Carboxylic acids trifluoroacetic acid

Unsymmetrical rrawj -1,4-difunctionalization of 1,3-cyclohexadienes occurs when the reagent system contains MeOH and a carboxylic acid. ° Trifluoroacetic acid is probably too acidic, some CFjCOONa is also added."... 

V. Selective Ring-opening of Cyclic Acetals with Carboxylic Acid-Trifluoroacetic Anhydride Mixtures... 

Carboxylic Acids. Carboxylic acids have been esterified to wood catalyzed with trifluoroacetic anhydride (72, 73). Several unsaturated carboxylic acids react with wood by the trifluoroacetic anhydride impelling method to give an increase in oven-dry volume and ASE, and a decrease in wood crystallinity and moisture content (74). Reactions of wood with p-methylcrotonic acid (Reaction 1) give a degree of substitution high enough to make the esterified wood soluble in acetone and CHCI3 to the extent of 30% (75). 

Methoxyimino-0 -(2-aminothiazol-4-yl)acetamido] cephalosporanic acid trifluoroacetic acid salt is dissolved in a solution of 272 mg of 1 -methyl-S-mercapto-l H-tetrazole, 555 mg of sodium bicarbonate and 68 mg of triethylbenzylammonium bromide in 10 ml of water. The solution is heated at 60°C in nitrogen atmosphere for 6 hours. After cooling, the reaction solution is passed through a column of Amberlite XAD-2 and eluted with water and then with 2.5% ethanol. The procedure yields sodium 7(3-[0 -methoxyimino-0 -(2-aminothiazol-4-yl)ace-tamido] -3-(1 -methyl-l H-tetrazol-5-ylthiomethyl)-3-cephem-4-carboxylate, MP 174°C to 175°C (decomposition). 

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. 

Thallium (ITT) salts of formic, acetic, and trifluoroacetic acids are prepared from the corresponding acid and thaUium(III) oxide (11). Other thaUium(III) carboxylates can be obtained from the metathesis of thaUium(III) acetate and the carboxyUc acid (12). They are colorless, hygroscopic soUds. 

The change of mechanism with tertiary alkyl esters is valuable in synthetic methodology because it permits certain esters to be hydrolyzed very selectively. The usual situation involves the use of t-butyl esters, which can be cleaved to carboxylic acids by action of acids such as p-toluenesulfonic acid or trifluoroacetic acid under anhydrous conditions where other esters are stable. 

Carboxylic acids react with trifluoroacetic anhydride to give mixed anhydrides that are especially useful for the acylation of hindered alcohols and phenols ... 

The latter is an exttemely reactive species. Trifluoroacetate is a good leaving group and facilitates cleavage of the O—Br bond. The acyl hypohalites are also the active halogenating species in solutions of the hypohalous acids in carboxylic acids, where they exist in equilibrium. 

Mixed anhydrides of a carboxylic acid and trifluoroacetic or triflic acids... 

Acylation of various oxygen functions by use of common and commercially available fluonnated carboxylic acid denvatives such as trifluoroacetic anhydride or the corresponding acyl halides have already been discussed sufficiently in the first edition [10] Therefore only exceptional observations will be described in this section In the past 15 years, many denvatizations of various nonfluonnated oxygen compounds by fluoroacylation were made for analytical purposes. Thus Mosher s acid chlorides for example became ready-to-use reagents for the determination of the enantiomeric purity of alcohols and amines by NMR or gas-liquid chromatographic (GLC) techniques [//] (equation 1)... 

The reduction is general for a variety of substituted benzophenones Such substituents as CH3 OH, OCH3, F, Br. N(CH3)2, NO2. COOH, COOCH3, NHCOC Hreaction conditions and do not alter the course of the reduction Diarylmethanols are reduced to diarylmethanes under the same conditions and probably are the intermediates in the reduction of ketones [26] Triethylsilane also can be used as a reducing agent in trifluoroacetic acid medium [27J This reagent is used for the reduction of benzoic acid and some other carboxylic acids under mild condiUons (equation 14) Some acids (phthalic, sue cinic, and 4-nitrobenzoic) are not reduced under these conditions [27]... 

Peroxytnfluoroacetic acid is used tor numerous oxidations of saturated hydrocarbons and aromatic compounds It oxidizes alkanes, alkanols, and carboxylic acids with formation of hydroxylation products [29] Oxidation of cyclohexane with peroxytnfluoroacetic acid proceeds at room temperature and leads to cyclohexyl trifluoroacetate in 75% yield, 1-octanol under similar conditions gives a mixture of isomeric octanediols in 59% yield, and palmitic acid gives a mixture of hydroxypalmitic acids in 70% yield [29]... 

For acrylate polymers with higher levels of carboxylic acids, THF can be modified by the addition of acids such as acetic, phosphoric, or trifluoroacetic. Levels as high as 10% acetic acid are considered acceptable by most manufacturers for their styrene/DVB columns. If such a modified mobile phase is used, it may need to be premixed rather than generated using a dynamic mixing HPLC pump because on-line mixing often leads to much noisier baselines, particularly when using a refractive index detector. 

The listing of p/acidity from one carboxylic acid to another. For example, trifluoroacetic acid (Ka = 0.59) is 33,000 times as strong as acetic acid (Ka = 1.75 X 10 3). How can we account for such differences ... 

Activating agents, such as trifluoroacetic anhydride 1,1 -carbonyldiimidazolc carbodiimides sulfonyl, tosyl, and picryl chlorides and a range of phosphorus derivatives can promote direct solution reactions between dicarboxylic acids and diols or diphenols in mild conditions. The activating agents are consumed during the reaction and, therefore, do not act as catalysts. These so-called direct polycondensation or activation polycondensation reactions proceed via the in situ transformation of one of the reactants, generally the carboxylic acid, into a more... 

Trifluoroacetic anhydride, which activates the polyesterification of 4-hy-droxybenzoic acid via the formation of a mixed anhydride,307 and 1,1 -carbonyldiimidazole308 were the first reported activating agents. The reaction between 1,1 -carbonyldiimidazolc and carboxylic acids proceeds through the formation of N-acylimidazolcs, which react with aliphatic diols in the presence of sodium ethoxide catalyst (Scheme 2.28). 

Studies on Trifluoroacetic Acid. Part I. Trifluoroacetic Anhydride as a Promotor of Ester Formation between Hydroxy-Compounds and Carboxylic Acids, E. J. Bourne, M. Stacey, J. C. Tatlow, and J. M. Tedder, J. Chem. Soc., (1949) 2976-2979. 

---