Hexafluoro-propanol

The polymers dissolve in l,l,l,3,3,3-hexafluoro-2-propanol [920-66-1/, hot phenols, and /V, /V- dim ethyl form am i de [68-12-2] near its boiling point. The excellent solvent resistance notwithstanding, solvents suitable for measurement of intrinsic viscosity, useflil for estimation of molecular weight, are known (13,15). 

Furthermore, the stereochemistry of the product 1 changes as the solvent is changed. In aqueous dioxane, the reaction proceeds with complete inversion, but in 1,1,1,3,3,3 hexafluoro-2-propanol with 100% retention. In acetic acid, the reaction occurs mainly with inversion (83%), but in formic acid the amount of retention (40%) is comparable to the amount of inversion (60%). Discuss these results, particularly with respect to the change of product composition and stereochemistry as a function of solvent. 

Controlling for these forces requires variation in the amount of salt, organic solvent, and the pFI of the mobile phase. It is impractical to perform such experiments with 50 mM formic acid an alternative additive must be used that maintains its chaotropic properties independent of salt content or pFI. Fortunately, mobile phases containing 50 mM hexafluoro-2-propanol (HFIP) afford a fractionation range comparable to that of the formic acid (Fig. 8.6), permitting the effects of these variables to be studied systematically. 

FIGURE 8.6 Comparison of hexafluoro-2-propanol (HFIP) with formic acid as a denaturing agent in SEC. Eiution positions of neutral amino acids were similar with both agents. The elution positions of Lys and Asp shifted dramatically in C, as shown by the tie lines, but this was an effect of pH (see Fig. 8.7). The elution positions of a-MSH and formic acid are shown to demonstrate that the amino acids eluted within Vo and V,. Column Same as Fig. 8.1. Flow rate 1.0 ml/min. Mobile phase As noted. Detection Aiij = 0.1 AUFS. 

Begue and coworkers recently achieved an improvement in this method by performing the epoxidation reaction in hexafluoro-2-propanol [120]. They found that the activity of hydrogen peroxide was significantly increased in this fluorous alcohol, in relation to trifluoroethanol, which allowed for the use of 30% aqueous H202. Interestingly, the nature of the substrate and the choice of additive turned out to have important consequences for the lifetime of the catalyst. Cyclic dis-ubstituted olefins were efficiently epoxidized with 0.1 mol% of MTO and 10 mol%... 

Figures 15 and 16 demonstrate folding in the l,l,l,3,3,3-hexafluoro-2-propanol/ethylene glycol (HFP/EG) mixture (1 2) and in 1,3-propandiol in comparison to Fig. 13, which describes helix formation in water. The structure formation is much more pronounced. This is indicated by the more negative signals of the CD spectrum at 198 nm. The negative values of 0 for the octamer increase from -1.8 x 10-4 deg cm2 dmol-1 in...

Fig. 15. Ellipticity of (Pro-Ala-Gly-Pro-Ala-Gly) (n = 5-8) in 1,1,1,3,3,3-hexafluoro-2-propanol/eth-ylene glycol (1 2), depending on the temperature under helix conditions...

In some cases, these organic solvents cause no stronger folding but adversely (Lys-Gly-Pro)n folds to a lower extent in l,l,l,3,3,3-hexafluoro-2-propanol/ethylene glycol or in 1,3-propandiol than in water (Table 3). 

Kwon and coworkers prepared a series of nano- to microstmctured biodegradable PCLA porous fabrics by electrospinning. The nanoscale-fiber porous fabrics were electrospun with PCLA (1 1 mole ratio, approximately 0.3-1.2 mm in diameter) using l,l,l,3,3,3-hexafluoro-2-propanol as a solvent. 

Walgers, R., Le, T, and Cammers-Good-win, a. An indirect chaotropic mechanism for the stabilization of helix conformation of a peptide in aqueous trifluo-roethanol and hexafluoro-2-propanol. /. Am. Chem. Soc. 1998, 720, 5073-5079. 

The polymer = 8.19 dlg in hexafluoro-2-propanol, HFIP, solution) in Figs 1 and 2 is prepared on photoirradiation by a 500 W super-high-pressure Hg lamp for several hours and subjected to the measurements without purification. The nmr peaks in Fig. 1 (5 9.36, 8.66 and 8.63, pyrazyl 7.35 and 7.23, phenylene 5.00, 4.93, 4.83 and 4.42, cyclobutane 4.05 and 1.10, ester) correspond precisely to the polymer structure which is predicted from the crystal structure of the monomer. The outstanding sharpness of all the peaks in this spectrum indicates that the photoproduct has few defects in its chemical structure. The X-ray patterns of the monomer and polymer in Fig. 2 show that they are nearly comparable to each other in crystallinity. These results indicate a strictly crystal-lattice controlled process for the four-centre-type photopolymerization of the [l OEt] crystal. 

In a related study, Lee-Ruff, Johnston, and co-workers photolyzed 9-hydroxy-9-fluorenecarboxylic acid in hexafluoro-2-propanol (HFIP) and detected a transient (x = ca. 20ps) with = 495nm and strong IR bands at 1575,1600, and 1620cm , which was assigned to zwitterion 20, in excellent agreement with the measured IR... 

We (fl) have reported the photophysical processes of a series of model esters of PET, and tentatively assigned the fluorescence and phosphorescence of the aromatic esters as (n, tt ) transitions, respectively. We (9) also performed an extensive study of the photophysical processes available to dimethyl terephthalate (DMT) in order to relate this monomeric species to the PET polymer. In 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) (Table I), DMT has three major,absorptions which are according to Platt, s notation 191 nm, A- B, e = 40,620 1 mole" cm"1 244 nm, A-dLaT e = 23,880 1 mole-) cm" 289 nm, A U, e = 1780 1 mole")cm. ... 

In the solvolysis of secondary alkyl sulfonates, competition between nucleophilic solvation and electron donation by the substituents results in a significantly solvent-dependent p, which varies from — 9 to — 1 on going from the non-nucleophilic hexafluoro-2-propanol to 80% aqueous ethanol (Bentley et al, 1981). In contrast, the p -invariance for alkene bromination in H20, M70, MeOH and AcOH [equations (22)-(25)] seems to imply a perfect balance between the two types of charge stabilization. However, this conclusion is probably risky since the nucleophilicities of the solvents implied in (22)-(25) do not vary markedly. Data in non-nucleophilic fluorinated solvents would therefore help to fill the gap in our knowledge. 

Although the selectivities are excellent, prolonged reaction times (2 1 days) are noted under these conditions. The addition of alcohols, particularly 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), was found to decrease reaction times (4 days to 36 h under identical conditions). In the presence of HFIP, Michael adducts are generated in comparable yields and selectivities suggesting that the principal role of the alcohol is catalyst turnover. 

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