Benzamidine

Benzamidine is an organic compound that consists of a benzene ring bearing an amidine substituent, with the formula C7H8N2. The amidine group, C(=NH)NH2, makes the molecule a relatively strong organic base and capable of forming a salt with acids. In practice, benzamidine is most commonly encountered as its hydrochloride salt, benzamidine hydrochloride, which is highly soluble in water.

Structure and properties. The molecule features a planar benzene ring attached to the sp2-hybridized amidine carbon. As a free base, benzamidine is a white solid that can be hygroscopic; the hydrochloride salt is a white crystalline material. The amidine functionality contributes to high basicity, with conjugate acids typically possessing high pKa values, reflecting strong basic character in many solvent systems. The compound is soluble in polar organic solvents and, as the hydrochloride salt, readily soluble in water.

Synthesis and availability. Benzamidine is commercially available and is prepared by standard methods used for amidines; various synthetic routes exist to introduce the amidine group onto a phenyl ring. The free base and the hydrochloride salt are both used, depending on the application.

Applications. In organic synthesis, benzamidine serves as a reagent and building block for introducing the amidine moiety into molecules. In biochemistry and protein chemistry, derivatives of benzamidine are employed as inhibitors of serine proteases such as trypsin and as ligands in affinity chromatography to capture proteases, reflecting its utility as a tool for studying proteolytic enzymes.

Safety. Benzamidine is an irritant and should be handled with appropriate precautions, including gloves and eye protection. It should be stored in a cool, dry place away from incompatible substances.