O-Phenyl chlorothionoformate is primarily used in organic synthesis as a versatile reagent for introducing the phenylthio group into various compounds. It is particularly valuable in the preparation of thioesters, which are intermediates in the synthesis of pharmaceuticals, agrochemicals, and other fine chemicals. Additionally, it serves as a key building block in the production of sulfur-containing heterocycles, which are important in medicinal chemistry for developing drugs with potential therapeutic applications. Its reactivity with nucleophiles makes it useful in cross-coupling reactions and the modification of biomolecules, aiding in the study of biochemical pathways and the development of novel bioactive compounds.