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Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of
thiosulfuric acid Thiosulfuric acid is the inorganic compound with the formula . It has attracted academic interest as a simple, easily accessed compound that is labile. It has few practical uses. Preparation and degradation The acid cannot be made by acidifying a ...
, e.g. sodium thiosulfate . Thiosulfate also refers to the esters of
thiosulfuric acid Thiosulfuric acid is the inorganic compound with the formula . It has attracted academic interest as a simple, easily accessed compound that is labile. It has few practical uses. Preparation and degradation The acid cannot be made by acidifying a ...
, e.g. ''O'',''S''-dimethyl thiosulfate . The prefix
thio- The prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry. For example, from the word ''ether,'' referring to an oxyg ...
indicates that the thiosulfate is a
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
with one oxygen replaced by sulfur. Thiosulfate is
tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
at the central S atom. Thiosulfate salts occur naturally. Thiosulfate ion has C3v symmetry, and is produced by certain biochemical processes. It rapidly dechlorinates water and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate salts are mainly used in dying in textiles and the bleaching of natural substances. Sodium thiosulfate, commonly called ''hypo'' (from "hyposulfite"), was widely used in photography to fix black and white negatives and prints after the developing stage; modern 'rapid' fixers use
ammonium thiosulfate Ammonium thiosulfate (ammonium thiosulphate in British English) is an inorganic compound with the formula . It is white crystalline solid with ammonia odor, readily soluble in water, slightly soluble in acetone and insoluble in ethanol and diethyl ...
as a fixing salt because it acts three to four times faster. Some bacteria can metabolise thiosulfates.


Formation

Thiosulfate ion is produced by the reaction of
sulfite Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are wide ...
ion with elemental sulfur, and by incomplete oxidation of
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
s (e.g.
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...
oxidation). Sodium thiosulfate can be formed by disproportionation of sulfur dissolving in sodium hydroxide (similar to phosphorus).


Reactions

Thiosulfate ions are stable only in neutral or
alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of ...
ne solutions, but not in
acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
solutions, due to disproportionation to
sulfite Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are wide ...
ions and sulfur, the sulfite ions being dehydrated to sulfur dioxide: : This reaction may be used to generate an
aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be ...
suspension of sulfur and demonstrate the Rayleigh scattering of light in physics. If
white light White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White on ...
is shone from below, blue light is seen from sideways and orange light from above, due to the same mechanisms that color the
sky The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space. In the field of astronomy, ...
at midday and dusk. Thiosulfate ions react with iodine to give
tetrathionate The tetrathionate anion, , is a sulfur oxoanion derived from the compound tetrathionic acid, H2S4O6. Two of the sulfur atoms present in the ion are in oxidation state 0 and two are in oxidation state +5. Alternatively, the compound can be viewed ...
ions: : This reaction is key for
iodometry Iodometry, known as iodometric titration, is a method of volumetric chemical analysis, a redox titration where the appearance or disappearance of elementary iodine indicates the end point. Note that iodometry involves indirect titration of iodi ...
. With
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...
(X = Br) and
chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...
(X = Cl), thiosulfate ions are
oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
to
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
ions: :


Reactions with metals and metal ions

Thiosulfate ion extensively forms diverse complexes with
transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
s. In the era of silver-based photography, thiosulfate ion was consumed on a large scale as a "fixer" reagent. This application exploits thiosulfate ion's ability to dissolve silver halides. Thiosulfate ion (as sodium thiosulfate) is also used to extract or leach gold and silver from their
ores Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April ...
as a less toxic alternative to
cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of a ...
ion. Also reflecting its affinity for
metals A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
, thiosulfate ion rapid corrodes metals in
acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
conditions. Steel and stainless steel are particularly sensitive to pitting corrosion induced by thiosulfate ions. Molybdenum improves the resistance of stainless steel toward pitting (AISI 316L hMo). In
alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of ...
aqueous conditions and medium temperature (60 °C),
carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
and stainless steel (AISI 304L, 316L) are not attacked, even at high concentration of base (30%w  KOH), thiosulfate ion (10%w) and in presence of
fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ty ...
ion (5%w  KF).


Occurrence

The very rare mineral sidpietersite, , as the presence of this anion in the mineral bazhenovite was recently disputed.


Nomenclature

Thiosulfate is an acceptable common name (but used almost always); functional replacement
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
name is sulfurothioate; the systematic additive IUPAC name is trioxidosulfidosulfate(2−) or trioxido-1''κ''3''O''-disulfate(''S''—''S'')(2−). The external sulfur atom has an oxidation state of –1 while the central sulfur atom has an oxidation state of +5. The oxygen atoms have an oxidation state of –2. On the other hand, the external sulfur atom has a valence of 2 while the central sulfur atom has a valence of 6. The oxygen atoms have a valence of 2.


Biochemistry

The enzyme rhodanase (thiosulfate sulfurtransferase) catalyzes the detoxification of
cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of a ...
ion by thiosulfate ion by transforming them into thiocyanate ion and
sulfite Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are wide ...
ion: : Sodium thiosulfate has been considered as an empirical treatment for cyanide poisoning, along with hydroxocobalamin. It is most effective in a pre-hospital setting, since immediate administration by emergency personnel is necessary to reverse rapid intracellular hypoxia caused by the inhibition of
cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
, at
complex IV The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory elec ...
. It activates thiosulfate sulfurtransferase ( TST) in mitochondria. TST is associated with protection against obesity and type II (insulin resistant) diabetes.


References


External links


''Thiosulfate ion'' General Chemistry Online, Frostburg State University
{{Antidotes * Corrosion Corrosive substances Sulfur oxyanions