Ammonium thiocyanate, addition

Thiooarbamide.—This is an example of a reversible reaction, in which either ammonium-thiocyanate or thiouiea when heated yields the same equilibiium mi.xttue. It may bo shown by melting a little thiourea for a minute, when the presence of thiocyanate is indicated by the addition of P eCl,. 

After the addition of the potassium iodide solution, run in standard 0.1M sodium thiosulphate until the brown colour of the iodine fades, then add 2 mL of starch solution, and continue the addition of the thiosulphate solution until the blue colour commences to fade. Then add about 1 g of potassium thiocyanate or ammonium thiocyanate, preferably as a 10 per cent aqueous solution the blue colour will instantly become more intense. Complete the titration as quickly as possible. The precipitate possesses a pale pink colour, and a distinct permanent end point is readily obtained. 

Note Soon after the addition of ammonium thiocyanate a white precipitate of silver thiocyanate is formed first and then a reddish-brown colour appears that fades out completely upon shaking thereby leaving a white precipitate of silver thiocyanate. The end-point is indicated by the appearance of a permanent faint reddish brown colour that does not vanish upon shaking. 

To a flask are added 200 gm (2.6 moles) of ammonium thiocyanate, 59 gm (1.0 mole) of 85% hydrazine hydrate, and 25 ml of water. The solution is refluxed for 3 hr under nitrogen, cooled, the sulfur filtered, and the filtrate allowed to cool for 10-18 hr. The product crystallizes slowly on standing and is filtered. The crude product, on recrystallization from a 1 1 water-ethanol mixture, gives 46 gm of thiosemicarbazide, m.p. 180°-182°C. Evaporation of the mother liquor to half its volume and then cooling give an additional 5 gm of product. The total yield is 57%. 

Chlorides, bromides, and iodides can be quantitatively determined by treatment with silver nitrate, and, with suitable precautions, the precipitated halide is washed, dried, and weighed. Chlorides in neutral soln. can be determined by F. Mohr s volumetric process 27 by titration with a standard soln. of silver nitrate with a little potassium chromate or sodium phosphate as indicator. When all the chloride has reacted with the silver nitrate, any further addition of this salt gives a yellow coloration with the phosphate, and a red coloration with the chromate. In J. Volhard s volumetric process, the chloride is treated with an excess of an acidified soln. of silver nitrate of known concentration. The excess of silver nitrate is filtered from the precipitated chloride, and titrated with a standard soln. of ammonium thiocyanate, NH4CN8—a little ferric alum is used as indicator. When the silver nitrate is all converted into thiocyanate AgN03-fNH4CNS=AgCNS +NH4NOS, the blood-red coloration of ferric thiocyanate appears. 

Selenious acid forms a sparingly soluble crystalline additive compound with thiocyanic aeid, known as thiocyanoselenious acid, H2Se03.2HCNS. This is formed when a mixture of an alkali selenite and ammonium thiocyanate in aqueous solution is treated with fairly concentrated hydrochloric acid. When warmed with water it decomposes, liberating selenium.2... 

The bomb contents are digested with concentrated hydrochloric acid, and material still undissolved is then digested with potassium hydroxide and hydrogen peroxide. A crude separation is made by a sulfide precipitation from the combined digestion solutions. The sulfides are dissolved in aqua regia, the solution is evaporated, and antimony in the residue is reduced to antimony (III) with hydroxylamine hydrochloride. The sample, in ammonium thiocyanate-hydrochloric acid medium, is loaded onto a Dowex 2 column (SCN" form). Arsenic and other impurities are eluted with aliquots of more dilute ammonium thiocyanate-hydrochloric acid solutions. Antimony is eluated with sulfuric acid and fixed in solution by addition of hydrochloric acid. The activity of the solution caused by the 0.56 MeV y-ray of 2.8-day 122Sb is counted. 

In organo-fluorine compounds fluorine atoms can be eliminated by nucleophilic sulfur species to form C —S bonds. In principle, the fluorine to be eliminated can be bonded to aliphatic or araliphatic compounds, as well as to aromatic or heterocyclic compounds however, the replacement proceeds more efficiently the more the fluorine is activated. Therefore, the synthetic usefulness of these reactions is the broadest with fluoroaromatic compounds, including heteroaromatics, with which the reactions often proceed smoothly under mild conditions. The nucleophilic sulfur compound to be reacted is. in most cases, an aliphatic or aromatic thiol or a metal sulfide, but reactions with, for example, thiourea or ammonium thiocyanate have also been described. The sulfur introduced this way can be either oxidized or removed by reduction, opening additional possibilities for modifications of the original fluoro compounds. 

In the case of sine, the ammonium thiocyanate solution is first added to the solution of the zinc salt and then the pyridine. The addition of pyridine to a solution of tine salts produces a white gelatinous precipitate. 

The carbamate is a major component of commercial ammonium carbonate. The dithiocarbamate, an intermediate in the preparation oi ammonium thiocyanate (Chap. 19), results from addition of ammonia to one of the double bonds of carbon bisulfide ... 

Determination of Orthophosphates.—(1) With Silver Nitrate.— This depends upon the precipitation of silver orthophosphate in solutions of low and controlled acidity. In the assay of commercial 85 per cent, phosphoric acid of density 1-710 the syrup is diluted to a convenient volume and an aliquot part is taken which contains about 0-1 gram of H3P04. It is neutralised to phenolphthalein with approximately decinormal alkali (free from chloride). 50 c.c. of decinormal silver nitrate are then added while the solution is kept neutral to litmus by stirring in zinc oxide or a suspension of the hydroxide. The whole or a measured part of the filtered solution is acidified with nitric acid and, after the addition of ferric alum, the unused silver nitrate is titrated with standard decinormal ammonium thiocyanate in the usual manner. Alkali phosphates may also be determined in this way. 

