1-Phenyl-2,2,2-trifluoroethanol

The hydrogen-bonding association of amino acid esters with 1-phenyl-2,2,2-trifluoroethanol is sufficient to permit NMR to be used as a method for determining the optical purities of a-amino acids [43]. 

Exercise 19-5 When optically active 1-phenylethanamine is dissolved in racemic 1-phenyl-2,2,2-trifluoroethanol, the 19F nmr resonance shows two sets of doublets separated by 2 Hz at 56 MHz. With the racemic amine, only a doublet 19F resonance is observed. 

The configurations of chiral thiiranes and thiirane 1-oxides can be determined by H NMR experiments in chiral solvents such as (R)-(-)- -phenyl-2,2,2-trifluoroethanol. The... 

More surprising, in view of its poor electrophilic character, is that phcnylnitrene, generated by deoxygenation of nitroso benzene with triethyl phosphite in a mixture of benzene and 2,2,2-trifluoroethanol, yields 1-phenyl-1//-azepine (26), a rare example of a stable 1-aryl-lH-azepine.170... 

Generation of phenylnitrcne by thermal decomposition of phenyl azide in the same solvent mixture, or by deoxygenation of nitrosobenzene with triethyl phosphite in the absence of the trifluoroethanol, fails to yield the 1//-azepine. The role of the alcohol in promoting l//-azepine formation is not understood. 

The 15N content was indeed lower when the experiment was performed This result justified the publication of a preliminary communication (Bergstrom et al., 1974). Later work (Hashida et al., 1978 Szele and Zollinger, 1978a Maurer et al., 1979) involving sophisticated statistical treatments suggested that, in a weakly nucleophilic solvent such as trifluoroethanol, the phenyl cation is formed in two steps and not in one, as in mechanism B (see Scheme 8-4 in Sec. 8.3), the first intermediate being a tight ion-molecule pair. 

The rate and equilibrium constants for the reactions of ring-substituted 1-phenylethyl carbocations (X-[6+]) in 50/50 (v/v) trifluoroethanol/water (Table 2 and Scheme 8),13 14 17 43, and for interconversion of ring-substituted 1-phenyl-... 

As previously mentioned above, the chiral recognition abilities of the phenyl-carbamates of polysaccharides are greatly influenced by the substituents on the phenyl groups. In order to evaluate the effect of the substituents on the interaction between CSPs and solutes, the retention times of acetone and the first-eluted isomer of l-(9-anthryl)-2,2,2-trifluoroethanol (39) on 3- and 4-substituted CSPs are plotted against the Hammett parameter a of the substituents (Figure 3.33).130 The retention times of acetone tend to increase as the electron-withdrawing power of the substituents increases, whereas those of the first-eluted isomer of 39 tend to decrease. These results indicate that... 

By the way, trifluoroacetaldehyde is a versatile fluoro building block. However the chemical or electrochemical oxidative transformation of trifluoro-ethanol to trifluoroacetaldehyde has been unsuccessful. Trifluoroacetaldehyde is therefore generally produced by the reduction of trifluoroacetic acid ester or acid chloride using an excess of LAH. The anodic substitution at fluoroaikyl phenyl sulfides is a useful alternative because it realizes the transformation of economical trifluoroethanol to highly valuable trifluoroacetaldehyde equivalents as shown in Scheme 6.5. 

Interesting results concerning phenyl group participation were observed with ( )-styryl(phenyl)iodonium tetrafluoroborate (26) using a deuterated substrate (eq 12)16 When 26-ad was heated in trifluoroethanol (TFE) at 60 °C, slow reaction gave die E isomer of substitution product 28 quantitatively, but the deuterium was completely scrambled between the a and p positions. This strongly indicates that a symmetrical intermediate is involved during the reaction and the most reasonable one is vinylenebenzenium ion (27) formed by phenyl participation. This intermediate also explain the exclusive formation of the retained ( )-28. 

Xlld does not involve the chiral center, so if the reaction takes place by this pathway, the migration of the alkyl group from sulfur to palladium (with the concomitant or subsequent loss of sulfur dioxide) must take place with inversion of configuration at carbon. Inversion of configuration at carbon has been observed in the reverse-type reaction, the sulfur dioxide insertion into a carbon-iron sigma bond (49). Nucleophilic displacement at carbon in compounds of type Xld is unusually difficult, so the reaction via the sulfite intermediate Xlld would appear to be more likely. Conversion of the tosylate of l-phenyl-2,2,2-trifluoroethanol to the corresponding chloride, a reaction which takes place in the presence of tetra- (n-butyl) ajnmonium chloride with inversion of configuration at carbon, requires 100°C for 24 hrs in dimethylsulfoxide. 

Thus the enantiotopic methyl groups of dimethylsulfoxide form an A3B3 spin system in l-phenyl-2,2,2-trifluoroethanol Figure 1.5 [42] ... 

It is not intended to extend this discussion of reactions of carbocations with water to consideration of the alcoholic solvents trifluoroethanol (TFE) and hexa-fluoroisopropanol (HFIP), which have been extensively studied and reviewed by McClelland and Steenken.3 However, an important point of interest of these solvents is that their reactivities toward carbocations are greatly reduced compared with water (by up to a factor of 104 in TFE and 108 in HFIP) and that differences in rate constants can be observed between cations which would react indiscriminately at the solvent relaxation limit in water. The following comparisons of rate constants for carbocations with similar pAR values reacting with hexafluoroiso-propanol241,242 reinforces the conclusion that structural variations in the cation lead to changes in intrinsic barrier and, for example, that phenyl substitution is probably associated with such an increase in going from benzyl to benzhydryl (although the benzyl cation itself is not shown). 

The thermal decomposition of diazo compounds in the presence of alcohols is a reliable method for the formation of methyl," benzhydryl,"" and phenyl ethers."" Dcdiazonialion of ben-zenediazonium tetrafluoroborate (15) in the presence of 2.2.2-trifluoroethanol gives exclusively ether 16 and fluorobenzene (17) in ca. 2 1 ratio."" ""... 

Under certain conditions the reduction of amides leads to primary alcohols (cf. method 428). Thus, phenylethylacetamide is reduced by sodium and absolute ethanol to 2-phenyl-1-butanol (75%). a-Naphthylacetamide is reduced by sodium amalgam and hydrochloric acid to a-naphthylcarbinol (63%). Trifluoroethanol is obtained by catalytic hydrogenation of tri-fluoroacetamide over a platinum catalyst. Hydrogenation of the corresponding ester over copper-chromium oxide failed. ... 

MILD AND SELECTIVE OXIDATION OF SULFUR COMPOUNDS IN TRIFLUOROETHANOL DIPHENYL DISULFIDE AND METHYL PHENYL SULFOXIDE... 

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