Rhodanide ions. Inorganic thiocyanates. Thiocyanate complexes

analytical group: CIˉ, Brˉ, Iˉ, BrO3ˉ, CNˉ ,SCNˉ-, S(2-)

The group reagent for anions of the second analytical group is an aqueous solution of silver nitrate AgN03 in dilute nitric acid (usually in a 2 mol/l solution of HN03). In the presence of silver cations, anions of this group form precipitates of silver salts, practically insoluble in water and dilute nitric acid. Is it true,

Silver sulfide Ag2S dissolves in nitric acid when heated. All anions of the second analytical group in aqueous solutions colorless, their barium salts are soluble in water. Sulfide ion S2- is a strong reducing agent (easily discolors iodine solution); chloride ion CI ˉ , bromide ion Br ˉ , iodide ion I ˉ , cyanide ion CN ˉ , thiocyanate ion (rhodanide ion) SCN ˉ (or NCS ˉ ) also have reducing properties, but less pronounced than those of the sulfide ion (for example, they discolor a solution of potassium permanganate). Bromate ion BrO3 in an acidic environment is an effective oxidizing agent.

Analytical reactions of chloride ion CIˉ.

Chloride ion SG is an anion of strong monobasic hydrochloric (hydrochloric, hydrochloric) acid HCI.

SG chloride ions form with silver cations Ag+ a white cheesy precipitate of silver chloride AgCl:

CI ˉ + Ag+ -> AgCl↓

When exposed to light, the precipitate darkens due to the release of finely dispersed metallic silver due to the photochemical decomposition of silver chloride. It dissolves in solutions of ammonia, ammonium carbonate, and sodium thiosulfate to form soluble silver(I) complexes.

Methodology. Add 3-4 drops of a solution of HCl, NaCl or KCI to the test tube and add a solution of silver nitrate drop by drop until the formation of a white precipitate of silver chloride stops.

Reaction with strong oxidizing agents. Chloride ions are oxidized by strong oxidizing agents (usually in an acidic environment), for example, potassium permanganate KMnO4, manganese dioxide MnO2, lead dioxide PbO2, etc., to molecular chlorine C12:

2MnO4 ˉ +10СI ˉ +16Н+ → 2Мn2+ + 5С12 + 8Н20

Mn02 + 2SG + 4H+ →C12 + Mn2+ + 2H20

The released chlorine gas is detected by the blueness of wet iodide-starch paper due to the formation of molecular iodine:

C12 + 2 I ˉ ->2СI ˉ +I2

Molecular iodine gives a blue molecular complex with starch on iodide-starch paper. Reducing agents, including Br, interfere ˉ , I ˉ also interact with oxidizing agents.

Methodology. Add 5-6 drops of a solution of HC1, NaCl or KS1 into a test tube, add 5-6 drops of a concentrated solution of KMP04 (or several crystals of KMP04), 2-3 drops of concentrated sulfuric acid and heat the mixture ( definitely under traction!). The initially formed pink-violet solution gradually becomes partially or completely discolored. A drop of the mixture is applied to iodide-starch paper.

A blue spot appears on the paper. You can also, without applying a drop of the mixture, bring wet iodide-starch paper to the opening of the test tube; the paper gradually turns blue.

Some other chloride ion reactions. Chloride ions form volatile chromyl chloride Cr02C12 (brown vapors) with potassium dichromate K2Cr2O7 in an acidic environment. Other reactions of chloride ions are also known, which are of less analytical interest.

Analytical reactions of bromide ion Brˉ. Bromide ion Br- is the anion of a strong monobasic hydrobromic (hydrobromic) acid HBr.

