A 4.0 M ammonia solution in methanol is commonly used as a strong basic reagent and deprotection reagent in organic synthesis and solid-phase synthesis.

Its purpose is to provide a concentrated source of ammonia for removing base-labile protecting groups cleaving certain chemical linkages and promoting ammonia-mediated transformations under controlled conditions.

The reagent consists of ammonia at a concentration of 4.0 molL dissolved in methanol. Ammonia provides the basic and nucleophilic activity while methanol serves as the solvent and provides a homogeneous reaction medium for processes requiring concentrated ammonia under predominantly organic conditions.