Nitrogen bromine compounds

Niobium Pentabromide, NbBrs.—This is the only bromine compound of niobium hitherto prepared. It is obtained by the action of bromine vapour on the coarsely powdered metal,2 or on a mixture of niobium pentoxide and carbon in the absence of air.2 In the latter case some of the oxybromide is also formed. Niobium pentabromide is a fine, purple-red powder, very similar to red phosphorus in appearance. The fused substance forms garnet-red prisms. On being strongly heated it becomes yellow, and volatilises. It melts at about 150° C., and distils undecomposed in an inert atmosphere at about 270° C. It can be distilled unchanged in an atmosphere of nitrogen or carbon dioxide. It is very hygroscopic, hydrolyses rapidly in damp air, and is decomposed by water with a hissing noise and considerable evolution of heat into niobie add and hydrobromic add. It is soluble in absolute alcohol and in dry ethyl bromide. 

Moreover, the cyclization of the azetidinonc 11a, performed with AT-bromosuccinimide in acetonitrile, afforded the bicyclic product 13a only in quantitative yield, which is an intermediate in the synthesis of carbapenems. Under the same reaction conditions, lib afforded 13b in quantitative yield. The stereochemistry of both 13a and 13b was assigned either by NOE experiments or X-ray crystallographic analysis. The reaction proceeds via the intermediate /V-brominated compound 12. Bromine then migrates to the double bond and the amidic nitrogen attacks the formed halonium ion to give 13237. 

Investigation of photochemical properties of molecules important for atmospheric chemistry, especially bromine and nitrogen containing compounds (Institut Jozef Stefan, Ljubljana). 

In many cases, the NOx family is formed as the sum of NO and N02, and accounts for the most reactive nitrogen species. The NOx/ NOy concentration ratio, which is often reported from field observations, is an indicator of the reactivity of odd nitrogen and its ability to destroy stratospheric ozone (or to affect other chemical families including chlorine and bromine compounds). The value of this ratio increases with altitude above 30 km to reach a value of nearly one in the upper stratosphere and mesosphere. It decreases substantially when the stratospheric aerosol load is enhanced, for example, after large volcanic eruptions (Fahey et al, 1993), and substantial amounts of nitrogen oxides are converted to nitric acid by heterogeneous reaction (5.152). It is also low in the polar regions, especially in air masses processed by polar stratospheric clouds. 

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