Platinum trifluoroacetates

Trifluoroacetic acid is the best solvent for several platinum-catalysed hydrogenation processes. For example the rate of reduction of ketones to secondary alcohols is about three times faster than in acetic acid. The ketones are taken in concentrated solutions to keep the reactions faster. 

In a potassium acetate-acetic acid medium, 2-fluoro- and 4-fluoroanisole can be oxidized at platinum to afford 2-acetoxy- and 4-acetoxyanisole, respectively [19]. Using a platinum anode in a trifluoroacetic acid-potassium tri-fluoroacetate solution, Blum and Ny-berg [20] electrooxidized hexafluoroben-zene to tetrafluorobenzoquinone in 75% yield, and octafluoronaphthalene was converted into hexafluoronaphthoquinone in 60% yield. 

Reaction conditions used for reduction of acridine [430,476, partly hydrogenated phenanthridine [477 and benzo f]quinoline [477 are shown in Schemes 38-40. Hydrogenation over platinum oxide in trifluoroacetic acid at 3.5 atm reduced only the carbocyclic rings in acridine and benzo[h]quinoline, leaving the pyridine rings intact [471]. 

Quinazoline was reduced by hydrogen over platinum oxide to 3,4-dihydro-quinazoline [489], and by sodium borohydride in trifluoroacetic acid to 1,2-dihydroquinazoline [490]. 

The analogous platinum complexes could be synthesized by a new synthetic route and have been structurally characterized [58], but can not be used as catalysts, since they immediately decompose in trifluoroacetic acid under formation of platinum black, whereas compoimds 18-22 form clear yellow solutions in the same solvens, which even after 20 hours do not show signs of decomposition according to a NMR analysis. Reprotonation of the carbene ligands to the corresponding bisimidazoUum salts can be excluded. The complexes are also stable against the addition of strong oxidants and no precipitation of palladium(II) salts was observed. 

Benzo ring reduction in acridine can be achieved in a variety of ways. 1,4,5,8-Tetrahydro-acridine is given by lithium in liquid ammonia and ethanol (Scheme 35) (69AJC1105). The symmetrical octahydroacridine (48) can be obtained by hydrogenation of acridine over platinum oxide in trifluoroacetic acid. The product is obtained in quantitative yield (Scheme... 

Benzo ring reduction is the main pathway in the platinum-catalyzed hydrogenation of benzo[ft]quinoline (54) in the presence of trifluoroacetic acid the products are shown in Scheme 39 (75JOC2729). 

Fig. 7. Comparison of experimental phase boundary concentrations between the isotropic and biphasic regions for various liquid-crystalline polymer solutions with the scaled particle theory for wormlike hard spherocylinders. ( ) schizophyllan water [65] (A) poly y-benzyl L-glutamate) (PBLG)-dimethylformamide (DMF) [66-69] (A) PBLG-m-cresoI [70] ( ) PBLG-dioxane [71] (O) PBLG-methylene chloride [71] (o) po y(n-hexyl isocyanate) (PHICH°Iuene at 10,25,30,40 °C [64] (O) PHIC-dichloromethane (DCM) at 20 °C [64] (5) a po y(yne)-platinum polymer (PYPt)-tuchIoroethane (TCE) [33] ( ) (hydroxypropyl)-cellulose (HPC)-water [34] ( ) HPC-dimethylacetamide (DMAc) [34] (N) (acetoxypropyl) cellulose (APC)-dibutylphthalate (DBP) [35] ( ) cellulose triacetate (CTA)-trifluoroacetic acid [72]...

Recent studies have shown that the reaction, as described by Eq. (11), also requires Pt(II) as a necessary catalyst (29, 84). A range of substituted benzenes has been examined, and by studying concurrent hydrogen-deuterium exchange, it was concluded that the two reactions had common intermediates (29). In this work aqueous acetic acid was used as the solvent, and reactions were followed by measuring the concentration of the chlorobenzene product. Of the several possible mechanisms for the oxidation that have been given (29), only one will be considered here this is the one that has received substantial support from the most recent work (84). In this study, the loss of reactant benzene, the formation of product chlorobenzene, and the formation of platinum(II) were monitored as the reaction proceeded. Also aqueous trifluoroacetic acid was used as the solvent, as it is known that acetic acid is oxidized to chloroacetic acid by platinum(IV) (18). 

The addition of trifluoroacetic acid to the palladium or platinum peroxide adducts with electrophilic alkenes results in the formation of epoxide in high yield and with high stereoselectivity.143,148 The mechanism shown in equation (51) has been suggested for this reaction.148... 

Platinum f-butyl peroxide trifluoroacetate, (CF CC PtlOOCCCh KCHaV COH j 2 (1). Mol. wt. 1168.72, orange powder. This peroxidic complex is prepared by the reaction of f-butyl hydroperoxide with (norbornadiene)Pt(CF3C02)2. 

METHYL KETONES 1-Chloro-l-(trimethylsilyl)ethyllithium. Palladium(II) chloride-Silver(I) acetate. Platinum t-butyl peroxide trifluoroacetate. 

The electrochemical behavior of malonyl-a-aminopyridines 661 was investigated by Gullu et al. in acetonitrile or a mixture of trifluoroacetic acid and dichloromethane containing tetrabutylammonium tetrafluoro-borate or triethylammonium trifluoroacetate in a water-jacketed, two-compartment glass cell equipped with a platinum disk anode at 1.50 V (Ag/ Ag+) and a carbon-rod secondary electrode (91T675). Controlled potential anodic oxidation of 661 afforded labile coupled carboxylic acids 662 (R2 = COOH), which easily decarboxylated to compounds 662 (R2 = H) under the work-up conditions. Sometimes, the carboxylic acid 662 (R2 = COOH) could be isolated or when the reaction mixture was treated with methanol, methyl ester 662 (R = H, R1 = Bu, R2 = COOMe) was obtained in 40% yield. 

Alcohols. Trifluoroethanol has been obtained by catalytic reduction of trifluoroacetic anhydride on platinum black.88 This reaction, which... 

Hypoxanthine (2 g) in trifluoroacetic acid (40 ml) was stirred and hydrogenated (100 bar/35°C/21 hr) over platinum oxide (0.1 g).31 The catalyst was filtered and the trifluoroacetic acid stripped under vacuum. The product was shown (potentiometric titration) to contain 1.9 moles of TFA. 

Hydrogenation of 2- and 4-phenyl- or -benzylpyridines usually occurs preferentially in the pyridine ring.18,27,29 In trifluoroacetic acid over platinum oxide, however, 4-phenyl- and 4-(3-phenylpropyl)pyridines gave the products hydrogenated in the benzene ring in 87 and 96% yields, respectively. The hydrogenation of 2-phenylpyridine... 

Tetrahydroacridine was hydrogenated to conditions employed. On the other hand, the hydrogenation of acridine over platinum oxide in trifluoroacetic acid leads to quantitative formation of. s-octahydro derivative (eq. 12.52).37... 

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