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.^[1] It is the product of the microbial action on phenanthrene.^[2]

Diphenic acid

Names
Preferred IUPAC name [1,1′-Biphenyl]-2,2′-dicarboxylic acid
Other names 2,2'-dibenzoic acid
Identifiers
CAS Number	482-05-3
3D model (JSmol)	Interactive image
ChEBI	CHEBI:23837
ChEMBL	ChEMBL79411
ChemSpider	9795
ECHA InfoCard	100.006.889
EC Number	207-576-4
Gmelin Reference	536420
PubChem CID	10210
UNII	QY5X735ZIM
CompTox Dashboard (EPA)	DTXSID0060064
InChI InChI=1S/C14H10O4/c15-13(16)11-7-3-1-5-9(11)10-6-2-4-8-12(10)14(17)18/h1-8H,(H,15,16)(H,17,18) Key: GWZCCUDJHOGOSO-UHFFFAOYSA-N
SMILES C1=CC=C(C(=C1)C2=CC=CC=C2C(=O)O)C(=O)O
Properties
Chemical formula	C14H10O4
Molar mass	242.230 g·mol−1
Appearance	white solid
Density	1.2917 g/cm3
Melting point	235.5 °C (455.9 °F; 508.6 K)
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335
Precautionary statements	P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The compound forms a variety of coordination polymers.^[3] It also exhibits atropisomerism. It can form an internal anhydride featuring a seven-membered ring fused to the two benzene rings.

Preparation

Diphenic acid is prepared from anthranilic acid by diazotization, followed by reduction with copper(I).^[4]

It can also be synthesized from the oxidation of phenanthrene by peracetic acid, which is first prepared from acetic acid and 90% hydrogen peroxide:^[5]

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.^[6][7] Similarly, phenanthrenequinone can be boiled in alcoholic potash (potassium hydroxide in alcohol) to give the potassium salt of diphenic acid,^[8] and can alternatively be photo-oxidized to diphenic acid.^[9]