Dimethyl sulfate is primarily used as a methylating agent in organic synthesis. It transfers methyl groups to nucleophiles such as amines, phenols, and thiols, making it valuable in the production of pharmaceuticals, dyes, and pesticides. It is especially effective in the methylation of aromatic compounds and is commonly used in laboratory-scale reactions where a strong methylating agent is required. Due to its high reactivity and toxicity, its use is typically restricted to controlled environments with strict safety protocols. It has also been used in the preparation of quaternary ammonium compounds and in the modification of nucleic acids for research purposes. However, because of its carcinogenicity and environmental hazards, safer alternatives like methyl iodide or dimethyl carbonate are increasingly preferred.