Sodium thiosulfate. Sodium thiosulfate Thiosulfate chemical formula

The antidote, which is used for poisoning with salts or other heavy metal compounds, has several names that are synonymous: sodium hyposulfite, sodium thiosulphate, sodium hyposulfate. But the most common name for this drug is sodium thiosulfate. Its use is due to the fact that the drug is relatively inexpensive and also non-toxic. It has been proven effective in treating poisoning with compounds of arsenic, copper, lead, mercury, bromine or iodine salts. As a result of interaction with them, sulfites are formed in the body, which are not toxic, as well as other non-toxic or low-toxic substances. Available in the form of powder and 30% solution in ampoules with a capacity of 5 ml, 10 ml and 50 ml.

Due to its unique properties, it is used (in combination with sodium nitrite) as an antidote for poisoning with cyanide compounds (cyanides), resulting in the formation of rhodanium compounds, which are less toxic. The mechanism of detoxification of poisoning and its salts is based on the conversion of cyanide into a relatively non-toxic thiocyanate ion. Under the action of the enzyme rhodonase, the formation of thiosulfate cyanide sulfur transferase occurs (present in many tissues, but mostly in the liver). The body itself has the ability to neutralize cyanide with the help of rhodonase, but only sodium thiosulfate can accelerate this slow process, the use of which contributes to the introduction of exogenous sulfur donors into the body.

Typically, sodium thiosulfate solution is used intravenously, orally, and through the skin. Intravenously, it is currently used as an antidote to treat cyanide poisoning and prevent and treat cancer. Usually 5-10 ml of sodium thiosulfate solution is administered, and 50 ml of solution is administered for lesions caused by cyanide compounds. In case of cyanide intoxication, there should be no delay in administering the antidote, since a rapid antidote cannot be ruled out. Therefore, patients are carefully observed in the first two days due to the possibility of recurrence of the symptoms of cyanide poisoning. In this case, sodium thiosulfate is additionally administered in half the dose. It is also used as a drug preservative.

Extensive experience (over a hundred years) has been accumulated in the safe use of sodium thiosulfate as a therapeutic agent. Data on its medical use have been documented since 1895. For example, for the combination therapy of arthritis, allergic diseases, and neuralgia, such a safe drug as sodium thiosulfate has long been known. Its use is effective as an antidepressant, antiarrhythmic and metabolic agent. Thiosulfate is unique in that it reacts with free radicals to form the compound sodium sulfate.

Hypersensitivity to a substance is the main indication for which sodium thiosulfate may be limited in use.

Contraindications: hypersensitivity, pregnancy and breastfeeding. It should be used to treat pregnant and lactating women only when absolutely necessary. Since animal reproduction studies have not been conducted with sodium thiosulfate, it is unknown whether it can interfere with reproduction or cause adverse effects on the embryo.

Sodium thiosulfate is a synthetic compound known in chemistry as sodium sulfate, and in the food industry as additive E539, approved for use in food production.

Sodium thiosulfate functions as an acidity regulator (antioxidant), anti-caking agent or preservative. The use of thiosulfate as a food additive allows you to increase shelf life and product quality, and prevent rotting, souring, and fermentation. In its pure form, this substance is involved in technological processes for the production of edible iodized salt as an iodine stabilizer and is used for processing baking flour, which is prone to caking and clumping.

The use of the food additive E539 is limited exclusively to the industrial sphere; the substance is not available for retail sale. For medical purposes, sodium thiosulfate is used as an antidote for severe poisoning and an anti-inflammatory agent for external use.

general information

Thiosulfate (hyposulfite) is an inorganic compound that is the sodium salt of thiosulfuric acid. The substance is a colorless, odorless powder, which upon closer examination turns out to be transparent monoclinic crystals.

Hyposulfite is an unstable compound that does not occur in nature. The substance forms a crystalline hydrate, which, when heated above 40 °C, melts in its own crystalline water and dissolves. Molten sodium thiosulfate is prone to supercooling, and at a temperature of about 220 ° C the compound is completely destroyed.

Sodium thiosulfate: synthesis

Sodium sulfate was first obtained artificially in the laboratory using the Leblanc method. This compound is a byproduct of soda production, which is formed by the oxidation of calcium sulfide. Interacting with oxygen, calcium sulfide is partially oxidized to thiosulfate, from which Na 2 S 2 O 3 is obtained using sodium sulfate.

Modern chemistry offers several methods for the synthesis of sodium sulfate:

• oxidation of sodium sulfides;
• boiling sulfur with sodium sulfite;
• interaction of hydrogen sulfide and sulfur oxide with sodium hydroxide;
• boiling sulfur with sodium hydroxide.

