Cyanide ion in aqueous solution

Frank SN, Bard AJ. 1977. Heterogeneous photocatalyst oxidation of cyanide ion in aqueous solutions at titanium dioxide powder. J Amer Chem Soc 99(l) 303-304. 

Elemental composition H 3.73%, C 44.44%, N 51.83%. HCN may be analyzed by GC or GC/MS. The aqueous solution may be directly injected onto the GC column and determined by an FID. For GC/MS determination, an alcoholic solution may be injected into the column. The characteristic mass ions are 27 and 26. The cyanide ion in aqueous solution also may be measured by cyanide ion-selective electrode, titrimetry, and by colorimetric methods (APHA, AWWA, WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). For colorimetric analysis, the aqueous solution may be treated with a dilute caustic soda solution, followed by treatment with chloramine-T, and then with pyridine-barbituric acid reagent. A red-blue color develops, the absorbance of which is measured by spectrophotometer at 578 nm. The concentration of CN is determined from a standard cahbration curve using KCN standards. 

Frank, S. N. Bard, A. J. Heterogeneous photocatalytic oxidation of cyanide ion in aqueous solutions at Ti02 powder, J. Am Chem Soc. 1977, 99, 303. 

On oxidation with halogens, the [Au(CN)2] ion forms irani-[Au(CN)2X2] (X = Cl, Br, 1). The cyanide complex anion, [Au(CN)4] , is prepared by the exchange reaction between [AuCU]" and CN" ions. The square-planar [Au(CN)4] anion further reacts with cyanide ions in aqueous solution to form [Au(CN)5] and [An(CN)6] ions. 

The benzoin condensation of benzaldehyde in the presence of the cyanide ion in aqueous solution is believed to have the following mechanism ... 

Cyanide Ion in Aqueous Solutions at Ti02 Powder. J. Am. Chem. 

Vapor-detector tubes sensitive to 1 ppm of HCN are available commercially. The presence of free cyanide ion in aqueous solution may be detected by treating an aliquot of the sample with ferrous sulfate and an excess of sulfuric acid. A precipitate of Prussian blue indicates that free cyanide ion is present. More sophisticated for continuous warning is the use of electrochemical sensors for HCN detection. 

Addition of cyanide ion to a,a-dihaloketones results in the formation of cyanoepoxides via cyanohydrin formation and subsequent dehydrobromination [117]. In this way, 3-ch]oro-3-bromopentan-2-one gives a virtually quantitative yield of cyanoepoxide consisting of 35% cis and 65% trans. The product is isomerised by pyridine to give the a-chloro-a-cyanoketone (42) which on further treatment with cyanide ion in aqueous solution gives the dicyanoepoxide (35% cis, 65% trans). 

Oxidation and Reduction.—Shinkai and co-workers have developed micellar models for flavin-dependent oxidases, which operate through the trapping of reactive carbanions. Thus 4-chlorobenzoylformic acid reacts with cyanide ion in aqueous solution to give 4,4 -dichlorobenzoin (72%) together with a small quantity of 4-chlorobenzoic acid (2.4%) formed by aerial oxidation of the carbanion. In the presence of a cationic surfactant micelle, the yield of oxidation product is greatly increased and there is a further rate acceleration in the presence of the hydrophobic flavin (34) since the mechanism shown (Scheme 2) is now strongly favoured. This type of reaction path also accounts for the oxidation of aromatic aldehydes in the same reaction system, and molecular oxygen may replace the flavin but with lower efficiency. The oxidation of nitroethane to acetaldehyde is catalysed by a similar combination of hydrophobic flavin and cationic surfactant and does not occur in their absence. 

Furfural undergoes condensation to furoin under the catal3rtic influence of cyanide ions in aqueous alcohol solution (compare Benzoin, Section IV,125) ... 

A competition between substitution and two kinds of quenching processes, either dependent or independent on the added nucleophile, is envisaged for the photosubstitutions of p-nitroanisole (pNA) ni.ns). With cyanide ions in aqueous aerated solution pNA is transformed on irradiation into 2-cyano-4-nitroanisole in high yield ns,ii8) probably via addition of cyanide to excited pNA. 

All ammonium salts are hydrolyzed in water, those of weak acids such as the acetate and the cyanide being very largely so. Anions of very weak acids cannot coexist with ammonium ions in aqueous solutions. For example, in the case of ammonium sulfide, a solution with a high enough pH to allow appreciable concentration of sulfide ions would have too much hydroxide to allow appreciable concentration of ammonium ions. 

