Diphenic acid

Diphenic acid, also known as Dibenzoic acid, is an organic compound with the formula (C6H4CO2H)2. It is the most studied of several isomeric dicarboxylic acids of biphenyl. It is a white solid that can be prepared in the laboratory from anthranilic acid via the diazonium salt. It is the product of the microbial action on phenanthrene.

The compound forms a variety of coordination polymers. It also exhibits atropisomerism. It can form an internal anhydride featuring a seven-membered ring fused to the two benzene rings.


 * Diphenic acidanhydride.svg

Preparation
Diphenic acid is prepared from anthranilic acid by diazotization, followed by reduction with copper(I).
 * Diphenic Acid Synthesis V.1.svg

It can also be synthesized from the oxidation of phenanthrene by peracetic acid, which is first prepared from acetic acid and 90% hydrogen peroxide:


 * CH3COOH + H2O2 ⇌ CH3COOOH + H2O


 * 4 CH3COOOH + C14H10 → 4 CH3COOH + C14H10O4

Phenanthrene can also be treated with other oxidizing agents (such as hydrogen peroxide, chromium trioxide, potassium dichromate, or potassium permanganate), which first yields phenanthrenequinone and gives diphenic acid on further oxidation. Similarly, phenanthrenequinone can be boiled in alcoholic potash (potassium hydroxide in alcohol) to give the potassium salt of diphenic acid, and can alternatively be photo-oxidized to diphenic acid.