Sodium Dithionite, Rongalite and Thiourea Oxides

The following sections are included:

• Acknowledgment
• Glossary
• Contents
• List of Figures
• List of Table
• About the Authors

Sodium dithionite (Na₂S₂O₄), sodium hydroxymethanesulfinate (rongalite) (HOCH₂SO₂Na) (HMS) and thiourea dioxide ((NH₂)₂CSO₂) (TDO) have long been used in chemistry and chemical technology as reductants [1]. Recently, new fields of their application have been developed: reduction of graphene [2-8] and graphite oxides [9], synthesis of metal sulfides [10,11] and nanometer metal powders [12], metallization of fibers [13], organic synthesis [1,14,15] including organocatalytic reactions [16-22] and finally nonlinear phenomena in chemical kinetics [1]. Many newly discovered “relatives” of these compounds have been synthesized [1]. In the past few years, new and important information has been published on dithionite, particularly on the synthesis of complexes with uranium and f-elements as well as with decamethylsamarocene [23-25]. Other notable examples include the studies on photoisomerization of photochromic dithionite complexes in chiral crystals [26-30] and synthesis of the first polythionite [31]. It is found that to receive stable polythionite salt, a countercation should be sufficiently large. The same conclusion has been drawn for sulfoxylates [32]. It is shown that the most convenient precursor for synthesis of sulfoxylates in aqueous solution is thiourea dioxide…

The following sections are included:

• Dithionites
• Sodium Hydroxymethanesulfinate (Rongalite) and Its Relatives
• Thiourea Oxides

The following sections are included:

• Dithionites
• Hydroxymethanesulfinates
• Thiourea Oxides

Commercially available sodium dithionite Na₂S₂O₄ is a white powder with a purity of approximately 88%. Main impurities are sodium sulfite, metabisulfite and thiosulfate [164]. Double recrystallization of commercial dithionite from 0.1 M NaOH.methanol under anaerobic conditions gives a product with a purity of 99 ± 1% [58]. Dithionite also forms dihydrate Na₂S₂O₄ · 2H₂O. Sodium dithionite dihydrate is very sensitive toward atmospheric oxygen in the finely crystalline state and it is oxidized under heat development, therefore, all further information refers to anhydrous sodium dithionite [164]. Sodium dithionite is highly soluble in water (182 g/L at 20°C) [164], but almost insoluble in organic solvents just as all the main group metal dithionites [60]. The other dithionite salt, [(C₂H₅)₄N]₂S₂O₄, is soluble in dimethylformamide, dimethylsulfoxide and acetonitrile [63]. The purity of lithium dithionite Li₂S₂O₄ is of 90–92% [59,165], potassium dithionite contains less than 70% K₂S₂O₄ [60]. The density and viscosity of aqueous solutions of sodium dithionite, sodium dithionite + sucrose and sodium dithionite + sodium hydroxide + sucrose over the temperature range (25–40°C) were measured by Vázquez and coworkers [166]. Data on toxicity and effects on human health are summarized in Ref. [164]. Particularly, the acute oral LD50 of sodium dithionite in rats is about 2500 mg/kg bw…

One of the important features of redox reactions of sulfur-containing reductants is that many times their reducing capability is not connected directly to the original sulfur-containing compound but rather to their decomposition products in solutions. It is well known that, for example, sulfoxylate ion or sulfur dioxide anion radical has much stronger reducing ability than the corresponding thiourea dioxide (TDO) or dithionite ion. As a result, decomposition of these reductants and their reactions with oxidants are closely interrelated. The stability of these compounds in aqueous solutions depends appreciably on the pH and on the presence of dissolved oxygen. Sodium dithionite and hydroxymethanesulfinate are less stable in acidic media, but in contrast to this TDO is unstable in alkaline solutions…

The following sections are included:

• Synthesis of Organofluorine Compounds
• Synthesis of Guanidines
• Synthesis of Sulfur-, Selenium- and Tellurium-Containing Compounds
• Reduction of Aldehydes, Ketones and Unsaturated Compounds
• Synthesis of Nitrogen-Containing Compounds
• Organocatalytic Reactions

The following sections are included:

• Reduction of Graphene and Graphite Oxides
• Reduction of Metal Complexes. Synthesis of Metals and Metal Sulfides
• Reduction of Halogen Compounds

The following sections are included:

• Textile Industry
• Paper Industry
• Polymerization Processes

In analytical chemistry, in addition to the analysis of nitrogen-containing compounds mentioned in a previous chapter, TDO can be employed for determination of organic disulfides [734], rhodium and iridium [735,736]. Thiourea dioxide can as well be used as an effective toning agent in photography [737]…

The following sections are included:

• Bibliography
• Index