This reaction is also used in the method of Holleman 2 as modified by Wilkie.3 A phosphate solution containing phenolphthalein is reddened by the addition of alkali, then just decolorised with nitric acid. An excess of standard silver nitrate is then added and decinormal sodium acetate and alkali to slight pink colour, followed by 2 c.c. of decinormal H2S04. The solution is diluted and filtered and the excess of silver determined by titration with decinormal ammonium thiocyanate. 

Iron (III) thiocyanate test This is another excellent test for cyanides and depends upon the direct combination of alkali cyanides with sulphur (best derived from an alkali or ammonium polysulphide). A little ammonium polysulphide solution is added to the potassium cyanide solution contained in a porcelain dish, and the whole evaporated to dryness on the water bath in the fume cupboard. The residue contains alkali and ammonium thiocyanates together with any residual polysulphide. The latter is destroyed by the addition of a few drops of hydrochloric acid. One or two drops of iron(III) chloride solution are then added. A blood-red colouration, due to the iron(III) thiocyanate complex, is produced immediately ... 

Ammonium thiocyanate solution yellow colouration in solution acidified with dilute hydrochloric acid, becoming blood-red upon the addition of zinc or of tin(II) chloride on account of the formation of hexathiocyanato-molybdate(III) [Mo(SCN)6]3 the latter is soluble in ether. The red colouration is produced in the presence of phosphoric acid (difference from iron). 

Ammonium thiocyanate (3.30mol) was added to 3,5-dimethylaniline (Imol) dissolved in 1.75 L DMF and the mixture reacted 3 hours. Thereafter, CUSO4 (1.65 mol) was added and the mixture stirred 3 days at ambient temperature. The mixture was poured into 8L water and the pH brought to 7.5 by the addition of NaHC03 (6.55 mol), extracted with EtOAc, and the product isolated after re-crystallization from hexane in 72% yield. H-NMR and IR data supplied. 

Phenylazo)phenyl Tellurium Thiocyanate Under an atmosphere of nitrogen, a solution of 152 mg (2 mmol) of ammonium thiocyanate in 40 ml dry methanol is slowly added to a stirred, refluxing mixture of 688 mg (2 mmol) of 2-(phenylazo)phenyl tellurium chloride and 50 ml dichloromethane. With constant stirring, the mixture is refluxed for 5 min after completion of the addition and then cooled to 20°. The solvents arc removed on a rotary evaporator. 200 ml dichloromethane are added, the mixture is vigorously stirred, and then filtered to remove insoluble ammonium chloride. The solvent is removed from the filtrate on a rotary evaporator. The residue is stirred with 8 ml methanol and then filtered. The filter cake is recrystallized from methanol to give orange-red crystals yield 60% m.p. 122° (dec.). 

In a 500-ml. three-necked flask fitted with a reflux condenser, a mechanical stirrer, and a 100-ml. dropping funnel are placed 17 g. (0.22 mole) of ammonium thiocyanate and 100 ml. of dry acetone (Note 1). Through the dropping funnel is added, with stirring, 28.2 g. (0.2 mole) of benzoyl chloride. After the addition is complete, the mixture is refluxed for 5 minutes. Then a solution of 18.6 g. (0.2 mole) of aniline in 50 ml. of dry acetone is added at such a rate that the solution refluxes gently. The mixture is poured carefully with stirring into 1.5 1. of water, and the resulting yellow precipitate (a-benzoyl- 8-phenylthiourea) is sepa-... 

Argentometric titration method has been applied to the determination of sulfonamide mixtures. The sulfonamides are quantitatively precipitated by the addition of excess standard silver nitrate solution, the precipitated silver salts removed by filtration, and the excess silver nitrate titrated with standard ammonium thiocyanate using ferric alum as indicator (32). 

Precipitation of silver azide from acetate solution and gravimetric determination of the silver as silver azide or silver chloride, or volumetrically by addition of an excess of standard silver nitrate solution and back-titration with standard ammonium thiocyanate using ferric alum as internal indicator. 

Yamaguchi, 1960). Its action is synergised by the addition of ammonium thiocyanate. A similar enhancement of action can be obtained by the addition of surfactants. 

The cerium(IV)-mediated generation of heteroatom radicals by oxidation of anions such as azides was discovered many years ago [10], However, Nair et al. applied this strategy for a C-S bond-forming reaction by oxidation of ammonium thiocyanate le only recently [11], Addition of thiocyanate radical to indole 18 provides an intermediate radical, which is further oxidized to the cation by CAN. Loss of proton from the cationic intermediate provides the substituted arene 19 in excellent yield (Scheme 6). 

The product is boiled with water, and the resulting precipitate of silver sulfide is collected by filtration, washed, dried, and weighed. Another sample of product is dissolved completely in concentrated nitric acid, any excess acid is removed by boiling, and the total silver ion is determined by titration with standard ammonium thiocyanate solution. Another sample of product is oxidized with concentrated nitric acid in a bomb tube, and after removal of silver and nitrate the sulfur is determined by precipitation as barium sulfate by addition of barium chloride solution. 

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