Sodium tetrathionate

Sodium tetrathionate dihydrate
Names
	IUPAC name Sodium (sulfonatodisulfanyl)sulfonate dihydrate
Identifiers
CAS Number	13721-29-4 dihydrate; 10101-86-7 anhydrous;
3D model (JSmol)	Interactive image;
ECHA InfoCard	100.208.917
PubChem CID	203055;
CompTox Dashboard (EPA)	DTXSID50160108 ;
	InChI InChI=1S/2Na.H2O6S4.2H2O/c;;1-9(2,3)7-8-10(4,5)6;;/h;;(H,1,2,3)(H,4,5,6);21H2/q2+1;;;/p-2 Key: HAEPBEMBOAIUPN-UHFFFAOYSA-L;
	SMILES O.O.[O-]S(=O)(=O)SSS(=O)(=O)[O-].[Na+].[Na+];
Properties
Chemical formula	Na2S4O6
Molar mass	306.2665 g/mol (dihydrate)
Appearance	white powder
Density	2.1 g/mL (25 °C)
Solubility in water	30.6 g/L (20 °C)
Hazards
NFPA 704 (fire diamond)	2 0 0
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Sodium tetrathionate is a salt of sodium and tetrathionate with the formula Na₂S₄O₆^. $x$ H₂O. The salt normally is obtained as the dihydrate ( $x$ = 2). It is a colorless, water-soluble solid. It is a member of the polythionates, which have the general formula [S_$n$(SO₃)₂]^2-. Other members include trithionite ( $n$ = 1), pentathionate ( $n$ = 3), hexathionate ( $n$ = 4).^[1]

Sodium tetrathionate is formed by the oxidation of sodium thiosulfate (Na₂S₂O₃), e.g. by the action of iodine:^[1]

2 Na₂S₂O₃ + I₂ → Na₂S₄O₆ + 2 NaI

The reaction is signaled by the decoloration of iodine. This reaction is the basis of iodometric titrations.

Other methods include the coupling of sodium bisulfite with disulfur dichloride:^[1]

2 NaHSO₃ + S₂Cl₂ → Na₂S₄O₆ + 2 HCl

The ion has ideal C₂ symmetry, like H₂S₂. The S-S-S dihedral angle is nearly 90°. The central S-S distance is 2.115 Å, 0.01 Å longer than the two other S-S distances as well as those distances in most polysulfanes.^[2]

Structure of tetrathionate as its dihydrated sodium salt.^[2]

References

^ ^a ^b ^c Greenwood, N. N.; Earnshaw, A. (2 January 1991). Chemistry of the Elements - 3rd Edition. Elsevier. doi:10.1016/C2013-0-11881-8. ISBN 978-1-4832-8008-0. OCLC 1040594550. Retrieved 2022-02-15.
^ ^a ^b P. C. Christidis; P. J. Rentzeperis; C. A. Bolos (4 January 1986). "Crystal structure and chirality of sodium tetrathionate dihydrate, Na₂S₄O₆·2H₂O". Zeitschrift für Kristallographie. 177 (1–2): 107–p116. Bibcode:1986ZK....177..107C. doi:10.1524/zkri.1986.177.1-2.107.

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[G&E-1] Greenwood, N. N.; Earnshaw, A. (2 January 1991). Chemistry of the Elements - 3rd Edition. Elsevier. doi:10.1016/C2013-0-11881-8. ISBN 978-1-4832-8008-0. OCLC 1040594550. Retrieved 2022-02-15.

[Zeit-2] P. C. Christidis; P. J. Rentzeperis; C. A. Bolos (4 January 1986). "Crystal structure and chirality of sodium tetrathionate dihydrate, Na₂S₄O₆·2H₂O". Zeitschrift für Kristallographie. 177 (1–2): 107–p116. Bibcode:1986ZK....177..107C. doi:10.1524/zkri.1986.177.1-2.107.

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