Methyl trifluoroacetate, reaction

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. 

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).

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. 

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

In Table 10 are listed solvent isotope effects for the water reaction, which, with the exception of the acid chlorides, N,0-diacetylserinamide, and methyl trifluoroacetate, have values of two or more. The smaller isotope effects for the acid chlorides are in accord with the partial S l... 

Simply changing the solvent in the Pd-based catalytic system from water to a mixture of water and a perfluorocarboxylic acid (some water was necessary for the reaction, see Scheme 4) had no significant effect on product composition formic acid was still the principal product from methane. However, the addition of copper (I) or (II) chloride to the reaction mixture had a dramatic effect. Methanol and its ester now became the preferred products, with virtually no acetic and little formic acid being formed [42b] The activation parameters for the overall reaction determined under the condition when the rate was first-order in both methane and carbon monoxide were A=2xl04 s 1 Ea=15.3 kcalmol-1. Since methyl trifluoroacetate is both volatile and easily hydrolyzed back to the acid and methanol, it should be possible to design a system where the acid is recycled and methanol is the end-product. 

Mechanism of Chlorination of ajS-Unsaturated Ketones in Methanol and in Trifluoroacetic Acid . Reactivity of Ethylenic Compounds. Bromination. XXXIII. Modification of Reaction Scheme in Trifluoroacetic Acid Solution [rate-determining step in CFj-COsH for bromination of RCHt CHtCHj is the disappearance (mechanism Ad%C, d) of a tight ion pair]. Solvent and Temperature Effects in the Neutral Hydrolysis of Methyl Trifluoroacetate and Chloromethyl Dichloroacetate in Dimethyl Sulphoxide-Water Mixtures . Electron Impact Studies. LiKXXVlII. Formation of an Adduct between the Trifluoroacetate Ion and Perfluoroacetic Anhydride by Ion Cyclotron Resonance . ... 

This reaction is part of the mechanism for reductive eliminations of alkyl halides from Pt(IV). As noted in Chapter 8 (reductive elimination), this reaction occurs by initial dissociation of iodide to generate a cationic Pt(IV) methyl complex and subsequent attack of iodide on the platinum(IV) methyl group to generate methyl iodide (Equation 11.13). The reductive elimination of methyl aryl ethers, methyl acetate, and methyl trifluoroacetate... 

Formation of Methyl Trifluoroacetate. In 1987, the conversion of methane to methyl trifluoroacetate mediated by palladium(II) acetate was reported, but the reaction was not catalytic at that time (eq. (16)) (31-33). 

A monophenylplatinum(ii) complex with trifluoroacetate and dmpe ligands 364, formed in situ from the reaction of benzene with the corresponding methyl(trifluoroacetate)platinum complex 363, undergoes disproportionation into a diphenylplatinum(ii) complex and a bis(trifluoroacetate)platinum(ii) complex (Equation (90)). The disproportionation... 

The blocking and deblocking of carboxyl groups occurs by reactions similar to those described for hydroxyl and amino groups. The most important protected derivatives are /-butyl, benzyl, and methyl esters. These may be cleaved in this order by trifluoroacetic acid, hydrogenolysis, and strong acid or base (J.F.W. McOmie, 1973). 2,2,2-Trihaloethyl esters are cleaved electro-lytically (M.F. Semmelhack, 1972) or by zinc in acetic acid like the Tbeoc- and Tceoc-protected hydroxyl and amino groups. 

Thallation of aromatic compounds with thallium tris(trifluoroacetate) proceeds more easily than mercuration. Transmetallation of organothallium compounds with Pd(II) is used for synthetic purposes. The reaction of alkenes with arylthallium compounds in the presence of Pd(Il) salt gives styrene derivatives (433). The reaction can be made catalytic by use of CuCl7[393,394], The aryla-tion of methyl vinyl ketone was carried out with the arylthallium compound 434[395]. The /9-alkoxythallium compound 435, obtained by oxythallation of styrene, is converted into acetophenone by the treatment with PdCh[396]. 

On reaction with /V-methyl- /V-phenylhydrazine, however, the hydrazone (47) can be isolated, which on further treatment with anhydrous trifluoroacetic acid gives an A/-aLkenylpyrazole (48) (eq. 9). 

Catalytic reduction of folic acid to 5,6,7,8-tetrahydrofolic acid (225) proceeds fast in trifluoroacetic acid (66HCA875), but a modified method using chemical reductants leads with sodium dithionite to 7,8-dihydrofolic acid (224). Further treatment with sodium borohydride gives (225) which has been converted into 5-formyl-(6i ,S)-5,6,7,8-tetrahydro-L-folic acid (leucovorin) (226) by reaction with methyl formate (equation 70) (80HCA2554). 

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). 

A synthesis for the enantiomerically pure 535 was developed starting with D-phenylalanine which upon reaction with methyl chloroformate gave 528 whose reaction with methoxylamine afforded 529. Cyclization with bis(trifluoroacetoxy)iodobenzene in presence of trifluoroacetic acid gave the tetrahydroquinoline derivative 530 which was demethoxylated to give 531. Treatment of 531 with either benzyl chloroformate or... 

Diels-Alder reactions Neutral ionic liquids have been found to be excellent solvents for the Diels-Alder reaction. The first example of a Diels-Alder reaction in an ionic liquid was the reaction of methyl acrylate with cyclopentadiene in [EtNH3][N03] [40], in which significant rate enhancement was observed. Howarth et al. investigated the role of chiral imidazolium chloride and trifluoroacetate salts (dissolved in dichloromethane) in the Diels-Alder reactions between cyclopentadiene and either crotonaldehyde or methacroline [41]. It should be noted that this paper describes one of the first examples of a chiral cationic ionic liquid being used in synthesis (Scheme 5.1-17). The enantioselectivity was found to be < 5 % in this reaction for both the endo (10 %) and the exo (90 %) isomers. 

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