Triethyloxonium tetrafluoroborate is widely used as a strong alkylating agent in organic synthesis. It is particularly effective for introducing ethyl groups into various substrates, making it valuable in the preparation of ethyl esters, ethers, and other ethylated compounds. Its application extends to the synthesis of complex molecules in pharmaceuticals and agrochemicals, where precise ethylation is required. Additionally, it is utilized in the preparation of onium salts, which are important in polymerization processes and as catalysts in certain reactions. Its ability to act as a potent electrophile also makes it useful in the modification of polymers and in the study of reaction mechanisms involving alkylation.