Sodium dithionite

Last updated
Sodium dithionite
Sodium-dithionite-2D.png
Sample of sodium dithionite.jpg
Names
Other names
D-Ox, Hydrolin, Reductone
sodium hydrosulfite, sodium sulfoxylate, Sulfoxylate
Vatrolite, Virtex L
Hydrosulfit, Prayon
Blankit, Albite A, Konite
Zepar, Burmol, Arostit
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.991 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-890-0
PubChem CID
RTECS number
  • JP2100000
UNII
UN number 1384
  • InChI=1S/2Na.H2O4S2/c;;1-5(2)6(3)4/h;;(H,1,2)(H,3,4)/q2*+1;/p-2
    Key: JVBXVOWTABLYPX-UHFFFAOYSA-L
  • [O-]S(=O)S(=O)[O-].[Na+].[Na+]
Properties
Na2S2O4
Molar mass 174.107 g/mol (anhydrous)
210.146 g/mol (dihydrate)
Appearancewhite to grayish crystalline powder
light-lemon colored flakes
Odor faint sulfur odor
Density 2.38 g/cm3 (anhydrous)
1.58 g/cm3 (dihydrate)
Melting point 52 °C (126 °F; 325 K)
Boiling point Decomposes
18.2 g/100 mL (anhydrous, 20 °C)
21.9 g/100 mL (Dihydrate, 20 °C)
Solubility slightly soluble in alcohol
Hazards
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-exclam.svg
Danger
H251, H302
P235+P410, P264, P270, P280, P301+P312, P330, P407, P413, P420, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
2
3
1
Flash point 100 °C (212 °F; 373 K)
200 °C (392 °F; 473 K)
Related compounds
Other anions
Sodium sulfite
Sodium sulfate
Related compounds
 Sodium thiosulfate
Sodium bisulfite
Sodium metabisulfite
Sodium bisulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions.

Contents

Structure

Packing of sodium dithionite ions in a crystal, showing the saw-horse geometry of the dianion. Color code: red = O, yellow = S. Sodium-dithionite-xtal-1992-3D-balls.png
Packing of sodium dithionite ions in a crystal, showing the saw-horse geometry of the dianion. Color code: red = O, yellow = S.

The structure has been examined by Raman spectroscopy and X-ray crystallography. The dithionite dianion has C
2 symmetry, with almost eclipsed with a 16° O-S-S-O torsional angle. In the dihydrated form (Na
2S
2O
4·2H
2O), the dithionite anion has gauche 56° O-S-S-O torsional angle. [1]

A weak S-S bond is indicated by the S-S distance of 239 pm, which is elongated by ca. 30 pm relative to a typical S-S bond. [2] Because this bond is fragile, the dithionite anion dissociates in solution into the [SO2]− radicals, as has been confirmed by EPR spectroscopy. It is also observed that 35S undergoes rapid exchange between S2O42− and SO2 in neutral or acidic solution, consistent with the weak S-S bond in the anion. [3]

Preparation

Sodium dithionite is produced industrially by reduction of sulfur dioxide. Approximately 300,000 tons were produced in 1990. [4] The route using zinc powder is a two-step process:

2 SO2 + Zn → ZnS2O4
ZnS2O4 + 2 NaOH → Na2S2O4 + Zn(OH)2

The sodium borohydride method obeys the following stoichiometry:

NaBH4 + 8 NaOH + 8 SO2 → 4 Na2S2O4 + NaBO2 + 6 H2O

Each equivalent of H− reduces two equivalents of sulfur dioxide. Formate has also been used as the reductant.

Properties and reactions

Hydrolysis

Sodium dithionite is stable when dry, but aqueous solutions deteriorate due to the following reaction:

2 S2O42− + H2O → S2O32− + 2 HSO3−

This behavior is consistent with the instability of dithionous acid. Thus, solutions of sodium dithionite cannot be stored for a long period of time. [3]

Anhydrous sodium dithionite decomposes to sodium sulfate and sulfur dioxide above 90 °C in the air. In absence of air, it decomposes quickly above 150 °C to sodium sulfite, sodium thiosulfate, sulfur dioxide and trace amount of sulfur.

