page_title: Pyridine
section_title: Physical properties
hierarchical_section_title: Pyridine / Properties / Physical properties
caption_attribution_description: English: Crystal structure of en:Pyridine Deutsch: Kristallsystruktur von de:Pyridin
context_page_description: Pyridine is a basic heterocyclic organic compound with the chemical formula C₅H₅N. It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. Today it is synthesized on the scale of about 20,000 tonnes per year worldwide.
context_section_description: The molecular electric dipole moment is 2.2 debyes. Pyridine is diamagnetic and has a diamagnetic susceptibility of −48.7 × 10⁻⁶ cm³·mol⁻¹. The standard enthalpy of formation is 100.2 kJ·mol⁻¹ in the liquid phase and 140.4 kJ·mol⁻¹ in the gas phase. At 25 °C pyridine has a viscosity of 0.88 mPa/s and thermal conductivity of 0.166 W·m⁻¹·K⁻¹. The enthalpy of vaporization is 35.09 kJ·mol⁻¹ at the boiling point and normal pressure. The enthalpy of fusion is 8.28 kJ·mol⁻¹ at the melting point.
  The critical parameters of pyridine are pressure 6.70 MPa, temperature 620 K and volume 229 cm³·mol⁻¹. In the temperature range 340–426 °C its vapor pressure p can be described with the Antoine equation
  where T is temperature, A = 4.16272, B = 1371.358 K and C = −58.496 K.
caption: Crystal structure of pyridine
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