phthalimide

Phthalimide, also known as benzene-1,2-dicarboximide or isoindoline-1,3-dione, is an aromatic imide derived from phthalic anhydride. Its chemical formula is C8H5NO2. The molecule consists of a benzene ring fused to a five-membered imide ring bearing an NH group; two adjacent carbonyl groups complete the imide moiety.

Preparation and structure

Phthalimide is commonly prepared by cyclodehydration of phthalic anhydride with ammonia under heating, forming the imide in good yields. It can also arise from reactions of phthalic anhydride with ammonium salts followed by cyclization. The product is a white crystalline solid.

Reactions and uses

The imide N–H is relatively acidic, enabling deprotonation with mild bases to give the phthalimide anion. This anion undergoes N-alkylation with primary alkyl halides to yield N-alkylphthalimides. Hydrazinolysis or hydrolysis of N-alkylphthalimides liberates primary amines, which is the basis of the Gabriel synthesis for amines. Phthalimide is also used as a protecting group for amines in multi-step organic synthesis.

Properties and safety

Phthalimide is a white crystalline solid that is sparingly soluble in water and soluble in many organic solvents; it is relatively thermally stable. Handling requires standard laboratory precautions, as it can be an irritant to skin, eyes, and the respiratory tract. Proper disposal and protective equipment are advised when handling this compound.