Trans-4-chlorocrotonic acid is primarily used as an intermediate in organic synthesis, particularly in the production of pharmaceuticals and agrochemicals. Its structure allows it to participate in various chemical reactions, making it valuable for creating complex molecules. It is often employed in the synthesis of active pharmaceutical ingredients (APIs) where its chlorinated and unsaturated properties are utilized to build specific molecular frameworks. Additionally, it serves as a precursor in the development of herbicides and pesticides, contributing to the control of weeds and pests in agricultural practices. Its reactivity also makes it useful in research and development for exploring new chemical pathways and compounds.