Trifluoroacetic anhydride acetylation catalyst

Furan can also be acylated by the Vilsmeier-Haack method. Acylation of furans can also be carried out with acid anhydrides and acyl halides in the presence of Friedel-Crafts catalysts (BF3-Et20, SnCU or H3PO4). Reactive anhydrides such as trifluoroacetic anhydride, however, require no catalyst. Acetylation with acetyl p-toluenesulfonate gives high yields. 

The early work was done with acetyl chloride catalyzed with lead acetate [2], propionic and butyric anhydrides in xylene without catalyst [49], and several unsaturated carboxylic acids in the presence of trifluoroacetic anhydride (TFAA) [62,63]. 

The fact that, in the reaction formulated above, anisole yields the acetyl and not the trifluoroacetyl derivative means that the mixed anhydride is a more reactive acylating agent than trifluoroacetic anhydride. However, the pure anhydride alone is capable of effecting acylation. It reacts with azulene (blue) in carbon tetrachloride without catalyst at room temperature to give 1-trifluoroacetylazulene (red) in high yield. "... 

Rapid acetylation of cellulose, during which, it is claimed, only about one bond per thousand D-glucose residues is broken, accompanies the use of a mixture of acetic anhydride and trifluoroacetic anhydride as the reaction medium. The preparation of a fibrous triacetate by treating cotton with acetic anhydride containing perchloric acid, as a catalyst, and amyl... 

The esterification reaction (Figure 3.14), using acetic anhydride or trifluoroacetic anhydride, may be catalyzed either by a Lewis acid (ZnCl2) or a base (AcONa). If the catalyst is acid, only the acetylated derivative of a-D-methylglucopyranose is formed. However, when a basic catalyst is used, only the most thermodynamically stable stereoisomer is formed. 

Trifluoroacetic anhydride is a most effective catalyst for the direct esterification of carboxylic acids by primary, secondary, and tertiary alcohols. Esterification proceeds under mild conditions via a mixed anhydride but is not successful with carboxylic acids of very low pKa and hydroxy acids when the reagent promotes lactonisation or polymerization [23, 24]. Dibasic acids may be esterified if they do not readily form cyclic anhydrides. Reagents such as trifluoromethane sulphonic anhydride [25], acetyl chloride [26], pyridine/p-toluene-sulphonyl chloride [27], sulphury chloride [28], thionyl chloride [29], and pyridine/phosphorus oxychloride [30] probably act in a similar way to trifluoracetic anhydride as reagents for direct esterification. 

The reaction is acid or base catalyzed. Many catalysts have been tried, including potassium acetate and sodium acetate (27), dimeth-ylformamide (DMF) (28-30), urea ammonium sulfate (29), magnesium perchlorate (31-33), trifluoroacetic acid (32), boron trifluoride (30), sodium acetate (31), potassium hydrogen phosphate (34), and y-rays (35). The best acetylation condition, however, is uncatalyzed acetic anhydride in xylene at 100-130 C (36). 

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