Alkali thiocyanates

Thiocyanate as BaS04. Treat the alkali thiocyanate solution with excess bromine water and heat for 1 hour on a water bath. Acidify the solution with hydrochloric acid and determine the sulphate formed by precipitating and weighing as BaS04 (Section 11.72) see also Section 11.75. 

Shipping, analysis, and safety factors are similar to those of ammonium thiocyanate, except that the alkali thiocyanates are more thermally stable. Sodium thiocyanate is best handled in 316 stainless steel. At room temperature where some iron contamination can be tolerated, type 304 can be used. Aluminum corrodes more rapidly than stainless steel, but some alloys can be used below 60°C. Some but not all mbber equipment is satisfactory. 

It may also be prepared by electrolysis of the alkali thiocyanates in aqueous or alcoholic solution, using a platinum gauze anode and a silver cathode. On evaporation under reduced pressure, thiocyanogen is obtained as a viscous oil, solidifying at —70° C.4... 

When an alkali thiocyanate is warmed with moderately concentrated sulphuric or hydrochloric acid, a yellow solid separates and carbonyl sulphide gas is evolved, which burns with a pale sulphurous flame. The yellow substance contains isoperthiocyanic acid, formed, together with hydrocyanic acid, according to the reaction ... 

The thiocyanates are generally soluble in water, the exceptions being those of lead, silver, mercury and copper. Most of them dissolve also in alcohol and ether. Aqueous solutions of the alkali thiocyanates undergo atmospheric oxidation under the influence of sunlight with solutions of medium concentration this change takes place rapidly, with separation of a yellow, amorphous precipitate consisting of pseudocyanogen sulphide, (CNS)3 (cf. p. 236). The concentration of thiocyanate most favourable to the separation of this sulphide is about 50 per cent, in summer and 10 per cent, in winter. In addition to this substance the products of the photochemical oxidation of potassium thiocyanate include hydrocyanic acid, sulphate, carbon dioxide, ammonia and ammonium salts ... 

Any pink colour that may develop in solutions of alkali thiocyanates on exposure to light is due to oxidation of traces of ferrous salts usually present by dissolved oxygen.3... 

The reaction between ferric salts and alkali thiocyanate, which constitutes the well-known test for ferric iron, has been the subject of much investigation.7 It may be represented simply thus,... 

The Complex Thiocyanates.—The alkali thiocyanates show a marked tendency to form double and complex salts with the thiocyanates of other metals. The double salts in general resemble in type the double halides. Such compounds as KAg(CNS)2 and K2Ag(CNS)3 may be considered as derivatives of di- and tri-thiocyanic acids, but in the salt (NH4)6Ag(CNS)6 the silver is not precipitated by the addition of chloride ion.8... 

Double Salts of Vanadous Thiocyanate.—When vanadous sulphate, V2(S04)3, in solution, is treated with barium thiocyanate, a green solution8 is obtained which is believed to contain vanadous thiocyanate, V(SCN)g, but attempts to isolate this compound have not met with success. Its double salts with the alkali thiocyanates have, however, been obtained in well-defined crystals when an alkali thiocyanate is substituted for the barium salt. The following are known —... 

The formation of the blue complex cobalt salt serves as a sensitive test for the detection of either cobaltous or mercuric ions with a sensitivity of ly Co or lOy of Hg in solution. Depending on the cation to be tested for, the test reagent consists of a concentrated solution of either mercuric chloride or cobaltous acetate containing alkali thiocyanate. The test may be carried out in one drop of liquid on a slide under a microscope (50-100X). Agitation of the drop with... 

The fixing process for paper and film is similar, but film and paper have their own unique characteristics and requirements. Until the 1970s, the primary agent used far fixing was sodium thiosulfate (hypo). Other fixing agents, though not as common, include ammonium thiosulfate, alkali thiocyanate, thiosinamine, cyanide, sodium sulfite, ammonia, thiourea, and... 

The Anunonium salt, (NH4)2Pt(CNS)4, has also been prepared4 by digesting ammonium chlor-platinite with a solution of an alkali thiocyanate until all has dissolved, and allowing to crystallise. It resembles the potassium salt. 

Alkali thiocyanates may be made the starting-point for the preparation of ferrocyanides. The potassium salt is mixed with twice the weight of iron filings necessary to form ferrous sulphide, and with double the quantity of ferrous hydroxide, m a freshly precipitated condition, to form ferrocyanide. The mixture is maintained for some twelve hours under agitation in a closed vessel at 110° to 120° C. Potassium ferrocyanide is formed, together with Prussian blue, and extracted from the residue with water.3... 

However, the authors discovered that in acetone, in the presence of Bu4PBr but in the absence of alkali thiocyanate, thiocyanates (1) were readily isomerized under mild conditions to the corresponding isothiocyanates (II) as shown in table 3-11. 

The full report of complex formation in the TiCl -KNCS-MeCN system has appeared. In the absence of the alkali thiocyanate, TiCl4 and MeCN form the adduct TiCl4,2MeCN. The i.r. and Raman spectra of this and its trideuterio analogue indicate a cis-stereochemistry. This would be the most likely stereochemistry for... 

White to yellow amorphous powder, d 2.85. Practically insol in water, dil acids, ale, acetone sol in NH4OH, ether, solns of alkali thiocyanates dec by coned mineral acids. 

It is advantageous to use nascent thiocyanogen for instance, bromine is added to a cooled solution of the organic compound and an alkali thiocyanate... 