Reaction with silver nitrate (pharmacopoeial). Bromide ions form a yellowish precipitate of silver bromide AgBr with silver cations:

Vg ˉ + Ag+ → AgBr↓

The silver bromide precipitate is practically insoluble in water, nitric acid, and ammonium carbonate solution. Partially soluble in concentrated ammonia solution (but much less so than silver chloride). Dissolves in sodium thiosulfate solution to form silver(I) thiosulfate complex 3-:

AgBr+2S2O3(2-) →3- + Br ˉ

Methodology. Add 3-4 drops of NaBr or KBr solution to the test tube and add 4 -5 drops of AgN03 solution. A light yellow precipitate of silver bromide precipitates.

Reaction with strong oxidizing agents (pharmacopoeial). Strong oxidizing agents (KMn04, Mn02, KBr03, sodium hypochlorite NaCIO, chlorine water, chloramine, etc.) in an acidic environment oxidize bromide ions to bromine, for example:

10Vr ˉ + 2MnO4 ˉ +16Н+ →5Вг2 + 2Мn(2+) +8Н20

2Br ˉ + С12 →Br2 + 2С1

5Вг ˉ + Вг03 ˉ + 6Н+ →ЗВг2 + ЗН20, etc.

The resulting molecular bromine, which gives the aqueous solution a yellow-brown color, can be extracted from the aqueous phase with organic solvents (chloroform, carbon tetrachloride, benzene, etc.), in which it is more soluble than in water. The organic layer turns yellow-brown or yellow-orange. Molecular bromine can also be detected by reaction with fuchsin-sulfuric acid on filter paper (the paper takes on a blue-violet color) as well as by reaction with fluorescein (red color). The reaction is interfered with by other reducing agents (sulfide, sulfite, thiosulfate, arsenite ions, etc.), which also interact with oxidizing agents. When bromide ions are oxidized with a large excess of chlorine water, yellow BrCl is formed and the solution turns yellow:

Br2+ Cl 2 → 2BrC1

Methodology. Add 3-4 drops of NaBr or KBr solution to the test tube, add 2-3 drops of H2S04 solution and 4 -5 drops of chlorine water (or chloramine). Shake the solution and add 4 -5 drops of chloroform and shake the mixture again. The lower organic layer turns dark yellow, orange or light brown. The color of the aqueous phase becomes pale yellow.

Analytical reactions of iodide ion G. Iodide ion G is an anion of strong monobasic hydroiodic (hydriodic) acid HI. In aqueous solutions, the iodide ion is colorless, does not hydrolyze, and has pronounced reducing properties, as the ligand forms stable iodide complexes with cations of many metals.

Reaction with silver nitrate (pharmacopoeial). Iodide ions are precipitated by silver cations from aqueous solutions in the form of a light yellow precipitate of silver iodide Agl:

I ˉ + Ag +→ AgI↓

The silver iodide precipitate is practically insoluble in water, nitric acid and ammonia. It dissolves in solutions of sodium thiosulfate and with a large excess of iodide ions in solution.

Methodology. Add 3-4 drops of KI solution to the test tube and add 4 -5 drops of AgN03 solution. A light yellow precipitate of silver iodide precipitates.

Reaction with oxidizing agents (pharmacopoeial - With NaN02 And FeCl3 as

oxidizing agents). Oxidizing agents (chlorine or bromine water, KMn04, KBrO3, NaN02, FeCl3, H202, etc.) in an acidic environment oxidize iodide ions I ˉ to iodine I2, for example:

2I ˉ + C12 →I2 + 2SG

2I ˉ + 2Fe3+ →I 2 + 2Fe2+

2I ˉ + 2NO2 ˉ + 4Н+ →I2 + 2NO + 2Н20

Chlorine water is most often used. The released iodine colors the solution yellow-brown. Molecular iodine can be extracted from the aqueous phase with chloroform, benzene and other immiscible organic solvents

with water, in which molecular iodine dissolves better than in water. The organic layer turns purple, and the aqueous layer turns light brown. When there is an excess of chlorine water, the resulting iodine is further oxidized to colorless iodic acid HIO3 and the solution becomes colorless:

I2 + 5С12 + 6Н20 → 2HIO3 + 10НCI

Reducing agents (S2-, S203(2-), SO3(2-)) interfere with the reaction,

also react with oxidizing agents.

