Gallium complexes azides

In the presence of gallium chloride, aluminum bromide, aluminum chloride, and ferric chloride, benzoyl azide is decomposed according to eq 2. Here complex formation is very fast, and the decomposition of the complex is the ratedetermining step. The halides do not complex with the phenyl isocyanate formed and, as a consequence, they are not consumed in the reaction. As long as benzoyl azide is in excess, the concentration of the complex is equal to the halide concentration and remains constant. The experimentally determined pseudo-zero-order rate constant depends therefore upon the first power of the initial halide concentration. When, however, the reaction is at a stage where the azide is no longer in excess, the rate of the reaction becomes first order with respect to benzoyl azide and zero order with respect to halide. PhCONj + AlBr, -r - PhCONrAlBr, r+-... 

The halides, GaQs, AlBrs, A1C13, and FeCl3, very probably also exist in dimeric form. With these halides, however, the complexation reaction with the azide is the fast step so that no square-root term is found in the kinetic equation. Arsenic trichloride, arsenic tribromide, phosphorus trichloride, and phosphorus pentachloride were without effect on the rate of decomposition of benzoyl azide. Finally, the authors have observed that the catalytic influence of boron tribromide was much higher than all the other halides. Its rate constant was estimated to be about 18 times larger than that for gallium chloride. 

Aluminum azide is obtained from reacting AICI3 with NaNs in THF, or from the reaction of A1H3-Et20 with HN3 in ether at low temperature. When trimethylamine adducts of alane are employed, solids thought to be azido complexes are produced (equation 7). Aluminium (and gallium) compounds X2M(N3), where X = Br or I, have been prepared by the reaction of MX3 with the halogen azide 7W3 in benzene. They are polymeric solids which show v(M—N3) modes near 490 cm" (M = Al), or 430 cm" (Ga) in the vibrational spectra. 

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