Rhodanic acid and thiocyanates. Reactions characteristic of Hg(NCS)2 Thiocyanate ion
analytical group: СIˉ, Вгˉ, Iˉ, BrO3ˉ, CNˉ , SCNˉ-, S(2-)
The group reagent for anions of the second analytical group is an aqueous solution of silver nitrate AgNO3 in dilute nitric acid (usually in a 2 mol/l solution of HNO3). In the presence of silver cations, the anions of this group form precipitates of silver salts, which are practically insoluble in water and in dilute nitric acid. Truth,
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 (thiocyanate ion) SCN ˉ (or NCS ˉ ) also have reducing properties, but less pronounced than those of the sulfide ion (for example, they discolor potassium permanganate solution). The bromate ion BrO3 in an acidic environment is an effective oxidizing agent.
Analytical reactions of the chloride ion CIˉ.
Chloride ion SG is an anion of a strong monobasic hydrochloric (hydrochloric, hydrochloric) acid HCI.
Chloride ions SG form with silver cations Ag+ a white cheesy precipitate of silver chloride AgCl:
CI ˉ + Ag+ -> AgCl↓
The precipitate darkens on standing in the light 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, sodium thiosulfate with the formation of soluble silver(I) complexes.
Methodology. 3-4 drops of a solution of HCl, NaCl or KCI are added to the test tube and a solution of silver nitrate is added dropwise 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 KMn04, manganese dioxide Mn02, lead dioxide Pb02, etc., to molecular chlorine C12:
2MnO4 ˉ +10СI ˉ + 16Н+ → 2Мn2+ + 5С12 + 8Н20
Mn02 + 2CH + 4H+ →C12 + Mn2+ + 2H20
The escaping gaseous chlorine is detected by the blueness of wet starch iodide paper due to the formation of molecular iodine:
C12 + 2 I ˉ ->2CI ˉ +I2
Molecular iodine gives a blue molecular complex with starch on starch iodide paper. Reducers interfere, including Br ˉ , I ˉ also interact with oxidizing agents.
Methodology. 5-6 drops of a solution of HC1, NaCl or KC1 are added to the test tube, 5-6 drops of a concentrated solution of KMnO4 (or several crystals of KMp04), 2-3 drops of concentrated sulfuric acid are added and the mixture is heated ( definitely under pressure!). The initially formed pink-violet solution gradually partially or completely discolors. A drop of the mixture is applied to starch iodide paper.
There is a blue spot on the paper. You can also, without applying a drop of the mixture, bring wet starch iodide paper to the opening of the test tube; the paper is turning blue.
Some other chloride ion reactions. Chloride ions form with potassium dichromate K2Cr2O7 in an acidic medium volatile chromyl chloride Cr02C12 (brown vapour). Other reactions of chloride ions are also known, which are of less analytical interest.
Analytical reactions of the bromide ion Brˉ. Bromide ion Br- - anion of a strong monobasic hydrobromic (hydrobromic) acid HBr.
Reaction with silver nitrate (pharmacopoeia). Bromide ions form a yellowish precipitate of silver bromide AgBr with silver cations:
Vg ˉ + Ag+ → AgBr↓
The precipitate of silver bromide is practically insoluble in water, in nitric acid, in ammonium carbonate solution. Partially soluble in concentrated ammonia solution (but much less 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 AgNO3 solution. A light yellow precipitate of silver bromide precipitates.
Reaction with strong oxidizing agents (pharmacopoeia). Strong oxidizing agents (KMp04, Mn02, KBr03, sodium hypochlorite NaCIO, chlorine water, chloramine, etc.) in an acidic environment oxidize bromide ions to bromine, for example:
10Vr ˉ + 2MnO4 ˉ +16H+ →5Br2 + 2Mn(2+) +8H20
2Br ˉ + С12 →Br2 + 2С1
5Vg ˉ + Vg03 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 dissolves more than in water. The organic layer turns yellow-brown or yellow-orange. Molecular bromine can also be detected by reaction with fuchsin-sulphurous acid on filter paper (the paper takes on a blue-violet color) and also by reaction with fluorescein (red color). The reaction is hindered 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. 3-4 drops of NaBr or KBr solution are added to the test tube, 2-3 drops of H2SO4 solution are added and 4 -5 drops of chlorine water (or chloramine). Shake the solution, 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 the iodide ion G. Iodide ion G is the anion of a strong monobasic hydroiodic (hydroiodic) acid HI. In aqueous solutions, the iodide ion is colorless, does not hydrolyze, and has pronounced reducing properties; as a ligand, it forms stable iodide complexes with cations of many metals.
