Acetic Acid, trifluoro

TABLE in-32. PHENYLATION OF THIAZOLE AND ALKYL-THIAZOLES IN TRIFLUORO ACETIC ACID SOLUTION WITH BEN20YLPEROXIDE (COM-PEirnON WITH BENZENE) AT 80°C (196). 

BBr3, CH2CI2, -10°, 1 h -> 25°, 2 h, 80-100% yield. Benzyl carbamates of larger peptides can be cleaved by boron tribromide in trifluoro-acetic acid, since the peptides are more soluble in acid than in methylene chloride. ... 

Figure 3 Reversed-phase chromatography of products after alkaline hydrolysis of /3-poly(L-malate), Discrete polymer products are formed, which differ in length by several units of L-malate. The absorbance at 220-nm wavelength was measured, (a) /3-Poly(L-malate) before hydrolysis, (b) After 10-min incubation in 20 mM NaOH at 37°C. (c) After 15 h in 20 mM NaOH at 37°C. (d) After I h in 500 mM NaOH at 100°C. High pressure chromatography (HPLC) on Waters reversed-phase Ci8- i-Bondapak. The methanol gradient (in water-trifluoro acetic acid, pH 3.0) was programmed as follows 0-40 min 0.3-23%, 40-47 min 23-40%, 47-49 min 40%, 49-54 min 40-0%. (d) Inset size exclusion chromatography after 3-min alkaline hydrolysis at pH 10.2. BioSil SEC 250 column of 300 mm x 7.8 mm size, 0.2 M potassium phosphate buffer pH 7.0.

Amino groups are often protected as their tert-butoxycarbonvl amide, or Boc, derivatives. The Boc protecting group is introduced by reaction of the amino acid with di-fert-butyl dicarbonate in a nucleophilic acyl substitution reaction and is removed by brief treatment with a strong organic acid such as trifluoro-acetic acid, CF3C02H. 

This method has been extended to include imines other than A -thia-zolines, hence enabling the synthesis of multi ring-fused 2-pyridones (28,30, and 33, Scheme 8). Thus, by reacting dihydroisoquinoUnes 27 or /1-carboUnes 29 with acyl Meldrum s acid derivatives 24, a set of new ring-fused heterocycles was prepared in moderate to excellent yields (a and b. Scheme 8). These systems were prepared by using trifluoro acetic acid (TFA) as a proton source instead of solutions saturated with HCl (g). The switch of acid proved to be advantageous since it reduced the formation of by-products and increased the isolated yields. From a practical point of view, TFA is also su-... 

When double bonds are reduced by lithium in ammonia or amines, the mechanism is similar to that of the Birch reduction (15-14). ° The reduction with trifluoro-acetic acid and EtsSiH has an ionic mechanism, with H coming in from the acid and H from the silane. In accord with this mechanism, the reaction can be applied only to those alkenes that when protonated can form a tertiary carbocation or one stabilized in some other way (e.g., by a OR substitution). It has been shown, by the detection of CIDNP, that reduction of a-methylstyrene by hydridopenta-carbonylmanganese(I) HMn(CO)5 involves free-radical addition. ... 

The primary rearranged products 71, 75,76, 77, 78 were converted to the corresponding ketones, 73, 80, 81, and the primary acyclic products 72 and 79 into their respective acyclic alcohols, 74 and 82. As the solvent polarity increased and the nucleophilicity decreased from acetic to formic to trifluoro-acetic acid, the rearranged products increased significantly from 27% to 91% for 69 and from 60% to 100% in the case of 70. The formation of the rearranged... 

HPLC High Performance Liquid Chromatography LHRH Lutenizing Hormone Releasing Hormone PTC Phase transfer catalyst SPPS Solid Phase Peptide Synthesis TFA Trifluoro acetic acid... 

The rate of solvolysis of the phosphinic chlorides (83a, b) in trifluoro-acetic acid and aqueous acetone (the composition of the latter solvent being chosen such that the rate of S nI solvolysis of Bu Cl was the same in both) have been examined to assess the possible operation of an 5 n1(P) ionization mechanism. In the more nucleophilic aqueous acetone solvent,... 

The successfully generated chalcones could be cleaved by treatment with trifluoro-acetic acid or used for the subsequent synthesis of pyrimidines [45], Condensation of the polymer-bound chalcones with benzamidine hydrochloride under microwave irradiation for 30 min furnished the corresponding pyrimidines in good yields after TFA-induced cleavage. This new robust support/linker system for SPOT synthesis has been demonstrated to be compatible with a range of organic reactions and highly applicable for microwave conditions. 

