Cyanide displacement

The reaction of 2-cyanoquinoxaline with the anion derived from acetophenone gives some 2-(2-quinoxalinyl)acetophenone (39) and some of the imine (40). The anion derived from benzylcyanide displaces cyanide ion from 2-cyanoquinoxaline to give the disubstituted acetonitrile 41.2"... 

Nitrite displaces cyanide bound to methe-moglobin and the released cyanide is oxidized to harmless cyanate. 

Silver is formed in nature as argentite. AgjS and horn silver. AgCl. The extraction of silver depends upon the fact that it very readily forms a dicyanoargentate(I) complex, [Ag(CN)2] (linear), and treatment of a silver ore with aqueous cyanide ion CN extracts the silver as this complex. The silver is then displaced from the complex by zinc ... 

The chlorination process, introduced in Europe in 1843, roasted ore with chlorides, followed by a hot brine leach and subsequent precipitation of the silver on copper. In 1887 it was discovered that gold and silver can be recovered by sodium cyanide, and this process displaced the dangerous chlorination process. By 1907 the cyanide process, where a cyanide solution is mixed with 2inc dust to precipitate the silver, was universally in use. 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

The capability of zinc to reduce the ions of many metals to theh metallic state is the basis of important appHcations. However, metals are removed from zinc solutions by displacement with finely divided zinc before winning by electrolysis. Gold and silver are displaced from cyanide leach solutions with zinc and the following metals are similarly recovered from various solutions platinum group, cadmium, indium, thallium, and sometimes copper. 

The waste gas remaining after removal of ammonia and recovery of hydrogen cyanide contains enough hydrogen and carbon monoxide that it is flammable and has enough heat value to make it a valuable fuel. It is usually used to displace other fuel ia boilers. 

Hydrogen cyanide is a weak acid and can readily be displaced from a solution of sodium cyanide by weak mineral acids or by reaction with carbon dioxide, eg, from the atmosphere however, the latter takes places at a slow rate. 

Potassium cyanide [151 -50-8] KCN, a white crystalline, deUquescent soHd, was initially used as a flux, andlater for electroplating, which is the single greatest use in the 1990s. The demand for potassium cyanide was met by the ferrocyanide process until the latter part of the nineteenth century, when the extraordinary demands of the gold mining industry for alkah cyanide resulted in the development of direct synthesis processes. When cheaper sodium cyanide became available, potassium cyanide was displaced in many uses. With the decline in the use of alkah cyanides for plating the demand for potassium cyanide continues to decline. The total world production in 1990 was estimated at about 4500 t, down from 7300 t in 1976. 

Halogenomethyl, hydroxymethyl and aminomethyl groups readily undergo displacement reactions with nucleophilic reagents. Both side-chain and nuclear substitution products have been obtained (Scheme 57). These two possibilities are exemplified by the reaction of furfuryl chloride with sodium cyanide (Scheme 58). 

Bromomethyl-5-methylthiophene gives normal displacement products with amines but it is isomerized on attempted reaction with copper(I) cyanide (Scheme 59) 48MI30200. Whereas 2-hydroxymethylthiophene reacts normally with hydrogen halides to give 2-halomethylthiophenes, reaction of 2-hydroxymethylfuran (2-furfuryl alcohol) with hydrochloric acid results in formation of laevulinic acid (151). 2-Furfuryl alcohol derivatives are... 

The 3-substituents in 3-nitro- and 3-phenylsulfonyl-2-isoxazolines were displaced by a variety of nucleophiles including thiolate, cyanide and azide ions, ammonia, hydride ions and alkoxides. The reaction is pictured as an addition-elimination sequence (Scheme 54) (72MI41605, 79JA1319, 78JOC2020). 

Phenylsulfonylfulminic acid, prepared as outlined in Scheme 110, reacted even with highly hindered alkenes such as tetramethylethylene. The phenylsulfonyl group was easily displaced by a variety of nucleophiles such as methoxide, cyanide and hydride (79JA1319). 

The formation of ethyl cyano(pentafluorophenyl)acetate illustrates the intermolecular nucleophilic displacement of fluoride ion from an aromatic ring by a stabilized carbanion. The reaction proceeds readily as a result of the activation imparted by the electron-withdrawing fluorine atoms. The selective hydrolysis of a cyano ester to a nitrile has been described. (Pentafluorophenyl)acetonitrile has also been prepared by cyanide displacement on (pentafluorophenyl)methyl halides. However, this direct displacement is always aecompanied by an undesirable side reaetion to yield 15-20% of 2,3-bis(pentafluoro-phenyl)propionitrile. 

The poisoning effect of molecules such as CO and PF3 (p. 495) arises simply from their ability to bond reversibly to haem in the same manner as O2, but much more strongly, so that oxygen transport is prevented. The cyanide ion CN can also displace O2 from oxyhaemoglobin but its very much greater toxicity at small concentrations stems not from this but from its interference with the action of cytochrome a. 

Bonnett et alJ observed the formation of the pyrrolidone hydrox-amic acid (66) as a by-product in the alkaline hydrolysis of a 2-cyano-nitrone (69). This displacement of cyanide by hydroxyl seems to be quite general. 

Halogeno compounds have been prepared by direct halogena-tion or by Sandmeyer reaction on 4-aminoisothiazoles. As expected from general considerations, a halogen atom in the 4-position is less reactive than one in the 5-position, but nitriles are obtained in good yield with cuprous cyanide at elevated temperatures. With butyllithium, lithiation occurs exclusively in the 5-position, and no evidence of halogen displacement has been obtained. ... 

It is often advantageous to proceed to a desired product through two nucleophilic displacements rather than directly when one can exploit a difference in the reactivity of two leaving groups. An example is the conversion of 4-chloro-2,6-dimethoxypyrimidine (109) (not satisfactorily reactive with sulfanilamide anion) by means of trimethylamine into the more reactive trimethylammonio derivative 110. Conversion of chloro-quinohnes and -pyrimi-dines into nitriles is best accomplished by conversion (with sulfite) into the sulfonic acids before reaction with cyanide. 

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