The above methods can produce sodium thiosulfate as a by-product of the reaction or in the form of an aqueous solution from which the liquid must be evaporated. An alkaline solution of sodium sulphate can be obtained by dissolving its sulfide in oxygen-saturated water.

The pure anhydrous compound thiosulfate is the result of the reaction of a sodium salt and nitrous acid with sulfur in a substance known as formamide. The synthesis reaction takes place at a temperature of 80 °C and lasts about half an hour; its products are thiosulfate and its oxide.

In all chemical reactions, hyposulfite acts as a strong reducing agent. In reactions with strong oxidizing agents, Na 2 S 2 O 3 is oxidized to sulfate or sulfuric acid, and with weak ones - to tetrathione salt. The oxidation reaction of thiosulfate is the basis of the iodometric method for determining substances.

The interaction of sodium thiosulfate with free chlorine, which is a strong oxidizing agent and toxic substance, deserves special attention. Hyposulfite is easily oxidized by chlorine and converts it into harmless water-soluble compounds. Thus, this compound prevents the destructive and toxic effects of chlorine.

In industrial conditions, thiosulfate is extracted from gas production waste. The most common raw material is illuminating gas, which is released during the coking process of coal and contains hydrogen sulfide impurities. Calcium sulfide is synthesized from it, which is subjected to hydrolysis and oxidation, after which it is combined with sodium sulfate to produce thiosulfate. Despite the multi-stage process, this method is considered the most cost-effective and environmentally friendly method for extracting hyposulfite.

Sodium thiosulfate: application

Sodium disulfide was used for a variety of purposes long before the compound was included in food supplements and medications. Antichlorine was used to impregnate gauze bandages and gas mask filters to protect the respiratory system from toxic chlorine during the First World War.

Modern areas of application of hyposulfite in industry:

• processing photographic film and recording images on photographic paper;
• dechlorination and bacteriological analysis of drinking water;
• removal of chlorine stains when bleaching fabrics;
• gold ore leaching;
• production of copper alloys and patina;
• leather tanning.

Sodium sulfate is used as a reagent in analytical and organic chemistry; it neutralizes strong acids and neutralizes heavy metals and their toxic compounds. The reactions of thiosulfate with various substances are the basis of iodometry and bromometry.

Food additive E539

Sodium thiosulfate is not a widely used food additive and is not freely available due to the instability of the compound and the toxicity of its breakdown products. Hyposulfite is involved in technological processes for the production of edible iodized salt and bakery products as an acidity regulator and anti-caking agent.

Additive E539 functions as an antioxidant and preservative in the manufacture of canned vegetables and fish, desserts and alcoholic beverages. This substance is also part of the chemicals used to treat the surface of fresh, dried and frozen vegetables and fruits.

Preservative and antioxidant E539 is used to improve the quality and increase the shelf life of such products:

• fresh and frozen vegetables, fruits, seafood;
• , nuts, seeds;
• vegetables, mushrooms and seaweed, canned in or oil;
• jams, jellies, candied fruits, fruit purees and fillings;
• fresh, frozen, smoked and dried fish, seafood, canned food;
• flour, starches, sauces, seasonings, vinegar, ;
• white and cane, sweeteners (dextrose and), sugar syrups;
• fruit and vegetable juices, sweet water, low-alcohol drinks, grape drinks.

When producing table iodized salt, the food additive E539 is used to stabilize iodine, which can significantly extend the shelf life of the product and preserve its nutritional value. The maximum permissible concentration of E539 in table salt is 250 mg per 1 kg.

In baking, sodium thiosulfate is actively used as part of various additives to improve product quality. Baking improvers are either oxidative or reductive. Anti-caking agent E539 is a restorative improver that allows you to change the properties.

Dough made from dense flour with short-tearing gluten is difficult to process, cakes, does not reach the required volume and cracks during baking. Anti-caking agent E539 destroys disulfide bonds and structures gluten proteins, as a result of which the dough rises well, the crumb becomes loose and elastic, and the crust does not crack during baking.

At enterprises, an anti-caking agent is added to flour along with yeast immediately before kneading the dough. The thiosulfate content in flour is 0.001-0.002% of its mass, depending on the manufacturing technology of the bakery product. Sanitary standards for the E539 additive are 50 mg per 1 kg of wheat flour.

Anti-caking agent E539 is used in technological processes in strict dosages, so there is no risk of thiosulfate poisoning when consuming flour products. Flour intended for retail sale is not processed before sale. Within normal limits, the supplement is safe and does not have a toxic effect on the body.