Redox reactions

Sodium dithionite is a reducing agent. At pH 7, the potential is -0.66 V compared to the normal hydrogen electrode. Redox occurs with formation of bisulfite: [5]

S2O42- + 2 H2O → 2 HSO3− + 2 e− + 2 H+

Sodium dithionite reacts with oxygen:

Na2S2O4 + O2 + H2O → NaHSO4 + NaHSO3

These reactions exhibit complex pH-dependent equilibria involving bisulfite, thiosulfate, and sulfur dioxide.

With organic carbonyls

In the presence of aldehydes, sodium dithionite reacts either to form α-hydroxy-sulfinates at room temperature or to reduce the aldehyde to the corresponding alcohol above a temperature of 85 °C. [6] [7] Some ketones are also reduced under similar conditions.

Uses

Industry

Sodium dithionite is used as a water-soluble reducing agent in some industrial dyeing processes. In the case of sulfur dyes and vat dyes, an otherwise water-insoluble dye can be reduced into its water-soluble alkali metal leuco salt. Indigo dye is sometimes processed in this way. [8]

Domestic and hobby uses

Sodium dithionite can also be used for water treatment, aquarium water conditioners, gas purification, cleaning, and stripping.In addition to the textile industry, this compound is used in industries concerned with leather, foods, polymers, photography, and many others, often as a decolourising agent. It is even used domestically as a decoloring agent for white laundry, when it has been accidentally stained by way of a dyed item slipping into the high temperature washing cycle. It is usually available in 5 gram sachets termed hydrosulfite after the antiquated name of the salt.

It is the active ingredient in "Iron Out Rust Stain Remover", a commercial rust product. [9]

Laboratory

Sodium dithionite is often used in physiology experiments as a means of lowering solutions' redox potential (Eo' -0.66 V vs SHE at pH 7). [10] Potassium ferricyanide is usually used as an oxidizing chemical in such experiments (Eo' ~ .436 V at pH 7). In addition, sodium dithionite is often used in soil chemistry experiments to determine the amount of iron that is not incorporated in primary silicate minerals. Hence, iron extracted by sodium dithionite is also referred to as "free iron."

Aqueous solutions of sodium dithionite were once used to produce 'Fieser's solution' for the removal of oxygen from a gas stream. [11] Pyrithione can be prepared in a two-step synthesis from 2-bromopyridine by oxidation to the N-oxide with a suitable peracid followed by substitution using sodium dithionite to introduce the thiol functional group. [12]

Photography

It is used in Kodak fogging developer, FD-70. This is used in the second step in processing black and white positive images, for making slides. It is part of the Kodak Direct Positive Film Developing Outfit. [13]

Safety

The wide use of sodium dithionite is attributable in part to its low toxicity LD50 at 2.5 g/kg (rats, oral). [4]

See also

Related Research Articles

<span class="mw-page-title-main">Nitrous acid</span> Chemical compound

Nitrous acid is a weak and monoprotic acid known only in solution, in the gas phase, and in the form of nitrite salts. It was discovered by Carl Wilhelm Scheele, who called it "phlogisticated acid of niter". Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.

<span class="mw-page-title-main">Sodium metabisulfite</span> Chemical compound

Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant, and preservative agent. When dissolved in water it forms sodium bisulfite.

<span class="mw-page-title-main">Sodium sulfite</span> Chemical compound

Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na2SO3. A white, water-soluble solid, it is used commercially as an antioxidant and preservative. It is also suitable for the softening of lignin in the pulping and refining processes of wood and lignocellulosic materials. A heptahydrate is also known but it is less useful because of its greater susceptibility toward oxidation by air.

