Trimethyloxonium tetrafluoroborate Me₃OBF₄ (sometimes called the "Meerwein salt" after Hans Meerwein) is a strong methylating agent. It is the methyl analog to triethyloxonium tetrafluoroborate. Commercially available, this compound is prepared similarly, by reaction of boron trifluoride etherate with dimethyl ether and epichlorohydrin.