Use in medicine and its effect on the body

Soda hyposulfite is included in the World Health Organization's list of essential medicines as one of the most effective and safe medicines. It is administered subcutaneously, intramuscularly and intravenously as an injection solution or used as an external agent.

At the beginning of the twentieth century, sodium thiosulfate was first used as an antidote for hydrocyanic acid poisoning. In combination with sodium nitrite, thiosulfate is recommended for particularly severe cases of cyanide poisoning and is administered intravenously to convert cyanide into non-toxic thiocyanates, which can then be safely excreted from the body.

Medical uses of sodium sulfate:

The effect of hyposulfite on the human body when consumed orally has not been studied, so it is impossible to judge the benefits and harms of the substance in its pure form or as part of food products. There have been no cases of poisoning with the E539 additive, so it is generally considered non-toxic.

Sodium thiosulfate and legislation

Sodium thiosulfate is included in the list of food additives approved for use in food production in Russia and Ukraine. Anti-caking agent and acidity regulator E539 are used in accordance with established sanitary and hygienic standards exclusively for industrial purposes.

Due to the fact that the effect of the chemical on the human body when administered orally has not yet been studied, the E539 additive is not approved for use in the EU and the USA.

DEFINITION

Sodium thiosulfate under normal conditions it is colorless monoclinic crystals (Fig. 1), relatively well soluble in water (41.2% at 20 o C, 69.86% at 80 o C).

Forms crystalline hydrates of the composition Na 2 S 2 O 3 × 5H 2 O, which in the molten state are prone to supercooling. When heated to a temperature of 220 o C, it decomposes. In OVR it exhibits strong restorative properties.

Rice. 1. Sodium thiosulfate. Appearance.

Chemical formula of sodium thiosulfate

The chemical formula of sodium thiosulfate is Na 2 S 2 O 3. It shows that this molecule contains two sodium atoms (Ar = 23 amu), two sulfur atoms (Ar = 32 amu) and three oxygen atoms (Ar = 16 amu. m.). Using the chemical formula, you can calculate the molecular weight of sodium thiosulfate:

Mr(Na 2 S 2 O 3) = 2×Ar(Na) + 2×Ar(S) + 3×Ar(O);

Mr(Na 2 S 2 O 3) = 2×23 + 2×32 + 3×16 = 46 + 64 + 48 = 158.

Graphic (structural) formula of sodium thiosulfate

The structural (graphic) formula of sodium thiosulfate is more clear. It shows how atoms are connected to each other inside a molecule:

Ionic formula

Sodium thiosulfate is an electrolyte that dissociates into ions in aqueous solution according to the following reaction equation:

Na 2 S 2 O 3 ↔ 2Na + + S 2 O 3 2- .

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Thermally very unstable:

In the presence of sulfuric acid it decomposes:

Reacts with alkalis:

Reacts with halogens:

Thiosulfuric acid

If you boil an aqueous solution of sodium sulfite with sulfur and, after filtering out the excess sulfur, leave it to cool, then colorless transparent crystals of a new substance are released from the solution, the composition of which is expressed by the formula. This substance is the sodium salt of thiosulfuric acid.

Thiosulfuric acid is unstable. Already at room temperature it disintegrates. Its salts, thiosulfates, are much more stable. Of these, the most commonly used is sodium thiosulfate, also known incorrectly as "hyposulfite".

When some acid, such as hydrochloric acid, is added to a solution of sodium thiosulfate, the smell of sulfur dioxide appears and after a while the liquid becomes cloudy from the released sulfur.

The study of the properties of sodium thiosulfate leads to the conclusion that the sulfur atoms included in its composition have different oxidation levels: one of them has an oxidation state of +4, the other has 0 . Sodium thiosulfate - reducing agent . Chlorine, bromine and other strong oxidizing agents oxidize it to sulfuric acid or its salt.

Thiosulf? are you- salts and esters of thiosulfuric acid, H2S2O3. Thiosulfates are unstable and therefore do not occur in nature. The most widely used are sodium thiosulfate and ammonium thiosulfate.

Structure. Structure of the thiosulfate ion

Thiosulfate ion is close in structure to sulfate ion. In the 2− tetrahedron, the S-S bond (1.97A) is longer than the S-O bonds

Sodium thiosulfate can be classified as rather unstable substances. Sodium thiosulfate decomposes when heated to 220°C: In the reaction of thermal decomposition of sodium thiosulfate, we obtain sodium polysulfide, which also further decomposes into sodium sulfide and elemental sulfur. Interaction with acids: it is impossible to isolate thiosulfuric acid (hydrogen thiosulfate) by the reaction of sodium thiosulfate with a strong acid, since it is unstable and immediately decomposes: Hydrochloric and nitric acids will also undergo the same reaction. Decomposition is accompanied by a discharge that has an unpleasant odor.

