Toxicity, aluminum synthesis

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

Caution. The synthesis should he conducted in a hood because of the possible toxicity of the unusually volatile aluminum complex. 

Fluorine Hydrofluoric acid (HF) is a by-product of aluminum production by electrolysis cind the synthesis of chlorofluorocarbons (CFCs). Although in water HF is a weak acid, it s extremely toxic. HF poisoning causes deep ulceration or scarring of body tissue with a delayed effect, slowly replacing calcium in bodily tissue (flesh and bones). There s no pain at first because it s a weak acid, but when the calcium in the bones starts to be replaced by the more electronegative fluorine it feels similar to growing pains, and may be too late. Merely five-minute iexposure to 10,000 ppm concentration in the air is fatal to humans. 

Oliveira, A. C., Valentini, A., Nobre, P. S. S., Fierro, J. L. G. Rangel, M. C. (2003). Non Toxic Fe-Based Catalysts for Styrene Synthesis. The Effect of Salt Precursor and Aluminum Promoter on the Catalytic Properties. Catal Today, 85, 49-57. 

H. E. L. Bonfim, A. C. Oliveira, M. C. Rangel, 2003, The effect of zinc on the catalytic activity of hematite in ethylbenzene dehydrogenation. React.Kinet. Catal. Lett, 80,359-364. A. C. Oliveira, A. Valentini, P. S. S. Nobre, J. L. G. Fierro, M. C. Rangel, 2003, Non toxic Fe-based catalysts for styrene synthesis. The effect of salt precursor and aluminum promoter on the catalytic properties. Catal. Today, 85,49-573. 

---