Thiosulfuric acid

Structural formula
General
Surname	Thiosulfuric acid
other names	Monosulfan monosulfonic acid
Molecular formula	H 2 S 2 O 3
Brief description	colorless, oily liquid (only below -30 ° C)
External identifiers / databases
CAS number 13686-28-7 PubChem 24478 ChemSpider 22886 DrugBank DB09499 Wikidata Q420074
properties
Molar mass	114.14 g mol −1
Physical state	liquid
pK s value	0.6 1.74
safety instructions
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

The thiosulfuric acid is an oxo acid of sulfur or a thioacid of the sulfuric acid , which is derived formally from the sulfuric acid, wherein an oxygen atom is replaced by a sulfur atom.

presentation

The anhydrous acid can be prepared by reacting hydrogen sulfide (H ₂ S) with sulfur trioxide (SO ₃ ) in diethyl ether at −20 ° C. From a temperature of −10 ° C, thiosulphuric acid breaks down again into H ₂ S and SO ₃ . Without ether, on the other hand, the equally easily decomposable Lewis adduct H ₂ S · SO _{3 is formed} .

properties

Thiosulfuric acid is in the SH form. The tautomeric structure with a double bond between the sulfur atoms is 41 kJ / mol more energetic. The two sulfur atoms have an average oxidation number of +2. H ₂ S ⁻¹ S ⁺⁵ O ₃

Salts of thiosulfuric acid

The salts of thiosulfuric acid, the thiosulphates , are stable in water. They can be made by boiling sulfite solutions with sulfur according to the following equation:

${\displaystyle \mathrm {S_{8}+8\ Na_{2}SO_{3}\longrightarrow 8\ Na_{2}S_{2}O_{3}} }$

Acidified thiosulphate solutions decompose with separation of sulfur:

${\displaystyle \mathrm {H_{2}S_{2}O_{3}\longrightarrow H_{2}O+SO_{2}+S} }$

Sodium thiosulfate is of practical importance as a fixing salt in photography . Thiosulfate ions have a reducing effect . It is used in bleaching plants to remove chlorine from chlorine-bleached fabrics. The quantitative reaction with iodine to form tetrathionate ions S ₄ O ₆ ²⁻ is used in analytical chemistry ( iodometry ).

Individual evidence

1. ↑ ^{a b c d e} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 .
2. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
3. ↑ Entry on thiosulfuric acid. In: Römpp Online . Georg Thieme Verlag, accessed on April 19, 2014.