Pseudohalides ethers

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

Ni(0) complexes react with halides and pseudohalides. Their reactions are somewhat different from those of Pd(0). Chlorides add to Ni(0) much more easily than to Pd(0). Even C—O bonds such as aryl alkyl ether bonds are cleaved with Ni(0) under certain conditions. Not only triflates, but also mesylates react with Ni(0). Oxidative addition to Ni(0) and subsequent transformations are summarized in Scheme 3.6. 

A typical reaction of halide ions is their combination with a halogen molecule X2 to give the linear trihalide ions. In accord with its postulated pseudohalide character, the dicyanophosphide ion adds bromine and iodine at room temperature to give anions of X type with PCCN as central member. The crown ether-sodium salts of these hypervalent anions, dicyanodihalophosphates (III), can be isolated in crystalline form. 

The selenosulfonates (26) comprise another class of selenenyl pseudohalides. They are stable, crystalline compounds available from the reaction of selenenyl halides with sulftnate salts (Scheme 10) or more conveniently from the oxidation of either sulfonohydrazides (ArS02NHNH2) or sulftnic acids (ArS02H) with benzeneseleninic acid (27) (equations 21 and 22). Selenosulfonates add to alkenes via an electrophilic mechanism catalyzed by boron trifluoride etherate, or via a radical mechanism initiated thermally or photolytically. The two reaction modes produce complementary regioselectivity, but only the electrophilic processes are stereospecific (anti). Similar radical additions to acetylenes and allenes have been reported, with the regio- and stereochemistry as shown in Scheme 11. When these selenosulfonation reactions are used in conjunction with subsequent selenoxide eliminations or [2,3] sigmatropic rearrangements, they provide access to a variety of unsaturated sulfone products. 

An alternative approach to 9-substituted acridinium salts and thence the corresponding acridines involves the conversion of 9-acridones into the 9-trifluoromethanesulphonyloxy acridinium salts (17), which react readily with halides, pseudohalides such as azide and isothiocyanate, and sulphur nucleophiles (B. Singer and G. Maas, Z. Naturforsch., 1984, 39b, 1399). The free base restilts on reaction with diisopropyletlylamine. 9,9 -Bisacridine ethers are also available by this methodology. 

Stability constant measurements for the aqueous Zn -azide system indicate that four mononuclear complexes of moderate stability are formed, whereas for mercury, maximum coordination of only two azide ligands is observed. Complexation of Cd " in aqueous NOJ-NJ yields the mixed species [Cd(N03)(N3) ] ( = 1-4). Crystallographic structural determinations of A2Zn(Ns)4 (A = K or Cs) have been reported the former exhibits isolated Zn(Ns)4 tetrahedra with linear azide (N—N = 1.18 A). Thermal decomposition of the above compounds yields nitrogen and ZnsN2 as the main products. A new a modification of Zn(Na)2 has been obtained by the use of an ethereal solution of The compounds and ZnLC (M = Zn or Cd X = halide or pseudohalide L =... 

Spectra of organotin pseudohalides are analysed and the structure of Me2Sn(NCS)2.2H2O.18-crown-6 shown to involve trans-substitution with H2O H-bonding to the ether. Me SnCl and K3Co(CN)g form... 

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