Cyanation metal-free

Keywords Cyanation, a-Cyanohydrin, a-Aminonitrile, Cyanide, HCN, TMSCN, Lewis acid, Metal-free, Organocatalyst, C=0 bond, C=N bond, Strecker, Reissert, Aldehydes, Ketones, Imines, Aldimines, Ketoimines... 

Strecker-type reaction of TMS cyanide with chiral sulfinimines gives diastereoselective cyanations at the imine carbon, at —78 °C in DMF, using simple metal-free Lewis base catalysts such as tetraalkylammonium carboxylates.73... 

The asymmetric cyanation of imines can also be mediated by organocata-lysts. The group of Jacobsen has developed a metal-free cyanation utilising thiourea (6.130) and this catalyst has recently been used in an asymmetric three... 

Azoles can form stable compounds in which metallic and metalloid atoms are linked to nitrogen. For example, pyrazoles and imidazoles Af-substituted by B, Si, P and Hg groups are made in this way. Imidazoles with a free NH group can be Af-trimethylsilylated and Af-cyanated (with cyanogen bromide). Imidazoles of low basicity can be Af-nitrated. 

The oxidation of free cyanide ion yields cyanogen or cyanate, never fulminate. It might seem that when the carbon atom is attached to hydrogen or a metal, addition of oxygen to the nitrogen atom should be possible, but there is no record of such an oxidation ever having been achieved. The reverse process, conversion of combined fulminate into combined cyanide, has, however, been demonstrated for platinum(II) and iron(ll) complexes. 

The fulminate ion, [CNO] , is an isomer of the cyanate ion. Fulminate salts can be reduced to cyanides but cannot be prepared by oxidation of them. The free acid readily polymerizes but is stable for short periods in Et20 at low temperature. Metal fulminates are highly explosive mercury(II) fulminate may be prepared by reaction 13.82 and is a dangerous detonator. 

Although the Pd(PPh3)4-catalyzed cyanation of aryl bromides with KCN or NaCN does not take place under ordinary conditions, Zn(CN)2 as the cyanide source enables the reaction in DMF at 80 °C. The solubility of Zn(CN)2 is lower than that of KCN or NaCN and the covalency of the Zn-CN bond is higher than that of K-CN or Na-CN. Therefore, the concentration of free CN must be a minimum in the reaction solution using Zn(CN)2 as the metal cyanide. Thus, Zn(CN)2 is probably able to maintain the active form of the Pd° catalyst over a longer period of time than KCN or NaCN (Scheme Zn(CN)2 is also an effective cyanide source for the Pd°-catalyzed reac-... 

A water sample taken hours after the accident 20 m from the spill site showed free cyanide concentrations of 79.5 mg/L. This sample did not include cyanates, thiocyanates, cyanogen, cyanogen chloride, ammonia, chloramine, or metal cyanide complexes that are forms of cyanide-related compounds (Moran, 1998). 

Although cyanide is necessary for the cyanation reaction, it also plays the role of an inhibitor in the catalytic reaction due to its tendency to coordinate to the Pd " " or Pd species, besides the role of an indispensable reaction component. In general, metal cyanides only partially dissolve in the organic solvent. However, free cyanide can deactivate Pd complexes to a significant extent. Therefore, in order to provide an efficient catalytic reaction, the cyanide concentration must be low or in the same order of magnitude as the catalyst metal concentration. 

In contrast to all the C-C bond formations described previously, C-H cyanations are much rarer. This might be due to the possible strong coordination of free CN ligands to transition metal centers, which would preclude C-H activation as the first step of the catalytic cycle for C-H functionalization. The first C-CN bond formation was reported in 2006 by Yu and coworkers along with a series of Cu-catalyzed and Cu-mediated C-H functionalizations of 2-phenyl pyridine (Scheme 23.24) [88]. C-CN bond formations can thus be achieved with Me SiCN or CH NO as cyanating reagents in the presence of 1 equivalent of Cu(OAc)2 and air. 

The cyanide is not detected by the conductivity detector of the ion chromatograph due to its low dissociation constant (pK = 9.2) [64]. An ion chromatography procedure has been used for the determination of free cyanide and metal-cyanide complexes in natural water and wastewater samples using oxidation of cyanide ion by sodium hypochlorite to the cyanate ion (pK = 3.66) and a conductivity detector. So, cyanide ions can now be measured indirectly by the conductivity detector. In this procedure, optimum operating conditions were examined. 

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