Methodology (oxidation of iodide ions with chlorine water). Add 2-3 drops of KI solution to the test tube and add chlorine water drop by drop until free iodine is released. Then add 3-5 drops of chloroform and shake the mixture. The organic layer turns purple due to the iodine that has passed into it from the aqueous phase. Add chlorine water dropwise again, shaking the test tube until the solution becomes discolored.

due to the oxidation of iodine to colorless iodic acid.

Oxidation reactions of bromide and iodide ions used to open Br ˉ and I ˉ in their presence together. To do this, to an aqueous sulfuric acid solution containing Br anions ˉ and I ˉ , add chlorine water and an organic solvent, immiscible with water, capable of extracting bromine and iodine from an aqueous solution (for example, chloroform). When interacting with chlorine water, iodide ions I are the first to oxidize ˉ to iodine I2. The organic layer turns purple - so

open iodide ions. Then, with the addition of chlorine water, iodine is oxidized to HIO3 and

the violet color of the organic layer disappears. Br bromide ions present in the solution ˉ are oxidized by chlorine water to molecular bromine Br2, which colors the organic phase orange - this is how bromide ions are discovered. Further addition of chlorine water leads to the formation of yellow BrCl and the organic layer takes on a yellow color.

Methodology. Add 2 drops of NaBr or KBr solution, 2 drops of KI solution, 5 drops of chloroform into the test tube and slowly, drop by drop, add chlorine water while shaking the test tube. First, iodine is formed and the organic layer turns purple, indicating the presence of iodide ions in the original aqueous solution. With further addition of chlorine water, the violet color of the organic phase disappears

(I2 is oxidized to HIO3) and it becomes orange-yellow (or brownish-yellow) due to the molecular bromine dissolved in it, which indicates the presence of bromide ions in the original aqueous solution. The addition of excess chlorine water leads to a change in the color of the organic phase to yellow due to the formation of BrCl.

Iodine-starch reaction. Molecular iodine, which appears during the oxidation of iodide ions with various oxidizing agents, is often discovered by reaction with starch, which forms a blue complex with iodine (more precisely, with triiodide ions I). The presence of iodine is judged by the appearance of a blue color.

Methodology.

a) Add 3-4 drops of KI solution, a drop of HC1 solution, 2-3 drops of oxidizing agent solution - KN02 or NaN02 into the test tube and add a drop freshly prepared aqueous starch solution. The mixture takes on a blue color.

b) On filter paper soaked freshly prepared starch solution, apply a drop of an oxidizing solution - NaN02 or KN02 and a drop of an acidified KI solution. The paper turns blue.

Reaction with lead salts. Iodide ions form with lead(P) cations Pb2+ yellow lead iodide precipitate RY2:

2I ˉ + Pb2 + →Ры2

The precipitate dissolves in water when heated. When the solution is cooled, lead iodide is released in the form of beautiful golden scaly crystals (the “golden shower” reaction).

Other reactions of iodide ions. Iodide ions enter into numerous reactions with various reagents. For example, with copper(II) salts they form a brown precipitate (a mixture of copper(I) iodide CuI and iodine I2), with mercury(II) salts - a red precipitate of mercury(II) iodide HgI2, with mercury(I) salts - a precipitate mercury(I) iodide Hg2I2 green, with bismuth salts

Ta(III) - precipitate of bismuth iodide (III) Bil3, black-brown, etc.

Analytical reactions of thiocyanate ion (rodanide ion) SCNˉ.

Thiocyanate ion (or thiocyanate ion), denoted by equivalent formulas SCN ˉ or NCS ˉ , strong thiocyanate anion

HSCN. Thiocyanate ion in aqueous solutions is colorless, does not hydrolyze, and has

redox properties, with various salts

metals forms stable thiocyanate complexes.

