Anions cyanide

There exist a number of d -synthons, which are stabilized by the delocalization of the electron pair into orbitals of hetero atoms, although the nucleophilic centre remains at the carbon atom. From nitroalkanes anions may be formed in aqueous solutions (e.g. CHjNOj pK, = 10.2). Nitromethane and -ethane anions are particularly useful in synthesis. The cyanide anion is also a classical d -synthon (HCN pK = 9.1). 

Carboxyl and nitrile groups are usually introduced in synthesis with commercial carboxylic acid derivatives, nitriles, or cyanide anion. Carbanions can be carboxylated with carbon dioxide (H.F. Ebel, 1970) or dialkyl carbonate (J. Schmidlin, 1957). 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

Nobes, Pople, Radotn, Handy and Knowles have studied the convergence of the Moller-Plesset orders in some detail. They computed the energies of hydrogen cyanide, cyanide anion and cyano radical through order 24 as well as at the full Configuration Interaction level. Here are some of their results ... 

HOMO of cyanide anion shows location of highest-energy electrons and identifies the most nucleophilic regions. 

Examine the highest-occupied molecular orbital (HOMO of cyanide anion. Is the larger lobe on carbon or nitrogen Would you expect cyanide to act as a carbon or nitrogei nucleophile Does this lead to the lower energy transitioi state (compare the energy of cyanide-l-methyl iodide ( attack and cyanide+methyl iodide N attack) ... 

Dinitro ketone 49 with potassium cyanide provided 5,6-dihydrooxazolo [3,2-/7][l,2,4]triazole 51. Its formation is due to the fact that primary attack by the cyanide anion is not directed at the ring C5 atom but rather at the carbonyl group to give the corresponding cyanohydrin 50 and the subsequent intramolecular displacement of the nitro group gives the final product (Scheme 8) (81 KGS 1403). 

Aromatic aldehydes 1 can undergo a condensation reaction to form a-hydroxy ketones 2 (also called benzoins) upon treatment with cyanide anions.This reaction, which is called benzoin condensation, works by that particular procedure with certain aromatic aldehydes and with glyoxals (RCOCHO). 

A cyanide anion as a nucleophile adds to an aldehyde molecule 1, leading to the anionic species 3. The acidity of the aldehydic proton is increased by the adjacent cyano group therefore the tautomeric carbanion species 4 can be formed and then add to another aldehyde molecule. In subsequent steps the product molecule becomes stabilized through loss of the cyanide ion, thus yielding the benzoin 2 ... 

Since the cyanide anion is an ambident nucleophile, isonitriles R—NC may be obtained as by-products. The reaction pathway to either nitrile or isonitrile can be controlled by proper choice of the counter cation for the cyanide anion. 

In addition to the tetrahedral and octahedral complexes mentioned above, there are two other types commonly found—the square planar and the linear. In the square planar complexes, the central atom has four near neighbors at the corners of a square. The coordination number is 4, the same number as in the tetrahedral complexes. An example of a square planar complex is the complex nickel cyanide anion, Ni(CN)4-2. 

Terminal alkynes can be converted readily into alkynylsilanes by reaction of the corresponding alkyne anion or its metalloid equivalent with a suitable chlorosilane (/). The reverse reaction, that of liberation of the alkyne, is quite facile, being effected by several reagent combinations, including hydroxide ion, methanolysis, fluoride anion, silver(i) followed by cyanide anion, and methyl lithium-lithium bromide (2). 

The strong affinity of the hard potential trimethylsilyl cation for the hard N-oxide moiety and of the soff cyanide anion (or the soff iodide anion) for the ad-... 

The biosorption capacity of Aspergillus niger was much greater than that of brewery yeast, and the biosorption capacity of metal-cyanide anion complexes was significantly lower than that of metal ion only. 

The small amounts of gold contained in low-grade ores can be extracted using a combination of oxidation and complexation. Gold is oxidized to Au, which forms a very strong complex with cyanide anions Au ((2 q) + l CN(a q) [Au (CN)2] aq) K -lx 10 Suppose that a sample of ore containing 2.5 X 10 mol of gold is extracted with 1.0 L of 4.0 X 10 M aqueous KCN solution. Calculate the concentrations of the three species involved in the complexation equilibrium. 

