(CAS NO.: ), which is also known as Oxonium, trimethyl- tetrafluoroborate(1-), could be produced through the following synthesis route.

A 500-ml., three-necked flask fitted with a mechanical stirrer, a Dewar condenser connected by a T-tube to a mineral oil bubbler and a source of dry nitrogen, and a gas-inlet tube connected to a source of dry is charged with 80 ml. of dichloromethane and 38.4 g. (33.3 ml., 0.271 mole) of boron trifluoride diethyl etherate. After establishing a nitrogen atmosphere in the flask, the condenser is filled with an acetone–dry ice mixture. With gentle stirring, dimethyl ether is passed into the solution until approximately 75 ml. has collected. The gas-inlet tube is replaced with a pressure-equalizing dropping funnel containing 28.4 g. (24.1 ml., 0.307 mole) of epichlorohydrin, which is added dropwise with vigorous stirring over a 15-minute period. The mixture is stirred overnight under an atmosphere of nitrogen. The stirrer is replaced by a filter stick, and the supernatant liquid is drawn off from the crystalline trimethyloxonium tetrafluoroborate, while keeping the mixture under nitrogen. The oxonium salt is washed with two 100-ml. portions of anhydrous dichloromethane and two 100-ml. portions of sodium-dried diethyl ether, and dried by passing a stream of nitrogen over the salt until the odor of ether is no longer detected, yielding 28–29 g. (92.5–96.5%) of a white crystalline solid, m.p. (sealed tube) 179.6–180.0° (dec.).