A detailed, multimethod study of hydrated Tl(III) cyanide species in aqueous solution reveals that Tl(III) forms very strong complexes with cyanide ions (even stronger than halide-Tl(III) interactions)." " Formation of a series of Tl(III) complexes T1(CN) n= -4t) has been established, and the solution structures and stability constants were reported. The mono- and dicyano complexes [Tl(CN)(OH2)5] and [Tl(CN)2(OH2)4] show six-coordinate thallium centers, whereas Tl(CN)3(OH2) and [T1(CN)4] have four-coordinate T1(III) ions. 

The octacyatiomolybdate(IV) anion [Mo(CN)g] " has long been known and characterized and many aspects of its chemistry have been reviewed.This complex is readily obtained from the addition of cyanide ions to aqueous solutions of Mo or Mo compounds. A simple preparation is by the reaction between molybdate(VI), K[BH4] and CN in the presence of acetic acid, followed by precipitation with ethanol. llie crystal structure of several complexes containing the [Mo(CN)g] anion have been reported. In K4[Mo(CN)g]-2H20, [C6H6N02]4[Mo(CN)g] and Rb4[Mo(CN)g] 3H20 dodecahedral coordination has been found, but all the bond lengths are equal, at 2.163(7) However, the molybdenum... 

All animal fibrous proteins tested accumulated gold-cyanide ion from aqueous solution. Adsorption was highest at pH 2 accumulations were up to 9.8% of the DW for wool, 8.6% for eggshell membrane, 7.1% for chicken feathers, and <3.9% for other materials. In the case of eggshell membrane, adsorbed gold was desorbed with 0.1 M NaOH and the material can be used repeatedly. Eggshell membrane could remove gold-cyanide ion at concentrations near 1.0p,g/L. 

Ohtaki H, Radnai T (1993) Structure and dynamics of hydrated ions. Chem Rev 93 1157-1204 BUxt J, Glaster J, Mink J et al (1995) Stmcture of thallium (111) chloride, bromide, and cyanide complexes in aqueous solution. J Am Chem Soc 117 5089-5104... 

Addition of hydrogen cyanide proceeds by way of cyanide ion. Because HCN is a weak acid, 9.31, the concentration of cyanide ion in aqueous HCN is too low for cyanohydrin formation to proceed at a reasonable rate. For this reason, cyanohydrin formation is generally carried out by dissolving NaCN or KCN in water and adjusting the pH of the solution to approximately 10.0, giving a solution in which HCN and CN are present in comparable concentrations. 

Hancock, P.D., Finkelstein, N.P., and Evers, A. (1972) Stabilities of the cyanide complexes of the IB group monovalent metal ions in aqueous solution. / Inorg. Nucl. Chem., 34 (12), 3747 -3751. 

Nitrogen.—Oxoanions. Peroxonitrite ion reacts with the nucleophiles cyanide, iodide, or thiocyanate in alkaline solution. These reactions involve an associative mechanism for oxygen atom transfer to the nucleophile, to leave nitrite ion. In aqueous solution the A -hydroxohydroxylamine-A -sulphonate anion (5) decomposes to nitrous oxide and sulphate. In the pH range 6—10 the rate law is... 

The complex cyanides of transition metals, especially the iron group, are very stable in aqueous solution. Their high co-ordination numbers mean the metal core of the complex is effectively shielded, and the metal-cyanide bonds, which share electrons with unfilled inner orbitals of the metal, may have a much more covalent character. Single electron transfer to the ferri-cyanide ion as a whole is easy (reducing it to ferrocyanide, with no alteration of co-ordination), but further reduction does not occur. 

A determination of dimethyl sulphoxide by Dizdar and Idjakovic" is based on the fact that it can cause changes in the visible absorption spectra of some metal compounds, especially transition metals, in aqueous solution. In these solutions water and sulphoxide evidently compete for places in the coordination sphere of the metal ions. The authors found the effect to be largest with ammonium ferric sulphate, (NH4)2S04 Fe2(S04)3T2H20, in dilute acid and related the observed increase in absorption at 410 nm with the concentration of dimethyl sulphoxide. Neither sulphide nor sulphone interfered. Toma and coworkers described a method, which may bear a relation to this group displacement in a sphere of coordination. They reacted sulphoxides (also cyanides and carbon monoxide) with excess sodium aquapentacyanoferrate" (the corresponding amminopentacyanoferrate complex was used) with which a 1 1 complex is formed. In the sulphoxide determination they then titrated spectrophotometrically with methylpyrazinium iodide, the cation of which reacts with the unused ferrate" complex to give a deep blue ion combination product (absorption maximum at 658 nm). 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

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