Pseudohalides, azides

Compounds in which the anomeric hydroxy group is replaced by a halogen atom are named as glycosyl halides. Pseudohalides (azides, thiocyanates etc.) are named similarly. 

The pseudohalide azide inhibits VCIPO. The first stmcturally characterised VHPO had in fact been crystallised in its azide-inhibited form. Inhibition has also been noted with hydroxylamine and hydrazine. Further, structural analogues of vanadate, such as [ALF4] and phosphate, are potent inhibitors. In turn, vanadate inhibits many phosphatases (and other phosphate-metabolising enzymes). On the other hand, apo-VHPOs can exhibit some phosphatase activity, and vanadate-inhibited phosphatases show some haloperoxidase activity. These phenomena will be discussed in Section 5.2.1. 

Addition of iodide and the pseudohalide azide (NJ) had a similar effect as addition of chloride, whereas addition of nitrate, sulfate or perchlorate ions had no effect. The oscillation period after the initial state was found to be identical with that of the unperturbed system. When the amount of chloride added is less than the amount of cerium(IV) present initially, no observable inhibition is expected. This system is more sensitive to addition of chloride after the oscillating reaction has started than to initial addition of chloride ions smaller amounts of chloride ions are required to induce inhibition or to suppress the oscillations completely. Because of this inhibitory effect, the glass vessels used to prepare the solutions for a Belousov-Zhabotinsky experiment should be clean and free of chloride ions. Moreover, in the preparation of the ferroin indicator solution 1,10-phenanthroline must be used in its free base form and not in the form of the hydrochloride salt. If one wants to monitor the periodic changes in the chemical potential of the solution, one must use a reference electrode that does not leak chloride ions. Conventional calomel electrodes or silver/silver chloride electrodes are not suitable, but double-junction version of these electrodes are adequate. 

Chemistry of Halides, Pseudohalides and Azides, Parts 1 and 2, Patai S, ... 

Nucleophiles like alcohols [2, S], hydrogen sulfide [2], thiols [2,10], ammonia, amines, hydrazines, hydroxylamines [2 11, 12, 13, 14, 75], azides [2], other pseudohalides [2], phosphonates [2,16,17,18,19, 20], and phosphanes [2,19] add rapidly across the CO or CN double bond to yield stable adducts The phosphonate adduets undergo a subsequent aleohol—lester rearrangement [19, 20] (equation 2)... 

There is an extensive chemistry associated with coordination compounds containing azide ions as a ligands. Like CN-, the azide ion is a pseudohalide ion, which means that it forms an insoluble silver salt, exists as the acid H-X, X-X is volatile, and it can combine with other pseudohalogens to give X-X. Although other pseudohalogens such as (CN)2 result from the oxidation of the CN- ion,... 

E. Bacciochi in The Chemistry of Functional Groups, The Chemistry of Halides, Pseudohalides and Azides, Suppl. D, Part 1 (Eds. S. Patai, Z. Rapport), Wiley, New York, 1983, pp. 161-201. 

A large amount of structural information is available for the pseudohalide complexes of Cu. Terminal,303-304 317 l,3- i304,318,319 and l,l- i3l8,319b 320 bound azide ligands have been found. For example,... 

A variety of preparative methods are available for the synthesis of metal pseudohalide complexes.202 209 The use of a large counterion like NEt4+, PPh4+ or (PPh3)2N+ is often important for the isolation of the water-free complexes. Furthermore, the presence of bulky counterions can have a stabilizing influence on the more or less explosive complexes containing azide anions. 

Transition-metal ions are employed as nodes and bifunctional ligands as spacers. Commonly used spacer ligands are pseudohalides such as cyanide, thiocyanate, and azide, and N-donor ligands such as pyrazine, 4,4 -bipyridine, and 2,2/-bipyrimidine. Besides discrete supermolecules, some one-, two-, and three-dimensional architectural motifs generated from this strategy are shown in Fig. 20.3.9. 

Infrared and Raman spectra of tetramethylantimony azide in the solid state and in dichloromethane solution indicate the presence of partly distorted tetrahedral Me4Sb+ cations201. A similar structure has also been proposed for Me4Sb(NCS) and Me4Sb(CN)201. Contrary to the alkyl derivatives, the tetraphenylantimony pseudohalides, PhtSbX (X = N3, NCO, NCS), however, have covalent pentacoordinated structure202. ... 

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. 

The azide ion is a good ligand, and it forms numerous complexes with metal ions. Chlorazide (C1N3) is an explosive compound prepared by the reaction of OCT and N3. As in the case of CN, the azide ion is a pseudohalide ion. Pseudohalogens are characterized by the formation of an insoluble silver salt, the acid H-X exists, X-X is volatile, and they combine with other... 

Organoaluminiun halides can be used to prepare pseudohalide derivatives, such as azides and cyanides, by salt metathesis. Azides are prepared by trimethylsUylhalide elimination (equation 14) and by reaction of a trialkylalnminnm with chloroazide, CIN3. Organoaluminnm cyanides have also been prepared by reactions of a trialkylalnminnm with HCN (eqnation 15). ... 

The azide ion (N3 ) is a Pseudohalide because its properties resemble those of the halides. The free ion has a linear N-N-N skeleton with equal N-N distances (1.167 A), but the anion coordinates terminally (137A) with an M-N-N angle of 116-140° and an N-N-N distortion of about 4° from linearity. Other possible modes of coordination are shown in (137B)-(144). As yet, there are no examples of (143). 

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