Mercuric trifluoroacetate

The structural elucidation of multiphase polymers is a continuing problem as, at times, the few commonly used staining reagents are not satisfactory. Osmium tetroxide has the widest range of applicability, but there are polymers that cannot be differentiated by this stain. Mercuric trifluoroacetate has been described for the staining of several polymers [154] polystyrene, poly(2,6-dimethyl-l,4-phenylene oxide) and saturated styrene-butadiene-styrene block copolymers (Kraton G, trademark. Shell Oil Company). 

The reaction of mercuric trifluoroacetate is said to take place by electrophilic substitution 

Trimmed and faced blocks are stained by immersion in a 10% solution of HgO in trifluoroacetic acid for 10-60 min. Samples are washed in a dilute solution of trifluoroacetic acid followed by distilled water. Poly(phenylene oxide) (PPO) appears to have a higher mercury uptake than polystyrene in a bonded laminate of the two films [6]. Blends made by coextrusion of Kraton G and PPO show dispersed particles in a matrix. Kraton G is the lighter contrast polymer as it seems to take up less of the stain than the PPO. In summary, mercuric trifluoroacetate staining has been shown for several polymers where the dispersed phase particles are differentiated by this stain. The method has limited application. 

The structural elucidation of multiphase polymers is a continuing problem as, at times, the few 

Unsaturated hydrocarbons, alcohols, ethers, amines Osmium tetroxide 

Unsaturated rubber (resor-cinol-formaldehyde-latex) Ebonite 

Saturated hydrocarbons (PE and PP) Chlorosulfonic acid/ uranyl acetate 

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We saw in Section 7.4 that alkenes react with water in the presence of mercuric acetate to yield a hvdroxymercuration product. Subsequent treatment with NaBH4 breaks the C-Hg bond and yields the alcohol. A similar alkoxymercuration reaction occurs when an alkenc is treated with an alcohol in the presence of mercuric acetate or, even better, mercuric trifluoroacetate, (Cl CCtitiHg. Demercura-tion by reaction with NaBH4 then yields an ether. The net result is Markovnikov addition of the alcohol to the alkene. 

Menthyl chloride, El reaction of, 392 E2 reaction of, 390 Mercapto group, 667 Mercuric trifluoroacetate. 

Reaction schemes. Arenes react with mercuric trifluoroacetate according to the equation29... 

Vinylic halides are unreactive (pp. 428, 433), but they can be hydrolyzed to ketones at room temperature with mercuric trifluoroacetate, or with mercuric acetate... 

Aromatic compounds react with mercuric salts to give arylmercury compounds.69 Mercuric acetate or mercuric trifluoroacetate are the usual reagents.70 The reaction shows substituent effects that are characteristic of electrophilic aromatic substitution.71 Mercuration is one of the few electrophilic aromatic substitutions in which proton loss from the a complex is rate determining. Mercuration of benzene shows an isotope effect kB/kD = 6,72 which indicates that the [Pg.1026]

A specific case of the carbonium ion mechanism [Eq. (5)] with reasonable plausibility is decarboxylation of metal arenoates by classic electrophilic aromatic substitution [Eq. (12)]. This mechanism would be favored by electron-donating substituents and has been invoked to explain the relative ease of decarboxylation of p-methoxybenzoic acid in molten mercuric trifluoroacetate (77) as well as the very facile decarboxylation on reaction of polymethoxybenzoic acids with mercuric acetate (18) (see below). 

When colloidal selenium was heated with mercuric trifluoroacetate or silver trifluoroacetate, bis(trifluoromethyl)diselenide was formed (43). Later work with selenium/silver carboxylate, RC02Ag (R = CF3, C2F5, or C3F7), mixtures at 280° C in a vacuum produced a mixture of the bis(perfluoroalkyl)selenide and the bis(perfluoroalkyl)diselenide (44). Formation of a polyselenium trifluoroacetate, which decarboxylates to produce the trifluoromethylselenides, was the proposed mechanism for R = CF3 (44). However, silver trifluoroacetate is a source of trifluoromethyl radicals when heated above 260° C (21), hence the trifluoromethylselenides may be formed by reaction of trifluoromethyl radicals with selenium, as in the reaction of CF3I with selenium [Eq. (34)] (45). 

