Cyanide, sulphide, iodide and bromide

Rocklin and Johnson [48] used an electrochemical detector in the ion chromatographic determination of cyanide and siolphide. They showed that by placing an ion exchange column in front of an electrochemical detector, using a silver working electrode, they were able to separate cyanide, sulphide, iodide and bromide and detect them in water samples at concentrations of 2, 30, 10 and lOpg L respectively. Cyanide and sulphide could be determined simultaneously. The method has been 

This method is based on the work of Pihlar and Kosta [50,51] who showed that a silver working electrode has the ability to produce a current that is linearly proportional to the concentration of cyanide in an amper-ometric electrochemical flow through cell. The reaction for cyanide is  

Under these conditions sulphides and halides produce insoluble precipitates rather than soluble complexes  

Rocklin and Johnson [49] overcame the latter problem by placing an ion exchange column in front of the electrochemical detector [119]. Cyanide and sulphide are separated and thus are determined simultaneously. Although bromide and iodide can be determined by ion chromatography with conductivity detection, the use of electrochemical detection results in greater selectivity as well as increased sensitivity. 

---

The chlorides, bromides, iodides, and cyanides are generally vigorously attacked by fluorine in the cold sulphides, nitrides, and phosphides are attacked in the cold or may be when warmed a little the oxides of the alkalies and alkaline earths are vigorously attacked with incandescence the other oxides usually require to be warmed. The sulphates usually require warming the nitrates generally resist attack even when warmed. The phosphates are more easily attacked than the sulphates. The carbonates of sodium, lithium, calcium, and lead are decomposed at ordinary temp, with incandescence, but potassium carbonate is not decomposed even at a dull red heat. Fluorine does not act on sodium bofate. Most of these reactions have been qualitatively studied by H. Moissan,15 and described in his monograph, Lefluor et ses composes (Paris, 1900). 

Various modifications of the amalgamation process have been employed in Mexico and Chile, but in recent years this method has been to a great extent supplanted by the cyanide process, described on p. 291. Extraction by amalgamation is more difficult with silver than with gold. Mercury liberates silver rapidly from the chloride, bromide, and iodide, and very slowly from the sulphide. Other ores have to be converted... 

The relative insolubility of some of the salts of silver is in the order chloride, cyanide, thiocyanate, bromide, iodide, and sulphide. The metal is usually estimated gravimetrically as chloride, or by electrolytic deposition. It can also be weighed as chromate.1 Other gravimetric methods are reduction to metal by hypophosphorous acid,2 and by alkaline glycerol and other reagents.3... 

Another important detector for ion chromatography is the electrochemical detector (ECD). This makes it possible to detect anions such as cyanide, nitrite, sulphide, bromide, iodide and sulphite with maximum sensitivity. Thanks to its specific detection capabilities it is also possible to identify these ions without interference alongside high concentrations of other ions which may also display similar retention values (Fig. 75). 

Discussion. The theory of the titration of cyanides with silver nitrate solution has been given in Section 10.44. All silver salts except the sulphide are readily soluble in excess of a solution of an alkali cyanide, hence chloride, bromide, and iodide do not interfere. The only difficulty in obtaining a sharp end point lies in the fact that silver cyanide is often precipitated in a curdy form which does not readily re-dissolve, and, moreover, the end point is not easy to detect with accuracy. 

Further applications of the determination of gas chromatography to the determination of anions in non saline waters are reviewed in Table 15.23. These include aminoacetates, arsenate, bromide, chloride, fluoride, iodide, cyanide, ethylene diamine tetraacetate, nitrate, phosphate, thiocyanate and sulphide. 

Aurous cyanide forms yellow, microscopic laminae, very slightly soluble in Water. It is more stable than aurous iodide, but at red heat is decomposed into gold and cyanogen. Its insolubility renders it immune to the action of dilute acids and hydrogen sulphide, but solutions of ammonia, potassium hydroxide, ammonium sulphide, and sodium thiosulphate dissolve it, probably forming complex derivatives. In aurous cyanide the tendency to form complex compounds is much more marked than in the corresponding chloride, bromide, and iodide.3 Its interaction with potassium ferrocyanide has been studied by Beutel.4... 

During the anodic polarization of a dropping mercury electrode the chloride, bromide, iodide, cyanide, thiocyanide and sulphide ions form slightly soluble salts or stable complexes with mercury. In the presence of these substances so-called anodic oxidation waves appear on polaro-graphic curves. The polarographic determination of chloride has received most attention. In many cases the dilution of the sample with 0.1 N H2SO4 is satisfactory and the solution can be polarographed directly [3]. 

Isopropyl Series. —iso-propyl mercuric hydroxide is formed by treating the halides with moist silver oxide, and has only been obtained in solution. It reacts with acids, giving rise to the following comj ounds chloride needles, M.jDt. 97° C. bromide needles, M.pt. 98° C. iodide plates, M.pt. 125° C. acetate M.pt. 95° C. cyanide, M.pt. 85° C. sulphide, M.jDt. 60° C. 

Test for Non-metallic Elements.—The substance to be analyzed is first decomposed by heating it with metallic sodium, and the resulting mixture, which may contain the following compounds of sodium, is analyzed chloride, bromide, iodide, phosphide, sulphide, cyanide, and sulphocyanide. The decomposition is accomplished as follows A clean, dry 6-inch test-tube is supported near the open end in a vertical position by means of a clamp and iron stand. A piece of sodium equal in size to a cube 3 mm. on each edge is cut and wiped free from oil by means of a filter paper. Any deposit on the sodium should be rejected,... 

The molecules of the types and of their derivatives were complete units, and the arrangement constituted a syst me unitaire . The sulphides, tellurides, oxides, acids, bases, salts, alcohols, ethers, etc., belong to the water type chlorides, bromides, iodides, fluorides and cyanides to the hydrochloric acid type nitrides, phosphides, arsenides, etc., to the ammonia type metallic hydrides and metals to the hydrogen type. More complicated compounds are formed by substitution of radicals for hydrogen in the types. Unknown compounds could be predicted in large numbers by this scheme of classification. 

Acyl cyanides are versatile synthetic intermediates and are generally prepared by the reaction of acid chlorides, acid bromides, and occasionally acid anhydrides with metal cyanides. It has now been found that the very reactive acyl iodides, used either preformed or generated in situ, are useful substrates for the preparation of ap-unsaturated and other acyl cyanides. Aryl acyl cyanides are obtained from the flash vacuum pyrolysis of 3-azido-l,2,4-oxadiazoles, and ethoxalyl cyanide from the reaction of di-n-heptyl sulphide with 2,3-dicyano-oxiran-2,3-dicarboxylate. The chemistry of acyl cyanides has been reviewed. ... 

Halogen detection. To a portion of the filtrate add excess of dilute nitric acid and boil in an evaporating basin for 10 minutes, or to half bulk, in order to remove any sulphide or cyanide, which interfere in the following test. Cool, and add dilute silver nitrate solution. A white or yeUow precipitate indicates the presence of chloride, bromide or iodide either singly or in admixture. 

---