trimethyloxonium

Trimethyloxonium is a chemical compound with the formula [(CH3)3O]+. It is a trialkyloxonium ion, characterized by a positively charged oxygen atom bonded to three methyl groups. This cation is typically found as a counterion in salts, such as trimethyloxonium tetrafluoroborate or trimethyloxonium hexafluorophosphate. These salts are potent methylating agents. The high electrophilicity of the oxonium cation makes it readily donate its methyl groups to nucleophiles. Trimethyloxonium salts are soluble in polar organic solvents. Their reactivity makes them useful in organic synthesis for the methylation of alcohols, amines, and carboxylic acids. Due to their highly reactive nature, they are generally prepared and used in situ or handled with care under anhydrous conditions to prevent decomposition. The positive charge is delocalized to some extent over the three methyl groups, but the central oxygen atom bears the majority of the positive formal charge. This compound is not found naturally and is synthesized in a laboratory setting. The preparation often involves the reaction of a methylating agent like methyl triflate with a Lewis base.