Although Hg(02CR)2 (R = m-MeOC6Br4 or o-MeC6Br4) could not be decarboxylated in boiling pyridine and pyridine/nitrobenzene, respectively, the corresponding acids were decarboxylated in molten mercuric trifluoroacetate [Eq. (62)] (75). The products were characterized as the... 

Mercuric carboxylates, which decarboxylate by a chain mechanism when initiated by peroxides, also decarboxylate under UV irradiation (123,128,129,131-140,142,144-146,153-155). In addition, decarboxylation was observed for mercuric benzoate and mercuric a-naphthoate (123). Side reactions [Eqs. (24), (25), (109)] observed in peroxide initiated reactions also occurred on UV irradiation, and mercurous salt formation [Eq.(24)] was more extensive under the latter conditions. Decarboxylation giving methylmercuric acetate occurred on irradiation of mercuric acetate in aqueous solution and is considered to be of environmental significance (156,157). Stepwise decarboxylation giving (CF3)2Hg occurred on irradiation of solid mercuric trifluoroacetate at -196° C (158), but, at 20° C, trifluoromethyl radicals diffused from the solid and dimerized (158). No other diorganomercurial has been formed by radical decarboxylation, and the reaction is not preparatively competitive with the thermal decarboxylation synthesis of (CF3)2Hg (26,27) (Section III,A). 

Diarylthioketones are converted in good yields into orthometallated complexes by diiron enneacarbonyl.141 These in turn can be transformed oxidatively (Ce4+) or photochemically into isobenzothiophenes (see Section IV,C,2), or by reaction with mercuric trifluoroacetate into isobenzofurans (Scheme 78)142 the formation of methoxy esters is a competing process in... 

A stereoselective cyclization of (Z)-(2R,3R,4R)-6-cyclohexyloxy-1,3,4-tribenzyloxy-5-hexen-2-ol promoted by mercuric trifluoroacetate or PhSeCl is successfully achieved (38). 2-Deoxy-0(-hexopyranoside derivative is obtained almost exclusively by the treatment of 22 with mercuric trifluoroacetate followed by reductive work up, while a predominant formation of the 3 3no 6r is achieved by the reaction of 22 with PhSeCl, and the successive deselenylation. 

Mercuric acetate and mercuric trifluoroacetate are the usual reagents.66 The synthetic utility of the mercuration reaction derives from subsequent transformations of the arylmercury compounds. As indicated in Section 7.3.3, arylmercury compounds are only weakly nucleophilic, but the carbon-mercury bond is reactive toward various electrophiles. The nitroso group can be introduced by reaction with nitrosyl chloride67 or nitrosonium tetrafluoroborate68 as the electrophile. Arylmercury compounds are also useful in certain palladium-catalyzed reactions, as discussed in Section 8.2. 

A different approach giving acceptable-to-good yields of NVC, and its 3,6-dihalo, 3,6-dialkyl, and 3,6-diacyl analogs, employed vinyl acetate and mercuric trifluoroacetate in trifluoroacetic acid at 95°C or mercuric acetate in acetone at 20°C, although the former workers state that 39 and 40 are formed when mercuric acetate is used as catalyst. ... 

Allyl alcohols readily react with trichloroacetonitrile to give the corresponding trichloroacetimidates 145. Activation of the double bond with electrophilic reagents results in ring closure to yield oxazolines 146. The most commonly employed electrophiles include iodine, iodine monochloride, phenylselenyl chloride, and mercuric trifluoroacetate. Other nitriles including cyanogen bromide and N,N-dimethylcyanamide can also be used. Since oxazolines readily hydrolyze to amides, the net effect of this reaction sequence is to produce p-amino alcohols 147 from an allyl alcohol. This strategy has been employed in numerous total syntheses of natural products. Examples are listed in Table 8.18 (Fig. 8.7 Scheme 8.43). ° ... 

