Glyoximates

The reactions of aqueous solutions of nickel(II) salts with hydroxide ions, with excess ammonia, with sulphide ion and with dimethyl-glyoxime (see above) all provide useful tests for nickel(II) ions. 

The reductions are effected in nature by ferredoxin (p. 1102). This behaviour can be reproduced surprisingly well by simpler, model compounds. Some of the best known of these are obtained by the addition of axial groups to the square-planar complexes of Co with Schiff bases, or substituted glyoximes (giving cobaloximes) as illustrated in Fig. 26.7. The reduced Co species of these, along with vitamin... 

Furazan 1 was first prepared and characterized in 1964 by melting glyoxime 2 with succinic anhydride in 57% yield (64JA1863, 65JOC1854). Its A-oxide, furoxan 3, has been in a focus of attention for chemists for more than a century, but was synthesized only in 1994 by oxidation of 2 with dinitrogen tetroxide in dichloromethane in 45% yield (94MC7) (Scheme 1). The A-oxide cannot be prepared by direct oxidation of furazan. 

One-pot procedures were utilized for the preparation of hydroxymethylfurox-ancarboxylic acid derivatives 91 and 92 starting from the cyclic glyoxime 73a (Scheme 42) [94GEP(O)4307105, 94WO20478, 95W019355]. 

Discussion. When dimethyl glyoxime is added to an alkaline solution of a nickel salt which has been treated with an oxidising agent (such as bromine), a red... 

Much of the recent literature relates to BfVbridged Co" cobaloximes based on dimethyl (89) or diphenyl glyoxime (104).110 The BfVbridged cobaloximes (e.g. 89) show greater stability to hydrolysis than analogous H-bridged species (e.g. 88). The diphenylglyoxime complexes (104) show enhanced air and hydrolytic stability... 

Cobalt, bis(dimethy glyoxime)isocyano-, 1, 186 Cobalt, bis(l,2-ethanediamine)bis(isothiocyanato)-chloride... 

Bis(glyoximato)cobalt(II) complexes of the types Co(DH)2B2 and Co(DH)2B2 (DH = disubstituted glyoxime, B = base, e.g. pyridine or triphenylphosphine) reduce benzyl bromide in benzene and acetone solutions ... 

The other common synthetic procedure for Bfx and Fx preparation is the oxidative cyclization of 1,2-dioximes. 1,2-Dioximes are excellent starting materials for the syntheses of the 1,2,5-oxadiazole N-oxide system in presence of oxidizing conditions to promote the cyclization. Its utiUty is restricted for Bfxs syntheses because the restriction of o-quinone dioximes availability, contrarily a-glyoximes, which are useful to prepare Fx, are more easily to prepare. In Table 1, products, conditions, and comments for the most recent Fx synthesis using 1,2-dioximes are shown. 

Table 1 General procedure to preparation of Bfx and Fx from a-glyoximes...

In the study of effects of ultrasound on the aqueous reactions of nickel, we found some interesting results, for example, the colloidal formation of Ni-DMG complex and degassing of NH3 during different experiments. When 25 ml of 0.001 M NiSC>4 solution was complexed with 5 ml of 1% dimethyl glyoxime (DMG) in faintly alkaline ammonia medium and sonicated for 30 minutes and compared with another set of 25 ml of complexed solution which was stirred mechanically, a colloidal solution of Ni-DMG complex was formed in sonicated condition. Particles of Ni-DMG complex did not settle even after keeping 3 1 h because of their smaller size, in sonicated solution, whereas in the unsonicated condition large particles of Ni-DMG complex settled down immediately. 

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