4-Aminobenzophenone CAS 1137-41-3

Introduction to 4-Aminobenzophenone

4-Aminobenzophenone is an aromatic organic compound built on a benzophenone backbone substituted with a primary amine group at the para position. Its molecular architecture combines a strong ultraviolet-absorbing carbonyl moiety with a highly nucleophilic amino group. At room temperature, the material appears as a pale yellow to yellow crystalline powder with a faint characteristic odor. It is practically insoluble in water but dissolves readily in ethanol, acetone and hot aromatic hydrocarbons.

The photoactive carbonyl group readily absorbs UV radiation and transitions to an excited triplet state to generate free radicals. The para-amino group enables smooth diazotization, acylation and alkylation reactions for constructing complex heterocyclic scaffolds. The extended conjugated pi-system also acts as a strong chromophore, imparting intense color and high lightfastness to downstream dye molecules.

4-Aminobenzophenone Chemical & Physical Properties

Applications of 4-Aminobenzophenone

UV-curable photoinitiators: Blended into free-radical polymerization systems for inks, adhesives and clear coats. The molecule absorbs long-wave UV light and initiates crosslinking of acrylate oligomers. It is often copolymerized with reactive monomers to create polymer-bound photoinitiators that eliminate surface migration and odor issues in food packaging applications.

Azo dye and pigment intermediates: Reacts with sodium nitrite and acid to form stable diazonium salts, which then couple with aromatic compounds to synthesize vibrant, high-molecular-weight azo dyes. The bulky benzophenone structure significantly enhances the thermal stability and lightfastness of the resulting colorants for textiles and plastics.

Pharmaceutical and agrochemical synthesis: Serves as a foundational building block for synthesizing biologically active molecules. The amine group undergoes condensation with various electrophiles to construct benzodiazepines, antihistamines and crop protection agents. Reaction pH is typically carefully buffered to prevent unwanted side reactions during complex multi-step syntheses.

Storage & Safety Precautions for 4-Aminobenzophenone

• Store in tightly sealed, opaque fiber drums or foil-lined bags in a cool, dark warehouse below 25 °C. The aromatic amine is highly photosensitive and prone to air oxidation, which darkens the powder and degrades its photochemical reactivity.
• Wear N95 respirators, safety goggles and nitrile gloves during dry blending and reactor charging operations. Fine dust is a respiratory sensitizer and mild skin irritant; avoid prolonged inhalation and skin contact.
• When preparing diazonium salts for dye coupling, maintain reaction temperature strictly between 0 °C and 5 °C. Exceeding this range causes rapid thermal decomposition of the diazonium intermediate, releasing nitrogen gas and drastically lowering final dye yield.

4-Aminobenzophenone FAQ

Q: How does 4-Aminobenzophenone function as a photoinitiator?

A: It absorbs UV radiation and transitions to an excited triplet state, then abstracts hydrogen from co-initiators to generate free radicals. This initiates rapid crosslinking of acrylic monomers in UV-curable inks and coatings without requiring deep-penetrating UV light.

Q: Why is 4-Aminobenzophenone used in dye synthesis?

A: It undergoes diazotization to form stable diazonium salts, which couple with compounds like 2-Naphthol to produce vibrant azo dyes. The bulky benzophenone structure enhances the lightfastness and thermal stability of final colorants for textiles and plastics.

Q: What storage conditions are required for 4-Aminobenzophenone?

A: It is photosensitive and prone to oxidation when exposed to light and air. Store the crystalline powder in tightly sealed, opaque fiber drums in a cool, dry warehouse. Low ambient humidity prevents moisture ingress and preserves chemical reactivity.