CAS Number 7772-98-7
·
Linear Formula Na2S2O3
·
Molecular Weight 158.11
·
EC Number 231-867-5
·
MDL number MFCD00003499
·
PubChem Substance ID 329763718
Sodium thiosulfate (Na2S2O3), also spelled sodium
thiosulphate, is a chemical and medication. As a medication it is used to treat cyanide poisoning and pityriasis versicolor.
Detailed description
It is an inorganic compound that is
typically available as the pentahydrate, Na2S2O3·5H2O. The solid is an efflorescent (loses water readily) crystalline substance
that dissolves well in water. It is also called sodium hyposulfite or “hypo”.[3]
It is on the World
Health Organization's List of Essential Medicines, the
most effective and safe medicines needed in a health
system.
Uses
Medical
uses
·
It is used as an antidote to cyanide
poisoning.[5][6] Thiosulfate serves as a sulfur donor for
the conversion of cyanide to thiocyanate (which
can then be safely excreted in the urine), catalyzed by the enzyme rhodanase. For this purpose it is used
together with sodium
nitrite.[2]
·
It has been used as treatment of calciphylaxis in hemodialysis people
with end-stage kidney disease.[7] There is apparently an incompletely
understood phenomenon whereby this causes severe metabolic acidosis in some
patients.[8][9]
·
In foot baths for prophylaxis of ringworm, and
as a topical antifungal agent
for tinea versicolor.
·
It is used in the management of extravasations during chemotherapy.
Sodium thiosulfate prevents alkylation and tissue destruction by providing a
substrate for the alkylating agents that have invaded the subcutaneous tissues.
The dose may be 2 ml of 0.17 M (a solution of 4 ml 10% sodium thiosulfate and 6
ml sterile water for injection). It may be instilled subcutaneously into
multiple sites using a small-gauge needle. Data are limited on this method with
few recommendations.[citation needed]
·
In measuring the volume of extracellular body fluid and the renal glomerular
filtration rate.[10]
Iodometry
In analytical chemistry, the most important use comes because
the thiosulfate anion reacts stoichiometrically with iodine in aqueous solution, reducing it to iodide as it is oxidized to tetrathionate:
2 S2O32− + I2 → S4O62− + 2 I−
Due to the quantitative nature of this reaction, as well as
because Na2S2O3·5H2O has an
excellent shelf-life, it is used as a titrant in iodometry. Na2S2O3·5H2O
is also a component of iodine clock experiments.
This particular use can be set up to measure the oxygen content
of water through a long series of reactions in the Winkler test for dissolved
oxygen. It is also used in estimating volumetrically the
concentrations of certain compounds in solution (hydrogen
peroxide, for instance) and in estimating the chlorine content in
commercial bleaching powder and water.
Photographic
processing
Silver halides,
e.g., AgBr, typical components of photographic
emulsions, dissolve upon treatment with aqueous thiosulfate:
2 S2O32− + AgBr → [Ag(S2O3)2]3− + Br−
This application as a photographic fixer was
discovered by John
Herschel. It is used for both film and photographic paper processing;
the sodium thiosulfate is known as a photographic fixer, and is often referred to as
'hypo', from the original chemical name, hyposulphite of soda.[11]
Gold
extraction
Sodium thiosulfate is a component of an alternative lixiviant to cyanide for extraction of gold.[12] However, it forms a strong soluble complex
with gold(I) ions, [Au(S2O3)2]3−. The
advantage of this approach is that thiosulfate is essentially not toxic and
that ore types that are refractory to gold
cyanidation (e.g. carbonaceous or Carlin-type ores) can
be leached by thiosulfate. Some problems with this alternative process include
the high consumption of thiosulfate, and the lack of a suitable recovery
technique, since [Au(S2O3)2]3− does not adsorb to activated
carbon, which is the standard technique used in gold cyanidation to
separate the gold complex from the ore slurry.
Neutralizing
chlorinated water
It is used to dechlorinate tap water including lowering chlorine
levels for use in aquaria and swimming pools and spas (e.g., following
superchlorination) and within water
treatment plants
to treat settled backwash water prior to release into rivers.[3] The reduction reaction is analogous to the
iodine reduction reaction.