Redox properties of sodium thiosulfate: due to the presence of sulfur atoms with an oxidation state of 0, the thiosulfate ion has reducing properties, for example, with weak oxidizing agents (I2, Fe3+), thiosulfate is oxidized to the tetrathionate ion: In an alkaline environment, the oxidation of sodium thiosulfate with iodine can proceed to sulfate.

And stronger oxidizing agents oxidize it to sulfate ion :

Strong reducing agents ion is reduced to S2- derivatives: Depending on conditions, sodium thiosulfate can exhibit both oxidizing and reducing properties.

Complexing properties of thiosulfates:

Thiosulfate ion is a strong complexing agent , used in photography to remove unreduced silver bromide from photographic film: The S2O32 ion is coordinated by metals through a sulfur atom, so thiosulfate complexes are easily converted into the corresponding sulfides.

Applications of sodium thiosulfate

Sodium thiosulfate is quite widely used both in everyday life and in industry. The main areas of application of sodium thiosulfate will be medicine, textile and mining industries, photography.

Sodium thiosulfate is used in the textile and paper industries to remove traces of chlorine after bleaching fabrics and paper, and in leather production it is used as a chromic acid reducer.

In the mining industry, sodium thiosulfate is used to extract silver from ores with low silver concentrations. Complex compounds of silver with thiosulfates are quite stable, at least more stable than complex compounds with fluorine, chlorine, bromides, and thiocyanates. Therefore, the isolation of silver in the form of a soluble complex compound of the composition or is industrially profitable. Work is underway on its use in gold extraction. But in this case, the instability constant of the complex compound is much higher and the complexes are less stable compared to silver ones.

The first use of sodium thiosulfate was in medicine. And to this day it has not lost its importance in medicine. True, other, more effective drugs have already been found for the treatment of many diseases, so sodium thiosulfate has begun to be used more widely in veterinary medicine. Sodium thiosulfate is used in medicine as an antidote for poisoning with arsenic, mercury and other heavy metals, cyanides (translates them into thiocyanates):

As mentioned above, the thiosulfate ion creates stable complex compounds with many metals, including many toxic heavy metals. The created complex compounds are low-toxic and are excreted from the body. This feature of sodium thiosulfate is the basis for its use in toxicology and treatment of poisoning.

Sodium thiosulfate is also used to disinfect the intestines in case of food poisoning, to treat scabies (together with hydrochloric acid), as an anti-inflammatory and anti-burn agent.

Sodium thiosulfate is widely used in analytical chemistry because it is a reagent in iodometry. Iodometry is one of the methods for quantitatively determining the concentrations of substances and to determine the concentration of iodine, a redox reaction with sodium thiosulfate is used:

A final fairly common use of sodium thiosulfate is its use as a fixative in photography. And although ordinary black and white photography has already given way to color photography and ordinary photographic film is used quite rarely, in many ways inferior to digital image recording, there are quite a few places where photographic plates and photographic film are still used. Examples include X-ray machines, both medical and industrial, scientific equipment, and phototelescopes.

In order for us to obtain a photographic image, it is enough for about 25% of the silver bromide in the photographic film to develop. And the rest of it remains in the photographic film and retains its photosensitivity. If the photographic film is exposed to light after development, then the undeveloped halogen silver that remains in it will be developed by the developer and the negative will darken. Even if all the developer is washed out, the negative will somehow darken in the light due to the decomposition of the silver halide.

To preserve the image on the film, the undeveloped silver halogen must be removed from it. To do this, an image fixation process is used, during which silver halides are converted into soluble compounds and washed out of the film or photograph. Sodium thiosulfate is used to fix the image.

Depending on the concentration of sodium thiosulfate in the solution, various compounds are formed. If the fixer solution contains a small amount of thiosulfate, then the reaction proceeds according to the equation:

The resulting silver thiosulfate is insoluble in water, so it is difficult to isolate it from the photographic layer; it is quite unstable and decomposes with the release of sulfuric acid:

Silver sulfide blackens the image and cannot be removed from the photo layer.

If there is excess sodium thiosulfate in the solution, complex silver salts will form:

The resulting complex salt, sodium thiosulfate argentate, is quite stable, but poorly soluble in water.