Reaction with silver nitrate Thiocyanate ion, when interacting with silver cations, forms a white cheesy precipitate of silver thiocyanate AgCSN:

SCN ˉ + Ag+ -> AgSCN

The precipitate is insoluble in mineral acids and in ammonium carbonate solution. Dissolves in aqueous ammonia, in solutions of sodium thiosulfate, potassium cyanide, with an excess of thiocyanate ions to form the corresponding soluble silver complexes:

AgSCN + 2NH3 →+ + SCN’ ˉ

AgSCN+ nS2O3(2-)→ (1-2n) + SCN ˉ (n = 2 and 3)

AgSCN+2CN ˉ "->ˉ +SCN ˉ

AgSCN+ (n-1)SCN ˉ →(1-n) (u = 3 and 4)

Methodology. Add 2-3 drops of a solution of potassium thiocyanate KSCN or ammonium thiocyanate NH4SCN into a test tube and add a solution of AgN03 drop by drop until a white precipitate of silver thiocyanate precipitates. Continue adding the KSCN or NH4SCN solution drop by drop, shaking the test tube, until the silver thiocyanate precipitate dissolves.

Reaction with cobalt(II) salts. Thiocyanate ions in the presence of cobalt(II) cations form blue tetrathiocyanatocobaltate(II) ions 2-, coloring the solution blue:

4NCS ˉ +Co2+ ↔ 2-

However, these complexes are not strong enough, with a not very large excess of NCS ions ˉ the equilibrium is shifted to the left and the solution turns not blue, but pink (color of cobalt(II) aqua complexes). To shift the equilibrium to the right, the reaction is carried out in a water-acetone medium or the complex is extracted with organic solvents in which it dissolves better than in water (for example, in a mixture of isoamyl alcohol and diethyl ether).

Reaction with iron(III) salts. Thiocyanate ions form red-colored iron(III) thiocyanate complexes with iron(III) cations in an acidic (to suppress iron(III) hydrolysis) environment

(3-n), where P= 1, 2,..., 6. All iron(III) complexes with different contents of thiocyanate groups are colored red and are in equilibrium with each other in solution. At elevated concentrations of NCS ions ˉ complexes with a large value dominate in the solution n, when reduced - with a lower value P. The resulting complexes can be extracted with organic solvents - diethyl ether, amyl alcohol, etc.

This. It can be carried out using the drop method on filter paper. Various anions interfere - S2-, SO3(2-), S2O3(2-), C2O4(2-), I ˉ ,NO2 ˉ etc.

Methodology. A drop of KNCS or NH+NCS solution and a pot of iron salt solution are applied to the filter paper. The paper turns red.

Reaction with iodate ions. In an acidic environment, thiocyanate ions are oxidized by iodate ions to release free iodine:

5SCN ˉ +6IO3 ˉ +H + +2H20 -> 5 SO4(2-) +5HCN+3I2

However, this reaction is interfered with by reducing anions, which also react with iodate ions. Since the reaction produces highly toxic hydrocyanic

acid HCN, then it should only be carried out under traction!

Methodology. The filter paper is wetted freshly prepared starch solution and dry. Receive starch paper. A drop of a dilute solution of HC1, a drop of a solution of KSCN and a drop of a solution of potassium iodate KO3 are applied to it. The paper turns blue due to the formation of a blue molecular complex of starch and iodine released during the reaction.

Some other reactions of thiocyanate ions. Thiocyanate ions are decomposed by solutions of H2S04, HN03 and strong oxidizing agents, and enter into numerous complexation, precipitation, redox and other reactions. So, for example, with mercury(II) nitrate Hg(N03)2 they form a white precipitate of mercury(II) thiocyanate Hg(SCN)2, soluble in an excess of SCN- ions; with Cu2+ cations -

soluble complexes of emerald green color or (with an excess of Cu2+ cations) a black precipitate of copper(II) thiocyanate Cu(SCN)2, which when heated turns into white copper(I) thiocyanate CuSCN - etc.