<span class="mw-page-title-main">Sodium thiosulfate</span> Chemical compound

Sodium thiosulfate is an inorganic compound with the formula Na2S2O3·(H2O)x. Typically it is available as the white or colorless pentahydrate, which is a white solid that dissolves well in water. The compound is a reducing agent and a ligand, and these properties underpin its applications.

In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation state. The reverse of disproportionation, such as when a compound in an intermediate oxidation state is formed from precursors of lower and higher oxidation states, is called comproportionation, also known as symproportionation.

<span class="mw-page-title-main">Sodium dithionate</span> Chemical compound

Sodium dithionate Na2S2O6 is an important compound for inorganic chemistry. It is also known under names disodium dithionate, sodium hyposulfate, and sodium metabisulfate. The sulfur can be considered to be in its +5 oxidation state.

<span class="mw-page-title-main">Bisulfite</span> Chemical compound or ion

The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion HSO−
3. Salts containing the HSO−
3 ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite dissolves in water to give a solution of Na+HSO−
3.

<span class="mw-page-title-main">Potassium metabisulfite</span> Chemical compound

Potassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent odour. It is mainly used as an antioxidant or chemical sterilant. As a disulfite, it is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. Potassium metabisulfite has a monoclinic crystal structure.

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<span class="mw-page-title-main">Dithionite</span> Oxyanion of sulfur at the oxidation number +3

The dithionite is the oxyanion with the formula [S2O4]2−. It is commonly encountered as the salt sodium dithionite. For historical reasons, it is sometimes called hydrosulfite, but it contains no hydrogen and is not a sulfite. The dianion has a steric number of 4 and trigonal pyramidal geometry.

Hyposulfite may refer to:

<span class="mw-page-title-main">Thiosulfate</span> Polyatomic ion (S2O3, charge –2)

Thiosulfate is an oxyanion of sulfur with the chemical formula S2O2−3. Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, such as sodium thiosulfate Na2S2O3 and ammonium thiosulfate (NH4)2S2O3. Thiosulfate salts occur naturally. Thiosulfate rapidly dechlorinates water, and is used to halt bleaching in the paper-making industry. Thiosulfate salts are mainly used for dyeing in textiles, and bleaching of natural substances.

<span class="mw-page-title-main">Rongalite</span> Chemical compound

Rongalite is a chemical compound with the molecular formula Na+HOCH2SO2−. This salt has many additional names, including Rongalit, sodium hydroxymethylsulfinate, sodium formaldehyde sulfoxylate, and Bruggolite. It is listed in the European Cosmetics Directive as sodium oxymethylene sulfoxylate (INCI). It is water-soluble and generally sold as the dihydrate. The compound and its derivatives are widely used in the dye industry. The structure of this salt has been confirmed by X-ray crystallography.

<span class="mw-page-title-main">Borohydride</span>

Borohydride refers to the anion [BH4]−, which is also called tetrahydridoborate, and its salts. Borohydride or hydroborate is also the term used for compounds containing [BH4−nXn]−, where n is an integer from 0 to 3, for example cyanoborohydride or cyanotrihydroborate [BH3(CN)]− and triethylborohydride or triethylhydroborate [BH(CH2CH3)3]−. Borohydrides find wide use as reducing agents in organic synthesis. The most important borohydrides are lithium borohydride and sodium borohydride, but other salts are well known. Tetrahydroborates are also of academic and industrial interest in inorganic chemistry.

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<span class="mw-page-title-main">Sodium bisulfite</span> Chemical compound

Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite is not a real compound, but a mixture of salts that dissolve in water to give solutions composed of sodium and bisulfite ions. It appears in form of white or yellowish-white crystals with an odor of sulfur dioxide. Regardless of its ill-defined nature, sodium bisulfite is used in many different industries such as a food additive with E number E222 in the food industry, a reducing agent in the cosmetic industry, and a decomposer of residual hypochlorite used in the bleaching industry.

<span class="mw-page-title-main">Sulfoxylic acid</span> Chemical compound

Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.

