Tail, perfluoroalkyl

These compounds present a new class of LC molecules having a perfluoroalkyl tail on one end and an ordinary alkyl tail on the other. Earlier studies of several groups indicated that terminal fluorination considerably extends the temperature range of the smectic phase [81]. Moreover, mesogens incorporating... 

A model with overlapping perfluoroalkyl tail should be excluded, since in this case the difference A is independent of the length of the fluorinated chain. The calculations for the molecular form factor gives a reasonable agreement with the intensities of successive (OOn) harmonics for the model with overlapping aromatic parts of the molecules and the tilt (approximately 35°) of perfloro chains [41c]. This model also satisfies fhe requiremenfs for dense Ailing of space. The smecfic layers in fhe dimeric smecfic phase are well defined (cr = 2.5-3 A) and consisf of fwo sublayers of fhe fluorinafed and aromafic parfs of fhe molecules. 

The fluorous alkylphosphines 2 [8, 12] and 3 [8, 13], containing one or two perfluoroalkyl tails, respectively, have also been prepared. Partition coefficients of the chiral fluorous monophosphines 3a-b were found to be lower than the values measured for the corresponding phosphines 1, which contain one extra perfluoroalkyl tail [13], In addition, fluorous phosphinites, phosphonites and phosphites 4a-e and diphosphonite 5 have become available [8, 14]. 

A cationic complex, formed in situ from 5 and [Rh(COD)2]OTf, was also active in biphasic hydrogenation [14]. No preference for the fluorous phase was found for ligands containing only one perfluoroalkyl tail, but neutral and cationic complexes, containing mono- and bidentate 4a or 5, respectively, were selectively dissolved in the fluorous phase. No leaching and recycling studies were performed. 

Another spacer which was used to insulate the phosphorus atom from the electron-withdrawing effect of the perfluoroalkyl tail is the -0-(CH2) - spacer that contains an electron-donating oxygen atom directly attached to the aryl ring [25]. Fluorous derivatives of triphenylphosphine containing this ether spacer (13a-c) were prepared, though the lower coupling constant of cis-... 

Perfluoroalkyl tail Hydrocarbon linker Junction spacer Polar head Figure 6.48 Creation of fluorinated surfactant derived from a sugar. 

In general, the rate of elimination of PFCAs and PFSAs decreases with increasing length of the perfluoroalkyl tail [23]. Differences in elimination of PFSAs and PFCAs have been... 

Henry s law constants, also known as air-water partitioning coefficients (Kaw). have been measured for the FTOHs in two studies (Table 3.2). Lei et a/. [71 ], reported log Kaw values that were all of a similar order of magnitude. The log Kaw values reported by Goss et al. [77] were much less than those reported by Lei et al. [71 ] and generally increased with increasing length of the perfluoroalkyl tail. To date, measured log Aw values have not been reported for the FSAs. 

Bioaccumulation studies of PFSAs ( = 6 and 8) and PFCAs ( = 7, 8, 10, 11 and 13) in rainbow trout (Oncorhynchus mykiss) have been conducted by Martin et al. [83, 84] (Table 3.2). These studies indicated that dietary exposure to PFSAs and PFCAs did not result in biomagnification. Bioaccumulation was observed for PFSAs and PFCAs consisting of more than six and seven carbon atoms respectively. The laboratory-based bioconcentration factor (log BCF) for PFOS was 3.04 L/kg and ranged from 0.602 to 4.36 L/kg for the PFCAs. Log BCFs were observed to increase with increasing length of the perfluoroalkyl tail and for the PFCAs increased by a factor of approximately 8 for each additional CF2 moiety for PFCAs ( = 8 to 12), but deviated from linearity for PFTetA. In addition, PFSAs were more bioaccumulative than PFCAs. 

Such amphiphiles by definition must possess a hydrophilic head group and a hydrophobic tail. The hydrophobic moiety may consist of one or two alkyl or perfluoroalkyl groups or in certain cases a single steroidal group. 

Pilston, R.L., and R.D. McCullough. 2000. Toward highly fluorescent polythiophenes Head-to-tail coupled copolymers of 3-(methoxyethoxyethoxymethyl)thiophene and 3-(perfluoroalkyl)thio-phene. Thesis. 

Separating and joining the hydrophobic/oleophobic tail and the hydrophilic group of the fluorinated surfactant is the critical organic linking group, often called the spacer [2-6]. Perfluoroalkyl acid (PFAA) surfactants such as perfluoroalkyl... 

The hydrophobic tail of the surfactant can consist of a hydrocarbon, perfluoroalkyl or polysdoxane group. The structure of the tail group such as its length or branching can significantly alter the physical behavior of the surfactant. 

The replacement of the hydrophobic tail by a perfluoroalkyl group could create a surface that is neither water nor hydrocarbon wet. 

According to the criteria for steric stabilization, the dispersant tail must be soluble in, or at least compatible with, the polymer. Solubility is governed by the principle that like dissolves like. In more scientific terms, it means that the dispersant tail and the polymer must be of similar polarity, or more precisely of similar solubility parameter. Therefore a perfluoroalkyl tail would be well suited to PTFE, an alkyl dispersant tail would be ideal for PE and polypropylene, and a high polarity PE oxide type tail would work in polymers such as PVC, PET, and nylons. 

As an alternative to the use of fluorous tag, fluorous aqueous biphasic systems have also been explored. Recently, fluorous biphasic system composed of fluorous Lewis acid ytterbium perfluorooctanesulfonate [Yb(OPf)3], fluorous solvent perfluorocarbon has been used in the synthesis of benzodiazepines from OPD and carbonyl compounds [127]. Conceptually, the fluorous catalyst with perfluoroalkylated tails can dissolve into the fluorous phase containing the product after the reaction. The study has been extended later to the use of fluorous aqueous emulsion expecting that the organic substrate will remain in the interfacial area between a fluorous phase and aqueous media. Thus another synthesis of benzodiazepines has been reported by the same group by carrying out the reaction in a fluorous aqueous emulsion system composed of perfluorooctane and potassium perfluorooctanesulfonate at room temperature (Scheme 38) [128]. Moreover, the emulsion could be recovered and recycled without significant loss of activity. 

SCHEME 69 Synthesis of acridines using Bronsted acid IL containing perfluoroalkyl tails. 

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