NIOBIUM.199 SODIUM BROMIDE

When a sample of the niobium (V) chloride-pyridine or niobium(V) bromide-pyridine reaction mixture was dissolved in dilute acid, filtered to remove precipitated niobium oxides, and treated with concentrated sodium hydroxide solution, the same set of spectra were observed for the resulting solution as for the l-(4-pyridyl) pyridinium dihalides. The spectra before and after heating the solutions from the reaction mixtures are shown in Figure 2. Here also the peaks occurred at 432 and 365 m/x, with the 432-m, peak absent after heating. 

Samples of the niobium (V) chloride or niobium (V) bromide-pyridine reaction mixtures were hydrolyzed in concentrated hydrochloric acid. Aliquots were diluted and neutralized with sodium carbonate to a pH of approximately 8. Sodium tetraphenylborate(III) solution then was added and a precipitate of l-(4-pyridyl) pyridinium tetraphenylborate(III) was produced. The precipitate was filtered and extracted with concentrated hydrochloric acid. The ultraviolet absorption spectrum of the extract is shown in Figure 3 for comparison with the spectrum of a known sample of l-(4-pyridyl) pyridinium dichloride in dilute hydrochloric acid. 

Bromine reacts with essentially all metals, except tantalum and niobium, although elevated temperatures are sometimes required, eg, soHd sodium does not react with dry bromine but sodium vapor reacts vigorously. Metals such as lead, magnesium, nickel, and silver react with bromine to form a surface coat of bromide that resists further attack. This protective coating allows lead and nickel to be used as linings in bromine containers. Metals tend to be corroded by bromine faster in the presence of moisture than without, probably because of the formation of hydrobromic and hypobromous acids. 

Toluene and THF were distilled from sodium benzophenone ketyl before use. Tantaliun bromide, niobiiun bromide, niobium chloride, cyclopentadienyl cobalt dicarbonyl, bis(l,5-cyclo-octadiene)diiridium(I) dichloride, tetraphenyltin, and tri-phenylphosphine were Aldrich products of the highest purities. All other reagents and solvents were purchased from Aldrich and used as received. 

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