Term: pitch
https://doi.org/10.1351/goldbook.P04677

Definition:
A residue from pyrolysis of organic material or tar distillation which is solid at room temperature, consisting of a complex mixture of numerous, essentially aromatic hydrocarbons and heterocyclic compounds. It exhibits a broad softening range instead of a defined melting temperature. When cooled from the melt, pitches solidify without crystallization.

Note: The ratio of aromatic to aliphatic hydrogen depends mainly on the source of the starting material. The hydrogen @A00442@ (ratio of aromatic to total hydrogen atoms) varies between 0.3 and 0.9. The aliphatic hydrogen in pitch is largely associated with alkyl side chains substituted on aromatic rings. The content of @H02798@ in pitches varies depending on their origins. Also, the softening temperature can vary in a broad range between about 320 and 570 K depending on the @M04000@ (@R05271@) and composition of the constituents.

Related Terms:
1) aromaticity (http://doi.org/10.1351/goldbook.A00442).
2) heterocyclic compounds (http://doi.org/10.1351/goldbook.H02798).
3) molecular weight (http://doi.org/10.1351/goldbook.M04000).
4) relative molecular mass (http://doi.org/10.1351/goldbook.R05271).
5) hydrocarbons (http://doi.org/10.1351/goldbook.H02889).
6) melting (http://doi.org/10.1351/goldbook.M03821).
7) crystallization (http://doi.org/10.1351/goldbook.C01434).
8) pyrolysis (http://doi.org/10.1351/goldbook.P04961).

Source: PAC, 1995, 67, 473. 'Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)' on page 500 (https://doi.org/10.1351/pac199567030473)

Citation: 'pitch' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04677

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