Reaction with silver nitrate (pharmacopoeia). 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↓
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 a solution.
Methodology. Add 3-4 drops of KI solution to the test tube, add 4 -5 drops of AgNO3 solution. A light yellow precipitate of silver iodide precipitates.
Reaction with oxidizing agents (pharmacopoeia - With NaN02 and FeCl3 as
oxidizers). Oxidizing agents (chlorine or bromine water, KMn04, KBrO3, NaN02, FeCl3, H20 2, etc.) in an acidic medium oxidize iodide ions I ˉ to iodine I2, for example:
2I ˉ + С12 →I2 + 2СГ
2I ˉ + 2Fe3+ →I 2 + 2Fe2+
2I ˉ + 2NO2 ˉ + 4Н+ →I2 + 2NO + 2Н20
Most often, chlorine water is used. The liberated iodine turns 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 is more soluble than in water. The organic layer turns purple and the aqueous layer turns light brown. With 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 interfere with the reaction (S2-, S203(2-), SO3(2-)) ,
also react with oxidizing agents.
Method (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 iodine transferred to it from the aqueous phase. Chlorine water is again added dropwise, shaking the test tube, until the solution becomes colorless.
due to the oxidation of iodine to colorless iodic acid.
Oxidation reactions of bromide and iodide ions used to open VR ˉ and I ˉ in their joint presence. To do this, to an aqueous sulfuric acid solution containing Br anions ˉ and I ˉ , add chlorine water and an organic solvent that is 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 be oxidized. ˉ to iodine I2. The organic layer turns purple - so
open iodide ions. Then, when chlorine water is added, iodine is oxidized to HIO3 and
the violet color of the organic layer disappears. The bromide ions Br present in the solution ˉ oxidized by chlorine water to molecular bromine Br2, which colors the organic phase already in orange - this is how bromide ions are opened. Further addition of chlorine water leads to the formation of yellow BrCl and the organic layer becomes yellow.
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, while shaking the tube, add chlorine water. Initially, iodine is formed and the organic layer turns purple, indicating the presence of iodide ions in the initial 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 molecular bromine dissolved in it, which indicates the presence of bromide ions in the initial aqueous solution. The addition of an excess of 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 occurs 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) 3-4 drops of KI solution, a drop of HC1 solution, 2-3 drops of an oxidizing agent solution - KN02 or NaN02 are added to the test tube and a drop is added freshly prepared aqueous solution of starch. The mixture turns blue.
b) On filter paper impregnated freshly prepared starch solution, apply a drop of an oxidizing agent solution - NaN02 or KN02 and a drop of an acidified KI solution. The paper is dyed blue.
Reaction with lead salts. Iodide ions form with lead(II) cations Pb2+ yellow precipitate of lead iodide PY2:
2I ˉ + Pb2 + →PY2
The precipitate dissolves in water when heated. When the solution is cooled, lead iodide is released in the form of beautiful golden scaly crystals (golden rain 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 salts of bismu-
ta(III) - black-brown precipitate of bismuth(III) iodide Bil3, etc.
Analytical reactions of thiocyanate ion (thiocyanate ion) SCNˉ.
Thiocyanate ion (or thiocyanate ion), denoted by the equivalent formulas SCN ˉ or NCS ˉ , the anion of strong thiocyanate
HSCN. Thiocyanate ion in aqueous solutions is colorless, does not hydrolyze, has
redox properties, with salts of various
metals forms stable thiocyanate complexes.
Reaction with silver nitrate The 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. It 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. 2-3 drops of a solution of potassium thiocyanate KSCN or ammonium thiocyanate NH4SCN are added to the test tube and AgNO3 solution is added dropwise until a white precipitate of silver thiocyanate precipitates. Continue adding the KSCN or NH4SCN solution dropwise, shaking the 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 pink rather than blue (color of cobalt(II) aquo complexes). To shift the equilibrium to the right, the reaction is carried out in an aqueous 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 iron(III) thiocyanate complexes with iron(III) cations in an acidic (to suppress iron(III) hydrolysis) medium.
