Trimethylboroxine

synthetischeTrimethylboroxine is prepared by heating B(CH3)3 and B2O3 together in a sealed tube. The B2O3 powder is made by dehydrating H3BO3 under vacuum over P2O5 , at 220℃. The very hygro-scopic oxide is placed with strict exclusion of moisture in a 200-ml. thick-wall Pyrex tube provided with a ground joint, and a melting-point capillary is fastened to the tube just below the joint. The tube is connected to a vacuum pump and immersed in liquid nitrogen, and when a high vacuum has been established, a quantity of B(CH3)3 equivalent to 4.25 g. (0.061 mole) of B2O3 is condensed in the tube. The tube is sealed off, heated to 600℃ and kept at this temperature for six hours; in the process the contents turn into a clear, colorless liquid. When the tube has cooled down, the tip is broken under a nitrogen blanket and sealed to a tube leading to the vacuum pump. The tube is evacuated and the contents of the tube are transferred into a -78℃ trap. The crude product is purified by removing volatile contaminants at -45℃ and then distilling the product from a -10℃ trap into a receiver held at -78℃.