The topic of sulfite food and beverage additives covers the application of sulfites in food chemistry. "Sulfite" is jargon that encompasses a variety of materials that are commonly used as preservatives or food additive in the production of diverse foods and beverages. Although sulfite salts are relatively nontoxic, their use has led to controversy, resulting in extensive regulations. Sulfites are a source of sulfur dioxide (SO2), a bactericide.

<span class="mw-page-title-main">Potassium thiosulfate</span> Chemical compound

Potassium thiosulfate, commonly abbreviated KTS, is an inorganic compound with the formula K2S2O3. This salt can form multiple hydrates, such as the monohydrate, dihydrate, and the pentahydrate, all of which are white or colorless solids. It is used as a fertilizer.

References

  1. ↑ Weinrach, J. B.; Meyer, D. R.; Guy, J. T.; Michalski, P. E.; Carter, K. L.; Grubisha, D. S.; Bennett, D. W. (1992). "A structural study of sodium dithionite and its ephemeral dihydrate: A new conformation for the dithionite ion". Journal of Crystallographic and Spectroscopic Research. 22 (3): 291–301. doi:10.1007/BF01199531. S2CID   97124638.
  2. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  3. 1 2 Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN   978-0-13-175553-6.
  4. 1 2 José Jiménez Barberá; Adolf Metzger; Manfred Wolf (15 June 2000). "Sulfites, Thiosulfates, and Dithionites". Ullmann's Encyclopedia of Industrial Chemistry. Wiley Online Library. doi:10.1002/14356007.a25_477. ISBN   978-3527306732.
  5. ↑ Mayhew, S. G. (2008). "The Redox Potential of Dithionite and SO−2 from Equilibrium Reactions with Flavodoxins, Methyl Viologen and Hydrogen plus Hydrogenase". European Journal of Biochemistry. 85 (2): 535–547. doi: 10.1111/j.1432-1033.1978.tb12269.x . PMID   648533.
  6. ↑ J. Org. Chem., 1980, 45 (21), pp 4126–4129, http://pubs.acs.org/doi/abs/10.1021/jo01309a011
  7. ↑ "Aldehyde sulfoxylate systemic fungicides". google.com. Archived from the original on 27 April 2018. Retrieved 27 April 2018.
  8. ↑ Božič, Mojca; Kokol, Vanja (2008). "Ecological alternatives to the reduction and oxidation processes in dyeing with vat and sulphur dyes". Dyes and Pigments. 76 (2): 299–309. doi:10.1016/j.dyepig.2006.05.041.
  9. ↑ "The Best Rust Removers for Restoring Every Surface". 23 March 2023.
  10. ↑ MAYHEW, Stephen G. (1978). "The Redox Potential of Dithionite and SO-2 from Equilibrium Reactions with Flavodoxins, Methyl Viologen and Hydrogen plus Hydrogenase". European Journal of Biochemistry. 85 (2): 535–547. doi: 10.1111/j.1432-1033.1978.tb12269.x . ISSN   0014-2956. PMID   648533.
  11. ↑ Kenneth L. Williamson "Reduction of Indigo: Sodium Hydrosulfite as a Reducing Agent" J. Chem. Educ., 1989, volume 66, p 359. doi : 10.1021/ed066p359.2
  12. ↑ Knight, David W.; Hartung, Jens (15 September 2006). "1-Hydroxypyridine-2(1H)-thione". 1-Hydroxypyridine-2(1H)-thione. Encyclopedia of Reagents for Organic Synthesis . John Wiley & Sons. doi:10.1002/047084289X.rh067.pub2. ISBN   978-0471936237.
  13. ↑ "Kodak Direct Positive Film 5246" (PDF). 125px.com. Kodak. Retrieved 6 November 2019.
  1. ↑ "Sodium dithionite - ipcs inchem" (PDF). www.inchem.org. Berliln, Germany. 2004. Archived from the original (PDF) on 17 April 2018. Retrieved 15 June 2018.
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