A second separation technique is leaching, which uses solubility properties to separate the components of an ore. For example, modem gold production depends on the extraction of tiny particles of gold from gold-bearing rock deposits. After the rock is crushed, it is treated with an aerated aqueous basic solution of sodium cyanide. Molecular oxygen oxidizes the metal, which forms a soluble coordination complex with the cyanide anion ... 

Copper nitrate reacts with sodamide and ammonia by forming explosive copper amides. The oxidising properties of this nitrate have led to violent detonations with ammonium hexacyanoferrates heated to 220 C in the presence of water traces, or dry at the same temperature, but in the presence of an excess of hexacyanoferrate. These accidents illustrate once more the incompatibility between compounds with a cyano group (or cyanide anion) and oxidants. An accident also occurred with a potassium hexacyanoferrate. 

Lead chromate gave rise to two accidents, which involved an alkaline (II) fenocyanide. They are explained by incompatibility between the cyano group (or cyanide anion) and oxidants. 

No new absorption bands are observed in other cases, largely due to the fact that the strong absorptions of the aromatic donors obstruct the UV-spectral measurements. For the complex between CBr4 and TMPD, the quantitative analyses of the temperature and concentration-dependent absorptions of the new band at 380 nm afford the extinction coefficient of ct = 3.2 x 103 M 1 cm x, as well as the thermodynamic parameters for complex formation AH = - 4.5 kcalM x, AS = - 14 e.u., and Kda = 0.3 M x at 295 K. Such thermodynamic characteristics are similar to those of the dihalogen complexes of as well as those of other acceptors with aromatic donors. Similar results are also obtained for CBr4 associates with halide and thio-cyanide anions [5,53]. 

The psychotropic (stimulant) action of amphetaminil (57) may be intrinsic or due to in vivo hydrolysis of the a-aminonitrile function—akin to a cyanohydrin—to liberate amphetamine itself. It is synthesized by forming the Schiff s base of amphetamine with benzaldehyde to give 56, and then nucleophilic attack on the latter with cyanide anion to... 

A similar result is obtained with respect to the cyanide anion CN. The following mode of HO MO extension 81> underlies the M—C—N type orientation in chelate compounds ... 

Free cyanide is the primary toxic agent in the aquatic environment. Free cyanide refers to the sum of molecular HCN and the cyanide anion (CN ), regardless of origin. In aqueous solution with pH 9.2 and lower, the majority of the free cyanide is in the form of molecular HCN. The chemical names for HCN include hydrogen cyanide, hydrocyanic acid, cyanohydric acid, and prussic acid. 

Complex cyanides are compounds in which the cyanide anion is incorporated into a complex or complexes. These compounds are different in chemical and toxicologic properties from simple cyanides. In solution, the stability of the cyanide complex varies with the type of cation and the complex that it forms. Some of these are dissociable in weak acids to give free cyanide and a cation, while other complexes require much stronger acidic conditions for dissociation. The least-stable complex metallocyanides include Zn(CN)42 , Cd(CN)3 , and Cd(CN)42 moderately stable complexes include Cu(CN)2, Cu(CN)32, Ni(CN)42, and Ag(CN)2 and the most stable complexes include Fe(CN)64, and Co(CN)6. The toxicity of complex cyanides is usually related to their ability to release cyanide ions in solution, which then enter into an equilibrium with HCN relatively small fluctuations in pH significantly affect their biocidal properties. 

The C,C-coupling reaction of BENAs with the cyanide anion can serve as a convenient procedure for the synthesis of substituted 5-aminoisoxazoles (451) from AN (519) (Scheme 3.242). The possible mechanistic scheme of the process... 

This process affords silyl derivatives of a-cyano oximes (452) as the primary products, detected by spectroscopic methods and, in some cases, can be isolated. Their desilylation gives aminooxazoles (451). (The synthesis of aminoisoxazoles by the reactions of the cyanide anion with nitrosoalkenes was also documented (503).) The reaction shown in Scheme 3.242 has a general character and can be performed with both terminal and internal BENAs, although special procedures are required for some functionalized BENAs. 

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