Boric acid (Sigma Aldrich)
Acetic Anhydride (Alfa Aesar)
Acetic Acid (Fisher Scientific)
Toluene (Sigma Aldrich)

B(OH)₃ (25 g, 0.4 mol), acetic acid (1.25 mL), and toluene (115 mL) were added to a three-necked round bottom flask equipped with a condenser and a thermometer. The mixture was stirred for thirty minutes at room temperature before addition of acetic anhydride (116 mL, 1.2 mol). The reaction temperature was raised to 45 ºC over one hour and then to 60 ºC over one and a half hours. The mixture was left to stir overnight. When the reaction completed, the cloudy-white mixture turned clear and the solution was cooled to room temperature. The precipitated B(OAc)₃ was isolated by filtration under dry N₂ as white powder (36.95 g, 48 % yield).

Use freshly opened bottle of acetic anhydride if possible.

¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.884 (s, 9H).

¹³C NMR (100 MHz, DMSO-d₆) δ ppm 21.47, 172.50.

Ritscher, J. S.; Kowalski, D. C.; McKeon, J. E. J. Chem. Ed. 1974, 51 (10), 688.