2,2,2-Trifluoroethanol acidity

Circular dichroism studies of isoleucine oligopeptides (as protein model compounds) were carried out in trifluoroethanol and trifluoroethanol/acidic and aqueous organic media (Goodman et a/., 1971b Toniolo, 1971a). The... 

Aqueous caprolactam is polymerized alone and in the presence of sebacic acid (S) or hexamethylenediamine (H).t After a 24-hr reaction time, the polymer is isolated and the end groups are analyzed by titrating the carboxyl groups with KOH in benzyl alcohol and the amino groups with p-toluenesulfonic acid in trifluoroethanol. The number of milliequivalents of carboxyl group per mole caprolactam converted to polymer, [A ], and the number of milliequivalents of amino groups per mole caprolactam converted to polymer, [B ], are given below for three different runs ... 

Difluoroethanol [359-13-7], F2CHCH2OH, is a colorless Hquid with an alcohol-like odor mp, 28.2°C, bp, 96°C d[, 1.3084 n], 1.3320 heat of combustion, —1026 kJ/mol(—245.3 kcal/mol). It is stable to distillation and miscible with water and many organic solvents. As expected, its acidity Hes between that of 2-fluoroethanol and 2,2,2-trifluoroethanol both ia the gas phase (25) and ia 50% aqueous ethanol solution (26), where its of 1.0 x 10 is about 4.8 times smaller than that of trifluoroethanol. 

Chemically, 2,2,2-trifluoroethanol behaves as a typical alcohol. It can be converted to trifluoroacetaldehyde [75-90-1] or trifluoroacetic acid [76-05-1] by various oxidi2iag agents such as aqueous chlorine solutions (51) or oxygen ia the preseace of a vanadium pentoxide catalyst (52). Under basic conditions, it adds to tetrafluoroethylene and acetylene to give, respectively, 1,1,2,2-tetrafluoroethyl 2/2/2 -trifluoroethyl ether [406-78-0] (53) and... 

Trifluoroethanol was first prepared by the catalytic reduction of trifluoroacetic anhydride [407-25-0] (58). Other methods iaclude the catalytic hydrogeaatioa of trifluoroacetamide [354-38-1] (59), the lithium aluminum hydride reductioa of trifluoroacetyl chloride [354-32-5] (60) or of trifluoroacetic acid or its esters (61,62), and the acetolysis of 2-chloro-l,l,l-trifluoroethane [75-88-7] followed by hydrolysis (60). More recently, the hydrogenation of... 

Trifluoroethanol [75-89-8J M 100.0, b 72.4°/738mm, d 1.400, pK 12.8. Dried with CaS04 and a little NaHCOa (to remove traces of acid). Highly TOXIC vapour. 

The easy liberation of trifluoroethanol from 2,2,2-tnfluoroethyl hydrogen 3,6-di methylphthalate can be accounted for by nng closure to form 3,6 dimethylphthalic anhydride [57] (equation 56) The carboxylate anion is the intermediate needed for nng closure because the rate increases as the pH, while still acidic, increases... 

Trifluoromethyl-l-phenylethyl tosylate has been used to differentiate as shown in Table 1, the solvolytic power of three fluorinated solvents and to compare these with formic and acetic acids The three fluorinated solvents are trifluoroacetic acid, trifluoroethanol, and 1,1,1,3,3,3-hexafluoroisopropyl alcohol [55]... 

The quantitative deprotection of phenol ethers can be achieved by the action of a catalytic amount of triflic acid in trifluoroethanol at -5 °C [86],... 

The greater positive character, hence the increased acidity, of the O—FI proton of 2,2,2-trifluoroethanol can be seen in the electrostatic potential maps displayed in Figure 1.8. 

FIGURE 1.8 Electrostatic potential maps of ethanol and 2,2,2-trifluoroethanol. As indicated by the more blue, less green color in the region near the OH proton in 2,2,2-trifluoroethanol, this proton bears a greater degree of positive charge and is more acidic than the OH proton in ethanol. 

Display and compare electrostatic potential maps for methanol, ethanol, 2-propanol and trifluoroethanol. Identify the acidic sites as those where the potential is most positive and, assuming that the more positive the potential the more acidic the site, rank the acidities of the compounds. Does increased alkyl substitution have a significant effect on acid strength What is the effect of replacing the methyl group in ethanol by a trifluoromethyl group Why Do you find a correlation between the most positive value of the potential and the experimental pKa ... 

For an a-helical fraction fH = 0,5 30% methanol, 20% ethanol, 15% i-propanol or 10% trifluoroethanol are necessary. Trifluoroethanol like perfluorinated alcohols, e.g. hexafluoroisopropanol is characterised on the hand by a strong acidic proton at the OG-group due to the —1-effect of the fluor atoms. On the other hand fluorocarbons are more hydrophobic than the hydrocarbons which is mainly due to the larger surface of the F compared with H. For this reason the critical micelle concentration of perfluorinated detergents is much lower than that of the corresponding hydrocarbon compounds. It was found that C4F7-derivatives act as detergents... 

Compounds with a smaller/C., and larger pKa are less acidic, whereas compounds with a larger/Ca and smaller plsimple alcohols like methanol and ethanol are about as acidic as water but substituent groups can have a significant effect, tert-Butyl alcohol is a weaker acid, for instance, and 2,2,2-trifluoroethanol is stronger. Phenols and thiols, the sulfur analogs of alcohols, are substantially more acidic than water. 

