Used as an intermediate in organic synthesis, particularly in the pharmaceutical industry for the preparation of active pharmaceutical ingredients (APIs). It serves as a protected form of 4-carboxybenzoic acid, where the tert-butoxycarbonyl (Boc) group acts as a protecting group for carboxylic acid functionalities during peptide synthesis and other multi-step syntheses. This allows selective reaction at other sites in the molecule without interference from the carboxylic acid group. After the desired transformations are complete, the Boc group can be easily removed under mild acidic conditions to regenerate the free carboxylic acid. Also employed in the synthesis of esters, amides, and heterocyclic compounds due to its stability and ease of handling.