Sodium dithionite

Description

Pale yellow powder that is used as a Reducing agent in dyeing Indigo and vat dyes. Sodium dithionite is also used to strip dyes from dyed textiles and reduce iron oxide stains to Ferrous oxide. Sodium dithionite was also used as a bleach for Leather and mechanical paper pulps but its use has declined in recent years due to poor color reversion properties (AIC Book and Paper Catalog).

Note: this is not the same compound as Sodium thiosulfate (Na2S2O3; also called sodium hyposulfite) that is used for fixation in photography.

Chemical structure

Synonyms and Related Terms

sodium thiosulfite; sodium hydrosulfite; sodium sulfoxylate

Physical and Chemical Properties

Soluble in water (pH = 6.0-7.5 for 1-6% solution). Insoluble in ethanol.

Composition	Na2S2O4
CAS	7775-14-6
Melting Point	52-55 C
Density	2.19 g/ml
Molecular Weight	mol. wt. = 174.1

Risks

• Fire risk in contact with moisture and air. Use dry sand to extinguish fires. Flash point=90 C
• Contact causes irritation
• Integra Chemc: SDS

Resources and Citations

• G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 786

• 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 Dictionary of Paper, American Paper Institute, New York, Fourth Edition, 1980

• Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976

• The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 8771

• Wikipedia: http://en.wikipedia.org/wiki/Sodium_dithionite (Accessed Jan. 6 2006)