Cyanide silver, reaction with

With alkali cyanides, a reaction via a SN2-mechanism takes place the alkyl halide is attacked by cyanide with the more nucleophilic carbon center rather than the nitrogen center, and the alkylnitrile is formed. In contrast, with silver cyanide the reaction proceeds by a SnI-mechanism, and an isonitrile is formed, since the carbenium intermediate reacts preferentially with the more electronegative center of the cyanide—i.e. the nitrogen (Kornblum s rule, HSAB concept). ... 

Silver cyanide, reaction with alkyl halides in synthesis of iso-cyamdes, 46, 77... 

The scope of the silver cyanide-catalyzed reaction of difunctional nucleophiles with alkyl isocyanides has been described in the earlier section on imidazoles an example of the use of this simple approach in benzimidazole synthesis is illustrated in Scheme 105.169... 

Silicon tetraisothiocyanate, reaction with 2,6-dimethylaniline to yield 2,6-diraethylphenyl thiourea, 46, 70 Silver cyanide, reaction with alkyl halides in synthesis of isocyanides, 46, 77... 

Of interest is the reaction with silver cyanide at low temperatures (—80°C) the thiocyanate forms initially and then, as shown by F NMR measurements, it undergoes a slow transmutation at 30°C into the isothiocyanate (67) ... 

Elemental composition Ag 75.26%, Cl 24.74%. The salt is dissolved in concentrated sulfuric acid, diluted, and analyzed for silver (see Silver). Solid powder may be characterized by its physical properties and its reaction with cyanide ion, forming the complex ion [Ag(CN)2]. ... 

The 6,7-dihydro-5/f -1,4-dioxepin (266) has been prepared (54CR(38)982). and more recently it has been shown that the 2,3-dihydro-5jF/-l,4-dioxepins (263) and (265) can be produced from 1,4-dioxine-halocarbene adducts (264), either by heating under reflux in xylene or by treatment with bases. The allylic chlorine atom in (263) is readily substituted by alkoxide or cyanide ions (77ZC331, 76UKZ968). Saturated rings of type (267) have been prepared by the treatment of cyclic acetals of ethane-1,2-diol with vinyl ethers in the presence of boron trifluoride, and l,4-dioxepan-5-one (268) has been prepared by the reaction of bromoform and silver nitrate with aqueous dioxane (60AG415). 

AgNOs + 4As = 3Ag + 2 As 203 + 3NO If the arsenic is added as a piece the silver is deposited in the form of a dull, white, smooth plating. The reaction does not go to completion even after several months contact. On the other hand, silver is completely displaced within a few hours from solutions saturated with silver nitrite or sulphate, and after a longer time from saturated aqueous solutions of silver acetate and tartrate. In each case arsenic goes into solution as the trioxide. With a solution of silver cyanide in aqueous potassium cyanide the reaction takes a different course, probably following the equation ... 

It has been known for many years that the reaction of cyanide ion with alkylating agents shows a dependency on the presence of metal ions. The classic application of this is the formation of nitriles by reaction with potassium cyanide and isonitriles from the reaction with silver cyanide (Fig. 5-59). 

Figure 5-59. The reaction of alkylating agents with potassium cyanide gives nitriles, whilst the reaction with silver cyanide gives isonitriles.

Ag+ preferentially reacts with the analyte to form a soluble salt or complex. During this addition, Ag+ reacts with the analyte only, and not the indicator. But when all the analyte is completely consumed by Ag+ and no more of it is left in the solution, addition of an excess drop of silver nitrate titrant produces an instant change in color because of its reaction with the silver-sensitive indicator. Some of the indicators used in the argentometric titrations are potassium chromate or dichlorofluorescein in chloride analysis and p -dime thy la m i nobe nzalrho da n i nc in cyanide analysis. Silver nitrate reacts with potassium chromate to form red silver chromate at the end point. This is an example of precipitation indicator, where the first excess of silver ion combines with the indicator chromate ion to form a bright red solid. This is also known as Mohr method. 

Diorganotetrapseudohalotellurates(IV) were obtained from tetrachlorotellurates(TV) or tetraiodotellurates(IV) via exchange reactions1 2. Silver cyanide was used to exchange chloride for cyanide1. Chloride and iodide were replaced by pseudohalides in reactions with potassium cyanate, potassium thiocyanate, or potassium azide. 

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