Potassium rhodanide (according to modern IUPAC nomenclature - potassium thiocyanate) - colorless and odorless crystals; when finely dispersed they become white. The substance has a bitter, pungent taste and is poisonous. Potassium rhodanide is highly soluble in many solvents such as water, amyl alcohol and ethanol.

Receipt

The substance is obtained only chemically; isolating it from natural sources (human blood and saliva) is extremely expensive. In order to synthesize potassium thiocyanate, it is necessary to mix solutions of ammonium thiocyanate and potassium hydroxide (the trivial name is potassium hydroxide).

The experiment is carried out under draft, because the released ammonia can cause chemical burns and poisoning; then the purified solution is filtered and the residue is evaporated until crystals of the required substance are obtained. With a product yield of up to seventy percent and a fairly pure sample of ammonium thiocyanate, this method is very effective.

Another method is to fuse sulfur with; however, this method of producing potassium thiocyanate is very dangerous due to the high toxicity of cyanide.

Application

Potassium thiocyanate, its derivatives and solutions with varying concentrations are used in several industries. For example:

• Textile industry.
• Film photography.
• Organic synthesis.
• Analytical chemistry.

Areas of use

1. In the textile industry. A solution of potassium thiocyanate is used for etching fabrics, for example silk, during dyeing and processing in order to preserve the original properties of the material.
2. In organic synthesis. Some organic substances, such as thiourea, synthetic mustard oil and various dyes, are synthesized from potassium thiocyanate. It is also used to obtain other thiocyanates, for example copper-2 thiocyanate.
3. In analytical chemistry, a solution of potassium thiocyanate is used to determine ferric iron cations in a substance. A case in point is the reaction involving potassium thiocyanate and also called "blood out of water", which produces the purplish-red potassium hexacyanoferrate 3; the trivial name is red blood salt. Thiocyanates are also used to separate rare metals such as thorium and lanthanum. Potassium rhodanide and jelly chloride have recently helped in obtaining artificial blood for filming, but this method is falling into the background due to the introduction of computer graphics into film production.
4. In agriculture, strong insecticides are obtained from solutions of thiocyanates. There are two possible reactions:

• The first is the production of thiocyanine gas by removing potassium from salt; Rodane is a rather dangerous gas for all living organisms and is rarely used.
• The second is the dissolution of potassium thiocyanate, the collection of hydrocyanic acid released during hydrolysis and the oxidation of the resulting substance to cyanide. Cyan is no less poisonous, but a heavier gas compared to rhodane, and therefore is more often used as an insecticide.

Potassium rhodanide is a toxic substance, the lethal dose of which is about 0.9 grams of the substance per kilogram of human weight when the compound is taken orally.

Availability

Potassium rhodanide can be bought at any chemical store, but in small quantities due to its fairly high toxicity. The average price of the reagent is four hundred rubles per kilogram; sales are most often limited to two kilograms per person.

Security

Due to its toxicity, potassium thiocyanate must be stored under special conditions in accordance with safety requirements when handling toxic substances:

1. It is strictly forbidden to take crystals and solutions of potassium thiocyanate orally, and it is highly undesirable for solutions with a high concentration of the main substance to come into contact with the skin.
2. Despite the fact that the drug is toxic only when used internally, it is advisable to work with the substance in rubber gloves and a lab coat, as with all chemical reagents in accordance with basic safety requirements.
3. The substance should be isolated from children and persons who do not have the knowledge of a laboratory technician, as this can cause unpleasant incidents with the loss of reagents, improper use and sudden death.
4. Since the substance is non-flammable and quite stable in the air, you can get by with storing the substance in the dark. dry cabinet. High humidity and direct sunlight should be avoided, as the reagent may deteriorate due to its decomposition into its constituent parts. Also, according to the NFPA 704 standard, the diamond marking contains the following symbols: 3 0 0 W, where 3 (on the blue diamond) is toxicity, 0 (on red and yellow) is flammability and reactivity, and W is a mark for interaction with water, with which releases toxic thiocyanic acid.