When there is a large excess of thiosulfates in the solution, complex silver complex salts that are highly soluble in water are formed:

These properties of sodium thiosulfate are the basis for its use as a fixative in photography.

Tetratnopic acid belongs to the group of polynoid acids. These are dibasic acids of a general formula, where they can take values ​​from 2 to 6, and possibly more. Polnithionic acids unstable and known only in aqueous solutions. Salts of polythioic acids—polythionates—are more stable; some of them are obtained in the form of crystals.

Polythionic acids - sulfur compounds with the general formula H2SnO6, where n>=2. Their salts are called polythionates.

Tetrathionate ion can be obtained by oxidation of the thiosulfate ion with iodine (the reaction is used in iodometry):

Pentationate ion obtained by the action of SCl2 on the thiosulfate ion and from Wackenroder's liquid by adding potassium acetate to it. First, prismatic crystals of potassium tetrathionate fall out, then plate-like crystals of potassium pentathionate, from which an aqueous solution of pentathionic acid is obtained by the action of tartaric acid.

Potassium hexathionate K2S6O6 best synthesized by the action of KNO2 on K2S2O3 in concentrated HCl at low temperatures.

An inorganic compound, sodium salt of thiosulfate acid with the composition Na 2 S 2 O 3. Under normal conditions, it is in the form of its crystalline hydrate Na 2 S 2 O 3 · 5H 2 O, which is colorless crystals; with slight heating it loses water of crystallization. Thiosulfate exhibits strong reducing properties and is capable of forming coordination compounds with metals.

The semi-lethal dose of sodium thiosulfate is 7.5 ± 0.752 g/kg body (for mice). Due to its low toxicity, thiosulfate can be freely used for medical purposes - it is an antidote for poisoning with cyanide and silver compounds.

Sodium thiosulfate is used in photography to dissolve silver bromide, and in the pulp, paper and textile industries to neutralize chlorine residues. Thiosulfate is a reagent for determining the content of iodine, bromine, chlorine and sulfur using the iodometry method. In the food industry, sodium thiosulfate is used as an antioxidant and sequestrant; in the international register of food additives it has code E539.

Physical properties

Pure sodium thiosulfate is a white, heavy powder, but under ordinary conditions it is in the form of its pentahydrate Na 2 S 2 O 3 · 5H 2 O, which crystallizes from solutions in the form of short prismatic or oblong crystals. In dry air, at 33 ° C, it loses moisture, and at 48 ° C, the thiosulfate dissolves in its own water of crystallization.

Receipt

In industry, sodium thiosulfate is synthesized by oxidation of sodium sulfide, hydrosulfide or polysulfides. In addition, one of the common methods is the interaction of sulfur with sodium sulfite:

The addition of sulfur to sulfite suspensions is carried out with constant stirring. The addition of cationic surfactants increases the wetting of sulfur and, accordingly, the reaction rate. The yield of the reaction depends on the temperature, the amount of sulfur and the intensity of stirring. Solutions of sodium thiosulfate are filtered hot, having previously gotten rid of excess sulfur, and when cooled, the hydrate Na 2 S 2 O 3 · 5H 2 O crystallizes from them, which dehydrates at a temperature of 60-105 ° C at atmospheric or reduced pressure. The purity of the product is about 99% and has minor impurities of sulfite and sodium sulfate.

Other industrial methods include treating sodium compounds with sulfur dioxide:

Sodium thiosulfate is also synthesized as a by-product in the production of sulfur dyes, where sodium polysulfides are oxidized by nitro compounds:

Chemical properties

Being in the form of crystalline hydrate under normal conditions, thiosulfate loses water upon low heating:

Further heating causes decomposition of the substance: with the formation of sulfur or sodium pentasulfide (with impurities of other polysulfides):

In a dark place, a thiosulfate solution can be stored for several months, but when boiled it immediately decomposes.

Thiosulfate is unstable to acids:

It is a strong reducing agent:

When interacting with halogens, thiosulfate reduces them to halides:

The latter reaction has found application in analytical chemistry in the titrimetric method of iodometry.

Thiosulfate participates in complexation reactions, binding compounds of certain metals, for example, silver:

Application

Sodium thiosulfate is widely used in photography to dissolve silver bromide from negatives or prints. In the pulp, paper and textile industries, thiosulfate is used to neutralize chlorine residues; it is involved in the dechlorination of water.

In mining, Na 2 S 2 O 3 acts as an extractant of silver from its ores. Thiosulfate is a reagent for determining the content of iodine, bromine, chlorine and sulfur using the iodometry method. Thiosulfate is also an antidote for poisoning with cyanide and silver compounds.

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