Trifluoroacetic acid on the

We have examined the effect of temperature and enzymes and other materials on the spectrum of the membrane fragment (4). As the temperature increases up to 120°C. the lipid chain [CH2]n signal becomes more prominent, suggesting that, at lower temperatures, the polymethylene chain is somehow inhibited in its molecular freedom. Treatment with phospholipase C removes the peak at 6.7t which we associate with the choline protons. Urea, which is known to have an unfolding effect on proteins, produces new peaks in the spectrum of the membrane which can be assigned to some of the constituent amino acids of the protein. There is, however, no marked increase in the polymethylene chain signal. The effect of trifluoroacetic acid on the membrane is to increase the intensity of the peak associated with the constituent amino acids of the protein, and now the polymethylene chain of the lipid is also clearly visible. 

The diarsaferrocenes also undergo deuterium exchange in di-trifluoroacetic acid On the contrary, 2,2, 5,5 -tetramethyl-l,l -distibaferrocene is destroyed by strong Lewis acids ... 

Methyl phenylpropiolate reacts with the selenolate PhC=CSe to give the diselenole (224). The action of trifluoroacetic acid on the tellurium analogue PhC=CTe Na" results in a mixture of ( )- and (Z)-ditellurafulvenes (225). The bis(ditelluro)tetracene (226) has been prepared by treatment of the corresponding tetrachlorotetracene with sodium telluride. ... 

Aniline that is orf/io-substituted with a hexa-2,5-dienyl side-chain undergoes catalytic, palladium-assisted cyclization to 2-propylquinoline (Scheme 34) this is only one of a series of ring-closure reactions involving palladium-promoted nucleophilic attack on an alkene. A tetrahydroquinoline (55) is produced by the action of trifluoroacetic acid on the hydroxylamine (54). This method has also been used to prepare l,4-benzoxazines. ... 

Methyl-3,4-dinitropyrrole (170) undergoes some interesting reactions with nucleophilic reagents. With methanolic sodium methoxide it yields a product (171) which on treatment with trifluoroacetic acid gives the 2-methoxypyrrole (172) 78CC564). 

Treatment of the indole derivative 290 with trifluoroacetic acid gave the addition product 291 that upon cyclization afforded the pyridoindole derivative 292 (81H713). Treatment of 290 which has a dioxopiperazine ring on C-3 with boron trifluoride etherate gave a mixture of pyrroloindole 293... 

On heating with sodium borohydride in glacial acetic acid. 5//-dibenz[/t,/ azepine (5) undergoes sequential acylation and reduction to yield 5-ethyl-5/7-dibcnz[A,/ ]azepine (8, R = Et).192 Similarly, reduction in trifluoroacetic acid produces the trifluoroethyl derivative 8 (R = CF3CH2 61% mp 69-70 C).193... 

The effect of catalysis by trifluoroacetic acid on chlorination in carbon tetrachloride has also been determined272. For 1,2,4,5-tetramethylbenzene, with low concentrations of catalyst, the order in catalyst is three-halves, but for toluene (which requires a higher concentration) the order is mixed three- and five-halves the indication is, therefore, that a minimum of three catalyst monomers (or one monomer and one dimer) are necessary. Since trifluoroacetic acid is very likely to be dimeric in carbon tetrachloride, the concentration of monomer is pro-... 

The effect of the buffer on the efficiency of electrospray ionization was mentioned earlier in Section 4.7.1. This is a good example of the dramatic effect that this may have - good chromatographic separation and ionization efficiency with formic, acetic and propionic acids, and good separation, although with complete suppression of ionization, with trifluoroacetic acid (TFA), the additive used for the protein application described previously. Post-column addition of propionic acid to the mobile phase containing TFA has been shown to reduce, or even... 

Several procedures were developed for the transformation (223—>-224). The most commonly used procedures are based on treatment of the nitroso acetal with benzene saturated with HC1 (204, 205) and by the addition of a catalytic amount of para -toluenesulfonic acid or trifluoroacetic acid (206). The introduction of branched radicals at the silicon atom decelerates elimination of silanol. 

Homoallylic alcohols can readily be prepared from commercially available tetraallytin and acetals or aminoacetals in the presence of trifluoroacetic acid on silica gel this provides an alternative to the reaction of an allylstannane with an aldehyde.278 By a similar mechanism, homoallylic peroxides can be prepared from monoperoxyacetals (Equations (99) and (100)).279... 

General. NMR spectra were obtained on a Bruker WM-250 instrument with tetramethylsilane (TMS) as internal standard. UV-visible spectra were taken on a Varian Cary 219. Fast-atom bombardment (FAB) mass spectrometry (MS) analysis were completed on a Vacuum Generators ZAB-2F double-focusing or a Varian MAT CH5 mass spectrometer equipped with an Ion Tech FAB Gun. Solvents for FAB matrix were made up of thioglycerol, dithiothreitol, and dithioerythretol (2 1 1) addition of 0.1M trifluoroacetic acid to the matrix facilitated the ionization of the porphyrins during FAB analysis.(13)... 

High yields of amines have also been obtained by reduction of amides with an excess of magnesium aluminum hydride (yield 100%) [577], with lithium trimethoxyaluminohydride at 25° (yield 83%) [94] with sodium bis(2-methoxy-ethoxy)aluminum hydride at 80° (yield 84.5%) [544], with alane in tetra-hydrofuran at 0-25° (isolated yields 46-93%) [994, 1117], with sodium boro-hydride and triethoxyoxonium fluoroborates at room temperature (yields 81-94%) [1121], with sodium borohydride in the presence of acetic or trifluoroacetic acid on refluxing (yields 20-92.5%) [1118], with borane in tetrahydrofuran on refluxing (isolated yields 79-84%) [1119], with borane-dimethyl sulflde complex (5 mol) in tetrahydrofuran on refluxing (isolated yields 37-89%) [1064], and by electrolysis in dilute sulfuric acid at 5° using a lead cathode (yields 63-76%) [1120]. 

The acylation of dibenzofuran is carried out under the usual Friedel-Crafts conditions with an acid chloride or an acid anhydride in the presence of aluminum chloride. Dibenzofuran on treatment with 2-trifluoromethane-sulfonyloxypyridine and benzoic acid in boiling trifluoroacetic acid produces the 2-benzoyl derivative in 75% yield. The species responsible for benzoyla-tion is probably a mixed anhydride of trifluoromethanesulfonic acid and benzoic acid. Dibenzofuran on treatment with 2-benzoyloxypyridine and trifluoroacetic acid also produces the 2-benzoyl compound (21%). The kinetics of the acetylation of dibenzofuran with acetyl chloride and aluminum chloride in nitroethane at 25"C have been studied. Only the 2-acetyl compound was detected by the methods used. The rate obtained is in general agreement with the studies mentioned previously. The rate of acetylation of diphenyl ether relative to toluene was 138 (+ 16), whereas that of dibenzofuran was 5.9 ( 0.3). In contrast, the benzoylation of dibenzofuran with benzoyl chloride in the presence of aluminum chloride in nitrobenzene at... 

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