And remember, chemical experiments are amazing and unique, but never neglect safety precautions!

Hydrogen acid- colorless, oily, very volatile, sharp-smelling, easily solidifying liquid (mp 5 °C). In its pure state it is very unstable and can only be stored at low temperatures (cooling mixture) or in a dilute (less than 5%) solution. When it decomposes, hydrogen cyanide is formed along with a yellow solid product, the so-called isoperthiocyanic acid H 2 C 2 N 2 S 3.

Hydrogen thiocyanate is miscible with water in all respects. Its aqueous solution is easily obtained by decomposing thiocyanates with acids or by passing a solution of ammonium thiocyanate through cation exchange resins (for example, levatite), pre-treated with HC1. In the anhydrous state, this compound is obtained by weakly heating dry thiocyanate of mercury or lead in a stream of hydrogen sulfide:

Pb(SCN) 2 + H 2 S → PbS + 2HSCN

Hydrogen rhodane is a strong acid. In aqueous solution, it, like hydrochloric acid, is almost completely or at least almost completely dissociated.

Salts of thiocyanate acid - thiocyanates - are easily obtained from cyanides by adding sulfur. Their chemical properties strongly resemble chlorides. Like the latter, thiocyanates form with silver nitrate a precipitate insoluble in water and dilute acids - silver thiocyanate AgSСN. A typical and very sensitive reaction to thiocyanates is the red color already mentioned above, which appears due to the formation of iron (III) thiocyanate during the interaction of Fe 3+ and SСN - ions. Rhodane ions themselves are colorless, as are their salts with colorless cations. Most of the thiocyanates are highly soluble in water. The thiocyanates of silver, mercury, copper and gold are insoluble. Lead thiocyanate is difficult to dissolve and is decomposed by boiling water.

With moderately concentrated (1:1) sulfuric acid, thiocyanates decompose to release COS:

MSCN + 2H 2 SO 4 + H 2 O → COS + NH 4 HSO 4 + MHSO 4

Some thiocyanates, as well as the SСN ion, add SO 2 in solution. This property can be used to remove SO 2 (and H 2 S) from gases and to obtain pure SO 2.

Technical application of thiocyanates is found primarily in textile dyeing. In technology, ammonium thiocyanate NH 4 SCN is mainly obtained by reacting NH 3 in an aqueous solution on CS 2 under pressure at a temperature of about 110 °C: 2NH 3 + CS 2 = NH 4 SCN + H 2 S. The release of hydrogen sulfide can be reduced by adding reaction mixture slaked lime H 2 S + Ca(OH) 2 → CaS + 2H 2 O. Ammonium rhodanide is a colorless salt that crystallizes in the form of plates or prisms with a specific gravity of 1.31 and a melting point of 159 ° C. It dissolves in water very easily and with strong cooling. In 100 g of water at 0 ºC 122, at 20 °C - 162 g of NH 4 SCN are dissolved. It is also easily soluble in alcohol. In laboratories, it is used as a reagent for iron (III) salts and for the determination of silver using the Volhard method.

Potassium rhodanide KSCN crystallizes in the form of colorless prisms with a specific gravity of 1.9. It melts at 161 °C. Molten salt is blue at 430°C, but when cooled it becomes colorless again.

It dissolves in water extremely easily and with strong cooling. In 100 g of water, 177 g of KSCN dissolve at 0 °C, at 20 °C - 217, and at 25 °C - 239 g. Potassium rhodanide is formed by fusing potassium cyanide with sulfur or by fusing yellow blood salt with potash and sulfur. It finds the same application as ammonium thiocyanate.

Very easily diffused, but at the same time crystallizing without water in the form of colorless rhombic tablets, sodium thiocyanate NaSСN is rarely used.