Although thiocyanogen does not react with benzene or naphthalene, it does react with more highly condensed aromatic compounds such as anthracene benzopyrene, etc.761 The substance may be added to a solution of thiocyanogen (for its preparation see page 104), but it is simpler to generate the thiocyanogen in situ. The (SCN)2 is produced in the reaction mixture from alkali thiocyanate and bromine or chlorine or from Cu(SCN)2. Suitable solvents for work with bromine or chlorine are acetic acid, methanol, and methyl acetate, the last two saturated with NaBr or NaCl. 

The classical, generally applicable method of preparing aliphatic thiocyanates (a) is to treat a halide with an alkali thiocyanate or ammonium thiocyanate ... 

Thioureas are obtained analogously by boiling an amine hydrochloride and an alkali thiocyanate in aqueous solution66 or an amine and a thioiso-cyanate in alcohol 67 aromatic thioisocyanates generally react even in the cold. Further, aqueous ammonia solutions are converted smoothly into mono-alkylthioureas by isothiocyanates.68 Isothiocyanates can be converted directly into symmetrical thioureas by boiling them in aqueous dimethylformamide or dimethyl sulfoxide the thiocarbamic acids formed as intermediates by partial hydrolysis add to unchanged isothiocyanate with loss of COS.69... 

Treatment of alkyl halides with alkali thiocyanates leads to replacement of the halogen with formation of thiocyanic esters (organic thiocyanates). However, it is impossible to foretell whether thiocyanic esters or the isothiocyanic esters ( mustard oils ) will be products by this method but in all cases the latter is the more stable, so that thiocyanates can be converted into isothiocyanates by heat. 

A remarkable formation of the 5-S,S-dimethylsulfilimine of 3-phenyl-1,2,4-thiadiazole (344) occurs on treatment of N-(N-chlorobenzimidoyl)-S,S-dimethylsulfilimine (343) with alkali thiocyanate. The starting material is accessible without difficulty from N-chlorobenzamidine (342). The reaction takes place exothermally in acetonitrile, and may possibly involve the mechanism shown in the scheme, which incidentally postulates a novel migration of the sulfonium group. According to the components from which the molecule is built up, the synthesis may also be included among those of type B.246... 

One of the first observations of such stepwise, separate phase transitions of the paraffinic part of an amphiphilic molecule was made on tetra-n-amyl ammonium thiocyanate At 315 K the crystals undergo a major first-order transition [AS = 71 J/(K mol) with a 4.8 % volume change]. The final transition to the isotropic, molten salt at 323 K is entropically smaller [AS. = 59 J/(K mol) with a n gible volume change]. Since typical alkali thiocyanate entropies of fusion are 30-40 J/(K mol) it is reasonable to assume that the high-temperature crystal state is that of a condis crystals with considerable conformational freedom. 

The colorimetric procedures, though tedious and time-consuming, remain useful when the Mo concentrations in soils and plats are low. The stannous chloride-thiocyanate procedure, originally described by Marmoy (1939), and revised by Evans et al. (1950), Purvis and Peterson (1956), and Johnson and Arkley (1954), is one of the most widely used methods for determination of total Mo in soils. This procedure is based on formation of the colored complex Fe[MoO(SCN)5] produced by the reaction of Mo with an alkali thiocyanate and excess Fe in the presence of a reducing agent, stannous chloride. Isoamyl alcohol dissolved in carbon tetrachloride (Chapman and Pratt, 1961) is used to extract the complex from the aqueous phase. The Mo content is determined by comparison of the absorbance of the sample with appropriate standards. 

In the present study, exchanges have been carried out by using phosphoric acid esters having oxyethylene chains, CH -(OCH CH ) -OPO H (n=l-3). It has been found that the resulting organic derivatives or y-zirconium phosphate behave like crown ethers, forming complexes with various alkali thiocyanates and iodides. 

The exchanged products ZrP-EtOj were separately dispersed in aqueous solutions of alkali salts MX (M=Li, Na, K, and Cs X=SCN, I, Br, and NO3) and then evaporated to dryness at 90 C. Figure 4 shows the basal spacings of the samples thus dried with alkali thiocyanates as a function of the molar mixed ratio MSCN/ZrP EtOj. The basal... 

Figure 4. Basal spacings of the derivatives ZrP-EtOj (n=l-3) mixed with alkali thiocyanates MSCN (M= Li, Na, K, and Cs) in varied molar ratio x= MSCN/ZrP-EtOn-...

The reaction (1) can be carried out in the presence of an alkali thiocyanate. Under these conditions, the CNS acts not only as indicator for the ferric salt, by producing the soluble red Fe(CNS)3, but it also reduces the concentration of the Fe+ ions, since Fe(CNS)3 is only sUghtly dissociated. Consequently, the rate of the reaction between Fe+ and 8203 ions, and therefore the velocity of all the partial reactions in which Fe+ ions participate, is decreased. Accordingly, the catalyzed acceleration due to copper salts is particularly evident under these conditions. Therefore, extremely small amounts of copper are definitely revealed by the more rapid fading of the color that results from the action of thiosulfate on ferric thiocyanate. 

Alkali thiocyanates react with iodates in acid solution ... 

A yellow-red precipitate is formed with acid solutions of alkali thiocyanates Idn. Limit 0.7 y HgOg). ... 

Whatever the explanation for the color change, the interesting fact remains that in molten potassium or sodium thiocyanate the sulphur is highly reactive and displays reactions which are not realizable in aqueous solutions of alkali thiocyanates. Among such reactions are formation of silver sulfide from metallic silver formation of sodium thiosulfate with sodium sulfite conversion of metal oxides and sulfates (even lead sulfate)... 

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