Hexafluoro-propanol, HFIP

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. ... 

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. 

As a third example for an organocatalytic reaction, based on multiple hydrogen bonding and mechanistically investigated by DFT, we selected olefin epoxidation with hydrogen peroxide in fluorinated alcohol solvents, such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) (Scheme 3.8). Here we encounter a new type of catalytic hydrogen bond the cooperative hydrogen bond. 

In early negative-ion ESI-MS studies, halogenated solvent additives were applied to reduce the risk of discharge formation (Ch. 6.3.2). The use of 1,1,1,3,3,3,-hexafluoro-2-propanol (HFIP) to the mobile phase was proposed for oligonucleotides [22]. This is for instance applied in the rapid characterization of synthetic oligonucleotides by microcapillary LC-MS on a quadrupole-time-of-flight hybrid (Q-TOF) instrument [20]. 

A synthesis of cross-conjugated 2-cyclopenten-l-ones from dialkenyl ketones is readily induced by TMSOTf (eq 73). A strong fluorine-directing effect has been observed for such Nazarov-type cycUzation, as mixtures of products have been observed for nonfluorinated dialkenyl ketones. The addition of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a cosolvent dramatically accelerates the cyclization. Other acids such as BF3-OEt2, FeCls, polyphosphoric acid, or TiOH are less effective while neither TMSI nor TMSOMe promote this cyclization at all in CH2CI2. 3-Ethoxycarbonyltetrahydro-)/-pyrones also undergo such Nazarov-type cyclization. ... 

This syn selectivity can be explained by considering the intermediate 98 with a Cu-containing six-membered ring. The relatively strong Lewis acidity of the CuOTf catalyst would favor the diastereoselective Henry reaction via this cyclic transition state. Finally, protonation of the Cu alkoxide 99 and aromatization furnishes the desired product 93 and regenerates the catalyst 95. The additive 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) enhances the release of the products 93 from the catalyst. These products 93 could be readily envisaged as key starting materials in the synthesis of hydroxytryptamines [33]. 

Figure 1. Chemical structures of used model molecules a) Cycloaliphatic epoxy resin (Araldite CY179), b) Methylcyclohexyl cyclohexanecarboxylate (Ester), c) Dicyclohexyl ketone d) cyclohexane oxide e) Bisphenol F epoxy resin (Epon 862), f) Bisphenol A epoxy resin (DER 331), g) Ethyl acetate, h) acetone, i) Phenol, j) 1,1,1,3,3,3 Hexafluoro-2-propanol (HFIP)...

You et al. [175] prepared blends of PGA and PLA at various ratios (90/10, 70/30, 50/50, and 30/70) by solution blending in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The blends were immiscible and phase separation was obvious. This was due to the fact that the crystalline structure of the components prevented miscibility. The phase morphology of the blends was cocontinuous phases, with a circular and homogeneous pore size distribution noticed by SEM after chloroform extraction of PLA (Figure 16.13). 

The CD spectrum was extended to 140 nm and three bands were measured in a 1,1,1,3,3,3-hexafluoro-2-propanol(HFIP) solution. 

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. 

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... 

Raw silk was dissolved in hexafluoro-iso-propanol (HFIP) [17, 33]. A typical working concentration for spinning was 2.5% (w/v) silk fibroin in HFIP. The spinning solution was pressed through a small needle (0 80-250 pm) into a precipitation bath (methanol for Bombyx mori silk proteins and acetone for Nephila clavipes silk proteins) and the silk solution immediately precipitated as a fiber. The best performing fibers approached the maximum strength measured for native fibers of Bombyx mori, but did not achieve the mechanical properties of natural spider silk. 

It was also found that the rearrangement of cyclic oximes into lactams in the presence of cyanuric chloride is markedly facilitated by the use of l,l,l,3,3,3-hexafluoro-2-propanol (HFIP) as solvent ... 

In 1998, Begue and coworkers reported on a very selective conversion of sulfides to sulfoxides in hexafluoro-2-propanol (HFIP) as solvent using 30% H2O2 as oxidant without the need for a catalyst (equation 54) . A variety of differently substituted acyclic sulfides and also a cyclic one could be cleanly oxidized to the sulfoxides in very good yields ranging from 82 to 99% and no sulfone formation was observed. C=C double bonds in the substrate are tolerated without being epoxidized. This excellent reactivity is explained... 

Treatment of the epoxy ether 97 with hexafluoro-2-propanol (HFIP) or trifluoroethanol provided the rearranged trifluoromethyl ketone 98 as a single stereoisomer. NMR data for 98 did not allow the unambiguous determination of the configuration at C-9, which was confirmed by the single crystal X-ray structure (Equation 8) <2002JOC1253>. 

Because the substituted benzene chromophores absorb in the 205- to 280-nm range and have low e values, the solvents used must be transparent down to at least 250 nm. This requirement is unnecessary for the more conjugated naphthalene and anthracene chromophores. The usual polar, nucleophilic solvents that have been used to observe ions and ion-derived products are various alcohols, water, or water mixed with a cosolvent such as dioxane for solubility reasons. Recently, and particularly for the observation of the intermediate carbocations by laser flash photolysis (LFP) methods, the strongly ionizing (high Tore values) but weakly nucleophilic Oow N values) alcohols, 2,2,2-trifluoroethanol (TFE) and l,l,l,3,3,3,-hexafluoro-2-propanol (HFIP), have been more commonly used. A limited list of polar solvents and their properties is given in Table 2 [23,24]. 

Another major advantage of using HH.C is that solvent additives can be used which help to suppress the formation of cation adducts. Apffel and co-woikers reported the use of hexafluoro-2-propanol (HFIP) for ESI-MS analysis of oUgonucleotides up to 74 bases long [17], Addition of HFIP to a water/methanol gradient allows good HPLC separation of oUgonucleotides and efficient electrospray ionisation with a minimum of cation adducts formed. 

In 2013, chiral imidazoline-aminophenol ligands 138 combined with copper salts were successfully applied by the same group in the AFC reaction of indoles with isatin-derived nitroalkenes 139. By employing the appropriate catalyst, CuOTf/138a or Cu(OTf)2/138a, the reaction of isatin-derived nitroalkene with indole proceeded smoothly to afford 3,3 -bisindole derivatives 140 in up to 99% yield with 92% ee. l,l,l,3,3,3-Hexafluoro-2-propanol (HFIP) was found to be crucial to this transformation, with a positive effect on catalyst activity (Scheme 6.61). 

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