Preparation of thiocyanates

The main methods for obtaining HNCS are the interaction of (E)NCS with KHSO 4 or ion exchange of aqueous solutions of NH 4 NCS (obtained by heating a mixture of ammonia and carbon disulfide). Rhodane or thiocyanine is usually prepared by the reactions:

Cu(SCN) 2 = CuSCN + 0.5(SCN) 2

Hg(SCN)2 + Br2 = HgBr2 + (SCN)2

Alkali metal and ammonium thiocyanates are obtained by trapping cyanide compounds contained in coke oven gas with solutions of the corresponding polysulfides. In addition, NH 4 NCS is obtained by reacting NH 3 with CS 2, and KNCS and NaNCS are obtained by fusing KCN or NaCN with sulfur.

KCN + S = KSCN(fusion)

Other thiocyanates are synthesized by the exchange reaction of sulfates, nitrates or metal halides with Ba, K or Na thiocyanate:

KSCN + AgNO 3 = AgSCN + KNO 3

or by the reaction of metal hydroxides or carbonates with HNCS:

HSCN + NaOH = NaSCN + H2O

CuSCNs are prepared from alkali metal thiocyanates, sodium hydrogen sulfite and copper sulfate. Ca(SCN) 2 *3H 2 O is obtained by the action of calcium oxide on ammonium thiocyanate.

Thiocyanate complexes

Thiocyanates form complex compounds in which the metal, depending on the donor-acceptor properties, the ligand can be coordinated both at the N atom and at the S atom.

Hg(YH) forms trigonal complexes of mercuric thiocyanate with pnitrobenzoylhydrazine (L). By reacting the corresponding Hg(SCN) 2 with pnitrobenzoylhydrazine and fusion at a temperature of 50-60 0 C, HgL(SCN) 2 was obtained. It has been experimentally established that this substance is insoluble in most organic solvents, moderately soluble in MeCN, and their solutions are not electrolytes. The spectrum of HgL(SCN) 2 shows bands C-N, C-S and C-S, which indicates the ring nature of the SCN group and its coordination with Hg 2+ through the S atom. Based on the fact that ligand L is monodentate and the SCN group is ring-shaped, it was concluded that that neutral Hg(SCN) 2 has a monomeric three-coordinate structure.

Applications of thiocyanates

Thiocyanates are used in industry. NH 4 SCN is used in electroplating, photography, dyeing and printing of fabrics (in particular, to preserve the properties of silk fabrics), for the preparation of cooling mixtures, for the production of cyanides and hexacyanoferrates (II), thiourea, guanidine, plastics, adhesives, herbicides.

NaSCN is used in photography, as a mordant for dyeing and printing fabrics, in medicine, as a laboratory reagent, in electroplating, for the preparation of artificial mustard oil, and in the rubber industry.

KSCN is used in the textile industry, in organic synthesis (for example, to obtain thiourea, artificial mustard oil or dyes), to obtain thiocyanates, cooling mixtures, insecticides.

Ca(SCN) 2 *3H 2 O is used as a mordant for dyeing or printing fabrics and as a solvent for cellulose, for the mercerization of cotton, in medicine instead of potassium iodide (for the treatment of atherosclerosis), for the production of hexacyanoferrates (II) or other thiocyanates, in the manufacture parchment.

CuSCN is used as a mordant in textile printing, in the manufacture of "marine paints" and in organic synthesis; Cu(SCN) 2 is used to prepare detonating capsules and matches. They are also used in analytical chemistry as reagents in rhodanometry and mercurimetry.

Thiocyanate complexes are used in photometric analysis for the determination of Co, Fe, Bi, Mo, W, Re, in rare metal technology for the separation of Zr and Hf, Th and Ti, Ga and Al, Ta and Nb, Th and La, to obtain spectrally pure La. Thiocyanates Nb(V) and Ta(V) are catalysts in the Friedel-Crafts reaction.

