Trifluoroacetic anhydride dehydrating agent

Dehydration of primary nitroalkanes with phenyl isocyanate or acetic anhydride in the presence of catalytic triethylamine affords nitrile oxides, which may be trapped as their 1,3-dipolar cycloadducts or allowed to dimerize to the corresponding furoxans. Other dehydrating agents that have been used include diketene, sulfuric acid and, when the a-methylene group is activated by electron-withdrawing groups, boron trifluoride in acetic anhydride, trifluoroacetic anhydride with triethylamine, and nitric acid in acetic acid. 

Trifluoroacetic anhydride can be used as an alternative dehydrating agent for phosphorous oxychloride as described below by the author ... 

On the other hand, 9-benzyl-2-(tritluoromethyl)hypoxanthinc (18) is prepared by acylation of 5-amino-l-benzylimidazole-4-carboxamide with trifluoroacetic anhydride and subsequent heating of the intermediate. A number of dehydration agents fail to effect this ring closure. ... 

Acylations with carboxylic acids and anhydrides have been carried out with sulfuric acid as both solvent and catalyst, the reactive acylating agents from acyl halides probably being haloacyloxonium ions. Trifluoroacetic anhydride offers a rather milder reagent for reactions of carboxylic acids, with mixed anhydrides being likely intermediates. However, polyphosphoric acid remains the most widely used dehydrating agent for acylations by carboxylic acids. 

The syntheses of dithiopyr (1), thiazopyr (2) and related compounds [4, 5] begin with a Hantzsch-type base-catalyzed intermolecular cyclization [22], which provides the dihydropyridines 4 (R = Me or Et). Two equivalents of methyl or ethyl trifiuoroacetoacetate (5, R = Me or Et) are allowed to react with one equivalent of isovaleraldehyde (6) in the presence of a base, like piperidine, in a suitable solvent at temperatures varying from room temperature to reflux. The intermediate dihydroxytetrahydropyran (structure not shown) is converted into the dihy-droxypiperidine 7 by reaction with a nitrogen source, such as ammonium hydroxide or ammonia gas. Reaction of 7 with a dehydrating agent, such as concentrated sulfuric acid, toluenesulfonic acid, or trifluoroacetic anhydride, gives a mixture... 

Oxidation of primary and secondary alcohols to aldehydes and ketones with DMSO, oxalyl chloride, and a base is knovm as Swem-oxidation. When using oxalyl chloride as the dehydration agent, the reaction must be kept colder than —60°C to avoid side reactions, such as Pummerer rearrangement. In contrast, when trifluoroacetic anhydride is used instead of oxalyl chloride, the reaction can be warmed to —30 °C without side reactions. Microflow systems offer a smart approach for controlling the reaction... 

Electrolytes I-III were prepared from TMSPIm precursor by adding (I) trifluoroacetic acid (TFA) or (II, III) acetic acid (AcOH) in a molar ratio of 1 5.5. Equivalents of 4.5 were used for solvolysis, and 1 equivalent served for protonation for formation of ionic liquid. In electrolyte III, a mixture of acetic anhydride as dehydrating agent, and lithium acetate dihydrate as a source of lithium ions were added. Solvolysis and condensation reactions of trimethoxysilanes were stimulated by heat treatment of the mixtures at 120 °C. Lastly, the product was heated under reduced pressure to remove the remaining volatile components from the electrolytes. 

---