Methyl trifluoroacetate

Irradiation at 20 C of perfluoro ethers containing a carbonyl group causes almost quantitative decarbonylation [179. Azindine undergoes photochemical addition with methyl trifluoroacetate [180 (equation 47). 

Thus curvature in an Arrhenius plot is sometimes ascribed to a nonzero value of ACp, the heat capacity of activation. As can be imagined, the experimental problem is very difficult, requiring rate constant measurements of high accuracy and precision. Figure 6-2 shows a curved Arrhenius plot for the neutral hydrolysis of methyl trifluoroacetate in aqueous dimethysulfoxide. The rate constants were measured by conductometry, their relative standard deviations being 0.014 to 0.076%. The value of ACp was estimated to be about — 200 J mol K, with an uncertainty of less than 10 J moE K. ... 

Figure 6-2. Curved Arrhenius plot for the hydrolysis of methyl trifluoroacetate in dimethylsulfoxide-water (mole fraction water = 0.973). ...

An alternative technique to NMR spectroscopy is chromatography. The partially functionalized sample is completely fimctionahzed with a group different from the one present, the product carefully de-polymerized, its structure examined with a chromatographic technique. For example, partially substituted CA was further derivatized with methyl vinyl ether, the product hydrolyzed, the monomers produced examined with gas chromatography [241]. HPLC has been advantageously applied for the determination of substitution pattern for CAs with DS 0.8 to 3.0, by employing the same approach, i.e., further derivatization of the partially derivatized polymer with methyl trifluoroacetate, followed by de-polymerization. The results obtained by this technique compared favorably with those obtained by NMR [242]. 

Kutsuna, S., Chen, L., Ohno, K., Tokuhashi, K., and Sekiya, A. Henry s law constants and hydrolysis rate constants of 2,2,2-trifluoroethyl acetate and methyl trifluoroacetate, Atmos. Environ., 38(5) 725-732, 2004. 

If the monomer is the trne reacting species and the reaction of the monomer with an electrophile is fast enough compared to the monomer-aggregate eqnilibrinm, then the rate should be independent of the electrophile concentration. This was indeed fonnd for the reaction of BuLi with methyl trifluoroacetate in diethyl ether the reaction was extremely fast (18.5 s at — 28 °C) and was 0th order with respect to the ester concentration. Reaction of benzonitrile with BuLi in diethyl ether was slower, bnt the rate increased with increasing the benzonitrile concentration and reached a maximnm valne similar to that (7 X 10 s at —82°C) with methyl trifinoroacetate and the reaction order approached 0. Thus, the rate-determining step for the reaction of benzonitrile changed with its concentration. 

Vanadium-catalyzed hydroxylation of benzene and cyclohexane has also been obtained with in situ generation of hydrogen peroxide from H2/O2 in the presence of palladium. A similar process has been settled for methane oxygenation to methyl trifluoroacetate and formic acid. Monoperoxovanadate, as well as copper hydroperoxides, have been indicated as the active species for the activation of the C—H bond of methane. 

Comisarow (1977) has shown that, in the gas phase, methoxide ions react readily with methyl trifluoroacetate and methyl benzoate by an SN2 mechanism, while no reaction is observed as a result of nucleophilic displacement at the carbonyl centre. As for the case above, the SN2 reaction is highly exothermic, while the same is not true for the equivalent of reaction (64b). There is at present no satisfactory explanation of why (64a) apparently proceeds very slowly in the gas phase. 

Fig. 12. First-order rate coefficients for the hydrolysis of weakly basic esters, as a function of acid concentration. Data for phenyl and methyl trifluoroacetates in HCIO, in 70% dioxan-water at 0°C (from refs. 89 and 90). and for o-nitrophenyl hydrogen oxalate in aqueous HCI at 25.5°C (from ref. 171 corrected for the reaction of the anion using pA", = 0.35).

