Thiocyanic acid HCNS

Thiocyanic acid, HCNS, often called sulphocyanic acid, resembles cyanic acid in properties. It can be obtained as a volatile, pungent liquid, which rapidly polymerizes to a solid. Potassium thiocyanate is formed by heating a solution of potassium cyanide with sulphur —... 

Thiocyanates and selenocyanates can be made by fusing the corresponding cyanide with S or Se. The SCN and SeCN ions are both linear, like OCN . (See p, 779 for TeCN ) Treatment of KSCN with dry KHSO4 produces free isothiocyanic acid HNCS, a white crystalline solid which is stable below 0° but which decomposes rapidly at room temperatures to HCN and a yellow solid H2C2N2S3. Thiocyanic acid, HSCN, (like HOCN) has not been prepared... 

Some carbon-sulfur compounds, such as CS (carbon disulfide), the thiocyanides, and thiocyanates -CNS, such as HCNS (thiocyanic acid), Pb(CNS) (lead thiocyanate), elc. 

Dilute hydrochloric acid hydrocyanic acid, HCN, with an odour reminiscent of bitter almonds, is evolved in the cold. It should be smelled with great caution. A more satisfactory method for identifying hydrocyanic acid consists in converting it into ammonium thiocyanate by allowing the vapour to come into contact with a little ammonium polysulphide on filter paper. The paper may be conveniently placed over the test-tube or dish in which the substance is being treated with the dilute acid. Upon adding a drop of iron(III) chloride solution and a drop of dilute hydrochloric acid to the filter paper, the characteristic red colouration, due to the iron(III) thiocyanate complex, Fe(SCN)3, is obtained (see reaction 6 below). Mercury(II) cyanide is not decomposed by dilute acids. 

Hydrocyanic acid, HCN Cyanic acid, HOCN Thiocyanic acid, HSCN Hydrazoic acid, HN3... 

CHNS HCNS = HC=N+S = [N(CH)S], (methylidyneammoniumyl)o sulfanide, (hydridocarbonato)sulfidonitrogen HNCS = [C(NH)S], (hydridonitrato)sulfidocarbon isothiocyanic acid HSCN = [CN(SH)], nitridosulfanidocarbon thiocyanic acid HSNC = [NC(SH)], X2-methylidenethiohydroxylamine, carbidosulfanidonitrogen ... 

In addition to HCN, cyanogen, thiocyanic acid, and thiocyanogen, Schmeltz and Hoffmann, in their 1977 review of A/-containing components of tobacco and tobacco smoke, listed thirty-one nitriles [see Table IX in (3491)]. Ishiguro and Sugawara, in their 1980 catalog (1884) of the chemical... 

Alkyl thiocyanates, R—S—C=N, of lower carbon numbers are highly toxic. These compounds liberate HCN as a result of metabolic processes and can cause death (Manahan 1989). Methyl thiocyanate [556-64-9] is highly toxic, with an intravenous LD50 value of 18 mg/kg in mice (NIOSH 1986). Ethyl thiocyanate [542-90-5], allyl thiocyanate [764-49-8], butyl thiocyanate [628-83-1], and amyl thiocyanate [32446-40-5] are all toxic compounds with an LD50 (subcutaneous) value of less than 100 mg/kg. The phenyl ester [5285-87-0] exhibits greater toxicity (intravenous LD50 value in mice 6.7 mg/kg) than that of the aliphatic esters of thiocyanic acid. 

The compounds with C-N bonds form a significant branch of inorganic chemistry of carbon, these are hydrogen cyanide (HCN) and the cyanides, cyanic acid (HNCO) and the cyanates, and thiocyanic acid (HNCS) and the thiocyanates. 

Nitric acid, fuming phite, thiocyanates Organic matter, nonmetals, most metals, ammonia, chlorosulfonic acid, chromium trioxide, cyanides, dichromates, hydrazines, hydrides, HCN, HI, hydrogen sulfide, sulfur dioxide, sulfur halides, sulfuric acid, flammable liquids... 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

Thiocyanate is separated from cyanide by distilling off HCN from a weakly acid medium. With bromine and chloramine-T, thiocyanate is converted into cyanogen bromide and cyanogen chloride, respectively, and determined as a polymethine dye by the benzidine-pyridine method or pyridine—barbituric acid method [38—40]. The latter method has been applied for continuous determination of thiocyanate in blood plasma and in urine [40]. 

HCN is not completely stable and is marketed as a stabilized (often with H3PO4), flammable, anhydrous material. It reacts when heated, or in the presence of base or water, and may polymerize violently in contact with strong acids (e.g., sulfuric acid). Polymerization, once initiated, can be autocatalytic and, under confined conditions, lead to an explosion. It can be removed from waste streams by conversion to ammonium thiocyanate, a process involving scmbbing the waste stream with elemental sulfur in water (http //www.chemalliance.org). 

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