Trifluoroacetic acid, photolysis

Attempts to effect ring expansion of methyl 2-azidobenzoate in the presence of other nucleophiles have failed. Thus, photolysis in tetrahydrofuran solution saturated with hydrogen sulfide, or with ammonia, produced methyl 2-aminobenzoate in 54 and 37 % yield, respectively, as the sole identifiable product.197 Photolysis of phenyl azide in ethanolic phenol gave 2-phenoxy-3//-azepine in poor yield (8 %).203,204 2-Mesityl-3//-azepine (10 %) is the surprising, and only tentatively explained, product from the photolysis of phenyl azide in mcsitylene in the presence of trifluoroacetic acid.179... 

Ellis DA, S A Mabury (2000) The aqueous photolysis of TFM and related trifluoromethylphenols. An alternate source of trifluoroacetic acid in the environment. Environ Sci Technol 34 632-637. 

The formation of the trinitromethyl adduct of PBN by photolysis of PBN and tetranitromethane (Okhlobystina et al., 1975) is an unequivocal case of inverted spin trapping. These components give an orange-red CT complex in, for example, dichloromethane when this solution is irradiated by light which only can excite the CT complex (A > 430 nm) the spin adduct (N02)3C-PBN is formed via reaction (46) (Eberson et al., 1994b). This adduct is highly persistent. When the solution is acidified by —2% trifluoroacetic acid, irradiation does not lead to spin adduct formation owing to protonation of trinitromethanide ion. 

The low-temperature photolysis at —150 °C in an ethanol-methanol mixture containing trifluoroacetic acid (0.01 M) adds another dimension to nitrosamine chemistry163 irradiation at 313 nm under these conditions gives a new species showing absorption at 391,... 

In the photolysis of difluorodiazirine (218) a singlet carbene was also observed (65JA758). Reactions of the difluorocarbene were especially studied with partners which are too reactive to be used in the presence of conventional carbene precursors, such as molecular chlorine and iodine, dinitrogen tetroxide, nitryl chloride, carboxylic acids and sulfonic acids. Thus chlorine, trifluoroacetic acid and trifluoromethanesulfonic acid reacted with difluorodiazirine under the conditions of its photolysis to form compounds (237)-(239) (64JHC233). 

The transient absorption spectrum of CF2 has been observed following the flash photolysis of trifluoroacetic acid under isothermal conditions 13... 

Compound (159) has an IR band at 1070 cm-1, in neutral solution or the solid state, consistent with the tetrazole structure. In trifluoroacetic acid this band is replaced by a typical azide absorption at 2140 cm-1. Only in this solvent will photolysis give a good yield (91%) of the pyrimidinoindole (160) (72JOC3216). 

Photolysis of these derivatives (at 300 nm in either acetic acid or acetonitrile in the presence of 1 M trifluoroacetic acid) produces a loss of C02. Intramolecular cyclization onto the imine moiety then leads to annulated compounds 72 (Scheme 12.21) [48],... 

In a study of the Hofmann-Loffler reaction, the jV-chloro-amine (8a) was irradiated in trifluoroacetic acid solution and underwent photolysis to yield the pyrrolidine (9a) together with the 205-isomer (9b) in a ratio 8 1. The starting amine (8b) was prepared by hydrogenation of (8c), followed by von Braun demethylation and hydrolysis of the JV-cyano-amine (8d) which was so formed. The n.m.r. spectrum of (8b) and of related amines in the presence of lanthanide shift reagents was discussed.10... 

A photoinduced electron transfer mechanism has been proposed by de Mayo and coworkers to explain the products arising from the irradiation of 1,1-di-p-anisylethene in benzene-trifluoroacetic acid solutions [73]. Photolysis (>430 nm) of the (di-p-anisylmethyl)methyl cation 30 resulted in electron transfer from the neutral substrate 29 as shown in the Scheme 10. No reaction occurred under these conditions in the absence of acid. The quantum yields of the photoproducts are... 

Photolysis of aromatic Schiffs bases in strongly acidic media results in cyclisation to phenanthridines (A. Padwa. Chem. Rev.. 1977, 77, 37). Irradiation of anils of polyfluoroaromatic ketones in trifluoroacetic acid also yields phenanthridines by oxidative cyclisation examples are quoted which involve cleavage of a C-F bond (N. I. Danilehko et al., Izvestia, 1980, 1606). 

Venkatasubramanian and Krishnamachari required deuterated oxazoles for a study of the flash photolysis of oxazole 1. They obtained (2-D)-oxazole 593 exclusively from 1 using CF3COOD and D2O (Scheme 1.162). The authors did not speculate about this surprising result. The reaction is selective for monodeu-teration, but 1 also suffers decomposition (up to 40%) under the reaction conditions leading to a mixture of 593 and deuterated pyrazines 594 n = 0-4. Trifluoroacetic acid-D was much more efficient than deuterosuUuric acid for this reaction. 

Aryl azides undergo indolization upon photolysis, and several examples are known (Scheme 8) [67-70]. Thus, p-phenyl-substituted (Me, OMe, Cl) azidopyrimi-dines 11 were converted to the corresponding 9H-pyrimido[4,5- ]indole (equation 1) [67, 68]. The azide precursor is in equilibrium with the ring-opened 8-phenyltetrazolo[l,5-c]pyrimidine (10) (in trifluoroacetic acid). Similarly, Da Settimo and colleagues synthesized the new ring system 67/-indolo[2,3- ][l,8]naphthyridine 12 by photolysis in trifluoroacetic acid of the equilibrium mixture of 4-phenyltetrazolo[l,5-fl][l,8]naphthyridines... 

Azides that are a- to a pyridine-like nitrogen usually exist predominantly in the tetrazole form and so difficulties are often encountered in their photolysis. Photolysis of tetrazoles has been found to be facilitated by the use of trifluoroacetic acid as solvent which converts the tetrazole to azide before nitrogen is lost ... 

Fig. 6.21 Time-resolved UV-visible spectra of l-cyclobutyl-2,4,6-trimethoxybenzenium ion obtained after 308-nm laser flash photolysis of oxadiazoline (34, R, R = (CH2>3) in hexafluor-oisopropanol containing 1.34 M trimethoxybenzene and 0.002 M 34 at 22 C. The data were collected at intervals of 260 ns open circles), 620 ns filled circles), 720 ps open squares), and 2.3 ps filled squares) after the laser pulse. The lower inset shows the time-resolved UV-visible spectra obtained after 308-nm laser flash photolysis of the same oxazoline in hexafluoroiso-propanol containing 0.002 M TFA at 22 °C with the data collected at tire same time intervals. Upper inset shows the time-resolved UV-visible absorption traces (overlayed and normalized) observed at 250 nm (a, stable intermediate b, decay) and 355 (growth) wavelengths following 308-nm laser flash of (a) the oxazoline in hexafluoroisopropanol, (b) in the presence of 0.002 M trifluoroacetic acid, and (c) in the presence of both 1.34 M trimethoxybenzene and 0.002 M trifluoroacetic acid [43]...

The formation of ethane by photolysis of acetic acid in the presence of UO2 presumably involves dimerization of the methyl radical. Support for such a photoreaction comes from electron paramagnetic resonance (EPR) spectroscopy experiments at 77 K where organic radicals are observed in the photolysis of acetic acid, trifluoroacetic acid, and succinic acid in the presence of... 

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