Hexafluoroisopropanol HFIP

The Shodex GPC HFIP series is packed with a hexafluoroisopropanol (HFIP) solvent. Engineered plastics, such as polyamides (nylon) and polyethylene terephthalate, were analyzed previously at a high temperature of about 140°C. Using FIFIP as an eluent, such engineered plastics can be analyzed at ordinary temperatures (Table 6.4). 

The use of hexafluoroisopropanol (HFIP) as an SEC eluent has become popular for the analysis of polyesters and polyamides. Conventional PS/DVB-based SEC columns have been widely used for HFIP applications, although the relatively high polarity of HFIP has led to some practical difficulties (1) the SEC calibration curve can exhibit excessive curvature, (2) polydisperse samples can exhibit dislocations or shoulders on the peaks, and (3) low molecular weight resolution can be lost, causing additive/system peaks to coelute with the low molecular weight tail of the polymer distribution... 

A major challenge in using interactive chromatography for polyamides is to find a suitable mobile phase (Mengerink et al., 2001, 2002 Weidner et al., 2004). Polyamides form semicrystalline morphologies that limit the solubility in organic solvents. Besides hot phenol, formic acid, and trifluoroethanol (TFE) (Mori and Barth, 1999), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) represents a suitable solvent for polyamides (Chen et al., 2002). These solvents are mainly used to analyze the molar mass distribution of polyamides by SEC. 

The described approach to this pharmaceutically important class of compounds [324] was also utilized by Bonnet-Delpon and coworkers one year later [325]. Interestingly, these authors employed hexafluoroisopropanol (HFIP) as solvent and were able to perform the domino process without adding any extra Lewis acid catalyst such as InCl3 due to the acidic properties of HFIP (pKa = 9.3) [326]. Besides di-hydrofuran or dihydropyran, they have also used acyclic enol ethers. 

The first problem encountered once the peptide has been successfully synthesized is that standard purification protocols fail. Although very hydrophobic peptides are soluble in acids such as TFA, these harsh conditions are not suitable for purification, because they can reduce column life times and denature native protein structures. Hence residual acid has to be removed, and many peptides can then be redissolved in mixtures of water and tert-butanol. Peptides with a strong tendency to aggregate may be dissolved either in trifluoroethanol (TFE), hexafluoroisopropanol (HFIP), mixtures of 1-propanol and 1-butanol, 20% acetic acid or 70-90% formic acid. 

In 2001, Albrecht Berkessel and Nadine Vogl reported on the Baeyer-Villiger oxidation with hydrogen peroxide in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as solvent in the presence of Brpnsted acid catalysts such as para-toluenesulfonic acid (equation 85) . Under these conditions cyclohexanone could be selectively transformed into the corresponding lactone within 40 min at 60 °C with a yield of 92%. Mechanistic investigations of Berkessel and coworkers revealed that this reaction in HFIP proceeds by a new mechanism, via spiro-bisperoxide 234 as intermediate, which then rearranges to form the lactone. The study illustrates the importance of HFIP as solvent for the reaction, which presumably allows the cationic rearrangement of the tetroxane intermediates. 

Alkenes, alkynes, and arenes become stronger bases in the singlet excited state. As a result, photoprotonation can occur under much more weakly acidic conditions than required in the ground state. Excited styrenes and phenylacetylenes, for example, are protonated by the solvent in 2,2,2-trifluoroethanol (TEE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), giving rise to phenethyl and a-arylvinylcations that can be observed by LFP (see Eq. 15). In a similar manner, benzenium ions can be observed by photoprotonation of electron-rich aromatics in FIFIP. " Equation 16 provides an example where the orientation of the protonation is different in the excited state from that of the ground state. 

All polyimide alloys were solution blended at a 50/50 weight ratio by codissolving the polymer pairs in a common solvent, such as methylene chloride (MeCl2) or a mixture of MeCl2 and hexafluoroisopropanol (HFIP), co-precipi-tating in methanol and then drying overnight under vacuum at 100 °C. 

Reaction of 234 with phenyliodine(m)bis(trifluoroacetate) (PIFA) afforded the 177-1-benzazepin-2-one 235 in moderate yield (52%) in hexafluoroisopropanol (HFIP) as solvent together with the spiro-cyclized 236 in 48% yield (Equation 32) <2003H(59)149>. 

Scanning force microscopy imaging provided further evidence for the successful conversion of the supramolecular polymers into covalent, conjugated polymers with retention of their hierarchical structure. First of all, SFM images obtained from any of the polymerizable macromonomers A-E looked virtually identical before and after polymerization. However, while the addition of a small amount of a deaggregating cosolvent such as hexafluoroisopropanol (HFIP) to the sample... 

To monitor both the copper and the polymer species during a PEEK/copper interface reaction, a PEEK overlayer thinner than 80 A, the approximate sampling depth of ESCA, was required. Centrifugal casting (3000 rpm for 15 sec) of an extract of PEEK in hexafluoroisopropanol (HFIP) onto copper disks proved successful for obtaining samples on which both PEEK and copper species could be detected by ESCA. The extract was obtained by passing a 20-30 wt. % suspension of PEEK in HFIP through a 0.5 pm Teflon filter. The solubility of a representative fraction of the PEEK in HFIP was verified by IR analysis. Comparison of the IR spectra from a PEEK/KBr pellet and the evaporated filtration product indicated identical spectra. 

Phenyliodine bis(trifluoroacetate) in combination with a Lewis acid has been shown to mediate selective oxidative cyanation of thiophenes at C-2 using TMSCN as the cyanide source <07JOC109>. Likewise, oxidative coupling of thiophenes with A-aromatic methanesulfonamides in the presence of PhI(OAc)2 in hexafluoroisopropanol (HFIP) takes place at C-2 of the thiophene, rendering for example the product 43 <07OL2553>. 

Hydrogen bond donor+acceptor water, methanol (MeOH), isopropanol (IPA), n-butanol, acetic acid (AcOH), trifluoroethanol (TFE), hexafluoroisopropanol (HFIP), ammonium hydroxide... 

More recently, hexafluoroisopropanol (HFIP) has been used successfully as a mobile phase for both poly-... 

All of these synthetic signal peptides, as well as peptides resembling the signal sequences of lysozyme and lipoprotein (Reddy and Nagaraj, 1985), became partially a helical in polyfluorinated alcohols [trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP)], which are more hydrophobic than water and have been used as models for the membrane interior. These solvents promote the formation of intramolecular hydrogen bonds, and consequently induce a-helix formation. In... 

Berkessel and Adrio report that the epoxidation rate by phenylarsonic acid using H2O2 is greatly accelerated by lO by the use of hexafluoroisopropanol (HFIP) as a solvent for substrates like cyclooctene or 1-octene [186]. The... 

In contrast, such peaks could be significantly displaced to high frequency when an alternative type of a-helix (airhelix) is present in which the amide plane might be tilted from the helical axis as previously proposed by Krimm and Dwivedi95 as the major form of transmembrane a-helix present in bR on the basis of an anomalously high frequency of the amide I band. The characteristic peak position of the l3C chemical shifts of the airhelix can be defined, taken similarly to the infrared spectra by using (Ala) dissolved in hexafluoroisopropanol (HFIP) solution,96 as demonstrated in Table 2, together with the l3C chemical shifts of... 

---