Inductive effects (Section 16.4) are also important in determining alcohol acidities. Electron-withdrawing halogen substituents, for example, stabilize an alkoxide ion by spreading out the charge over a larger volume, thus making the alcohol more acidic. Compare, for example, the acidities of ethanol (p/tcrt-butyl alcohol (p/

A few other successful 13C 1-NMR determinations should be mentioned. Hunt et al. [28] used 13C NMR to characterise fractions of extracted analytes of PAG and sorbitan ester samples and identified Irganox 1010. H and 13C NMR have been used to identify the main organic components of a breathable diaper back-sheet as LLDPE and pentaerythritol tetra-octyl ester (PETO) [233]. The equally present AOs Irganox 1010 and Irgafos 168 were not detected without extraction. Barendswaard et al. [234] have reported fully assigned 13C solution spectra of these two antioxidants. Chimas-sorb 944 in a polyamide matrix can be determined by H or 13C 1-NMR using solvents such as formic acid, trifluoroacetic acid or trifluoroethanol [235], Both H and 13C NMR have been used to follow the chemistry of a bis-phenoxidemethylaluminum complex (reaction product of BHT and trimethylaluminum) by exposure in air. Pierre and van Bree [216] also used 13C NMR to... 

Polyamides Formic acid, TFA-di, trifluoroethanol-d3, H2S04, DMF-d7 (for semi-aromatics) 60-70... 

The use of ethanol as an achiral auxiliary gave the adduct 53 with 55% ee, while neopentyl alcohol and methanol gave 96 and 87% ee, respectively. These results suggested that the achiral alcohol might exert a steric effect on the stereoselectivity. However, the increase in enantioselectivity from 55% to about 96% when 2,2,2-trifluoroethanol (TFE) was used instead of ethanol indicates a possible significant inductive effect also. Good enantioselectivities were also obtained with carboxylic acids and phenols. 

A trend emerged in that the best conditions involved either the use of a Lewis acid additive (BF3 OMe2) or a more polar solvent-such as trifluoroethanol (TFE), although the beneficial effect of TFE did depend on the ligand employed [27]. The... 

A variety of cleavage conditions have been reported for the release of amines from a solid support. Triazene linker 52 prepared from Merrifield resin in three steps was used for the solid-phase synthesis of aliphatic amines (Scheme 22) [61]. The triazenes were stable to basic conditions and the amino products were released in high yields upon treatment with mild acids. Alternatively, base labile linker 53 synthesized from a-bromo-p-toluic acid in two steps was used to anchor amino functions (Scheme 23) [62]. Cleavage was accomplished by oxidation of the thioether to the sulfone with m-chloroperbenzoic acid followed by 13-elimination with a 10% solution of NH4OH in 2,2,2-trifluoroethanol. A linker based on l-(4,4 -dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) primary amine protecting group was developed for attaching amino functions (Scheme 24) [65]. Linker 54 was stable to both acidic and basic conditions and the final products were cleaved from the resin by treatment with hydrazine or transamination with ra-propylamine. 

A gas liquid chromatographic assay for determining the quantity and composition of fatty acids is based on conversion of the acids by means of CDI with methanol, ethanol, trifluoroethanol, pentafluoropropanol, or heptafluorobutanol into the corresponding esters. The alcohols in question were chosen because of the short retention times of their esters.1333... 

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. 

Fig. 5 Logarithmic plots of rate-equilibrium data for the formation and reaction of ring-substituted 1-phenylethyl carbocations X-[6+] in 50/50 (v/v) trifluoroethanol/water at 25°C (data from Table 2). Correlation of first-order rate constants hoh for the addition of water to X-[6+] (Y) and second-order rate constants ( h)so1v for the microscopic reverse specific-acid-catalyzed cleavage of X-[6]-OH to form X-[6+] ( ) with the equilibrium constants KR for nucleophilic addition of water to X-[6+]. Correlation of first-order rate constants kp for deprotonation of X-[6+] ( ) and second-order rate constants ( hW for the microscopic reverse protonation of X-[7] by hydronium ion ( ) with the equilibrium constants Xaik for deprotonation of X-[6+]. The points at which equal rate constants are observed for reaction in the forward and reverse directions (log ATeq = 0) are indicated by arrows.

Fig. 14 Typical log k/YBr plots for assisted and unassisted alkene brominations. Allylbenzene and 1-pentene, less crowded than cis-methyl-t-butylethylene and methylideneadamantane, exhibit the smallest m-values. The points corresponding to acetic acid (O) and trifluoroethanol (A), two weakly nucleophilic solvents, are below the regression line for water, methanol, ethanol and their aqueous mixtures ( ) of similar nucleophilicity. In contrast, they are on the line for the branched alkenes where steric crowding inhibits nucleophilic assistance by alcoholic solvents (Ruasse et al, 1991, Ruasse and Motallebi, 1991).

It should be noted at this point that primary and secondary reaction products can be distinguished not only by kinetic data (13) but also by suppression of the secondary reactions. E.g substitution of 2,2,2-trifluoroethanol for p-dioxane as solvent for HCoCCO) suppresses homologation and methane formation addition of a phosphine to give the less acidic catalyst HCo(CO)3PR3 has the same effect, as has the substitution of the less acidic catalyst HMn(CO)5. 

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