The resultant resins were separately treated with trifluoro-acetic acid water (95 5 v/v) (2 mL) for 5 min at ambient temperature and filtered. In each case, the filtrate was collected into a preweighed test tube. The resin was washed with an... 

Fig. 2.5.11. (a) APCI-LC-MS(+), (b) ESI-LC-MS(-t-), (c) ESI-LC-MS(+), (d) ESI-LC-MS(+), (e) APCI-LC-MS(—) and (f) ESI-LC-MS(—) reconstructed ion chromatograms (RIC) of methanolic solution of the household detergent mixture as in Fig. 2.5.2. Chromatographic conditions (a), (b), (e), and (f) RP-Cig, methanol/water gradient elution (c) ion-pairing RP-Cla using trifluoro acetic acid (TFA) (5 mmol), methanol/water gradient elution (d) isocratic elution performed on PLRP-column, eluent methanol/water methane...

Figure 3.15 Chromatogram of fibre-type proteins on polystyrene gels having different pore sizes. Column A, PLRP-S 300 A, 15 cm x 4.6 mm i.d. B, PLRP-S 1000 A (polystyrene gel), 15 cm x 4.6 mm i.d. eluent, 15 min linear gradient from 20% of 0.25% trifluoroacetic acid to 60% of 0.25% trifluoro-acetic acid in 95% aqueous acetonitrile flow rate, 1.0 ml min-1 detection, UV220 nm. Peaks 1, collagen (Mr 120 000) and 2, fibrinogen (Mr 340 000). (Reproduced by permission from Polymer Laboratories data)...

As observed, aromatic hydrocarbons gave products of protonation on dissolution in hydrofluoric acid. Oxidation into aromatic cation-radicals did not take place (Kon and Blois 1958). Trifluoro-acetic acid is able to transform aromatics into cation-radicals. This acid is considered a middle-powered one-electron oxidant (Eberson and Radnor 1991). Its oxidative ability can be enhanced in the presence of lead tetraacetate. This mixture, however, should be used carefully to avoid oxidation deeper than the one-electron removal. Thus, oxidation of 1,2-phenylenediamine by the system Pb(OCOCH3)4 -I- CE3COOH -P CH2CI2 leads to the formation of either primary or secondary cation-radicals. The primary product is the cation radical of initial phenylenediamine, whereas the secondary product is the cation radical of dihydrophenazine (Omelka et al. 2001). Sulfuric acid is also used as an one-electron oxidant, especially for aromatic hydrocarbons. In this case, generation of cation radicals proceeds simultaneously with the hydrocarbon protonation and sulfonation (Weissmann et al. 1957). 

The monocation [61] and the dication [62] of 2-aminopyrimidine have been fully characterized by nmr (Wagner and von Philipsbom, 1970). The monocation [61] is present in trifluoro-acetic acid, but the two NH2-protons remain equivalent even at low... 

Thianthrene, 68 X = Y = S, radical-cation is obtained by oxidation in trifluoro-acetic acid containing perchloric acid and the evaporation of the solvent [232], It shows electrophilic behaviour on the sulphur atom. When the electrochemical oxidation of thianthrene is carried out in aqueous acetic acid, the monoxide is obtained... 

The addition of phosphine to olefins is accelerated by acidic and basic catalysts. Under the influence of non-oxidising acids or Lewis acid such as, for example, methanesulphonic acid, benzenesulphonic acid, trifluoro-acetic acid or boron trifluoride phosphine is quickly added to olefins at pressures of 20-40 at, and temperatures of 30-60 °C. It is assumed that the reaction proceeds via a carbonium ion which is first formed thus ... 

Di-t-butylcyclopenta-l,2,3-dithiazole (52) is protonated reversibly on nitrogen by trifluoro-acetic acid in CDCI3 to produce a violet solution of salt (53) (Scheme 3) <85TL189>. 

Deprotection of urethane-protected tertiary (3-hydroxy amides 37 with trifluoro-acetic acid followed by spontaneous cyclization of the liberated hydroxy amide affords oxazolines 38. The rate of deprotection is further accelerated by the addition of CaCl2. Examples are shown in Table 8.6 (Fig. 8.4 Scheme 8.15). 

HPLC water containing 005%trifluoro-acetic acid Lichrospher Cl 8 (5mm, 250 mm x 4.6 mm 1 D.) Himatanthus sucuuba/ bark and latex methanol/ water (1 1) plumieride, isoplumieride and demethylplumieride [73]... 