The homologous azirine (143) with a one-atom bridge gave quite different results.70 Photolysis led to the 3,5-fused bicyclic dihydropyrrole (144). The isomeric azirine (145) also led to (144), although the initial products included dihydropyrrole (146) which apparently converted to (144) as photolysis continued. Azirines (143) and (145) were shown to not interconvert and die postulated two discrete azomethine ylides were trapped with methyl trifluoroacetate. Formation of dihydropyrrole (144) was explained based on a two-step cycloaddition process involving a common diradical intermediate. The observation of (146) from photolysis of (145) but not (143) can be explained based on extinction coefficient differences. Azirine (145) has a high extinction coefficient as does (146). The initial product (146) can then be optically pumped to (144) with a low extinction coefficient. Azirine (143) also has a low extinction coefficient and any (146) that formed from it would be optically pumped to (144) before observa-... 

This form of activated DMSO is stable below —30°C, but suffer a Pummerer rearrangement above this temperature, resulting in the formation of methylthio-methyl trifluoroacetate (23). In fact, compound 23 reacts with alcohols in the presence of an amine, resulting in a very quick trifluoroacetylation. However, this trifluoroacetylation pathway is not operative in a properly perfonned Omura-Sharma-Swem oxidation, because alcohols are previously transfonned in afkoxy-dimethylsulfonium salts 24. 

A study of gas-phase reactions of benzyl and methoxide anions with alkyl formate and other esters has revealed some differences in behaviour of these anions of comparable basicity.184 The delocalized benzyl anion and localized methoxide ion engage in exclusive transacylation and proton transfer, respectively, on reaction with alkyl formates. However, proton transfer is sufficiently exothermic to dominate when benzyl anion reacts with methyl acetate. Both anions react with methyl benzoate, methyl trifluoroacetate, and methyl cyanoformate by competing transacylation and S 2 reactions. 

Methyl formate Methyl acetate Methyl propionate Methyl isobutyrate Methyl difluoroacetate Methyl trifluoroacetate Methyl monochloroacetate Methyl dichloroacetate Ethyl trichloroacetate Methyl trichloroacetate Methyl cyanoacetate Methyl methoxyacetate Methyl benzoate... 

The rate constant for the hydrolysis of t-butyl chloride at 298 K decreases as x2 increases in DMSO + water mixtures (Heinonen and Tommila, 1965). A clear-cut contrast between TA and TNAN mixtures is shown by the volumes of activation and related parameters for the solvolysis of benzyl chloride in acetone + water (TA) and DMSO + water mixtures (Fig. 57). Thus, in the latter system, the curves show no marked extrema but there is a shallow minimum in AV near x2 = 0 4. Extrema in Sm AH and T. 5m AS for the hydrolysis of benzyl chloride are also smoothed out when the co-solvent is changed from acetone to DMSO (Tommila, 1966). A similar trend is observed in the kinetic parameters for the hydrolysis of chloromethyl and methyl trifluoroacetates (Cleve, 1972a). For example, in the case of the chloro derivative, 6mACp decreases gradually over the range 0 < x2 < 0-2 for DMSO + water mixtures, whereas a minimum is observed in this range for acetone + water mixtures. 

Methylene-1-oxo-1,2,3,4-tetrahydro-naphthalene l(2//)-Naph-thalenone, 3,4-dihydro-2-methylene- (8,9) (13203-73-1) N-Methylanilinium trifluoroacetate Aniline, A-methyl-, trifluo-roacetate (8) Benzenamine, /V-methyl-, trifluoroacetate (9) (29885-95-8)... 

Trifluoroacetic acid at 300-390 °C produces mainly carbon dioxide, difluoro-methyl trifluoroacetate, carbon monoxide and trifluoroacetyl fluoride. Blake and Pritchard propose that the decomposition proceeds through the elimination of hydrogen fluoride, followed by the formation of difluorocarbene which largely adds to trifluoroacetic acid to form the difluoromethyl ester. The kinetic order is about 0.5 and the overall activation energy for the formation of carbon dioxide and the difluoromethyl ester is about 45 kcal.mole" ... 

Problem 21.5 Methyl trifluoroacetate, CFiCOOCH , is more reactive than methyl acetate, CH3COOCH3, in nucleophilic acyl substitution reactions. Explain. 

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