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White to yellowish crystals that are used to detect the presence of mechanical wood pulp in paper. Phloroglucinol test solution contains Hydrochloric acid and ethanol. A drop placed on the paper will turn red when Lignin is present (detection limit is about 5%). Iron will react with phloroglucinol giving a purple product. Once the two-part solution is mixed, it has a shelf life of 2-3 months (TAPPI T401).

Synonyms and Related Terms

phloroglucinol dihydrate; 1,3,5-benzenetriol; 1,3,5-trihydroxybenzene; phloroglucine; phloroglucin stain

Chemical structure



  • Decomposes in light; store in dark container.
  • Inhalation and skin contact may cause irritation.
  • ThermoFisher: SDS

Physical and Chemical Properties

  • Soluble in ethanol, pyridine, ether. Slightly soluble in water.
  • Detection limit is about 5% when used as a stain to detect mechanical wood pulp.
Composition C6H3(OH)3
CAS 108-73-6
Melting Point 212-218 C
Molecular Weight mol. wt.=126.11

Resources and Citations

  • AIC Book and Paper Catalog, 10. Spot Tests, page 12.
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • Book and Paper Group, Paper Conservation Catalog, AIC, 1984, 1989
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 7482