He Sodium thiosulphate Is an important inorganic salt with several medical uses. Also called sodium hyposulphite and its formula is Na 2 S2O 3 .
Sodium thiosulfate is also available as its pentahydrate salt (Na 2 S 2 OR 3 .5H 2 OR). It is an ionic compound formed by two sodium cations (Na + ) And the negatively charged thiosulfate anion (S 2 OR 3 - ), In which the central sulfur atom is attached to three atoms of oxygen and another atom of sulfur (hence the prefix uncle), through single and double bonds with resonance character. The solid exists in a monoclinic crystalline structure.
Figure 1: Structure of sodium thiosulfate.
Sodium thiosulphate can be prepared by heating the sulfur with an aqueous solution of sodium sulphite or an aqueous solution of sodium hydroxide.
6NaOH + 4S → Na 2 S 2 OR 3 + 2Na 2 S + 3H 2 OR
Sodium thiosulfate is a drug on the World Health Organization's Essential List of Medicines, the most effective and safe medicines needed in a health system (Sodium Thiosulfate Formula, S.F.).
Physical and chemical properties of sodium thiosulfate
Sodium thiosulphate has a molecular weight of 158.11 g / mol for its anhydrous form and 248.18 g / mol for the pentahydrate form. In addition, it has a density of 1.667 g / ml (National Center for Biotechnology Information, 2017).
Sodium thiosulfate are colorless monoclinic crystals without a characteristic aroma. Said solid is efflorescence, which means that it can be reduced to dust by itself by loss of crystallization water upon exposure to air. Their appearance is shown in figure 2.
Figure 2: appearance of sodium thiosulfate.
The compound has a melting point of 48 ° C for the pentahydrate form and from 100 ° C begins to decompose. The na 2 S 2 OR 3 Is very soluble in water being able to dissolve 70 grams for each 100 milliliters of solvent. The compound is practically insoluble in ethanol (Royal Society of Chemistry, 2015).
Sodium thiosulfate is a neutral salt that readily dissociates in water to give sodium and thiosulfate ions. Na 2 S 2 OR 3 Is a stable solid under normal conditions, but decomposes on heating to give sodium sulfate and sodium polysulphide:
4Na 2 S 2 OR 3 → 3Na 2 SW 4 Na 2 S 5
It also decomposes when treated with dilute acids to give sulfur and sulfur dioxide (called the clock reaction):
Na 2 S 2 OR 3 + 2HCl → 2NaCl + S + SO 2 + H 2 OR
It reacts stoichiometrically (in equimolar amounts) with aqueous iodine solutions, so it is widely used in laboratories for iodine-based titrations.
Reactivity and hazards
Sodium thiosulphate mono crystals.
Sodium thiosulphate is not a toxic material and is used for medical purposes. However, when decomposed, it produces toxic vapors of sulfur oxide, which may cause irritation to eyes, skin and mucous membranes.
The compound may irritate the eyes, skin and respiratory tract. The substance is toxic to the lungs and mucous membranes. Repeated or prolonged exposure to the substance may cause damage to the organs.
If the compound comes into contact with the eyes, contact lenses should be checked and removed. Immediately flush eyes with copious amounts of water for at least 15 minutes with cold water.
In case of skin contact, rinse the affected area immediately with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Cover irritated skin with an emollient. Wash clothing and shoes before reuse. If the contact is severe, wash with a disinfectant soap and cover the skin contaminated with an anti-bacterial cream
In case of inhalation, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen.
If the compound is ingested, do not induce vomiting unless directed to do so by medical personnel. Loosen tight clothing such as a shirt collar, belt or tie.
In all cases, immediate medical attention should be obtained. (Material Safety Data Sheet Sodium thiosulfate anhydrous, 2013).
Applications
Medicine
Sodium thiosulfate may be used to decrease some of the side effects of cisplatin (a cancer drug). 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.
It is also used with another drug in the emergency treatment of cyanide poisoning (U.S. National Library of Medicine, S.F.).
In such treatment, sodium nitrite is injected intravenously to produce hemoglobin that combines with the cyanide ion by temporarily converting it into the cyanemetoglobin form. Subsequently the sodium thiosulfate is injected.
Thiosulfate serves as a substrate for the rhodanase enzyme, which catalyzes the conversion of cyanide into the much less toxic thiocyanate, which is excreted in the urine (HSDB: SODIUM THIOSULFATE, 2003).
Sodium thiosulfate is also used as a treatment for calciphylaxis in people on hemodialysis with end-stage renal disease. Apparently there is a phenomenon not completely understood, by which this causes severe metabolic acidosis in some patients.
Iodometry
Sodium thiosulphate reacts stoichiometrically with iodine to give iodide according to the reaction:
2Na 2 S 2 OR 3 + I2 → S 4 OR 6 2- + 2I -
This property causes the compound to be used as a titrant in iodine determination.
This particular use can be established to measure the oxygen content of the water through a long series of reactions in the Winkler test for dissolved oxygen.
It is also used in the volumetric estimation of the concentrations of certain compounds in solution (hydrogen peroxide, for example) and in the estimation of the chlorine content in the commercial bleach powder and water.
Water softening
Sodium thiosulfate is used to dechlorinate water, including reducing chlorine levels for use in aquaria and swimming pools and spas and within water treatment plants to treat subsequent wash water established prior to release into the rivers.
The reduction reaction is analogous to the iodine reduction reaction, the thiosulfate reduces the hypochlorite (active ingredient in the bleach) and, by doing so, oxidizes to sulfate. The complete reaction is:
4NaClO + Na 2 S 2 OR 3 + 2NaOH → 4NaCl + 2Na 2 SW 4 + H 2 OR
Extraction of gold
Sodium thiosulfate is a component used as an alternative leaching agent to cyanide for the extraction of gold. However, it forms a strong soluble complex with the ions gold (I), [Au (S 2 OR 3 ) 2 ] 3- .
The advantage of this approach is that thiosulfate is not essentially toxic and that types of ore that are refractory to gold cyanidation may be leached by thiosulfate (M.G Aylmore, 2001).
References
- EMBL-EBI. (2016, June 1). Sodium thiosulfate. Retrieved from ebi.ac.uk: ebi.ac.uk.
- HSDB: SODIUM THIOSULFATE. (2003, May 3). Retrieved from toxnet: toxnet.nlm.nih.gov.
- G Aylmore, D. M. (2001). Thiosulfate leaching of gold-A review. Minerals Engineering Volume 14, Issue 2, 135-174. Sciencedirect.com.
- Material Safety Data Sheet Sodium thiosulfate anhydrous. (2013, May 21). Retrieved from sciencelab.com.
- National Center for Biotechnology Information. . (2017, March 18). PubChem Compound Database; CID = 24477. Retrieved from pubchem.ncbi.nlm.nih.gov.
- Royal Society of Chemistry. (2015). Sodium thiosulfate. Recovered from chemspider.com.
- Sodium Thiosulfate Formula. (S.F.) Recovered from softschools: softschools.com.
- S. National Library of Medicine. (S.F.). Sodium Thiosulfate (Into to twenty). Retrieved from ncbi.nlm.nih.gov.