(3-n), where P= 1, 2,..., 6. All iron(III) complexes with different contents of thiocyanato groups are colored red and in solution are in equilibrium with each other. At elevated concentrations of NCS ions ˉ complexes with a large value dominate in solution n, at low - 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 by the drip method on filter paper. Various anions interfere - S2-, SO3 (2-), S203 (2-), C2O4 (2-), I ˉ , NO2 ˉ etc.
Methodology. A drop of KNCS or NH+NCS solution and a pot of iron(III) salt solution are applied to the filter paper. The paper is dyed red.
Reaction with iodate ions. In an acidic environment, thiocyanate ions are oxidized by iodate ions with the release of free iodine:
5SCN ˉ +6IO3 ˉ +Н + +2H20 -> 5 SO4(2-) +5HCN+3I2
However, this reaction is hindered 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. Wet the filter paper freshly prepared starch solution and dried. 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 KIO3 are applied to it. The paper turns blue due to the formation of a blue molecular complex of starch with iodine released during the reaction.
Some other reactions of thiocyanate ions. Thiocyanate ions are decomposed by solutions of H2SO4, HN03 and strong oxidizing agents, enter into numerous reactions of complex formation, precipitation, redox and other reactions. For example, with mercury(II) nitrate Hg(N03)2 they form a white precipitate of mercury(II) thiocyanate Hg(SCN)2, which is soluble with an excess of SCN- ions; with Cu2+ cations -
soluble emerald-green complexes 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.
Rhodanic acid- colorless, oily, very volatile, strong-smelling, easily solidifying liquid (mp. 5 °C). In its pure state, it is very unstable and can only be stored at low temperature (refrigerant 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 .
Hydrothianoic acid 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) pretreated with HC1. In the anhydrous state, this compound is obtained by slightly heating dry mercury or lead thiocyanate in a stream of hydrogen sulfide:
Pb(SCN) 2 + H 2 S → PbS + 2HSCN
Hydrogen thiocyanate is a strong acid. In aqueous solution, it, like hydrochloric acid, is almost completely or at least almost completely dissociated.
Hydrothiocyanate salts - thiocyanates (thiocyanates) are easily obtained from cyanides by adding sulfur. Chemically, they strongly resemble chlorides. Like the latter, thiocyanates form with silver nitrate a precipitate insoluble in water and dilute acids - silver thiocyanate AgSCN. 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 SCN - ions. The rhodan ions themselves are colorless, as are their salts with colorless cations. Most of the thiocyanates are highly soluble in water. Silver, mercury, copper and gold thiocyanates are insoluble. It is difficult to dissolve lead thiocyanate, which decomposes in boiling water.
With moderately concentrated (1:1) sulfuric acid, thiocyanates decompose with the release of COS:
MSCN + 2H 2 SO 4 + H 2 O → COS + NH 4 HSO 4 + MHSO 4
Some thiocyanates, as well as the SCN ion - in solution, attach SO 2. This property can be used to remove SO 2 (and H 2 S) from gases and produce pure SO 2 .
The technical application of thiocyanate is found primarily in the dyeing of fabrics. In technology, ammonium thiocyanate NH 4 SCN is mainly obtained by acting NH 3 in an aqueous solution on CS 2 under pressure at a temperature of about 110 ° C: 2NH 3 + CS 2 \u003d NH 4 SСN + H 2 S. The release of hydrogen sulfide can be reduced by adding to the reaction mixture is slaked lime H 2 S + Ca (OH) 2 → CaS + 2H 2 O. Ammonium thiocyanate 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 dissolve, at 20 °C - 162 g of NH 4 SСN. 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 by the Folgard method.
Potassium thiocyanate KSCN crystallizes as colorless prisms with a specific gravity of 1.9. It melts at 161°C. Molten salt at 430 °C is colored blue, and when cooled it becomes colorless again.
It dissolves in water extremely easily and with strong cooling. In 100 g of water at 0 ° C, 177 dissolves, at 20 ° C - 217, and at 25 ° C - 239 g of KSCN. Potassium thiocyanate 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 deliquescent, but at the same time crystallizing without water in the form of colorless rhombic plates, sodium thiocyanate NaSCN is little used.
Obtaining thiocyanates
The main methods for obtaining HNCS are the interaction of (E)NCS with KHSO 4 or the ion exchange of aqueous solutions of NH 4 NCS (obtained by heating a mixture of ammonia and carbon disulfide). Rhodan or thiocyan is usually obtained 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 made by reacting NH 3 with CS 2 , and KNCS and NaNCS are made 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 reacting metal hydroxides or carbonates with HNCS:
HSCN + NaOH = NaSCN + H2O
CuSCN are obtained from alkali metal thiocyanates, sodium hydrosulfite and copper sulfate. Ca(SCN) 2 *3H 2 O is obtained by the action of calcium oxide on ammonium thiocyanate.
