lecularly or intermolecularly, in particular with a relatively acidic hydrogen bound to a heteroatom. In addition, as described in section 1.4, strongly electron-withdrawing per-fluoroalkyl groups increase the acidity of proximate functional groups such as alcohol, amine, amide, and carboxylic acid. 

ILs, fluoroalkyl-functionalized ILs exhibited a higher separation for CO2/CH4 and a lower one for CO2/N2. The authors tried to correlate the selectivity with the molar volume and the solubility parameters 5 derived from chemical group contributions [74] and concluded that the model was able to predict trends in CO2 separations however, no absolute values could be calculated via this method. 

Common inoiganic anions (X ) are halide, tetrachloroaluminate (also tetra-chlorofenate and tetiachloioindate), tetrafluoioborate, hexafluoiophosphate, and bis(trifluoromethylsulfonyl)iniide, and common organic anions are derivatives of sulfate or sulfonate esters, trifluoroacetate, lactate, acetate, or dicyanamide. Substituents (R-groups) on the cation are usually alkyl chains, but can contain any of a variety of functional groups such as fluoroalkyl, alkenyl, methoxy, or hydroxyl [67-69], Some typical examples of common anions are BF , PFg, B(CN) , CH-... 

To aid in the characterization of the modified polymer samp os 1-10, and of the mixtures 11 and 12 obtained from functionalizing the two cycloalkanes, we prepared the model fluoroalkanols 13 and 14 as shown in Equation 2 (11-12), and the model fluoroalkyl ethers 15 and 16 as shown in Equation 3 1 3). Compounds 13 and 15 were previously isolated by- the Dupont group (8) from their mixture 11. Products 13-16 proved to be good comparison compounds for the infrared spectra, and particularly- for the 19F-NMR spectra. The I9F-NMR signal for the fluoroalkanol is approximately 1 ppm downfield from that of the fluo-roalky.l ether, which is enough to get semiquantitative ratios of... 

Unlike the approach in which LB multilayers are formed from polymerizable fluoromonomers followed by UV-polymerization,69 we started to use functional fluoropolymers for the preparation of LB films. These films seem to be better, because in the case of monomeric LB film the polymerization process causes contraction and hence possible defects in the final cured film. Two different kinds of functional amphiphilic fluoropolymers were used for LB-film preparation. One type (referred to in Section 7.4.2), which has large fluoroalkyl groups as side... 

Fluorination has an important indirect impact on hydrogen bonds, via neighbouring functions (hydroxyl, amine, carbonyl, hydrogen). The electron-withdrawing effect of fluorine atom and of fluoroalkyl groups (CF2, CF3, etc.) deeply modifies the pKg of neighbouring functions, and hence their character of hydrogen bond donors or acceptors (Table 1). 

Peptidyl fluoromethyl ketones are widely used as fairly potent inhibitors for a variety of proteases, including serine, cysteine, and aspartyl proteases. Unlike other halomethyl ketones (Section 15.1.3), fluoromethyl ketones are reversible transition-state mimics. The electron-withdrawing fluorine(s) next to the carbonyl group enhances the electrophilicity of the a-fluoroalkyl ketone functionality, thereby making the carbonyl more susceptible to nucleophilic attack. a-Fluoroalkyl ketones are good mimics of peptide bonds due to the small size of the fluorine and the stability of C F bonds. There are three general classes of peptidyl fluoromethyl ketones fluoromethyl ketones (irreversible inhibitors of cysteine proteases), difluoromethyl ketones (reversible inhibitors of both serine and aspartyl proteases), and trifluoromethyl/perfluoroalkyl ketones, which typically exist in hydrated forms and are excellent inhibitors of both serine and cysteine proteasesJ1 ... 

---