In another study, 25 was found to rearrange to a mixture of 135 and 136 (Scheme 45).84 In the thermal reaction, 136 increased at the expense of 135 with increasing solvent polarity, showing that migration to C involved a more polar transition state. With increasing acid concentration [trifluoro-acetic acid (TFA) in dioxane] the rate of reaction increased rapidly, and the isomer ratio 135 136 changed from 78 22 in pure dioxane to 10 90 in 5 AT... 

Figure 13. Comparison of UV and MS chromatograms using a 1.0-mm i.d. column packed with a 5-pm diameter Supelcosil C-18. LC-MS interface used aerosol spray deposition on a moving belt. Peaks correspond from left to right to 0.2 pg each of resorcinol, 1,5-dihydroxynaphthol, and 2-methyl-phenol. Conditions 41% acetonitrile and 59% water (v/v) with 0.1% trifluoro-acetic acid at a flow rate of 40 pL/min. A, UV trace at 280 nm, 0.015 AUFS B, MS trace, selected ion chromatogram. (Reproduced from reference 54.

Anodic oxidation of 4 -substituted 2-nitrobenzenesulfenanilide in CH3CN-ethyltributylammonium trifluoromethanesulfonate, containing 1% trifluoro-acetic acid and 1% trifluoroacetic anhydride, is reported to give 2,7-disubsti-tuted phenazines in 24-56% yield.113... 

To a solution of 2-(trimethylsilyl)ethyl CMmethyl 5-acetamido-4,7,8,9-tetra-0-acetyl-3,5-dideoxy-D-g/ycero-a-D-galacto-2-nonulopyranosylonate)-(2->3)-2,4,6-tri-0-benzoyl-P-D-galactopyranose (295 mg, 0.28 mmol) in 2 mL of dichloromethane was added trifluoro-acetic acid (2 mL) at 0°C, and the stirring was continued for 2 h at 0°C. Ethyl acetate (3 mL) and toluene (3 ml) were added and the solvents were evaporated. A second portion of toluene was added and the evaporation was repeated. Purification by flash chromatography on silica gel column with dichloromethane-methanol (20 1) gave the hemiacetal 21 (267 mg, quantitative) mp 85°C. 

The protonation of the analogous titanocene complex 55 with trifluoro-acetic acid led to similar products methanethiol and bis(trifluoroacetato) titanocene. When 55 was treated with Mel, rather than the corresponding iodide complex, the cationic Me+ adduct 123 was obtained with iodide as a counterion. However, the acylation of 55 with acetyl chloride afforded the chloride 124 related to 122 (Scheme 30).67... 

Triazine furnishes the species 31 when a solution in trifluoro-acetic acid is titrated with water. The new upheld signals thus produced in PMR spectra are not seen when the hydrogen atom on C-5 is replaced by a methyl group. The hydration is reversible by basification.53 Acidification of an aqueous solution of the anhydrous sodium salt of 3-hydroxy-l,2,4-triazine precipitated a hydrate of the neutral species, and elemental analysis combined with PMR (r5 4.62) indicated structure 32. This substance was not dehydrated during sublimation or heating in distilling toluene.54... 

HPLC analysis. The HPLC system consisted of a Waters 590 chromatography pump, a Waters R401 differential refractometer and a Perkin Elmer ISS-100 autosampler. A Biorad HPX87H column (strong ion exchange resin in H+ form) was used with 3 10 3 M trifluoro acetic acid as mobile phase at 60 °C. 

The separation of protein test mixtures on very short C 8 columns yielded surprising results (Fig. 18). The resolution obtained with a 6.3 x 4.6 mm column was about 2.25 or 2.22 times better than with a 45 x 4.6 mm column when the flow rate was low (0.25 or 0.5 ml/min, respectively) and the volumetric gradient rate large (16% B/ml). The gradient components were A water and B 2-propanol, both with 0.1% trifluoro-acetic acid (TFA)73). Even a column (better to say, a disk) 1.6 mm in length and 4.1 mm in diameter was effective in separating ribonuclease A, cytochrome C, and ovalbumin. Of course, the sample capacity of such a short column was very low 73). 

Polymerization of styrene initiated by trifluoro-acetic acid (3) is another example of the same phenomenon. Addition of styrene to tri-fluoroacetic acid yields polystyrene of M. W. 20,000 to 30,000 while the addition of trifluoro-acetic acid to styrene does not produce any polymer Trifluoro-acetate counter ions, formed in the first process, are strongly stabilized by the solvent (trifluoro-acetic acid) through powerful hydrogen bonds, and hence their capacity to recombine with the growing carbonium ion is greatly reduced. In the second process, the counter ions are formed in a hydrocarbon millieu (styrene) of low solvation power. Their recombination with carbonium ions remains therefore unhindered and consequently the formation of a polymer is prevented. 

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