Use of Acetic Acid as an Acetylating Agent of Alcohols and Phenols Catalyzed by Recyclable Solid Acids

Abstract

Acetic acid is one of the simplest carboxylic acid, and an important chemical and industrial chemical for different uses. It is employed, for example, in the production of cellulose and, in the food, diluted acetic acid acts as an acidity and as a condiment. The global demand of acetic acid is very important, around 6.5 million tonnes per year. The acetylation reaction of organic compounds is one of the most frequently used transformations in organic synthesis. Among the various protected groups used for the hydroxyl function, the acetyl group is the most convenient in view of its easy introduction, being stable to the acidic reaction condition and also easily removable by mild alkaline hydrolysis. The most common and inexpensive reagent used to perform the acetylation is the acetic anhydride however, from an environmental point of view, a much convenient method for performing the acetylation is the use of acetic acid as acetylating agent, because only water is produced as by product, and it is a relative cheaper route for industrial purposes when compared to anhydrides or acid chlorides. In this chapter we reviewed the performance of different recyclable solid acids synthesized in our laboratory as catalysts for the use of acetic acid as acetylating agent: 1) alcohols and phenols acetylation using borated zirconia; 2) alcohols and phenols acetylation using borated zirconia modified with ammonium metatungstate; 3) isoamyl alcohol acetylation using tungstophosphoric acid supported on zirconia; and 4) isoamyl alcohol acetylation using partially substituted Cs and K salts of tungstophosphoric acid. The alcohols and phenols acetylation with the borated zirconia-based catalysts gave very good yields to the desired products with very high selectivity, though the alcohol and phenol structure is a key in the yield to the acetylation product. The zirconiasupported tungstophosphoric acid prepared by the incipient wetness impregnation led to obtain isoamyl acetate with high activity and selectivity, and similar results were obtained using the Cs and K tungstophosphates, observing a correlation with the acidic properties of the catalysts.