In pH testing of bleach substances, sodium thiosulfate neutralizes
the color-removing effects of bleach and allows one to test the pH of bleach
solutions with liquid indicators. The relevant reaction is akin to the iodine
reaction: thiosulfate reduces the hypochlorite (active ingredient in bleach)
and in so doing becomes oxidized to sulfate. The complete reaction is:
4 NaClO + Na2S2O3 + 2 NaOH → 4 NaCl + 2 Na2SO4 + H2O
Similarly, sodium thiosulfate reacts with bromine,
removing the free bromine from solution. Solutions of sodium thiosulfate are
commonly used as a precaution in chemistry laboratories when working with
bromine and for the safe disposal of bromine, iodine, or other strong
oxidizers.
Other
Sodium thiosulfate is also used:
·
As a component in hand
warmers and
other chemical heating
pads that
produce heat by exothermic crystallization of a supercooled solution.
·
In bacteriological water assessment, as it promotes the
survival of coliform organisms by neutralizing residual chlorine.[13]:249[14]:572
·
To demonstrate the concept of supercooling in
physics classes: Sodium thiosulfate, when heated, dissolves in its own water of crystallisation. This
solution can be cooled to room temperature without recrystallisation. When
crystallisation is induced by the addition of a small seed crystal, the sudden
temperature rise can be experienced by touch.
·
Often used in pharmaceutical preparations as an anionic
surfactant to aid in dispersion
Structure
Two polymorphs are known of the pentahydrate. The anhydrous salt
exists in several polymorphs.[3] In the solid state, the thiosulfate anion is tetrahedral in shape and is notionally
derived by replacing one of the oxygen atoms by a sulfur atom in a sulfate anion. The S-S distance indicates a single
bond, implying that the terminal sulfur bears significant negative charge and
the S-O interactions have more double-bond character.
Production
On an industrial scale, sodium thiosulfate is produced chiefly
from liquid waste products of sodium
sulfide or
sulfur dye manufacture.[15]
In the laboratory, this salt can be prepared by heating an
aqueous solution of sodium
sulfite with sulfur or by boiling aqueous sodium
hydroxide and
sulfur according to this equation:[16]
6 NaOH + 4 S → 2 Na2S + Na2S2O3 + 3 H2O
Principal
reactions
Upon heating to 300 °C, it decomposes to sodium sulfate and
sodium polysulfide:
4 Na2S2O3 → 3 Na2SO4 + Na2S5
Thiosulfate salts characteristically decompose upon treatment
with acids. Initial protonation occurs at sulfur. When the protonation is
conducted in diethyl
ether at
−78 °C, H2S2O3(thiosulfuric acid) can be obtained. It is a
somewhat strong acid with pKas of 0.6 and 1.7 for the first and
second dissociations, respectively.
Under normal conditions, acidification of solutions of this salt
excess with even dilute acids results in complete decomposition to sulfur, sulfur
dioxide, and water:[15]
Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O
This reaction is known as a "clock
reaction", because when the sulfur reaches a certain concentration,
the solution turns from colourless to a pale yellow. This reaction has been
employed to generate colloidal sulfur. This process is used to demonstrate the
concept of reaction
rate in
chemistry classes.
Aluminium
cation reaction
Sodium thiosulfate is also used in analytical chemistry. It can,
when heated with a sample containing aluminium cations, produce a white
precipitate:
2 Al3+ + 3 S2O32− + 3 H2O → 3 SO2 + 3 S + 2 Al(OH)3
Organic
chemistry
Alkylation of sodium thiosulphate gives S-alkylthiosulfonates,
which are called Bunte salts. This reaction is employed in one
synthesis of the industrial reagent thioglycolic acid:
ClCH2CO2H + Na2S2O3 → Na[O3S2CH2CO2H]
+ NaCl
Na[O3S2CH2CO2H]
+ H2O → HSCH2CO2H + NaHSO4
$68.48/KG OR $31.12/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
website: www.franchiseminerals.com
No comments:
Post a Comment