Diphenyl ((C6H5)2) is a white crystalline solid insoluble in water. It is obtained from benzene or toluene and is extremely toxic. Its main usage is as one of the components of heat-transfer fluids capable of operating at temperatures around 700 K.
Below are some of its physical characteristics:
| Molecular weight: 154.21 | Critical temperature: 789 K |
| Melting point:342.4 K | Critical pressure: 3.85 MPa |
| Normal boiling point: 528.4 K | Critical density: 323 kg/m3 |