Complex compounds of thiocyanates
Thiocyanates form complex compounds in which the metal, depending on the donor-acceptor properties of the ligand, can be coordinated both at the N atom and at the S atom.
Hg(HH) forms trigonal complexes of mercury thiocyanate with pnitrobenzoylhydrazine (L). The interaction of the corresponding Hg(SCN) 2 with pnitrobenzoylhydrazine and fusion at a temperature of 50-60 0 C gave HgL(SCN) 2 . 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 C-N, C-S and C-S bands, which indicates the ring nature of the SCN group and its coordination with Hg 2+ through the S atom. that neutral Hg(SCN) 2 has a monomeric three-coordination structure.
The use 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 in dyeing and printing fabrics, in medicine, as a laboratory reagent, in electroplating, in 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 cotton mercerization, 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 make detonating capsules and matches. They are also used in analytical chemistry as reagents in rhodanometry and mercurymetry.
Thiocyanate complexes are used in photometric analysis to determine Co, Fe, Bi, Mo, W, Re, in rare metal technology to separate Zr and Hf, Th and Ti, Ga and Al, Ta and Nb, Th and La, to obtain spectrally pure La. Nb(V) and Ta(V) thiocyanates are catalysts in the Friedel-Crafts reaction.
2.5. Thiocyanate (thiocyanate) mercury (YY)
Hg(SCN) 2 is a poisonous, odorless, white crystalline powder. It dissolves well in hot water. It is poorly soluble in cold water (0.07 g per 100 g at 25 ° C) and in any esters. We will also dissolve in solutions of ammonia salts, in alcohol and in KSCN, in hydrochloric acid, as well as in solutions of thiocyanates with the formation of a complex ion. It is stable in air, but releases thiocyanate ions during long-term storage. Heat of formation of mercury thiocyanate (HJ) DH 0 arr. \u003d 231.6 kJ / mol, and the decomposition temperature is T 0 decomp. =165 0 C.
History reference
The first to receive 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, made a “sausage” out of the isolated substance and dried it, and then set it on fire for the sake of curiosity. The "sausage" caught fire, and a miracle happened: a long black-and-yellow "snake" crawled out and grew out of a nondescript white lump, wriggling, and growing. 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 then they began to call it the "Pharaoh's snake".
Obtaining Hg(SCN)2
Hg(SCN) 2 is formed by the interaction of KSCN with the Hg(JJ) salt:
Hg(NO 3 ) 2 +2KSCN = Hg(SCN) 2 v+2KNO 3
Or Hg(NO 3 ) 2 + 2NH 4 NCS = Hg(NCS) 2 v + 2NH 4 NO 3
The second reaction is exothermic.
Reactions characteristic of Hg(NCS)2
Hg (NCS) 2 dissolves in a solution of potassium thiocyanate to form a complex compound of tetrathiocyanomercurat (YI) potassium (white needle-like crystals, readily soluble in cold water, in alcohol, less soluble in any ethers):
Hg (NCS) 2 + 2KSCN \u003d K 2
Mercury(II) thiocyanate, after ignition, rapidly decomposes to form black mercury(II) sulfide HgS, yellow bulky carbon nitride of the 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:
2Hg(NCS) 2 = 2HgS + C 3 N 4 +CS 2
CS2 + 3O2 = CO2 + 2SO2
Carbon nitride swells with the resulting gases, while 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) thiocyanate 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. It is used in photography to enhance the negative. Interesting for laboratory work.
Toxicological aspects
Thiocyanates have a harmful effect on all living organisms. Therefore, in the process of working with them, contact with mucous membranes, eyes and skin should be avoided.
When small amounts of thiocyanates enter the body for a long time, the latter have a thyreostatic effect. Goiter and dystrophic processes in various organs can develop.
Symptoms of acute poisoning are shortness of breath, wheezing, impaired coordination of movements, constriction of the pupils, convulsions, diarrhea, jumps in blood pressure, cardiac disturbances and mental disorders.
In case of acute poisoning, it is necessary to stop contact of the victim with the substance. The victim needs warmth, rest and antidote therapy (nitrites, aminophenols, thiosulfates, organic cobalt compounds).
