Used primarily as an ethylating agent in organic synthesis, especially in the production of dyes, pharmaceuticals, and agrochemicals. It transfers ethyl groups to various substrates, facilitating the formation of esters, ethers, and quaternary ammonium compounds. Commonly employed in the manufacture of surfactants and fabric softeners due to its ability to modify organic molecules for enhanced solubility or reactivity. Also utilized in research settings for alkylation of nucleic acids and proteins, though its use is limited due to high toxicity and carcinogenic potential. Requires careful handling in industrial applications because of its corrosive and mutagenic properties.