2.5. Mercury thiocyanate (rhodanide)

Hg(SCN) 2 is a poisonous, odorless, white crystalline powder. Dissolves well in hot water. It is poorly soluble in cold water (0.07 g per 100 g at 25 ° C) and in any ethers. It is also soluble in solutions of ammonia salts, in alcohol and in KSCN, in hydrochloric acid, as well as in solutions of thiocyanates to form a complex ion. It is stable in air, but releases thiocyanate ions during long-term storage. Heat of formation of mercury thiocyanate (YY) DN 0 arr. =231.6 kJ/mol, and the decomposition temperature is T 0 decomposition. =165 0 C.

Historical reference

The first to obtain mercury(II) thiocyanate was the young German scientist Friedrich Wöller, who was later credited with the discovery of thiocyanic acid.

One day in the fall of 1820, a very young medical student at the University of Heidelberg, Friedrich Wöller, mixing aqueous solutions of ammonium thiocyanate NH 4 NCS and mercury nitrate Hg (NO 3) 2, discovered that a white cheesy precipitate of an unknown substance precipitated from the solution. Wöller filtered the solution and dried the precipitate, molded the isolated substance into a “sausage” and dried it, and then set it on fire out of curiosity. The “sausage” caught fire, and a miracle happened: from the inconspicuous white lump, writhing and crawling out and growing, a long black and yellow “snake”. As it turned out later, Wöller was the first to obtain mercury (II) thiocyanate Hg(NCS) 2. From the beginning, the experiment was called Wöller’s thiocyanate “snake”, and only later they began to call it “Pharaoh’s snake”.

Preparation of Hg(SCN)2

Hg(SCN) 2 is formed by the interaction of KSCN with the Hg(III) salt:

Hg(NO 3 ) 2 +2KSCN = Hg(SCN) 2 v+2KNO 3

Or Нg(NO 3 ) 2 + 2 NH 4 NCS = Нg(NCS) 2 v+2NH 4 NO 3

The second reaction is exothermic.

Reactions characteristic of Нg(NCS)2

Нg(NCS) 2 dissolves in a solution of potassium thiocyanate to form the complex compound potassium tetrathiocyanmercurate (III) (white needle crystals, highly soluble in cold water, in alcohol, less soluble in any ethers):

Нg(NCS) 2 + 2KSCN = K 2

Mercury(II) thiocyanate, after ignition, quickly decomposes to form black mercury(II) sulfide HgS, yellow bulky carbon nitride of composition C 3 N 4 and carbon disulfide CS 2, which ignites and burns in air, forming carbon dioxide CO 2 and sulfur dioxide SO 2:

2Нg(NCS) 2 = 2HgS + C 3 N 4 +CS 2

CS2 + 3O2 = CO2 + 2SO2

Carbon nitride swells with the resulting gases; when moving, it captures black mercury(II) sulfide, and a yellow-black porous mass is obtained. The blue flame from which the “snake” crawls out is the flame of burning carbon disulfide CS 2.

Application

Mercury (II) rhodanide is used in analytical chemistry for the determination of cobalt, halides, cyanides, sulfides, and thiosulfates, for spectrophotometric measurements of the concentration of isocaproic acid chloride in production. It is a complexing agent. Used in inorganic synthesis. Used in photography to enhance the negative. Interesting for laboratory work.

Toxicological aspects

Thiocyanates have harmful effects on all living organisms. Therefore, when working with them, you should avoid contact of these substances with mucous membranes, eyes and skin.

When small amounts of thiocyanates enter the body over a long period of time, the latter have a thyreostatic effect. Goiter and degenerative processes in various organs may develop.

Symptoms of acute poisoning include shortness of breath, wheezing, poor coordination of movements, constriction of the pupils, convulsions, diarrhea, surges in blood pressure, cardiac dysfunction and mental disorders.

In case of acute poisoning, it is necessary to stop the victim’s contact with the substance. The victim needs warmth, rest and antidote therapy (nitrites, aminophenols, thiosulfates, organic cobalt compounds).