Anti-Markovnikov hydration of a vinyl chloride via oxymertcuration with mercuric trifluoroacetate in methanol was surprising [128]. However, it might be speculated that solvent modified Hg(II) species show a higher affinity for the chlorine atom than the rc-bond. The resultingchloronium ion is susceptible to attack by methanol in a manner analogous to Michael addition. Ejection of ClHgY is expected to be followed by a 1,2-hydride shift. 

The oxymercuration procedure (with mercuric trifluoroacetate) has been used to open cyclopropane rings, e.g.,158... 

Lactonization Cydization of the thioester 1 cannot be effected with mercuric trifluoroacetate or coppcr(I) trifluroacctatc. The usual reagents used for this reaction (6, 582. 7, 444) are ineffective, but cydization is effected with CuOTf complexed With benzene. Two isomeric lactones (2 and 3) are obtained in 62% yield. One of IhcNC is the acetate, of the pyrrolizidine alkaloid crobarbatine. Unfortunately dcucctylation of these products is accompanied by further hydrolysis to the pyrrolizidine unit (retronecine). 

Alkenes can be converted to ethers by the electrophilic addition of mercuric trifluoroacetate, followed by addition of an alcohol. An organomercuric intermediate is obtained that can be reduced with sodium borohydride to yield the ether ... 

Fig. Synthesis of an ether from an alkene using mercuric trifluoroacetate.

Mercuric trifluoroacetate, Hg(02CCF3)2i Adds to alkenes in the presence of alcohol, giving a-alkoxy organomercury compounds that can be reduced with NaBH4 to yield ethers. The overall reaction effects a net addition of an alcohol to an alkene (Section 18.2). 

In the total synthesis of the macrolide antibiotic methymycin 49), Masamune and coworkers [28] developed a new macrolactonization method which makes use of the electrophilicity of Hg(II) toward bivalent sulfur. It involves the S -f-butyl thiolester 44 of the hydroxy acid 41 and employs mercuric trifluoroacetate as an activating agent. The required S -r-butyl thiolester 44 can be prepared in high... 

In Masamune s methymycin synthesis [28b], the S-r-butyl thioester 47 upon treatment with 2 equiv of mercuric trifluoroacetate in acetonitrile solution (0.01 M) at room temperature for 1 h afforded the lactone 48 in up to 30% yield (Scheme 15). 

Nishimura O, Kitada C, Fujino M. New method for removing the S-p-methoxybenzyl and S-tert-butyl groups of cysteine residues with mercuric trifluoroacetate. Chem. Pharm. Bull. 1978 26 1576-1585. 

Oxidation of hydrazones of benzyl ketones with mercurous trifluoroacetate in refluxing ether or in dioxane at 40-50 °C induces the elimination of nitrogen and formation of acetylenes in moderate yields (equation 109). Oxygenated solvents which... 

Mercurous trifluoroacetate, HgOCOCFs, converts ketone monohy-drazones into acetylenes [ 5],... 

Mercuric trifluoroacetate, Hg(OCOCFj>2> parallels the actions of mercuric oxide. It oxidizes hydroquinones to quinones [353] and hydrazones to diazo compounds [406]. 

Conversion to ortho- and para-quinones is by far the most common oxidation of phenols. Mercuric oxide or mercuric trifluoroacetate [583], lead dioxide [430], chromium trioxide [559], bromine [732], 2,3 dichloro-5,6-dicyano-/> benzoquinone (DDQ) [977], Fremy salt [487, 488, 489], and hydrogen peroxide in the presence of horseradish peroxidase [7958] are the most widely used oxidants (equations 310 and 311). 

Red mercuric oxide is less reactive [387], Less often, oxidations are carried out with silver oxide [370, mercurous tri-fluoroacetate [405], mercuric trifluoroacetate [406], lead tetraacetate [445], manganese dioxide [370], and nickel peroxide [955]. The most common solvents are pentane, petroleum ether, benzene, toluene, ether, and ben-zonitrile. Basic catalysts such as alcoholic potassium hydroxide are sometimes used. Anhydrous calcium oxide, sodium sulfate, and magnesium sulfate are frequently added to remove the water of reaction. The reaction temperatures range from room temperature to the reflux temperature of the solvents. 

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